Cutis

The Diagnosis: Mycobacterial Infection

An injury sustained in a wet environment that results in chronic indolent abscesses, nodules, or draining sinus tracts suggests a mycobacterial infection. In our patient, a culture revealed MycobacteriuM fortuitum, which is classified in the rapid grower nontuberculous mycobacteria (NTM) group, along with Mycobacterium chelonae and Mycobacterium abscessus.¹ The patient’s history of skin injury while cutting wet grass and the common presence of M fortuitum in the environment suggested that the organism entered the wound. The patient healed completely following surgical excision and a 2-month course of clarithromycin 1 g daily and rifampin 600 mg daily.

MycobacteriuM fortuitum was first isolated from an amphibian source in 1905 and later identified in a human with cutaneous infection in 1938. It commonly is found in soil and water.2 Skin and soft-tissue infections with M fortuitum usually are acquired from direct entry of the organism through a damaged skin barrier from trauma, medical injection, surgery, or tattoo placement.^2,3

Skin lesions caused by NTM often are nonspecific and can mimic a variety of other dermatologic conditions, making clinical diagnosis challenging. As such, cutaneous manifestations of M fortuitum infection can include recurrent cutaneous abscesses, nodular lesions, chronic discharging sinuses, cellulitis, and surgical site infections.4 Although cutaneous infection with M fortuitum classically manifests with a single subcutaneous nodule at the site of trauma or surgery,⁵ it also can manifest as multiple draining sinus tracts, as seen in our patient. Hence, the diagnosis and treatment of cutaneous NTM infection is challenging, especially when M fortuitum skin manifestations can take up to 4 to 6 weeks to develop after inoculation. Diagnosis often requires a detailed patient history, tissue cultures, and histopathology.⁵

In recent years, rapid detection with polymerase chain reaction (PCR) techniques has been employed more widely. Notably, a molecular system based on multiplex real-time PCR with high-resolution melting was shown to have a sensitivity of up to 54% for distinguishing M fortuitum from other NTM.⁶ More recently, a 2-step real-time PCR method has demonstrated diagnostic sensitivity and specificity for differentiating NTM from Mycobacterium tuberculosis infections and identifying the causative NTM agent.⁷

Compared to immunocompetent individuals, those who are immunocompromised are more susceptible to less pathogenic strains of NTM, which can cause dissemination and lead to tenosynovitis, myositis, osteomyelitis, and septic arthritis.^8-12 Nonetheless, cases of infections with NTM—including M fortuitum—are becoming harder to treat. Several single nucleotide polymorphisms and point mutations have been demonstrated in the ribosomal RNA methylase gene erm(39) related to clarithromycin resistance and in the rrl gene related to linezolid resistance.¹³ Due to increasing inducible resistance to common classes of antibiotics, such as macrolides and linezolid, treatment of M fortuitum requires multidrug regimens.^13,14 Drug susceptibility testing also may be required, as M fortuitum has shown low resistance to tigecycline, tetracycline, cefmetazole, imipenem, and aminoglycosides (eg, amikacin, tobramycin, neomycin, gentamycin). Surgery is an important adjunctive tool in treating M fortuitum infections; patients with a single lesion are more likely to undergo surgical treatment alone or in combination with antibiotic therapy.¹⁵ More recently, antimicrobial photodynamic therapy has been explored as an alternative to eliminate NTM, including M fortuitum.¹⁶

The differential diagnosis for skin lesions manifesting with draining fistulae and sinus tracts includes conditions with infectious (cellulitis and chromomycosis) and inflammatory (pyoderma gangrenosum [PG] and hidradenitis suppurativa [HS]) causes.

Cellulitis is a common infection of the skin and subcutaneous tissue that predominantly is caused by gram-positive organisms such as β-hemolytic streptococci.¹⁷ Clinical manifestations include acute skin erythema, swelling, tenderness, and warmth. The legs are the most common sites of infection, but any area of the skin can be involved.17 Cellulitis comprises 10% of all infectious disease hospitalizations and up to 11% of all dermatologic admissions.^18,19 It frequently is misdiagnosed, perhaps due to the lack of a reliable confirmatory laboratory test or imaging study, in addition to the plethora of diseases that mimic cellulitis, such as stasis dermatitis, lipodermatosclerosis, contact dermatitis, lymphedema, eosinophilic cellulitis, and papular urticaria.^20,21 The consequences of misdiagnosis include but are not limited to unnecessary hospitalizations, inappropriate antibiotic use, and delayed management of the disease; thus, there is an urgent need for a reliable standard test to confirm the diagnosis, especially among nonspecialist physicians. ²⁰ Most patients with uncomplicated cellulitis can be treated with empiric oral antibiotics that target β-hemolytic streptococci (ie, penicillin V potassium, amoxicillin).¹⁷ Methicillin-resistant Staphylococcus aureus coverage generally is unnecessary for nonpurulent cellulitis, but clinicians can consider adding amoxicillin-clavulanate, dicloxacillin, and cephalexin to the regimen. For purulent cellulitis, incision and drainage should be performed. In severe cases that manifest with sepsis, altered mental status, or hemodynamic instability, inpatient management is required.¹⁷

Chromomycosis (also known as chromoblastomycosis) is a chronic, indolent, granulomatous, suppurative mycosis of the skin and subcutaneous tissue²² that is caused by traumatic inoculation of various fungi of the order Chaetothyriales and family Herpotrichiellaceae, which are present in soil, plants, and decomposing wood. Chromomycosis is prevalent in tropical and subtropical regions.^23,24 Clinically, it manifests as oligosymptomatic or asymptomatic lesions around an infection site that can manifest as papules with centrifugal growth evolving into nodular, verrucous, plaque, tumoral, or atrophic forms.²² Diagnosis is made with direct microscopy using potassium hydroxide, which reveals muriform bodies. Fungal culture in Sabouraud agar also can be used to isolate the causative pathogen.²² Unfortunately, chromomycosis is difficult to treat, with low cure rates and high relapse rates. Antifungal agents combined with surgery, cryotherapy, or thermotherapy often are used, with cure rates ranging from 15% to 80%.^22,25

Pyoderma gangrenosum is a reactive noninfectious inflammatory dermatosis associated with inflammatory bowel disease and rheumatoid arthritis. The exact etiology is not clearly understood, but it generally is considered an autoinflammatory disorder.²⁶ The most common form—classical PG—occurs in approximately 85% of cases and manifests as a painful erythematous lesion that progresses to a blistered or necrotic ulcer. It primarily affects the lower legs but can occur in other body sites.²⁷ The diagnosis is based on clinical symptoms after excluding other similar conditions; histopathology of biopsied wound tissues often are required for confirmation. Treatment of PG starts with fast-acting immunosuppressive drugs (corticosteroids and/or cyclosporine) followed by slowacting immunosuppressive drugs (biologics).²⁶

Hidradenitis suppurativa is a chronic recurrent disease of the hair follicle unit that develops after puberty.²⁸ Clinically, HS manifests with painful nodules, abscesses, chronically draining fistulas, and scarring in areas of the body rich in apocrine glands.^29,30 Treatment of HS is challenging due to its diverse clinical manifestations and unclear etiology. Topical therapy, systemic treatments, biologic agents, surgery, and light therapy have shown variable results.^28,31

The Diagnosis: Mycobacterial Infection

An injury sustained in a wet environment that results in chronic indolent abscesses, nodules, or draining sinus tracts suggests a mycobacterial infection. In our patient, a culture revealed MycobacteriuM fortuitum, which is classified in the rapid grower nontuberculous mycobacteria (NTM) group, along with Mycobacterium chelonae and Mycobacterium abscessus.¹ The patient’s history of skin injury while cutting wet grass and the common presence of M fortuitum in the environment suggested that the organism entered the wound. The patient healed completely following surgical excision and a 2-month course of clarithromycin 1 g daily and rifampin 600 mg daily.

MycobacteriuM fortuitum was first isolated from an amphibian source in 1905 and later identified in a human with cutaneous infection in 1938. It commonly is found in soil and water.2 Skin and soft-tissue infections with M fortuitum usually are acquired from direct entry of the organism through a damaged skin barrier from trauma, medical injection, surgery, or tattoo placement.^2,3

Skin lesions caused by NTM often are nonspecific and can mimic a variety of other dermatologic conditions, making clinical diagnosis challenging. As such, cutaneous manifestations of M fortuitum infection can include recurrent cutaneous abscesses, nodular lesions, chronic discharging sinuses, cellulitis, and surgical site infections.4 Although cutaneous infection with M fortuitum classically manifests with a single subcutaneous nodule at the site of trauma or surgery,⁵ it also can manifest as multiple draining sinus tracts, as seen in our patient. Hence, the diagnosis and treatment of cutaneous NTM infection is challenging, especially when M fortuitum skin manifestations can take up to 4 to 6 weeks to develop after inoculation. Diagnosis often requires a detailed patient history, tissue cultures, and histopathology.⁵

In recent years, rapid detection with polymerase chain reaction (PCR) techniques has been employed more widely. Notably, a molecular system based on multiplex real-time PCR with high-resolution melting was shown to have a sensitivity of up to 54% for distinguishing M fortuitum from other NTM.⁶ More recently, a 2-step real-time PCR method has demonstrated diagnostic sensitivity and specificity for differentiating NTM from Mycobacterium tuberculosis infections and identifying the causative NTM agent.⁷

Compared to immunocompetent individuals, those who are immunocompromised are more susceptible to less pathogenic strains of NTM, which can cause dissemination and lead to tenosynovitis, myositis, osteomyelitis, and septic arthritis.^8-12 Nonetheless, cases of infections with NTM—including M fortuitum—are becoming harder to treat. Several single nucleotide polymorphisms and point mutations have been demonstrated in the ribosomal RNA methylase gene erm(39) related to clarithromycin resistance and in the rrl gene related to linezolid resistance.¹³ Due to increasing inducible resistance to common classes of antibiotics, such as macrolides and linezolid, treatment of M fortuitum requires multidrug regimens.^13,14 Drug susceptibility testing also may be required, as M fortuitum has shown low resistance to tigecycline, tetracycline, cefmetazole, imipenem, and aminoglycosides (eg, amikacin, tobramycin, neomycin, gentamycin). Surgery is an important adjunctive tool in treating M fortuitum infections; patients with a single lesion are more likely to undergo surgical treatment alone or in combination with antibiotic therapy.¹⁵ More recently, antimicrobial photodynamic therapy has been explored as an alternative to eliminate NTM, including M fortuitum.¹⁶

The differential diagnosis for skin lesions manifesting with draining fistulae and sinus tracts includes conditions with infectious (cellulitis and chromomycosis) and inflammatory (pyoderma gangrenosum [PG] and hidradenitis suppurativa [HS]) causes.

Cellulitis is a common infection of the skin and subcutaneous tissue that predominantly is caused by gram-positive organisms such as β-hemolytic streptococci.¹⁷ Clinical manifestations include acute skin erythema, swelling, tenderness, and warmth. The legs are the most common sites of infection, but any area of the skin can be involved.17 Cellulitis comprises 10% of all infectious disease hospitalizations and up to 11% of all dermatologic admissions.^18,19 It frequently is misdiagnosed, perhaps due to the lack of a reliable confirmatory laboratory test or imaging study, in addition to the plethora of diseases that mimic cellulitis, such as stasis dermatitis, lipodermatosclerosis, contact dermatitis, lymphedema, eosinophilic cellulitis, and papular urticaria.^20,21 The consequences of misdiagnosis include but are not limited to unnecessary hospitalizations, inappropriate antibiotic use, and delayed management of the disease; thus, there is an urgent need for a reliable standard test to confirm the diagnosis, especially among nonspecialist physicians. ²⁰ Most patients with uncomplicated cellulitis can be treated with empiric oral antibiotics that target β-hemolytic streptococci (ie, penicillin V potassium, amoxicillin).¹⁷ Methicillin-resistant Staphylococcus aureus coverage generally is unnecessary for nonpurulent cellulitis, but clinicians can consider adding amoxicillin-clavulanate, dicloxacillin, and cephalexin to the regimen. For purulent cellulitis, incision and drainage should be performed. In severe cases that manifest with sepsis, altered mental status, or hemodynamic instability, inpatient management is required.¹⁷

Chromomycosis (also known as chromoblastomycosis) is a chronic, indolent, granulomatous, suppurative mycosis of the skin and subcutaneous tissue²² that is caused by traumatic inoculation of various fungi of the order Chaetothyriales and family Herpotrichiellaceae, which are present in soil, plants, and decomposing wood. Chromomycosis is prevalent in tropical and subtropical regions.^23,24 Clinically, it manifests as oligosymptomatic or asymptomatic lesions around an infection site that can manifest as papules with centrifugal growth evolving into nodular, verrucous, plaque, tumoral, or atrophic forms.²² Diagnosis is made with direct microscopy using potassium hydroxide, which reveals muriform bodies. Fungal culture in Sabouraud agar also can be used to isolate the causative pathogen.²² Unfortunately, chromomycosis is difficult to treat, with low cure rates and high relapse rates. Antifungal agents combined with surgery, cryotherapy, or thermotherapy often are used, with cure rates ranging from 15% to 80%.^22,25

Pyoderma gangrenosum is a reactive noninfectious inflammatory dermatosis associated with inflammatory bowel disease and rheumatoid arthritis. The exact etiology is not clearly understood, but it generally is considered an autoinflammatory disorder.²⁶ The most common form—classical PG—occurs in approximately 85% of cases and manifests as a painful erythematous lesion that progresses to a blistered or necrotic ulcer. It primarily affects the lower legs but can occur in other body sites.²⁷ The diagnosis is based on clinical symptoms after excluding other similar conditions; histopathology of biopsied wound tissues often are required for confirmation. Treatment of PG starts with fast-acting immunosuppressive drugs (corticosteroids and/or cyclosporine) followed by slowacting immunosuppressive drugs (biologics).²⁶

Hidradenitis suppurativa is a chronic recurrent disease of the hair follicle unit that develops after puberty.²⁸ Clinically, HS manifests with painful nodules, abscesses, chronically draining fistulas, and scarring in areas of the body rich in apocrine glands.^29,30 Treatment of HS is challenging due to its diverse clinical manifestations and unclear etiology. Topical therapy, systemic treatments, biologic agents, surgery, and light therapy have shown variable results.^28,31

The Diagnosis: Mycobacterial Infection

An injury sustained in a wet environment that results in chronic indolent abscesses, nodules, or draining sinus tracts suggests a mycobacterial infection. In our patient, a culture revealed MycobacteriuM fortuitum, which is classified in the rapid grower nontuberculous mycobacteria (NTM) group, along with Mycobacterium chelonae and Mycobacterium abscessus.¹ The patient’s history of skin injury while cutting wet grass and the common presence of M fortuitum in the environment suggested that the organism entered the wound. The patient healed completely following surgical excision and a 2-month course of clarithromycin 1 g daily and rifampin 600 mg daily.

MycobacteriuM fortuitum was first isolated from an amphibian source in 1905 and later identified in a human with cutaneous infection in 1938. It commonly is found in soil and water.2 Skin and soft-tissue infections with M fortuitum usually are acquired from direct entry of the organism through a damaged skin barrier from trauma, medical injection, surgery, or tattoo placement.^2,3

Skin lesions caused by NTM often are nonspecific and can mimic a variety of other dermatologic conditions, making clinical diagnosis challenging. As such, cutaneous manifestations of M fortuitum infection can include recurrent cutaneous abscesses, nodular lesions, chronic discharging sinuses, cellulitis, and surgical site infections.4 Although cutaneous infection with M fortuitum classically manifests with a single subcutaneous nodule at the site of trauma or surgery,⁵ it also can manifest as multiple draining sinus tracts, as seen in our patient. Hence, the diagnosis and treatment of cutaneous NTM infection is challenging, especially when M fortuitum skin manifestations can take up to 4 to 6 weeks to develop after inoculation. Diagnosis often requires a detailed patient history, tissue cultures, and histopathology.⁵

In recent years, rapid detection with polymerase chain reaction (PCR) techniques has been employed more widely. Notably, a molecular system based on multiplex real-time PCR with high-resolution melting was shown to have a sensitivity of up to 54% for distinguishing M fortuitum from other NTM.⁶ More recently, a 2-step real-time PCR method has demonstrated diagnostic sensitivity and specificity for differentiating NTM from Mycobacterium tuberculosis infections and identifying the causative NTM agent.⁷

Compared to immunocompetent individuals, those who are immunocompromised are more susceptible to less pathogenic strains of NTM, which can cause dissemination and lead to tenosynovitis, myositis, osteomyelitis, and septic arthritis.^8-12 Nonetheless, cases of infections with NTM—including M fortuitum—are becoming harder to treat. Several single nucleotide polymorphisms and point mutations have been demonstrated in the ribosomal RNA methylase gene erm(39) related to clarithromycin resistance and in the rrl gene related to linezolid resistance.¹³ Due to increasing inducible resistance to common classes of antibiotics, such as macrolides and linezolid, treatment of M fortuitum requires multidrug regimens.^13,14 Drug susceptibility testing also may be required, as M fortuitum has shown low resistance to tigecycline, tetracycline, cefmetazole, imipenem, and aminoglycosides (eg, amikacin, tobramycin, neomycin, gentamycin). Surgery is an important adjunctive tool in treating M fortuitum infections; patients with a single lesion are more likely to undergo surgical treatment alone or in combination with antibiotic therapy.¹⁵ More recently, antimicrobial photodynamic therapy has been explored as an alternative to eliminate NTM, including M fortuitum.¹⁶

The differential diagnosis for skin lesions manifesting with draining fistulae and sinus tracts includes conditions with infectious (cellulitis and chromomycosis) and inflammatory (pyoderma gangrenosum [PG] and hidradenitis suppurativa [HS]) causes.

Cellulitis is a common infection of the skin and subcutaneous tissue that predominantly is caused by gram-positive organisms such as β-hemolytic streptococci.¹⁷ Clinical manifestations include acute skin erythema, swelling, tenderness, and warmth. The legs are the most common sites of infection, but any area of the skin can be involved.17 Cellulitis comprises 10% of all infectious disease hospitalizations and up to 11% of all dermatologic admissions.^18,19 It frequently is misdiagnosed, perhaps due to the lack of a reliable confirmatory laboratory test or imaging study, in addition to the plethora of diseases that mimic cellulitis, such as stasis dermatitis, lipodermatosclerosis, contact dermatitis, lymphedema, eosinophilic cellulitis, and papular urticaria.^20,21 The consequences of misdiagnosis include but are not limited to unnecessary hospitalizations, inappropriate antibiotic use, and delayed management of the disease; thus, there is an urgent need for a reliable standard test to confirm the diagnosis, especially among nonspecialist physicians. ²⁰ Most patients with uncomplicated cellulitis can be treated with empiric oral antibiotics that target β-hemolytic streptococci (ie, penicillin V potassium, amoxicillin).¹⁷ Methicillin-resistant Staphylococcus aureus coverage generally is unnecessary for nonpurulent cellulitis, but clinicians can consider adding amoxicillin-clavulanate, dicloxacillin, and cephalexin to the regimen. For purulent cellulitis, incision and drainage should be performed. In severe cases that manifest with sepsis, altered mental status, or hemodynamic instability, inpatient management is required.¹⁷

Chromomycosis (also known as chromoblastomycosis) is a chronic, indolent, granulomatous, suppurative mycosis of the skin and subcutaneous tissue²² that is caused by traumatic inoculation of various fungi of the order Chaetothyriales and family Herpotrichiellaceae, which are present in soil, plants, and decomposing wood. Chromomycosis is prevalent in tropical and subtropical regions.^23,24 Clinically, it manifests as oligosymptomatic or asymptomatic lesions around an infection site that can manifest as papules with centrifugal growth evolving into nodular, verrucous, plaque, tumoral, or atrophic forms.²² Diagnosis is made with direct microscopy using potassium hydroxide, which reveals muriform bodies. Fungal culture in Sabouraud agar also can be used to isolate the causative pathogen.²² Unfortunately, chromomycosis is difficult to treat, with low cure rates and high relapse rates. Antifungal agents combined with surgery, cryotherapy, or thermotherapy often are used, with cure rates ranging from 15% to 80%.^22,25

Pyoderma gangrenosum is a reactive noninfectious inflammatory dermatosis associated with inflammatory bowel disease and rheumatoid arthritis. The exact etiology is not clearly understood, but it generally is considered an autoinflammatory disorder.²⁶ The most common form—classical PG—occurs in approximately 85% of cases and manifests as a painful erythematous lesion that progresses to a blistered or necrotic ulcer. It primarily affects the lower legs but can occur in other body sites.²⁷ The diagnosis is based on clinical symptoms after excluding other similar conditions; histopathology of biopsied wound tissues often are required for confirmation. Treatment of PG starts with fast-acting immunosuppressive drugs (corticosteroids and/or cyclosporine) followed by slowacting immunosuppressive drugs (biologics).²⁶

Hidradenitis suppurativa is a chronic recurrent disease of the hair follicle unit that develops after puberty.²⁸ Clinically, HS manifests with painful nodules, abscesses, chronically draining fistulas, and scarring in areas of the body rich in apocrine glands.^29,30 Treatment of HS is challenging due to its diverse clinical manifestations and unclear etiology. Topical therapy, systemic treatments, biologic agents, surgery, and light therapy have shown variable results.^28,31

The Diagnosis: Erythema Nodosum Leprosum

Erythema nodosum leprosum (ENL) is a type 2 reaction sometimes seen in patients infected with Mycobacterium leprae—primarily those with lepromatous or borderline lepromatous subtypes. Clinically, ENL manifests with abrupt onset of tender erythematous papules with associated fevers and general malaise. Studies have demonstrated a complex immune system reaction in ENL, but the detailed pathophysiology is not fully understood.¹ Biopsies conducted within 24 hours of lesion formation are most elucidating. Foamy histiocytes admixed with neutrophils are seen in the subcutis, often causing a lobular panniculitis (quiz image).² Neutrophils rarely are seen in other types of leprosy and thus are a useful diagnostic clue for ENL. Vasculitis of small- to medium-sized vessels can be seen but is not a necessary diagnostic criterion. Fite staining will highlight many acid-fast bacilli within the histiocytes (Figure 1).

Erythema nodosum leprosum is treated with a combination of immunosuppressants such as prednisone and thalidomide. Our patient was taking triple-antibiotic therapy—dapsone, rifampin, and clofazimine—for lepromatous leprosy when the erythematous papules developed on the arms and legs. After a skin biopsy confirmed the diagnosis of ENL, he was started on prednisone 20 mg daily with plans for close follow-up. Unfortunately, the patient was subsequently lost to follow-up.

Acute febrile neutrophilic dermatosis (also known as Sweet syndrome) is an acute inflammatory disease characterized by abrupt onset of painful erythematous papules, plaques, or nodules on the skin. It often is seen in association with preceding infections (especially those in the upper respiratory or gastrointestinal tracts), hematologic malignancies, inflammatory bowel disease, or exposure to certain classes of medications (eg, granulocyte colony-stimulating factor, tyrosine kinase inhibitors, various antibiotics).³ Histologically, acute febrile neutrophilic dermatosis is characterized by dense neutrophilic infiltrates, often with notable dermal edema (Figure 2).⁴ Many cases also show leukocytoclastic vasculitis; however, foamy histiocytes are not a notable component of the inflammatory infiltrate, though a histiocytoid form of acute febrile neutrophilic dermatosis has been described.⁵ Infections must be rigorously ruled out prior to diagnosing a patient with acute febrile neutrophilic dermatosis, making it a diagnosis of exclusion.

Cutaneous coccidioidomycosis is an infection caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. Cutaneous disease is rare but can occur from direct inoculation or dissemination from pulmonary disease in immunocompetent or immunocompromised patients. Papules, pustules, or plaques are seen clinically. Histologically, cutaneous coccidioidomycosis shows spherules that vary from 10 to 100 μm and are filled with multiple smaller endospores (Figure 3).⁶ Pseudoepitheliomatous hyperplasia with dense suppurative and granulomatous infiltrates also is seen.

Erythema induratum is characterized by tender nodules on the lower extremities and has a substantial female predominance. Many cases are associated with Mycobacterium tuberculosis infection. The bacteria are not seen directly in the skin but are instead detectable through DNA polymerase chain reaction testing or investigation of other organ systems.^7,8 Histologically, lesions show a lobular panniculitis with a mixed infiltrate. Vasculitis is seen in approximately 90% of erythema induratum cases vs approximately 25% of classic ENL cases (Figure 4),^2,9 which has led some to use the term nodular vasculitis to describe this disease entity. Nodular vasculitis is considered by others to be a distinct disease entity in which there are clinical and histologic features similar to erythema induratum but no evidence of M tuberculosis infection.⁹

Polyarteritis nodosa is a vasculitis that affects medium- sized vessels of various organ systems. The presenting signs and symptoms vary based on the affected organ systems. Palpable to retiform purpura, livedo racemosa, subcutaneous nodules, or ulcers are seen when the skin is involved. The histologic hallmark is necrotizing vasculitis of medium-sized arterioles (Figure 5), although leukocytoclastic vasculitis of small-caliber vessels also can be seen in biopsies of affected skin.¹⁰ The vascular changes are said to be segmental, with uninvolved segments interspersed with involved segments. Antineutrophil cytoplasmic antibody (ANCA)– associated vasculitis also must be considered when one sees leukocytoclastic vasculitis of small-caliber vessels in the skin, as it can be distinguished most readily by detecting circulating antibodies specific for myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA).

The Diagnosis: Erythema Nodosum Leprosum

Erythema nodosum leprosum (ENL) is a type 2 reaction sometimes seen in patients infected with Mycobacterium leprae—primarily those with lepromatous or borderline lepromatous subtypes. Clinically, ENL manifests with abrupt onset of tender erythematous papules with associated fevers and general malaise. Studies have demonstrated a complex immune system reaction in ENL, but the detailed pathophysiology is not fully understood.¹ Biopsies conducted within 24 hours of lesion formation are most elucidating. Foamy histiocytes admixed with neutrophils are seen in the subcutis, often causing a lobular panniculitis (quiz image).² Neutrophils rarely are seen in other types of leprosy and thus are a useful diagnostic clue for ENL. Vasculitis of small- to medium-sized vessels can be seen but is not a necessary diagnostic criterion. Fite staining will highlight many acid-fast bacilli within the histiocytes (Figure 1).

Erythema nodosum leprosum is treated with a combination of immunosuppressants such as prednisone and thalidomide. Our patient was taking triple-antibiotic therapy—dapsone, rifampin, and clofazimine—for lepromatous leprosy when the erythematous papules developed on the arms and legs. After a skin biopsy confirmed the diagnosis of ENL, he was started on prednisone 20 mg daily with plans for close follow-up. Unfortunately, the patient was subsequently lost to follow-up.

Acute febrile neutrophilic dermatosis (also known as Sweet syndrome) is an acute inflammatory disease characterized by abrupt onset of painful erythematous papules, plaques, or nodules on the skin. It often is seen in association with preceding infections (especially those in the upper respiratory or gastrointestinal tracts), hematologic malignancies, inflammatory bowel disease, or exposure to certain classes of medications (eg, granulocyte colony-stimulating factor, tyrosine kinase inhibitors, various antibiotics).³ Histologically, acute febrile neutrophilic dermatosis is characterized by dense neutrophilic infiltrates, often with notable dermal edema (Figure 2).⁴ Many cases also show leukocytoclastic vasculitis; however, foamy histiocytes are not a notable component of the inflammatory infiltrate, though a histiocytoid form of acute febrile neutrophilic dermatosis has been described.⁵ Infections must be rigorously ruled out prior to diagnosing a patient with acute febrile neutrophilic dermatosis, making it a diagnosis of exclusion.

Cutaneous coccidioidomycosis is an infection caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. Cutaneous disease is rare but can occur from direct inoculation or dissemination from pulmonary disease in immunocompetent or immunocompromised patients. Papules, pustules, or plaques are seen clinically. Histologically, cutaneous coccidioidomycosis shows spherules that vary from 10 to 100 μm and are filled with multiple smaller endospores (Figure 3).⁶ Pseudoepitheliomatous hyperplasia with dense suppurative and granulomatous infiltrates also is seen.

Erythema induratum is characterized by tender nodules on the lower extremities and has a substantial female predominance. Many cases are associated with Mycobacterium tuberculosis infection. The bacteria are not seen directly in the skin but are instead detectable through DNA polymerase chain reaction testing or investigation of other organ systems.^7,8 Histologically, lesions show a lobular panniculitis with a mixed infiltrate. Vasculitis is seen in approximately 90% of erythema induratum cases vs approximately 25% of classic ENL cases (Figure 4),^2,9 which has led some to use the term nodular vasculitis to describe this disease entity. Nodular vasculitis is considered by others to be a distinct disease entity in which there are clinical and histologic features similar to erythema induratum but no evidence of M tuberculosis infection.⁹

Polyarteritis nodosa is a vasculitis that affects medium- sized vessels of various organ systems. The presenting signs and symptoms vary based on the affected organ systems. Palpable to retiform purpura, livedo racemosa, subcutaneous nodules, or ulcers are seen when the skin is involved. The histologic hallmark is necrotizing vasculitis of medium-sized arterioles (Figure 5), although leukocytoclastic vasculitis of small-caliber vessels also can be seen in biopsies of affected skin.¹⁰ The vascular changes are said to be segmental, with uninvolved segments interspersed with involved segments. Antineutrophil cytoplasmic antibody (ANCA)– associated vasculitis also must be considered when one sees leukocytoclastic vasculitis of small-caliber vessels in the skin, as it can be distinguished most readily by detecting circulating antibodies specific for myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA).

The Diagnosis: Erythema Nodosum Leprosum

Erythema nodosum leprosum (ENL) is a type 2 reaction sometimes seen in patients infected with Mycobacterium leprae—primarily those with lepromatous or borderline lepromatous subtypes. Clinically, ENL manifests with abrupt onset of tender erythematous papules with associated fevers and general malaise. Studies have demonstrated a complex immune system reaction in ENL, but the detailed pathophysiology is not fully understood.¹ Biopsies conducted within 24 hours of lesion formation are most elucidating. Foamy histiocytes admixed with neutrophils are seen in the subcutis, often causing a lobular panniculitis (quiz image).² Neutrophils rarely are seen in other types of leprosy and thus are a useful diagnostic clue for ENL. Vasculitis of small- to medium-sized vessels can be seen but is not a necessary diagnostic criterion. Fite staining will highlight many acid-fast bacilli within the histiocytes (Figure 1).

Erythema nodosum leprosum is treated with a combination of immunosuppressants such as prednisone and thalidomide. Our patient was taking triple-antibiotic therapy—dapsone, rifampin, and clofazimine—for lepromatous leprosy when the erythematous papules developed on the arms and legs. After a skin biopsy confirmed the diagnosis of ENL, he was started on prednisone 20 mg daily with plans for close follow-up. Unfortunately, the patient was subsequently lost to follow-up.

Acute febrile neutrophilic dermatosis (also known as Sweet syndrome) is an acute inflammatory disease characterized by abrupt onset of painful erythematous papules, plaques, or nodules on the skin. It often is seen in association with preceding infections (especially those in the upper respiratory or gastrointestinal tracts), hematologic malignancies, inflammatory bowel disease, or exposure to certain classes of medications (eg, granulocyte colony-stimulating factor, tyrosine kinase inhibitors, various antibiotics).³ Histologically, acute febrile neutrophilic dermatosis is characterized by dense neutrophilic infiltrates, often with notable dermal edema (Figure 2).⁴ Many cases also show leukocytoclastic vasculitis; however, foamy histiocytes are not a notable component of the inflammatory infiltrate, though a histiocytoid form of acute febrile neutrophilic dermatosis has been described.⁵ Infections must be rigorously ruled out prior to diagnosing a patient with acute febrile neutrophilic dermatosis, making it a diagnosis of exclusion.

Cutaneous coccidioidomycosis is an infection caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. Cutaneous disease is rare but can occur from direct inoculation or dissemination from pulmonary disease in immunocompetent or immunocompromised patients. Papules, pustules, or plaques are seen clinically. Histologically, cutaneous coccidioidomycosis shows spherules that vary from 10 to 100 μm and are filled with multiple smaller endospores (Figure 3).⁶ Pseudoepitheliomatous hyperplasia with dense suppurative and granulomatous infiltrates also is seen.

Erythema induratum is characterized by tender nodules on the lower extremities and has a substantial female predominance. Many cases are associated with Mycobacterium tuberculosis infection. The bacteria are not seen directly in the skin but are instead detectable through DNA polymerase chain reaction testing or investigation of other organ systems.^7,8 Histologically, lesions show a lobular panniculitis with a mixed infiltrate. Vasculitis is seen in approximately 90% of erythema induratum cases vs approximately 25% of classic ENL cases (Figure 4),^2,9 which has led some to use the term nodular vasculitis to describe this disease entity. Nodular vasculitis is considered by others to be a distinct disease entity in which there are clinical and histologic features similar to erythema induratum but no evidence of M tuberculosis infection.⁹

Polyarteritis nodosa is a vasculitis that affects medium- sized vessels of various organ systems. The presenting signs and symptoms vary based on the affected organ systems. Palpable to retiform purpura, livedo racemosa, subcutaneous nodules, or ulcers are seen when the skin is involved. The histologic hallmark is necrotizing vasculitis of medium-sized arterioles (Figure 5), although leukocytoclastic vasculitis of small-caliber vessels also can be seen in biopsies of affected skin.¹⁰ The vascular changes are said to be segmental, with uninvolved segments interspersed with involved segments. Antineutrophil cytoplasmic antibody (ANCA)– associated vasculitis also must be considered when one sees leukocytoclastic vasculitis of small-caliber vessels in the skin, as it can be distinguished most readily by detecting circulating antibodies specific for myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA).

Prurigo nodularis (PN)(also called chronic nodular prurigo, prurigo nodularis of Hyde, or picker’s nodules) was first characterized by James Hyde in 1909.^1-3 Prurigo nodularis manifests with symmetrical, intensely pruritic, eroded, or hyperkeratotic nodules or papules on the extremities and trunk.^1,2,4,5 Studies have shown that individuals with PN experience pruritus, sleep loss, decreased social functioning from the appearance of the nodules, and a higher incidence of anxiety and depression, causing a negative impact on their quality of life.^2,6 In addition, the manifestation of PN has been linked to neurologic and psychiatric disorders; however, PN also can be idiopathic and manifest without underlying illnesses.^2,6,7

Prurigo nodularis has been associated with other dermatologic conditions such as atopic dermatitis (up to 50%), lichen planus, keratoacanthomas (KAs), and bullous pemphigoid.^7-9 It also has been linked to systemic diseases in 38% to 50% of cases, including chronic kidney disease, liver disease, type 2 diabetes mellitus, malignancies (hematopoietic, liver, and skin), and HIV infection.^6,8,10

The pathophysiology of PN is highly complex and has yet to be fully elucidated. It is thought to be due to dysregulation and interaction of the increase in neural and immunologic responses of proinflammatory and pruritogenic cytokines.^2,11 Treatments aim to break the itch-scratch cycle that perpetuates this disorder; however, this proves difficult, as PN is associated with a higher itch intensity than atopic dermatitis and psoriasis.¹⁰ Therefore, most patients attempt multiple forms of treatment for PN, ranging from topical therapies, oral immunosuppressants, and phototherapy to the newest and only medication approved by the US Food and Drug Administration for the treatment of PN—dupilumab.^1,7,11 Herein, we provide an updated review of PN with a focus on its epidemiology, histopathology and pathophysiology, comorbidities, clinical presentation, differential diagnosis, and current treatment options.

Epidemiology

There are few studies on the epidemiology of PN; however, middle-aged populations with underlying dermatologic or psychiatric disorders tend to be impacted most frequently.^2,12,13 In 2016, it was estimated that almost 88,000 individuals had PN in the United States, with the majority being female; however, this estimate only took into account those aged 18 to 64 years and utilized data from IBM MarketScan Commercial Claims and Encounters Database (IBM Watson Health) from October 2015 to December 2016.¹⁴ More recently, a retrospective database analysis estimated the prevalence of PN in the United States to be anywhere from 36.7 to 43.9 cases per 100,000 individuals. However, this retrospective review utilized the International Classification of Diseases, Tenth Revision code; PN has 2 codes associated with the diagnosis, and the coding accuracy is unknown.¹⁵ Sutaria et al¹⁶ looked at racial disparities in patients with PN utilizing data from TriNetX and found that patients who received a diagnosis of PN were more likely to be women, non-Hispanic, and Black compared with control patients. However, these estimates are restricted to the health care organizations within this database.

In 2018, Poland reported an annual prevalence of 6.52 cases per 100,000 individuals,¹⁷ while England reported a yearly prevalence of 3.27 cases per 100,000 individuals.¹⁸ Both countries reported most cases were female. However, these studies are not without limitations. Poland only uses the primary diagnosis code for medical billing to simplify clinical coding, thus underestimating the actual prevalence; furthermore, clinical codes more often than not are assigned by someone other than the diagnosing physician, leaving room for error.¹⁷ In addition, England’s PN estimate utilized diagnosis data from primary care and inpatient datasets, leaving out outpatient datasets in which patients with PN may have been referred and obtained the diagnosis, potentially underestimating the prevalence in this population.¹⁸

In contrast, Korea estimated the annual prevalence of PN to be 4.82 cases per 1000 dermatology outpatients, with the majority being men, based on results from a cross-sectional study among outpatients from the Catholic Medical Center. Although this is the largest health organization in Korea, the scope of this study is limited and lacks data from other medical centers in Korea.¹⁹

Histopathology and Pathophysiology

Almost all cells in the skin are involved in PN: keratinocytes, mast cells, dendritic cells, endothelial cells, lymphocytes, eosinophils, collagen fibers, and nerve fibers.^11,20 Classically, PN manifests as a dome-shaped lesion with hyperkeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia with increased thickness of the papillary dermis consisting of coarse collagen with compact interstitial and circumvascular infiltration as well as increased lymphocytes and histocytes in the superficial dermis (Figure 1).²⁰ Hyperkeratosis is thought to be due to either the alteration of keratinocyte structures from scratching or keratinocyte abnormalities triggering PN.²¹ However, the increase in keratinocytes, which secrete nerve growth factor, allows for neuronal hyperplasia within the dermis.²² Nerve growth factor can stimulate keratinocyte proliferation²³ in addition to the upregulation of substance P (SP), a tachykinin that triggers vascular dilation and pruritus in the skin.²⁴ The density of SP nerve fibers in the dermis increases in PN, causing proinflammatory effects, upregulating the immune response to promote endothelial hyperplasia and increased vascularization.²⁵ The increase in these fibers may lead to pruritus associated with PN.^2,26

Many inflammatory cytokines and mediators also have been implicated in PN. Increased messenger RNA expression of IL-4, IL-17, IL-22, and IL-31 has been described in PN lesions.^3,27 Furthermore, studies also have reported increased helper T cell (T_H2) cytokines, including IL-4, IL-5, IL-10, and IL-13, in the dermis of PN lesions in patients without a history of atopy.^3,28 These pruritogenic cytokines in conjunction with the SP fibers may create an intractable itch for those with PN. The interaction and culmination of the neural and immune responses make PN a complex condition to treat with the multifactorial interaction of systems. 

Comorbidities

Prurigo nodularis has been associated with a wide array of comorbidities; however, the direction of the relationship between PN and these conditions makes it difficult to discern if PN is a primary or secondary condition.²⁹ Prurigo nodularis commonly has been connected to other inflammatory dermatoses, with a link to atopic dermatitis being the strongest.^5,29 However, PN also has been linked to other pruritic inflammatory cutaneous disorders, including psoriasis, cutaneous T-cell lymphoma, lichen planus, and dermatitis herpetiformis.^14,29

Huang et al¹⁴ found an increased likelihood of psychiatric illnesses in patients with PN, including eating disorders, nonsuicidal self-injury disorder, attention-deficit/hyperactivity disorder, schizophrenia, mood disorders, anxiety, and substance abuse disorders. Treatments directed at the neural aspect of PN have included selective serotonin reuptake inhibitors (SSRIs), which also are utilized to treat these mental health disorders.

Furthermore, systemic diseases also have been found to be associated with PN, including hypertension, type 2 diabetes mellitus, chronic kidney disease, heart failure, cerebrovascular disease, coronary heart disease, and chronic obstructive pulmonary disease.¹⁴ The relationship between PN and systemic conditions may be due to increased systemic inflammation and dysregulation of neural and metabolic functions implicated in these conditions from increased pruritic manifestations.^29,30 However, studies also have connected PN to infectious conditions such as HIV. One study found that patients with PN had 2.68 higher odds of infection with HIV compared to age- and sex-matched controls.¹⁴ It is unknown if these conditions contributed to the development of PN or PN contributed to the development of these disorders.

Clinical Presentations

Prurigo nodularis is a chronic inflammatory skin disease that typically manifests with multiple severely pruritic, dome-shaped, firm, hyperpigmented papulonodules with central scale or crust, often with erosion, due to chronic repetitive scratching and picking secondary to pruritic systemic or dermatologic diseases or psychological disorders (Figure 2).^1,2,4,5,8,31 Most often, diagnosis of PN is based on history and physical examination of the lesion; however, biopsies may be performed. These nodules commonly manifest with ulceration distributed symmetrically on extensor extremities in easy-to-reach places, sparing the mid back (called the butterfly sign).⁸ Lesions—either a few or hundreds—can range from a few millimeters to 2 to 3 cm.^8,32 The lesions differ in appearance depending on the pigment in the patient’s skin. In patients with darker skin tones, hyperpigmented or hypopigmented papulonodules are not uncommon, while those with fairer skin tones tend to present with erythema.³¹

Differential Diagnosis

Because of the variation in manifestation of PN, these lesions may resemble other cutaneous conditions. If the lesions are hyperkeratotic, they can mimic hypertrophic lichen planus, which mainfests with hyperkeratotic plaques or nodules on the lower extremities.^8,29 In addition, the histopathology of lichen planus resembles the appearance of PN, with epidermal hyperplasia, hypergranulosis, hyperkeratosis, and increased fibroblasts and capillaries.^8,29

Pemphigoid nodularis is a rare subtype of bullous pemphigoid that exhibits characteristics of PN with pruritic plaques and erosions.^8,29,33 The patient population for pemphigoid nodularis tends to be aged 50 to 60 years, and females are affected more frequently than males. However, pemphigoid nodularis may manifest with blistering and large plaques, which are not seen commonly with PN.²⁹ On histopathology, pemphigoid nodularis deposits IgG and C3 on the basement membrane and has subepidermal clefting, unlike PN.^7,29

Actinic prurigo manifests with pruritic papules or nodules post–UV exposure to unprotected skin.^8,29,33 This rare condition usually manifests with cheilitis and conjunctivitis. Unlike PN, which commonly affects elderly populations, actinic prurigo typically is found in young females.^8,29 Cytologic examination shows hyperkeratosis, spongiosis, and acanthosis of the epidermis with lymphocytic perivascular infiltration of the dermis.³⁴

Neurotic excoriations also tend to mimic PN with raised excoriated lesions; however, this disorder is due to neurotic picking of the skin without associated pruritus or true hyperkeratosis.^8,29,33 Histopathology shows epidermal crusting with inflammation of the upper dermis.³⁵

Infiltrative cutaneous squamous cell carcinoma (SCC) may imitate PN in appearance. It manifests as tender, ulcerated, scaly plaques or nodules. Histopathology shows cytologic atypia with an infiltrative architectural pattern and presence of collections of compact keratin and parakeratin (called keratin pearls).

Keratoacanthomas can resemble PN lesions. They usually manifest as nodules measuring 1 to 2 cm in diameter and 0.5 cm thick, resembling crateriform tumors.³⁶ On histopathology, KAs can resemble SCCs; however, KAs tend to manifest more frequently with a keratin-filled crater with a ground-glass appearance.³⁶

Inverted follicular keratosis commonly manifests on the face in elderly men as a single, flesh-colored, verrucous papule that may resemble PN. However, cytology of inverted follicular keratosis is characterized by proliferation and squamous eddies.³⁷ Consideration of the histologic findings and clinical appearance are important to differentiate between PN and cutaneous SCC.

Pseudoepitheliomatous hyperplasia is a benign condition that manifests as a plaque or nodule with crust, scale, or ulceration. Histologically, this condition presents with hyperplastic proliferation of the epidermis and adnexal epithelium.³⁸ The clinical and histologic appearance can mimic PN and other cutaneous eruptions with epidermal hyperplasia. 

In clinical cases that are resistant to treatment, biopsy is the best approach to diagnose the lesion. Due to similarities in physical appearance and superficial histologic presentation of PN, KAs from SCC, hypertrophic lichen planus, and other hyperkeratotic lesions, the biopsy should be taken at the base of the lesion to sample deeper layers of skin to differentiate these dermatologic disorders.

Management

Current treatments for PN yield varied results. Many patients with moderate to severe PN attempt multiple therapies before seeing improvement.³¹ Treatments include topical, oral, and injectable medications and are either directed at the neural or immune components of PN due to the interplay between increased nerve fibers in the lesions (neural axis) as well as increases in cytokines and other immunologic mediators (immune axis) of this condition. However, the FDA recently approved the first treatment for PN—dupilumab—which is an injectable IL-4 receptor antagonist directed at the immunologic interactions affiliated with PN.

Immune-Mediated Topical Therapies—Immunologic topical therapies include corticosteroids, calcipotriol, and calcineurin inhibitors. Studies that have analyzed these treatments are limited to case reports and small intraindividual and randomized controlled trials (Table 1). Topical therapies usually are first-line agents for most patients. Adverse effects include transient irritation of the skin.^40,42,43

Supplements—N-acetyl cysteine is an over-the-counter supplement that has been reported to improve symptoms in patients with skin-picking disorders.⁴⁸ The mechanism of action includes antioxidant effects such as decreasing reactive oxygen species, decreasing inflammatory markers, regulating neurotransmitters, and inhibiting hyperkeratosis.⁴⁹ N-acetyl cysteine has been poorly studied for its application in PN. A small study of 3 patients with subacute PN receiving 1200 mg of oral N-acetyl cysteine reported varying levels of improvement in skin appearance and reduction in skin picking.⁵⁰

Phototherapy—Phototherapy, a typical first- or second-line treatment modality for PN, targets both the neural- and immune-mediated aspects associated with pruritus in PN (Table 1).⁵¹ UV light can penetrate through the epidermal layer of the skin and reach the keratinocytes, which play a role in the immune-related response of PN. In addition, the cutaneous sensory nerves are located in the upper dermal layer, from which nerve fibers grow and penetrate into the epidermis, thereby interacting with the keratinocytes where pruritic signals are transmitted from the periphery up to the brain.⁵¹

Studies analyzing the effects of phototherapy on PN are limited to case series and a small randomized controlled trial. However, this trial has shown improvements in pruritus in the participants. Adverse effects include transient burning and erythema at the treated sites.^44,45

Immune-Mediated Oral Therapies—Immunologic-targeted oral therapies include bilastine, methotrexate, and cyclosporine (Table 2).^52,53 Bilastine efficacy was analyzed in a small phase 3, open-label, multicenter study in Japan; however, patients were allowed to use topical steroids in conjunction with the oral antihistamine.⁵⁴ Methotrexate and cyclosporine are immunosuppressive medications and were analyzed in small retrospective studies. Both treatments yielded notable relief for patients; however, 38.5% (15/39) of patients receiving methotrexate experienced adverse events, and 50.0% (4/8) experienced adverse events with cyclosporine.^52,53

Thalidomide was studied in a small retrospective case review that showed notable improvement in PN. Dosages of thalidomide varied, but on average the dose was 100 mg/d. However, greater than 50% of patients experienced at least 1 adverse effect with this treatment.⁶³

A study performed in Italy showed promising results for patients treated with pregabalin, with 70.0% (21/30) continuing to take pregabalin for almost 2 years following completion of the initial 3-month trial.⁵⁵ Naltrexone decreased pruritus in more than half of patients (9/17).⁵⁹ Amitriptyline yielded improvements in patients with PN; however, disease recurred in 5 patients (29%) after 7 months.⁶² A study performed in Germany reported promising results for paroxetine and fluvoxamine; however, some patients enrolled in the study had some form of psychiatric disorder.⁶¹

Serlopitant, aprepitant, and nalbuphine were studied in randomized controlled trials. The serlopitant trials were the largest of the neurally mediated oral medication studies; one showed substantial improvement in patients with PN,⁵⁶ while the most recent trial did not show significant improvement (ClinicalTrials.gov identifier NCT03546816).⁵⁷ On the other hand, aprepitant showed no major difference between the experimental and placebo groups.⁵⁸ Nalbuphine 162 mg twice daily showed greater improvement in PN than nalbuphine 81 mg twice daily.⁶⁰

Immune-Mediated Injectable Therapies—Immune-targeted injectables include nemolizumab and dupilumab (Table 2). Nemolizumab is an IL-31 antagonist that has been studied in a small randomized controlled trial that showed great success in decreasing pruritus associated with PN.⁶⁴ IL-31 has been implicated in PN, and inhibition of the IL-31 receptor has been shown to disrupt the itch-scratch cycle of PN. Dupilumab is a monoclonal antibody against the IL-4 and IL-13 receptors, and it is the only FDA-approved treatment for PN.⁶⁵ Blockage of these protein receptors decreases type 2 inflammation and chronic pruritus.^66,67 Dupilumab is FDA approved for the treatment of atopic dermatitis and recently was approved for adults with PN. Dupilumab acts to block the shared α-subunit of the pruritogenic cytokines IL-4 and IL-13 pathways,²⁹ thereby breaking the itch-scratch cycle associated with PN and allowing for the healing of these lesions. Results from 2 clinical trials showed substantially reduced itch in patients with PN.⁶⁵ Dupilumab also was approved by the European Medicines Agency for moderate to severe PN.⁶⁸

Conclusion

Prurigo nodularis is a chronic condition that affects patient quality of life and can mimic various dermatologic conditions. The epidemiology and pathophysiology of PN have not been fully expounded. More research should be conducted to determine the underpinnings of PN to help identify more consistently effective therapies for this complex condition.

Prurigo nodularis (PN)(also called chronic nodular prurigo, prurigo nodularis of Hyde, or picker’s nodules) was first characterized by James Hyde in 1909.^1-3 Prurigo nodularis manifests with symmetrical, intensely pruritic, eroded, or hyperkeratotic nodules or papules on the extremities and trunk.^1,2,4,5 Studies have shown that individuals with PN experience pruritus, sleep loss, decreased social functioning from the appearance of the nodules, and a higher incidence of anxiety and depression, causing a negative impact on their quality of life.^2,6 In addition, the manifestation of PN has been linked to neurologic and psychiatric disorders; however, PN also can be idiopathic and manifest without underlying illnesses.^2,6,7

Prurigo nodularis has been associated with other dermatologic conditions such as atopic dermatitis (up to 50%), lichen planus, keratoacanthomas (KAs), and bullous pemphigoid.^7-9 It also has been linked to systemic diseases in 38% to 50% of cases, including chronic kidney disease, liver disease, type 2 diabetes mellitus, malignancies (hematopoietic, liver, and skin), and HIV infection.^6,8,10

The pathophysiology of PN is highly complex and has yet to be fully elucidated. It is thought to be due to dysregulation and interaction of the increase in neural and immunologic responses of proinflammatory and pruritogenic cytokines.^2,11 Treatments aim to break the itch-scratch cycle that perpetuates this disorder; however, this proves difficult, as PN is associated with a higher itch intensity than atopic dermatitis and psoriasis.¹⁰ Therefore, most patients attempt multiple forms of treatment for PN, ranging from topical therapies, oral immunosuppressants, and phototherapy to the newest and only medication approved by the US Food and Drug Administration for the treatment of PN—dupilumab.^1,7,11 Herein, we provide an updated review of PN with a focus on its epidemiology, histopathology and pathophysiology, comorbidities, clinical presentation, differential diagnosis, and current treatment options.

Epidemiology

There are few studies on the epidemiology of PN; however, middle-aged populations with underlying dermatologic or psychiatric disorders tend to be impacted most frequently.^2,12,13 In 2016, it was estimated that almost 88,000 individuals had PN in the United States, with the majority being female; however, this estimate only took into account those aged 18 to 64 years and utilized data from IBM MarketScan Commercial Claims and Encounters Database (IBM Watson Health) from October 2015 to December 2016.¹⁴ More recently, a retrospective database analysis estimated the prevalence of PN in the United States to be anywhere from 36.7 to 43.9 cases per 100,000 individuals. However, this retrospective review utilized the International Classification of Diseases, Tenth Revision code; PN has 2 codes associated with the diagnosis, and the coding accuracy is unknown.¹⁵ Sutaria et al¹⁶ looked at racial disparities in patients with PN utilizing data from TriNetX and found that patients who received a diagnosis of PN were more likely to be women, non-Hispanic, and Black compared with control patients. However, these estimates are restricted to the health care organizations within this database.

In 2018, Poland reported an annual prevalence of 6.52 cases per 100,000 individuals,¹⁷ while England reported a yearly prevalence of 3.27 cases per 100,000 individuals.¹⁸ Both countries reported most cases were female. However, these studies are not without limitations. Poland only uses the primary diagnosis code for medical billing to simplify clinical coding, thus underestimating the actual prevalence; furthermore, clinical codes more often than not are assigned by someone other than the diagnosing physician, leaving room for error.¹⁷ In addition, England’s PN estimate utilized diagnosis data from primary care and inpatient datasets, leaving out outpatient datasets in which patients with PN may have been referred and obtained the diagnosis, potentially underestimating the prevalence in this population.¹⁸

In contrast, Korea estimated the annual prevalence of PN to be 4.82 cases per 1000 dermatology outpatients, with the majority being men, based on results from a cross-sectional study among outpatients from the Catholic Medical Center. Although this is the largest health organization in Korea, the scope of this study is limited and lacks data from other medical centers in Korea.¹⁹

Histopathology and Pathophysiology

Almost all cells in the skin are involved in PN: keratinocytes, mast cells, dendritic cells, endothelial cells, lymphocytes, eosinophils, collagen fibers, and nerve fibers.^11,20 Classically, PN manifests as a dome-shaped lesion with hyperkeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia with increased thickness of the papillary dermis consisting of coarse collagen with compact interstitial and circumvascular infiltration as well as increased lymphocytes and histocytes in the superficial dermis (Figure 1).²⁰ Hyperkeratosis is thought to be due to either the alteration of keratinocyte structures from scratching or keratinocyte abnormalities triggering PN.²¹ However, the increase in keratinocytes, which secrete nerve growth factor, allows for neuronal hyperplasia within the dermis.²² Nerve growth factor can stimulate keratinocyte proliferation²³ in addition to the upregulation of substance P (SP), a tachykinin that triggers vascular dilation and pruritus in the skin.²⁴ The density of SP nerve fibers in the dermis increases in PN, causing proinflammatory effects, upregulating the immune response to promote endothelial hyperplasia and increased vascularization.²⁵ The increase in these fibers may lead to pruritus associated with PN.^2,26

Many inflammatory cytokines and mediators also have been implicated in PN. Increased messenger RNA expression of IL-4, IL-17, IL-22, and IL-31 has been described in PN lesions.^3,27 Furthermore, studies also have reported increased helper T cell (T_H2) cytokines, including IL-4, IL-5, IL-10, and IL-13, in the dermis of PN lesions in patients without a history of atopy.^3,28 These pruritogenic cytokines in conjunction with the SP fibers may create an intractable itch for those with PN. The interaction and culmination of the neural and immune responses make PN a complex condition to treat with the multifactorial interaction of systems. 

Comorbidities

Prurigo nodularis has been associated with a wide array of comorbidities; however, the direction of the relationship between PN and these conditions makes it difficult to discern if PN is a primary or secondary condition.²⁹ Prurigo nodularis commonly has been connected to other inflammatory dermatoses, with a link to atopic dermatitis being the strongest.^5,29 However, PN also has been linked to other pruritic inflammatory cutaneous disorders, including psoriasis, cutaneous T-cell lymphoma, lichen planus, and dermatitis herpetiformis.^14,29

Huang et al¹⁴ found an increased likelihood of psychiatric illnesses in patients with PN, including eating disorders, nonsuicidal self-injury disorder, attention-deficit/hyperactivity disorder, schizophrenia, mood disorders, anxiety, and substance abuse disorders. Treatments directed at the neural aspect of PN have included selective serotonin reuptake inhibitors (SSRIs), which also are utilized to treat these mental health disorders.

Furthermore, systemic diseases also have been found to be associated with PN, including hypertension, type 2 diabetes mellitus, chronic kidney disease, heart failure, cerebrovascular disease, coronary heart disease, and chronic obstructive pulmonary disease.¹⁴ The relationship between PN and systemic conditions may be due to increased systemic inflammation and dysregulation of neural and metabolic functions implicated in these conditions from increased pruritic manifestations.^29,30 However, studies also have connected PN to infectious conditions such as HIV. One study found that patients with PN had 2.68 higher odds of infection with HIV compared to age- and sex-matched controls.¹⁴ It is unknown if these conditions contributed to the development of PN or PN contributed to the development of these disorders.

Clinical Presentations

Prurigo nodularis is a chronic inflammatory skin disease that typically manifests with multiple severely pruritic, dome-shaped, firm, hyperpigmented papulonodules with central scale or crust, often with erosion, due to chronic repetitive scratching and picking secondary to pruritic systemic or dermatologic diseases or psychological disorders (Figure 2).^1,2,4,5,8,31 Most often, diagnosis of PN is based on history and physical examination of the lesion; however, biopsies may be performed. These nodules commonly manifest with ulceration distributed symmetrically on extensor extremities in easy-to-reach places, sparing the mid back (called the butterfly sign).⁸ Lesions—either a few or hundreds—can range from a few millimeters to 2 to 3 cm.^8,32 The lesions differ in appearance depending on the pigment in the patient’s skin. In patients with darker skin tones, hyperpigmented or hypopigmented papulonodules are not uncommon, while those with fairer skin tones tend to present with erythema.³¹

Differential Diagnosis

Because of the variation in manifestation of PN, these lesions may resemble other cutaneous conditions. If the lesions are hyperkeratotic, they can mimic hypertrophic lichen planus, which mainfests with hyperkeratotic plaques or nodules on the lower extremities.^8,29 In addition, the histopathology of lichen planus resembles the appearance of PN, with epidermal hyperplasia, hypergranulosis, hyperkeratosis, and increased fibroblasts and capillaries.^8,29

Pemphigoid nodularis is a rare subtype of bullous pemphigoid that exhibits characteristics of PN with pruritic plaques and erosions.^8,29,33 The patient population for pemphigoid nodularis tends to be aged 50 to 60 years, and females are affected more frequently than males. However, pemphigoid nodularis may manifest with blistering and large plaques, which are not seen commonly with PN.²⁹ On histopathology, pemphigoid nodularis deposits IgG and C3 on the basement membrane and has subepidermal clefting, unlike PN.^7,29

Actinic prurigo manifests with pruritic papules or nodules post–UV exposure to unprotected skin.^8,29,33 This rare condition usually manifests with cheilitis and conjunctivitis. Unlike PN, which commonly affects elderly populations, actinic prurigo typically is found in young females.^8,29 Cytologic examination shows hyperkeratosis, spongiosis, and acanthosis of the epidermis with lymphocytic perivascular infiltration of the dermis.³⁴

Neurotic excoriations also tend to mimic PN with raised excoriated lesions; however, this disorder is due to neurotic picking of the skin without associated pruritus or true hyperkeratosis.^8,29,33 Histopathology shows epidermal crusting with inflammation of the upper dermis.³⁵

Infiltrative cutaneous squamous cell carcinoma (SCC) may imitate PN in appearance. It manifests as tender, ulcerated, scaly plaques or nodules. Histopathology shows cytologic atypia with an infiltrative architectural pattern and presence of collections of compact keratin and parakeratin (called keratin pearls).

Keratoacanthomas can resemble PN lesions. They usually manifest as nodules measuring 1 to 2 cm in diameter and 0.5 cm thick, resembling crateriform tumors.³⁶ On histopathology, KAs can resemble SCCs; however, KAs tend to manifest more frequently with a keratin-filled crater with a ground-glass appearance.³⁶

Inverted follicular keratosis commonly manifests on the face in elderly men as a single, flesh-colored, verrucous papule that may resemble PN. However, cytology of inverted follicular keratosis is characterized by proliferation and squamous eddies.³⁷ Consideration of the histologic findings and clinical appearance are important to differentiate between PN and cutaneous SCC.

Pseudoepitheliomatous hyperplasia is a benign condition that manifests as a plaque or nodule with crust, scale, or ulceration. Histologically, this condition presents with hyperplastic proliferation of the epidermis and adnexal epithelium.³⁸ The clinical and histologic appearance can mimic PN and other cutaneous eruptions with epidermal hyperplasia. 

In clinical cases that are resistant to treatment, biopsy is the best approach to diagnose the lesion. Due to similarities in physical appearance and superficial histologic presentation of PN, KAs from SCC, hypertrophic lichen planus, and other hyperkeratotic lesions, the biopsy should be taken at the base of the lesion to sample deeper layers of skin to differentiate these dermatologic disorders.

Management

Current treatments for PN yield varied results. Many patients with moderate to severe PN attempt multiple therapies before seeing improvement.³¹ Treatments include topical, oral, and injectable medications and are either directed at the neural or immune components of PN due to the interplay between increased nerve fibers in the lesions (neural axis) as well as increases in cytokines and other immunologic mediators (immune axis) of this condition. However, the FDA recently approved the first treatment for PN—dupilumab—which is an injectable IL-4 receptor antagonist directed at the immunologic interactions affiliated with PN.

Immune-Mediated Topical Therapies—Immunologic topical therapies include corticosteroids, calcipotriol, and calcineurin inhibitors. Studies that have analyzed these treatments are limited to case reports and small intraindividual and randomized controlled trials (Table 1). Topical therapies usually are first-line agents for most patients. Adverse effects include transient irritation of the skin.^40,42,43

Supplements—N-acetyl cysteine is an over-the-counter supplement that has been reported to improve symptoms in patients with skin-picking disorders.⁴⁸ The mechanism of action includes antioxidant effects such as decreasing reactive oxygen species, decreasing inflammatory markers, regulating neurotransmitters, and inhibiting hyperkeratosis.⁴⁹ N-acetyl cysteine has been poorly studied for its application in PN. A small study of 3 patients with subacute PN receiving 1200 mg of oral N-acetyl cysteine reported varying levels of improvement in skin appearance and reduction in skin picking.⁵⁰

Phototherapy—Phototherapy, a typical first- or second-line treatment modality for PN, targets both the neural- and immune-mediated aspects associated with pruritus in PN (Table 1).⁵¹ UV light can penetrate through the epidermal layer of the skin and reach the keratinocytes, which play a role in the immune-related response of PN. In addition, the cutaneous sensory nerves are located in the upper dermal layer, from which nerve fibers grow and penetrate into the epidermis, thereby interacting with the keratinocytes where pruritic signals are transmitted from the periphery up to the brain.⁵¹

Studies analyzing the effects of phototherapy on PN are limited to case series and a small randomized controlled trial. However, this trial has shown improvements in pruritus in the participants. Adverse effects include transient burning and erythema at the treated sites.^44,45

Immune-Mediated Oral Therapies—Immunologic-targeted oral therapies include bilastine, methotrexate, and cyclosporine (Table 2).^52,53 Bilastine efficacy was analyzed in a small phase 3, open-label, multicenter study in Japan; however, patients were allowed to use topical steroids in conjunction with the oral antihistamine.⁵⁴ Methotrexate and cyclosporine are immunosuppressive medications and were analyzed in small retrospective studies. Both treatments yielded notable relief for patients; however, 38.5% (15/39) of patients receiving methotrexate experienced adverse events, and 50.0% (4/8) experienced adverse events with cyclosporine.^52,53

Thalidomide was studied in a small retrospective case review that showed notable improvement in PN. Dosages of thalidomide varied, but on average the dose was 100 mg/d. However, greater than 50% of patients experienced at least 1 adverse effect with this treatment.⁶³

A study performed in Italy showed promising results for patients treated with pregabalin, with 70.0% (21/30) continuing to take pregabalin for almost 2 years following completion of the initial 3-month trial.⁵⁵ Naltrexone decreased pruritus in more than half of patients (9/17).⁵⁹ Amitriptyline yielded improvements in patients with PN; however, disease recurred in 5 patients (29%) after 7 months.⁶² A study performed in Germany reported promising results for paroxetine and fluvoxamine; however, some patients enrolled in the study had some form of psychiatric disorder.⁶¹

Serlopitant, aprepitant, and nalbuphine were studied in randomized controlled trials. The serlopitant trials were the largest of the neurally mediated oral medication studies; one showed substantial improvement in patients with PN,⁵⁶ while the most recent trial did not show significant improvement (ClinicalTrials.gov identifier NCT03546816).⁵⁷ On the other hand, aprepitant showed no major difference between the experimental and placebo groups.⁵⁸ Nalbuphine 162 mg twice daily showed greater improvement in PN than nalbuphine 81 mg twice daily.⁶⁰

Immune-Mediated Injectable Therapies—Immune-targeted injectables include nemolizumab and dupilumab (Table 2). Nemolizumab is an IL-31 antagonist that has been studied in a small randomized controlled trial that showed great success in decreasing pruritus associated with PN.⁶⁴ IL-31 has been implicated in PN, and inhibition of the IL-31 receptor has been shown to disrupt the itch-scratch cycle of PN. Dupilumab is a monoclonal antibody against the IL-4 and IL-13 receptors, and it is the only FDA-approved treatment for PN.⁶⁵ Blockage of these protein receptors decreases type 2 inflammation and chronic pruritus.^66,67 Dupilumab is FDA approved for the treatment of atopic dermatitis and recently was approved for adults with PN. Dupilumab acts to block the shared α-subunit of the pruritogenic cytokines IL-4 and IL-13 pathways,²⁹ thereby breaking the itch-scratch cycle associated with PN and allowing for the healing of these lesions. Results from 2 clinical trials showed substantially reduced itch in patients with PN.⁶⁵ Dupilumab also was approved by the European Medicines Agency for moderate to severe PN.⁶⁸

Conclusion

Prurigo nodularis is a chronic condition that affects patient quality of life and can mimic various dermatologic conditions. The epidemiology and pathophysiology of PN have not been fully expounded. More research should be conducted to determine the underpinnings of PN to help identify more consistently effective therapies for this complex condition.

Prurigo nodularis (PN)(also called chronic nodular prurigo, prurigo nodularis of Hyde, or picker’s nodules) was first characterized by James Hyde in 1909.^1-3 Prurigo nodularis manifests with symmetrical, intensely pruritic, eroded, or hyperkeratotic nodules or papules on the extremities and trunk.^1,2,4,5 Studies have shown that individuals with PN experience pruritus, sleep loss, decreased social functioning from the appearance of the nodules, and a higher incidence of anxiety and depression, causing a negative impact on their quality of life.^2,6 In addition, the manifestation of PN has been linked to neurologic and psychiatric disorders; however, PN also can be idiopathic and manifest without underlying illnesses.^2,6,7

Prurigo nodularis has been associated with other dermatologic conditions such as atopic dermatitis (up to 50%), lichen planus, keratoacanthomas (KAs), and bullous pemphigoid.^7-9 It also has been linked to systemic diseases in 38% to 50% of cases, including chronic kidney disease, liver disease, type 2 diabetes mellitus, malignancies (hematopoietic, liver, and skin), and HIV infection.^6,8,10

The pathophysiology of PN is highly complex and has yet to be fully elucidated. It is thought to be due to dysregulation and interaction of the increase in neural and immunologic responses of proinflammatory and pruritogenic cytokines.^2,11 Treatments aim to break the itch-scratch cycle that perpetuates this disorder; however, this proves difficult, as PN is associated with a higher itch intensity than atopic dermatitis and psoriasis.¹⁰ Therefore, most patients attempt multiple forms of treatment for PN, ranging from topical therapies, oral immunosuppressants, and phototherapy to the newest and only medication approved by the US Food and Drug Administration for the treatment of PN—dupilumab.^1,7,11 Herein, we provide an updated review of PN with a focus on its epidemiology, histopathology and pathophysiology, comorbidities, clinical presentation, differential diagnosis, and current treatment options.

Epidemiology

There are few studies on the epidemiology of PN; however, middle-aged populations with underlying dermatologic or psychiatric disorders tend to be impacted most frequently.^2,12,13 In 2016, it was estimated that almost 88,000 individuals had PN in the United States, with the majority being female; however, this estimate only took into account those aged 18 to 64 years and utilized data from IBM MarketScan Commercial Claims and Encounters Database (IBM Watson Health) from October 2015 to December 2016.¹⁴ More recently, a retrospective database analysis estimated the prevalence of PN in the United States to be anywhere from 36.7 to 43.9 cases per 100,000 individuals. However, this retrospective review utilized the International Classification of Diseases, Tenth Revision code; PN has 2 codes associated with the diagnosis, and the coding accuracy is unknown.¹⁵ Sutaria et al¹⁶ looked at racial disparities in patients with PN utilizing data from TriNetX and found that patients who received a diagnosis of PN were more likely to be women, non-Hispanic, and Black compared with control patients. However, these estimates are restricted to the health care organizations within this database.

In 2018, Poland reported an annual prevalence of 6.52 cases per 100,000 individuals,¹⁷ while England reported a yearly prevalence of 3.27 cases per 100,000 individuals.¹⁸ Both countries reported most cases were female. However, these studies are not without limitations. Poland only uses the primary diagnosis code for medical billing to simplify clinical coding, thus underestimating the actual prevalence; furthermore, clinical codes more often than not are assigned by someone other than the diagnosing physician, leaving room for error.¹⁷ In addition, England’s PN estimate utilized diagnosis data from primary care and inpatient datasets, leaving out outpatient datasets in which patients with PN may have been referred and obtained the diagnosis, potentially underestimating the prevalence in this population.¹⁸

In contrast, Korea estimated the annual prevalence of PN to be 4.82 cases per 1000 dermatology outpatients, with the majority being men, based on results from a cross-sectional study among outpatients from the Catholic Medical Center. Although this is the largest health organization in Korea, the scope of this study is limited and lacks data from other medical centers in Korea.¹⁹

Histopathology and Pathophysiology

Almost all cells in the skin are involved in PN: keratinocytes, mast cells, dendritic cells, endothelial cells, lymphocytes, eosinophils, collagen fibers, and nerve fibers.^11,20 Classically, PN manifests as a dome-shaped lesion with hyperkeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia with increased thickness of the papillary dermis consisting of coarse collagen with compact interstitial and circumvascular infiltration as well as increased lymphocytes and histocytes in the superficial dermis (Figure 1).²⁰ Hyperkeratosis is thought to be due to either the alteration of keratinocyte structures from scratching or keratinocyte abnormalities triggering PN.²¹ However, the increase in keratinocytes, which secrete nerve growth factor, allows for neuronal hyperplasia within the dermis.²² Nerve growth factor can stimulate keratinocyte proliferation²³ in addition to the upregulation of substance P (SP), a tachykinin that triggers vascular dilation and pruritus in the skin.²⁴ The density of SP nerve fibers in the dermis increases in PN, causing proinflammatory effects, upregulating the immune response to promote endothelial hyperplasia and increased vascularization.²⁵ The increase in these fibers may lead to pruritus associated with PN.^2,26

Many inflammatory cytokines and mediators also have been implicated in PN. Increased messenger RNA expression of IL-4, IL-17, IL-22, and IL-31 has been described in PN lesions.^3,27 Furthermore, studies also have reported increased helper T cell (T_H2) cytokines, including IL-4, IL-5, IL-10, and IL-13, in the dermis of PN lesions in patients without a history of atopy.^3,28 These pruritogenic cytokines in conjunction with the SP fibers may create an intractable itch for those with PN. The interaction and culmination of the neural and immune responses make PN a complex condition to treat with the multifactorial interaction of systems. 

Comorbidities

Prurigo nodularis has been associated with a wide array of comorbidities; however, the direction of the relationship between PN and these conditions makes it difficult to discern if PN is a primary or secondary condition.²⁹ Prurigo nodularis commonly has been connected to other inflammatory dermatoses, with a link to atopic dermatitis being the strongest.^5,29 However, PN also has been linked to other pruritic inflammatory cutaneous disorders, including psoriasis, cutaneous T-cell lymphoma, lichen planus, and dermatitis herpetiformis.^14,29

Huang et al¹⁴ found an increased likelihood of psychiatric illnesses in patients with PN, including eating disorders, nonsuicidal self-injury disorder, attention-deficit/hyperactivity disorder, schizophrenia, mood disorders, anxiety, and substance abuse disorders. Treatments directed at the neural aspect of PN have included selective serotonin reuptake inhibitors (SSRIs), which also are utilized to treat these mental health disorders.

Furthermore, systemic diseases also have been found to be associated with PN, including hypertension, type 2 diabetes mellitus, chronic kidney disease, heart failure, cerebrovascular disease, coronary heart disease, and chronic obstructive pulmonary disease.¹⁴ The relationship between PN and systemic conditions may be due to increased systemic inflammation and dysregulation of neural and metabolic functions implicated in these conditions from increased pruritic manifestations.^29,30 However, studies also have connected PN to infectious conditions such as HIV. One study found that patients with PN had 2.68 higher odds of infection with HIV compared to age- and sex-matched controls.¹⁴ It is unknown if these conditions contributed to the development of PN or PN contributed to the development of these disorders.

Clinical Presentations

Prurigo nodularis is a chronic inflammatory skin disease that typically manifests with multiple severely pruritic, dome-shaped, firm, hyperpigmented papulonodules with central scale or crust, often with erosion, due to chronic repetitive scratching and picking secondary to pruritic systemic or dermatologic diseases or psychological disorders (Figure 2).^1,2,4,5,8,31 Most often, diagnosis of PN is based on history and physical examination of the lesion; however, biopsies may be performed. These nodules commonly manifest with ulceration distributed symmetrically on extensor extremities in easy-to-reach places, sparing the mid back (called the butterfly sign).⁸ Lesions—either a few or hundreds—can range from a few millimeters to 2 to 3 cm.^8,32 The lesions differ in appearance depending on the pigment in the patient’s skin. In patients with darker skin tones, hyperpigmented or hypopigmented papulonodules are not uncommon, while those with fairer skin tones tend to present with erythema.³¹

Differential Diagnosis

Because of the variation in manifestation of PN, these lesions may resemble other cutaneous conditions. If the lesions are hyperkeratotic, they can mimic hypertrophic lichen planus, which mainfests with hyperkeratotic plaques or nodules on the lower extremities.^8,29 In addition, the histopathology of lichen planus resembles the appearance of PN, with epidermal hyperplasia, hypergranulosis, hyperkeratosis, and increased fibroblasts and capillaries.^8,29

Pemphigoid nodularis is a rare subtype of bullous pemphigoid that exhibits characteristics of PN with pruritic plaques and erosions.^8,29,33 The patient population for pemphigoid nodularis tends to be aged 50 to 60 years, and females are affected more frequently than males. However, pemphigoid nodularis may manifest with blistering and large plaques, which are not seen commonly with PN.²⁹ On histopathology, pemphigoid nodularis deposits IgG and C3 on the basement membrane and has subepidermal clefting, unlike PN.^7,29

Actinic prurigo manifests with pruritic papules or nodules post–UV exposure to unprotected skin.^8,29,33 This rare condition usually manifests with cheilitis and conjunctivitis. Unlike PN, which commonly affects elderly populations, actinic prurigo typically is found in young females.^8,29 Cytologic examination shows hyperkeratosis, spongiosis, and acanthosis of the epidermis with lymphocytic perivascular infiltration of the dermis.³⁴

Neurotic excoriations also tend to mimic PN with raised excoriated lesions; however, this disorder is due to neurotic picking of the skin without associated pruritus or true hyperkeratosis.^8,29,33 Histopathology shows epidermal crusting with inflammation of the upper dermis.³⁵

Infiltrative cutaneous squamous cell carcinoma (SCC) may imitate PN in appearance. It manifests as tender, ulcerated, scaly plaques or nodules. Histopathology shows cytologic atypia with an infiltrative architectural pattern and presence of collections of compact keratin and parakeratin (called keratin pearls).

Keratoacanthomas can resemble PN lesions. They usually manifest as nodules measuring 1 to 2 cm in diameter and 0.5 cm thick, resembling crateriform tumors.³⁶ On histopathology, KAs can resemble SCCs; however, KAs tend to manifest more frequently with a keratin-filled crater with a ground-glass appearance.³⁶

Inverted follicular keratosis commonly manifests on the face in elderly men as a single, flesh-colored, verrucous papule that may resemble PN. However, cytology of inverted follicular keratosis is characterized by proliferation and squamous eddies.³⁷ Consideration of the histologic findings and clinical appearance are important to differentiate between PN and cutaneous SCC.

Pseudoepitheliomatous hyperplasia is a benign condition that manifests as a plaque or nodule with crust, scale, or ulceration. Histologically, this condition presents with hyperplastic proliferation of the epidermis and adnexal epithelium.³⁸ The clinical and histologic appearance can mimic PN and other cutaneous eruptions with epidermal hyperplasia. 

In clinical cases that are resistant to treatment, biopsy is the best approach to diagnose the lesion. Due to similarities in physical appearance and superficial histologic presentation of PN, KAs from SCC, hypertrophic lichen planus, and other hyperkeratotic lesions, the biopsy should be taken at the base of the lesion to sample deeper layers of skin to differentiate these dermatologic disorders.

Management

Current treatments for PN yield varied results. Many patients with moderate to severe PN attempt multiple therapies before seeing improvement.³¹ Treatments include topical, oral, and injectable medications and are either directed at the neural or immune components of PN due to the interplay between increased nerve fibers in the lesions (neural axis) as well as increases in cytokines and other immunologic mediators (immune axis) of this condition. However, the FDA recently approved the first treatment for PN—dupilumab—which is an injectable IL-4 receptor antagonist directed at the immunologic interactions affiliated with PN.

Immune-Mediated Topical Therapies—Immunologic topical therapies include corticosteroids, calcipotriol, and calcineurin inhibitors. Studies that have analyzed these treatments are limited to case reports and small intraindividual and randomized controlled trials (Table 1). Topical therapies usually are first-line agents for most patients. Adverse effects include transient irritation of the skin.^40,42,43

Supplements—N-acetyl cysteine is an over-the-counter supplement that has been reported to improve symptoms in patients with skin-picking disorders.⁴⁸ The mechanism of action includes antioxidant effects such as decreasing reactive oxygen species, decreasing inflammatory markers, regulating neurotransmitters, and inhibiting hyperkeratosis.⁴⁹ N-acetyl cysteine has been poorly studied for its application in PN. A small study of 3 patients with subacute PN receiving 1200 mg of oral N-acetyl cysteine reported varying levels of improvement in skin appearance and reduction in skin picking.⁵⁰

Phototherapy—Phototherapy, a typical first- or second-line treatment modality for PN, targets both the neural- and immune-mediated aspects associated with pruritus in PN (Table 1).⁵¹ UV light can penetrate through the epidermal layer of the skin and reach the keratinocytes, which play a role in the immune-related response of PN. In addition, the cutaneous sensory nerves are located in the upper dermal layer, from which nerve fibers grow and penetrate into the epidermis, thereby interacting with the keratinocytes where pruritic signals are transmitted from the periphery up to the brain.⁵¹

Studies analyzing the effects of phototherapy on PN are limited to case series and a small randomized controlled trial. However, this trial has shown improvements in pruritus in the participants. Adverse effects include transient burning and erythema at the treated sites.^44,45

Immune-Mediated Oral Therapies—Immunologic-targeted oral therapies include bilastine, methotrexate, and cyclosporine (Table 2).^52,53 Bilastine efficacy was analyzed in a small phase 3, open-label, multicenter study in Japan; however, patients were allowed to use topical steroids in conjunction with the oral antihistamine.⁵⁴ Methotrexate and cyclosporine are immunosuppressive medications and were analyzed in small retrospective studies. Both treatments yielded notable relief for patients; however, 38.5% (15/39) of patients receiving methotrexate experienced adverse events, and 50.0% (4/8) experienced adverse events with cyclosporine.^52,53

Thalidomide was studied in a small retrospective case review that showed notable improvement in PN. Dosages of thalidomide varied, but on average the dose was 100 mg/d. However, greater than 50% of patients experienced at least 1 adverse effect with this treatment.⁶³

A study performed in Italy showed promising results for patients treated with pregabalin, with 70.0% (21/30) continuing to take pregabalin for almost 2 years following completion of the initial 3-month trial.⁵⁵ Naltrexone decreased pruritus in more than half of patients (9/17).⁵⁹ Amitriptyline yielded improvements in patients with PN; however, disease recurred in 5 patients (29%) after 7 months.⁶² A study performed in Germany reported promising results for paroxetine and fluvoxamine; however, some patients enrolled in the study had some form of psychiatric disorder.⁶¹

Serlopitant, aprepitant, and nalbuphine were studied in randomized controlled trials. The serlopitant trials were the largest of the neurally mediated oral medication studies; one showed substantial improvement in patients with PN,⁵⁶ while the most recent trial did not show significant improvement (ClinicalTrials.gov identifier NCT03546816).⁵⁷ On the other hand, aprepitant showed no major difference between the experimental and placebo groups.⁵⁸ Nalbuphine 162 mg twice daily showed greater improvement in PN than nalbuphine 81 mg twice daily.⁶⁰

Immune-Mediated Injectable Therapies—Immune-targeted injectables include nemolizumab and dupilumab (Table 2). Nemolizumab is an IL-31 antagonist that has been studied in a small randomized controlled trial that showed great success in decreasing pruritus associated with PN.⁶⁴ IL-31 has been implicated in PN, and inhibition of the IL-31 receptor has been shown to disrupt the itch-scratch cycle of PN. Dupilumab is a monoclonal antibody against the IL-4 and IL-13 receptors, and it is the only FDA-approved treatment for PN.⁶⁵ Blockage of these protein receptors decreases type 2 inflammation and chronic pruritus.^66,67 Dupilumab is FDA approved for the treatment of atopic dermatitis and recently was approved for adults with PN. Dupilumab acts to block the shared α-subunit of the pruritogenic cytokines IL-4 and IL-13 pathways,²⁹ thereby breaking the itch-scratch cycle associated with PN and allowing for the healing of these lesions. Results from 2 clinical trials showed substantially reduced itch in patients with PN.⁶⁵ Dupilumab also was approved by the European Medicines Agency for moderate to severe PN.⁶⁸

Conclusion

Prurigo nodularis is a chronic condition that affects patient quality of life and can mimic various dermatologic conditions. The epidemiology and pathophysiology of PN have not been fully expounded. More research should be conducted to determine the underpinnings of PN to help identify more consistently effective therapies for this complex condition.

To the Editor:

Pityriasis rubra pilaris (PRP) is a rare papulosquamous condition with an unknown pathogenesis and limited efficacy data, which can make treatment challenging. Some cases of PRP spontaneously resolve in a few months, which is most common in the pediatric population.¹ Pityriasis rubra pilaris in adults is likely to persist for years, and spontaneous resolution is unpredictable. Randomized clinical trials are difficult to perform due to the rarity of PRP.

Although there is no cure and no standard protocol for treating PRP, systemic retinoids historically are considered first-line therapy for moderate to severe cases.² Additional management approaches include symptomatic control with moisturizers and psychological support. Alternative systemic treatments for moderate to severe cases include methotrexate, phototherapy, and cyclosporine.²

Pityriasis rubra pilaris demonstrates a favorable response to methotrexate treatment, especially in type I cases; however, patients on this alternative therapy should be monitored for severe adverse effects (eg, hepatotoxicity, pancytopenia, pneumonitis).² Phototherapy should be approached with caution. Narrowband UVB, UVA1, and psoralen plus UVA therapy have successfully treated PRP; however, the response is variable. In some cases, the opposite effect can occur, in which the condition is photoaggravated. Phototherapy is a valid alternative form of treatment when used in combination with acitretin, and a phototest should be performed prior to starting this regimen. Cyclosporine is another immunosuppressant that can be considered for PRP treatment, though there are limited data demonstrating its efficacy.²

The introduction of biologic agents has changed the treatment approach for many dermatologic diseases, including PRP. Given the similar features between psoriasis and PRP, the biologics prescribed for psoriasis therapy also are used for patients with PRP that is challenging to treat, such as anti–tumor necrosis factor α inhibitors and IL inhibitors—specifically IL-17 and IL-23. Remission has been achieved with the use of biologics in combination with retinoid therapy.²

Biologic therapies used for PRP effectively inhibit cytokines and reduce the overall inflammatory processes involved in the development of the scaly patches and plaques seen in this condition. However, most reported clinical experiences are case studies, and more research in the form of randomized clinical trials is needed to understand the efficacy and long-term effects of this form of treatment in PRP. We present a case of a patient with refractory adult subtype I PRP that was successfully treated with the IL-23 inhibitor risankizumab.

A 65-year-old man was referred to Florida Academic Dermatology Center (Coral Gables, Florida) with biopsy-proven PRP diagnosed 1 year prior. The patient reported experiencing a debilitating quality of life in the year since diagnosis (Figure 1). Treatment attempts with dupilumab, tralokinumab, intramuscular steroid injections, and topical corticosteroids had failed (Figure 2). Following evaluation at Florida Academic Dermatology Center, the patient was started on acitretin 25 mg every other day and received an initial subcutaneous injection of ixekizumab 160 mg (an IL-17 inhibitor) followed 2 weeks later by a second injection of 80 mg. After the 2 doses of ixekizumab, the patient’s condition worsened with the development of pinpoint hemorrhagic lesions. The medication was discontinued, and he was started on risankizumab 150 mg at the approved dosing regimen for plaque psoriasis in combination with the acitretin therapy. Prior to starting risankizumab, the affected body surface area (BSA) was 80%. At 1-month follow-up, he showed improvement with reduction in scaling and erythema and an affected BSA of 30% (Figure 3). At 4-month follow-up, he continued showing improvement with an affected BSA of 10% (Figure 4). Acitretin was discontinued, and the patient has been successfully maintained on risankizumab 150 mg/mL subcutaneous injections every 12 weeks since.

To the Editor:

Pityriasis rubra pilaris (PRP) is a rare papulosquamous condition with an unknown pathogenesis and limited efficacy data, which can make treatment challenging. Some cases of PRP spontaneously resolve in a few months, which is most common in the pediatric population.¹ Pityriasis rubra pilaris in adults is likely to persist for years, and spontaneous resolution is unpredictable. Randomized clinical trials are difficult to perform due to the rarity of PRP.

Although there is no cure and no standard protocol for treating PRP, systemic retinoids historically are considered first-line therapy for moderate to severe cases.² Additional management approaches include symptomatic control with moisturizers and psychological support. Alternative systemic treatments for moderate to severe cases include methotrexate, phototherapy, and cyclosporine.²

Pityriasis rubra pilaris demonstrates a favorable response to methotrexate treatment, especially in type I cases; however, patients on this alternative therapy should be monitored for severe adverse effects (eg, hepatotoxicity, pancytopenia, pneumonitis).² Phototherapy should be approached with caution. Narrowband UVB, UVA1, and psoralen plus UVA therapy have successfully treated PRP; however, the response is variable. In some cases, the opposite effect can occur, in which the condition is photoaggravated. Phototherapy is a valid alternative form of treatment when used in combination with acitretin, and a phototest should be performed prior to starting this regimen. Cyclosporine is another immunosuppressant that can be considered for PRP treatment, though there are limited data demonstrating its efficacy.²

The introduction of biologic agents has changed the treatment approach for many dermatologic diseases, including PRP. Given the similar features between psoriasis and PRP, the biologics prescribed for psoriasis therapy also are used for patients with PRP that is challenging to treat, such as anti–tumor necrosis factor α inhibitors and IL inhibitors—specifically IL-17 and IL-23. Remission has been achieved with the use of biologics in combination with retinoid therapy.²

Biologic therapies used for PRP effectively inhibit cytokines and reduce the overall inflammatory processes involved in the development of the scaly patches and plaques seen in this condition. However, most reported clinical experiences are case studies, and more research in the form of randomized clinical trials is needed to understand the efficacy and long-term effects of this form of treatment in PRP. We present a case of a patient with refractory adult subtype I PRP that was successfully treated with the IL-23 inhibitor risankizumab.

A 65-year-old man was referred to Florida Academic Dermatology Center (Coral Gables, Florida) with biopsy-proven PRP diagnosed 1 year prior. The patient reported experiencing a debilitating quality of life in the year since diagnosis (Figure 1). Treatment attempts with dupilumab, tralokinumab, intramuscular steroid injections, and topical corticosteroids had failed (Figure 2). Following evaluation at Florida Academic Dermatology Center, the patient was started on acitretin 25 mg every other day and received an initial subcutaneous injection of ixekizumab 160 mg (an IL-17 inhibitor) followed 2 weeks later by a second injection of 80 mg. After the 2 doses of ixekizumab, the patient’s condition worsened with the development of pinpoint hemorrhagic lesions. The medication was discontinued, and he was started on risankizumab 150 mg at the approved dosing regimen for plaque psoriasis in combination with the acitretin therapy. Prior to starting risankizumab, the affected body surface area (BSA) was 80%. At 1-month follow-up, he showed improvement with reduction in scaling and erythema and an affected BSA of 30% (Figure 3). At 4-month follow-up, he continued showing improvement with an affected BSA of 10% (Figure 4). Acitretin was discontinued, and the patient has been successfully maintained on risankizumab 150 mg/mL subcutaneous injections every 12 weeks since.

To the Editor:

Pityriasis rubra pilaris (PRP) is a rare papulosquamous condition with an unknown pathogenesis and limited efficacy data, which can make treatment challenging. Some cases of PRP spontaneously resolve in a few months, which is most common in the pediatric population.¹ Pityriasis rubra pilaris in adults is likely to persist for years, and spontaneous resolution is unpredictable. Randomized clinical trials are difficult to perform due to the rarity of PRP.

Although there is no cure and no standard protocol for treating PRP, systemic retinoids historically are considered first-line therapy for moderate to severe cases.² Additional management approaches include symptomatic control with moisturizers and psychological support. Alternative systemic treatments for moderate to severe cases include methotrexate, phototherapy, and cyclosporine.²

Pityriasis rubra pilaris demonstrates a favorable response to methotrexate treatment, especially in type I cases; however, patients on this alternative therapy should be monitored for severe adverse effects (eg, hepatotoxicity, pancytopenia, pneumonitis).² Phototherapy should be approached with caution. Narrowband UVB, UVA1, and psoralen plus UVA therapy have successfully treated PRP; however, the response is variable. In some cases, the opposite effect can occur, in which the condition is photoaggravated. Phototherapy is a valid alternative form of treatment when used in combination with acitretin, and a phototest should be performed prior to starting this regimen. Cyclosporine is another immunosuppressant that can be considered for PRP treatment, though there are limited data demonstrating its efficacy.²

The introduction of biologic agents has changed the treatment approach for many dermatologic diseases, including PRP. Given the similar features between psoriasis and PRP, the biologics prescribed for psoriasis therapy also are used for patients with PRP that is challenging to treat, such as anti–tumor necrosis factor α inhibitors and IL inhibitors—specifically IL-17 and IL-23. Remission has been achieved with the use of biologics in combination with retinoid therapy.²

Biologic therapies used for PRP effectively inhibit cytokines and reduce the overall inflammatory processes involved in the development of the scaly patches and plaques seen in this condition. However, most reported clinical experiences are case studies, and more research in the form of randomized clinical trials is needed to understand the efficacy and long-term effects of this form of treatment in PRP. We present a case of a patient with refractory adult subtype I PRP that was successfully treated with the IL-23 inhibitor risankizumab.

A 65-year-old man was referred to Florida Academic Dermatology Center (Coral Gables, Florida) with biopsy-proven PRP diagnosed 1 year prior. The patient reported experiencing a debilitating quality of life in the year since diagnosis (Figure 1). Treatment attempts with dupilumab, tralokinumab, intramuscular steroid injections, and topical corticosteroids had failed (Figure 2). Following evaluation at Florida Academic Dermatology Center, the patient was started on acitretin 25 mg every other day and received an initial subcutaneous injection of ixekizumab 160 mg (an IL-17 inhibitor) followed 2 weeks later by a second injection of 80 mg. After the 2 doses of ixekizumab, the patient’s condition worsened with the development of pinpoint hemorrhagic lesions. The medication was discontinued, and he was started on risankizumab 150 mg at the approved dosing regimen for plaque psoriasis in combination with the acitretin therapy. Prior to starting risankizumab, the affected body surface area (BSA) was 80%. At 1-month follow-up, he showed improvement with reduction in scaling and erythema and an affected BSA of 30% (Figure 3). At 4-month follow-up, he continued showing improvement with an affected BSA of 10% (Figure 4). Acitretin was discontinued, and the patient has been successfully maintained on risankizumab 150 mg/mL subcutaneous injections every 12 weeks since.

Dermatology remains one of the most competitive specialties in the residency match, with successful applicants demonstrating a well-rounded application reflecting not only their academic excellence but also their dedication to research, community service, and hands-on clinical experience.¹ A growing emphasis on scholarly activities has made it crucial for applicants to stand out, with an increasing number opting to take gap years to engage in focused research endeavors.² In highly competitive specialties such as dermatology, successful applicants now report more than 20 research items on average.^3,4 This trend also is evident in primary care specialties, which have seen a 2- to 3-fold increase in reported research activities. The average unmatched applicant today lists more research items than the average matched applicant did a decade ago, underscoring the growing emphasis on scholarly activity.³

Ideally, graduate medical education should foster an environment of inquiry and scholarship, where residents develop new knowledge, evaluate research findings, and cultivate lifelong habits of inquiry. The Accreditation Council for Graduate Medical Education requires residents to engage in scholarship, such as case reports, research reviews, and original research.⁵ Research during residency has been linked to several benefits, including enhanced patient care through improved critical appraisal skills, clinical reasoning, and lifelong learning.^6,7 Additionally, students and residents who publish research are more likely to achieve higher rank during residency and pursue careers in academic medicine, potentially helping to address the decline in clinician investigators.^8,9 Publishing and presenting research also can enhance a residency program’s reputation, making it more attractive to competitive applicants, and may be beneficial for residents seeking jobs or fellowships.⁶

Dermatology residency programs vary in their structure and support for resident research. One survey revealed that many programs lack the necessary support, structure, and resources to effectively promote and maintain research training.¹ Additionally, residents have less exposure to researchers who could serve as mentors due to the growing demands placed on attending physicians in teaching hospitals.¹⁰

The Research Arms Race

The growing emphasis on scholarly activity for residency and fellowship applicants coupled with the use of research productivity to differentiate candidates has led some to declare a “research arms race” in residency selection.³ As one author stated, “We need less research, better research, and research done for the right reasons.”¹¹ Indeed, most articles authored by medical students are short reviews or case reports, with the majority (59% [207/350]) being cited zero times, according to one analysis.¹² Given the variable research infrastructure between programs and the decreasing availability of research mentors despite the growing emphasis on scholarly activity, applicants face an unfortunate dilemma. Until the system changes, those who protest this research arms race by not engaging in substantial scholarly activity are less likely to match into competitive specialties. Thus, the race continues.

The Value of Mentorship

Resident research success is impacted by having an effective faculty research mentor.¹³ Although all medical research at the student or resident levels should be conducted with a faculty mentor to oversee it, finding a mentor can be challenging. If a resident’s program boasts a strong research infrastructure or prolific faculty, building relationships with potential mentors is a logical first step for residents wishing to engage in research; however, if suitable mentors are lacking, efforts should be made by residents to establish these connections elsewhere, such as attending society meetings to network with potential mentors and applying to formal mentorship programs (eg, the American Society for Dermatologic Surgery’s Preceptor Program, the Women’s Dermatologic Society’s Mentorship Award). Unsolicited email inquiries asking, “Hi Dr. X, my name is Y, and I was wondering if you have any research projects I could help with?” often go unanswered. Instead, consider emailing or approaching potential mentors with a more developed proposition, such as the following example:

Hello Dr. X, my name is Y. I have enjoyed reading your publications on A, which inspired me to think about B. I reviewed the literature and noticed a potential to enhance our current understanding on the topic. My team and I conducted a systematic review of the available literature and drafted a manuscript summarizing our findings. Given your expertise in this field, would you be willing to collaborate on this paper? We would be grateful for your critical eye, suggestions for improvement, and overall thoughts.

This approach demonstrates initiative, provides a clear plan, and shows respect for the mentor’s expertise, increasing the likelihood of a positive response and fruitful collaboration. Assuming the resident’s working draft meets the potential mentor’s basic expectations, such a display of initiative is likely to impress them, and they may then offer opportunities to engage in meaningful research projects in the future. Everyone benefits! These efforts to establish connections with mentors can pave the way to further collaboration and meaningful research opportunities for dermatology residents.

The Systematic Review: An Attractive Option For Residents

There are several potential avenues for students or residents interested in pursuing research. Case reports and case series are relatively easy to compile, can be completed quickly, and often require minimal guidance from a faculty mentor; however, case reports rank low in the research hierarchy. Conversely, prospective blinded clinical trials provide some of the highest-quality evidence available but are challenging to conduct without a practicing faculty member to provide a patient cohort, often require extensive funding, and may involve complex statistical analyses beyond the expertise of most students or residents. Additionally, they may take years to complete, often extending beyond residency or fellowship application deadlines.

Most medical applicants likely hold at least some hesitation in churning out vast amounts of low-quality research merely to boost their publication count for the match process. Ideally, those who pursue scholarly activity should be driven by a genuine desire to contribute meaningfully to the medical literature. One particularly valuable avenue for trainees wishing to engage in research is the systematic review, which aims to identify, evaluate, and summarize the findings of all relevant individual studies regarding a research topic and answer a focused question. If performed thoughtfully, a systematic review can meaningfully contribute to the medical literature without requiring access to a prospectively followed cohort of patients or the constant supervision of a faculty mentor. Sure, systematic reviews may not be as robust as prospective cohort clinical trials, but they often provide comprehensive insights and are considered valuable contributions to evidence-based medicine. With the help of co-residents or medical students, a medical reference librarian, and a statistician—along with a working understanding of universally accepted quality measures—a resident physician and their team can produce a systematic review that ultimately may merit publication in a top-tier medical journal.

The remainder of this column will outline a streamlined approach to the systematic review writing process, specifically tailored for medical residents who may not have affiliations to a prolific research department or established relationships with faculty mentors in their field of interest. The aim is to offer a basic framework to help residents navigate the complexities of conducting and writing a high-quality, impactful systematic review. It is important to emphasize that resident research should always be conducted under the guidance of a faculty mentor, and this approach is not intended to encourage independent research and publication by residents. Instead, it provides steps that can be undertaken with a foundational understanding of accepted principles, allowing residents to compile a working draft of a manuscript in collaboration with a trusted faculty mentor.

The Systematic Review: A Simple Approach

Step 1: Choose a Topic—Once a resident has decided to embark on conducting a systematic review, the first step is to choose a topic, which requires consideration of several factors to ensure relevance, feasibility, and impact. Begin by identifying areas of clinical uncertainty or controversy in which a comprehensive synthesis of the literature could provide valuable insights. Often, such a topic can be gleaned from the conclusion section of other primary studies; statements such as “further study is needed to determine the efficacy of X” or “systematic reviews would be beneficial to ascertaining the impact of Y” may be a great place to start.

Next, ensure that sufficient primary studies exist to support a robust review or meta-analysis by conducting a preliminary literature search, which will confirm that the chosen topic is both researchable and relevant. A narrow, focused, well-defined topic likely will prove more feasible to review than a broad, ill-defined one. Once a topic is selected, it is advisable to discuss it with a faculty mentor before starting the literature search to ensure the topic’s feasibility and clinical relevance, helping to guide your research in a meaningful direction.

When deciding between a systematic review and a meta-analysis, the nature of the research question is an influential factor. A systematic review is particularly suitable for addressing broad questions or topics when the aim is to summarize and synthesize all relevant research studies; for example, a systematic review may investigate the various treatment options for atopic dermatitis and their efficacy, which allows for a comprehensive overview of the available treatments—both the interventions and the outcomes. In contrast, a meta-analysis is ideal for collecting and statistically combining quantitative data from multiple primary studies, provided there are enough relevant studies available in the literature.

Step 2: Build a Team—Recruiting a skilled librarian to assist with Medical Subject Headings (MeSH) terms and retrieving relevant papers is crucial for conducting a high-quality systematic review or meta-analysis. Medical librarians specializing in health sciences enhance the efficiency, comprehensiveness, and reliability of your literature search, substantially boosting your work’s credibility. These librarians are well versed in medical databases such as PubMed and Embase. Begin by contacting your institution’s library services, as there often are valuable resources and personnel available to assist you. Personally, I was surprised to find a librarian at my institution specifically dedicated to helping medical residents with such projects! These professionals are eager to help, and if provided with the scope and goal of your project, they can deliver literature search results in a digestible format. Similarly, seeking the expertise of a medical statistician is crucial to the accuracy and legitimacy of your study. In your final paper, it is important to recognize the contributions of the librarian and statistician, either as co-authors or in the acknowledgments section.

In addition, recruiting colleagues or medical students can be an effective strategy to make the project more feasible and offer collaborative benefits for all parties involved. Given the growing emphasis on research for residency and fellowship admissions, there usually is no shortage of motivated volunteers.

Next, identify the software tool you will use for your systematic review. Options range from simple spreadsheets such as Microsoft Excel to reference managers such as EndNote or Mendeley or dedicated systematic review tools. Academic institutions may subscribe to paid services such as Covidence (https://www.covidence.org), or you can utilize free alternatives such as Rayyan (https://www.rayyan.ai). Investing time in learning to navigate dedicated systematic review software can greatly enhance efficiency and reduce frustrations compared to more basic methods. Ultimately, staying organized, thorough, and committed is key.

Step 3: Conduct the Literature Review—At this point, your research topic has been decided, a medical reference librarian has provided the results of a comprehensive literature search, and a software tool has been chosen. The next task is to read hundreds or thousands of papers—easy, right? With your dedicated team assembled, the workload can be divided and conquered. The first step involves screening out duplicate and irrelevant studies based on titles and abstracts. Next, review the remaining papers in more detail. Those that pass this preliminary screen should be read in their entirety, and only the papers relevant to the research topic should be included in the final synthesis. If there are uncertainties about a study’s relevance, consulting a faculty mentor is advisable. To ensure the systematic review is as thorough as possible, pay special attention to the references section of each paper, as cited references can reveal relevant studies that may have been missed in the literature search.

Once all relevant papers are compiled and read, the relevant data points should be extracted and imputed into a data sheet. Collaborating with a medical statistician is crucial at this stage, as they can provide guidance on the most effective ways to structure and input data. After all studies are included, the relevant statistical analyses on the resultant dataset can be run.

Step 4: Write the Paper—In 2020, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was developed to ensure transparent and complete reporting of systematic reviews. A full discussion of PRISMA guidelines is beyond the scope of this paper; Page et al¹⁴ provided a summary, checklist, and flow diagram that is available online (https://www.prisma-statement.org). Following the PRISMA checklist and guidelines ensures a high-quality, transparent, and reliable systematic review. These guidelines not only help streamline and simplify the writing process but also enhance its efficiency and effectiveness. Discovering the PRISMA checklist can be transformative, providing a valuable roadmap that guides the author through each step of the reporting process, helping to avoid common pitfalls. This structured approach ultimately leads to a more comprehensive and trustworthy review.

Step 5: Make Finishing Touches—At this stage in the systematic review process, the studies have been compiled and thoroughly analyzed and the statistical analysis has been conducted. The results have been organized within a structured framework following the PRISMA checklist. With these steps completed, the next task is to finalize the manuscript and seek a final review from the senior author or faculty mentor. To streamline this process, it is beneficial to adhere to the formatting guidelines of the specific medical journal you intend to submit to. Check the author guidelines on the journal’s website and review recent systematic reviews published there as a reference. Even if you have not chosen a journal yet, formatting your manuscript according to a prestigious journal’s general style provides a strong foundation that can be easily adapted to fit another journal’s requirements if necessary.

Final Thoughts

Designing and conducting a systematic review is no easy task, but it can be a valuable skill for dermatology residents aiming to contribute meaningfully to the medical literature. The process of compiling a systematic review offers an opportunity for developing critical research skills, from formulating a research question to synthesizing evidence and presenting findings in a clear methodical way. Engaging in systematic review writing not only enhances the resident’s understanding of a particular topic but also demonstrates a commitment to scholarly activity—a key factor in an increasingly competitive residency and fellowship application environment.

The basic steps outlined in this article are just one way in which residents can begin to navigate the complexities of medical research, specifically the systematic review process. By assembling a supportive team, utilizing available resources, and adhering to established guidelines such as PRISMA, one can produce a high-quality, impactful review. Ultimately, the systematic review process is not just about publication—it is about fostering a habit of inquiry, improving patient care, and contributing to the ever-evolving field of medicine. With dedication and collaboration, even the most challenging aspects of research can be tackled, paving the way for future opportunities and professional growth. In this way, perhaps one day the spirit of the “research race” can shift from a frantic sprint to a graceful marathon, where each mile is run with heart and every step is filled with purpose.

Dermatology remains one of the most competitive specialties in the residency match, with successful applicants demonstrating a well-rounded application reflecting not only their academic excellence but also their dedication to research, community service, and hands-on clinical experience.¹ A growing emphasis on scholarly activities has made it crucial for applicants to stand out, with an increasing number opting to take gap years to engage in focused research endeavors.² In highly competitive specialties such as dermatology, successful applicants now report more than 20 research items on average.^3,4 This trend also is evident in primary care specialties, which have seen a 2- to 3-fold increase in reported research activities. The average unmatched applicant today lists more research items than the average matched applicant did a decade ago, underscoring the growing emphasis on scholarly activity.³

Ideally, graduate medical education should foster an environment of inquiry and scholarship, where residents develop new knowledge, evaluate research findings, and cultivate lifelong habits of inquiry. The Accreditation Council for Graduate Medical Education requires residents to engage in scholarship, such as case reports, research reviews, and original research.⁵ Research during residency has been linked to several benefits, including enhanced patient care through improved critical appraisal skills, clinical reasoning, and lifelong learning.^6,7 Additionally, students and residents who publish research are more likely to achieve higher rank during residency and pursue careers in academic medicine, potentially helping to address the decline in clinician investigators.^8,9 Publishing and presenting research also can enhance a residency program’s reputation, making it more attractive to competitive applicants, and may be beneficial for residents seeking jobs or fellowships.⁶

Dermatology residency programs vary in their structure and support for resident research. One survey revealed that many programs lack the necessary support, structure, and resources to effectively promote and maintain research training.¹ Additionally, residents have less exposure to researchers who could serve as mentors due to the growing demands placed on attending physicians in teaching hospitals.¹⁰

The Research Arms Race

The growing emphasis on scholarly activity for residency and fellowship applicants coupled with the use of research productivity to differentiate candidates has led some to declare a “research arms race” in residency selection.³ As one author stated, “We need less research, better research, and research done for the right reasons.”¹¹ Indeed, most articles authored by medical students are short reviews or case reports, with the majority (59% [207/350]) being cited zero times, according to one analysis.¹² Given the variable research infrastructure between programs and the decreasing availability of research mentors despite the growing emphasis on scholarly activity, applicants face an unfortunate dilemma. Until the system changes, those who protest this research arms race by not engaging in substantial scholarly activity are less likely to match into competitive specialties. Thus, the race continues.

The Value of Mentorship

Resident research success is impacted by having an effective faculty research mentor.¹³ Although all medical research at the student or resident levels should be conducted with a faculty mentor to oversee it, finding a mentor can be challenging. If a resident’s program boasts a strong research infrastructure or prolific faculty, building relationships with potential mentors is a logical first step for residents wishing to engage in research; however, if suitable mentors are lacking, efforts should be made by residents to establish these connections elsewhere, such as attending society meetings to network with potential mentors and applying to formal mentorship programs (eg, the American Society for Dermatologic Surgery’s Preceptor Program, the Women’s Dermatologic Society’s Mentorship Award). Unsolicited email inquiries asking, “Hi Dr. X, my name is Y, and I was wondering if you have any research projects I could help with?” often go unanswered. Instead, consider emailing or approaching potential mentors with a more developed proposition, such as the following example:

Hello Dr. X, my name is Y. I have enjoyed reading your publications on A, which inspired me to think about B. I reviewed the literature and noticed a potential to enhance our current understanding on the topic. My team and I conducted a systematic review of the available literature and drafted a manuscript summarizing our findings. Given your expertise in this field, would you be willing to collaborate on this paper? We would be grateful for your critical eye, suggestions for improvement, and overall thoughts.

This approach demonstrates initiative, provides a clear plan, and shows respect for the mentor’s expertise, increasing the likelihood of a positive response and fruitful collaboration. Assuming the resident’s working draft meets the potential mentor’s basic expectations, such a display of initiative is likely to impress them, and they may then offer opportunities to engage in meaningful research projects in the future. Everyone benefits! These efforts to establish connections with mentors can pave the way to further collaboration and meaningful research opportunities for dermatology residents.

The Systematic Review: An Attractive Option For Residents

There are several potential avenues for students or residents interested in pursuing research. Case reports and case series are relatively easy to compile, can be completed quickly, and often require minimal guidance from a faculty mentor; however, case reports rank low in the research hierarchy. Conversely, prospective blinded clinical trials provide some of the highest-quality evidence available but are challenging to conduct without a practicing faculty member to provide a patient cohort, often require extensive funding, and may involve complex statistical analyses beyond the expertise of most students or residents. Additionally, they may take years to complete, often extending beyond residency or fellowship application deadlines.

Most medical applicants likely hold at least some hesitation in churning out vast amounts of low-quality research merely to boost their publication count for the match process. Ideally, those who pursue scholarly activity should be driven by a genuine desire to contribute meaningfully to the medical literature. One particularly valuable avenue for trainees wishing to engage in research is the systematic review, which aims to identify, evaluate, and summarize the findings of all relevant individual studies regarding a research topic and answer a focused question. If performed thoughtfully, a systematic review can meaningfully contribute to the medical literature without requiring access to a prospectively followed cohort of patients or the constant supervision of a faculty mentor. Sure, systematic reviews may not be as robust as prospective cohort clinical trials, but they often provide comprehensive insights and are considered valuable contributions to evidence-based medicine. With the help of co-residents or medical students, a medical reference librarian, and a statistician—along with a working understanding of universally accepted quality measures—a resident physician and their team can produce a systematic review that ultimately may merit publication in a top-tier medical journal.

The remainder of this column will outline a streamlined approach to the systematic review writing process, specifically tailored for medical residents who may not have affiliations to a prolific research department or established relationships with faculty mentors in their field of interest. The aim is to offer a basic framework to help residents navigate the complexities of conducting and writing a high-quality, impactful systematic review. It is important to emphasize that resident research should always be conducted under the guidance of a faculty mentor, and this approach is not intended to encourage independent research and publication by residents. Instead, it provides steps that can be undertaken with a foundational understanding of accepted principles, allowing residents to compile a working draft of a manuscript in collaboration with a trusted faculty mentor.

The Systematic Review: A Simple Approach

Step 1: Choose a Topic—Once a resident has decided to embark on conducting a systematic review, the first step is to choose a topic, which requires consideration of several factors to ensure relevance, feasibility, and impact. Begin by identifying areas of clinical uncertainty or controversy in which a comprehensive synthesis of the literature could provide valuable insights. Often, such a topic can be gleaned from the conclusion section of other primary studies; statements such as “further study is needed to determine the efficacy of X” or “systematic reviews would be beneficial to ascertaining the impact of Y” may be a great place to start.

Next, ensure that sufficient primary studies exist to support a robust review or meta-analysis by conducting a preliminary literature search, which will confirm that the chosen topic is both researchable and relevant. A narrow, focused, well-defined topic likely will prove more feasible to review than a broad, ill-defined one. Once a topic is selected, it is advisable to discuss it with a faculty mentor before starting the literature search to ensure the topic’s feasibility and clinical relevance, helping to guide your research in a meaningful direction.

When deciding between a systematic review and a meta-analysis, the nature of the research question is an influential factor. A systematic review is particularly suitable for addressing broad questions or topics when the aim is to summarize and synthesize all relevant research studies; for example, a systematic review may investigate the various treatment options for atopic dermatitis and their efficacy, which allows for a comprehensive overview of the available treatments—both the interventions and the outcomes. In contrast, a meta-analysis is ideal for collecting and statistically combining quantitative data from multiple primary studies, provided there are enough relevant studies available in the literature.

Step 2: Build a Team—Recruiting a skilled librarian to assist with Medical Subject Headings (MeSH) terms and retrieving relevant papers is crucial for conducting a high-quality systematic review or meta-analysis. Medical librarians specializing in health sciences enhance the efficiency, comprehensiveness, and reliability of your literature search, substantially boosting your work’s credibility. These librarians are well versed in medical databases such as PubMed and Embase. Begin by contacting your institution’s library services, as there often are valuable resources and personnel available to assist you. Personally, I was surprised to find a librarian at my institution specifically dedicated to helping medical residents with such projects! These professionals are eager to help, and if provided with the scope and goal of your project, they can deliver literature search results in a digestible format. Similarly, seeking the expertise of a medical statistician is crucial to the accuracy and legitimacy of your study. In your final paper, it is important to recognize the contributions of the librarian and statistician, either as co-authors or in the acknowledgments section.

In addition, recruiting colleagues or medical students can be an effective strategy to make the project more feasible and offer collaborative benefits for all parties involved. Given the growing emphasis on research for residency and fellowship admissions, there usually is no shortage of motivated volunteers.

Next, identify the software tool you will use for your systematic review. Options range from simple spreadsheets such as Microsoft Excel to reference managers such as EndNote or Mendeley or dedicated systematic review tools. Academic institutions may subscribe to paid services such as Covidence (https://www.covidence.org), or you can utilize free alternatives such as Rayyan (https://www.rayyan.ai). Investing time in learning to navigate dedicated systematic review software can greatly enhance efficiency and reduce frustrations compared to more basic methods. Ultimately, staying organized, thorough, and committed is key.

Step 3: Conduct the Literature Review—At this point, your research topic has been decided, a medical reference librarian has provided the results of a comprehensive literature search, and a software tool has been chosen. The next task is to read hundreds or thousands of papers—easy, right? With your dedicated team assembled, the workload can be divided and conquered. The first step involves screening out duplicate and irrelevant studies based on titles and abstracts. Next, review the remaining papers in more detail. Those that pass this preliminary screen should be read in their entirety, and only the papers relevant to the research topic should be included in the final synthesis. If there are uncertainties about a study’s relevance, consulting a faculty mentor is advisable. To ensure the systematic review is as thorough as possible, pay special attention to the references section of each paper, as cited references can reveal relevant studies that may have been missed in the literature search.

Once all relevant papers are compiled and read, the relevant data points should be extracted and imputed into a data sheet. Collaborating with a medical statistician is crucial at this stage, as they can provide guidance on the most effective ways to structure and input data. After all studies are included, the relevant statistical analyses on the resultant dataset can be run.

Step 4: Write the Paper—In 2020, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was developed to ensure transparent and complete reporting of systematic reviews. A full discussion of PRISMA guidelines is beyond the scope of this paper; Page et al¹⁴ provided a summary, checklist, and flow diagram that is available online (https://www.prisma-statement.org). Following the PRISMA checklist and guidelines ensures a high-quality, transparent, and reliable systematic review. These guidelines not only help streamline and simplify the writing process but also enhance its efficiency and effectiveness. Discovering the PRISMA checklist can be transformative, providing a valuable roadmap that guides the author through each step of the reporting process, helping to avoid common pitfalls. This structured approach ultimately leads to a more comprehensive and trustworthy review.

Step 5: Make Finishing Touches—At this stage in the systematic review process, the studies have been compiled and thoroughly analyzed and the statistical analysis has been conducted. The results have been organized within a structured framework following the PRISMA checklist. With these steps completed, the next task is to finalize the manuscript and seek a final review from the senior author or faculty mentor. To streamline this process, it is beneficial to adhere to the formatting guidelines of the specific medical journal you intend to submit to. Check the author guidelines on the journal’s website and review recent systematic reviews published there as a reference. Even if you have not chosen a journal yet, formatting your manuscript according to a prestigious journal’s general style provides a strong foundation that can be easily adapted to fit another journal’s requirements if necessary.

Final Thoughts

Designing and conducting a systematic review is no easy task, but it can be a valuable skill for dermatology residents aiming to contribute meaningfully to the medical literature. The process of compiling a systematic review offers an opportunity for developing critical research skills, from formulating a research question to synthesizing evidence and presenting findings in a clear methodical way. Engaging in systematic review writing not only enhances the resident’s understanding of a particular topic but also demonstrates a commitment to scholarly activity—a key factor in an increasingly competitive residency and fellowship application environment.

The basic steps outlined in this article are just one way in which residents can begin to navigate the complexities of medical research, specifically the systematic review process. By assembling a supportive team, utilizing available resources, and adhering to established guidelines such as PRISMA, one can produce a high-quality, impactful review. Ultimately, the systematic review process is not just about publication—it is about fostering a habit of inquiry, improving patient care, and contributing to the ever-evolving field of medicine. With dedication and collaboration, even the most challenging aspects of research can be tackled, paving the way for future opportunities and professional growth. In this way, perhaps one day the spirit of the “research race” can shift from a frantic sprint to a graceful marathon, where each mile is run with heart and every step is filled with purpose.

Dermatology remains one of the most competitive specialties in the residency match, with successful applicants demonstrating a well-rounded application reflecting not only their academic excellence but also their dedication to research, community service, and hands-on clinical experience.¹ A growing emphasis on scholarly activities has made it crucial for applicants to stand out, with an increasing number opting to take gap years to engage in focused research endeavors.² In highly competitive specialties such as dermatology, successful applicants now report more than 20 research items on average.^3,4 This trend also is evident in primary care specialties, which have seen a 2- to 3-fold increase in reported research activities. The average unmatched applicant today lists more research items than the average matched applicant did a decade ago, underscoring the growing emphasis on scholarly activity.³

Ideally, graduate medical education should foster an environment of inquiry and scholarship, where residents develop new knowledge, evaluate research findings, and cultivate lifelong habits of inquiry. The Accreditation Council for Graduate Medical Education requires residents to engage in scholarship, such as case reports, research reviews, and original research.⁵ Research during residency has been linked to several benefits, including enhanced patient care through improved critical appraisal skills, clinical reasoning, and lifelong learning.^6,7 Additionally, students and residents who publish research are more likely to achieve higher rank during residency and pursue careers in academic medicine, potentially helping to address the decline in clinician investigators.^8,9 Publishing and presenting research also can enhance a residency program’s reputation, making it more attractive to competitive applicants, and may be beneficial for residents seeking jobs or fellowships.⁶

Dermatology residency programs vary in their structure and support for resident research. One survey revealed that many programs lack the necessary support, structure, and resources to effectively promote and maintain research training.¹ Additionally, residents have less exposure to researchers who could serve as mentors due to the growing demands placed on attending physicians in teaching hospitals.¹⁰

The Research Arms Race

The growing emphasis on scholarly activity for residency and fellowship applicants coupled with the use of research productivity to differentiate candidates has led some to declare a “research arms race” in residency selection.³ As one author stated, “We need less research, better research, and research done for the right reasons.”¹¹ Indeed, most articles authored by medical students are short reviews or case reports, with the majority (59% [207/350]) being cited zero times, according to one analysis.¹² Given the variable research infrastructure between programs and the decreasing availability of research mentors despite the growing emphasis on scholarly activity, applicants face an unfortunate dilemma. Until the system changes, those who protest this research arms race by not engaging in substantial scholarly activity are less likely to match into competitive specialties. Thus, the race continues.

The Value of Mentorship

Resident research success is impacted by having an effective faculty research mentor.¹³ Although all medical research at the student or resident levels should be conducted with a faculty mentor to oversee it, finding a mentor can be challenging. If a resident’s program boasts a strong research infrastructure or prolific faculty, building relationships with potential mentors is a logical first step for residents wishing to engage in research; however, if suitable mentors are lacking, efforts should be made by residents to establish these connections elsewhere, such as attending society meetings to network with potential mentors and applying to formal mentorship programs (eg, the American Society for Dermatologic Surgery’s Preceptor Program, the Women’s Dermatologic Society’s Mentorship Award). Unsolicited email inquiries asking, “Hi Dr. X, my name is Y, and I was wondering if you have any research projects I could help with?” often go unanswered. Instead, consider emailing or approaching potential mentors with a more developed proposition, such as the following example:

Hello Dr. X, my name is Y. I have enjoyed reading your publications on A, which inspired me to think about B. I reviewed the literature and noticed a potential to enhance our current understanding on the topic. My team and I conducted a systematic review of the available literature and drafted a manuscript summarizing our findings. Given your expertise in this field, would you be willing to collaborate on this paper? We would be grateful for your critical eye, suggestions for improvement, and overall thoughts.

This approach demonstrates initiative, provides a clear plan, and shows respect for the mentor’s expertise, increasing the likelihood of a positive response and fruitful collaboration. Assuming the resident’s working draft meets the potential mentor’s basic expectations, such a display of initiative is likely to impress them, and they may then offer opportunities to engage in meaningful research projects in the future. Everyone benefits! These efforts to establish connections with mentors can pave the way to further collaboration and meaningful research opportunities for dermatology residents.

The Systematic Review: An Attractive Option For Residents

There are several potential avenues for students or residents interested in pursuing research. Case reports and case series are relatively easy to compile, can be completed quickly, and often require minimal guidance from a faculty mentor; however, case reports rank low in the research hierarchy. Conversely, prospective blinded clinical trials provide some of the highest-quality evidence available but are challenging to conduct without a practicing faculty member to provide a patient cohort, often require extensive funding, and may involve complex statistical analyses beyond the expertise of most students or residents. Additionally, they may take years to complete, often extending beyond residency or fellowship application deadlines.

Most medical applicants likely hold at least some hesitation in churning out vast amounts of low-quality research merely to boost their publication count for the match process. Ideally, those who pursue scholarly activity should be driven by a genuine desire to contribute meaningfully to the medical literature. One particularly valuable avenue for trainees wishing to engage in research is the systematic review, which aims to identify, evaluate, and summarize the findings of all relevant individual studies regarding a research topic and answer a focused question. If performed thoughtfully, a systematic review can meaningfully contribute to the medical literature without requiring access to a prospectively followed cohort of patients or the constant supervision of a faculty mentor. Sure, systematic reviews may not be as robust as prospective cohort clinical trials, but they often provide comprehensive insights and are considered valuable contributions to evidence-based medicine. With the help of co-residents or medical students, a medical reference librarian, and a statistician—along with a working understanding of universally accepted quality measures—a resident physician and their team can produce a systematic review that ultimately may merit publication in a top-tier medical journal.

The remainder of this column will outline a streamlined approach to the systematic review writing process, specifically tailored for medical residents who may not have affiliations to a prolific research department or established relationships with faculty mentors in their field of interest. The aim is to offer a basic framework to help residents navigate the complexities of conducting and writing a high-quality, impactful systematic review. It is important to emphasize that resident research should always be conducted under the guidance of a faculty mentor, and this approach is not intended to encourage independent research and publication by residents. Instead, it provides steps that can be undertaken with a foundational understanding of accepted principles, allowing residents to compile a working draft of a manuscript in collaboration with a trusted faculty mentor.

The Systematic Review: A Simple Approach

Step 1: Choose a Topic—Once a resident has decided to embark on conducting a systematic review, the first step is to choose a topic, which requires consideration of several factors to ensure relevance, feasibility, and impact. Begin by identifying areas of clinical uncertainty or controversy in which a comprehensive synthesis of the literature could provide valuable insights. Often, such a topic can be gleaned from the conclusion section of other primary studies; statements such as “further study is needed to determine the efficacy of X” or “systematic reviews would be beneficial to ascertaining the impact of Y” may be a great place to start.

Next, ensure that sufficient primary studies exist to support a robust review or meta-analysis by conducting a preliminary literature search, which will confirm that the chosen topic is both researchable and relevant. A narrow, focused, well-defined topic likely will prove more feasible to review than a broad, ill-defined one. Once a topic is selected, it is advisable to discuss it with a faculty mentor before starting the literature search to ensure the topic’s feasibility and clinical relevance, helping to guide your research in a meaningful direction.

When deciding between a systematic review and a meta-analysis, the nature of the research question is an influential factor. A systematic review is particularly suitable for addressing broad questions or topics when the aim is to summarize and synthesize all relevant research studies; for example, a systematic review may investigate the various treatment options for atopic dermatitis and their efficacy, which allows for a comprehensive overview of the available treatments—both the interventions and the outcomes. In contrast, a meta-analysis is ideal for collecting and statistically combining quantitative data from multiple primary studies, provided there are enough relevant studies available in the literature.

Step 2: Build a Team—Recruiting a skilled librarian to assist with Medical Subject Headings (MeSH) terms and retrieving relevant papers is crucial for conducting a high-quality systematic review or meta-analysis. Medical librarians specializing in health sciences enhance the efficiency, comprehensiveness, and reliability of your literature search, substantially boosting your work’s credibility. These librarians are well versed in medical databases such as PubMed and Embase. Begin by contacting your institution’s library services, as there often are valuable resources and personnel available to assist you. Personally, I was surprised to find a librarian at my institution specifically dedicated to helping medical residents with such projects! These professionals are eager to help, and if provided with the scope and goal of your project, they can deliver literature search results in a digestible format. Similarly, seeking the expertise of a medical statistician is crucial to the accuracy and legitimacy of your study. In your final paper, it is important to recognize the contributions of the librarian and statistician, either as co-authors or in the acknowledgments section.

In addition, recruiting colleagues or medical students can be an effective strategy to make the project more feasible and offer collaborative benefits for all parties involved. Given the growing emphasis on research for residency and fellowship admissions, there usually is no shortage of motivated volunteers.

Next, identify the software tool you will use for your systematic review. Options range from simple spreadsheets such as Microsoft Excel to reference managers such as EndNote or Mendeley or dedicated systematic review tools. Academic institutions may subscribe to paid services such as Covidence (https://www.covidence.org), or you can utilize free alternatives such as Rayyan (https://www.rayyan.ai). Investing time in learning to navigate dedicated systematic review software can greatly enhance efficiency and reduce frustrations compared to more basic methods. Ultimately, staying organized, thorough, and committed is key.

Step 3: Conduct the Literature Review—At this point, your research topic has been decided, a medical reference librarian has provided the results of a comprehensive literature search, and a software tool has been chosen. The next task is to read hundreds or thousands of papers—easy, right? With your dedicated team assembled, the workload can be divided and conquered. The first step involves screening out duplicate and irrelevant studies based on titles and abstracts. Next, review the remaining papers in more detail. Those that pass this preliminary screen should be read in their entirety, and only the papers relevant to the research topic should be included in the final synthesis. If there are uncertainties about a study’s relevance, consulting a faculty mentor is advisable. To ensure the systematic review is as thorough as possible, pay special attention to the references section of each paper, as cited references can reveal relevant studies that may have been missed in the literature search.

Once all relevant papers are compiled and read, the relevant data points should be extracted and imputed into a data sheet. Collaborating with a medical statistician is crucial at this stage, as they can provide guidance on the most effective ways to structure and input data. After all studies are included, the relevant statistical analyses on the resultant dataset can be run.

Step 4: Write the Paper—In 2020, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was developed to ensure transparent and complete reporting of systematic reviews. A full discussion of PRISMA guidelines is beyond the scope of this paper; Page et al¹⁴ provided a summary, checklist, and flow diagram that is available online (https://www.prisma-statement.org). Following the PRISMA checklist and guidelines ensures a high-quality, transparent, and reliable systematic review. These guidelines not only help streamline and simplify the writing process but also enhance its efficiency and effectiveness. Discovering the PRISMA checklist can be transformative, providing a valuable roadmap that guides the author through each step of the reporting process, helping to avoid common pitfalls. This structured approach ultimately leads to a more comprehensive and trustworthy review.

Step 5: Make Finishing Touches—At this stage in the systematic review process, the studies have been compiled and thoroughly analyzed and the statistical analysis has been conducted. The results have been organized within a structured framework following the PRISMA checklist. With these steps completed, the next task is to finalize the manuscript and seek a final review from the senior author or faculty mentor. To streamline this process, it is beneficial to adhere to the formatting guidelines of the specific medical journal you intend to submit to. Check the author guidelines on the journal’s website and review recent systematic reviews published there as a reference. Even if you have not chosen a journal yet, formatting your manuscript according to a prestigious journal’s general style provides a strong foundation that can be easily adapted to fit another journal’s requirements if necessary.

Final Thoughts

Designing and conducting a systematic review is no easy task, but it can be a valuable skill for dermatology residents aiming to contribute meaningfully to the medical literature. The process of compiling a systematic review offers an opportunity for developing critical research skills, from formulating a research question to synthesizing evidence and presenting findings in a clear methodical way. Engaging in systematic review writing not only enhances the resident’s understanding of a particular topic but also demonstrates a commitment to scholarly activity—a key factor in an increasingly competitive residency and fellowship application environment.

The basic steps outlined in this article are just one way in which residents can begin to navigate the complexities of medical research, specifically the systematic review process. By assembling a supportive team, utilizing available resources, and adhering to established guidelines such as PRISMA, one can produce a high-quality, impactful review. Ultimately, the systematic review process is not just about publication—it is about fostering a habit of inquiry, improving patient care, and contributing to the ever-evolving field of medicine. With dedication and collaboration, even the most challenging aspects of research can be tackled, paving the way for future opportunities and professional growth. In this way, perhaps one day the spirit of the “research race” can shift from a frantic sprint to a graceful marathon, where each mile is run with heart and every step is filled with purpose.

Financial relationships between physicians and industry are prevalent and complex and may have implications for patient care. A 2007 study reported that 94% of 3167 physicians surveyed had established some form of paid relationship with companies in the pharmaceutical industry.¹ To facilitate increased transparency around these relationships, lawmakers passed the Physician Payments Sunshine Act in 2010, which requires pharmaceutical companies and device manufacturers to report all payments made to physicians.² Mandatory disclosures include meals, honoraria, travel expenses, grants, and ownership or investment interests greater than $10. The information is displayed publicly in the Open Payments database (OPD)(https://openpayments-data.cms.gov/), a platform run by the Centers for Medicare and Medicaid Services.

The OPD allows for in-depth analyses of industry payments made to physicians. Many medical specialties—including orthopedics,^3-5 plastic surgery,^6,7 ophthalmology,⁸ and gastroenterology⁹—have published extensive literature characterizing the nature of these payments and disparities in the distribution of payments based on sex, geographic distribution, and other factors. After the first full year of OPD data collection for dermatology in 2014, Feng et al¹⁰ examined the number, amount, and nature of industry payments to dermatologists, as well as their geographic distribution for that year. As a follow-up to this initial research, Schlager et al¹¹ characterized payments made to dermatologists for the year 2016 and found an increase in the total payments, mean payments, and number of dermatologists receiving payments compared with the 2014 data.

Our study aimed to characterize the last 5 years of available OPD data—from January 1, 2017, to December 31, 2021—to further explore trends in industry payments made to dermatologists. In particular, we examined the effects of the COVID-19 pandemic on payments as well as sex disparities and the distribution of industry payments.

Methods

We performed a retrospective analysis of the OPD for the general payment datasets from January 1, 2017, to December 31, 2021. The results were filtered to include only payments made to dermatologists, excluding physicians from other specialties, physician assistants, and other types of practitioners. Data for each physician were grouped by National Provider Identifier (NPI) for providers included in the set, allowing for analysis at the individual level. Data on sex were extracted from the National Plan & Provider Enumeration System’s monthly data dissemination for NPIs for July 2023 (when the study was conducted) and were joined to the OPD data using the NPI number reported for each physician. All data were extracted, transformed, and analyzed using R software (version 4.2.1). Figures and visualizations were produced using Microsoft Excel 2016.

Results

In 2017, a total of 358,884 payments were made by industry to dermatologists, accounting for nearly $58.0 million. The mean total value of payments received per dermatologist was $5231.74, and the mean payment amount was $161.49. In 2018, the total number of payments increased year-over-year by 5.5% (378,509 payments), the total value of payments received increased by 7.5% (approximately $62.3 million), and the mean total value of payments received per dermatologist increased by 5.3% ($5508.98). In 2019, the total number of payments increased by 3.0% (389,670 total payments), the total value of payments recieved increased by 13.2% (approximately $70.5 million), and the mean total value of payments received per dermatologist increased by 11.3% ($6133.45). All of these values decreased in 2020, likely due to COVID-19–related restrictions on travel and meetings (total number of payments, 208,470 [−46.5%]; total value of payments received, approximately $37.5 million [−46.9%], mean total value of payments received per dermatologist, $3757.27 [−38.7%]), but the mean payment amount remained stable at $179.47. In 2021, the total number of payments (295,808 [+41.9%]), total value of payments received (approximately $50.3 million [+34.4%]), and mean total value of payments received per dermatologist ($4707.88 [+25.3%]) all rebounded, but not to pre-2020 levels (Table 1). When looking at the geographic distribution of payments, the top 5 states receiving the highest total value of payments during the study period included California ($41.51 million), New York ($32.26 million), Florida ($21.38 million), Texas ($19.93 million), and Pennsylvania ($11.69 million).

For each year from 2017 to 2021, more than 80% of payments made to dermatologists were less than $50. The majority (60.7%–75.8%) were in the $10 to $50 range. Between 4% and 5% of payments were more than $1000 for each year. Fewer than 10% of dermatologists received more than $5000 in total payments per year. Most dermatologists (33.3%–36.9%) received $100 to $500 per year. The distribution of payments stratified by number of payments made by amount and payment amount per dermatologist is further delineated in Table 2.

Comment

Benefits of Physician Relationships With Industry—The Physician Payments Sunshine Act increased transparency of industry payments to physicians by creating the OPD through which these relationships can be reported.¹² The effects of these relationships on treatment practices have been the subject of many studies in recent years. Some have suggested that industry ties may impact prescription patterns of endorsed medications.¹³ It also has been reported that the chance of a research study identifying a positive outcome for a particular treatment is higher when the study is funded by a pharmaceutical company compared to other sponsors.¹⁴ On the other hand, some researchers have argued that, when established and maintained in an ethical manner, industry-physician relationships may help practitioners stay updated on the newest treatment paradigms and benefit patient care.¹⁵ Industry relationships may help drive innovation of new products with direct input from frontline physicians who take care of the patients these products aim to help.

Limitations of the OPD—Critics of the OPD have argued that the reported data lack sufficient context and are not easily interpretable by most patients.¹⁶ In addition, many patients might not know about the existence of the database. Indeed, one national survey-based study showed that only 12% of 3542 respondents knew that this information was publicly available, and only 5% knew whether their own physician had received industry payments.¹⁷

Increased Payments From Industry—Our analysis builds on previously reported data in dermatology from 2014 to 2016.^10,11 We found that the trends of increasing numbers and dollar amounts of payments made by industry to dermatologists continued from 2017 to 2019, which may reflect the intended effects of the Physician Payments Sunshine Act, as more payments are being reported in a transparent manner. It also shows that relationships between industry and dermatologists have become more commonplace over time.

It is important to consider these trends in the context of overall Medicare expenditures and prescription volumes. Between 2008 and 2021, prescription volumes have been increasing at a rate of 1% to 4% per year, with 2020 being an exception as the volume decreased slightly from the year prior due to COVID-19 (−3%). Similarly, total Medicare and Medicaid expenditures have been growing at a rate of almost 5% per year.¹⁸ Based on our study results, it appears the total value of payments made between 2017 and 2021 increased at a rate that outpaced prescription volume and expenditures; however, it is difficult to draw conclusions about the relationship between payments made to dermatologists and spending without examining prescriptions specific to dermatologists in the OPD dataset. This relationship could be further explored in future studies.

COVID-19 Restrictions Impacted Payments in 2021—We hypothesize that COVID-19–related restrictions on traveling and in-person meetings led to a decrease in the number of payments, total payment amount, and mean total value of payments received per dermatologist. Notably, compensation for services other than consulting, including speaking fees, had the most precipitous decrease in total payment amount. On the other hand, honoraria and consulting fees were least impacted, as many dermatologists were still able to maintain relationships with industry on an advisory basis without traveling. From 2020 to 2021, the number of total payments and dollar amounts increased with easing of COVID-19 restrictions; however, they had not yet rebounded to 2019 levels during the study period. It will be interesting to continue monitoring these trends once data from future years become available.

Top-Compensated Dermatologists—Our study results also show that for all years from 2017 through 2021, the majority of industry payments were made to a small concentrated percentage of top-compensated dermatologists, which may reflect larger and more frequent payments to those identified by pharmaceutical companies as thought leaders and key opinion leaders in the field or those who are more willing to establish extensive ties with industry. Similarly skewed distributions in payments have been shown in other medical subspecialties including neurosurgery, plastic surgery, otolaryngology, and orthopedics.^4,6,19,20 It also is apparent that the majority of compensated dermatologists in the OPD maintain relatively small ties with industry. For every year from 2017 to 2021, more than half of compensated dermatologists received total payments of less than $500 per year, most of which stemmed from the food and beverage category. Interestingly, a prior study showed that patient perceptions of industry-physician ties may be more strongly impacted by the payment category than the amount.²¹ For example, respondents viewed payments for meals and lodging more negatively, as they were seen more as personal gifts without direct benefit to patients. Conversely, respondents held more positive views of physicians who received free drug samples, which were perceived as benefiting patients, as well as those receiving consulting fees, which were perceived as a signal of physician expertise. Notably, in the same study, physicians who received no payments from industry were seen as honest but also were viewed by some respondents as being inexperienced or uninformed about new treatments.²¹

The contribution and public perception of dermatologists who conduct investigator-initiated research utilizing other types of funding (eg, government grants) also are important to consider but were not directly assessed within the scope of the current study.

Sex Disparities in Compensation—Multiple studies in the literature have demonstrated that sex inequities exist across medical specialties.^22,23 In dermatology, although women make up slightly more than 50% of board-certified dermatologists, they continue to be underrepresented compared with men in leadership positions, academic rank, research funding, and lectureships at national meetings.^24-27 In survey-based studies specifically examining gender-based physician compensation, male dermatologists were found to earn higher salaries than their female counterparts in both private practice and academic settings, even after adjusting for work hours, practice characteristics, and academic rank.^28,29

Our study contributes to the growing body of evidence suggesting that sex inequities also may exist with regard to financial payments from industry. Our results showed that, although the number of male and female dermatologists with industry relationships was similar each year, the number of payments made and total payment amount were both significantly (P<.001) higher for male dermatologists from 2017 through 2021. In 2021, the mean payment amount ($201.57 for male dermatologists; $117.73 for female dermatologists) and mean total amount of payments received ($6172.89 and $2957.79, respectively) also were significantly higher for male compared with female dermatologists (P<.001). The cause of this disparity likely is multifactorial and warrants additional studies in the future. One hypothesis in the existing literature is that male physicians may be more inclined to seek out relationships with industry; it also is possible that disparities in research funding, academic rank, and speaking opportunities at national conferences detailed previously may contribute to inequities in industry payments as companies seek out perceived leaders in the field.³⁰

Limitations and Future Directions—Several important limitations of our study warrant further consideration. As with any database study, the accuracy of the results presented and the conclusions drawn are highly dependent on the precision of the available data, which is reliant on transparent documentation by pharmaceutical companies and physicians. There are no independent methods of verifying the information reported. There have been reports in the literature questioning the utility of the OPD data and risk for misinterpretation.^16,31 Furthermore, the OPD only includes companies whose products are covered by government-sponsored programs, such as Medicare and Medicaid, and therefore does not encompass the totality of industry-dermatologist relationships. We also focused specifically on board-certified dermatologists and did not analyze the extent of industry relationships involving residents, nurses, physician assistants, and other critical members of health care teams that may impact patient care. Differences between academic and private practice payments also could not be examined using the OPD but could present an interesting area for future studies.

Despite these limitations, our study was extensive, using the publicly available OPD to analyze trends and disparities in financial relationships between dermatologists and industry partners from 2017 through 2021. Notably, these findings are not intended to provide judgment or seek to tease out financial relationships that are beneficial for patient care from those that are not; rather, they are intended only to lend additional transparency, provoke thought, and encourage future studies and discussion surrounding this important topic.

Conclusion

Financial relationships between dermatologists and industry are complex and are becoming more prevalent, as shown in our study. These relationships may be critical to facilitate novel patient-centered research and growth in the field of dermatology; however, they also have the potential to be seen as bias in patient care. Transparent reporting of these relationships is an important step in future research regarding the effects of different payment types and serves as the basis for further understanding industry-dermatologist relationships as well as any inequities that exist in the distribution of payments. We encourage all dermatologists to review their public profiles in the OPD. Physicians have the opportunity to review all payment data reported by companies and challenge the accuracy of the data if necessary.

Financial relationships between physicians and industry are prevalent and complex and may have implications for patient care. A 2007 study reported that 94% of 3167 physicians surveyed had established some form of paid relationship with companies in the pharmaceutical industry.¹ To facilitate increased transparency around these relationships, lawmakers passed the Physician Payments Sunshine Act in 2010, which requires pharmaceutical companies and device manufacturers to report all payments made to physicians.² Mandatory disclosures include meals, honoraria, travel expenses, grants, and ownership or investment interests greater than $10. The information is displayed publicly in the Open Payments database (OPD)(https://openpayments-data.cms.gov/), a platform run by the Centers for Medicare and Medicaid Services.

The OPD allows for in-depth analyses of industry payments made to physicians. Many medical specialties—including orthopedics,^3-5 plastic surgery,^6,7 ophthalmology,⁸ and gastroenterology⁹—have published extensive literature characterizing the nature of these payments and disparities in the distribution of payments based on sex, geographic distribution, and other factors. After the first full year of OPD data collection for dermatology in 2014, Feng et al¹⁰ examined the number, amount, and nature of industry payments to dermatologists, as well as their geographic distribution for that year. As a follow-up to this initial research, Schlager et al¹¹ characterized payments made to dermatologists for the year 2016 and found an increase in the total payments, mean payments, and number of dermatologists receiving payments compared with the 2014 data.

Our study aimed to characterize the last 5 years of available OPD data—from January 1, 2017, to December 31, 2021—to further explore trends in industry payments made to dermatologists. In particular, we examined the effects of the COVID-19 pandemic on payments as well as sex disparities and the distribution of industry payments.

Methods

We performed a retrospective analysis of the OPD for the general payment datasets from January 1, 2017, to December 31, 2021. The results were filtered to include only payments made to dermatologists, excluding physicians from other specialties, physician assistants, and other types of practitioners. Data for each physician were grouped by National Provider Identifier (NPI) for providers included in the set, allowing for analysis at the individual level. Data on sex were extracted from the National Plan & Provider Enumeration System’s monthly data dissemination for NPIs for July 2023 (when the study was conducted) and were joined to the OPD data using the NPI number reported for each physician. All data were extracted, transformed, and analyzed using R software (version 4.2.1). Figures and visualizations were produced using Microsoft Excel 2016.

Results

In 2017, a total of 358,884 payments were made by industry to dermatologists, accounting for nearly $58.0 million. The mean total value of payments received per dermatologist was $5231.74, and the mean payment amount was $161.49. In 2018, the total number of payments increased year-over-year by 5.5% (378,509 payments), the total value of payments received increased by 7.5% (approximately $62.3 million), and the mean total value of payments received per dermatologist increased by 5.3% ($5508.98). In 2019, the total number of payments increased by 3.0% (389,670 total payments), the total value of payments recieved increased by 13.2% (approximately $70.5 million), and the mean total value of payments received per dermatologist increased by 11.3% ($6133.45). All of these values decreased in 2020, likely due to COVID-19–related restrictions on travel and meetings (total number of payments, 208,470 [−46.5%]; total value of payments received, approximately $37.5 million [−46.9%], mean total value of payments received per dermatologist, $3757.27 [−38.7%]), but the mean payment amount remained stable at $179.47. In 2021, the total number of payments (295,808 [+41.9%]), total value of payments received (approximately $50.3 million [+34.4%]), and mean total value of payments received per dermatologist ($4707.88 [+25.3%]) all rebounded, but not to pre-2020 levels (Table 1). When looking at the geographic distribution of payments, the top 5 states receiving the highest total value of payments during the study period included California ($41.51 million), New York ($32.26 million), Florida ($21.38 million), Texas ($19.93 million), and Pennsylvania ($11.69 million).

For each year from 2017 to 2021, more than 80% of payments made to dermatologists were less than $50. The majority (60.7%–75.8%) were in the $10 to $50 range. Between 4% and 5% of payments were more than $1000 for each year. Fewer than 10% of dermatologists received more than $5000 in total payments per year. Most dermatologists (33.3%–36.9%) received $100 to $500 per year. The distribution of payments stratified by number of payments made by amount and payment amount per dermatologist is further delineated in Table 2.

Comment

Benefits of Physician Relationships With Industry—The Physician Payments Sunshine Act increased transparency of industry payments to physicians by creating the OPD through which these relationships can be reported.¹² The effects of these relationships on treatment practices have been the subject of many studies in recent years. Some have suggested that industry ties may impact prescription patterns of endorsed medications.¹³ It also has been reported that the chance of a research study identifying a positive outcome for a particular treatment is higher when the study is funded by a pharmaceutical company compared to other sponsors.¹⁴ On the other hand, some researchers have argued that, when established and maintained in an ethical manner, industry-physician relationships may help practitioners stay updated on the newest treatment paradigms and benefit patient care.¹⁵ Industry relationships may help drive innovation of new products with direct input from frontline physicians who take care of the patients these products aim to help.

Limitations of the OPD—Critics of the OPD have argued that the reported data lack sufficient context and are not easily interpretable by most patients.¹⁶ In addition, many patients might not know about the existence of the database. Indeed, one national survey-based study showed that only 12% of 3542 respondents knew that this information was publicly available, and only 5% knew whether their own physician had received industry payments.¹⁷

Increased Payments From Industry—Our analysis builds on previously reported data in dermatology from 2014 to 2016.^10,11 We found that the trends of increasing numbers and dollar amounts of payments made by industry to dermatologists continued from 2017 to 2019, which may reflect the intended effects of the Physician Payments Sunshine Act, as more payments are being reported in a transparent manner. It also shows that relationships between industry and dermatologists have become more commonplace over time.

It is important to consider these trends in the context of overall Medicare expenditures and prescription volumes. Between 2008 and 2021, prescription volumes have been increasing at a rate of 1% to 4% per year, with 2020 being an exception as the volume decreased slightly from the year prior due to COVID-19 (−3%). Similarly, total Medicare and Medicaid expenditures have been growing at a rate of almost 5% per year.¹⁸ Based on our study results, it appears the total value of payments made between 2017 and 2021 increased at a rate that outpaced prescription volume and expenditures; however, it is difficult to draw conclusions about the relationship between payments made to dermatologists and spending without examining prescriptions specific to dermatologists in the OPD dataset. This relationship could be further explored in future studies.

COVID-19 Restrictions Impacted Payments in 2021—We hypothesize that COVID-19–related restrictions on traveling and in-person meetings led to a decrease in the number of payments, total payment amount, and mean total value of payments received per dermatologist. Notably, compensation for services other than consulting, including speaking fees, had the most precipitous decrease in total payment amount. On the other hand, honoraria and consulting fees were least impacted, as many dermatologists were still able to maintain relationships with industry on an advisory basis without traveling. From 2020 to 2021, the number of total payments and dollar amounts increased with easing of COVID-19 restrictions; however, they had not yet rebounded to 2019 levels during the study period. It will be interesting to continue monitoring these trends once data from future years become available.

Top-Compensated Dermatologists—Our study results also show that for all years from 2017 through 2021, the majority of industry payments were made to a small concentrated percentage of top-compensated dermatologists, which may reflect larger and more frequent payments to those identified by pharmaceutical companies as thought leaders and key opinion leaders in the field or those who are more willing to establish extensive ties with industry. Similarly skewed distributions in payments have been shown in other medical subspecialties including neurosurgery, plastic surgery, otolaryngology, and orthopedics.^4,6,19,20 It also is apparent that the majority of compensated dermatologists in the OPD maintain relatively small ties with industry. For every year from 2017 to 2021, more than half of compensated dermatologists received total payments of less than $500 per year, most of which stemmed from the food and beverage category. Interestingly, a prior study showed that patient perceptions of industry-physician ties may be more strongly impacted by the payment category than the amount.²¹ For example, respondents viewed payments for meals and lodging more negatively, as they were seen more as personal gifts without direct benefit to patients. Conversely, respondents held more positive views of physicians who received free drug samples, which were perceived as benefiting patients, as well as those receiving consulting fees, which were perceived as a signal of physician expertise. Notably, in the same study, physicians who received no payments from industry were seen as honest but also were viewed by some respondents as being inexperienced or uninformed about new treatments.²¹

The contribution and public perception of dermatologists who conduct investigator-initiated research utilizing other types of funding (eg, government grants) also are important to consider but were not directly assessed within the scope of the current study.

Sex Disparities in Compensation—Multiple studies in the literature have demonstrated that sex inequities exist across medical specialties.^22,23 In dermatology, although women make up slightly more than 50% of board-certified dermatologists, they continue to be underrepresented compared with men in leadership positions, academic rank, research funding, and lectureships at national meetings.^24-27 In survey-based studies specifically examining gender-based physician compensation, male dermatologists were found to earn higher salaries than their female counterparts in both private practice and academic settings, even after adjusting for work hours, practice characteristics, and academic rank.^28,29

Our study contributes to the growing body of evidence suggesting that sex inequities also may exist with regard to financial payments from industry. Our results showed that, although the number of male and female dermatologists with industry relationships was similar each year, the number of payments made and total payment amount were both significantly (P<.001) higher for male dermatologists from 2017 through 2021. In 2021, the mean payment amount ($201.57 for male dermatologists; $117.73 for female dermatologists) and mean total amount of payments received ($6172.89 and $2957.79, respectively) also were significantly higher for male compared with female dermatologists (P<.001). The cause of this disparity likely is multifactorial and warrants additional studies in the future. One hypothesis in the existing literature is that male physicians may be more inclined to seek out relationships with industry; it also is possible that disparities in research funding, academic rank, and speaking opportunities at national conferences detailed previously may contribute to inequities in industry payments as companies seek out perceived leaders in the field.³⁰

Limitations and Future Directions—Several important limitations of our study warrant further consideration. As with any database study, the accuracy of the results presented and the conclusions drawn are highly dependent on the precision of the available data, which is reliant on transparent documentation by pharmaceutical companies and physicians. There are no independent methods of verifying the information reported. There have been reports in the literature questioning the utility of the OPD data and risk for misinterpretation.^16,31 Furthermore, the OPD only includes companies whose products are covered by government-sponsored programs, such as Medicare and Medicaid, and therefore does not encompass the totality of industry-dermatologist relationships. We also focused specifically on board-certified dermatologists and did not analyze the extent of industry relationships involving residents, nurses, physician assistants, and other critical members of health care teams that may impact patient care. Differences between academic and private practice payments also could not be examined using the OPD but could present an interesting area for future studies.

Despite these limitations, our study was extensive, using the publicly available OPD to analyze trends and disparities in financial relationships between dermatologists and industry partners from 2017 through 2021. Notably, these findings are not intended to provide judgment or seek to tease out financial relationships that are beneficial for patient care from those that are not; rather, they are intended only to lend additional transparency, provoke thought, and encourage future studies and discussion surrounding this important topic.

Conclusion

Financial relationships between dermatologists and industry are complex and are becoming more prevalent, as shown in our study. These relationships may be critical to facilitate novel patient-centered research and growth in the field of dermatology; however, they also have the potential to be seen as bias in patient care. Transparent reporting of these relationships is an important step in future research regarding the effects of different payment types and serves as the basis for further understanding industry-dermatologist relationships as well as any inequities that exist in the distribution of payments. We encourage all dermatologists to review their public profiles in the OPD. Physicians have the opportunity to review all payment data reported by companies and challenge the accuracy of the data if necessary.

Financial relationships between physicians and industry are prevalent and complex and may have implications for patient care. A 2007 study reported that 94% of 3167 physicians surveyed had established some form of paid relationship with companies in the pharmaceutical industry.¹ To facilitate increased transparency around these relationships, lawmakers passed the Physician Payments Sunshine Act in 2010, which requires pharmaceutical companies and device manufacturers to report all payments made to physicians.² Mandatory disclosures include meals, honoraria, travel expenses, grants, and ownership or investment interests greater than $10. The information is displayed publicly in the Open Payments database (OPD)(https://openpayments-data.cms.gov/), a platform run by the Centers for Medicare and Medicaid Services.

The OPD allows for in-depth analyses of industry payments made to physicians. Many medical specialties—including orthopedics,^3-5 plastic surgery,^6,7 ophthalmology,⁸ and gastroenterology⁹—have published extensive literature characterizing the nature of these payments and disparities in the distribution of payments based on sex, geographic distribution, and other factors. After the first full year of OPD data collection for dermatology in 2014, Feng et al¹⁰ examined the number, amount, and nature of industry payments to dermatologists, as well as their geographic distribution for that year. As a follow-up to this initial research, Schlager et al¹¹ characterized payments made to dermatologists for the year 2016 and found an increase in the total payments, mean payments, and number of dermatologists receiving payments compared with the 2014 data.

Our study aimed to characterize the last 5 years of available OPD data—from January 1, 2017, to December 31, 2021—to further explore trends in industry payments made to dermatologists. In particular, we examined the effects of the COVID-19 pandemic on payments as well as sex disparities and the distribution of industry payments.

Methods

We performed a retrospective analysis of the OPD for the general payment datasets from January 1, 2017, to December 31, 2021. The results were filtered to include only payments made to dermatologists, excluding physicians from other specialties, physician assistants, and other types of practitioners. Data for each physician were grouped by National Provider Identifier (NPI) for providers included in the set, allowing for analysis at the individual level. Data on sex were extracted from the National Plan & Provider Enumeration System’s monthly data dissemination for NPIs for July 2023 (when the study was conducted) and were joined to the OPD data using the NPI number reported for each physician. All data were extracted, transformed, and analyzed using R software (version 4.2.1). Figures and visualizations were produced using Microsoft Excel 2016.

Results

In 2017, a total of 358,884 payments were made by industry to dermatologists, accounting for nearly $58.0 million. The mean total value of payments received per dermatologist was $5231.74, and the mean payment amount was $161.49. In 2018, the total number of payments increased year-over-year by 5.5% (378,509 payments), the total value of payments received increased by 7.5% (approximately $62.3 million), and the mean total value of payments received per dermatologist increased by 5.3% ($5508.98). In 2019, the total number of payments increased by 3.0% (389,670 total payments), the total value of payments recieved increased by 13.2% (approximately $70.5 million), and the mean total value of payments received per dermatologist increased by 11.3% ($6133.45). All of these values decreased in 2020, likely due to COVID-19–related restrictions on travel and meetings (total number of payments, 208,470 [−46.5%]; total value of payments received, approximately $37.5 million [−46.9%], mean total value of payments received per dermatologist, $3757.27 [−38.7%]), but the mean payment amount remained stable at $179.47. In 2021, the total number of payments (295,808 [+41.9%]), total value of payments received (approximately $50.3 million [+34.4%]), and mean total value of payments received per dermatologist ($4707.88 [+25.3%]) all rebounded, but not to pre-2020 levels (Table 1). When looking at the geographic distribution of payments, the top 5 states receiving the highest total value of payments during the study period included California ($41.51 million), New York ($32.26 million), Florida ($21.38 million), Texas ($19.93 million), and Pennsylvania ($11.69 million).

For each year from 2017 to 2021, more than 80% of payments made to dermatologists were less than $50. The majority (60.7%–75.8%) were in the $10 to $50 range. Between 4% and 5% of payments were more than $1000 for each year. Fewer than 10% of dermatologists received more than $5000 in total payments per year. Most dermatologists (33.3%–36.9%) received $100 to $500 per year. The distribution of payments stratified by number of payments made by amount and payment amount per dermatologist is further delineated in Table 2.

Comment

Benefits of Physician Relationships With Industry—The Physician Payments Sunshine Act increased transparency of industry payments to physicians by creating the OPD through which these relationships can be reported.¹² The effects of these relationships on treatment practices have been the subject of many studies in recent years. Some have suggested that industry ties may impact prescription patterns of endorsed medications.¹³ It also has been reported that the chance of a research study identifying a positive outcome for a particular treatment is higher when the study is funded by a pharmaceutical company compared to other sponsors.¹⁴ On the other hand, some researchers have argued that, when established and maintained in an ethical manner, industry-physician relationships may help practitioners stay updated on the newest treatment paradigms and benefit patient care.¹⁵ Industry relationships may help drive innovation of new products with direct input from frontline physicians who take care of the patients these products aim to help.

Limitations of the OPD—Critics of the OPD have argued that the reported data lack sufficient context and are not easily interpretable by most patients.¹⁶ In addition, many patients might not know about the existence of the database. Indeed, one national survey-based study showed that only 12% of 3542 respondents knew that this information was publicly available, and only 5% knew whether their own physician had received industry payments.¹⁷

Increased Payments From Industry—Our analysis builds on previously reported data in dermatology from 2014 to 2016.^10,11 We found that the trends of increasing numbers and dollar amounts of payments made by industry to dermatologists continued from 2017 to 2019, which may reflect the intended effects of the Physician Payments Sunshine Act, as more payments are being reported in a transparent manner. It also shows that relationships between industry and dermatologists have become more commonplace over time.

It is important to consider these trends in the context of overall Medicare expenditures and prescription volumes. Between 2008 and 2021, prescription volumes have been increasing at a rate of 1% to 4% per year, with 2020 being an exception as the volume decreased slightly from the year prior due to COVID-19 (−3%). Similarly, total Medicare and Medicaid expenditures have been growing at a rate of almost 5% per year.¹⁸ Based on our study results, it appears the total value of payments made between 2017 and 2021 increased at a rate that outpaced prescription volume and expenditures; however, it is difficult to draw conclusions about the relationship between payments made to dermatologists and spending without examining prescriptions specific to dermatologists in the OPD dataset. This relationship could be further explored in future studies.

COVID-19 Restrictions Impacted Payments in 2021—We hypothesize that COVID-19–related restrictions on traveling and in-person meetings led to a decrease in the number of payments, total payment amount, and mean total value of payments received per dermatologist. Notably, compensation for services other than consulting, including speaking fees, had the most precipitous decrease in total payment amount. On the other hand, honoraria and consulting fees were least impacted, as many dermatologists were still able to maintain relationships with industry on an advisory basis without traveling. From 2020 to 2021, the number of total payments and dollar amounts increased with easing of COVID-19 restrictions; however, they had not yet rebounded to 2019 levels during the study period. It will be interesting to continue monitoring these trends once data from future years become available.

Top-Compensated Dermatologists—Our study results also show that for all years from 2017 through 2021, the majority of industry payments were made to a small concentrated percentage of top-compensated dermatologists, which may reflect larger and more frequent payments to those identified by pharmaceutical companies as thought leaders and key opinion leaders in the field or those who are more willing to establish extensive ties with industry. Similarly skewed distributions in payments have been shown in other medical subspecialties including neurosurgery, plastic surgery, otolaryngology, and orthopedics.^4,6,19,20 It also is apparent that the majority of compensated dermatologists in the OPD maintain relatively small ties with industry. For every year from 2017 to 2021, more than half of compensated dermatologists received total payments of less than $500 per year, most of which stemmed from the food and beverage category. Interestingly, a prior study showed that patient perceptions of industry-physician ties may be more strongly impacted by the payment category than the amount.²¹ For example, respondents viewed payments for meals and lodging more negatively, as they were seen more as personal gifts without direct benefit to patients. Conversely, respondents held more positive views of physicians who received free drug samples, which were perceived as benefiting patients, as well as those receiving consulting fees, which were perceived as a signal of physician expertise. Notably, in the same study, physicians who received no payments from industry were seen as honest but also were viewed by some respondents as being inexperienced or uninformed about new treatments.²¹

The contribution and public perception of dermatologists who conduct investigator-initiated research utilizing other types of funding (eg, government grants) also are important to consider but were not directly assessed within the scope of the current study.

Sex Disparities in Compensation—Multiple studies in the literature have demonstrated that sex inequities exist across medical specialties.^22,23 In dermatology, although women make up slightly more than 50% of board-certified dermatologists, they continue to be underrepresented compared with men in leadership positions, academic rank, research funding, and lectureships at national meetings.^24-27 In survey-based studies specifically examining gender-based physician compensation, male dermatologists were found to earn higher salaries than their female counterparts in both private practice and academic settings, even after adjusting for work hours, practice characteristics, and academic rank.^28,29

Our study contributes to the growing body of evidence suggesting that sex inequities also may exist with regard to financial payments from industry. Our results showed that, although the number of male and female dermatologists with industry relationships was similar each year, the number of payments made and total payment amount were both significantly (P<.001) higher for male dermatologists from 2017 through 2021. In 2021, the mean payment amount ($201.57 for male dermatologists; $117.73 for female dermatologists) and mean total amount of payments received ($6172.89 and $2957.79, respectively) also were significantly higher for male compared with female dermatologists (P<.001). The cause of this disparity likely is multifactorial and warrants additional studies in the future. One hypothesis in the existing literature is that male physicians may be more inclined to seek out relationships with industry; it also is possible that disparities in research funding, academic rank, and speaking opportunities at national conferences detailed previously may contribute to inequities in industry payments as companies seek out perceived leaders in the field.³⁰

Limitations and Future Directions—Several important limitations of our study warrant further consideration. As with any database study, the accuracy of the results presented and the conclusions drawn are highly dependent on the precision of the available data, which is reliant on transparent documentation by pharmaceutical companies and physicians. There are no independent methods of verifying the information reported. There have been reports in the literature questioning the utility of the OPD data and risk for misinterpretation.^16,31 Furthermore, the OPD only includes companies whose products are covered by government-sponsored programs, such as Medicare and Medicaid, and therefore does not encompass the totality of industry-dermatologist relationships. We also focused specifically on board-certified dermatologists and did not analyze the extent of industry relationships involving residents, nurses, physician assistants, and other critical members of health care teams that may impact patient care. Differences between academic and private practice payments also could not be examined using the OPD but could present an interesting area for future studies.

Despite these limitations, our study was extensive, using the publicly available OPD to analyze trends and disparities in financial relationships between dermatologists and industry partners from 2017 through 2021. Notably, these findings are not intended to provide judgment or seek to tease out financial relationships that are beneficial for patient care from those that are not; rather, they are intended only to lend additional transparency, provoke thought, and encourage future studies and discussion surrounding this important topic.

Conclusion

Financial relationships between dermatologists and industry are complex and are becoming more prevalent, as shown in our study. These relationships may be critical to facilitate novel patient-centered research and growth in the field of dermatology; however, they also have the potential to be seen as bias in patient care. Transparent reporting of these relationships is an important step in future research regarding the effects of different payment types and serves as the basis for further understanding industry-dermatologist relationships as well as any inequities that exist in the distribution of payments. We encourage all dermatologists to review their public profiles in the OPD. Physicians have the opportunity to review all payment data reported by companies and challenge the accuracy of the data if necessary.

To the Editor:

Chronic cutaneous lupus erythematosus (CCLE) is an inflammatory condition with myriad cutaneous manifestations. Most forms of CCLE have the potential to progress to systemic lupus erythematosus (SLE).¹

Blaschkolinear lupus erythematosus (BLE) is an exceedingly rare subtype of cutaneous lupus erythematosus that usually manifests during childhood as linear plaques along the lines of Blaschko.^2,3 Under normal conditions, Blaschko lines are not noticeable; they correspond to the direction of ectodermal cell migration during cutaneous embryogenesis.^4,5 The embryonic cells travel ventrolaterally, forming a V-shaped pattern on the back, an S-shaped pattern on the trunk, and an hourglass-shaped pattern on the face with several perpendicular intersections near the mouth and nose.⁶ During their migration, the cells are susceptible to somatic mutations and clonal expansion, resulting in a monoclonal population of genetically heterogenous cells. This phenomenon is known as somatic mosaicism and may lead to an increased susceptibility to an array of congenital and inflammatory dermatoses, such as cutaneous lupus erythematosus.⁴ Blaschkolinear entities tend to manifest in a unilateral distribution following exposure to a certain environmental trigger, such as trauma, viral illness, or UV radiation, although a trigger is not always present.⁷ We report a case of BLE manifesting on the head and neck in an adult patient.

A 46-year-old man presented with a pruritic rash of 3 months’ duration on the right cheek that extended inferiorly to the right upper chest. He had a medical history of well-controlled psoriasis, and he denied any antecedent trauma, fevers, chills, arthralgia, or night sweats. There had been no improvement with mometasone ointment 0.1% applied daily for 2 months as prescribed by his primary care provider. Physical examination revealed indurated, red-brown, atrophic plaques in a blaschkolinear distribution around the nose, right upper jaw, right side of the neck, and right upper chest (Figure, A).

To the Editor:

Chronic cutaneous lupus erythematosus (CCLE) is an inflammatory condition with myriad cutaneous manifestations. Most forms of CCLE have the potential to progress to systemic lupus erythematosus (SLE).¹

Blaschkolinear lupus erythematosus (BLE) is an exceedingly rare subtype of cutaneous lupus erythematosus that usually manifests during childhood as linear plaques along the lines of Blaschko.^2,3 Under normal conditions, Blaschko lines are not noticeable; they correspond to the direction of ectodermal cell migration during cutaneous embryogenesis.^4,5 The embryonic cells travel ventrolaterally, forming a V-shaped pattern on the back, an S-shaped pattern on the trunk, and an hourglass-shaped pattern on the face with several perpendicular intersections near the mouth and nose.⁶ During their migration, the cells are susceptible to somatic mutations and clonal expansion, resulting in a monoclonal population of genetically heterogenous cells. This phenomenon is known as somatic mosaicism and may lead to an increased susceptibility to an array of congenital and inflammatory dermatoses, such as cutaneous lupus erythematosus.⁴ Blaschkolinear entities tend to manifest in a unilateral distribution following exposure to a certain environmental trigger, such as trauma, viral illness, or UV radiation, although a trigger is not always present.⁷ We report a case of BLE manifesting on the head and neck in an adult patient.

A 46-year-old man presented with a pruritic rash of 3 months’ duration on the right cheek that extended inferiorly to the right upper chest. He had a medical history of well-controlled psoriasis, and he denied any antecedent trauma, fevers, chills, arthralgia, or night sweats. There had been no improvement with mometasone ointment 0.1% applied daily for 2 months as prescribed by his primary care provider. Physical examination revealed indurated, red-brown, atrophic plaques in a blaschkolinear distribution around the nose, right upper jaw, right side of the neck, and right upper chest (Figure, A).

To the Editor:

Chronic cutaneous lupus erythematosus (CCLE) is an inflammatory condition with myriad cutaneous manifestations. Most forms of CCLE have the potential to progress to systemic lupus erythematosus (SLE).¹

Blaschkolinear lupus erythematosus (BLE) is an exceedingly rare subtype of cutaneous lupus erythematosus that usually manifests during childhood as linear plaques along the lines of Blaschko.^2,3 Under normal conditions, Blaschko lines are not noticeable; they correspond to the direction of ectodermal cell migration during cutaneous embryogenesis.^4,5 The embryonic cells travel ventrolaterally, forming a V-shaped pattern on the back, an S-shaped pattern on the trunk, and an hourglass-shaped pattern on the face with several perpendicular intersections near the mouth and nose.⁶ During their migration, the cells are susceptible to somatic mutations and clonal expansion, resulting in a monoclonal population of genetically heterogenous cells. This phenomenon is known as somatic mosaicism and may lead to an increased susceptibility to an array of congenital and inflammatory dermatoses, such as cutaneous lupus erythematosus.⁴ Blaschkolinear entities tend to manifest in a unilateral distribution following exposure to a certain environmental trigger, such as trauma, viral illness, or UV radiation, although a trigger is not always present.⁷ We report a case of BLE manifesting on the head and neck in an adult patient.

A 46-year-old man presented with a pruritic rash of 3 months’ duration on the right cheek that extended inferiorly to the right upper chest. He had a medical history of well-controlled psoriasis, and he denied any antecedent trauma, fevers, chills, arthralgia, or night sweats. There had been no improvement with mometasone ointment 0.1% applied daily for 2 months as prescribed by his primary care provider. Physical examination revealed indurated, red-brown, atrophic plaques in a blaschkolinear distribution around the nose, right upper jaw, right side of the neck, and right upper chest (Figure, A).

The Diagnosis: Pityriasis Lichenoides et Varioliformis Acuta

Sectioned punch biopsies were performed on the patient’s right arm. Histopathology showed acanthosis and parakeratosis in the epidermis, with vacuolar degeneration and dyskeratosis in the basal layer. Dermal changes included extravasated red blood cells in the papillary dermis as well as perivascular lymphocytic infiltrates in both the papillary and reticular dermis (Figure). Direct immunofluorescence of a perilesional biopsy using anti–human IgG, IgM, IgA, C3, and fibrin conjugates showed no findings of immune deposition. Biopsy results were consistent with pityriasis lichenoides et varioliformis acuta (PLEVA), and the patient was treated with a 5-day course of oral azithromycin, triamcinolone ointment 0.1% twice daily, and phototherapy with narrowband UVB ³ times weekly. Rapid improvement was noted at 2-month follow-up.

Pityriasis lichenoides et varioliformis acuta is a form of pityriasis lichenoides, a group of inflammatory dermatoses that are characterized clinically by successive crops of morphologically diverse lesions. Epidemiologic studies have shown a slight male predominance. It primarily affects children and young adults, with peak ages of 8 and 32 years in pediatric and adult populations, respectively.¹

The pathogenesis of PLEVA remains unclear. An abnormal immune response to Toxoplasma, Epstein-Barr virus, HIV, and other pathogens has been suggested based on serologic evidence of concurrent disease activity with the onset of lesions as well as cutaneous improvement in some patients after treatment of the infection.¹ A T-cell lymphoproliferative etiology also has been considered based on histopathologic similarities between PLEVA and lymphomatoid papulosis (LyP) as well as findings of clonality in T-cell receptor gene rearrangement in many patients.^1,2 Some clinicians consider LyP and PLEVA as separate entities on one disease spectrum.

Eruptions of PLEVA tend to favor the trunk and proximal extremities. Lesions may begin as macules measuring 2 to 3 mm in diameter that quickly evolve into papules with fine scale that remains attached centrally. Ulcerations with hemorrhagic crusts also may be noted as the lesions progress in stage. The rash may persist for weeks to years, and overlapping crops of macules and papules at varying stages of development may be seen in the same patient.¹

Histopathologic findings of PLEVA include spongiosis, dyskeratosis, parakeratosis, and focal keratinocyte necrosis within the epidermis, as well as vacuolar degeneration of the basal layer. Lymphocyte and erythrocyte extravasation may extend into the epidermis. Dermal findings may include edema and wedge-shaped perivascular lymphocytic infiltrates extending into the reticular dermis.¹

Important differential diagnoses to consider include LyP, mycosis fungoides (MF), pemphigus foliaceus, and varicella. Lymphomatoid papulosis is a benign CD30+ lymphoproliferative disorder that is characterized by an indolent course of recurrent, often self-resolving papules that occur most frequently on the trunk, arms, and legs of older patients. There are several histologic subtypes of LyP, but the most common (type A) may manifest with wedge-shaped perivascular lymphocytic infiltrates in the dermis, similar to PLEVA. T-cell receptor gene rearrangement studies characteristically reveal clonality in LyP, and clonality has been reported in PLEVA. However, LyP demonstrates a higher cytologic grade and lacks the characteristic parakeratotic scale and superficial dermal microhemorrhage of PLEVA.³

Mycosis fungoides is a malignant lymphoproliferative disorder that is characterized by an indolent clinical course of persistent patches, plaques, or tumors of various sizes that often manifest in non–sun-exposed areas of the skin. Early stages of MF are difficult to detect histologically, but biopsies may show atypical lymphocytes with hyperchromatic, irregularly contoured nuclei arranged along the basal layer of the epidermis. Epidermal aggregates of atypical lymphocytes (also known as Pautrier microabscesses) are considered highly specific for MF. T-cell receptor and immunopathologic studies also are important adjuncts in the diagnosis of MF.⁴

Pemphigus foliaceus is an autoimmune blistering disease caused by antibodies directed against desmoglein 1, which is found in the granular layer of the epidermis. It manifests with a subtle onset of scattered crusted lesions in the seborrheic areas, such as the scalp, face, chest, and upper back. Histopathologic findings of early blisters may include acantholysis and dyskeratosis in the stratum granulosum as well as vacuolization of the granular layer. The blisters may coalesce into superficial bullae containing fibrin and neutrophils. Immunofluorescence studies that demonstrate intraepidermal C3 and IgG deposition are key to the diagnosis of pemphigus.⁵

Varicella (also known as chickenpox) manifests with crops of vesicles on an erythematous base in a centripetal distribution favoring the trunk and proximal extremities. It often is preceded by prodromal fever, malaise, and myalgia. Histopathologic evaluation of varicella is uncommon but may reveal acantholysis, multinucleation, and nuclear margination of keratinocytes. Viral culture or nucleic acid amplification testing of lesions can be used to verify the diagnosis.⁶

Most cases of PLEVA resolve without intervention.7 Treatment is directed at speeding recovery, providing symptomatic relief, and limiting permanent sequelae. Topical steroids often are used to alleviate inflammation and pruritus. Systemic antibiotics such as doxycycline, minocycline, and erythromycin have been used for their anti-inflammatory properties. Phototherapy of various wavelengths, including broadband and narrowband UVB as well as psoralen plus UVA, have led to improvements in affected patients. Refractory disease may warrant consideration of therapy with methotrexate, acitretin, dapsone, or cyclosporine.⁷

There have been rare reports of PLEVA evolving into its potentially lethal variant, febrile ulceronecrotic Mucha-Habermann disease, which is differentiated by the presence of systemic manifestations, including high fever, sore throat, diarrhea, central nervous system symptoms, abdominal pain, interstitial pneumonitis, splenomegaly, arthritis, sepsis, megaloblastic anemia, or conjunctival ulcers. The orogenital mucosa may be affected. Cutaneous lesions may rapidly progress to large, generalized, coalescent ulcers with necrotic crusts and vasculitic features on biopsy.8 Malignant transformation of PLEVA into LyP or MF rarely may occur and warrants continued follow-up of unresolved lesions.⁹

The Diagnosis: Pityriasis Lichenoides et Varioliformis Acuta

Sectioned punch biopsies were performed on the patient’s right arm. Histopathology showed acanthosis and parakeratosis in the epidermis, with vacuolar degeneration and dyskeratosis in the basal layer. Dermal changes included extravasated red blood cells in the papillary dermis as well as perivascular lymphocytic infiltrates in both the papillary and reticular dermis (Figure). Direct immunofluorescence of a perilesional biopsy using anti–human IgG, IgM, IgA, C3, and fibrin conjugates showed no findings of immune deposition. Biopsy results were consistent with pityriasis lichenoides et varioliformis acuta (PLEVA), and the patient was treated with a 5-day course of oral azithromycin, triamcinolone ointment 0.1% twice daily, and phototherapy with narrowband UVB ³ times weekly. Rapid improvement was noted at 2-month follow-up.

Pityriasis lichenoides et varioliformis acuta is a form of pityriasis lichenoides, a group of inflammatory dermatoses that are characterized clinically by successive crops of morphologically diverse lesions. Epidemiologic studies have shown a slight male predominance. It primarily affects children and young adults, with peak ages of 8 and 32 years in pediatric and adult populations, respectively.¹

The pathogenesis of PLEVA remains unclear. An abnormal immune response to Toxoplasma, Epstein-Barr virus, HIV, and other pathogens has been suggested based on serologic evidence of concurrent disease activity with the onset of lesions as well as cutaneous improvement in some patients after treatment of the infection.¹ A T-cell lymphoproliferative etiology also has been considered based on histopathologic similarities between PLEVA and lymphomatoid papulosis (LyP) as well as findings of clonality in T-cell receptor gene rearrangement in many patients.^1,2 Some clinicians consider LyP and PLEVA as separate entities on one disease spectrum.

Eruptions of PLEVA tend to favor the trunk and proximal extremities. Lesions may begin as macules measuring 2 to 3 mm in diameter that quickly evolve into papules with fine scale that remains attached centrally. Ulcerations with hemorrhagic crusts also may be noted as the lesions progress in stage. The rash may persist for weeks to years, and overlapping crops of macules and papules at varying stages of development may be seen in the same patient.¹

Histopathologic findings of PLEVA include spongiosis, dyskeratosis, parakeratosis, and focal keratinocyte necrosis within the epidermis, as well as vacuolar degeneration of the basal layer. Lymphocyte and erythrocyte extravasation may extend into the epidermis. Dermal findings may include edema and wedge-shaped perivascular lymphocytic infiltrates extending into the reticular dermis.¹

Important differential diagnoses to consider include LyP, mycosis fungoides (MF), pemphigus foliaceus, and varicella. Lymphomatoid papulosis is a benign CD30+ lymphoproliferative disorder that is characterized by an indolent course of recurrent, often self-resolving papules that occur most frequently on the trunk, arms, and legs of older patients. There are several histologic subtypes of LyP, but the most common (type A) may manifest with wedge-shaped perivascular lymphocytic infiltrates in the dermis, similar to PLEVA. T-cell receptor gene rearrangement studies characteristically reveal clonality in LyP, and clonality has been reported in PLEVA. However, LyP demonstrates a higher cytologic grade and lacks the characteristic parakeratotic scale and superficial dermal microhemorrhage of PLEVA.³

Mycosis fungoides is a malignant lymphoproliferative disorder that is characterized by an indolent clinical course of persistent patches, plaques, or tumors of various sizes that often manifest in non–sun-exposed areas of the skin. Early stages of MF are difficult to detect histologically, but biopsies may show atypical lymphocytes with hyperchromatic, irregularly contoured nuclei arranged along the basal layer of the epidermis. Epidermal aggregates of atypical lymphocytes (also known as Pautrier microabscesses) are considered highly specific for MF. T-cell receptor and immunopathologic studies also are important adjuncts in the diagnosis of MF.⁴

Pemphigus foliaceus is an autoimmune blistering disease caused by antibodies directed against desmoglein 1, which is found in the granular layer of the epidermis. It manifests with a subtle onset of scattered crusted lesions in the seborrheic areas, such as the scalp, face, chest, and upper back. Histopathologic findings of early blisters may include acantholysis and dyskeratosis in the stratum granulosum as well as vacuolization of the granular layer. The blisters may coalesce into superficial bullae containing fibrin and neutrophils. Immunofluorescence studies that demonstrate intraepidermal C3 and IgG deposition are key to the diagnosis of pemphigus.⁵

Varicella (also known as chickenpox) manifests with crops of vesicles on an erythematous base in a centripetal distribution favoring the trunk and proximal extremities. It often is preceded by prodromal fever, malaise, and myalgia. Histopathologic evaluation of varicella is uncommon but may reveal acantholysis, multinucleation, and nuclear margination of keratinocytes. Viral culture or nucleic acid amplification testing of lesions can be used to verify the diagnosis.⁶

Most cases of PLEVA resolve without intervention.7 Treatment is directed at speeding recovery, providing symptomatic relief, and limiting permanent sequelae. Topical steroids often are used to alleviate inflammation and pruritus. Systemic antibiotics such as doxycycline, minocycline, and erythromycin have been used for their anti-inflammatory properties. Phototherapy of various wavelengths, including broadband and narrowband UVB as well as psoralen plus UVA, have led to improvements in affected patients. Refractory disease may warrant consideration of therapy with methotrexate, acitretin, dapsone, or cyclosporine.⁷

There have been rare reports of PLEVA evolving into its potentially lethal variant, febrile ulceronecrotic Mucha-Habermann disease, which is differentiated by the presence of systemic manifestations, including high fever, sore throat, diarrhea, central nervous system symptoms, abdominal pain, interstitial pneumonitis, splenomegaly, arthritis, sepsis, megaloblastic anemia, or conjunctival ulcers. The orogenital mucosa may be affected. Cutaneous lesions may rapidly progress to large, generalized, coalescent ulcers with necrotic crusts and vasculitic features on biopsy.8 Malignant transformation of PLEVA into LyP or MF rarely may occur and warrants continued follow-up of unresolved lesions.⁹

The Diagnosis: Pityriasis Lichenoides et Varioliformis Acuta

Sectioned punch biopsies were performed on the patient’s right arm. Histopathology showed acanthosis and parakeratosis in the epidermis, with vacuolar degeneration and dyskeratosis in the basal layer. Dermal changes included extravasated red blood cells in the papillary dermis as well as perivascular lymphocytic infiltrates in both the papillary and reticular dermis (Figure). Direct immunofluorescence of a perilesional biopsy using anti–human IgG, IgM, IgA, C3, and fibrin conjugates showed no findings of immune deposition. Biopsy results were consistent with pityriasis lichenoides et varioliformis acuta (PLEVA), and the patient was treated with a 5-day course of oral azithromycin, triamcinolone ointment 0.1% twice daily, and phototherapy with narrowband UVB ³ times weekly. Rapid improvement was noted at 2-month follow-up.

Pityriasis lichenoides et varioliformis acuta is a form of pityriasis lichenoides, a group of inflammatory dermatoses that are characterized clinically by successive crops of morphologically diverse lesions. Epidemiologic studies have shown a slight male predominance. It primarily affects children and young adults, with peak ages of 8 and 32 years in pediatric and adult populations, respectively.¹

The pathogenesis of PLEVA remains unclear. An abnormal immune response to Toxoplasma, Epstein-Barr virus, HIV, and other pathogens has been suggested based on serologic evidence of concurrent disease activity with the onset of lesions as well as cutaneous improvement in some patients after treatment of the infection.¹ A T-cell lymphoproliferative etiology also has been considered based on histopathologic similarities between PLEVA and lymphomatoid papulosis (LyP) as well as findings of clonality in T-cell receptor gene rearrangement in many patients.^1,2 Some clinicians consider LyP and PLEVA as separate entities on one disease spectrum.

Eruptions of PLEVA tend to favor the trunk and proximal extremities. Lesions may begin as macules measuring 2 to 3 mm in diameter that quickly evolve into papules with fine scale that remains attached centrally. Ulcerations with hemorrhagic crusts also may be noted as the lesions progress in stage. The rash may persist for weeks to years, and overlapping crops of macules and papules at varying stages of development may be seen in the same patient.¹

Histopathologic findings of PLEVA include spongiosis, dyskeratosis, parakeratosis, and focal keratinocyte necrosis within the epidermis, as well as vacuolar degeneration of the basal layer. Lymphocyte and erythrocyte extravasation may extend into the epidermis. Dermal findings may include edema and wedge-shaped perivascular lymphocytic infiltrates extending into the reticular dermis.¹

Important differential diagnoses to consider include LyP, mycosis fungoides (MF), pemphigus foliaceus, and varicella. Lymphomatoid papulosis is a benign CD30+ lymphoproliferative disorder that is characterized by an indolent course of recurrent, often self-resolving papules that occur most frequently on the trunk, arms, and legs of older patients. There are several histologic subtypes of LyP, but the most common (type A) may manifest with wedge-shaped perivascular lymphocytic infiltrates in the dermis, similar to PLEVA. T-cell receptor gene rearrangement studies characteristically reveal clonality in LyP, and clonality has been reported in PLEVA. However, LyP demonstrates a higher cytologic grade and lacks the characteristic parakeratotic scale and superficial dermal microhemorrhage of PLEVA.³

Mycosis fungoides is a malignant lymphoproliferative disorder that is characterized by an indolent clinical course of persistent patches, plaques, or tumors of various sizes that often manifest in non–sun-exposed areas of the skin. Early stages of MF are difficult to detect histologically, but biopsies may show atypical lymphocytes with hyperchromatic, irregularly contoured nuclei arranged along the basal layer of the epidermis. Epidermal aggregates of atypical lymphocytes (also known as Pautrier microabscesses) are considered highly specific for MF. T-cell receptor and immunopathologic studies also are important adjuncts in the diagnosis of MF.⁴

Pemphigus foliaceus is an autoimmune blistering disease caused by antibodies directed against desmoglein 1, which is found in the granular layer of the epidermis. It manifests with a subtle onset of scattered crusted lesions in the seborrheic areas, such as the scalp, face, chest, and upper back. Histopathologic findings of early blisters may include acantholysis and dyskeratosis in the stratum granulosum as well as vacuolization of the granular layer. The blisters may coalesce into superficial bullae containing fibrin and neutrophils. Immunofluorescence studies that demonstrate intraepidermal C3 and IgG deposition are key to the diagnosis of pemphigus.⁵

Varicella (also known as chickenpox) manifests with crops of vesicles on an erythematous base in a centripetal distribution favoring the trunk and proximal extremities. It often is preceded by prodromal fever, malaise, and myalgia. Histopathologic evaluation of varicella is uncommon but may reveal acantholysis, multinucleation, and nuclear margination of keratinocytes. Viral culture or nucleic acid amplification testing of lesions can be used to verify the diagnosis.⁶

Most cases of PLEVA resolve without intervention.7 Treatment is directed at speeding recovery, providing symptomatic relief, and limiting permanent sequelae. Topical steroids often are used to alleviate inflammation and pruritus. Systemic antibiotics such as doxycycline, minocycline, and erythromycin have been used for their anti-inflammatory properties. Phototherapy of various wavelengths, including broadband and narrowband UVB as well as psoralen plus UVA, have led to improvements in affected patients. Refractory disease may warrant consideration of therapy with methotrexate, acitretin, dapsone, or cyclosporine.⁷

There have been rare reports of PLEVA evolving into its potentially lethal variant, febrile ulceronecrotic Mucha-Habermann disease, which is differentiated by the presence of systemic manifestations, including high fever, sore throat, diarrhea, central nervous system symptoms, abdominal pain, interstitial pneumonitis, splenomegaly, arthritis, sepsis, megaloblastic anemia, or conjunctival ulcers. The orogenital mucosa may be affected. Cutaneous lesions may rapidly progress to large, generalized, coalescent ulcers with necrotic crusts and vasculitic features on biopsy.8 Malignant transformation of PLEVA into LyP or MF rarely may occur and warrants continued follow-up of unresolved lesions.⁹

The Cutis Editorial Board is now accepting applications for the 2025 Resident Corner column. The Editorial Board will select 2 to 3 residents to serve as the Resident Corner columnists for 1 year. Articles are posted online only at www.mdedge.com/dermatology but will be referenced in Index Medicus. All applicants must be current residents and will be in residency throughout 2025.

For consideration, send your curriculum vitae along with a brief (not to exceed 500 words) statement of why you enjoy Cutis and what you can offer your fellow residents in contributing a monthly column.

A signed letter of recommendation from the Director of the dermatology residency program also should be supplied.

All materials should be submitted via email to Alicia Sonners ([email protected]) by November 1. The residents who are selected to write the column for the upcoming year will be notified by November 15.

We look forward to continuing to educate dermatology residents on topics that are most important to them!

The Cutis Editorial Board is now accepting applications for the 2025 Resident Corner column. The Editorial Board will select 2 to 3 residents to serve as the Resident Corner columnists for 1 year. Articles are posted online only at www.mdedge.com/dermatology but will be referenced in Index Medicus. All applicants must be current residents and will be in residency throughout 2025.

For consideration, send your curriculum vitae along with a brief (not to exceed 500 words) statement of why you enjoy Cutis and what you can offer your fellow residents in contributing a monthly column.

A signed letter of recommendation from the Director of the dermatology residency program also should be supplied.

All materials should be submitted via email to Alicia Sonners ([email protected]) by November 1. The residents who are selected to write the column for the upcoming year will be notified by November 15.

We look forward to continuing to educate dermatology residents on topics that are most important to them!

The Cutis Editorial Board is now accepting applications for the 2025 Resident Corner column. The Editorial Board will select 2 to 3 residents to serve as the Resident Corner columnists for 1 year. Articles are posted online only at www.mdedge.com/dermatology but will be referenced in Index Medicus. All applicants must be current residents and will be in residency throughout 2025.

For consideration, send your curriculum vitae along with a brief (not to exceed 500 words) statement of why you enjoy Cutis and what you can offer your fellow residents in contributing a monthly column.

A signed letter of recommendation from the Director of the dermatology residency program also should be supplied.

All materials should be submitted via email to Alicia Sonners ([email protected]) by November 1. The residents who are selected to write the column for the upcoming year will be notified by November 15.

We look forward to continuing to educate dermatology residents on topics that are most important to them!