Dermatopathology

The Diagnosis: Endocrine Mucin-Producing Sweat Gland Carcinoma

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare cutaneous adnexal tumor that characteristically presents as slowgrowing, flesh-colored papules, nodules, or cystic lesions around the periorbital skin in elderly female patients.¹ Histopathology of EMPSGCs reveals well-circumscribed multinodular dermal lesions that can be either cystic or solid and often are arranged in papillary and cribriform patterns (quiz image). Nests of uniform tumor cells are composed of small- to medium-sized epithelial cells with monomorphic nuclei showing fine to stippled chromatin.² Histologically, EMPSGC resembles a solid papillary carcinoma of the breast, which is attributed to their common embryologic origin.³ Intracytoplasmic and extracellular mucin often are seen on hematoxylin and eosin staining.² Variable immunohistochemical stain expression has been reported, including positive staining with synaptophysin and chromogranin. Other markers include cytokeratin CAM 5.2, epithelial membrane antigen, estrogen or progesterone receptors, and cytokeratin 7.⁴ Endocrine mucin-producing sweat gland carcinoma is thought to be a precursor to invasive neuroendocrine-type primary cutaneous mucinous carcinoma. Primary cutaneous mucinous carcinoma has been associated with EMPSGC in approximately 35.7% of cases. Histologically, primary cutaneous mucinous carcinoma that has transformed from EMPSGC would show an infiltration of tumor nests with desmoplastic stroma or mucin pools with clusters of tumor cells.²

Primary cutaneous adenoid cystic carcinoma is a rare malignant tumor that often presents on the head and neck. It usually appears as a single, slowly growing subcutaneous nodule or multinodular plaque.^5,6 Histologic features include basaloid cells in alternating tubular and cribriform patterns. The cribriform areas are composed of pseudoglandular adenoid spaces that contain mucin, basement membrane zone material, and cellular debris from necrotic neoplastic cells (Figure 1).⁷ Primary cutaneous adenoid cystic carcinoma predominantly is dermal with extension to the subcutaneous tissue. True ductal structures that demonstrate decapitation secretion also may be present.⁷

Basal cell carcinoma (adenoid type) presents as a pigmented or nonpigmented nodule or ulcer on sunexposed areas of the head and neck. Histopathology reveals basaloid cells surrounding islands of connective tissue resulting in a lacelike pattern (Figure 2). The lumina may contain a colloidal substance or amorphous granular material.⁸ The characteristic features of basal cell carcinomas, such as nests of basaloid cells with peripheral palisading cells, retraction of adjacent stroma, increased apoptosis and mitotic figures, and connection to the epidermis, can be helpful to distinguish basal cell carcinoma histologically from EMPSGC.²

Apocrine hidrocystomas clinically present as round, flesh-colored, shiny or translucent, dome-shaped papules or nodules near the eyelid margin or lateral canthus.⁹ Histologically, they are composed of proliferating apocrine secretory coils with an epithelial side of cuboidal or columnar cells and a luminal side exhibiting decapitation secretion (Figure 3).² An epidermal connection is absent.⁹ Apocrine hidrocystomas may exhibit complex architecture and papillary ductal hyperplasia that are difficult to distinguish from EMPSGC, especially if EMPSGC presents with cystic morphology. Apocrine cytomorphology and the lack of neuroendocrine marker expression and mucin production distinguish apocrine hidrocystomas. Furthermore, hidrocystomas infrequently demonstrate the nodular, solid, cribriform areas appreciated in EMPSGC.²

Microcystic adnexal carcinoma is a rare, slowly growing, locally aggressive sweat gland tumor that commonly presents as a flesh-colored to yellow papule, nodule, or plaque on the central face.¹⁰ Histopathologic examination reveals both eccrine and follicular differentiation. Keratin cysts, bland keratinocyte cords, and epithelium with ductal differentiation is observed in the superficial layers (Figure 4). Deep invasion into the subcutis and perineural invasion frequently is observed.

The Diagnosis: Endocrine Mucin-Producing Sweat Gland Carcinoma

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare cutaneous adnexal tumor that characteristically presents as slowgrowing, flesh-colored papules, nodules, or cystic lesions around the periorbital skin in elderly female patients.¹ Histopathology of EMPSGCs reveals well-circumscribed multinodular dermal lesions that can be either cystic or solid and often are arranged in papillary and cribriform patterns (quiz image). Nests of uniform tumor cells are composed of small- to medium-sized epithelial cells with monomorphic nuclei showing fine to stippled chromatin.² Histologically, EMPSGC resembles a solid papillary carcinoma of the breast, which is attributed to their common embryologic origin.³ Intracytoplasmic and extracellular mucin often are seen on hematoxylin and eosin staining.² Variable immunohistochemical stain expression has been reported, including positive staining with synaptophysin and chromogranin. Other markers include cytokeratin CAM 5.2, epithelial membrane antigen, estrogen or progesterone receptors, and cytokeratin 7.⁴ Endocrine mucin-producing sweat gland carcinoma is thought to be a precursor to invasive neuroendocrine-type primary cutaneous mucinous carcinoma. Primary cutaneous mucinous carcinoma has been associated with EMPSGC in approximately 35.7% of cases. Histologically, primary cutaneous mucinous carcinoma that has transformed from EMPSGC would show an infiltration of tumor nests with desmoplastic stroma or mucin pools with clusters of tumor cells.²

Primary cutaneous adenoid cystic carcinoma is a rare malignant tumor that often presents on the head and neck. It usually appears as a single, slowly growing subcutaneous nodule or multinodular plaque.^5,6 Histologic features include basaloid cells in alternating tubular and cribriform patterns. The cribriform areas are composed of pseudoglandular adenoid spaces that contain mucin, basement membrane zone material, and cellular debris from necrotic neoplastic cells (Figure 1).⁷ Primary cutaneous adenoid cystic carcinoma predominantly is dermal with extension to the subcutaneous tissue. True ductal structures that demonstrate decapitation secretion also may be present.⁷

Basal cell carcinoma (adenoid type) presents as a pigmented or nonpigmented nodule or ulcer on sunexposed areas of the head and neck. Histopathology reveals basaloid cells surrounding islands of connective tissue resulting in a lacelike pattern (Figure 2). The lumina may contain a colloidal substance or amorphous granular material.⁸ The characteristic features of basal cell carcinomas, such as nests of basaloid cells with peripheral palisading cells, retraction of adjacent stroma, increased apoptosis and mitotic figures, and connection to the epidermis, can be helpful to distinguish basal cell carcinoma histologically from EMPSGC.²

Apocrine hidrocystomas clinically present as round, flesh-colored, shiny or translucent, dome-shaped papules or nodules near the eyelid margin or lateral canthus.⁹ Histologically, they are composed of proliferating apocrine secretory coils with an epithelial side of cuboidal or columnar cells and a luminal side exhibiting decapitation secretion (Figure 3).² An epidermal connection is absent.⁹ Apocrine hidrocystomas may exhibit complex architecture and papillary ductal hyperplasia that are difficult to distinguish from EMPSGC, especially if EMPSGC presents with cystic morphology. Apocrine cytomorphology and the lack of neuroendocrine marker expression and mucin production distinguish apocrine hidrocystomas. Furthermore, hidrocystomas infrequently demonstrate the nodular, solid, cribriform areas appreciated in EMPSGC.²

Microcystic adnexal carcinoma is a rare, slowly growing, locally aggressive sweat gland tumor that commonly presents as a flesh-colored to yellow papule, nodule, or plaque on the central face.¹⁰ Histopathologic examination reveals both eccrine and follicular differentiation. Keratin cysts, bland keratinocyte cords, and epithelium with ductal differentiation is observed in the superficial layers (Figure 4). Deep invasion into the subcutis and perineural invasion frequently is observed.

The Diagnosis: Endocrine Mucin-Producing Sweat Gland Carcinoma

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare cutaneous adnexal tumor that characteristically presents as slowgrowing, flesh-colored papules, nodules, or cystic lesions around the periorbital skin in elderly female patients.¹ Histopathology of EMPSGCs reveals well-circumscribed multinodular dermal lesions that can be either cystic or solid and often are arranged in papillary and cribriform patterns (quiz image). Nests of uniform tumor cells are composed of small- to medium-sized epithelial cells with monomorphic nuclei showing fine to stippled chromatin.² Histologically, EMPSGC resembles a solid papillary carcinoma of the breast, which is attributed to their common embryologic origin.³ Intracytoplasmic and extracellular mucin often are seen on hematoxylin and eosin staining.² Variable immunohistochemical stain expression has been reported, including positive staining with synaptophysin and chromogranin. Other markers include cytokeratin CAM 5.2, epithelial membrane antigen, estrogen or progesterone receptors, and cytokeratin 7.⁴ Endocrine mucin-producing sweat gland carcinoma is thought to be a precursor to invasive neuroendocrine-type primary cutaneous mucinous carcinoma. Primary cutaneous mucinous carcinoma has been associated with EMPSGC in approximately 35.7% of cases. Histologically, primary cutaneous mucinous carcinoma that has transformed from EMPSGC would show an infiltration of tumor nests with desmoplastic stroma or mucin pools with clusters of tumor cells.²

Primary cutaneous adenoid cystic carcinoma is a rare malignant tumor that often presents on the head and neck. It usually appears as a single, slowly growing subcutaneous nodule or multinodular plaque.^5,6 Histologic features include basaloid cells in alternating tubular and cribriform patterns. The cribriform areas are composed of pseudoglandular adenoid spaces that contain mucin, basement membrane zone material, and cellular debris from necrotic neoplastic cells (Figure 1).⁷ Primary cutaneous adenoid cystic carcinoma predominantly is dermal with extension to the subcutaneous tissue. True ductal structures that demonstrate decapitation secretion also may be present.⁷

Basal cell carcinoma (adenoid type) presents as a pigmented or nonpigmented nodule or ulcer on sunexposed areas of the head and neck. Histopathology reveals basaloid cells surrounding islands of connective tissue resulting in a lacelike pattern (Figure 2). The lumina may contain a colloidal substance or amorphous granular material.⁸ The characteristic features of basal cell carcinomas, such as nests of basaloid cells with peripheral palisading cells, retraction of adjacent stroma, increased apoptosis and mitotic figures, and connection to the epidermis, can be helpful to distinguish basal cell carcinoma histologically from EMPSGC.²

Apocrine hidrocystomas clinically present as round, flesh-colored, shiny or translucent, dome-shaped papules or nodules near the eyelid margin or lateral canthus.⁹ Histologically, they are composed of proliferating apocrine secretory coils with an epithelial side of cuboidal or columnar cells and a luminal side exhibiting decapitation secretion (Figure 3).² An epidermal connection is absent.⁹ Apocrine hidrocystomas may exhibit complex architecture and papillary ductal hyperplasia that are difficult to distinguish from EMPSGC, especially if EMPSGC presents with cystic morphology. Apocrine cytomorphology and the lack of neuroendocrine marker expression and mucin production distinguish apocrine hidrocystomas. Furthermore, hidrocystomas infrequently demonstrate the nodular, solid, cribriform areas appreciated in EMPSGC.²

Microcystic adnexal carcinoma is a rare, slowly growing, locally aggressive sweat gland tumor that commonly presents as a flesh-colored to yellow papule, nodule, or plaque on the central face.¹⁰ Histopathologic examination reveals both eccrine and follicular differentiation. Keratin cysts, bland keratinocyte cords, and epithelium with ductal differentiation is observed in the superficial layers (Figure 4). Deep invasion into the subcutis and perineural invasion frequently is observed.

To the Editor:

A 44-year-old woman presented with a low-grade fever (temperature, 38.0 °C) and painful acral lesions of 1 week’s duration. She had a history of hepatitis C viral infection and intravenous (IV) drug use, as well as polymicrobial infective endocarditis that involved the tricuspid and aortic valves; pathogenic organisms were identified via blood culture as Enterococcus faecalis, Serratia species, Streptococcus viridans, and Candida albicans. The patient had received a mechanical aortic valve and bioprosthetic tricuspid valve replacement 5 months prior with warfarin therapy and had completed a postsurgical 6-week course of high-dose micafungin. She reported that she had developed painful, violaceous, thin papules on the plantar surface of the left foot 2 weeks prior to presentation. Her symptoms improved with a short systemic steroid taper; however, within a week she developed new tender, erythematous, thin papules on the plantar surface of the right foot and the palmar surface of the left hand with associated lower extremity swelling. She denied other symptoms, including fever, chills, neurologic symptoms, shortness of breath, chest pain, nausea, vomiting, hematuria, and hematochezia. Due to worsening cutaneous findings, the patient presented to the emergency department, prompting hospital admission for empiric antibacterial therapy with vancomycin and piperacillin-tazobactam for suspected infectious endocarditis. Dermatology was consulted after 1 day of antibacterial therapy without improvement to determine the etiology of the patient’s skin findings.

Physical examination revealed the patient was afebrile with partially blanching violaceous to purpuric, tender, edematous papules on the left fourth and fifth finger pads, as well as scattered, painful, purpuric patches with stellate borders on the right plantar foot (Figure 1). Laboratory test results revealed mild anemia (hemoglobin, 11.9 g/dL [reference range, 12.0–15.0 g/dL], mild neutrophilia (neutrophils, 8.4×10⁹/L [reference range, 1.9–7.9×10⁹/L], elevated acute-phase reactants (erythrocyte sedimentation rate, 71 mm/h [reference range, 0–20 mm/h]; C-reactive protein, 5.7 mg/dL [reference range, 0.0–0.5 mg/dL]), and positive hepatitis C virus antibody with an undetectable viral load. At the time of dermatologic evaluation, admission blood cultures and transthoracic echocardiogram were negative. Additionally, a transesophageal echocardiogram, limited by artifact from the mechanical aortic valve, was equivocal for valvular pathology. Subsequent ophthalmologic evaluation was negative for lesions associated with endocarditis, such as retinal hemorrhages.

Punch biopsies of the left fourth finger pad were submitted for histopathologic analysis and tissue cultures. Histopathology demonstrated deep dermal perivascular neutrophilic inflammation with multiple intravascular thrombi, perivascular fibrin, and karyorrhectic debris (Figure 2). Periodic acid–Schiff and Grocott-Gomori methenamine-silver stains revealed fungal spores with rare pseudohyphae within the thrombosed vascular spaces and the perivascular dermis, consistent with fungal septic emboli (Figure 3).

Empiric systemic antifungal coverage composed of IV liposomal amphotericin B and oral flucytosine was initiated, and the patient’s tender acral papules rapidly improved. Within 48 hours of biopsy, skin tissue culture confirmed the presence of C albicans. Four days after the preliminary dermatopathology report, confirmatory blood cultures resulted with pansensitive C albicans. Final tissue and blood cultures were negative for bacteria including mycobacteria. In addition to a 6-week course of IV amphotericin B and flucytosine, repeat surgical intervention was considered, and lifelong suppressive antifungal oral therapy was recommended. Unfortunately, the patient did not present for follow-up. Three months later, she presented to the emergency department with peritonitis; in the operating room, she was found to have ischemia of the entirety of the small and large intestines and died shortly thereafter.

Fungal endocarditis is rare, tending to develop in patient populations with particular risk factors such as immune compromise, structural heart defects or prosthetic valves, and IV drug use. Candida infective endocarditis (CIE) represents less than 2% of infective endocarditis cases and carries a high mortality rate (30%–80%).^1-3 Diagnosis may be challenging, as the clinical presentation varies widely. Although some patients may present with classic features of infective endocarditis, including fever, cardiac murmurs, and positive blood cultures, many cases of infective endocarditis present with nonspecific symptoms, raising a broad clinical differential diagnosis. Delay in diagnosis, which is seen in 82% of patients with fungal endocarditis, may be attributed to the slow progression of symptoms, inconclusive cardiac imaging, or negative blood cultures seen in almost one-third of cases.^2,3 The feared complication of systemic embolization via infective endocarditis may occur in up to one-half of cases, with the highest rates associated with staphylococcal or fungal pathogens.² The risk for embolization in fungal endocarditis is independent of the size of the cardiac valve vegetations; accordingly, sequelae of embolic complications may arise despite negative cardiac imaging.⁴ Embolic complications, which typically are seen within the first 2 to 4 weeks of treatment, may serve as the presenting feature of endocarditis and may even occur after completion of antimicrobial therapy.

Detection of cutaneous manifestations of infective endocarditis, including Janeway lesions, Osler nodes, and splinter hemorrhages, may allow for earlier diagnosis. Despite eponymous recognition, Janeway lesions and Osler nodes are relatively uncommon manifestations of infective endocarditis and may be found in only 5% to 15% of cases.⁵ Biopsies of suspected Janeway lesions and Osler nodes may allow for recognition of relevant vascular pathology, identification of the causative pathogen, and strong support for the diagnosis of infective endocarditis.^4-7

The initial photomicrograph of corresponding Janeway lesion histopathology was published by Kerr in 1955 and revealed dermal microabscesses posited to be secondary to bacterial emboli.^8,9 Additional cases through the years have reported overlapping histopathologic features of Janeway lesions and Osler nodes, with the latter often defined by the presence of vasculitis.⁴ Although there appears to be ongoing debate and overlap between the 2 integumentary findings, a general consensus on differentiation takes into account both the clinical signs and symptoms as well as the histopathologic findings.^10,11

Osler nodes present as tender, violaceous, subcutaneous nodules on the acral surfaces, usually on the pads of the fingers and toes.⁵ The pathogenesis involves the deposition of immune complexes as a sequela of vascular occlusion by microthrombi classically seen in the late phase of subacute endocarditis. Janeway lesions present as nontender erythematous macules on the acral surfaces and are thought to represent microthrombi with dermal microabscesses, more common in acute endocarditis. Our patient demonstrated features of both Osler nodes and Janeway lesions. Despite the presence of fungal thrombi—a pathophysiology closer to that of Janeway lesions—the clinical presentation of painful acral nodules affecting finger pads and histologic features of vasculitis may be better characterized as Osler nodes. Regardless of pathogenesis, these cutaneous findings serve as a minor clinical criterion in the Duke criteria for the diagnosis of infective endocarditis when present.¹²

Candida infective endocarditis should be suspected in a patient with a history of valvular disease or prior infective endocarditis with fungemia, unexplained neurologic signs, or manifestations of peripheral embolization despite negative blood cultures.³ Particularly in the setting of negative cardiac imaging, recognition of CIE requires heightened diagnostic acumen and clinicopathologic correlation. Although culture and pathologic examination of valvular vegetations represents the gold standard for diagnosis of CIE, aspiration and culture of easily accessible septic emboli may provide rapid identification of the etiologic pathogen. In 1976, Alpert et al¹³ identified C albicans from an aspirated Osler node. Postmortem examination revealed extensive involvement of the homograft valve and aortic root with C albicans.¹³ Many other examples exist in the literature demonstrating matching pathogenic isolates from microbiologic cultures of skin and blood.^4,9,14,15 Thadepalli and Francis⁷ investigated 26 cases of endocarditis in heroin users in which the admitting diagnosis was endocarditis in only 4 cases. The etiologic pathogen was aspirated from secondary sites of localized infections secondary to emboli, including cutaneous lesions in 10 of the cases. Gram stain and culture revealed the causative organism leading to the ultimate diagnosis and management in 17 of 26 patients with endocarditis.⁷

The incidence of fungal endocarditis is increasing, with a reported 67% of cases caused by nosocomial infection.¹ Given the rising incidence of fungal endocarditis and its accompanying diagnostic difficulties, including frequently negative blood cultures and cardiac imaging, clinicians must perform careful skin examinations, employ judicious use of skin biopsy, and carefully correlate clinical and pathologic findings to improve recognition of this disease and guide patient care.

To the Editor:

A 44-year-old woman presented with a low-grade fever (temperature, 38.0 °C) and painful acral lesions of 1 week’s duration. She had a history of hepatitis C viral infection and intravenous (IV) drug use, as well as polymicrobial infective endocarditis that involved the tricuspid and aortic valves; pathogenic organisms were identified via blood culture as Enterococcus faecalis, Serratia species, Streptococcus viridans, and Candida albicans. The patient had received a mechanical aortic valve and bioprosthetic tricuspid valve replacement 5 months prior with warfarin therapy and had completed a postsurgical 6-week course of high-dose micafungin. She reported that she had developed painful, violaceous, thin papules on the plantar surface of the left foot 2 weeks prior to presentation. Her symptoms improved with a short systemic steroid taper; however, within a week she developed new tender, erythematous, thin papules on the plantar surface of the right foot and the palmar surface of the left hand with associated lower extremity swelling. She denied other symptoms, including fever, chills, neurologic symptoms, shortness of breath, chest pain, nausea, vomiting, hematuria, and hematochezia. Due to worsening cutaneous findings, the patient presented to the emergency department, prompting hospital admission for empiric antibacterial therapy with vancomycin and piperacillin-tazobactam for suspected infectious endocarditis. Dermatology was consulted after 1 day of antibacterial therapy without improvement to determine the etiology of the patient’s skin findings.

Physical examination revealed the patient was afebrile with partially blanching violaceous to purpuric, tender, edematous papules on the left fourth and fifth finger pads, as well as scattered, painful, purpuric patches with stellate borders on the right plantar foot (Figure 1). Laboratory test results revealed mild anemia (hemoglobin, 11.9 g/dL [reference range, 12.0–15.0 g/dL], mild neutrophilia (neutrophils, 8.4×10⁹/L [reference range, 1.9–7.9×10⁹/L], elevated acute-phase reactants (erythrocyte sedimentation rate, 71 mm/h [reference range, 0–20 mm/h]; C-reactive protein, 5.7 mg/dL [reference range, 0.0–0.5 mg/dL]), and positive hepatitis C virus antibody with an undetectable viral load. At the time of dermatologic evaluation, admission blood cultures and transthoracic echocardiogram were negative. Additionally, a transesophageal echocardiogram, limited by artifact from the mechanical aortic valve, was equivocal for valvular pathology. Subsequent ophthalmologic evaluation was negative for lesions associated with endocarditis, such as retinal hemorrhages.

Punch biopsies of the left fourth finger pad were submitted for histopathologic analysis and tissue cultures. Histopathology demonstrated deep dermal perivascular neutrophilic inflammation with multiple intravascular thrombi, perivascular fibrin, and karyorrhectic debris (Figure 2). Periodic acid–Schiff and Grocott-Gomori methenamine-silver stains revealed fungal spores with rare pseudohyphae within the thrombosed vascular spaces and the perivascular dermis, consistent with fungal septic emboli (Figure 3).

Empiric systemic antifungal coverage composed of IV liposomal amphotericin B and oral flucytosine was initiated, and the patient’s tender acral papules rapidly improved. Within 48 hours of biopsy, skin tissue culture confirmed the presence of C albicans. Four days after the preliminary dermatopathology report, confirmatory blood cultures resulted with pansensitive C albicans. Final tissue and blood cultures were negative for bacteria including mycobacteria. In addition to a 6-week course of IV amphotericin B and flucytosine, repeat surgical intervention was considered, and lifelong suppressive antifungal oral therapy was recommended. Unfortunately, the patient did not present for follow-up. Three months later, she presented to the emergency department with peritonitis; in the operating room, she was found to have ischemia of the entirety of the small and large intestines and died shortly thereafter.

Fungal endocarditis is rare, tending to develop in patient populations with particular risk factors such as immune compromise, structural heart defects or prosthetic valves, and IV drug use. Candida infective endocarditis (CIE) represents less than 2% of infective endocarditis cases and carries a high mortality rate (30%–80%).^1-3 Diagnosis may be challenging, as the clinical presentation varies widely. Although some patients may present with classic features of infective endocarditis, including fever, cardiac murmurs, and positive blood cultures, many cases of infective endocarditis present with nonspecific symptoms, raising a broad clinical differential diagnosis. Delay in diagnosis, which is seen in 82% of patients with fungal endocarditis, may be attributed to the slow progression of symptoms, inconclusive cardiac imaging, or negative blood cultures seen in almost one-third of cases.^2,3 The feared complication of systemic embolization via infective endocarditis may occur in up to one-half of cases, with the highest rates associated with staphylococcal or fungal pathogens.² The risk for embolization in fungal endocarditis is independent of the size of the cardiac valve vegetations; accordingly, sequelae of embolic complications may arise despite negative cardiac imaging.⁴ Embolic complications, which typically are seen within the first 2 to 4 weeks of treatment, may serve as the presenting feature of endocarditis and may even occur after completion of antimicrobial therapy.

Detection of cutaneous manifestations of infective endocarditis, including Janeway lesions, Osler nodes, and splinter hemorrhages, may allow for earlier diagnosis. Despite eponymous recognition, Janeway lesions and Osler nodes are relatively uncommon manifestations of infective endocarditis and may be found in only 5% to 15% of cases.⁵ Biopsies of suspected Janeway lesions and Osler nodes may allow for recognition of relevant vascular pathology, identification of the causative pathogen, and strong support for the diagnosis of infective endocarditis.^4-7

The initial photomicrograph of corresponding Janeway lesion histopathology was published by Kerr in 1955 and revealed dermal microabscesses posited to be secondary to bacterial emboli.^8,9 Additional cases through the years have reported overlapping histopathologic features of Janeway lesions and Osler nodes, with the latter often defined by the presence of vasculitis.⁴ Although there appears to be ongoing debate and overlap between the 2 integumentary findings, a general consensus on differentiation takes into account both the clinical signs and symptoms as well as the histopathologic findings.^10,11

Osler nodes present as tender, violaceous, subcutaneous nodules on the acral surfaces, usually on the pads of the fingers and toes.⁵ The pathogenesis involves the deposition of immune complexes as a sequela of vascular occlusion by microthrombi classically seen in the late phase of subacute endocarditis. Janeway lesions present as nontender erythematous macules on the acral surfaces and are thought to represent microthrombi with dermal microabscesses, more common in acute endocarditis. Our patient demonstrated features of both Osler nodes and Janeway lesions. Despite the presence of fungal thrombi—a pathophysiology closer to that of Janeway lesions—the clinical presentation of painful acral nodules affecting finger pads and histologic features of vasculitis may be better characterized as Osler nodes. Regardless of pathogenesis, these cutaneous findings serve as a minor clinical criterion in the Duke criteria for the diagnosis of infective endocarditis when present.¹²

Candida infective endocarditis should be suspected in a patient with a history of valvular disease or prior infective endocarditis with fungemia, unexplained neurologic signs, or manifestations of peripheral embolization despite negative blood cultures.³ Particularly in the setting of negative cardiac imaging, recognition of CIE requires heightened diagnostic acumen and clinicopathologic correlation. Although culture and pathologic examination of valvular vegetations represents the gold standard for diagnosis of CIE, aspiration and culture of easily accessible septic emboli may provide rapid identification of the etiologic pathogen. In 1976, Alpert et al¹³ identified C albicans from an aspirated Osler node. Postmortem examination revealed extensive involvement of the homograft valve and aortic root with C albicans.¹³ Many other examples exist in the literature demonstrating matching pathogenic isolates from microbiologic cultures of skin and blood.^4,9,14,15 Thadepalli and Francis⁷ investigated 26 cases of endocarditis in heroin users in which the admitting diagnosis was endocarditis in only 4 cases. The etiologic pathogen was aspirated from secondary sites of localized infections secondary to emboli, including cutaneous lesions in 10 of the cases. Gram stain and culture revealed the causative organism leading to the ultimate diagnosis and management in 17 of 26 patients with endocarditis.⁷

The incidence of fungal endocarditis is increasing, with a reported 67% of cases caused by nosocomial infection.¹ Given the rising incidence of fungal endocarditis and its accompanying diagnostic difficulties, including frequently negative blood cultures and cardiac imaging, clinicians must perform careful skin examinations, employ judicious use of skin biopsy, and carefully correlate clinical and pathologic findings to improve recognition of this disease and guide patient care.

To the Editor:

A 44-year-old woman presented with a low-grade fever (temperature, 38.0 °C) and painful acral lesions of 1 week’s duration. She had a history of hepatitis C viral infection and intravenous (IV) drug use, as well as polymicrobial infective endocarditis that involved the tricuspid and aortic valves; pathogenic organisms were identified via blood culture as Enterococcus faecalis, Serratia species, Streptococcus viridans, and Candida albicans. The patient had received a mechanical aortic valve and bioprosthetic tricuspid valve replacement 5 months prior with warfarin therapy and had completed a postsurgical 6-week course of high-dose micafungin. She reported that she had developed painful, violaceous, thin papules on the plantar surface of the left foot 2 weeks prior to presentation. Her symptoms improved with a short systemic steroid taper; however, within a week she developed new tender, erythematous, thin papules on the plantar surface of the right foot and the palmar surface of the left hand with associated lower extremity swelling. She denied other symptoms, including fever, chills, neurologic symptoms, shortness of breath, chest pain, nausea, vomiting, hematuria, and hematochezia. Due to worsening cutaneous findings, the patient presented to the emergency department, prompting hospital admission for empiric antibacterial therapy with vancomycin and piperacillin-tazobactam for suspected infectious endocarditis. Dermatology was consulted after 1 day of antibacterial therapy without improvement to determine the etiology of the patient’s skin findings.

Physical examination revealed the patient was afebrile with partially blanching violaceous to purpuric, tender, edematous papules on the left fourth and fifth finger pads, as well as scattered, painful, purpuric patches with stellate borders on the right plantar foot (Figure 1). Laboratory test results revealed mild anemia (hemoglobin, 11.9 g/dL [reference range, 12.0–15.0 g/dL], mild neutrophilia (neutrophils, 8.4×10⁹/L [reference range, 1.9–7.9×10⁹/L], elevated acute-phase reactants (erythrocyte sedimentation rate, 71 mm/h [reference range, 0–20 mm/h]; C-reactive protein, 5.7 mg/dL [reference range, 0.0–0.5 mg/dL]), and positive hepatitis C virus antibody with an undetectable viral load. At the time of dermatologic evaluation, admission blood cultures and transthoracic echocardiogram were negative. Additionally, a transesophageal echocardiogram, limited by artifact from the mechanical aortic valve, was equivocal for valvular pathology. Subsequent ophthalmologic evaluation was negative for lesions associated with endocarditis, such as retinal hemorrhages.

Punch biopsies of the left fourth finger pad were submitted for histopathologic analysis and tissue cultures. Histopathology demonstrated deep dermal perivascular neutrophilic inflammation with multiple intravascular thrombi, perivascular fibrin, and karyorrhectic debris (Figure 2). Periodic acid–Schiff and Grocott-Gomori methenamine-silver stains revealed fungal spores with rare pseudohyphae within the thrombosed vascular spaces and the perivascular dermis, consistent with fungal septic emboli (Figure 3).

Empiric systemic antifungal coverage composed of IV liposomal amphotericin B and oral flucytosine was initiated, and the patient’s tender acral papules rapidly improved. Within 48 hours of biopsy, skin tissue culture confirmed the presence of C albicans. Four days after the preliminary dermatopathology report, confirmatory blood cultures resulted with pansensitive C albicans. Final tissue and blood cultures were negative for bacteria including mycobacteria. In addition to a 6-week course of IV amphotericin B and flucytosine, repeat surgical intervention was considered, and lifelong suppressive antifungal oral therapy was recommended. Unfortunately, the patient did not present for follow-up. Three months later, she presented to the emergency department with peritonitis; in the operating room, she was found to have ischemia of the entirety of the small and large intestines and died shortly thereafter.

Fungal endocarditis is rare, tending to develop in patient populations with particular risk factors such as immune compromise, structural heart defects or prosthetic valves, and IV drug use. Candida infective endocarditis (CIE) represents less than 2% of infective endocarditis cases and carries a high mortality rate (30%–80%).^1-3 Diagnosis may be challenging, as the clinical presentation varies widely. Although some patients may present with classic features of infective endocarditis, including fever, cardiac murmurs, and positive blood cultures, many cases of infective endocarditis present with nonspecific symptoms, raising a broad clinical differential diagnosis. Delay in diagnosis, which is seen in 82% of patients with fungal endocarditis, may be attributed to the slow progression of symptoms, inconclusive cardiac imaging, or negative blood cultures seen in almost one-third of cases.^2,3 The feared complication of systemic embolization via infective endocarditis may occur in up to one-half of cases, with the highest rates associated with staphylococcal or fungal pathogens.² The risk for embolization in fungal endocarditis is independent of the size of the cardiac valve vegetations; accordingly, sequelae of embolic complications may arise despite negative cardiac imaging.⁴ Embolic complications, which typically are seen within the first 2 to 4 weeks of treatment, may serve as the presenting feature of endocarditis and may even occur after completion of antimicrobial therapy.

Detection of cutaneous manifestations of infective endocarditis, including Janeway lesions, Osler nodes, and splinter hemorrhages, may allow for earlier diagnosis. Despite eponymous recognition, Janeway lesions and Osler nodes are relatively uncommon manifestations of infective endocarditis and may be found in only 5% to 15% of cases.⁵ Biopsies of suspected Janeway lesions and Osler nodes may allow for recognition of relevant vascular pathology, identification of the causative pathogen, and strong support for the diagnosis of infective endocarditis.^4-7

The initial photomicrograph of corresponding Janeway lesion histopathology was published by Kerr in 1955 and revealed dermal microabscesses posited to be secondary to bacterial emboli.^8,9 Additional cases through the years have reported overlapping histopathologic features of Janeway lesions and Osler nodes, with the latter often defined by the presence of vasculitis.⁴ Although there appears to be ongoing debate and overlap between the 2 integumentary findings, a general consensus on differentiation takes into account both the clinical signs and symptoms as well as the histopathologic findings.^10,11

Osler nodes present as tender, violaceous, subcutaneous nodules on the acral surfaces, usually on the pads of the fingers and toes.⁵ The pathogenesis involves the deposition of immune complexes as a sequela of vascular occlusion by microthrombi classically seen in the late phase of subacute endocarditis. Janeway lesions present as nontender erythematous macules on the acral surfaces and are thought to represent microthrombi with dermal microabscesses, more common in acute endocarditis. Our patient demonstrated features of both Osler nodes and Janeway lesions. Despite the presence of fungal thrombi—a pathophysiology closer to that of Janeway lesions—the clinical presentation of painful acral nodules affecting finger pads and histologic features of vasculitis may be better characterized as Osler nodes. Regardless of pathogenesis, these cutaneous findings serve as a minor clinical criterion in the Duke criteria for the diagnosis of infective endocarditis when present.¹²

Candida infective endocarditis should be suspected in a patient with a history of valvular disease or prior infective endocarditis with fungemia, unexplained neurologic signs, or manifestations of peripheral embolization despite negative blood cultures.³ Particularly in the setting of negative cardiac imaging, recognition of CIE requires heightened diagnostic acumen and clinicopathologic correlation. Although culture and pathologic examination of valvular vegetations represents the gold standard for diagnosis of CIE, aspiration and culture of easily accessible septic emboli may provide rapid identification of the etiologic pathogen. In 1976, Alpert et al¹³ identified C albicans from an aspirated Osler node. Postmortem examination revealed extensive involvement of the homograft valve and aortic root with C albicans.¹³ Many other examples exist in the literature demonstrating matching pathogenic isolates from microbiologic cultures of skin and blood.^4,9,14,15 Thadepalli and Francis⁷ investigated 26 cases of endocarditis in heroin users in which the admitting diagnosis was endocarditis in only 4 cases. The etiologic pathogen was aspirated from secondary sites of localized infections secondary to emboli, including cutaneous lesions in 10 of the cases. Gram stain and culture revealed the causative organism leading to the ultimate diagnosis and management in 17 of 26 patients with endocarditis.⁷

The incidence of fungal endocarditis is increasing, with a reported 67% of cases caused by nosocomial infection.¹ Given the rising incidence of fungal endocarditis and its accompanying diagnostic difficulties, including frequently negative blood cultures and cardiac imaging, clinicians must perform careful skin examinations, employ judicious use of skin biopsy, and carefully correlate clinical and pathologic findings to improve recognition of this disease and guide patient care.

The Diagnosis: Annular Elastolytic Giant Cell Granuloma

Histologic examination of the shave biopsies showed a granulomatous infiltrate of small lymphocytes, histiocytes, and multinucleated giant cells. The giant cells have abundant eosinophilic cytoplasm, with several also containing fragments of basophilic elastic fibers (elastophagocytosis)(Figure). Additionally, the granulomas revealed no signs of necrosis, making an infectious source unlikely, and examination under polarized light was negative for foreign material. These clinical and histologic findings were diagnostic for annular elastolytic giant cell granuloma (AEGCG).

Annular elastolytic giant cell granuloma is a rare chronic inflammatory disorder that classically presents on sun-exposed skin as annular plaques with elevated borders and atrophic centers.^1-4 Histologically, AEGCG is characterized by diffuse granulomatous infiltrates composed of multinucleated giant cells, histiocytes, and lymphocytes in the dermis, along with phagocytosis of elastic fibers by multinucleated giant cells.⁵ The underlying etiology and pathogenesis of AEGCG remains unknown.⁶

Annular elastolytic giant cell granuloma commonly affects females aged 35 to 75 years; however, cases have been reported in the male and pediatric patient populations.^1,2 Documented cases are known to last from 1 month to 10 years.^7,8 Although the mechanisms underlying the development of AEGCG remain to be elucidated, studies have determined that the skin disorder is associated with sarcoidosis, molluscum contagiosum, amyloidosis, diabetes mellitus, and cutaneous T-cell lymphoma.⁹ Diabetes mellitus is the most common comorbidity associated with AEGCG, and it is theorized that diabetes contributes to the increased incidence of AEGCG in this population by inducing damage to elastic fibers in the skin.¹⁰ One study that examined 50 cases of AEGCG found that 38 patients had serum glucose levels evaluated, with 8 cases being subsequently diagnosed with diabetes mellitus and 6 cases with apparent impaired glucose tolerance, indicating that 37% of the sample population with AEGCG who were evaluated for metabolic disease were found to have definitive or latent type 2 diabetes mellitus.¹¹ Although AEGCG is a rare disorder, a substantial number of patients diagnosed with AEGCG also have diabetes mellitus, making it important to consider screening all patients with AEGCG for diabetes given the ease and widely available resources to check glucose levels.

Actinic granuloma, granuloma annulare, atypical facial necrobiosis lipoidica, granuloma multiforme, secondary syphilis, tinea corporis, and erythema annulare centrifugum most commonly are included in the differential diagnosis with AEGCG; histopathology is the key determinant in discerning between these conditions.¹² Our patient presented with typical annular plaques overlying hyperpigmented telangiectatic patches. With known type 2 diabetes mellitus and the clinical findings, granuloma annulare, erythema annulare centrifugum, and AEGCG remained high on the differential.

No standard of care exists for AEGCG due to its rare nature and tendency to spontaneously resolve. The most common first-line treatment includes topical and intralesional steroids, topical pimecrolimus, and the use of sunscreen and other sun-protective measures. UV radiation, specifically UVA, has been determined to be a causal factor for AEGCG by changing the antigenicity of elastic fibers and producing an immune response in individuals with fair skin.¹³ Further, resistant cases of AEGCG successfully have been treated with cyclosporine, systemic steroids, antimalarials, dapsone, and oral retinoids.^14,15 Some studies reported partial regression or full resolution with topical tretinoin; adalimumab; clobetasol ointment; or a combination of corticosteroids, antihistamines, and hydroxychloroquine.² Only 1 case series using sulfasalazine reported worsening symptoms after treatment initiation.¹⁶ Our patient deferred systemic medications and was treated with 4 weeks of topical triamcinolone followed by 4 weeks of topical tacrolimus with minimal improvement. At the time of diagnosis, our patient also was encouraged to use sun-protective measures. At 6-month follow-up, the lesions remained stable, and the decision was made to continue with photoprotection.

The Diagnosis: Annular Elastolytic Giant Cell Granuloma

Histologic examination of the shave biopsies showed a granulomatous infiltrate of small lymphocytes, histiocytes, and multinucleated giant cells. The giant cells have abundant eosinophilic cytoplasm, with several also containing fragments of basophilic elastic fibers (elastophagocytosis)(Figure). Additionally, the granulomas revealed no signs of necrosis, making an infectious source unlikely, and examination under polarized light was negative for foreign material. These clinical and histologic findings were diagnostic for annular elastolytic giant cell granuloma (AEGCG).

Annular elastolytic giant cell granuloma is a rare chronic inflammatory disorder that classically presents on sun-exposed skin as annular plaques with elevated borders and atrophic centers.^1-4 Histologically, AEGCG is characterized by diffuse granulomatous infiltrates composed of multinucleated giant cells, histiocytes, and lymphocytes in the dermis, along with phagocytosis of elastic fibers by multinucleated giant cells.⁵ The underlying etiology and pathogenesis of AEGCG remains unknown.⁶

Annular elastolytic giant cell granuloma commonly affects females aged 35 to 75 years; however, cases have been reported in the male and pediatric patient populations.^1,2 Documented cases are known to last from 1 month to 10 years.^7,8 Although the mechanisms underlying the development of AEGCG remain to be elucidated, studies have determined that the skin disorder is associated with sarcoidosis, molluscum contagiosum, amyloidosis, diabetes mellitus, and cutaneous T-cell lymphoma.⁹ Diabetes mellitus is the most common comorbidity associated with AEGCG, and it is theorized that diabetes contributes to the increased incidence of AEGCG in this population by inducing damage to elastic fibers in the skin.¹⁰ One study that examined 50 cases of AEGCG found that 38 patients had serum glucose levels evaluated, with 8 cases being subsequently diagnosed with diabetes mellitus and 6 cases with apparent impaired glucose tolerance, indicating that 37% of the sample population with AEGCG who were evaluated for metabolic disease were found to have definitive or latent type 2 diabetes mellitus.¹¹ Although AEGCG is a rare disorder, a substantial number of patients diagnosed with AEGCG also have diabetes mellitus, making it important to consider screening all patients with AEGCG for diabetes given the ease and widely available resources to check glucose levels.

Actinic granuloma, granuloma annulare, atypical facial necrobiosis lipoidica, granuloma multiforme, secondary syphilis, tinea corporis, and erythema annulare centrifugum most commonly are included in the differential diagnosis with AEGCG; histopathology is the key determinant in discerning between these conditions.¹² Our patient presented with typical annular plaques overlying hyperpigmented telangiectatic patches. With known type 2 diabetes mellitus and the clinical findings, granuloma annulare, erythema annulare centrifugum, and AEGCG remained high on the differential.

No standard of care exists for AEGCG due to its rare nature and tendency to spontaneously resolve. The most common first-line treatment includes topical and intralesional steroids, topical pimecrolimus, and the use of sunscreen and other sun-protective measures. UV radiation, specifically UVA, has been determined to be a causal factor for AEGCG by changing the antigenicity of elastic fibers and producing an immune response in individuals with fair skin.¹³ Further, resistant cases of AEGCG successfully have been treated with cyclosporine, systemic steroids, antimalarials, dapsone, and oral retinoids.^14,15 Some studies reported partial regression or full resolution with topical tretinoin; adalimumab; clobetasol ointment; or a combination of corticosteroids, antihistamines, and hydroxychloroquine.² Only 1 case series using sulfasalazine reported worsening symptoms after treatment initiation.¹⁶ Our patient deferred systemic medications and was treated with 4 weeks of topical triamcinolone followed by 4 weeks of topical tacrolimus with minimal improvement. At the time of diagnosis, our patient also was encouraged to use sun-protective measures. At 6-month follow-up, the lesions remained stable, and the decision was made to continue with photoprotection.

The Diagnosis: Annular Elastolytic Giant Cell Granuloma

Histologic examination of the shave biopsies showed a granulomatous infiltrate of small lymphocytes, histiocytes, and multinucleated giant cells. The giant cells have abundant eosinophilic cytoplasm, with several also containing fragments of basophilic elastic fibers (elastophagocytosis)(Figure). Additionally, the granulomas revealed no signs of necrosis, making an infectious source unlikely, and examination under polarized light was negative for foreign material. These clinical and histologic findings were diagnostic for annular elastolytic giant cell granuloma (AEGCG).

Annular elastolytic giant cell granuloma is a rare chronic inflammatory disorder that classically presents on sun-exposed skin as annular plaques with elevated borders and atrophic centers.^1-4 Histologically, AEGCG is characterized by diffuse granulomatous infiltrates composed of multinucleated giant cells, histiocytes, and lymphocytes in the dermis, along with phagocytosis of elastic fibers by multinucleated giant cells.⁵ The underlying etiology and pathogenesis of AEGCG remains unknown.⁶

Annular elastolytic giant cell granuloma commonly affects females aged 35 to 75 years; however, cases have been reported in the male and pediatric patient populations.^1,2 Documented cases are known to last from 1 month to 10 years.^7,8 Although the mechanisms underlying the development of AEGCG remain to be elucidated, studies have determined that the skin disorder is associated with sarcoidosis, molluscum contagiosum, amyloidosis, diabetes mellitus, and cutaneous T-cell lymphoma.⁹ Diabetes mellitus is the most common comorbidity associated with AEGCG, and it is theorized that diabetes contributes to the increased incidence of AEGCG in this population by inducing damage to elastic fibers in the skin.¹⁰ One study that examined 50 cases of AEGCG found that 38 patients had serum glucose levels evaluated, with 8 cases being subsequently diagnosed with diabetes mellitus and 6 cases with apparent impaired glucose tolerance, indicating that 37% of the sample population with AEGCG who were evaluated for metabolic disease were found to have definitive or latent type 2 diabetes mellitus.¹¹ Although AEGCG is a rare disorder, a substantial number of patients diagnosed with AEGCG also have diabetes mellitus, making it important to consider screening all patients with AEGCG for diabetes given the ease and widely available resources to check glucose levels.

Actinic granuloma, granuloma annulare, atypical facial necrobiosis lipoidica, granuloma multiforme, secondary syphilis, tinea corporis, and erythema annulare centrifugum most commonly are included in the differential diagnosis with AEGCG; histopathology is the key determinant in discerning between these conditions.¹² Our patient presented with typical annular plaques overlying hyperpigmented telangiectatic patches. With known type 2 diabetes mellitus and the clinical findings, granuloma annulare, erythema annulare centrifugum, and AEGCG remained high on the differential.

No standard of care exists for AEGCG due to its rare nature and tendency to spontaneously resolve. The most common first-line treatment includes topical and intralesional steroids, topical pimecrolimus, and the use of sunscreen and other sun-protective measures. UV radiation, specifically UVA, has been determined to be a causal factor for AEGCG by changing the antigenicity of elastic fibers and producing an immune response in individuals with fair skin.¹³ Further, resistant cases of AEGCG successfully have been treated with cyclosporine, systemic steroids, antimalarials, dapsone, and oral retinoids.^14,15 Some studies reported partial regression or full resolution with topical tretinoin; adalimumab; clobetasol ointment; or a combination of corticosteroids, antihistamines, and hydroxychloroquine.² Only 1 case series using sulfasalazine reported worsening symptoms after treatment initiation.¹⁶ Our patient deferred systemic medications and was treated with 4 weeks of topical triamcinolone followed by 4 weeks of topical tacrolimus with minimal improvement. At the time of diagnosis, our patient also was encouraged to use sun-protective measures. At 6-month follow-up, the lesions remained stable, and the decision was made to continue with photoprotection.

SAN DIEGO – As with many markers for the evaluation of challenging melanocytic lesions, preferentially expressed antigen in melanoma (PRAME) has its benefits and drawbacks, according to Cora Humberson, MD.

“I’m a fan, but there are issues with it,” Dr. Humberson, dermatopathology coordinator in the department of pathology at Scripps MD Anderson Cancer Center, San Diego, said at the annual Cutaneous Malignancy Update. “It’s all in how you use it.”

PRAME is part of the cancer/testis (CT) antigens, of which more than 40 have now been identified. They are encoded by genes that are normally expressed only in the human germ line, but are also expressed in various tumor types, including melanoma and carcinomas of the bladder, lung, and liver. “The biological function of these antigens is not fully understood, but they may act as a repressor of retinoic acid, potentially inhibiting differentiation, inhibiting proliferation arrest – things that we associate with malignancy,” she said at the meeting, which was hosted by Scripps MD Anderson Cancer Center. “These immunogenic proteins are being pursued as targets for therapeutic cancer vaccines,” she noted.

CT antigens are also being evaluated for their role in oncogenesis, she added. Recapitulation of portions of the germline gene-expression might contribute characteristic features to the neoplastic phenotype, including immortality, invasiveness, immune evasion, and metastatic capacity.

According to Dr. Humberson, PRAME can be used to differentiate comingled nevus and melanoma, to distinguish between nevoid melanoma and nevus, and for melanoma margin assessment in sun-damaged skin. One potential pitfall is that sun-damaged melanocytes may express PRAME. “The older the person and the more sun damage [they have], the more likely you are to see this, but the melanocytes won’t be grouped, they’ll be scattered,” she said.

Another pitfall is that less than 15% of nevi may express PRAME. “PRAME can be expressed in scars, so if you’re looking at a spindle cell lesion, be aware that you might be looking at a scar if you’re seeing PRAME expression,” she added. She also noted that PRAME immunohistochemistry (IHC) expression is not a prognostic biomarker in thin melanomas.

If fewer than 25% of cells in a melanocytic lesion express PRAME, most published assessments of PRAME IHC favor nevi as the diagnosis. “If more than 75% are expressing it, it favors melanoma,” Dr. Humberson said. “There’s a big category in between. It’s not that 30% is more likely benign or that 60% is more likely malignant; you can’t really depend upon [PRAME] if you’re in this range.”

A diagnostic accuracy study found that when more than 75% of cells express PRAME, the marker has a sensitivity of 0.63 and a specificity of 0.97.

Selected PRAME-related published references she recommended include: J Cutan Pathol. 2021;48(9):1115-23; Diagnostics. 2022 Sep 9; 12(9):2197, and J Cutan Pathol. 2022;49(9):829-32.

Dr. Humberson reported having no relevant disclosures.

SAN DIEGO – As with many markers for the evaluation of challenging melanocytic lesions, preferentially expressed antigen in melanoma (PRAME) has its benefits and drawbacks, according to Cora Humberson, MD.

“I’m a fan, but there are issues with it,” Dr. Humberson, dermatopathology coordinator in the department of pathology at Scripps MD Anderson Cancer Center, San Diego, said at the annual Cutaneous Malignancy Update. “It’s all in how you use it.”

PRAME is part of the cancer/testis (CT) antigens, of which more than 40 have now been identified. They are encoded by genes that are normally expressed only in the human germ line, but are also expressed in various tumor types, including melanoma and carcinomas of the bladder, lung, and liver. “The biological function of these antigens is not fully understood, but they may act as a repressor of retinoic acid, potentially inhibiting differentiation, inhibiting proliferation arrest – things that we associate with malignancy,” she said at the meeting, which was hosted by Scripps MD Anderson Cancer Center. “These immunogenic proteins are being pursued as targets for therapeutic cancer vaccines,” she noted.

CT antigens are also being evaluated for their role in oncogenesis, she added. Recapitulation of portions of the germline gene-expression might contribute characteristic features to the neoplastic phenotype, including immortality, invasiveness, immune evasion, and metastatic capacity.

According to Dr. Humberson, PRAME can be used to differentiate comingled nevus and melanoma, to distinguish between nevoid melanoma and nevus, and for melanoma margin assessment in sun-damaged skin. One potential pitfall is that sun-damaged melanocytes may express PRAME. “The older the person and the more sun damage [they have], the more likely you are to see this, but the melanocytes won’t be grouped, they’ll be scattered,” she said.

Another pitfall is that less than 15% of nevi may express PRAME. “PRAME can be expressed in scars, so if you’re looking at a spindle cell lesion, be aware that you might be looking at a scar if you’re seeing PRAME expression,” she added. She also noted that PRAME immunohistochemistry (IHC) expression is not a prognostic biomarker in thin melanomas.

If fewer than 25% of cells in a melanocytic lesion express PRAME, most published assessments of PRAME IHC favor nevi as the diagnosis. “If more than 75% are expressing it, it favors melanoma,” Dr. Humberson said. “There’s a big category in between. It’s not that 30% is more likely benign or that 60% is more likely malignant; you can’t really depend upon [PRAME] if you’re in this range.”

A diagnostic accuracy study found that when more than 75% of cells express PRAME, the marker has a sensitivity of 0.63 and a specificity of 0.97.

Selected PRAME-related published references she recommended include: J Cutan Pathol. 2021;48(9):1115-23; Diagnostics. 2022 Sep 9; 12(9):2197, and J Cutan Pathol. 2022;49(9):829-32.

Dr. Humberson reported having no relevant disclosures.

SAN DIEGO – As with many markers for the evaluation of challenging melanocytic lesions, preferentially expressed antigen in melanoma (PRAME) has its benefits and drawbacks, according to Cora Humberson, MD.

“I’m a fan, but there are issues with it,” Dr. Humberson, dermatopathology coordinator in the department of pathology at Scripps MD Anderson Cancer Center, San Diego, said at the annual Cutaneous Malignancy Update. “It’s all in how you use it.”

PRAME is part of the cancer/testis (CT) antigens, of which more than 40 have now been identified. They are encoded by genes that are normally expressed only in the human germ line, but are also expressed in various tumor types, including melanoma and carcinomas of the bladder, lung, and liver. “The biological function of these antigens is not fully understood, but they may act as a repressor of retinoic acid, potentially inhibiting differentiation, inhibiting proliferation arrest – things that we associate with malignancy,” she said at the meeting, which was hosted by Scripps MD Anderson Cancer Center. “These immunogenic proteins are being pursued as targets for therapeutic cancer vaccines,” she noted.

CT antigens are also being evaluated for their role in oncogenesis, she added. Recapitulation of portions of the germline gene-expression might contribute characteristic features to the neoplastic phenotype, including immortality, invasiveness, immune evasion, and metastatic capacity.

According to Dr. Humberson, PRAME can be used to differentiate comingled nevus and melanoma, to distinguish between nevoid melanoma and nevus, and for melanoma margin assessment in sun-damaged skin. One potential pitfall is that sun-damaged melanocytes may express PRAME. “The older the person and the more sun damage [they have], the more likely you are to see this, but the melanocytes won’t be grouped, they’ll be scattered,” she said.

Another pitfall is that less than 15% of nevi may express PRAME. “PRAME can be expressed in scars, so if you’re looking at a spindle cell lesion, be aware that you might be looking at a scar if you’re seeing PRAME expression,” she added. She also noted that PRAME immunohistochemistry (IHC) expression is not a prognostic biomarker in thin melanomas.

If fewer than 25% of cells in a melanocytic lesion express PRAME, most published assessments of PRAME IHC favor nevi as the diagnosis. “If more than 75% are expressing it, it favors melanoma,” Dr. Humberson said. “There’s a big category in between. It’s not that 30% is more likely benign or that 60% is more likely malignant; you can’t really depend upon [PRAME] if you’re in this range.”

A diagnostic accuracy study found that when more than 75% of cells express PRAME, the marker has a sensitivity of 0.63 and a specificity of 0.97.

Selected PRAME-related published references she recommended include: J Cutan Pathol. 2021;48(9):1115-23; Diagnostics. 2022 Sep 9; 12(9):2197, and J Cutan Pathol. 2022;49(9):829-32.

Dr. Humberson reported having no relevant disclosures.

The Diagnosis: Marjolin Ulcer

A skin biopsy during his prior hospital admission demonstrated an ulcer with granulation tissue and mixed inflammation, and the patient was discharged with close outpatient follow-up. Two repeat skin biopsies from the peripheral margin at the time of the outpatient follow-up confirmed an invasive, well-differentiated squamous cell carcinoma (Figure), consistent with a Marjolin ulcer. Radiography demonstrated multiple left iliac chain and inguinal lymphadenopathies with extensive subcutaneous disease overlying the left medial tibia. After tumor board discussion, surgery was not recommended due to the size and likely penetration into the muscle. The patient began treatment with cemiplimab-rwlc, a PD-1 inhibitor. Within 4 cycles of treatment, he had improved pain and ambulation, and a 3-month follow-up positron emission tomography scan revealed decreased lymph node and cutaneous metabolic activity as well as clinical improvement.

Marjolin ulcers are rare and aggressive squamous cell carcinomas that arise from chronic wounds such as burn scars or pressure ulcers.¹ Although an underlying well-differentiated squamous cell carcinoma is the most common etiology, patients also may present with underlying basal cell carcinomas, melanomas, or angiosarcomas.² The exact pathogenesis underlying the malignant degeneration is unclear but appears to be driven by chronic inflammation. Patients classically present with a nonhealing ulcer associated with raised, friable, or crusty borders, as well as surrounding scar tissue. There is a median latency of 30 years after the trauma, though acute transformation within 12 months of an injury is possible.³ The diagnosis is confirmed with a peripheral wound biopsy. Surgical excision with wide margins remains the most common and effective intervention, especially for localized disease.¹ The addition of lymph node dissection remains controversial, but treatment decisions can be guided by radiographic staging.⁴

The prognosis of Marjolin ulcers remains poor, with a predicted 5-year survival rate ranging from 43% to 58%.¹ Dermatologists and trainees should be aware of Marjolin ulcers, especially as a mimicker of other chronic ulcerating conditions. Among the differential diagnosis, ulcerative lichen planus is a condition that commonly affects the oral and genital regions; however, patients with erosive lichen planus may develop an increased risk for the subsequent development of squamous cell carcinoma in the region.⁵ Furthermore, arterial ulcers typically develop on the distal lower extremities with other signs of chronic ischemia, including absent peripheral pulses, atrophic skin, hair loss, and ankle-brachial indices less than 0.5. Conversely, a venous ulcer classically affects the medial malleolus and will have evidence of venous insufficiency, including stasis dermatitis and peripheral edema.⁶

The Diagnosis: Marjolin Ulcer

A skin biopsy during his prior hospital admission demonstrated an ulcer with granulation tissue and mixed inflammation, and the patient was discharged with close outpatient follow-up. Two repeat skin biopsies from the peripheral margin at the time of the outpatient follow-up confirmed an invasive, well-differentiated squamous cell carcinoma (Figure), consistent with a Marjolin ulcer. Radiography demonstrated multiple left iliac chain and inguinal lymphadenopathies with extensive subcutaneous disease overlying the left medial tibia. After tumor board discussion, surgery was not recommended due to the size and likely penetration into the muscle. The patient began treatment with cemiplimab-rwlc, a PD-1 inhibitor. Within 4 cycles of treatment, he had improved pain and ambulation, and a 3-month follow-up positron emission tomography scan revealed decreased lymph node and cutaneous metabolic activity as well as clinical improvement.

Marjolin ulcers are rare and aggressive squamous cell carcinomas that arise from chronic wounds such as burn scars or pressure ulcers.¹ Although an underlying well-differentiated squamous cell carcinoma is the most common etiology, patients also may present with underlying basal cell carcinomas, melanomas, or angiosarcomas.² The exact pathogenesis underlying the malignant degeneration is unclear but appears to be driven by chronic inflammation. Patients classically present with a nonhealing ulcer associated with raised, friable, or crusty borders, as well as surrounding scar tissue. There is a median latency of 30 years after the trauma, though acute transformation within 12 months of an injury is possible.³ The diagnosis is confirmed with a peripheral wound biopsy. Surgical excision with wide margins remains the most common and effective intervention, especially for localized disease.¹ The addition of lymph node dissection remains controversial, but treatment decisions can be guided by radiographic staging.⁴

The prognosis of Marjolin ulcers remains poor, with a predicted 5-year survival rate ranging from 43% to 58%.¹ Dermatologists and trainees should be aware of Marjolin ulcers, especially as a mimicker of other chronic ulcerating conditions. Among the differential diagnosis, ulcerative lichen planus is a condition that commonly affects the oral and genital regions; however, patients with erosive lichen planus may develop an increased risk for the subsequent development of squamous cell carcinoma in the region.⁵ Furthermore, arterial ulcers typically develop on the distal lower extremities with other signs of chronic ischemia, including absent peripheral pulses, atrophic skin, hair loss, and ankle-brachial indices less than 0.5. Conversely, a venous ulcer classically affects the medial malleolus and will have evidence of venous insufficiency, including stasis dermatitis and peripheral edema.⁶

The Diagnosis: Marjolin Ulcer

A skin biopsy during his prior hospital admission demonstrated an ulcer with granulation tissue and mixed inflammation, and the patient was discharged with close outpatient follow-up. Two repeat skin biopsies from the peripheral margin at the time of the outpatient follow-up confirmed an invasive, well-differentiated squamous cell carcinoma (Figure), consistent with a Marjolin ulcer. Radiography demonstrated multiple left iliac chain and inguinal lymphadenopathies with extensive subcutaneous disease overlying the left medial tibia. After tumor board discussion, surgery was not recommended due to the size and likely penetration into the muscle. The patient began treatment with cemiplimab-rwlc, a PD-1 inhibitor. Within 4 cycles of treatment, he had improved pain and ambulation, and a 3-month follow-up positron emission tomography scan revealed decreased lymph node and cutaneous metabolic activity as well as clinical improvement.

Marjolin ulcers are rare and aggressive squamous cell carcinomas that arise from chronic wounds such as burn scars or pressure ulcers.¹ Although an underlying well-differentiated squamous cell carcinoma is the most common etiology, patients also may present with underlying basal cell carcinomas, melanomas, or angiosarcomas.² The exact pathogenesis underlying the malignant degeneration is unclear but appears to be driven by chronic inflammation. Patients classically present with a nonhealing ulcer associated with raised, friable, or crusty borders, as well as surrounding scar tissue. There is a median latency of 30 years after the trauma, though acute transformation within 12 months of an injury is possible.³ The diagnosis is confirmed with a peripheral wound biopsy. Surgical excision with wide margins remains the most common and effective intervention, especially for localized disease.¹ The addition of lymph node dissection remains controversial, but treatment decisions can be guided by radiographic staging.⁴

The prognosis of Marjolin ulcers remains poor, with a predicted 5-year survival rate ranging from 43% to 58%.¹ Dermatologists and trainees should be aware of Marjolin ulcers, especially as a mimicker of other chronic ulcerating conditions. Among the differential diagnosis, ulcerative lichen planus is a condition that commonly affects the oral and genital regions; however, patients with erosive lichen planus may develop an increased risk for the subsequent development of squamous cell carcinoma in the region.⁵ Furthermore, arterial ulcers typically develop on the distal lower extremities with other signs of chronic ischemia, including absent peripheral pulses, atrophic skin, hair loss, and ankle-brachial indices less than 0.5. Conversely, a venous ulcer classically affects the medial malleolus and will have evidence of venous insufficiency, including stasis dermatitis and peripheral edema.⁶

The Diagnosis: Cutaneous Crohn Disease

Kinyoun and Grocott-Gomori methenamine-silver staining of the labial biopsy were negative for mycobacteria and fungi, respectively. A complete blood cell count, erythrocyte sedimentation rate, C-reactive protein, celiac disease serologies, stool occult blood, and stool calprotectin laboratory test results were within reference range. Magnetic resonance imaging of the pelvis demonstrated an anal fissure extending from the anal verge at the 6 o’clock position, abnormal T2 bright signal in the skin of the buttocks and perineum extending to the labia, and mild mucosal enhancement of the rectal and anal mucosa. Esophagogastroduodenoscopy and magnetic resonance elastography were unremarkable. Colonoscopy demonstrated scattered superficial erythematous patches and erosions in the rectum. Histologically, there was mild to moderately active colitis in the rectum with no evidence of chronicity. Given our patient’s labial edema and exophytic papulonodule (Figure 1) in the setting of nonspecific gastrointestinal symptoms and granulomatous dermatitis seen on pathology (Figure 2), she was diagnosed with cutaneous Crohn disease (CD).

In our patient, labial biopsy was necessary to definitively diagnose CD. Prior to biopsy of the lesion, our patient was diagnosed with irritable bowel syndrome with constipation leading to an anal fissure and skin tag due to lack of laboratory, imaging, and colonoscopy findings commonly associated with CD. Her biopsy results and gastrointestinal symptoms made these diagnoses, as well as condyloma or a large sentinel skin tag, less likely.

Extraintestinal findings of CD, especially cutaneous manifestations, are relatively frequent and may be present in as many as 44% of patients.^1,2 Cutaneous CD often is characterized based on pathogenic mechanisms as either reactive, associated, or CD specific. Reactive cutaneous manifestations include erythema nodosum, pyoderma gangrenosum, and oral aphthae. Associated cutaneous manifestations include vitiligo, palmar erythema, and palmoplantar pustulosis.² Crohn disease–specific manifestations, including genital or extragenital metastatic CD (MCD), fistulas, and oral involvement, are granulomatous in nature, similar to intestinal CD. Genital manifestations of MCD include edema, erythema, fissures, and/or ulceration of the vulva, penis, or scrotum. Labial swelling is the most common presenting symptom of MCD in females in both pediatric and adult age groups.² Lymphedema, skin tags, and condylomalike growths also can be seen but are relatively less common.²

Given the labial edema, exophytic papulonodule, and granulomatous dermatitis seen on histopathology, our patient likely fit into the MCD category.² In adults, most instances of MCD arise in the setting of well-established intestinal CD disease,3 whereas in children 86% of cases occur in patients without concurrent intestinal CD.²

Given the nonspecific and variable presentation of MCD, the differential diagnosis is broad. The differential diagnosis could include infectious etiologies such as condyloma acuminatum (human papillomavirus); syphilitic chancre; or mycobacterial, bacterial, fungal, or parasitic vulvovaginitis. Sexual abuse, sarcoidosis, Behçet disease, or hidradenitis suppurativa, among other diagnoses, also should be considered. Diagnostic workup should include biopsy of the lesion with special stains, polarizing microscopy, and tissue cultures.⁴ A thorough evaluation for gastrointestinal CD should be completed after diagnosis.³

The clinical course of vulvar CD can be unpredictable, with some cases healing spontaneously but most persisting despite treatment and sometimes prompting surgical removal.^2,4 Early recognition is crucial, as long-standing MCD lesions can be therapy resistant.⁵ Due to the rarity of the condition and lack of data, there is a lack of treatment consensus for MCD. In 2014, the American Academy of Dermatology published treatment guidelines recommending superpotent topical steroids or topical tacrolimus as first-line therapy. Next-line therapy includes oral metronidazole, followed by prednisolone if still symptomatic.³ Treatment-resistant disease can warrant treatment with immunomodulators or tumor necrosis factor α inhibitors. Our patient was started on adalimumab; after just 2 months of therapy, the labial swelling decreased and the exophytic nodule was less firm and smaller.

Metastatic CD is a rare manifestation of cutaneous CD and can be present in the absence of gastrointestinal disease.³ This case demonstrates the importance of recognizing the cutaneous signs of CD and the necessity of lesional biopsy for the diagnosis of MCD, as our patient presented with nonspecific gastrointestinal symptoms and a diagnostic workup, including endoscopies, that proved inconclusive for the diagnosis of CD.

The Diagnosis: Cutaneous Crohn Disease

Kinyoun and Grocott-Gomori methenamine-silver staining of the labial biopsy were negative for mycobacteria and fungi, respectively. A complete blood cell count, erythrocyte sedimentation rate, C-reactive protein, celiac disease serologies, stool occult blood, and stool calprotectin laboratory test results were within reference range. Magnetic resonance imaging of the pelvis demonstrated an anal fissure extending from the anal verge at the 6 o’clock position, abnormal T2 bright signal in the skin of the buttocks and perineum extending to the labia, and mild mucosal enhancement of the rectal and anal mucosa. Esophagogastroduodenoscopy and magnetic resonance elastography were unremarkable. Colonoscopy demonstrated scattered superficial erythematous patches and erosions in the rectum. Histologically, there was mild to moderately active colitis in the rectum with no evidence of chronicity. Given our patient’s labial edema and exophytic papulonodule (Figure 1) in the setting of nonspecific gastrointestinal symptoms and granulomatous dermatitis seen on pathology (Figure 2), she was diagnosed with cutaneous Crohn disease (CD).

In our patient, labial biopsy was necessary to definitively diagnose CD. Prior to biopsy of the lesion, our patient was diagnosed with irritable bowel syndrome with constipation leading to an anal fissure and skin tag due to lack of laboratory, imaging, and colonoscopy findings commonly associated with CD. Her biopsy results and gastrointestinal symptoms made these diagnoses, as well as condyloma or a large sentinel skin tag, less likely.

Extraintestinal findings of CD, especially cutaneous manifestations, are relatively frequent and may be present in as many as 44% of patients.^1,2 Cutaneous CD often is characterized based on pathogenic mechanisms as either reactive, associated, or CD specific. Reactive cutaneous manifestations include erythema nodosum, pyoderma gangrenosum, and oral aphthae. Associated cutaneous manifestations include vitiligo, palmar erythema, and palmoplantar pustulosis.² Crohn disease–specific manifestations, including genital or extragenital metastatic CD (MCD), fistulas, and oral involvement, are granulomatous in nature, similar to intestinal CD. Genital manifestations of MCD include edema, erythema, fissures, and/or ulceration of the vulva, penis, or scrotum. Labial swelling is the most common presenting symptom of MCD in females in both pediatric and adult age groups.² Lymphedema, skin tags, and condylomalike growths also can be seen but are relatively less common.²

Given the labial edema, exophytic papulonodule, and granulomatous dermatitis seen on histopathology, our patient likely fit into the MCD category.² In adults, most instances of MCD arise in the setting of well-established intestinal CD disease,3 whereas in children 86% of cases occur in patients without concurrent intestinal CD.²

Given the nonspecific and variable presentation of MCD, the differential diagnosis is broad. The differential diagnosis could include infectious etiologies such as condyloma acuminatum (human papillomavirus); syphilitic chancre; or mycobacterial, bacterial, fungal, or parasitic vulvovaginitis. Sexual abuse, sarcoidosis, Behçet disease, or hidradenitis suppurativa, among other diagnoses, also should be considered. Diagnostic workup should include biopsy of the lesion with special stains, polarizing microscopy, and tissue cultures.⁴ A thorough evaluation for gastrointestinal CD should be completed after diagnosis.³

The clinical course of vulvar CD can be unpredictable, with some cases healing spontaneously but most persisting despite treatment and sometimes prompting surgical removal.^2,4 Early recognition is crucial, as long-standing MCD lesions can be therapy resistant.⁵ Due to the rarity of the condition and lack of data, there is a lack of treatment consensus for MCD. In 2014, the American Academy of Dermatology published treatment guidelines recommending superpotent topical steroids or topical tacrolimus as first-line therapy. Next-line therapy includes oral metronidazole, followed by prednisolone if still symptomatic.³ Treatment-resistant disease can warrant treatment with immunomodulators or tumor necrosis factor α inhibitors. Our patient was started on adalimumab; after just 2 months of therapy, the labial swelling decreased and the exophytic nodule was less firm and smaller.

Metastatic CD is a rare manifestation of cutaneous CD and can be present in the absence of gastrointestinal disease.³ This case demonstrates the importance of recognizing the cutaneous signs of CD and the necessity of lesional biopsy for the diagnosis of MCD, as our patient presented with nonspecific gastrointestinal symptoms and a diagnostic workup, including endoscopies, that proved inconclusive for the diagnosis of CD.

The Diagnosis: Cutaneous Crohn Disease

Kinyoun and Grocott-Gomori methenamine-silver staining of the labial biopsy were negative for mycobacteria and fungi, respectively. A complete blood cell count, erythrocyte sedimentation rate, C-reactive protein, celiac disease serologies, stool occult blood, and stool calprotectin laboratory test results were within reference range. Magnetic resonance imaging of the pelvis demonstrated an anal fissure extending from the anal verge at the 6 o’clock position, abnormal T2 bright signal in the skin of the buttocks and perineum extending to the labia, and mild mucosal enhancement of the rectal and anal mucosa. Esophagogastroduodenoscopy and magnetic resonance elastography were unremarkable. Colonoscopy demonstrated scattered superficial erythematous patches and erosions in the rectum. Histologically, there was mild to moderately active colitis in the rectum with no evidence of chronicity. Given our patient’s labial edema and exophytic papulonodule (Figure 1) in the setting of nonspecific gastrointestinal symptoms and granulomatous dermatitis seen on pathology (Figure 2), she was diagnosed with cutaneous Crohn disease (CD).

In our patient, labial biopsy was necessary to definitively diagnose CD. Prior to biopsy of the lesion, our patient was diagnosed with irritable bowel syndrome with constipation leading to an anal fissure and skin tag due to lack of laboratory, imaging, and colonoscopy findings commonly associated with CD. Her biopsy results and gastrointestinal symptoms made these diagnoses, as well as condyloma or a large sentinel skin tag, less likely.

Extraintestinal findings of CD, especially cutaneous manifestations, are relatively frequent and may be present in as many as 44% of patients.^1,2 Cutaneous CD often is characterized based on pathogenic mechanisms as either reactive, associated, or CD specific. Reactive cutaneous manifestations include erythema nodosum, pyoderma gangrenosum, and oral aphthae. Associated cutaneous manifestations include vitiligo, palmar erythema, and palmoplantar pustulosis.² Crohn disease–specific manifestations, including genital or extragenital metastatic CD (MCD), fistulas, and oral involvement, are granulomatous in nature, similar to intestinal CD. Genital manifestations of MCD include edema, erythema, fissures, and/or ulceration of the vulva, penis, or scrotum. Labial swelling is the most common presenting symptom of MCD in females in both pediatric and adult age groups.² Lymphedema, skin tags, and condylomalike growths also can be seen but are relatively less common.²

Given the labial edema, exophytic papulonodule, and granulomatous dermatitis seen on histopathology, our patient likely fit into the MCD category.² In adults, most instances of MCD arise in the setting of well-established intestinal CD disease,3 whereas in children 86% of cases occur in patients without concurrent intestinal CD.²

Given the nonspecific and variable presentation of MCD, the differential diagnosis is broad. The differential diagnosis could include infectious etiologies such as condyloma acuminatum (human papillomavirus); syphilitic chancre; or mycobacterial, bacterial, fungal, or parasitic vulvovaginitis. Sexual abuse, sarcoidosis, Behçet disease, or hidradenitis suppurativa, among other diagnoses, also should be considered. Diagnostic workup should include biopsy of the lesion with special stains, polarizing microscopy, and tissue cultures.⁴ A thorough evaluation for gastrointestinal CD should be completed after diagnosis.³

The clinical course of vulvar CD can be unpredictable, with some cases healing spontaneously but most persisting despite treatment and sometimes prompting surgical removal.^2,4 Early recognition is crucial, as long-standing MCD lesions can be therapy resistant.⁵ Due to the rarity of the condition and lack of data, there is a lack of treatment consensus for MCD. In 2014, the American Academy of Dermatology published treatment guidelines recommending superpotent topical steroids or topical tacrolimus as first-line therapy. Next-line therapy includes oral metronidazole, followed by prednisolone if still symptomatic.³ Treatment-resistant disease can warrant treatment with immunomodulators or tumor necrosis factor α inhibitors. Our patient was started on adalimumab; after just 2 months of therapy, the labial swelling decreased and the exophytic nodule was less firm and smaller.

Metastatic CD is a rare manifestation of cutaneous CD and can be present in the absence of gastrointestinal disease.³ This case demonstrates the importance of recognizing the cutaneous signs of CD and the necessity of lesional biopsy for the diagnosis of MCD, as our patient presented with nonspecific gastrointestinal symptoms and a diagnostic workup, including endoscopies, that proved inconclusive for the diagnosis of CD.

The Diagnosis: Pseudoangiomatous Squamous Cell Carcinoma

Pseudoangiomatous squamous cell carcinoma (PSCC), a variant of acantholytic squamous cell carcinoma (SCC), is a rare epithelial neoplasm that can mimic angiosarcoma.¹ Clinically, PSCC presents as a white-gray ulcer or nodular pink tumor on sun-exposed areas, typically on the head and neck. Due to its increased potential for metastasis, this variant of SCC is considered particularly aggressive. Histologically, PSCC shows nests of acantholytic atypical keratinocytes arranged in anastomosing arrays that form pseudovascular or pseudoglandular structures.² Acantholytic spaces frequently are filled with erythrocytes. Immunohistochemically, PSCC tumor cells express classic squamous markers such as cytokeratin (CK) 5 and p63 but not vascular markers such as CD31, CD34, and von Willebrand factor.³ In our patient, histopathology of the lesion revealed invasive nests, lobules, and interconnected columns of well-differentiated squamous tumor cells that emanated from the base of the epidermis. The tumor exhibited acantholysis forming ectatic and slitlike spaces, some of which contained erythrocytes. The neoplastic cells, including those lining pseudovascular spaces, positively stained for CK5 (Figure 1A) and nuclear p63 but lacked reactivity to CD31 (Figure 1B) and CD34, corroborating squamous and not vascular differentiation. Current treatment guidelines include Mohs micrographic surgery, excisional surgery, or radiation.⁴ Our patient’s lesion was completely removed by Mohs micrographic surgery. Three months later, there was no evidence of recurrence.

Angiosarcoma is an aggressive neoplasm associated with a poor prognosis and 5-year survival rate of 30% to 40%. The etiology of angiosarcoma still is unclear, but identified risk factors include prior radiation therapy, lymphedema (Stewart-Treves syndrome), and genetic predisposition.⁵ In the skin, angiosarcoma often occurs in the head and neck region, accounting for 60% of cutaneous cases.^5,6 Early in the disease, most patients present with a bruiselike lesion on the scalp or forehead, often delaying the diagnosis.⁶ As the cancer progresses, tissue infiltration, edema, and hemorrhage contribute to the formation of violaceous nodules, which eventually prompt for biopsy. Angiosarcoma spans a broad histologic spectrum depending on the cytology of malignant cells (eg, spindle, small round, epithelioid) and their capacity for vasoformation. Welldifferentiated angiosarcoma shows retiform slitlike spaces in between collagen bundles that are lined by hyperchromatic hobnailing endothelial cells (Figure 2).⁷ Epithelioid angiosarcoma can be mistaken for SCC.⁸ Immunohistochemically, angiosarcoma stains positively for CD31, CD34, ETS-related gene 1, D2-40, and factor VIII.9 In our patient, the neoplasm was negative for vascular markers CD31 and CD34.

Bacillary angiomatosis (BA), caused by Bartonella henselae, is a rare disease that first was identified in HIV patients with diminished CD4+ T-cell counts. In the skin, BA often manifests as centrally ulcerated, single or clustered, reddish-purple nodules.¹⁰ Histologically, it is characterized by highly vascularized, histiocyterich infiltrates with admixed neutrophils and plasma cells (Figure 3). Capillaries often proliferate in a lobular fashion.¹¹ Atypical cytology with areas of necrosis may mimic angiosarcoma.¹² The pathognomonic feature of BA is the presence of enlarged histiocytes with pink-purplish cytoplasm corresponding to intracytoplasmic aggregates of bacteria, which can be revealed by Warthin-Starry or Grocott-Gomori methenamine-silver staining. Immunohistochemically, proliferative benign capillaries are highlighted by CD34 and CD31, and histiocytes are decorated by CD68.¹² This diagnosis was excluded based on the patient’s history, clinical presentation, and positive staining for CK5 and p63.

Squamoid eccrine ductal carcinoma is an exceedingly rare subtype of eccrine carcinoma that mimics SCC both clinically and histologically.¹³ It most often occurs on the head and neck of elderly patients. This neoplasm can look similar to SCC and its variants, including PSCC. Histologically, squamoid eccrine ductal carcinoma exhibits a biphasic growth pattern.¹⁴ Well-differentiated squamous dysplasia transitions to carcinoma with eccrine duct formation as the tumor percolates deep into the dermis (Figure 4). As a result, superficial skin biopsies often lead to an incorrect diagnosis.¹⁵ Unlike SCC, the risk for locoregional and widespread metastasis is elevated. Identifying ducts in the deep aspect of the tumor is critical, thus immunohistochemical staining for carcinoembryonic antigen and epithelial membrane antigen is paramount for the diagnosis.¹⁵ Pseudoangiomatous SCC will stain negative for carcinoembryonic antigen, as was the case in our patient.

Pseudoepitheliomatous hyperplasia is a benign histologic reaction that can result from trauma, chronic inflammation (ie, pyoderma gangrenosum), tattoo placement, underlying neoplasia or fungal infection, or a spider bite reaction.^14,15 It most commonly is seen as a well-demarcated nodule or plaque associated with scaling or crusting. Papules vary in size from less than 1 cm to several centimeters. Histologically, it is defined by an acanthotic proliferation of the adnexal epithelium and epidermis (Figure 5).^16,17 Irregular strands, cords, and nests of squamoid cells can extend into the dermis.¹⁸ It can closely mimic SCC, but there are a few key differences. Pseudoepitheliomatous hyperplasia will not display atypical mitotic figures or atypical nuclei and will never invade lymphatics or vascular systems.¹⁹ Pseudoepitheliomatous hyperplasia shows identical histology to well-differentiated SCC, and thus clinicopathologic correlation and mindful histologic evaluation are crucial. The presence of an increased influx of neutrophils and histiocytes should prompt for microbial stains or deeper sectioning. A superficial biopsy should be followed by a deep biopsy. In our patient, microorganismal stains were negative.

The Diagnosis: Pseudoangiomatous Squamous Cell Carcinoma

Pseudoangiomatous squamous cell carcinoma (PSCC), a variant of acantholytic squamous cell carcinoma (SCC), is a rare epithelial neoplasm that can mimic angiosarcoma.¹ Clinically, PSCC presents as a white-gray ulcer or nodular pink tumor on sun-exposed areas, typically on the head and neck. Due to its increased potential for metastasis, this variant of SCC is considered particularly aggressive. Histologically, PSCC shows nests of acantholytic atypical keratinocytes arranged in anastomosing arrays that form pseudovascular or pseudoglandular structures.² Acantholytic spaces frequently are filled with erythrocytes. Immunohistochemically, PSCC tumor cells express classic squamous markers such as cytokeratin (CK) 5 and p63 but not vascular markers such as CD31, CD34, and von Willebrand factor.³ In our patient, histopathology of the lesion revealed invasive nests, lobules, and interconnected columns of well-differentiated squamous tumor cells that emanated from the base of the epidermis. The tumor exhibited acantholysis forming ectatic and slitlike spaces, some of which contained erythrocytes. The neoplastic cells, including those lining pseudovascular spaces, positively stained for CK5 (Figure 1A) and nuclear p63 but lacked reactivity to CD31 (Figure 1B) and CD34, corroborating squamous and not vascular differentiation. Current treatment guidelines include Mohs micrographic surgery, excisional surgery, or radiation.⁴ Our patient’s lesion was completely removed by Mohs micrographic surgery. Three months later, there was no evidence of recurrence.

Angiosarcoma is an aggressive neoplasm associated with a poor prognosis and 5-year survival rate of 30% to 40%. The etiology of angiosarcoma still is unclear, but identified risk factors include prior radiation therapy, lymphedema (Stewart-Treves syndrome), and genetic predisposition.⁵ In the skin, angiosarcoma often occurs in the head and neck region, accounting for 60% of cutaneous cases.^5,6 Early in the disease, most patients present with a bruiselike lesion on the scalp or forehead, often delaying the diagnosis.⁶ As the cancer progresses, tissue infiltration, edema, and hemorrhage contribute to the formation of violaceous nodules, which eventually prompt for biopsy. Angiosarcoma spans a broad histologic spectrum depending on the cytology of malignant cells (eg, spindle, small round, epithelioid) and their capacity for vasoformation. Welldifferentiated angiosarcoma shows retiform slitlike spaces in between collagen bundles that are lined by hyperchromatic hobnailing endothelial cells (Figure 2).⁷ Epithelioid angiosarcoma can be mistaken for SCC.⁸ Immunohistochemically, angiosarcoma stains positively for CD31, CD34, ETS-related gene 1, D2-40, and factor VIII.9 In our patient, the neoplasm was negative for vascular markers CD31 and CD34.

Bacillary angiomatosis (BA), caused by Bartonella henselae, is a rare disease that first was identified in HIV patients with diminished CD4+ T-cell counts. In the skin, BA often manifests as centrally ulcerated, single or clustered, reddish-purple nodules.¹⁰ Histologically, it is characterized by highly vascularized, histiocyterich infiltrates with admixed neutrophils and plasma cells (Figure 3). Capillaries often proliferate in a lobular fashion.¹¹ Atypical cytology with areas of necrosis may mimic angiosarcoma.¹² The pathognomonic feature of BA is the presence of enlarged histiocytes with pink-purplish cytoplasm corresponding to intracytoplasmic aggregates of bacteria, which can be revealed by Warthin-Starry or Grocott-Gomori methenamine-silver staining. Immunohistochemically, proliferative benign capillaries are highlighted by CD34 and CD31, and histiocytes are decorated by CD68.¹² This diagnosis was excluded based on the patient’s history, clinical presentation, and positive staining for CK5 and p63.

Squamoid eccrine ductal carcinoma is an exceedingly rare subtype of eccrine carcinoma that mimics SCC both clinically and histologically.¹³ It most often occurs on the head and neck of elderly patients. This neoplasm can look similar to SCC and its variants, including PSCC. Histologically, squamoid eccrine ductal carcinoma exhibits a biphasic growth pattern.¹⁴ Well-differentiated squamous dysplasia transitions to carcinoma with eccrine duct formation as the tumor percolates deep into the dermis (Figure 4). As a result, superficial skin biopsies often lead to an incorrect diagnosis.¹⁵ Unlike SCC, the risk for locoregional and widespread metastasis is elevated. Identifying ducts in the deep aspect of the tumor is critical, thus immunohistochemical staining for carcinoembryonic antigen and epithelial membrane antigen is paramount for the diagnosis.¹⁵ Pseudoangiomatous SCC will stain negative for carcinoembryonic antigen, as was the case in our patient.

Pseudoepitheliomatous hyperplasia is a benign histologic reaction that can result from trauma, chronic inflammation (ie, pyoderma gangrenosum), tattoo placement, underlying neoplasia or fungal infection, or a spider bite reaction.^14,15 It most commonly is seen as a well-demarcated nodule or plaque associated with scaling or crusting. Papules vary in size from less than 1 cm to several centimeters. Histologically, it is defined by an acanthotic proliferation of the adnexal epithelium and epidermis (Figure 5).^16,17 Irregular strands, cords, and nests of squamoid cells can extend into the dermis.¹⁸ It can closely mimic SCC, but there are a few key differences. Pseudoepitheliomatous hyperplasia will not display atypical mitotic figures or atypical nuclei and will never invade lymphatics or vascular systems.¹⁹ Pseudoepitheliomatous hyperplasia shows identical histology to well-differentiated SCC, and thus clinicopathologic correlation and mindful histologic evaluation are crucial. The presence of an increased influx of neutrophils and histiocytes should prompt for microbial stains or deeper sectioning. A superficial biopsy should be followed by a deep biopsy. In our patient, microorganismal stains were negative.

The Diagnosis: Pseudoangiomatous Squamous Cell Carcinoma

Pseudoangiomatous squamous cell carcinoma (PSCC), a variant of acantholytic squamous cell carcinoma (SCC), is a rare epithelial neoplasm that can mimic angiosarcoma.¹ Clinically, PSCC presents as a white-gray ulcer or nodular pink tumor on sun-exposed areas, typically on the head and neck. Due to its increased potential for metastasis, this variant of SCC is considered particularly aggressive. Histologically, PSCC shows nests of acantholytic atypical keratinocytes arranged in anastomosing arrays that form pseudovascular or pseudoglandular structures.² Acantholytic spaces frequently are filled with erythrocytes. Immunohistochemically, PSCC tumor cells express classic squamous markers such as cytokeratin (CK) 5 and p63 but not vascular markers such as CD31, CD34, and von Willebrand factor.³ In our patient, histopathology of the lesion revealed invasive nests, lobules, and interconnected columns of well-differentiated squamous tumor cells that emanated from the base of the epidermis. The tumor exhibited acantholysis forming ectatic and slitlike spaces, some of which contained erythrocytes. The neoplastic cells, including those lining pseudovascular spaces, positively stained for CK5 (Figure 1A) and nuclear p63 but lacked reactivity to CD31 (Figure 1B) and CD34, corroborating squamous and not vascular differentiation. Current treatment guidelines include Mohs micrographic surgery, excisional surgery, or radiation.⁴ Our patient’s lesion was completely removed by Mohs micrographic surgery. Three months later, there was no evidence of recurrence.

Angiosarcoma is an aggressive neoplasm associated with a poor prognosis and 5-year survival rate of 30% to 40%. The etiology of angiosarcoma still is unclear, but identified risk factors include prior radiation therapy, lymphedema (Stewart-Treves syndrome), and genetic predisposition.⁵ In the skin, angiosarcoma often occurs in the head and neck region, accounting for 60% of cutaneous cases.^5,6 Early in the disease, most patients present with a bruiselike lesion on the scalp or forehead, often delaying the diagnosis.⁶ As the cancer progresses, tissue infiltration, edema, and hemorrhage contribute to the formation of violaceous nodules, which eventually prompt for biopsy. Angiosarcoma spans a broad histologic spectrum depending on the cytology of malignant cells (eg, spindle, small round, epithelioid) and their capacity for vasoformation. Welldifferentiated angiosarcoma shows retiform slitlike spaces in between collagen bundles that are lined by hyperchromatic hobnailing endothelial cells (Figure 2).⁷ Epithelioid angiosarcoma can be mistaken for SCC.⁸ Immunohistochemically, angiosarcoma stains positively for CD31, CD34, ETS-related gene 1, D2-40, and factor VIII.9 In our patient, the neoplasm was negative for vascular markers CD31 and CD34.

Bacillary angiomatosis (BA), caused by Bartonella henselae, is a rare disease that first was identified in HIV patients with diminished CD4+ T-cell counts. In the skin, BA often manifests as centrally ulcerated, single or clustered, reddish-purple nodules.¹⁰ Histologically, it is characterized by highly vascularized, histiocyterich infiltrates with admixed neutrophils and plasma cells (Figure 3). Capillaries often proliferate in a lobular fashion.¹¹ Atypical cytology with areas of necrosis may mimic angiosarcoma.¹² The pathognomonic feature of BA is the presence of enlarged histiocytes with pink-purplish cytoplasm corresponding to intracytoplasmic aggregates of bacteria, which can be revealed by Warthin-Starry or Grocott-Gomori methenamine-silver staining. Immunohistochemically, proliferative benign capillaries are highlighted by CD34 and CD31, and histiocytes are decorated by CD68.¹² This diagnosis was excluded based on the patient’s history, clinical presentation, and positive staining for CK5 and p63.

Squamoid eccrine ductal carcinoma is an exceedingly rare subtype of eccrine carcinoma that mimics SCC both clinically and histologically.¹³ It most often occurs on the head and neck of elderly patients. This neoplasm can look similar to SCC and its variants, including PSCC. Histologically, squamoid eccrine ductal carcinoma exhibits a biphasic growth pattern.¹⁴ Well-differentiated squamous dysplasia transitions to carcinoma with eccrine duct formation as the tumor percolates deep into the dermis (Figure 4). As a result, superficial skin biopsies often lead to an incorrect diagnosis.¹⁵ Unlike SCC, the risk for locoregional and widespread metastasis is elevated. Identifying ducts in the deep aspect of the tumor is critical, thus immunohistochemical staining for carcinoembryonic antigen and epithelial membrane antigen is paramount for the diagnosis.¹⁵ Pseudoangiomatous SCC will stain negative for carcinoembryonic antigen, as was the case in our patient.

Pseudoepitheliomatous hyperplasia is a benign histologic reaction that can result from trauma, chronic inflammation (ie, pyoderma gangrenosum), tattoo placement, underlying neoplasia or fungal infection, or a spider bite reaction.^14,15 It most commonly is seen as a well-demarcated nodule or plaque associated with scaling or crusting. Papules vary in size from less than 1 cm to several centimeters. Histologically, it is defined by an acanthotic proliferation of the adnexal epithelium and epidermis (Figure 5).^16,17 Irregular strands, cords, and nests of squamoid cells can extend into the dermis.¹⁸ It can closely mimic SCC, but there are a few key differences. Pseudoepitheliomatous hyperplasia will not display atypical mitotic figures or atypical nuclei and will never invade lymphatics or vascular systems.¹⁹ Pseudoepitheliomatous hyperplasia shows identical histology to well-differentiated SCC, and thus clinicopathologic correlation and mindful histologic evaluation are crucial. The presence of an increased influx of neutrophils and histiocytes should prompt for microbial stains or deeper sectioning. A superficial biopsy should be followed by a deep biopsy. In our patient, microorganismal stains were negative.

The Diagnosis: Atypical Mycobacterial Infection

The history of rapid growth followed by shrinkage as well as the craterlike clinical appearance of our patient’s lesion were suspicious for the keratoacanthoma variant of squamous cell carcinoma (SCC). Periodic acid–Schiff green staining was negative for fungal or bacterial organisms, and the biopsy findings of keratinocyte atypia and irregular epidermal proliferation seemed to confirm our suspicion for well-differentiated SCC (Figure 1). Our patient subsequently was scheduled for Mohs micrographic surgery. Fortunately, a sample of tissue had been sent for panculture—bacterial, fungal, and mycobacterial—to rule out infectious etiologies, given the history of possible traumatic inoculation, and returned positive for Mycobacterium marinum infection prior to the surgery. Mohs surgery was canceled, and he was referred to an infectious disease specialist who started antibiotic treatment with azithromycin, ethambutol, and rifabutin. After 1 month of treatment the lesion substantially improved (Figure 2), further supporting the diagnosis of M marinum infection over SCC.

The differential diagnosis also included sporotrichosis, leishmaniasis, and chromoblastomycosis. Sporotrichosis lesions typically develop as multiple nodules and ulcers along a path of lymphatic drainage and can exhibit asteroid bodies and cigar-shaped yeast forms on histology. Chromoblastomycosis may display pseudoepitheliomatous hyperplasia and granulomatous inflammation; however, pathognomonic pigmented Medlar bodies also likely would be present.¹ Leishmaniasis has a wide variety of presentations; however, it typically occurs in patients with exposure to endemic areas outside of the United States. Although leishmaniasis may demonstrate pseudoepitheliomatous hyperplasia, ulceration, and mixed inflammation on histology, it also likely would show amastigotes within dermal macrophages.²

Atypical mycobacterial infections initially may be misdiagnosed as SCC due to their tendency to induce irregular acanthosis in the form of pseudoepitheliomatous hyperplasia as well as mild keratinocyte atypia secondary to inflammation.^3,4 Our case is unique because it occurred with M marinum infection specifically. The histopathologic findings of M marinum infections are variable and may additionally include granulomas, most commonly suppurative; intraepithelial abscesses; small vessel proliferation; dermal fibrosis; multinucleated giant cells; and transepidermal elimination.^4,5 Periodic acid–Schiff, Ziehl-Neelsen (acid-fast bacilli), and Fite staining may be used to distinguish M marinum infection from SCC but have low sensitivities (approximately 30%). Culture remains the most reliable test, with a sensitivity of nearly 80%.^5-7 In our patient, a Periodic acid–Schiff stain was obtained prior to receiving culture results, and acid-fast bacilli and Fite staining were added after the culture returned positive; however, all 3 stains failed to highlight any mycobacteria.

The primary risk factor for infection with M marinum is contact with aquatic environments or marine animals, and most cases involve the fingers or the hand.⁶ After we reached the diagnosis and further discussed the patient’s history, he recalled fishing for and cleaning raw shrimp around the time that he had a splinter. The Infectious Diseases Society of America recommends a treatment course extending 1 to 2 months after clinical symptoms resolve with ethambutol in addition to clarithromycin or azithromycin.⁸ If the infection is near a joint, rifampin should be empirically added to account for a potentially deeper infection. Imaging should be obtained to evaluate for joint space involvement, with magnetic resonance imaging being the preferred modality. If joint space involvement is confirmed, surgical debridement is indicated. Surgical debridement also is indicated for infections that fail to respond to antibiotic therapy.⁸

This case highlights M marinum infection as a potential mimicker of SCC, particularly if the biopsy is relatively superficial, as often occurs when obtained via the common shave technique. The distinction is critical, as M marinum infection is highly treatable and inappropriate surgery on the typical hand and finger locations may subject patients to substantial morbidity, such as the need for a skin graft, reduced mobility from scarring, or risk for serious wound infection.⁹ For superficial biopsies of an atypical squamous process, pathologists also may consider routinely recommending tissue culture, especially for hand and finger locations or when a history of local trauma is reported, instead of recommending complete excision or repeat biopsy alone.

The Diagnosis: Atypical Mycobacterial Infection

The history of rapid growth followed by shrinkage as well as the craterlike clinical appearance of our patient’s lesion were suspicious for the keratoacanthoma variant of squamous cell carcinoma (SCC). Periodic acid–Schiff green staining was negative for fungal or bacterial organisms, and the biopsy findings of keratinocyte atypia and irregular epidermal proliferation seemed to confirm our suspicion for well-differentiated SCC (Figure 1). Our patient subsequently was scheduled for Mohs micrographic surgery. Fortunately, a sample of tissue had been sent for panculture—bacterial, fungal, and mycobacterial—to rule out infectious etiologies, given the history of possible traumatic inoculation, and returned positive for Mycobacterium marinum infection prior to the surgery. Mohs surgery was canceled, and he was referred to an infectious disease specialist who started antibiotic treatment with azithromycin, ethambutol, and rifabutin. After 1 month of treatment the lesion substantially improved (Figure 2), further supporting the diagnosis of M marinum infection over SCC.

The differential diagnosis also included sporotrichosis, leishmaniasis, and chromoblastomycosis. Sporotrichosis lesions typically develop as multiple nodules and ulcers along a path of lymphatic drainage and can exhibit asteroid bodies and cigar-shaped yeast forms on histology. Chromoblastomycosis may display pseudoepitheliomatous hyperplasia and granulomatous inflammation; however, pathognomonic pigmented Medlar bodies also likely would be present.¹ Leishmaniasis has a wide variety of presentations; however, it typically occurs in patients with exposure to endemic areas outside of the United States. Although leishmaniasis may demonstrate pseudoepitheliomatous hyperplasia, ulceration, and mixed inflammation on histology, it also likely would show amastigotes within dermal macrophages.²

Atypical mycobacterial infections initially may be misdiagnosed as SCC due to their tendency to induce irregular acanthosis in the form of pseudoepitheliomatous hyperplasia as well as mild keratinocyte atypia secondary to inflammation.^3,4 Our case is unique because it occurred with M marinum infection specifically. The histopathologic findings of M marinum infections are variable and may additionally include granulomas, most commonly suppurative; intraepithelial abscesses; small vessel proliferation; dermal fibrosis; multinucleated giant cells; and transepidermal elimination.^4,5 Periodic acid–Schiff, Ziehl-Neelsen (acid-fast bacilli), and Fite staining may be used to distinguish M marinum infection from SCC but have low sensitivities (approximately 30%). Culture remains the most reliable test, with a sensitivity of nearly 80%.^5-7 In our patient, a Periodic acid–Schiff stain was obtained prior to receiving culture results, and acid-fast bacilli and Fite staining were added after the culture returned positive; however, all 3 stains failed to highlight any mycobacteria.

The primary risk factor for infection with M marinum is contact with aquatic environments or marine animals, and most cases involve the fingers or the hand.⁶ After we reached the diagnosis and further discussed the patient’s history, he recalled fishing for and cleaning raw shrimp around the time that he had a splinter. The Infectious Diseases Society of America recommends a treatment course extending 1 to 2 months after clinical symptoms resolve with ethambutol in addition to clarithromycin or azithromycin.⁸ If the infection is near a joint, rifampin should be empirically added to account for a potentially deeper infection. Imaging should be obtained to evaluate for joint space involvement, with magnetic resonance imaging being the preferred modality. If joint space involvement is confirmed, surgical debridement is indicated. Surgical debridement also is indicated for infections that fail to respond to antibiotic therapy.⁸

This case highlights M marinum infection as a potential mimicker of SCC, particularly if the biopsy is relatively superficial, as often occurs when obtained via the common shave technique. The distinction is critical, as M marinum infection is highly treatable and inappropriate surgery on the typical hand and finger locations may subject patients to substantial morbidity, such as the need for a skin graft, reduced mobility from scarring, or risk for serious wound infection.⁹ For superficial biopsies of an atypical squamous process, pathologists also may consider routinely recommending tissue culture, especially for hand and finger locations or when a history of local trauma is reported, instead of recommending complete excision or repeat biopsy alone.

The Diagnosis: Atypical Mycobacterial Infection

The history of rapid growth followed by shrinkage as well as the craterlike clinical appearance of our patient’s lesion were suspicious for the keratoacanthoma variant of squamous cell carcinoma (SCC). Periodic acid–Schiff green staining was negative for fungal or bacterial organisms, and the biopsy findings of keratinocyte atypia and irregular epidermal proliferation seemed to confirm our suspicion for well-differentiated SCC (Figure 1). Our patient subsequently was scheduled for Mohs micrographic surgery. Fortunately, a sample of tissue had been sent for panculture—bacterial, fungal, and mycobacterial—to rule out infectious etiologies, given the history of possible traumatic inoculation, and returned positive for Mycobacterium marinum infection prior to the surgery. Mohs surgery was canceled, and he was referred to an infectious disease specialist who started antibiotic treatment with azithromycin, ethambutol, and rifabutin. After 1 month of treatment the lesion substantially improved (Figure 2), further supporting the diagnosis of M marinum infection over SCC.

The differential diagnosis also included sporotrichosis, leishmaniasis, and chromoblastomycosis. Sporotrichosis lesions typically develop as multiple nodules and ulcers along a path of lymphatic drainage and can exhibit asteroid bodies and cigar-shaped yeast forms on histology. Chromoblastomycosis may display pseudoepitheliomatous hyperplasia and granulomatous inflammation; however, pathognomonic pigmented Medlar bodies also likely would be present.¹ Leishmaniasis has a wide variety of presentations; however, it typically occurs in patients with exposure to endemic areas outside of the United States. Although leishmaniasis may demonstrate pseudoepitheliomatous hyperplasia, ulceration, and mixed inflammation on histology, it also likely would show amastigotes within dermal macrophages.²

Atypical mycobacterial infections initially may be misdiagnosed as SCC due to their tendency to induce irregular acanthosis in the form of pseudoepitheliomatous hyperplasia as well as mild keratinocyte atypia secondary to inflammation.^3,4 Our case is unique because it occurred with M marinum infection specifically. The histopathologic findings of M marinum infections are variable and may additionally include granulomas, most commonly suppurative; intraepithelial abscesses; small vessel proliferation; dermal fibrosis; multinucleated giant cells; and transepidermal elimination.^4,5 Periodic acid–Schiff, Ziehl-Neelsen (acid-fast bacilli), and Fite staining may be used to distinguish M marinum infection from SCC but have low sensitivities (approximately 30%). Culture remains the most reliable test, with a sensitivity of nearly 80%.^5-7 In our patient, a Periodic acid–Schiff stain was obtained prior to receiving culture results, and acid-fast bacilli and Fite staining were added after the culture returned positive; however, all 3 stains failed to highlight any mycobacteria.

The primary risk factor for infection with M marinum is contact with aquatic environments or marine animals, and most cases involve the fingers or the hand.⁶ After we reached the diagnosis and further discussed the patient’s history, he recalled fishing for and cleaning raw shrimp around the time that he had a splinter. The Infectious Diseases Society of America recommends a treatment course extending 1 to 2 months after clinical symptoms resolve with ethambutol in addition to clarithromycin or azithromycin.⁸ If the infection is near a joint, rifampin should be empirically added to account for a potentially deeper infection. Imaging should be obtained to evaluate for joint space involvement, with magnetic resonance imaging being the preferred modality. If joint space involvement is confirmed, surgical debridement is indicated. Surgical debridement also is indicated for infections that fail to respond to antibiotic therapy.⁸

This case highlights M marinum infection as a potential mimicker of SCC, particularly if the biopsy is relatively superficial, as often occurs when obtained via the common shave technique. The distinction is critical, as M marinum infection is highly treatable and inappropriate surgery on the typical hand and finger locations may subject patients to substantial morbidity, such as the need for a skin graft, reduced mobility from scarring, or risk for serious wound infection.⁹ For superficial biopsies of an atypical squamous process, pathologists also may consider routinely recommending tissue culture, especially for hand and finger locations or when a history of local trauma is reported, instead of recommending complete excision or repeat biopsy alone.

The Diagnosis: Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis)

A skin biopsy of the right lower extremity demonstrated diffuse interstitial, perivascular, and periadnexal neutrophilic dermal infiltrate in the reticular dermis (Figure 1), consistent with a diagnosis of Sweet syndrome without evidence of leukemia cutis or infection. The firm erythematous papulonodules with follicular accentuation on the face (Figure 2) also were confirmed as Sweet syndrome on histopathology. Concern for leukemic transformation was confirmed with bone biopsy revealing acute myeloid leukemia (AML). Our patient began a short course of prednisone, and the cutaneous lesions improved during hospitalization; however, he was lost to follow-up.

Sweet syndrome (also known as acute febrile neutrophilic dermatosis) is a rare inflammatory skin condition typically characterized by asymmetric, painful, erythematous to violaceous papules, plaques, or nodules involving the arms, face, and neck.¹ It most commonly occurs in women and typically presents in patients aged 47 to 57 years. Although the pathogenesis of neutrophilic dermatoses is not completely understood, they are believed to be due to altered expression of inflammatory cytokines, irregular neutrophil function, and a genetic predisposition.² There are 3 main categories of Sweet syndrome: classical (or idiopathic), drug induced, and malignancy associated.¹ The lesions associated with Sweet syndrome vary from a few millimeters to several centimeters and may be annular or targetoid in the later stages. They also may form bullae and ulcerate. Fever, leukocytosis, and elevated acute-phase reactants also are common on presentation.1 Histopathologic analysis demonstrates an intense neutrophilic infiltrate within the reticular dermis with marked leukocytoclasia. Admixed within the neutrophil polymorphs are variable numbers of lymphocytes and histiocytes. Edema in the upper dermis also is characteristic.³ The exact pathogenesis of Sweet syndrome has yet to be elucidated but may involve a combination of cytokine dysregulation, hypersensitivity reactions, and genetics.⁴ Our case demonstrates 3 distinct morphologies of Sweet syndrome in a single patient, including classic edematous plaques, agminated targetoid plaques, and ulceration. Based on the clinical presentation, diagnostic workup for an undiagnosed malignancy was warranted, which confirmed AML. The malignancy-associated form of Sweet syndrome accounts for a substantial portion of cases, with approximately 21% of patients diagnosed with Sweet syndrome having an underlying malignancy, commonly a hematologic malignancy or myeloproliferative disorder with AML being the most common.¹

The differential diagnosis for Sweet syndrome includes cutaneous small vessel vasculitis, which commonly presents with symmetric palpable purpura of the legs. Lesions may be round, port wine–colored plaques and even may form ulcers, vesicles, and targetoid lesions. However, skin biopsy shows polymorphonuclear infiltrate affecting postcapillary venules, fibrinoid deposits, and extravasation of red blood cells.⁵ Leukemia cutis describes any type of leukemia that manifests in the skin. It typically presents as violaceous or red-brown papules, nodules, and plaques most commonly on the legs. Histopathology varies by immunophenotype but generally demonstrates perivascular or periadnexal involvement or a diffuse, interstitial, or nodular infiltrate of the dermis or subcutis.⁶ Neutrophilic eccrine hidradenitis describes an aseptic neutrophilic infiltration around eccrine coils and glands. It may present as papules or plaques that usually are erythematous but also may be pigmented. Lesions can be asymptomatic or painful as in Sweet syndrome and are distributed proximally or on the distal extremities. Histopathologic examination demonstrates the degeneration of the eccrine gland and neutrophilic inflammatory infiltrates.⁷ Lastly, necrotizing fasciitis is a life-threatening infection of the deep soft tissue and fascia, classically caused by group A Streptococcus. The infected site may have erythema, tenderness, fluctuance, necrosis, and bullae.8 Although our patient had a fever, he did not display the tachycardia, hypotension, tachypnea, and rapid deterioration that is common in necrotizing fasciitis.

Sweet syndrome may present with various morphologies within the same patient. Painful, erythematous to violaceous papules, plaques, nodules, bullae, and ulcers may be seen. A workup for an underlying malignancy may be warranted based on clinical presentation. Most patients have a rapid and dramatic response to systemic corticosteroids.

The Diagnosis: Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis)

A skin biopsy of the right lower extremity demonstrated diffuse interstitial, perivascular, and periadnexal neutrophilic dermal infiltrate in the reticular dermis (Figure 1), consistent with a diagnosis of Sweet syndrome without evidence of leukemia cutis or infection. The firm erythematous papulonodules with follicular accentuation on the face (Figure 2) also were confirmed as Sweet syndrome on histopathology. Concern for leukemic transformation was confirmed with bone biopsy revealing acute myeloid leukemia (AML). Our patient began a short course of prednisone, and the cutaneous lesions improved during hospitalization; however, he was lost to follow-up.

Sweet syndrome (also known as acute febrile neutrophilic dermatosis) is a rare inflammatory skin condition typically characterized by asymmetric, painful, erythematous to violaceous papules, plaques, or nodules involving the arms, face, and neck.¹ It most commonly occurs in women and typically presents in patients aged 47 to 57 years. Although the pathogenesis of neutrophilic dermatoses is not completely understood, they are believed to be due to altered expression of inflammatory cytokines, irregular neutrophil function, and a genetic predisposition.² There are 3 main categories of Sweet syndrome: classical (or idiopathic), drug induced, and malignancy associated.¹ The lesions associated with Sweet syndrome vary from a few millimeters to several centimeters and may be annular or targetoid in the later stages. They also may form bullae and ulcerate. Fever, leukocytosis, and elevated acute-phase reactants also are common on presentation.1 Histopathologic analysis demonstrates an intense neutrophilic infiltrate within the reticular dermis with marked leukocytoclasia. Admixed within the neutrophil polymorphs are variable numbers of lymphocytes and histiocytes. Edema in the upper dermis also is characteristic.³ The exact pathogenesis of Sweet syndrome has yet to be elucidated but may involve a combination of cytokine dysregulation, hypersensitivity reactions, and genetics.⁴ Our case demonstrates 3 distinct morphologies of Sweet syndrome in a single patient, including classic edematous plaques, agminated targetoid plaques, and ulceration. Based on the clinical presentation, diagnostic workup for an undiagnosed malignancy was warranted, which confirmed AML. The malignancy-associated form of Sweet syndrome accounts for a substantial portion of cases, with approximately 21% of patients diagnosed with Sweet syndrome having an underlying malignancy, commonly a hematologic malignancy or myeloproliferative disorder with AML being the most common.¹

The differential diagnosis for Sweet syndrome includes cutaneous small vessel vasculitis, which commonly presents with symmetric palpable purpura of the legs. Lesions may be round, port wine–colored plaques and even may form ulcers, vesicles, and targetoid lesions. However, skin biopsy shows polymorphonuclear infiltrate affecting postcapillary venules, fibrinoid deposits, and extravasation of red blood cells.⁵ Leukemia cutis describes any type of leukemia that manifests in the skin. It typically presents as violaceous or red-brown papules, nodules, and plaques most commonly on the legs. Histopathology varies by immunophenotype but generally demonstrates perivascular or periadnexal involvement or a diffuse, interstitial, or nodular infiltrate of the dermis or subcutis.⁶ Neutrophilic eccrine hidradenitis describes an aseptic neutrophilic infiltration around eccrine coils and glands. It may present as papules or plaques that usually are erythematous but also may be pigmented. Lesions can be asymptomatic or painful as in Sweet syndrome and are distributed proximally or on the distal extremities. Histopathologic examination demonstrates the degeneration of the eccrine gland and neutrophilic inflammatory infiltrates.⁷ Lastly, necrotizing fasciitis is a life-threatening infection of the deep soft tissue and fascia, classically caused by group A Streptococcus. The infected site may have erythema, tenderness, fluctuance, necrosis, and bullae.8 Although our patient had a fever, he did not display the tachycardia, hypotension, tachypnea, and rapid deterioration that is common in necrotizing fasciitis.

Sweet syndrome may present with various morphologies within the same patient. Painful, erythematous to violaceous papules, plaques, nodules, bullae, and ulcers may be seen. A workup for an underlying malignancy may be warranted based on clinical presentation. Most patients have a rapid and dramatic response to systemic corticosteroids.

The Diagnosis: Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis)

A skin biopsy of the right lower extremity demonstrated diffuse interstitial, perivascular, and periadnexal neutrophilic dermal infiltrate in the reticular dermis (Figure 1), consistent with a diagnosis of Sweet syndrome without evidence of leukemia cutis or infection. The firm erythematous papulonodules with follicular accentuation on the face (Figure 2) also were confirmed as Sweet syndrome on histopathology. Concern for leukemic transformation was confirmed with bone biopsy revealing acute myeloid leukemia (AML). Our patient began a short course of prednisone, and the cutaneous lesions improved during hospitalization; however, he was lost to follow-up.

Sweet syndrome (also known as acute febrile neutrophilic dermatosis) is a rare inflammatory skin condition typically characterized by asymmetric, painful, erythematous to violaceous papules, plaques, or nodules involving the arms, face, and neck.¹ It most commonly occurs in women and typically presents in patients aged 47 to 57 years. Although the pathogenesis of neutrophilic dermatoses is not completely understood, they are believed to be due to altered expression of inflammatory cytokines, irregular neutrophil function, and a genetic predisposition.² There are 3 main categories of Sweet syndrome: classical (or idiopathic), drug induced, and malignancy associated.¹ The lesions associated with Sweet syndrome vary from a few millimeters to several centimeters and may be annular or targetoid in the later stages. They also may form bullae and ulcerate. Fever, leukocytosis, and elevated acute-phase reactants also are common on presentation.1 Histopathologic analysis demonstrates an intense neutrophilic infiltrate within the reticular dermis with marked leukocytoclasia. Admixed within the neutrophil polymorphs are variable numbers of lymphocytes and histiocytes. Edema in the upper dermis also is characteristic.³ The exact pathogenesis of Sweet syndrome has yet to be elucidated but may involve a combination of cytokine dysregulation, hypersensitivity reactions, and genetics.⁴ Our case demonstrates 3 distinct morphologies of Sweet syndrome in a single patient, including classic edematous plaques, agminated targetoid plaques, and ulceration. Based on the clinical presentation, diagnostic workup for an undiagnosed malignancy was warranted, which confirmed AML. The malignancy-associated form of Sweet syndrome accounts for a substantial portion of cases, with approximately 21% of patients diagnosed with Sweet syndrome having an underlying malignancy, commonly a hematologic malignancy or myeloproliferative disorder with AML being the most common.¹

The differential diagnosis for Sweet syndrome includes cutaneous small vessel vasculitis, which commonly presents with symmetric palpable purpura of the legs. Lesions may be round, port wine–colored plaques and even may form ulcers, vesicles, and targetoid lesions. However, skin biopsy shows polymorphonuclear infiltrate affecting postcapillary venules, fibrinoid deposits, and extravasation of red blood cells.⁵ Leukemia cutis describes any type of leukemia that manifests in the skin. It typically presents as violaceous or red-brown papules, nodules, and plaques most commonly on the legs. Histopathology varies by immunophenotype but generally demonstrates perivascular or periadnexal involvement or a diffuse, interstitial, or nodular infiltrate of the dermis or subcutis.⁶ Neutrophilic eccrine hidradenitis describes an aseptic neutrophilic infiltration around eccrine coils and glands. It may present as papules or plaques that usually are erythematous but also may be pigmented. Lesions can be asymptomatic or painful as in Sweet syndrome and are distributed proximally or on the distal extremities. Histopathologic examination demonstrates the degeneration of the eccrine gland and neutrophilic inflammatory infiltrates.⁷ Lastly, necrotizing fasciitis is a life-threatening infection of the deep soft tissue and fascia, classically caused by group A Streptococcus. The infected site may have erythema, tenderness, fluctuance, necrosis, and bullae.8 Although our patient had a fever, he did not display the tachycardia, hypotension, tachypnea, and rapid deterioration that is common in necrotizing fasciitis.

Sweet syndrome may present with various morphologies within the same patient. Painful, erythematous to violaceous papules, plaques, nodules, bullae, and ulcers may be seen. A workup for an underlying malignancy may be warranted based on clinical presentation. Most patients have a rapid and dramatic response to systemic corticosteroids.

The Diagnosis: Hybrid Schwannoma-Perineurioma

Hybrid nerve sheath tumors are rare entities that display features of more than one nerve sheath tumor such as neurofibromas, schwannomas, and perineuriomas.¹ These tumors often are found in the dermis or subcutaneous tissue of the extremities and abdomen²; however, cases of hybrid peripheral nerve sheath tumors have been reported in many anatomical locations without a gender predilection.³ The most common type of hybrid nerve sheath tumor is a schwannoma-perineurioma.^3,4 Histologically, they are well-circumscribed lesions composed of both spindled Schwann cells with plump nuclei and spindled perineural cells with more elongated thin nuclei.⁵ Although the Schwann cell component tends to predominate, the 2 cell populations interdigitate, making it challenging to definitively distinguish them by hematoxylin and eosin staining alone.4 However, immunohistochemical (IHC) staining can be used to help distinguish the 2 separate cell populations. Staining for S-100 and SRY-box transcription factor 10 (SOX-10) will be positive in the Schwann cell component, and staining for epithelial membrane antigen, Claudin-1, or glucose transporter-1 (Figure 1) will be positive in the perineural component. Other hybrid forms of benign nerve sheath tumors include neurofibroma-schwannoma and neurofibromaperineurioma.⁴ Neurofibroma-schwannomas usually have a schwannoma component containing Antoni A areas with palisading Verocay bodies. The neurofibroma cells typically have wavy elongated nuclei, fibroblasts, and mucinous myxoid material.³ Neurofibroma-perineurioma is the least common hybrid tumor. These hybrid tumors have a plexiform neurofibroma appearance with areas of perineural differentiation, which can be difficult to identify on routine histology and typically will require IHC staining to appreciate. The neurofibroma component will stain positive for S-100 and negative for markers of perineural differentiation, including epithelial membrane antigen, glucose transporter-1, and Claudin-1.³ Although schwannoma-perineuriomas are benign sporadic tumors not associated with neurofibromatosis, neurofibromaschwannomas are associated with neurofibromatosis types 1 and 2 (NF1 and NF2). Neurofibroma-perineurioma tumors usually are associated with only NF1.^3,6

Schwannomas typically present in middle-aged patients as tumors located on flexor surfaces.⁷ Although perineural cells can be seen at the periphery of a schwannoma forming a capsule, they do not interdigitate between the Schwann cells. Schwannomas are composed almost entirely of well-differentiated Schwann cells.^1,4,8 Schwannomas classically are well-circumscribed, encapsulated, biphasic lesions with alternating compact areas (Antoni A) and loosely arranged areas (Antoni B). The spindled cells occasionally may display nuclear palisading within the Antoni A areas, known as Verocay bodies (Figure 2). Antoni B areas are more disorganized and hypocellular with variable macrophage infiltrate.^1,4,8 The Schwann cells predominantly will have bland cytologic features, but scattered areas of degenerative nuclear atypia (also known as ancient change) may be present.⁴ Multiple schwannomas are associated with NF2 gene mutations and loss of merlin protein.8 There are different subtypes of schwannomas, including cellular and plexiform schwannomas.⁴ Because schwannomas are benign nerve sheath lesions, treatment typically consists of excision with careful dissection around the involved nerve.⁹

Neurofibromas are the most common peripheral nerve sheath tumors of the skin with no notable anatomic prediction, though one study found them to be more prevalent in the upper extremities.¹⁰ They typically present as sporadic solitary lesions, but multiple lesions may appear as superficial pedunculated growths that present in those aged 20 to 30 years.¹¹ Microscopically, neurofibromas typically are not well circumscribed and have an infiltrative growth pattern. Neurofibromas are composed of cytologically bland spindled Schwann cells with thin wavy nuclei in a variable myxoid stroma (Figure 3). In addition to Schwann cells, neurofibromas contain other cell components, including fibroblasts, mast cells, perineurial-like cells, and residual axons.⁴ Neurofibromas typically are located in the dermis but may extend into the subcutaneous tissue. Clinically, the overlying skin may show hyperpigmentation.8 Neurofibromas can be localized, diffuse, or plexiform, with the majority being localized. Diffuse neurofibromas clinically have a raised plaque appearance. Treatment is unnecessary because these lesions are benign.⁷

Desmoplastic melanoma (DM) is another diagnosis in the differential for this case. Patients with DM are older compared to non-DM melanoma patients, with a male predilection.¹² Desmoplastic melanomas are more likely to be located on the head and neck. In approximately one-third of cases, no in situ component will be identified, leading to confusion of the dermal lesion as a neural lesion or an area of scar formation. Microscopically, DM presents as a variable cellular infiltrative tumor composed of spindle cells with varying degrees of nuclear atypia. The spindled melanocytes are within a collagenous (desmoplastic) stroma (Figure 4).¹³ Desmoplastic melanoma has been described with a low mitotic index, leading to misdiagnosis with benign spindle cell neoplasms.¹⁴ The spindle cells should be positive for S-100 and SOX-10 with IHC staining. Unlike other melanomas, human melanoma black 45 and Melan-A often are negative or only focally positive. Treatment of DM is similar to non-DM in that wide local excision usually is employed. A systematic review evaluating sentinel lymph node biopsy (SLNB) recommended consideration of SLNB in mixed DM but not for pure DM, as rates of positive SLNB were much lower in the latter.¹⁵

Patients with malignant peripheral nerve sheath tumor (MPNST) usually present with an enlarging mass, pain, or neurologic symptoms. Most cases of MPNST are located on the trunk or extremities.¹⁶ Plexiform neurofibromas, especially in adults with NF1, have the potential to transform into an MPNST.⁴ In fact, MPNST is the most common malignancy in patients with NF1.¹⁷ Pediatric cancer survivors also are predisposed to MPNST, with a 40-fold increase in incidence compared to the general population.¹⁸ Transformation from schwannoma to MPNST is rare but has been reported.⁸ Histologically, spindle cells easily can be appreciated with a fasciculated growth pattern (Figure 5). Mitotic activity and tumor necrosis may be present. Diagnosis of these tumors historically has been challenging, though recent research has identified inactivation of polycomb repressive complex 2 in 70% to 90% of MPNSTs. Because of polycomb repressive complex 2 inactivation, there is loss of stone H3K27 trimethylation that can be capitalized on for MPNST diagnosis.¹⁹ Negative IHC staining for H3K27 trimethylation has been found to be highly specific for MPNST. Negative staining for different cytokeratin and melanoma markers can be helpful in differentiating it from carcinomas and melanoma. The only curative treatment for MPNST is complete excision, leaving patients with recurrent, refractory, and metastatic cases to be encouraged for enrollment in clinical trials. The 5-year survival rates for patients with MPNST reported in the literature range from 20% to 50%.²⁰

The Diagnosis: Hybrid Schwannoma-Perineurioma

Hybrid nerve sheath tumors are rare entities that display features of more than one nerve sheath tumor such as neurofibromas, schwannomas, and perineuriomas.¹ These tumors often are found in the dermis or subcutaneous tissue of the extremities and abdomen²; however, cases of hybrid peripheral nerve sheath tumors have been reported in many anatomical locations without a gender predilection.³ The most common type of hybrid nerve sheath tumor is a schwannoma-perineurioma.^3,4 Histologically, they are well-circumscribed lesions composed of both spindled Schwann cells with plump nuclei and spindled perineural cells with more elongated thin nuclei.⁵ Although the Schwann cell component tends to predominate, the 2 cell populations interdigitate, making it challenging to definitively distinguish them by hematoxylin and eosin staining alone.4 However, immunohistochemical (IHC) staining can be used to help distinguish the 2 separate cell populations. Staining for S-100 and SRY-box transcription factor 10 (SOX-10) will be positive in the Schwann cell component, and staining for epithelial membrane antigen, Claudin-1, or glucose transporter-1 (Figure 1) will be positive in the perineural component. Other hybrid forms of benign nerve sheath tumors include neurofibroma-schwannoma and neurofibromaperineurioma.⁴ Neurofibroma-schwannomas usually have a schwannoma component containing Antoni A areas with palisading Verocay bodies. The neurofibroma cells typically have wavy elongated nuclei, fibroblasts, and mucinous myxoid material.³ Neurofibroma-perineurioma is the least common hybrid tumor. These hybrid tumors have a plexiform neurofibroma appearance with areas of perineural differentiation, which can be difficult to identify on routine histology and typically will require IHC staining to appreciate. The neurofibroma component will stain positive for S-100 and negative for markers of perineural differentiation, including epithelial membrane antigen, glucose transporter-1, and Claudin-1.³ Although schwannoma-perineuriomas are benign sporadic tumors not associated with neurofibromatosis, neurofibromaschwannomas are associated with neurofibromatosis types 1 and 2 (NF1 and NF2). Neurofibroma-perineurioma tumors usually are associated with only NF1.^3,6

Schwannomas typically present in middle-aged patients as tumors located on flexor surfaces.⁷ Although perineural cells can be seen at the periphery of a schwannoma forming a capsule, they do not interdigitate between the Schwann cells. Schwannomas are composed almost entirely of well-differentiated Schwann cells.^1,4,8 Schwannomas classically are well-circumscribed, encapsulated, biphasic lesions with alternating compact areas (Antoni A) and loosely arranged areas (Antoni B). The spindled cells occasionally may display nuclear palisading within the Antoni A areas, known as Verocay bodies (Figure 2). Antoni B areas are more disorganized and hypocellular with variable macrophage infiltrate.^1,4,8 The Schwann cells predominantly will have bland cytologic features, but scattered areas of degenerative nuclear atypia (also known as ancient change) may be present.⁴ Multiple schwannomas are associated with NF2 gene mutations and loss of merlin protein.8 There are different subtypes of schwannomas, including cellular and plexiform schwannomas.⁴ Because schwannomas are benign nerve sheath lesions, treatment typically consists of excision with careful dissection around the involved nerve.⁹

Neurofibromas are the most common peripheral nerve sheath tumors of the skin with no notable anatomic prediction, though one study found them to be more prevalent in the upper extremities.¹⁰ They typically present as sporadic solitary lesions, but multiple lesions may appear as superficial pedunculated growths that present in those aged 20 to 30 years.¹¹ Microscopically, neurofibromas typically are not well circumscribed and have an infiltrative growth pattern. Neurofibromas are composed of cytologically bland spindled Schwann cells with thin wavy nuclei in a variable myxoid stroma (Figure 3). In addition to Schwann cells, neurofibromas contain other cell components, including fibroblasts, mast cells, perineurial-like cells, and residual axons.⁴ Neurofibromas typically are located in the dermis but may extend into the subcutaneous tissue. Clinically, the overlying skin may show hyperpigmentation.8 Neurofibromas can be localized, diffuse, or plexiform, with the majority being localized. Diffuse neurofibromas clinically have a raised plaque appearance. Treatment is unnecessary because these lesions are benign.⁷

Desmoplastic melanoma (DM) is another diagnosis in the differential for this case. Patients with DM are older compared to non-DM melanoma patients, with a male predilection.¹² Desmoplastic melanomas are more likely to be located on the head and neck. In approximately one-third of cases, no in situ component will be identified, leading to confusion of the dermal lesion as a neural lesion or an area of scar formation. Microscopically, DM presents as a variable cellular infiltrative tumor composed of spindle cells with varying degrees of nuclear atypia. The spindled melanocytes are within a collagenous (desmoplastic) stroma (Figure 4).¹³ Desmoplastic melanoma has been described with a low mitotic index, leading to misdiagnosis with benign spindle cell neoplasms.¹⁴ The spindle cells should be positive for S-100 and SOX-10 with IHC staining. Unlike other melanomas, human melanoma black 45 and Melan-A often are negative or only focally positive. Treatment of DM is similar to non-DM in that wide local excision usually is employed. A systematic review evaluating sentinel lymph node biopsy (SLNB) recommended consideration of SLNB in mixed DM but not for pure DM, as rates of positive SLNB were much lower in the latter.¹⁵

Patients with malignant peripheral nerve sheath tumor (MPNST) usually present with an enlarging mass, pain, or neurologic symptoms. Most cases of MPNST are located on the trunk or extremities.¹⁶ Plexiform neurofibromas, especially in adults with NF1, have the potential to transform into an MPNST.⁴ In fact, MPNST is the most common malignancy in patients with NF1.¹⁷ Pediatric cancer survivors also are predisposed to MPNST, with a 40-fold increase in incidence compared to the general population.¹⁸ Transformation from schwannoma to MPNST is rare but has been reported.⁸ Histologically, spindle cells easily can be appreciated with a fasciculated growth pattern (Figure 5). Mitotic activity and tumor necrosis may be present. Diagnosis of these tumors historically has been challenging, though recent research has identified inactivation of polycomb repressive complex 2 in 70% to 90% of MPNSTs. Because of polycomb repressive complex 2 inactivation, there is loss of stone H3K27 trimethylation that can be capitalized on for MPNST diagnosis.¹⁹ Negative IHC staining for H3K27 trimethylation has been found to be highly specific for MPNST. Negative staining for different cytokeratin and melanoma markers can be helpful in differentiating it from carcinomas and melanoma. The only curative treatment for MPNST is complete excision, leaving patients with recurrent, refractory, and metastatic cases to be encouraged for enrollment in clinical trials. The 5-year survival rates for patients with MPNST reported in the literature range from 20% to 50%.²⁰

The Diagnosis: Hybrid Schwannoma-Perineurioma

Hybrid nerve sheath tumors are rare entities that display features of more than one nerve sheath tumor such as neurofibromas, schwannomas, and perineuriomas.¹ These tumors often are found in the dermis or subcutaneous tissue of the extremities and abdomen²; however, cases of hybrid peripheral nerve sheath tumors have been reported in many anatomical locations without a gender predilection.³ The most common type of hybrid nerve sheath tumor is a schwannoma-perineurioma.^3,4 Histologically, they are well-circumscribed lesions composed of both spindled Schwann cells with plump nuclei and spindled perineural cells with more elongated thin nuclei.⁵ Although the Schwann cell component tends to predominate, the 2 cell populations interdigitate, making it challenging to definitively distinguish them by hematoxylin and eosin staining alone.4 However, immunohistochemical (IHC) staining can be used to help distinguish the 2 separate cell populations. Staining for S-100 and SRY-box transcription factor 10 (SOX-10) will be positive in the Schwann cell component, and staining for epithelial membrane antigen, Claudin-1, or glucose transporter-1 (Figure 1) will be positive in the perineural component. Other hybrid forms of benign nerve sheath tumors include neurofibroma-schwannoma and neurofibromaperineurioma.⁴ Neurofibroma-schwannomas usually have a schwannoma component containing Antoni A areas with palisading Verocay bodies. The neurofibroma cells typically have wavy elongated nuclei, fibroblasts, and mucinous myxoid material.³ Neurofibroma-perineurioma is the least common hybrid tumor. These hybrid tumors have a plexiform neurofibroma appearance with areas of perineural differentiation, which can be difficult to identify on routine histology and typically will require IHC staining to appreciate. The neurofibroma component will stain positive for S-100 and negative for markers of perineural differentiation, including epithelial membrane antigen, glucose transporter-1, and Claudin-1.³ Although schwannoma-perineuriomas are benign sporadic tumors not associated with neurofibromatosis, neurofibromaschwannomas are associated with neurofibromatosis types 1 and 2 (NF1 and NF2). Neurofibroma-perineurioma tumors usually are associated with only NF1.^3,6

Schwannomas typically present in middle-aged patients as tumors located on flexor surfaces.⁷ Although perineural cells can be seen at the periphery of a schwannoma forming a capsule, they do not interdigitate between the Schwann cells. Schwannomas are composed almost entirely of well-differentiated Schwann cells.^1,4,8 Schwannomas classically are well-circumscribed, encapsulated, biphasic lesions with alternating compact areas (Antoni A) and loosely arranged areas (Antoni B). The spindled cells occasionally may display nuclear palisading within the Antoni A areas, known as Verocay bodies (Figure 2). Antoni B areas are more disorganized and hypocellular with variable macrophage infiltrate.^1,4,8 The Schwann cells predominantly will have bland cytologic features, but scattered areas of degenerative nuclear atypia (also known as ancient change) may be present.⁴ Multiple schwannomas are associated with NF2 gene mutations and loss of merlin protein.8 There are different subtypes of schwannomas, including cellular and plexiform schwannomas.⁴ Because schwannomas are benign nerve sheath lesions, treatment typically consists of excision with careful dissection around the involved nerve.⁹

Neurofibromas are the most common peripheral nerve sheath tumors of the skin with no notable anatomic prediction, though one study found them to be more prevalent in the upper extremities.¹⁰ They typically present as sporadic solitary lesions, but multiple lesions may appear as superficial pedunculated growths that present in those aged 20 to 30 years.¹¹ Microscopically, neurofibromas typically are not well circumscribed and have an infiltrative growth pattern. Neurofibromas are composed of cytologically bland spindled Schwann cells with thin wavy nuclei in a variable myxoid stroma (Figure 3). In addition to Schwann cells, neurofibromas contain other cell components, including fibroblasts, mast cells, perineurial-like cells, and residual axons.⁴ Neurofibromas typically are located in the dermis but may extend into the subcutaneous tissue. Clinically, the overlying skin may show hyperpigmentation.8 Neurofibromas can be localized, diffuse, or plexiform, with the majority being localized. Diffuse neurofibromas clinically have a raised plaque appearance. Treatment is unnecessary because these lesions are benign.⁷

Desmoplastic melanoma (DM) is another diagnosis in the differential for this case. Patients with DM are older compared to non-DM melanoma patients, with a male predilection.¹² Desmoplastic melanomas are more likely to be located on the head and neck. In approximately one-third of cases, no in situ component will be identified, leading to confusion of the dermal lesion as a neural lesion or an area of scar formation. Microscopically, DM presents as a variable cellular infiltrative tumor composed of spindle cells with varying degrees of nuclear atypia. The spindled melanocytes are within a collagenous (desmoplastic) stroma (Figure 4).¹³ Desmoplastic melanoma has been described with a low mitotic index, leading to misdiagnosis with benign spindle cell neoplasms.¹⁴ The spindle cells should be positive for S-100 and SOX-10 with IHC staining. Unlike other melanomas, human melanoma black 45 and Melan-A often are negative or only focally positive. Treatment of DM is similar to non-DM in that wide local excision usually is employed. A systematic review evaluating sentinel lymph node biopsy (SLNB) recommended consideration of SLNB in mixed DM but not for pure DM, as rates of positive SLNB were much lower in the latter.¹⁵

Patients with malignant peripheral nerve sheath tumor (MPNST) usually present with an enlarging mass, pain, or neurologic symptoms. Most cases of MPNST are located on the trunk or extremities.¹⁶ Plexiform neurofibromas, especially in adults with NF1, have the potential to transform into an MPNST.⁴ In fact, MPNST is the most common malignancy in patients with NF1.¹⁷ Pediatric cancer survivors also are predisposed to MPNST, with a 40-fold increase in incidence compared to the general population.¹⁸ Transformation from schwannoma to MPNST is rare but has been reported.⁸ Histologically, spindle cells easily can be appreciated with a fasciculated growth pattern (Figure 5). Mitotic activity and tumor necrosis may be present. Diagnosis of these tumors historically has been challenging, though recent research has identified inactivation of polycomb repressive complex 2 in 70% to 90% of MPNSTs. Because of polycomb repressive complex 2 inactivation, there is loss of stone H3K27 trimethylation that can be capitalized on for MPNST diagnosis.¹⁹ Negative IHC staining for H3K27 trimethylation has been found to be highly specific for MPNST. Negative staining for different cytokeratin and melanoma markers can be helpful in differentiating it from carcinomas and melanoma. The only curative treatment for MPNST is complete excision, leaving patients with recurrent, refractory, and metastatic cases to be encouraged for enrollment in clinical trials. The 5-year survival rates for patients with MPNST reported in the literature range from 20% to 50%.²⁰