Dermatopathology

New Year, New Codes: A Win-Win for Digital Pathology

In July 2022, the American Medical Association CPT (Current Procedural Terminology) Editorial Panel released 13 new digital pathology add-on Category III codes for 2023 that the College of American Pathologists successfully advocated for inclusion.¹ These codes are for reporting additional clinical staff work and service requirements associated with digitizing glass microscope slides for primary diagnosis (Table). They go into effect on January 1, 2023.

Although there is no additional compensation with the new Category III codes, dermatopathology laboratories will be able to report when they have made a diagnosis using digital pathology. The new CPT codes will provide payers with data they need to directly understand the utilization and increased value of digital pathology, which will bring dermatopathology laboratories one step closer to receiving additional reimbursement for digital interpretation.

The adoption of digital pathology has been accelerating in the United States but still lags behind many European countries where reimbursement for digital pathology has been established for many years. Many of the barriers to digital pathology have improved—cloud storage is more affordable, scanners have a higher throughput, digital pathology platforms have improved, and the US Food and Drug Administration has granted approvals for digital pathology. Digital pathology allows for more efficient workflow, which results in increased productivity and a reduction in turnaround times. It also allows for a wide spectrum of clinical applications and more innovation as well as research and educational applications.

The new Category III codes cannot be reported solely for archival purposes (eg, after the Category I service has already been performed and reported), solely for educational purposes (eg, when services are not used for individual patient reporting), solely for developing a database for training or validation of artificial intelligence algorithms, and solely for clinical conference presentations (eg, tumor board interdisciplinary conferences).

The new codes are a major victory for the adoption and future compensation for digital pathology.

New Year, New Cuts: Proposed 2023 Medicare Policy and Payment Changes for Dermatologists

The United States Spent $3.8 Trillion on Health Care in 2019: Where Did It Go?—In 2019, approximately $3.8 trillion was spent on health care in the United States (Figure 1). Physician services accounted for approximately 15% of total health care spending.²

Medicare Payments for Physician Services—Medicare payments for physician services are determined by a relative value unit (RVU) multiplied by a conversion factor (CF). Relative value units were set up in 1992 by what is now the Centers for Medicare & Medicaid Services, and they calculated the time it took a physician to complete a task or RVU and multiplied it by $32.00 (CF).³

Thirty years later—in 2022—the CF is $34.61. If the CF had increased with inflation, it would be $59.00. If the Proposed Rule is adopted, the 2023 fee schedule payment formula would decrease by 4.4% (to $33.08) relative to that of the 2022 fee schedule ($34.61), which is a decrease of 8.2% since 2019 ($36.04). This decrease is due to expiration of the 3% increase to Medicare fee schedule payments for 2022 required by the Protecting Medicare and American Farmers from Sequester Cuts Act and the required budget neutrality adjustment required by changes in RVUs. Medicare physician payment has declined 22% from 2001 to 2022 (Figure 2).^4,5

The adjustments to the CF typically are made based on 3 factors: (1) the Medicare Economic Index; (2) expenditure target “performance adjustment”; and (3) miscellaneous adjustments, including those for “budget neutrality” required by law.

Medicare Physician Payments Compared With Other Provider Types and Inflation—The proposed Medicare physician payment policy is unsustainable for outpatient dermatologists. Practice overhead has increased markedly since 1992. Other service providers, such as those in skilled nursing facilities and hospitals (Figure 3), have received favorable payment increases compared with practice cost inflation and the Consumer Price Index.^3-6 Flat reimbursement affects all physicians who accept insurance, as even private insurers base their reimbursement on Medicare.

In addition, there are other issues resulting in decreased physician payments when evaluation and management services are reported with same-day procedures using modifier −25 as well as preserving or finding alternative strategies for 10- and 90-day global period payments for medical procedures. When Medicare cuts physician payments, dermatologists find it difficult to own and operate their own practices, resulting in health market consolidation, limited competition, increased health care costs, limited patient access to care, and decreased quality of health care.

Medicare Payment Reform—Medicare payment reform is necessary to stop annual payment cuts and create a stable predictable payment system that ensures patient access to quality, value-based care. Medicare physician payment reform needs to happen at a national level. The American Academy of Dermatology Association (AADA) is working with the House of Medicine and the medical specialty community to develop specific proposals, such as “Characteristics of a Rational Medicare Physician Payment System,” to reform Medicare’s payment system.⁷ Advocacy groups, including the AADA, have been working to mitigate the proposed 2023 cuts by engaging with Congress and urging them to act before these changes go into effect on January 1, 2023.

Make Advocacy Your New Year’s Resolution: AADA’s Top Advocacy Priorities

The AADA’s top priority is Medicare payment policies.³ In addition, the AADA is working on drug access and cost by cutting the bureaucratic red tape caused by prior authorization (PA) and step therapy policies. The AADA collaborates with manufacturers, the health care community, policymakers, private payers, pharmacists, pharmacy benefit managers, and patients to minimize and/or eliminate barriers that patients face in accessing needed medications. Specifically, the AADA advocates for legislation that limits obstacles associated with health insurance step therapy requirements, streamlines PA, and prohibits mid-year formulary changes.⁸

Step therapy requires that patients first try a medication specified by the insurance company; the therapy must fail before the patient is placed on the medication originally prescribed by the provider. Regarding PA, the AADA tries to ensure that determinations are standardized, requires the speed of determinations to be quantified and minimized, and ensures that PA and appeals policies do not unduly burden physicians or patients in accessing optimal drug therapy.⁸

Another advocacy priority is telehealth. The AADA is advocating for legislation on expansion of telehealth in underserved areas and modifications to state licensure requirements, liability issues, and reimbursement for store-and-forward technology. The AADA is involved in protecting scope of practice, truth in advertising, and access to specialty care, as well as monitoring legislation and regulation concerning the potential environmental impact of sunscreen ingredients, indoor tanning restrictions, and skin cancer prevention.⁸

Advocacy Matters and Makes a Difference—It is important to learn about and support advocacy priorities and efforts and join forces to protect your practice. The AADA advocacy priorities are to protect the value of dermatology services, mobilize dermatologists for political action, ensure dermatologists can participate in new payment models, and strengthen the profession.⁹ Physician advocacy is no longer an elective pursuit. We need to be involved and engaged through our medical societies to help patients, communities, and ourselves. All of us are in it together, and a collaborative collective voice can make a difference. Take action, join the AADA, and contact Congress today to stop Medicare payment cuts (https://takeaction.aad.org/).

New Year, New Codes: A Win-Win for Digital Pathology

In July 2022, the American Medical Association CPT (Current Procedural Terminology) Editorial Panel released 13 new digital pathology add-on Category III codes for 2023 that the College of American Pathologists successfully advocated for inclusion.¹ These codes are for reporting additional clinical staff work and service requirements associated with digitizing glass microscope slides for primary diagnosis (Table). They go into effect on January 1, 2023.

Although there is no additional compensation with the new Category III codes, dermatopathology laboratories will be able to report when they have made a diagnosis using digital pathology. The new CPT codes will provide payers with data they need to directly understand the utilization and increased value of digital pathology, which will bring dermatopathology laboratories one step closer to receiving additional reimbursement for digital interpretation.

The adoption of digital pathology has been accelerating in the United States but still lags behind many European countries where reimbursement for digital pathology has been established for many years. Many of the barriers to digital pathology have improved—cloud storage is more affordable, scanners have a higher throughput, digital pathology platforms have improved, and the US Food and Drug Administration has granted approvals for digital pathology. Digital pathology allows for more efficient workflow, which results in increased productivity and a reduction in turnaround times. It also allows for a wide spectrum of clinical applications and more innovation as well as research and educational applications.

The new Category III codes cannot be reported solely for archival purposes (eg, after the Category I service has already been performed and reported), solely for educational purposes (eg, when services are not used for individual patient reporting), solely for developing a database for training or validation of artificial intelligence algorithms, and solely for clinical conference presentations (eg, tumor board interdisciplinary conferences).

The new codes are a major victory for the adoption and future compensation for digital pathology.

New Year, New Cuts: Proposed 2023 Medicare Policy and Payment Changes for Dermatologists

The United States Spent $3.8 Trillion on Health Care in 2019: Where Did It Go?—In 2019, approximately $3.8 trillion was spent on health care in the United States (Figure 1). Physician services accounted for approximately 15% of total health care spending.²

Medicare Payments for Physician Services—Medicare payments for physician services are determined by a relative value unit (RVU) multiplied by a conversion factor (CF). Relative value units were set up in 1992 by what is now the Centers for Medicare & Medicaid Services, and they calculated the time it took a physician to complete a task or RVU and multiplied it by $32.00 (CF).³

Thirty years later—in 2022—the CF is $34.61. If the CF had increased with inflation, it would be $59.00. If the Proposed Rule is adopted, the 2023 fee schedule payment formula would decrease by 4.4% (to $33.08) relative to that of the 2022 fee schedule ($34.61), which is a decrease of 8.2% since 2019 ($36.04). This decrease is due to expiration of the 3% increase to Medicare fee schedule payments for 2022 required by the Protecting Medicare and American Farmers from Sequester Cuts Act and the required budget neutrality adjustment required by changes in RVUs. Medicare physician payment has declined 22% from 2001 to 2022 (Figure 2).^4,5

The adjustments to the CF typically are made based on 3 factors: (1) the Medicare Economic Index; (2) expenditure target “performance adjustment”; and (3) miscellaneous adjustments, including those for “budget neutrality” required by law.

Medicare Physician Payments Compared With Other Provider Types and Inflation—The proposed Medicare physician payment policy is unsustainable for outpatient dermatologists. Practice overhead has increased markedly since 1992. Other service providers, such as those in skilled nursing facilities and hospitals (Figure 3), have received favorable payment increases compared with practice cost inflation and the Consumer Price Index.^3-6 Flat reimbursement affects all physicians who accept insurance, as even private insurers base their reimbursement on Medicare.

In addition, there are other issues resulting in decreased physician payments when evaluation and management services are reported with same-day procedures using modifier −25 as well as preserving or finding alternative strategies for 10- and 90-day global period payments for medical procedures. When Medicare cuts physician payments, dermatologists find it difficult to own and operate their own practices, resulting in health market consolidation, limited competition, increased health care costs, limited patient access to care, and decreased quality of health care.

Medicare Payment Reform—Medicare payment reform is necessary to stop annual payment cuts and create a stable predictable payment system that ensures patient access to quality, value-based care. Medicare physician payment reform needs to happen at a national level. The American Academy of Dermatology Association (AADA) is working with the House of Medicine and the medical specialty community to develop specific proposals, such as “Characteristics of a Rational Medicare Physician Payment System,” to reform Medicare’s payment system.⁷ Advocacy groups, including the AADA, have been working to mitigate the proposed 2023 cuts by engaging with Congress and urging them to act before these changes go into effect on January 1, 2023.

Make Advocacy Your New Year’s Resolution: AADA’s Top Advocacy Priorities

The AADA’s top priority is Medicare payment policies.³ In addition, the AADA is working on drug access and cost by cutting the bureaucratic red tape caused by prior authorization (PA) and step therapy policies. The AADA collaborates with manufacturers, the health care community, policymakers, private payers, pharmacists, pharmacy benefit managers, and patients to minimize and/or eliminate barriers that patients face in accessing needed medications. Specifically, the AADA advocates for legislation that limits obstacles associated with health insurance step therapy requirements, streamlines PA, and prohibits mid-year formulary changes.⁸

Step therapy requires that patients first try a medication specified by the insurance company; the therapy must fail before the patient is placed on the medication originally prescribed by the provider. Regarding PA, the AADA tries to ensure that determinations are standardized, requires the speed of determinations to be quantified and minimized, and ensures that PA and appeals policies do not unduly burden physicians or patients in accessing optimal drug therapy.⁸

Another advocacy priority is telehealth. The AADA is advocating for legislation on expansion of telehealth in underserved areas and modifications to state licensure requirements, liability issues, and reimbursement for store-and-forward technology. The AADA is involved in protecting scope of practice, truth in advertising, and access to specialty care, as well as monitoring legislation and regulation concerning the potential environmental impact of sunscreen ingredients, indoor tanning restrictions, and skin cancer prevention.⁸

Advocacy Matters and Makes a Difference—It is important to learn about and support advocacy priorities and efforts and join forces to protect your practice. The AADA advocacy priorities are to protect the value of dermatology services, mobilize dermatologists for political action, ensure dermatologists can participate in new payment models, and strengthen the profession.⁹ Physician advocacy is no longer an elective pursuit. We need to be involved and engaged through our medical societies to help patients, communities, and ourselves. All of us are in it together, and a collaborative collective voice can make a difference. Take action, join the AADA, and contact Congress today to stop Medicare payment cuts (https://takeaction.aad.org/).

New Year, New Codes: A Win-Win for Digital Pathology

In July 2022, the American Medical Association CPT (Current Procedural Terminology) Editorial Panel released 13 new digital pathology add-on Category III codes for 2023 that the College of American Pathologists successfully advocated for inclusion.¹ These codes are for reporting additional clinical staff work and service requirements associated with digitizing glass microscope slides for primary diagnosis (Table). They go into effect on January 1, 2023.

Although there is no additional compensation with the new Category III codes, dermatopathology laboratories will be able to report when they have made a diagnosis using digital pathology. The new CPT codes will provide payers with data they need to directly understand the utilization and increased value of digital pathology, which will bring dermatopathology laboratories one step closer to receiving additional reimbursement for digital interpretation.

The adoption of digital pathology has been accelerating in the United States but still lags behind many European countries where reimbursement for digital pathology has been established for many years. Many of the barriers to digital pathology have improved—cloud storage is more affordable, scanners have a higher throughput, digital pathology platforms have improved, and the US Food and Drug Administration has granted approvals for digital pathology. Digital pathology allows for more efficient workflow, which results in increased productivity and a reduction in turnaround times. It also allows for a wide spectrum of clinical applications and more innovation as well as research and educational applications.

The new Category III codes cannot be reported solely for archival purposes (eg, after the Category I service has already been performed and reported), solely for educational purposes (eg, when services are not used for individual patient reporting), solely for developing a database for training or validation of artificial intelligence algorithms, and solely for clinical conference presentations (eg, tumor board interdisciplinary conferences).

The new codes are a major victory for the adoption and future compensation for digital pathology.

New Year, New Cuts: Proposed 2023 Medicare Policy and Payment Changes for Dermatologists

The United States Spent $3.8 Trillion on Health Care in 2019: Where Did It Go?—In 2019, approximately $3.8 trillion was spent on health care in the United States (Figure 1). Physician services accounted for approximately 15% of total health care spending.²

Medicare Payments for Physician Services—Medicare payments for physician services are determined by a relative value unit (RVU) multiplied by a conversion factor (CF). Relative value units were set up in 1992 by what is now the Centers for Medicare & Medicaid Services, and they calculated the time it took a physician to complete a task or RVU and multiplied it by $32.00 (CF).³

Thirty years later—in 2022—the CF is $34.61. If the CF had increased with inflation, it would be $59.00. If the Proposed Rule is adopted, the 2023 fee schedule payment formula would decrease by 4.4% (to $33.08) relative to that of the 2022 fee schedule ($34.61), which is a decrease of 8.2% since 2019 ($36.04). This decrease is due to expiration of the 3% increase to Medicare fee schedule payments for 2022 required by the Protecting Medicare and American Farmers from Sequester Cuts Act and the required budget neutrality adjustment required by changes in RVUs. Medicare physician payment has declined 22% from 2001 to 2022 (Figure 2).^4,5

The adjustments to the CF typically are made based on 3 factors: (1) the Medicare Economic Index; (2) expenditure target “performance adjustment”; and (3) miscellaneous adjustments, including those for “budget neutrality” required by law.

Medicare Physician Payments Compared With Other Provider Types and Inflation—The proposed Medicare physician payment policy is unsustainable for outpatient dermatologists. Practice overhead has increased markedly since 1992. Other service providers, such as those in skilled nursing facilities and hospitals (Figure 3), have received favorable payment increases compared with practice cost inflation and the Consumer Price Index.^3-6 Flat reimbursement affects all physicians who accept insurance, as even private insurers base their reimbursement on Medicare.

In addition, there are other issues resulting in decreased physician payments when evaluation and management services are reported with same-day procedures using modifier −25 as well as preserving or finding alternative strategies for 10- and 90-day global period payments for medical procedures. When Medicare cuts physician payments, dermatologists find it difficult to own and operate their own practices, resulting in health market consolidation, limited competition, increased health care costs, limited patient access to care, and decreased quality of health care.

Medicare Payment Reform—Medicare payment reform is necessary to stop annual payment cuts and create a stable predictable payment system that ensures patient access to quality, value-based care. Medicare physician payment reform needs to happen at a national level. The American Academy of Dermatology Association (AADA) is working with the House of Medicine and the medical specialty community to develop specific proposals, such as “Characteristics of a Rational Medicare Physician Payment System,” to reform Medicare’s payment system.⁷ Advocacy groups, including the AADA, have been working to mitigate the proposed 2023 cuts by engaging with Congress and urging them to act before these changes go into effect on January 1, 2023.

Make Advocacy Your New Year’s Resolution: AADA’s Top Advocacy Priorities

The AADA’s top priority is Medicare payment policies.³ In addition, the AADA is working on drug access and cost by cutting the bureaucratic red tape caused by prior authorization (PA) and step therapy policies. The AADA collaborates with manufacturers, the health care community, policymakers, private payers, pharmacists, pharmacy benefit managers, and patients to minimize and/or eliminate barriers that patients face in accessing needed medications. Specifically, the AADA advocates for legislation that limits obstacles associated with health insurance step therapy requirements, streamlines PA, and prohibits mid-year formulary changes.⁸

Step therapy requires that patients first try a medication specified by the insurance company; the therapy must fail before the patient is placed on the medication originally prescribed by the provider. Regarding PA, the AADA tries to ensure that determinations are standardized, requires the speed of determinations to be quantified and minimized, and ensures that PA and appeals policies do not unduly burden physicians or patients in accessing optimal drug therapy.⁸

Another advocacy priority is telehealth. The AADA is advocating for legislation on expansion of telehealth in underserved areas and modifications to state licensure requirements, liability issues, and reimbursement for store-and-forward technology. The AADA is involved in protecting scope of practice, truth in advertising, and access to specialty care, as well as monitoring legislation and regulation concerning the potential environmental impact of sunscreen ingredients, indoor tanning restrictions, and skin cancer prevention.⁸

Advocacy Matters and Makes a Difference—It is important to learn about and support advocacy priorities and efforts and join forces to protect your practice. The AADA advocacy priorities are to protect the value of dermatology services, mobilize dermatologists for political action, ensure dermatologists can participate in new payment models, and strengthen the profession.⁹ Physician advocacy is no longer an elective pursuit. We need to be involved and engaged through our medical societies to help patients, communities, and ourselves. All of us are in it together, and a collaborative collective voice can make a difference. Take action, join the AADA, and contact Congress today to stop Medicare payment cuts (https://takeaction.aad.org/).

The Diagnosis: Mid-Borderline Multibacillary Leprosy

The biopsies showed a granulomatous dermatitis involving the dermis and subcutaneous adipose tissue (Figure, A). Fite staining also revealed numerous acid-fast bacilli (AFB) throughout the dermis (Figure, B); however, polymerase chain reaction (PCR) for Mycobacterium tuberculosis was negative, and concomitant AFB tissue culture showed no growth after 8 weeks of incubation from the left wrist biopsy (Table). Interestingly, a left inguinal lymph node biopsy performed 6 months prior to presentation that helped to establish the diagnosis of follicular lymphoma also revealed nonnecrotizing granulomas and the presence of rare AFB; this formalin-fixed specimen subsequently tested negative for M tuberculosis and nontuberculous mycobacteria (NTM) by broad-range PCR. Due to a high index of suspicion, another unpreserved skin biopsy of the right knee was sent for NTM testing with PCR. Primers to 16S ribosomal RNA and the beta subunit of RNA polymerase, rpoB, gene detected Mycobacterium leprae DNA, leading to the diagnosis of mid-borderline (or borderline-borderline) multibacillary leprosy. Our patient subsequently reported subtle hypoesthesia of the plaques on the knees. He recalled eating undercooked armadillo meat in the southern United States more than 30 years prior to admission. In addition, he had a history of being incarcerated in the northeastern United States. This case was reported to the National Hansen’s Disease Program, and our patient was started on a 2-year course of daily clarithromycin, daily minocycline, and once-monthly moxifloxacin. His family also was evaluated and did not have any skin lesions concerning for leprosy.

Leprosy is a major global health concern, transmitted via breaks in the skin, respiratory secretions, and contact with armadillos. It continues to be endemic in India, Brazil, and Indonesia.¹ In the United States where leprosy is nonendemic, 159 new cases were detected in 2020; the most notable risk factors in the United States are armadillo exposure and travel history.^2,3Mycobacterium leprae are intracellular bacilli that preferentially infect macrophages and Schwann cells, resulting in erythematous or hypopigmented skin lesions that often are anesthetic. Mycobacterium leprae has the longest doubling time of all bacteria with unknown in vitro growth requirements and a typical in vivo incubation period of 2 to 10 years.⁴ Therefore, in vitro cultures will yield no growth, as seen in our case. In our patient, Fite stain showed acid-fast organisms in multiple tissue specimens, but AFB cultures demonstrated no growth after 8 weeks of incubation. Although clinicopathologic correlation is most important, PCR analysis can help to assist in the diagnosis of leprosy. Unpreserved tissue should be used when possible, as the fixation process may adversely affect the analytic sensitivity of subsequent PCR-based assays.⁵ In our case, NTM were not detected by PCR in the inguinal lymph node specimen despite demonstrating rare AFB staining. This result likely was multifactorial, including the effect of formalin fixation and paraffin embedding as well as concomitant low biomass.

Leprosy is known as a great imitator, and clinical manifestations (both neurologic and cutaneous) depend on host immune response to the mycobacteria. Although tuberculoid leprosy (associated with T helper type 1 immune response) is distinguished by few asymmetric, well-demarcated, and often hypopigmented plaques, lepromatous leprosy (associated with T helper type 2 response) is characterized by numerous symmetric and poorly defined lesions. Borderline leprosy, as seen in our patient, is the most common type of leprosy and shows features of both tuberculoid and lepromatous leprosy.⁴ It also may be particularly difficult to diagnose.^6,7 Borderline-borderline leprosy involves lesions that mostly are of the lepromatous type and symmetric but also may include raised plaques, as in tuberculoid leprosy.⁴ Plaques in an annular configuration with central clearing, as seen in our patient, are considered suggestive.⁸ Histopathology of borderline-borderline leprosy lesions shows subepidermal clear zones, and granulomas are more diffuse than in tuberculoid leprosy.⁴

Given the noncaseating granulomatous dermatitis seen on histopathology and the relatively higher incidence of sarcoidosis in our region of practice, our initial differential included sarcoidosis and other granulomatous disorders such as granuloma annulare. Interestingly, sarcoidosis has been misdiagnosed as leprosy on multiple occasions in countries where leprosy is endemic.^9,10 Localized cutaneous leishmaniasis typically presents with infiltrated plaques and nodules that may ulcerate; diffuse and disseminated as well as mucocutaneous presentations may occur depending on the species and severity of infection. Parasitized macrophages containing amastigotes may be seen in the dermis highlighted by CD1a immunostaining. Mycosis fungoides presents as papulosquamous patches or plaques, often favoring sunprotected sites; the hypopigmented variant may mimic the central clearing seen in leprosy.

The diagnosis of leprosy can be challenging due to varying clinical presentation; indolent growth of the causative organism; and indeterminate nature of stains, including the Fite stain. Although leprosy is an uncommon diagnosis, this case underscores the need to keep it in the differential of granulomatous dermatoses in the appropriate clinical setting, particularly in patients with risk factors for exposure.⁸

The Diagnosis: Mid-Borderline Multibacillary Leprosy

The biopsies showed a granulomatous dermatitis involving the dermis and subcutaneous adipose tissue (Figure, A). Fite staining also revealed numerous acid-fast bacilli (AFB) throughout the dermis (Figure, B); however, polymerase chain reaction (PCR) for Mycobacterium tuberculosis was negative, and concomitant AFB tissue culture showed no growth after 8 weeks of incubation from the left wrist biopsy (Table). Interestingly, a left inguinal lymph node biopsy performed 6 months prior to presentation that helped to establish the diagnosis of follicular lymphoma also revealed nonnecrotizing granulomas and the presence of rare AFB; this formalin-fixed specimen subsequently tested negative for M tuberculosis and nontuberculous mycobacteria (NTM) by broad-range PCR. Due to a high index of suspicion, another unpreserved skin biopsy of the right knee was sent for NTM testing with PCR. Primers to 16S ribosomal RNA and the beta subunit of RNA polymerase, rpoB, gene detected Mycobacterium leprae DNA, leading to the diagnosis of mid-borderline (or borderline-borderline) multibacillary leprosy. Our patient subsequently reported subtle hypoesthesia of the plaques on the knees. He recalled eating undercooked armadillo meat in the southern United States more than 30 years prior to admission. In addition, he had a history of being incarcerated in the northeastern United States. This case was reported to the National Hansen’s Disease Program, and our patient was started on a 2-year course of daily clarithromycin, daily minocycline, and once-monthly moxifloxacin. His family also was evaluated and did not have any skin lesions concerning for leprosy.

Leprosy is a major global health concern, transmitted via breaks in the skin, respiratory secretions, and contact with armadillos. It continues to be endemic in India, Brazil, and Indonesia.¹ In the United States where leprosy is nonendemic, 159 new cases were detected in 2020; the most notable risk factors in the United States are armadillo exposure and travel history.^2,3Mycobacterium leprae are intracellular bacilli that preferentially infect macrophages and Schwann cells, resulting in erythematous or hypopigmented skin lesions that often are anesthetic. Mycobacterium leprae has the longest doubling time of all bacteria with unknown in vitro growth requirements and a typical in vivo incubation period of 2 to 10 years.⁴ Therefore, in vitro cultures will yield no growth, as seen in our case. In our patient, Fite stain showed acid-fast organisms in multiple tissue specimens, but AFB cultures demonstrated no growth after 8 weeks of incubation. Although clinicopathologic correlation is most important, PCR analysis can help to assist in the diagnosis of leprosy. Unpreserved tissue should be used when possible, as the fixation process may adversely affect the analytic sensitivity of subsequent PCR-based assays.⁵ In our case, NTM were not detected by PCR in the inguinal lymph node specimen despite demonstrating rare AFB staining. This result likely was multifactorial, including the effect of formalin fixation and paraffin embedding as well as concomitant low biomass.

Leprosy is known as a great imitator, and clinical manifestations (both neurologic and cutaneous) depend on host immune response to the mycobacteria. Although tuberculoid leprosy (associated with T helper type 1 immune response) is distinguished by few asymmetric, well-demarcated, and often hypopigmented plaques, lepromatous leprosy (associated with T helper type 2 response) is characterized by numerous symmetric and poorly defined lesions. Borderline leprosy, as seen in our patient, is the most common type of leprosy and shows features of both tuberculoid and lepromatous leprosy.⁴ It also may be particularly difficult to diagnose.^6,7 Borderline-borderline leprosy involves lesions that mostly are of the lepromatous type and symmetric but also may include raised plaques, as in tuberculoid leprosy.⁴ Plaques in an annular configuration with central clearing, as seen in our patient, are considered suggestive.⁸ Histopathology of borderline-borderline leprosy lesions shows subepidermal clear zones, and granulomas are more diffuse than in tuberculoid leprosy.⁴

Given the noncaseating granulomatous dermatitis seen on histopathology and the relatively higher incidence of sarcoidosis in our region of practice, our initial differential included sarcoidosis and other granulomatous disorders such as granuloma annulare. Interestingly, sarcoidosis has been misdiagnosed as leprosy on multiple occasions in countries where leprosy is endemic.^9,10 Localized cutaneous leishmaniasis typically presents with infiltrated plaques and nodules that may ulcerate; diffuse and disseminated as well as mucocutaneous presentations may occur depending on the species and severity of infection. Parasitized macrophages containing amastigotes may be seen in the dermis highlighted by CD1a immunostaining. Mycosis fungoides presents as papulosquamous patches or plaques, often favoring sunprotected sites; the hypopigmented variant may mimic the central clearing seen in leprosy.

The diagnosis of leprosy can be challenging due to varying clinical presentation; indolent growth of the causative organism; and indeterminate nature of stains, including the Fite stain. Although leprosy is an uncommon diagnosis, this case underscores the need to keep it in the differential of granulomatous dermatoses in the appropriate clinical setting, particularly in patients with risk factors for exposure.⁸

The Diagnosis: Mid-Borderline Multibacillary Leprosy

The biopsies showed a granulomatous dermatitis involving the dermis and subcutaneous adipose tissue (Figure, A). Fite staining also revealed numerous acid-fast bacilli (AFB) throughout the dermis (Figure, B); however, polymerase chain reaction (PCR) for Mycobacterium tuberculosis was negative, and concomitant AFB tissue culture showed no growth after 8 weeks of incubation from the left wrist biopsy (Table). Interestingly, a left inguinal lymph node biopsy performed 6 months prior to presentation that helped to establish the diagnosis of follicular lymphoma also revealed nonnecrotizing granulomas and the presence of rare AFB; this formalin-fixed specimen subsequently tested negative for M tuberculosis and nontuberculous mycobacteria (NTM) by broad-range PCR. Due to a high index of suspicion, another unpreserved skin biopsy of the right knee was sent for NTM testing with PCR. Primers to 16S ribosomal RNA and the beta subunit of RNA polymerase, rpoB, gene detected Mycobacterium leprae DNA, leading to the diagnosis of mid-borderline (or borderline-borderline) multibacillary leprosy. Our patient subsequently reported subtle hypoesthesia of the plaques on the knees. He recalled eating undercooked armadillo meat in the southern United States more than 30 years prior to admission. In addition, he had a history of being incarcerated in the northeastern United States. This case was reported to the National Hansen’s Disease Program, and our patient was started on a 2-year course of daily clarithromycin, daily minocycline, and once-monthly moxifloxacin. His family also was evaluated and did not have any skin lesions concerning for leprosy.

Leprosy is a major global health concern, transmitted via breaks in the skin, respiratory secretions, and contact with armadillos. It continues to be endemic in India, Brazil, and Indonesia.¹ In the United States where leprosy is nonendemic, 159 new cases were detected in 2020; the most notable risk factors in the United States are armadillo exposure and travel history.^2,3Mycobacterium leprae are intracellular bacilli that preferentially infect macrophages and Schwann cells, resulting in erythematous or hypopigmented skin lesions that often are anesthetic. Mycobacterium leprae has the longest doubling time of all bacteria with unknown in vitro growth requirements and a typical in vivo incubation period of 2 to 10 years.⁴ Therefore, in vitro cultures will yield no growth, as seen in our case. In our patient, Fite stain showed acid-fast organisms in multiple tissue specimens, but AFB cultures demonstrated no growth after 8 weeks of incubation. Although clinicopathologic correlation is most important, PCR analysis can help to assist in the diagnosis of leprosy. Unpreserved tissue should be used when possible, as the fixation process may adversely affect the analytic sensitivity of subsequent PCR-based assays.⁵ In our case, NTM were not detected by PCR in the inguinal lymph node specimen despite demonstrating rare AFB staining. This result likely was multifactorial, including the effect of formalin fixation and paraffin embedding as well as concomitant low biomass.

Leprosy is known as a great imitator, and clinical manifestations (both neurologic and cutaneous) depend on host immune response to the mycobacteria. Although tuberculoid leprosy (associated with T helper type 1 immune response) is distinguished by few asymmetric, well-demarcated, and often hypopigmented plaques, lepromatous leprosy (associated with T helper type 2 response) is characterized by numerous symmetric and poorly defined lesions. Borderline leprosy, as seen in our patient, is the most common type of leprosy and shows features of both tuberculoid and lepromatous leprosy.⁴ It also may be particularly difficult to diagnose.^6,7 Borderline-borderline leprosy involves lesions that mostly are of the lepromatous type and symmetric but also may include raised plaques, as in tuberculoid leprosy.⁴ Plaques in an annular configuration with central clearing, as seen in our patient, are considered suggestive.⁸ Histopathology of borderline-borderline leprosy lesions shows subepidermal clear zones, and granulomas are more diffuse than in tuberculoid leprosy.⁴

Given the noncaseating granulomatous dermatitis seen on histopathology and the relatively higher incidence of sarcoidosis in our region of practice, our initial differential included sarcoidosis and other granulomatous disorders such as granuloma annulare. Interestingly, sarcoidosis has been misdiagnosed as leprosy on multiple occasions in countries where leprosy is endemic.^9,10 Localized cutaneous leishmaniasis typically presents with infiltrated plaques and nodules that may ulcerate; diffuse and disseminated as well as mucocutaneous presentations may occur depending on the species and severity of infection. Parasitized macrophages containing amastigotes may be seen in the dermis highlighted by CD1a immunostaining. Mycosis fungoides presents as papulosquamous patches or plaques, often favoring sunprotected sites; the hypopigmented variant may mimic the central clearing seen in leprosy.

The diagnosis of leprosy can be challenging due to varying clinical presentation; indolent growth of the causative organism; and indeterminate nature of stains, including the Fite stain. Although leprosy is an uncommon diagnosis, this case underscores the need to keep it in the differential of granulomatous dermatoses in the appropriate clinical setting, particularly in patients with risk factors for exposure.⁸

The Diagnosis: Solitary Sclerotic Fibroma

Based on the clinical and histologic findings, the patient was diagnosed with solitary sclerotic fibroma (SF). Sclerotic fibroma is a rare benign tumor that first was described in 1972 by Weary et al¹ in the oral mucosa of a patient with Cowden syndrome, a genodermatosis associated with multiple benign and malignant tumors. Rapini and Golitz² reported solitary SF in 11 otherwise-healthy individuals with no signs of multiple hamartoma syndrome. Solitary SF is a sporadic benign condition, whereas multiple lesions are suggestive of Cowden syndrome. Solitary SF most commonly appears as an asymptomatic white-yellow papule or nodule on the head or neck, though larger tumors have been reported on the trunk and extremities.³ Histologic features of solitary SF include a well-circumscribed dermal nodule composed of eosinophilic dense collagen bundles arranged in a plywoodlike pattern (Figure). Immunohistochemistry is positive for CD34 and vimentin but negative for S-100, epithelial membrane antigen, and neuron-specific enolase.⁴

The differential diagnosis of solitary SF of the head and neck includes sebaceous adenoma, pilar cyst, nodular basal cell carcinoma, and giant molluscum contagiosum. Sebaceous adenomas usually are solitary yellow nodules less than 1 cm in diameter and located on the head and neck. They are the most common sebaceous neoplasm associated with Muir-Torre syndrome, an autosomal-dominant disorder characterized by sebaceous adenoma or carcinoma and colorectal cancer. Histopathology demonstrates well-circumscribed, round aggregations of mature lipid-filled sebocytes with a rim of basaloid germinative cells at the periphery. Pilar cysts typically are flesh-colored subcutaneous nodules on the scalp that are freely mobile over underlying tissue. Histopathology shows stratified squamous epithelium lining and trichilemmal keratinization. Nodular basal cell carcinoma has a pearly translucent appearance and arborizing telangiectases. Histopathology demonstrates nests of basaloid cells with palisading of the cells at the periphery. Giant solitary molluscum contagiosum is a dome-shaped, flesh-colored nodule with central umbilication. Histopathology reveals hyperplastic squamous epithelium with characteristic eosinophilic inclusion bodies above the basal layer.

Solitary SF can be difficult to diagnose based solely on the clinical presentation; thus biopsy with histologic evaluation is recommended. If SF is confirmed, the clinician should inquire about a family history of Cowden syndrome and then perform a total-body skin examination to check for multiple SF and other clinical hamartomas of Cowden syndrome such as trichilemmomas, acral keratosis, and oral papillomas.

The Diagnosis: Solitary Sclerotic Fibroma

Based on the clinical and histologic findings, the patient was diagnosed with solitary sclerotic fibroma (SF). Sclerotic fibroma is a rare benign tumor that first was described in 1972 by Weary et al¹ in the oral mucosa of a patient with Cowden syndrome, a genodermatosis associated with multiple benign and malignant tumors. Rapini and Golitz² reported solitary SF in 11 otherwise-healthy individuals with no signs of multiple hamartoma syndrome. Solitary SF is a sporadic benign condition, whereas multiple lesions are suggestive of Cowden syndrome. Solitary SF most commonly appears as an asymptomatic white-yellow papule or nodule on the head or neck, though larger tumors have been reported on the trunk and extremities.³ Histologic features of solitary SF include a well-circumscribed dermal nodule composed of eosinophilic dense collagen bundles arranged in a plywoodlike pattern (Figure). Immunohistochemistry is positive for CD34 and vimentin but negative for S-100, epithelial membrane antigen, and neuron-specific enolase.⁴

The differential diagnosis of solitary SF of the head and neck includes sebaceous adenoma, pilar cyst, nodular basal cell carcinoma, and giant molluscum contagiosum. Sebaceous adenomas usually are solitary yellow nodules less than 1 cm in diameter and located on the head and neck. They are the most common sebaceous neoplasm associated with Muir-Torre syndrome, an autosomal-dominant disorder characterized by sebaceous adenoma or carcinoma and colorectal cancer. Histopathology demonstrates well-circumscribed, round aggregations of mature lipid-filled sebocytes with a rim of basaloid germinative cells at the periphery. Pilar cysts typically are flesh-colored subcutaneous nodules on the scalp that are freely mobile over underlying tissue. Histopathology shows stratified squamous epithelium lining and trichilemmal keratinization. Nodular basal cell carcinoma has a pearly translucent appearance and arborizing telangiectases. Histopathology demonstrates nests of basaloid cells with palisading of the cells at the periphery. Giant solitary molluscum contagiosum is a dome-shaped, flesh-colored nodule with central umbilication. Histopathology reveals hyperplastic squamous epithelium with characteristic eosinophilic inclusion bodies above the basal layer.

Solitary SF can be difficult to diagnose based solely on the clinical presentation; thus biopsy with histologic evaluation is recommended. If SF is confirmed, the clinician should inquire about a family history of Cowden syndrome and then perform a total-body skin examination to check for multiple SF and other clinical hamartomas of Cowden syndrome such as trichilemmomas, acral keratosis, and oral papillomas.

The Diagnosis: Solitary Sclerotic Fibroma

Based on the clinical and histologic findings, the patient was diagnosed with solitary sclerotic fibroma (SF). Sclerotic fibroma is a rare benign tumor that first was described in 1972 by Weary et al¹ in the oral mucosa of a patient with Cowden syndrome, a genodermatosis associated with multiple benign and malignant tumors. Rapini and Golitz² reported solitary SF in 11 otherwise-healthy individuals with no signs of multiple hamartoma syndrome. Solitary SF is a sporadic benign condition, whereas multiple lesions are suggestive of Cowden syndrome. Solitary SF most commonly appears as an asymptomatic white-yellow papule or nodule on the head or neck, though larger tumors have been reported on the trunk and extremities.³ Histologic features of solitary SF include a well-circumscribed dermal nodule composed of eosinophilic dense collagen bundles arranged in a plywoodlike pattern (Figure). Immunohistochemistry is positive for CD34 and vimentin but negative for S-100, epithelial membrane antigen, and neuron-specific enolase.⁴

The differential diagnosis of solitary SF of the head and neck includes sebaceous adenoma, pilar cyst, nodular basal cell carcinoma, and giant molluscum contagiosum. Sebaceous adenomas usually are solitary yellow nodules less than 1 cm in diameter and located on the head and neck. They are the most common sebaceous neoplasm associated with Muir-Torre syndrome, an autosomal-dominant disorder characterized by sebaceous adenoma or carcinoma and colorectal cancer. Histopathology demonstrates well-circumscribed, round aggregations of mature lipid-filled sebocytes with a rim of basaloid germinative cells at the periphery. Pilar cysts typically are flesh-colored subcutaneous nodules on the scalp that are freely mobile over underlying tissue. Histopathology shows stratified squamous epithelium lining and trichilemmal keratinization. Nodular basal cell carcinoma has a pearly translucent appearance and arborizing telangiectases. Histopathology demonstrates nests of basaloid cells with palisading of the cells at the periphery. Giant solitary molluscum contagiosum is a dome-shaped, flesh-colored nodule with central umbilication. Histopathology reveals hyperplastic squamous epithelium with characteristic eosinophilic inclusion bodies above the basal layer.

Solitary SF can be difficult to diagnose based solely on the clinical presentation; thus biopsy with histologic evaluation is recommended. If SF is confirmed, the clinician should inquire about a family history of Cowden syndrome and then perform a total-body skin examination to check for multiple SF and other clinical hamartomas of Cowden syndrome such as trichilemmomas, acral keratosis, and oral papillomas.

To the Editor:

The posttraumatic pseudolipoma (PTL) is a painless localized mass comprised of unencapsulated adipose tissue that develops at the site of acute or prolonged blunt soft tissue trauma. It may be round or fusiform in shape and has areas of saponification leading to fat necrosis.¹ Posttraumatic pseudolipomas are 12 times more likely to occur in females, which may be attributed to sex-determined adipose tissue distribution or cosmetic concerns.² Most PTLs are found in areas of the body with high adiposity, including the hip, thigh, and gluteal regions.³ A patient history of a traumatic event resulting in a hematoma and a subsequent latent period of several months to years before the pseudolipoma formation occurs is common.^1,2,4-6

A 27-year-old woman presented to the family medicine clinic for examination of a deformity on the right buttock. She noticed a soft protruding mass months after landing on the buttocks and on top of a stick during routine physical training. Prior ultrasonography of the deformity proved unhelpful in determining the etiology. Physical examination revealed a protruding, 2-cm, flesh-colored mass on the right buttock intergluteal fold that was soft, compressible, and nontender (Figure 1). There was no capsule, nodule, loculation, or sinus tract. The patient underwent excisional resection with findings of benign-appearing unencapsulated adipose tissue (Figure 2). The wound was closed without difficulty. After several weeks, she had a well-healing scar without contour deficits of the buttocks. Two to 3 months after the initial repair, the patient presented to the family medicine clinic with recurrence of the fatty protrusion. She was referred for consultation and definitive management to a plastic surgeon but was lost to follow up.

In a systematic review of the literature to research pathogenesis theories, a PubMed search of articles indexed for MEDLINE using the terms trauma and pseudolipoma, lipoma, fat, or adipose yielded 45 citations, with only 10 publications addressing the pathology specific to pseudolipomas. Two leading theories of the pathogenesis of PTLs include the adipose herniation pathway and the inflammatory proliferation pathway.^4,5

Adipose tissue comprises fat lobules that are organized underneath the supportive elastic fascial layers. Injury from forces exceeding the fascial strength is the basis for the oldest pathogenesis theory. The adipose herniation theory suggests that fat lobules are displaced through the damaged septae, allowing for the development of an epidermal pseudolipoma at the site of blunt trauma.⁷ This theory has been supported by many case reports; however, more recent reports have identified a larger number of PTL cases that showed no identifiable disruptions in the fascia.^1,4,8

In 1997, the inflammatory proliferation theory began to gain attention. The theory describes how local tissue trauma leads to the release of inflammatory cytokines, which successively signals the development of preadipocytes or adipose tissue–derived stem cells (ASCs) into mature adipocytes.⁴ Most patients report a history of a hematoma in the area of pseudolipoma development, which strongly supports this newer theory. Studies exploring hematomas have found elevated levels of growth factors and inflammatory markers.^2,9 In particular, tumor necrosis factor α, peroxisome proliferator–activated receptor γ, vascular endothelial growth factor, and IL-6 and IL-8 may foster an environment in which adipogenic cells are both chemotaxed to the area of trauma and differentiated to white adipose tissue.^2,10

Despite addressing the role of the preadipocyte, the available research fails to address the general development of mesenchymal cells into the preadipocyte. White adipose tissue develops at sites of neovascularization and frequently has been observed spreading into the nearby tissue toward other blood vessels. Furthermore, these white adipose tissue expansions remain reliant on multiple growth factors and cell-signaling molecules.¹⁰ Numerous investigations into stem cell grafting have found that implantation of ASCs in vivo within animal models does not result in the proliferation and differentiation of ASCs unless specific conditions have been met such as prior tissue injury or immunodeficiency.^10-12 These investigations support and expand on the inflammatory proliferation pathway. Thus, most of the true PTLs in the available research appear as de novo tumors and are more congruent with the inflammatory proliferation model.^1,2,4-6,8

Typical treatment of a PTL is surgical excision or liposuction depending on the pathology and size of the pseudolipoma. Biopsy examination prior to liposuction is critical for evaluation of liposarcoma and may help identify damage to Scarpa fascia. Recurrence of a PTL is rare regardless of treatment method; however, in a study of 31 PTL cases, only 6 were pathologically identified as PTLs without fibrous material.¹

Our patient experienced a blunt trauma to the buttocks and subsequently developed a PTL that was surgically excised and recurred within 3 months. Research surrounding the pathogenesis of the PTL has evolved from the theory of physical herniation of adipose tissue to an inflammatory differentiation of preadipocytes, but there is still much to learn about how and why it occurs and the mesenchymal differentiation following tissue injury.

To the Editor:

The posttraumatic pseudolipoma (PTL) is a painless localized mass comprised of unencapsulated adipose tissue that develops at the site of acute or prolonged blunt soft tissue trauma. It may be round or fusiform in shape and has areas of saponification leading to fat necrosis.¹ Posttraumatic pseudolipomas are 12 times more likely to occur in females, which may be attributed to sex-determined adipose tissue distribution or cosmetic concerns.² Most PTLs are found in areas of the body with high adiposity, including the hip, thigh, and gluteal regions.³ A patient history of a traumatic event resulting in a hematoma and a subsequent latent period of several months to years before the pseudolipoma formation occurs is common.^1,2,4-6

A 27-year-old woman presented to the family medicine clinic for examination of a deformity on the right buttock. She noticed a soft protruding mass months after landing on the buttocks and on top of a stick during routine physical training. Prior ultrasonography of the deformity proved unhelpful in determining the etiology. Physical examination revealed a protruding, 2-cm, flesh-colored mass on the right buttock intergluteal fold that was soft, compressible, and nontender (Figure 1). There was no capsule, nodule, loculation, or sinus tract. The patient underwent excisional resection with findings of benign-appearing unencapsulated adipose tissue (Figure 2). The wound was closed without difficulty. After several weeks, she had a well-healing scar without contour deficits of the buttocks. Two to 3 months after the initial repair, the patient presented to the family medicine clinic with recurrence of the fatty protrusion. She was referred for consultation and definitive management to a plastic surgeon but was lost to follow up.

In a systematic review of the literature to research pathogenesis theories, a PubMed search of articles indexed for MEDLINE using the terms trauma and pseudolipoma, lipoma, fat, or adipose yielded 45 citations, with only 10 publications addressing the pathology specific to pseudolipomas. Two leading theories of the pathogenesis of PTLs include the adipose herniation pathway and the inflammatory proliferation pathway.^4,5

Adipose tissue comprises fat lobules that are organized underneath the supportive elastic fascial layers. Injury from forces exceeding the fascial strength is the basis for the oldest pathogenesis theory. The adipose herniation theory suggests that fat lobules are displaced through the damaged septae, allowing for the development of an epidermal pseudolipoma at the site of blunt trauma.⁷ This theory has been supported by many case reports; however, more recent reports have identified a larger number of PTL cases that showed no identifiable disruptions in the fascia.^1,4,8

In 1997, the inflammatory proliferation theory began to gain attention. The theory describes how local tissue trauma leads to the release of inflammatory cytokines, which successively signals the development of preadipocytes or adipose tissue–derived stem cells (ASCs) into mature adipocytes.⁴ Most patients report a history of a hematoma in the area of pseudolipoma development, which strongly supports this newer theory. Studies exploring hematomas have found elevated levels of growth factors and inflammatory markers.^2,9 In particular, tumor necrosis factor α, peroxisome proliferator–activated receptor γ, vascular endothelial growth factor, and IL-6 and IL-8 may foster an environment in which adipogenic cells are both chemotaxed to the area of trauma and differentiated to white adipose tissue.^2,10

Despite addressing the role of the preadipocyte, the available research fails to address the general development of mesenchymal cells into the preadipocyte. White adipose tissue develops at sites of neovascularization and frequently has been observed spreading into the nearby tissue toward other blood vessels. Furthermore, these white adipose tissue expansions remain reliant on multiple growth factors and cell-signaling molecules.¹⁰ Numerous investigations into stem cell grafting have found that implantation of ASCs in vivo within animal models does not result in the proliferation and differentiation of ASCs unless specific conditions have been met such as prior tissue injury or immunodeficiency.^10-12 These investigations support and expand on the inflammatory proliferation pathway. Thus, most of the true PTLs in the available research appear as de novo tumors and are more congruent with the inflammatory proliferation model.^1,2,4-6,8

Typical treatment of a PTL is surgical excision or liposuction depending on the pathology and size of the pseudolipoma. Biopsy examination prior to liposuction is critical for evaluation of liposarcoma and may help identify damage to Scarpa fascia. Recurrence of a PTL is rare regardless of treatment method; however, in a study of 31 PTL cases, only 6 were pathologically identified as PTLs without fibrous material.¹

Our patient experienced a blunt trauma to the buttocks and subsequently developed a PTL that was surgically excised and recurred within 3 months. Research surrounding the pathogenesis of the PTL has evolved from the theory of physical herniation of adipose tissue to an inflammatory differentiation of preadipocytes, but there is still much to learn about how and why it occurs and the mesenchymal differentiation following tissue injury.

To the Editor:

The posttraumatic pseudolipoma (PTL) is a painless localized mass comprised of unencapsulated adipose tissue that develops at the site of acute or prolonged blunt soft tissue trauma. It may be round or fusiform in shape and has areas of saponification leading to fat necrosis.¹ Posttraumatic pseudolipomas are 12 times more likely to occur in females, which may be attributed to sex-determined adipose tissue distribution or cosmetic concerns.² Most PTLs are found in areas of the body with high adiposity, including the hip, thigh, and gluteal regions.³ A patient history of a traumatic event resulting in a hematoma and a subsequent latent period of several months to years before the pseudolipoma formation occurs is common.^1,2,4-6

A 27-year-old woman presented to the family medicine clinic for examination of a deformity on the right buttock. She noticed a soft protruding mass months after landing on the buttocks and on top of a stick during routine physical training. Prior ultrasonography of the deformity proved unhelpful in determining the etiology. Physical examination revealed a protruding, 2-cm, flesh-colored mass on the right buttock intergluteal fold that was soft, compressible, and nontender (Figure 1). There was no capsule, nodule, loculation, or sinus tract. The patient underwent excisional resection with findings of benign-appearing unencapsulated adipose tissue (Figure 2). The wound was closed without difficulty. After several weeks, she had a well-healing scar without contour deficits of the buttocks. Two to 3 months after the initial repair, the patient presented to the family medicine clinic with recurrence of the fatty protrusion. She was referred for consultation and definitive management to a plastic surgeon but was lost to follow up.

In a systematic review of the literature to research pathogenesis theories, a PubMed search of articles indexed for MEDLINE using the terms trauma and pseudolipoma, lipoma, fat, or adipose yielded 45 citations, with only 10 publications addressing the pathology specific to pseudolipomas. Two leading theories of the pathogenesis of PTLs include the adipose herniation pathway and the inflammatory proliferation pathway.^4,5

Adipose tissue comprises fat lobules that are organized underneath the supportive elastic fascial layers. Injury from forces exceeding the fascial strength is the basis for the oldest pathogenesis theory. The adipose herniation theory suggests that fat lobules are displaced through the damaged septae, allowing for the development of an epidermal pseudolipoma at the site of blunt trauma.⁷ This theory has been supported by many case reports; however, more recent reports have identified a larger number of PTL cases that showed no identifiable disruptions in the fascia.^1,4,8

In 1997, the inflammatory proliferation theory began to gain attention. The theory describes how local tissue trauma leads to the release of inflammatory cytokines, which successively signals the development of preadipocytes or adipose tissue–derived stem cells (ASCs) into mature adipocytes.⁴ Most patients report a history of a hematoma in the area of pseudolipoma development, which strongly supports this newer theory. Studies exploring hematomas have found elevated levels of growth factors and inflammatory markers.^2,9 In particular, tumor necrosis factor α, peroxisome proliferator–activated receptor γ, vascular endothelial growth factor, and IL-6 and IL-8 may foster an environment in which adipogenic cells are both chemotaxed to the area of trauma and differentiated to white adipose tissue.^2,10

Despite addressing the role of the preadipocyte, the available research fails to address the general development of mesenchymal cells into the preadipocyte. White adipose tissue develops at sites of neovascularization and frequently has been observed spreading into the nearby tissue toward other blood vessels. Furthermore, these white adipose tissue expansions remain reliant on multiple growth factors and cell-signaling molecules.¹⁰ Numerous investigations into stem cell grafting have found that implantation of ASCs in vivo within animal models does not result in the proliferation and differentiation of ASCs unless specific conditions have been met such as prior tissue injury or immunodeficiency.^10-12 These investigations support and expand on the inflammatory proliferation pathway. Thus, most of the true PTLs in the available research appear as de novo tumors and are more congruent with the inflammatory proliferation model.^1,2,4-6,8

Typical treatment of a PTL is surgical excision or liposuction depending on the pathology and size of the pseudolipoma. Biopsy examination prior to liposuction is critical for evaluation of liposarcoma and may help identify damage to Scarpa fascia. Recurrence of a PTL is rare regardless of treatment method; however, in a study of 31 PTL cases, only 6 were pathologically identified as PTLs without fibrous material.¹

Our patient experienced a blunt trauma to the buttocks and subsequently developed a PTL that was surgically excised and recurred within 3 months. Research surrounding the pathogenesis of the PTL has evolved from the theory of physical herniation of adipose tissue to an inflammatory differentiation of preadipocytes, but there is still much to learn about how and why it occurs and the mesenchymal differentiation following tissue injury.

The Diagnosis: Immunotherapy-Related Lichenoid Drug Eruption

Direct immunofluorescence was negative, and histopathology revealed a lichenoid interface dermatitis, minimal parakeratosis, and saw-toothed rete ridges (Figure 1). He was diagnosed with an immunotherapyrelated lichenoid drug eruption based on the morphology of the skin lesions and clinicopathologic correlation. Bullous pemphigoid and lichen planus pemphigoides were ruled out given the negative direct immunofluorescence findings. Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) was not consistent with the clinical presentation, especially given the lack of mucosal findings. The histology also was not consistent, as the biopsy specimen lacked apoptotic and necrotic keratinocytes to the degree seen in SJS/TEN and also had a greater degree of inflammatory infiltrate. Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome was ruled out given the lack of systemic findings, including facial swelling and lymphadenopathy and the clinical appearance of the rash. No morbilliform features were present, which is the most common presentation of DRESS syndrome.

Checkpoint inhibitor (CPI) therapy has become the cornerstone in management of certain advanced malignancies.¹ Checkpoint inhibitors block cytotoxic T lymphocyte–associated protein 4, programmed cell death-1, and/or programmed cell death ligand-1, allowing activated T cells to infiltrate the tumor microenvironment and destroy malignant cells. Checkpoint inhibitors are approved for the treatment of melanoma, cutaneous squamous cell carcinoma, and Merkel cell carcinoma and are being investigated in various other cutaneous and soft tissue malignancies.^1-3

Although CPIs have shown substantial efficacy in the management of advanced malignancies, immune-related adverse events (AEs) are common due to nonspecific immune activation.² Immune-related cutaneous AEs are the most common immune-related AEs, occurring in 30% to 50% of patients who undergo treatment.^2-5 Common immune-related cutaneous AEs include maculopapular, psoriasiform, and lichenoid dermatitis, as well as pruritus without dermatitis.^2,3,6 Other reactions include but are not limited to bullous pemphigoid, vitiligolike depigmentation, and alopecia.^2,3 Immune-related cutaneous AEs usually are self-limited; however, severe life-threatening reactions such as the spectrum of SJS/TEN and DRESS syndrome also can occur.^2-4 Immune-related cutaneous AEs are graded based on the Common Terminology Criteria for Adverse Events: grade 1 reactions are asymptomatic and cover less than 10% of the patient’s body surface area (BSA), grade 2 reactions have mild symptoms and cover 10% to 30% of the patient’s BSA, grade 3 reactions have moderate to severe symptoms and cover greater than 30% of the patient’s BSA, and grade 4 reactions are life-threatening.^2,3 With prompt recognition and adequate treatment, mild to moderate immune-related cutaneous AEs—grades 1 and 2—largely are reversible, and less than 5% require discontinuation of therapy.^2,3,6 It has been suggested that immune-related cutaneous AEs may be a positive prognostic factor in the treatment of underlying malignancy, indicating adequate immune activation targeting the malignant cells.⁶

Although our patient had some typical violaceous, flat-topped papules and plaques with Wickham striae, he also had atypical findings for a lichenoid reaction. Given the endorsement of blisters, it is possible that some of these lesions initially were bullous and subsequently ruptured, leaving behind erosions. However, in other areas, there also were eroded papules and ulcerations without a reported history of excoriation, scratching, picking, or prior bullae, including difficult-to-reach areas such as the back. It is favored that these lesions represented a robust lichenoid dermatitis leading to erosive and ulcerated lesions, similar to the formation of bullous lichen planus. Lichenoid eruptions secondary to immunotherapy are well-known phenomena, but a PubMed search of articles indexed for MEDLINE using the terms ulcer, lichenoid, and immunotherapy revealed only 2 cases of ulcerative lichenoid eruptions: a localized digital erosive lichenoid dermatitis and a widespread ulcerative lichenoid drug eruption without true erosions.7,8 However, widespread erosive and ulcerated lichenoid reactions are rare.

Lichenoid eruptions most strongly are associated with anti–programmed cell death-1/ programmed cell death ligand-1 therapy, occurring in 20% of patients undergoing treatment.³ Lichenoid eruptions present as discrete, pruritic, erythematous, violaceous papules and plaques on the chest and back and rarely may involve the limbs, palmoplantar surfaces, and oral mucosa.^2,3,6 Histopathologic features include a dense bandlike lymphocytic infiltrate in the dermis with scattered apoptotic keratinocytes in the basal layer of the epidermis.^2,4,6 Grades 1 to 2 lesions can be managed with high-potency topical corticosteroids without CPI dose interruption, with more extensive grade 2 lesions requiring systemic corticosteroids.^2,6,9 Lichenoid eruptions grade 3 or higher also require systemic corticosteroid therapy CPI therapy cessation until the eruption has receded to grade 0 to 1.² Alternative treatment options for high-grade toxicity include phototherapy and acitretin.^2,4,9

Our patient was treated with cessation of immunotherapy and initiation of a systemic corticosteroid taper, acitretin, and narrowband UVB therapy. After 6 weeks of treatment, the pain and pruritus improved and the rash had resolved in some areas while it had taken on a more classic lichenoid appearance with violaceous scaly papules and plaques (Figure 2) in areas of prior ulcers and erosions. He no longer had any bullae, erosions, or ulcers.

The Diagnosis: Immunotherapy-Related Lichenoid Drug Eruption

Direct immunofluorescence was negative, and histopathology revealed a lichenoid interface dermatitis, minimal parakeratosis, and saw-toothed rete ridges (Figure 1). He was diagnosed with an immunotherapyrelated lichenoid drug eruption based on the morphology of the skin lesions and clinicopathologic correlation. Bullous pemphigoid and lichen planus pemphigoides were ruled out given the negative direct immunofluorescence findings. Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) was not consistent with the clinical presentation, especially given the lack of mucosal findings. The histology also was not consistent, as the biopsy specimen lacked apoptotic and necrotic keratinocytes to the degree seen in SJS/TEN and also had a greater degree of inflammatory infiltrate. Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome was ruled out given the lack of systemic findings, including facial swelling and lymphadenopathy and the clinical appearance of the rash. No morbilliform features were present, which is the most common presentation of DRESS syndrome.

Checkpoint inhibitor (CPI) therapy has become the cornerstone in management of certain advanced malignancies.¹ Checkpoint inhibitors block cytotoxic T lymphocyte–associated protein 4, programmed cell death-1, and/or programmed cell death ligand-1, allowing activated T cells to infiltrate the tumor microenvironment and destroy malignant cells. Checkpoint inhibitors are approved for the treatment of melanoma, cutaneous squamous cell carcinoma, and Merkel cell carcinoma and are being investigated in various other cutaneous and soft tissue malignancies.^1-3

Although CPIs have shown substantial efficacy in the management of advanced malignancies, immune-related adverse events (AEs) are common due to nonspecific immune activation.² Immune-related cutaneous AEs are the most common immune-related AEs, occurring in 30% to 50% of patients who undergo treatment.^2-5 Common immune-related cutaneous AEs include maculopapular, psoriasiform, and lichenoid dermatitis, as well as pruritus without dermatitis.^2,3,6 Other reactions include but are not limited to bullous pemphigoid, vitiligolike depigmentation, and alopecia.^2,3 Immune-related cutaneous AEs usually are self-limited; however, severe life-threatening reactions such as the spectrum of SJS/TEN and DRESS syndrome also can occur.^2-4 Immune-related cutaneous AEs are graded based on the Common Terminology Criteria for Adverse Events: grade 1 reactions are asymptomatic and cover less than 10% of the patient’s body surface area (BSA), grade 2 reactions have mild symptoms and cover 10% to 30% of the patient’s BSA, grade 3 reactions have moderate to severe symptoms and cover greater than 30% of the patient’s BSA, and grade 4 reactions are life-threatening.^2,3 With prompt recognition and adequate treatment, mild to moderate immune-related cutaneous AEs—grades 1 and 2—largely are reversible, and less than 5% require discontinuation of therapy.^2,3,6 It has been suggested that immune-related cutaneous AEs may be a positive prognostic factor in the treatment of underlying malignancy, indicating adequate immune activation targeting the malignant cells.⁶

Although our patient had some typical violaceous, flat-topped papules and plaques with Wickham striae, he also had atypical findings for a lichenoid reaction. Given the endorsement of blisters, it is possible that some of these lesions initially were bullous and subsequently ruptured, leaving behind erosions. However, in other areas, there also were eroded papules and ulcerations without a reported history of excoriation, scratching, picking, or prior bullae, including difficult-to-reach areas such as the back. It is favored that these lesions represented a robust lichenoid dermatitis leading to erosive and ulcerated lesions, similar to the formation of bullous lichen planus. Lichenoid eruptions secondary to immunotherapy are well-known phenomena, but a PubMed search of articles indexed for MEDLINE using the terms ulcer, lichenoid, and immunotherapy revealed only 2 cases of ulcerative lichenoid eruptions: a localized digital erosive lichenoid dermatitis and a widespread ulcerative lichenoid drug eruption without true erosions.7,8 However, widespread erosive and ulcerated lichenoid reactions are rare.

Lichenoid eruptions most strongly are associated with anti–programmed cell death-1/ programmed cell death ligand-1 therapy, occurring in 20% of patients undergoing treatment.³ Lichenoid eruptions present as discrete, pruritic, erythematous, violaceous papules and plaques on the chest and back and rarely may involve the limbs, palmoplantar surfaces, and oral mucosa.^2,3,6 Histopathologic features include a dense bandlike lymphocytic infiltrate in the dermis with scattered apoptotic keratinocytes in the basal layer of the epidermis.^2,4,6 Grades 1 to 2 lesions can be managed with high-potency topical corticosteroids without CPI dose interruption, with more extensive grade 2 lesions requiring systemic corticosteroids.^2,6,9 Lichenoid eruptions grade 3 or higher also require systemic corticosteroid therapy CPI therapy cessation until the eruption has receded to grade 0 to 1.² Alternative treatment options for high-grade toxicity include phototherapy and acitretin.^2,4,9

Our patient was treated with cessation of immunotherapy and initiation of a systemic corticosteroid taper, acitretin, and narrowband UVB therapy. After 6 weeks of treatment, the pain and pruritus improved and the rash had resolved in some areas while it had taken on a more classic lichenoid appearance with violaceous scaly papules and plaques (Figure 2) in areas of prior ulcers and erosions. He no longer had any bullae, erosions, or ulcers.

The Diagnosis: Immunotherapy-Related Lichenoid Drug Eruption

Direct immunofluorescence was negative, and histopathology revealed a lichenoid interface dermatitis, minimal parakeratosis, and saw-toothed rete ridges (Figure 1). He was diagnosed with an immunotherapyrelated lichenoid drug eruption based on the morphology of the skin lesions and clinicopathologic correlation. Bullous pemphigoid and lichen planus pemphigoides were ruled out given the negative direct immunofluorescence findings. Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) was not consistent with the clinical presentation, especially given the lack of mucosal findings. The histology also was not consistent, as the biopsy specimen lacked apoptotic and necrotic keratinocytes to the degree seen in SJS/TEN and also had a greater degree of inflammatory infiltrate. Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome was ruled out given the lack of systemic findings, including facial swelling and lymphadenopathy and the clinical appearance of the rash. No morbilliform features were present, which is the most common presentation of DRESS syndrome.

Checkpoint inhibitor (CPI) therapy has become the cornerstone in management of certain advanced malignancies.¹ Checkpoint inhibitors block cytotoxic T lymphocyte–associated protein 4, programmed cell death-1, and/or programmed cell death ligand-1, allowing activated T cells to infiltrate the tumor microenvironment and destroy malignant cells. Checkpoint inhibitors are approved for the treatment of melanoma, cutaneous squamous cell carcinoma, and Merkel cell carcinoma and are being investigated in various other cutaneous and soft tissue malignancies.^1-3

Although CPIs have shown substantial efficacy in the management of advanced malignancies, immune-related adverse events (AEs) are common due to nonspecific immune activation.² Immune-related cutaneous AEs are the most common immune-related AEs, occurring in 30% to 50% of patients who undergo treatment.^2-5 Common immune-related cutaneous AEs include maculopapular, psoriasiform, and lichenoid dermatitis, as well as pruritus without dermatitis.^2,3,6 Other reactions include but are not limited to bullous pemphigoid, vitiligolike depigmentation, and alopecia.^2,3 Immune-related cutaneous AEs usually are self-limited; however, severe life-threatening reactions such as the spectrum of SJS/TEN and DRESS syndrome also can occur.^2-4 Immune-related cutaneous AEs are graded based on the Common Terminology Criteria for Adverse Events: grade 1 reactions are asymptomatic and cover less than 10% of the patient’s body surface area (BSA), grade 2 reactions have mild symptoms and cover 10% to 30% of the patient’s BSA, grade 3 reactions have moderate to severe symptoms and cover greater than 30% of the patient’s BSA, and grade 4 reactions are life-threatening.^2,3 With prompt recognition and adequate treatment, mild to moderate immune-related cutaneous AEs—grades 1 and 2—largely are reversible, and less than 5% require discontinuation of therapy.^2,3,6 It has been suggested that immune-related cutaneous AEs may be a positive prognostic factor in the treatment of underlying malignancy, indicating adequate immune activation targeting the malignant cells.⁶

Although our patient had some typical violaceous, flat-topped papules and plaques with Wickham striae, he also had atypical findings for a lichenoid reaction. Given the endorsement of blisters, it is possible that some of these lesions initially were bullous and subsequently ruptured, leaving behind erosions. However, in other areas, there also were eroded papules and ulcerations without a reported history of excoriation, scratching, picking, or prior bullae, including difficult-to-reach areas such as the back. It is favored that these lesions represented a robust lichenoid dermatitis leading to erosive and ulcerated lesions, similar to the formation of bullous lichen planus. Lichenoid eruptions secondary to immunotherapy are well-known phenomena, but a PubMed search of articles indexed for MEDLINE using the terms ulcer, lichenoid, and immunotherapy revealed only 2 cases of ulcerative lichenoid eruptions: a localized digital erosive lichenoid dermatitis and a widespread ulcerative lichenoid drug eruption without true erosions.7,8 However, widespread erosive and ulcerated lichenoid reactions are rare.

Lichenoid eruptions most strongly are associated with anti–programmed cell death-1/ programmed cell death ligand-1 therapy, occurring in 20% of patients undergoing treatment.³ Lichenoid eruptions present as discrete, pruritic, erythematous, violaceous papules and plaques on the chest and back and rarely may involve the limbs, palmoplantar surfaces, and oral mucosa.^2,3,6 Histopathologic features include a dense bandlike lymphocytic infiltrate in the dermis with scattered apoptotic keratinocytes in the basal layer of the epidermis.^2,4,6 Grades 1 to 2 lesions can be managed with high-potency topical corticosteroids without CPI dose interruption, with more extensive grade 2 lesions requiring systemic corticosteroids.^2,6,9 Lichenoid eruptions grade 3 or higher also require systemic corticosteroid therapy CPI therapy cessation until the eruption has receded to grade 0 to 1.² Alternative treatment options for high-grade toxicity include phototherapy and acitretin.^2,4,9

Our patient was treated with cessation of immunotherapy and initiation of a systemic corticosteroid taper, acitretin, and narrowband UVB therapy. After 6 weeks of treatment, the pain and pruritus improved and the rash had resolved in some areas while it had taken on a more classic lichenoid appearance with violaceous scaly papules and plaques (Figure 2) in areas of prior ulcers and erosions. He no longer had any bullae, erosions, or ulcers.

To the Editor:

The Moderna COVID-19 messenger RNA (mRNA) vaccine was authorized for use on December 18, 2020, with the second dose beginning on January 15, 2021.^1-3 Some individuals who received the Moderna vaccine experienced an intense rash known as “COVID arm,” a harmless but bothersome adverse effect that typically appears within a week and is a localized and transient immunogenic response.⁴ COVID arm differs from most vaccine adverse effects. The rash emerges not immediately but 5 to 9 days after the initial dose—on average, 1 week later. Apart from being itchy, the rash does not appear to be harmful and is not a reason to hesitate getting vaccinated.

Dermatologists and allergists have been studying this adverse effect, which has been formally termed delayed cutaneous hypersensitivity. Of potential clinical consequence is that the efficacy of the mRNA COVID-19 vaccine may be harmed if postvaccination dermal reactions necessitate systemic corticosteroid therapy. Because this vaccine stimulates an immune response as viral RNA integrates in cells secondary to production of the spike protein of the virus, the skin may be affected secondarily and manifestations of any underlying disease may be aggravated.⁵ We report a patient who developed a psoriasiform dermatitis after the first dose of the Moderna vaccine.

A 65-year-old woman presented to her primary care physician because of the severity of psoriasiform dermatitis that developed 5 days after she received the first dose of the Moderna COVID-19 mRNA vaccine. The patient had a medical history of Sjögren syndrome. Her medication history was negative, and her family history was negative for autoimmune disease. Physical examination by primary care revealed an erythematous scaly rash with plaques and papules on the neck and back (Figure 1). The patient presented again to primary care 2 days later with swollen, painful, discolored digits (Figure 2) and a stiff, sore neck.

Laboratory results were positive for anti–Sjögren syndrome–related antigens A and B. A complete blood cell count; comprehensive metabolic panel; erythrocyte sedimentation rate; and assays of rheumatoid factor, C-reactive protein, and anti–cyclic citrullinated peptide were within reference range. A biopsy of a lesion on the back showed psoriasiform dermatitis with confluent parakeratosis and scattered necrotic keratinocytes. There was superficial perivascular inflammation with rare eosinophils (Figure 3).

The patient was treated with a course of systemic corticosteroids. The rash resolved in 1 week. She did not receive the second dose due to the rash.

Two mRNA COVID-19 vaccines—Pfizer BioNTech and Moderna—have been granted emergency use authorization by the US Food and Drug Administration.⁶ The safety profile of the mRNA-1273 vaccine for the median 2-month follow-up showed no safety concerns.³ Minor localized adverse effects (eg, pain, redness, swelling) have been observed more frequently with the vaccines than with placebo. Systemic symptoms, such as fever, fatigue, headache, and muscle and joint pain, also were seen somewhat more often with the vaccines than with placebo; most such effects occurred 24 to 48 hours after vaccination.^3,6,7 The frequency of unsolicited adverse events and serious adverse events reported during the 28-day period after vaccination generally was similar among participants in the vaccine and placebo groups.³

There are 2 types of reactions to COVID-19 vaccination: immediate and delayed. Immediate reactions usually are due to anaphylaxis, requiring prompt recognition and treatment with epinephrine to stop rapid progression of life-threatening symptoms. Delayed reactions include localized reactions, such as urticaria and benign exanthema; serum sickness and serum sickness–like reactions; fever; and rare skin, organ, and neurologic sequelae.^1,6-8

Cutaneous manifestations, present in 16% to 50% of patients with Sjögren syndrome, are considered one of the most common extraglandular presentations of the syndrome. They are classified as nonvascular (eg, xerosis, angular cheilitis, eyelid dermatitis, annular erythema) and vascular (eg, Raynaud phenomenon, vasculitis).^9-11 Our patient did not have any of those findings. She had not taken any medications before the rash appeared, thereby ruling out a drug reaction.

The differential for our patient included post–urinary tract infection immune-reactive arthritis and rash, which is not typical with Escherichia coli infection but is described with infection with Chlamydia species and Salmonella species. Moreover, post–urinary tract infection immune-reactive arthritis and rash appear mostly on the palms and soles. Systemic lupus erythematosus–like rashes have a different histology and appear on sun-exposed areas; our patient’s rash was found mainly on unexposed areas.¹²

Because our patient received the Moderna vaccine 5 days before the rash appeared and later developed swelling of the digits with morning stiffness, a delayed serum sickness–like reaction secondary to COVID-19 vaccination was possible.^3,6

COVID-19 mRNA vaccines developed by Pfizer-BioNTech and Moderna incorporate a lipid-based nanoparticle carrier system that prevents rapid enzymatic degradation of mRNA and facilitates in vivo delivery of mRNA. This lipid-based nanoparticle carrier system is further stabilized by a polyethylene glycol 2000 lipid conjugate that provides a hydrophilic layer, thus prolonging half-life. The presence of lipid polyethylene glycol 2000 in mRNA vaccines has led to concern that this component could be implicated in anaphylaxis.⁶

COVID-19 antigens can give rise to varying clinical manifestations that are directly related to viral tissue damage or are indirectly induced by the antiviral immune response.^13,14 Hyperactivation of the immune system to eradicate COVID-19 may trigger autoimmunity; several immune-mediated disorders have been described in individuals infected with SARS-CoV-2. Dermal manifestations include cutaneous rash and vasculitis.^13-16 Crucial immunologic steps occur during SARS-CoV-2 infection that may link autoimmunity to COVID-19.^13,14 In preliminary published data on the efficacy of the Moderna vaccine on 45 trial enrollees, 3 did not receive the second dose of vaccination, including 1 who developed urticaria on both legs 5 days after the first dose.¹

Introduction of viral RNA can induce autoimmunity that can be explained by various phenomena, including epitope spreading, molecular mimicry, cryptic antigen, and bystander activation. Remarkably, more than one-third of immunogenic proteins in SARS-CoV-2 have potentially problematic homology to proteins that are key to the human adaptive immune system.⁵

Moreover, SARS-CoV-2 seems to induce organ injury through alternative mechanisms beyond direct viral infection, including immunologic injury. In some situations, hyperactivation of the immune response to SARS-CoV-2 RNA can result in autoimmune disease. COVID-19 has been associated with immune-mediated systemic or organ-selective manifestations, some of which fulfill the diagnostic or classification criteria of specific autoimmune diseases. It is unclear whether those medical disorders are the result of transitory postinfectious epiphenomena.⁵

A few studies have shown that patients with rheumatic disease have an incidence and prevalence of COVID-19 that is similar to the general population. A similar pattern has been detected in COVID-19 morbidity and mortality rates, even among patients with an autoimmune disease, such as rheumatoid arthritis and Sjögren syndrome.^5,17 Furthermore, exacerbation of preexisting rheumatic symptoms may be due to hyperactivation of antiviral pathways in a person with an autoimmune disease.^17-19 The findings in our patient suggested a direct role for the vaccine in skin manifestations, rather than for reactivation or development of new systemic autoimmune processes, such as systemic lupus erythematosus.

Exacerbation of psoriasis following COVID-19 vaccination has been described²⁰; however, the case patient did not have a history of psoriasis. The mechanism(s) of such exacerbation remain unclear; COVID-19 vaccine–induced helper T cells (T_H17) may play a role.²¹ Other skin manifestations encountered following COVID-19 vaccination include lichen planus, leukocytoclastic vasculitic rash, erythema multiforme–like rash, and pityriasis rosea–like rash.^22-25 The immune mechanisms of these manifestations remain unclear.

The clinical presentation of delayed vaccination reactions can be attributed to the timing of symptoms and, in this case, the immune-mediated background of a psoriasiform reaction. Although adverse reactions to the SARS-CoV-2 mRNA vaccine are rare, more individuals should be studied after vaccination to confirm and better understand this phenomenon.

To the Editor:

The Moderna COVID-19 messenger RNA (mRNA) vaccine was authorized for use on December 18, 2020, with the second dose beginning on January 15, 2021.^1-3 Some individuals who received the Moderna vaccine experienced an intense rash known as “COVID arm,” a harmless but bothersome adverse effect that typically appears within a week and is a localized and transient immunogenic response.⁴ COVID arm differs from most vaccine adverse effects. The rash emerges not immediately but 5 to 9 days after the initial dose—on average, 1 week later. Apart from being itchy, the rash does not appear to be harmful and is not a reason to hesitate getting vaccinated.

Dermatologists and allergists have been studying this adverse effect, which has been formally termed delayed cutaneous hypersensitivity. Of potential clinical consequence is that the efficacy of the mRNA COVID-19 vaccine may be harmed if postvaccination dermal reactions necessitate systemic corticosteroid therapy. Because this vaccine stimulates an immune response as viral RNA integrates in cells secondary to production of the spike protein of the virus, the skin may be affected secondarily and manifestations of any underlying disease may be aggravated.⁵ We report a patient who developed a psoriasiform dermatitis after the first dose of the Moderna vaccine.

A 65-year-old woman presented to her primary care physician because of the severity of psoriasiform dermatitis that developed 5 days after she received the first dose of the Moderna COVID-19 mRNA vaccine. The patient had a medical history of Sjögren syndrome. Her medication history was negative, and her family history was negative for autoimmune disease. Physical examination by primary care revealed an erythematous scaly rash with plaques and papules on the neck and back (Figure 1). The patient presented again to primary care 2 days later with swollen, painful, discolored digits (Figure 2) and a stiff, sore neck.

Laboratory results were positive for anti–Sjögren syndrome–related antigens A and B. A complete blood cell count; comprehensive metabolic panel; erythrocyte sedimentation rate; and assays of rheumatoid factor, C-reactive protein, and anti–cyclic citrullinated peptide were within reference range. A biopsy of a lesion on the back showed psoriasiform dermatitis with confluent parakeratosis and scattered necrotic keratinocytes. There was superficial perivascular inflammation with rare eosinophils (Figure 3).

The patient was treated with a course of systemic corticosteroids. The rash resolved in 1 week. She did not receive the second dose due to the rash.

Two mRNA COVID-19 vaccines—Pfizer BioNTech and Moderna—have been granted emergency use authorization by the US Food and Drug Administration.⁶ The safety profile of the mRNA-1273 vaccine for the median 2-month follow-up showed no safety concerns.³ Minor localized adverse effects (eg, pain, redness, swelling) have been observed more frequently with the vaccines than with placebo. Systemic symptoms, such as fever, fatigue, headache, and muscle and joint pain, also were seen somewhat more often with the vaccines than with placebo; most such effects occurred 24 to 48 hours after vaccination.^3,6,7 The frequency of unsolicited adverse events and serious adverse events reported during the 28-day period after vaccination generally was similar among participants in the vaccine and placebo groups.³

There are 2 types of reactions to COVID-19 vaccination: immediate and delayed. Immediate reactions usually are due to anaphylaxis, requiring prompt recognition and treatment with epinephrine to stop rapid progression of life-threatening symptoms. Delayed reactions include localized reactions, such as urticaria and benign exanthema; serum sickness and serum sickness–like reactions; fever; and rare skin, organ, and neurologic sequelae.^1,6-8

Cutaneous manifestations, present in 16% to 50% of patients with Sjögren syndrome, are considered one of the most common extraglandular presentations of the syndrome. They are classified as nonvascular (eg, xerosis, angular cheilitis, eyelid dermatitis, annular erythema) and vascular (eg, Raynaud phenomenon, vasculitis).^9-11 Our patient did not have any of those findings. She had not taken any medications before the rash appeared, thereby ruling out a drug reaction.

The differential for our patient included post–urinary tract infection immune-reactive arthritis and rash, which is not typical with Escherichia coli infection but is described with infection with Chlamydia species and Salmonella species. Moreover, post–urinary tract infection immune-reactive arthritis and rash appear mostly on the palms and soles. Systemic lupus erythematosus–like rashes have a different histology and appear on sun-exposed areas; our patient’s rash was found mainly on unexposed areas.¹²

Because our patient received the Moderna vaccine 5 days before the rash appeared and later developed swelling of the digits with morning stiffness, a delayed serum sickness–like reaction secondary to COVID-19 vaccination was possible.^3,6

COVID-19 mRNA vaccines developed by Pfizer-BioNTech and Moderna incorporate a lipid-based nanoparticle carrier system that prevents rapid enzymatic degradation of mRNA and facilitates in vivo delivery of mRNA. This lipid-based nanoparticle carrier system is further stabilized by a polyethylene glycol 2000 lipid conjugate that provides a hydrophilic layer, thus prolonging half-life. The presence of lipid polyethylene glycol 2000 in mRNA vaccines has led to concern that this component could be implicated in anaphylaxis.⁶

COVID-19 antigens can give rise to varying clinical manifestations that are directly related to viral tissue damage or are indirectly induced by the antiviral immune response.^13,14 Hyperactivation of the immune system to eradicate COVID-19 may trigger autoimmunity; several immune-mediated disorders have been described in individuals infected with SARS-CoV-2. Dermal manifestations include cutaneous rash and vasculitis.^13-16 Crucial immunologic steps occur during SARS-CoV-2 infection that may link autoimmunity to COVID-19.^13,14 In preliminary published data on the efficacy of the Moderna vaccine on 45 trial enrollees, 3 did not receive the second dose of vaccination, including 1 who developed urticaria on both legs 5 days after the first dose.¹

Introduction of viral RNA can induce autoimmunity that can be explained by various phenomena, including epitope spreading, molecular mimicry, cryptic antigen, and bystander activation. Remarkably, more than one-third of immunogenic proteins in SARS-CoV-2 have potentially problematic homology to proteins that are key to the human adaptive immune system.⁵

Moreover, SARS-CoV-2 seems to induce organ injury through alternative mechanisms beyond direct viral infection, including immunologic injury. In some situations, hyperactivation of the immune response to SARS-CoV-2 RNA can result in autoimmune disease. COVID-19 has been associated with immune-mediated systemic or organ-selective manifestations, some of which fulfill the diagnostic or classification criteria of specific autoimmune diseases. It is unclear whether those medical disorders are the result of transitory postinfectious epiphenomena.⁵

A few studies have shown that patients with rheumatic disease have an incidence and prevalence of COVID-19 that is similar to the general population. A similar pattern has been detected in COVID-19 morbidity and mortality rates, even among patients with an autoimmune disease, such as rheumatoid arthritis and Sjögren syndrome.^5,17 Furthermore, exacerbation of preexisting rheumatic symptoms may be due to hyperactivation of antiviral pathways in a person with an autoimmune disease.^17-19 The findings in our patient suggested a direct role for the vaccine in skin manifestations, rather than for reactivation or development of new systemic autoimmune processes, such as systemic lupus erythematosus.

Exacerbation of psoriasis following COVID-19 vaccination has been described²⁰; however, the case patient did not have a history of psoriasis. The mechanism(s) of such exacerbation remain unclear; COVID-19 vaccine–induced helper T cells (T_H17) may play a role.²¹ Other skin manifestations encountered following COVID-19 vaccination include lichen planus, leukocytoclastic vasculitic rash, erythema multiforme–like rash, and pityriasis rosea–like rash.^22-25 The immune mechanisms of these manifestations remain unclear.

The clinical presentation of delayed vaccination reactions can be attributed to the timing of symptoms and, in this case, the immune-mediated background of a psoriasiform reaction. Although adverse reactions to the SARS-CoV-2 mRNA vaccine are rare, more individuals should be studied after vaccination to confirm and better understand this phenomenon.

To the Editor:

The Moderna COVID-19 messenger RNA (mRNA) vaccine was authorized for use on December 18, 2020, with the second dose beginning on January 15, 2021.^1-3 Some individuals who received the Moderna vaccine experienced an intense rash known as “COVID arm,” a harmless but bothersome adverse effect that typically appears within a week and is a localized and transient immunogenic response.⁴ COVID arm differs from most vaccine adverse effects. The rash emerges not immediately but 5 to 9 days after the initial dose—on average, 1 week later. Apart from being itchy, the rash does not appear to be harmful and is not a reason to hesitate getting vaccinated.

Dermatologists and allergists have been studying this adverse effect, which has been formally termed delayed cutaneous hypersensitivity. Of potential clinical consequence is that the efficacy of the mRNA COVID-19 vaccine may be harmed if postvaccination dermal reactions necessitate systemic corticosteroid therapy. Because this vaccine stimulates an immune response as viral RNA integrates in cells secondary to production of the spike protein of the virus, the skin may be affected secondarily and manifestations of any underlying disease may be aggravated.⁵ We report a patient who developed a psoriasiform dermatitis after the first dose of the Moderna vaccine.

A 65-year-old woman presented to her primary care physician because of the severity of psoriasiform dermatitis that developed 5 days after she received the first dose of the Moderna COVID-19 mRNA vaccine. The patient had a medical history of Sjögren syndrome. Her medication history was negative, and her family history was negative for autoimmune disease. Physical examination by primary care revealed an erythematous scaly rash with plaques and papules on the neck and back (Figure 1). The patient presented again to primary care 2 days later with swollen, painful, discolored digits (Figure 2) and a stiff, sore neck.

Laboratory results were positive for anti–Sjögren syndrome–related antigens A and B. A complete blood cell count; comprehensive metabolic panel; erythrocyte sedimentation rate; and assays of rheumatoid factor, C-reactive protein, and anti–cyclic citrullinated peptide were within reference range. A biopsy of a lesion on the back showed psoriasiform dermatitis with confluent parakeratosis and scattered necrotic keratinocytes. There was superficial perivascular inflammation with rare eosinophils (Figure 3).

The patient was treated with a course of systemic corticosteroids. The rash resolved in 1 week. She did not receive the second dose due to the rash.

Two mRNA COVID-19 vaccines—Pfizer BioNTech and Moderna—have been granted emergency use authorization by the US Food and Drug Administration.⁶ The safety profile of the mRNA-1273 vaccine for the median 2-month follow-up showed no safety concerns.³ Minor localized adverse effects (eg, pain, redness, swelling) have been observed more frequently with the vaccines than with placebo. Systemic symptoms, such as fever, fatigue, headache, and muscle and joint pain, also were seen somewhat more often with the vaccines than with placebo; most such effects occurred 24 to 48 hours after vaccination.^3,6,7 The frequency of unsolicited adverse events and serious adverse events reported during the 28-day period after vaccination generally was similar among participants in the vaccine and placebo groups.³

There are 2 types of reactions to COVID-19 vaccination: immediate and delayed. Immediate reactions usually are due to anaphylaxis, requiring prompt recognition and treatment with epinephrine to stop rapid progression of life-threatening symptoms. Delayed reactions include localized reactions, such as urticaria and benign exanthema; serum sickness and serum sickness–like reactions; fever; and rare skin, organ, and neurologic sequelae.^1,6-8

Cutaneous manifestations, present in 16% to 50% of patients with Sjögren syndrome, are considered one of the most common extraglandular presentations of the syndrome. They are classified as nonvascular (eg, xerosis, angular cheilitis, eyelid dermatitis, annular erythema) and vascular (eg, Raynaud phenomenon, vasculitis).^9-11 Our patient did not have any of those findings. She had not taken any medications before the rash appeared, thereby ruling out a drug reaction.

The differential for our patient included post–urinary tract infection immune-reactive arthritis and rash, which is not typical with Escherichia coli infection but is described with infection with Chlamydia species and Salmonella species. Moreover, post–urinary tract infection immune-reactive arthritis and rash appear mostly on the palms and soles. Systemic lupus erythematosus–like rashes have a different histology and appear on sun-exposed areas; our patient’s rash was found mainly on unexposed areas.¹²

Because our patient received the Moderna vaccine 5 days before the rash appeared and later developed swelling of the digits with morning stiffness, a delayed serum sickness–like reaction secondary to COVID-19 vaccination was possible.^3,6

COVID-19 mRNA vaccines developed by Pfizer-BioNTech and Moderna incorporate a lipid-based nanoparticle carrier system that prevents rapid enzymatic degradation of mRNA and facilitates in vivo delivery of mRNA. This lipid-based nanoparticle carrier system is further stabilized by a polyethylene glycol 2000 lipid conjugate that provides a hydrophilic layer, thus prolonging half-life. The presence of lipid polyethylene glycol 2000 in mRNA vaccines has led to concern that this component could be implicated in anaphylaxis.⁶

COVID-19 antigens can give rise to varying clinical manifestations that are directly related to viral tissue damage or are indirectly induced by the antiviral immune response.^13,14 Hyperactivation of the immune system to eradicate COVID-19 may trigger autoimmunity; several immune-mediated disorders have been described in individuals infected with SARS-CoV-2. Dermal manifestations include cutaneous rash and vasculitis.^13-16 Crucial immunologic steps occur during SARS-CoV-2 infection that may link autoimmunity to COVID-19.^13,14 In preliminary published data on the efficacy of the Moderna vaccine on 45 trial enrollees, 3 did not receive the second dose of vaccination, including 1 who developed urticaria on both legs 5 days after the first dose.¹

Introduction of viral RNA can induce autoimmunity that can be explained by various phenomena, including epitope spreading, molecular mimicry, cryptic antigen, and bystander activation. Remarkably, more than one-third of immunogenic proteins in SARS-CoV-2 have potentially problematic homology to proteins that are key to the human adaptive immune system.⁵

Moreover, SARS-CoV-2 seems to induce organ injury through alternative mechanisms beyond direct viral infection, including immunologic injury. In some situations, hyperactivation of the immune response to SARS-CoV-2 RNA can result in autoimmune disease. COVID-19 has been associated with immune-mediated systemic or organ-selective manifestations, some of which fulfill the diagnostic or classification criteria of specific autoimmune diseases. It is unclear whether those medical disorders are the result of transitory postinfectious epiphenomena.⁵

A few studies have shown that patients with rheumatic disease have an incidence and prevalence of COVID-19 that is similar to the general population. A similar pattern has been detected in COVID-19 morbidity and mortality rates, even among patients with an autoimmune disease, such as rheumatoid arthritis and Sjögren syndrome.^5,17 Furthermore, exacerbation of preexisting rheumatic symptoms may be due to hyperactivation of antiviral pathways in a person with an autoimmune disease.^17-19 The findings in our patient suggested a direct role for the vaccine in skin manifestations, rather than for reactivation or development of new systemic autoimmune processes, such as systemic lupus erythematosus.

Exacerbation of psoriasis following COVID-19 vaccination has been described²⁰; however, the case patient did not have a history of psoriasis. The mechanism(s) of such exacerbation remain unclear; COVID-19 vaccine–induced helper T cells (T_H17) may play a role.²¹ Other skin manifestations encountered following COVID-19 vaccination include lichen planus, leukocytoclastic vasculitic rash, erythema multiforme–like rash, and pityriasis rosea–like rash.^22-25 The immune mechanisms of these manifestations remain unclear.

The clinical presentation of delayed vaccination reactions can be attributed to the timing of symptoms and, in this case, the immune-mediated background of a psoriasiform reaction. Although adverse reactions to the SARS-CoV-2 mRNA vaccine are rare, more individuals should be studied after vaccination to confirm and better understand this phenomenon.

The Diagnosis: Tuberous Xanthoma

The skin biopsy revealed a nodular collection of foam cells (quiz image [bottom]). Tuberous xanthoma was the most likely diagnosis based on the patient’s history as well as the clinical and histologic findings. Tuberous xanthomas are flat or elevated nodules in the dermis and subcutaneous tissue, commonly occurring on the skin over the joints.¹ Smaller nodules and papules often are referred to as tuberoeruptive xanthomas and exist on a continuum with the larger tuberous xanthomas. All xanthomas appear histologically similar, with collections of foam cells present within the dermis.² Foam cells form when serum lipoproteins diffuse through capillary walls, deposit in the skin or tendons, and are scavenged by monocytes.3 Tuberous xanthomas, along with tendinous, eruptive, and planar xanthomas, are the most likely to be associated with hyperlipidemia.⁴ They may indicate an underlying disorder of lipid metabolism, such as familial hypercholesterolemia.^1,3 This is the most common cause of inheritable cardiovascular disease, with a prevalence of approximately 1:250.² Premature cardiovascular disease risk increases 2 to 4 times in patients with familial hypercholesterolemia and tendinous xanthomas,¹ illustrating that recognition of cutaneous lesions can lead to earlier diagnosis and prevention of patient morbidity and mortality.

Juvenile xanthogranuloma typically presents as smooth yellow papules or nodules on the head and neck, with a characteristic “setting-sun” appearance (ie, yellow center with an erythematous halo) on dermoscopy.⁵ Histologically, juvenile xanthogranulomas are composed of foam cells and a mixed lymphohistiocytic infiltrate with eosinophils within the dermis. Giant cells with a ring of nuclei surrounded by cytoplasm containing lipid vacuoles (called Touton giant cells) are characteristic (Figure 1). In contrast to tuberous xanthomas, juvenile xanthogranulomas often present within the first year of life.⁶

Keloid scars are more prevalent in patients with skin of color. They are characterized by eosinophilic keloidal collagen with a whorled proliferation of fibroblasts on histology (Figure 2).⁷ They occur spontaneously or at sites of injury and present as bluish-red or flesh-colored firm papules or nodules.⁸ In our patient, keloid scars were an unlikely diagnosis due to the lack of trauma and the absence of keloidal collagen on histology.

Necrobiosis lipoidica diabeticorum typically presents as an erythematous, yellow-brown, circular plaque on the anterior lower leg in patients with diabetes mellitus; it rarely occurs in children.⁹ Microscopy shows palisaded granulomas surrounding necrobiotic collagen arranged horizontally in a layer cake–like fashion (Figure 3).^9,10 The etiology of necrobiosis lipoidica diabeticorum currently is unknown, though immune complex deposition may contribute to its pathology. It has been associated with type 1 diabetes mellitus, though severity of the lesions is not associated with extent of glycemic control.¹⁰

Rosai-Dorfman disease is an uncommon disorder characterized by a proliferation of histiocytes that most often presents as bilateral cervical lymphadenopathy in children and young adults but rarely can present with cutaneous lesions when extranodal involvement is present.^11,12 The cutaneous form most commonly presents as red papules or nodules. On histology, the lesions exhibit a nodular dermal proliferation of histiocytes and smaller lymphocytoid cells with a marbled or starry sky–like appearance on low power (Figure 4). On higher magnification, the characteristic finding of emperipolesis can be seen.11 On immunohistochemistry, the histiocytes stain positively for CD68 and S-100. Although the pathogenesis currently is unknown, evidence of clonality indicates the disease may be related to a neoplastic process.¹²

The Diagnosis: Tuberous Xanthoma

The skin biopsy revealed a nodular collection of foam cells (quiz image [bottom]). Tuberous xanthoma was the most likely diagnosis based on the patient’s history as well as the clinical and histologic findings. Tuberous xanthomas are flat or elevated nodules in the dermis and subcutaneous tissue, commonly occurring on the skin over the joints.¹ Smaller nodules and papules often are referred to as tuberoeruptive xanthomas and exist on a continuum with the larger tuberous xanthomas. All xanthomas appear histologically similar, with collections of foam cells present within the dermis.² Foam cells form when serum lipoproteins diffuse through capillary walls, deposit in the skin or tendons, and are scavenged by monocytes.3 Tuberous xanthomas, along with tendinous, eruptive, and planar xanthomas, are the most likely to be associated with hyperlipidemia.⁴ They may indicate an underlying disorder of lipid metabolism, such as familial hypercholesterolemia.^1,3 This is the most common cause of inheritable cardiovascular disease, with a prevalence of approximately 1:250.² Premature cardiovascular disease risk increases 2 to 4 times in patients with familial hypercholesterolemia and tendinous xanthomas,¹ illustrating that recognition of cutaneous lesions can lead to earlier diagnosis and prevention of patient morbidity and mortality.

Juvenile xanthogranuloma typically presents as smooth yellow papules or nodules on the head and neck, with a characteristic “setting-sun” appearance (ie, yellow center with an erythematous halo) on dermoscopy.⁵ Histologically, juvenile xanthogranulomas are composed of foam cells and a mixed lymphohistiocytic infiltrate with eosinophils within the dermis. Giant cells with a ring of nuclei surrounded by cytoplasm containing lipid vacuoles (called Touton giant cells) are characteristic (Figure 1). In contrast to tuberous xanthomas, juvenile xanthogranulomas often present within the first year of life.⁶

Keloid scars are more prevalent in patients with skin of color. They are characterized by eosinophilic keloidal collagen with a whorled proliferation of fibroblasts on histology (Figure 2).⁷ They occur spontaneously or at sites of injury and present as bluish-red or flesh-colored firm papules or nodules.⁸ In our patient, keloid scars were an unlikely diagnosis due to the lack of trauma and the absence of keloidal collagen on histology.

Necrobiosis lipoidica diabeticorum typically presents as an erythematous, yellow-brown, circular plaque on the anterior lower leg in patients with diabetes mellitus; it rarely occurs in children.⁹ Microscopy shows palisaded granulomas surrounding necrobiotic collagen arranged horizontally in a layer cake–like fashion (Figure 3).^9,10 The etiology of necrobiosis lipoidica diabeticorum currently is unknown, though immune complex deposition may contribute to its pathology. It has been associated with type 1 diabetes mellitus, though severity of the lesions is not associated with extent of glycemic control.¹⁰

Rosai-Dorfman disease is an uncommon disorder characterized by a proliferation of histiocytes that most often presents as bilateral cervical lymphadenopathy in children and young adults but rarely can present with cutaneous lesions when extranodal involvement is present.^11,12 The cutaneous form most commonly presents as red papules or nodules. On histology, the lesions exhibit a nodular dermal proliferation of histiocytes and smaller lymphocytoid cells with a marbled or starry sky–like appearance on low power (Figure 4). On higher magnification, the characteristic finding of emperipolesis can be seen.11 On immunohistochemistry, the histiocytes stain positively for CD68 and S-100. Although the pathogenesis currently is unknown, evidence of clonality indicates the disease may be related to a neoplastic process.¹²

The Diagnosis: Tuberous Xanthoma

The skin biopsy revealed a nodular collection of foam cells (quiz image [bottom]). Tuberous xanthoma was the most likely diagnosis based on the patient’s history as well as the clinical and histologic findings. Tuberous xanthomas are flat or elevated nodules in the dermis and subcutaneous tissue, commonly occurring on the skin over the joints.¹ Smaller nodules and papules often are referred to as tuberoeruptive xanthomas and exist on a continuum with the larger tuberous xanthomas. All xanthomas appear histologically similar, with collections of foam cells present within the dermis.² Foam cells form when serum lipoproteins diffuse through capillary walls, deposit in the skin or tendons, and are scavenged by monocytes.3 Tuberous xanthomas, along with tendinous, eruptive, and planar xanthomas, are the most likely to be associated with hyperlipidemia.⁴ They may indicate an underlying disorder of lipid metabolism, such as familial hypercholesterolemia.^1,3 This is the most common cause of inheritable cardiovascular disease, with a prevalence of approximately 1:250.² Premature cardiovascular disease risk increases 2 to 4 times in patients with familial hypercholesterolemia and tendinous xanthomas,¹ illustrating that recognition of cutaneous lesions can lead to earlier diagnosis and prevention of patient morbidity and mortality.

Juvenile xanthogranuloma typically presents as smooth yellow papules or nodules on the head and neck, with a characteristic “setting-sun” appearance (ie, yellow center with an erythematous halo) on dermoscopy.⁵ Histologically, juvenile xanthogranulomas are composed of foam cells and a mixed lymphohistiocytic infiltrate with eosinophils within the dermis. Giant cells with a ring of nuclei surrounded by cytoplasm containing lipid vacuoles (called Touton giant cells) are characteristic (Figure 1). In contrast to tuberous xanthomas, juvenile xanthogranulomas often present within the first year of life.⁶

Keloid scars are more prevalent in patients with skin of color. They are characterized by eosinophilic keloidal collagen with a whorled proliferation of fibroblasts on histology (Figure 2).⁷ They occur spontaneously or at sites of injury and present as bluish-red or flesh-colored firm papules or nodules.⁸ In our patient, keloid scars were an unlikely diagnosis due to the lack of trauma and the absence of keloidal collagen on histology.

Necrobiosis lipoidica diabeticorum typically presents as an erythematous, yellow-brown, circular plaque on the anterior lower leg in patients with diabetes mellitus; it rarely occurs in children.⁹ Microscopy shows palisaded granulomas surrounding necrobiotic collagen arranged horizontally in a layer cake–like fashion (Figure 3).^9,10 The etiology of necrobiosis lipoidica diabeticorum currently is unknown, though immune complex deposition may contribute to its pathology. It has been associated with type 1 diabetes mellitus, though severity of the lesions is not associated with extent of glycemic control.¹⁰

Rosai-Dorfman disease is an uncommon disorder characterized by a proliferation of histiocytes that most often presents as bilateral cervical lymphadenopathy in children and young adults but rarely can present with cutaneous lesions when extranodal involvement is present.^11,12 The cutaneous form most commonly presents as red papules or nodules. On histology, the lesions exhibit a nodular dermal proliferation of histiocytes and smaller lymphocytoid cells with a marbled or starry sky–like appearance on low power (Figure 4). On higher magnification, the characteristic finding of emperipolesis can be seen.11 On immunohistochemistry, the histiocytes stain positively for CD68 and S-100. Although the pathogenesis currently is unknown, evidence of clonality indicates the disease may be related to a neoplastic process.¹²

The correct answer is (D), molluscum contagiosum. Upon surgical excision, the pathology indicated the lesion was consistent with molluscum contagiosum.

Molluscum contagiosum is a benign skin disorder caused by a pox virus and is frequently seen in children. This disease is transmitted primarily through direct skin contact with an infected individual.¹ Contaminated fomites have been suggested as another source of infection.² The typical lesion appears dome-shaped, round, and pinkish-purple in color.¹ The incubation period ranges from 2 weeks to 6 months and is typically self-limited in immunocompetent hosts; however, in immunocompromised persons, molluscum contagiosum lesions may present atypically such that they are larger in size and/or resemble malignancies, such as basal cell carcinoma or keratoacanthoma (for single lesions), or other infectious diseases, such as cryptococcosis and histoplasmosis (for more numerous lesions).^{3,4 A} giant atypical molluscum contagiosum is rarely seen in healthy individuals.
 

What’s on the differential?

The recent episode of bleeding raises concern for other neoplastic processes of the skin including squamous cell carcinoma or basal cell carcinoma as well as cutaneous metastatic rhabdoid tumor, given the patient’s history.

Eruptive keratoacanthomas are also reported in patients taking nivolumab, an anti-PD-1 immunotherapy, which the patient has received for treatment of his recurrent metastatic rhabdoid tumor.⁵ More common entities such as a pyogenic granuloma or verruca are also included on the differential. The initial presentation of the lesion, however, is more consistent with the pearly umbilicated papules associated with molluscum contagiosum.

Comments from Dr. Eichenfield

This is a very hard diagnosis to make with the clinical findings and history.

Molluscum contagiosum infections are common, but with this patient’s medical history, biopsy and excision with pathologic examination was an appropriate approach to make a certain diagnosis.

Ms. Moyal is a research associate in the division of pediatric and adolescent dermatology at the University of California, San Diego, and Rady Children’s Hospital, San Diego. Dr. Eichenfield is vice chair of the department of dermatology and professor of dermatology and pediatrics at the University of California, San Diego, and Rady Children’s Hospital, San Diego.

References

1. Brown J et al. Int J Dermatol. 2006 Feb;45(2):93-9.

2. Hanson D and Diven DG. Dermatol Online J. 2003 Mar;9(2).

3. Badri T and Gandhi GR. Molluscum contagiosum. 2022. In: StatPearls [Internet]. Treasure Island, Fla.: StatPearls Publishing.

4. Schwartz JJ and Myskowski PL. J Am Acad Dermatol. 1992 Oct 1;27(4):583-8.

5. Antonov NK et al. JAAD Case Rep. 2019 Apr 5;5(4):342-5.

The correct answer is (D), molluscum contagiosum. Upon surgical excision, the pathology indicated the lesion was consistent with molluscum contagiosum.

Molluscum contagiosum is a benign skin disorder caused by a pox virus and is frequently seen in children. This disease is transmitted primarily through direct skin contact with an infected individual.¹ Contaminated fomites have been suggested as another source of infection.² The typical lesion appears dome-shaped, round, and pinkish-purple in color.¹ The incubation period ranges from 2 weeks to 6 months and is typically self-limited in immunocompetent hosts; however, in immunocompromised persons, molluscum contagiosum lesions may present atypically such that they are larger in size and/or resemble malignancies, such as basal cell carcinoma or keratoacanthoma (for single lesions), or other infectious diseases, such as cryptococcosis and histoplasmosis (for more numerous lesions).^{3,4 A} giant atypical molluscum contagiosum is rarely seen in healthy individuals.
 

What’s on the differential?

The recent episode of bleeding raises concern for other neoplastic processes of the skin including squamous cell carcinoma or basal cell carcinoma as well as cutaneous metastatic rhabdoid tumor, given the patient’s history.

Eruptive keratoacanthomas are also reported in patients taking nivolumab, an anti-PD-1 immunotherapy, which the patient has received for treatment of his recurrent metastatic rhabdoid tumor.⁵ More common entities such as a pyogenic granuloma or verruca are also included on the differential. The initial presentation of the lesion, however, is more consistent with the pearly umbilicated papules associated with molluscum contagiosum.

Comments from Dr. Eichenfield

This is a very hard diagnosis to make with the clinical findings and history.

Molluscum contagiosum infections are common, but with this patient’s medical history, biopsy and excision with pathologic examination was an appropriate approach to make a certain diagnosis.

Ms. Moyal is a research associate in the division of pediatric and adolescent dermatology at the University of California, San Diego, and Rady Children’s Hospital, San Diego. Dr. Eichenfield is vice chair of the department of dermatology and professor of dermatology and pediatrics at the University of California, San Diego, and Rady Children’s Hospital, San Diego.

References

1. Brown J et al. Int J Dermatol. 2006 Feb;45(2):93-9.

2. Hanson D and Diven DG. Dermatol Online J. 2003 Mar;9(2).

3. Badri T and Gandhi GR. Molluscum contagiosum. 2022. In: StatPearls [Internet]. Treasure Island, Fla.: StatPearls Publishing.

4. Schwartz JJ and Myskowski PL. J Am Acad Dermatol. 1992 Oct 1;27(4):583-8.

5. Antonov NK et al. JAAD Case Rep. 2019 Apr 5;5(4):342-5.

The correct answer is (D), molluscum contagiosum. Upon surgical excision, the pathology indicated the lesion was consistent with molluscum contagiosum.

Molluscum contagiosum is a benign skin disorder caused by a pox virus and is frequently seen in children. This disease is transmitted primarily through direct skin contact with an infected individual.¹ Contaminated fomites have been suggested as another source of infection.² The typical lesion appears dome-shaped, round, and pinkish-purple in color.¹ The incubation period ranges from 2 weeks to 6 months and is typically self-limited in immunocompetent hosts; however, in immunocompromised persons, molluscum contagiosum lesions may present atypically such that they are larger in size and/or resemble malignancies, such as basal cell carcinoma or keratoacanthoma (for single lesions), or other infectious diseases, such as cryptococcosis and histoplasmosis (for more numerous lesions).^{3,4 A} giant atypical molluscum contagiosum is rarely seen in healthy individuals.
 

What’s on the differential?

The recent episode of bleeding raises concern for other neoplastic processes of the skin including squamous cell carcinoma or basal cell carcinoma as well as cutaneous metastatic rhabdoid tumor, given the patient’s history.

Eruptive keratoacanthomas are also reported in patients taking nivolumab, an anti-PD-1 immunotherapy, which the patient has received for treatment of his recurrent metastatic rhabdoid tumor.⁵ More common entities such as a pyogenic granuloma or verruca are also included on the differential. The initial presentation of the lesion, however, is more consistent with the pearly umbilicated papules associated with molluscum contagiosum.

Comments from Dr. Eichenfield

This is a very hard diagnosis to make with the clinical findings and history.

Molluscum contagiosum infections are common, but with this patient’s medical history, biopsy and excision with pathologic examination was an appropriate approach to make a certain diagnosis.

Ms. Moyal is a research associate in the division of pediatric and adolescent dermatology at the University of California, San Diego, and Rady Children’s Hospital, San Diego. Dr. Eichenfield is vice chair of the department of dermatology and professor of dermatology and pediatrics at the University of California, San Diego, and Rady Children’s Hospital, San Diego.

References

1. Brown J et al. Int J Dermatol. 2006 Feb;45(2):93-9.

2. Hanson D and Diven DG. Dermatol Online J. 2003 Mar;9(2).

3. Badri T and Gandhi GR. Molluscum contagiosum. 2022. In: StatPearls [Internet]. Treasure Island, Fla.: StatPearls Publishing.

4. Schwartz JJ and Myskowski PL. J Am Acad Dermatol. 1992 Oct 1;27(4):583-8.

5. Antonov NK et al. JAAD Case Rep. 2019 Apr 5;5(4):342-5.

The Diagnosis: IgA Pemphigus

Histopathology revealed a neutrophilic pustule and vesicle formation underlying the corneal layer (Figure). Direct immunofluorescence (DIF) showed weak positive staining for IgA within the intercellular keratinocyte in the epithelial compartment and a negative pattern with IgG, IgM, C3, and fibrinogen. The patient received a 40-mg intralesional triamcinolone injection and was placed on an oral prednisone 50-mg taper within 5 days. The plaques, bullae, and pustules began to resolve, but the lesions returned 1 day later. Oral prednisone 10 mg daily was initiated for 1 month, which resulted in full resolution of the lesions.

IgA pemphigus is a rare autoimmune disorder characterized by the occurrence of painful pruritic blisters caused by circulating IgA antibodies, which react against keratinocyte cellular components responsible for mediating cell-to-cell adherence.¹ The etiology of IgA pemphigus presently remains elusive, though it has been reported to occur concomitantly with several chronic malignancies and inflammatory conditions. Although its etiology is unknown, IgA pemphigus most commonly is treated with oral dapsone and corticosteroids.²

IgA pemphigus can be divided into 2 primary subtypes: subcorneal pustular dermatosis and intraepidermal neutrophilic dermatosis.^1,3 The former is characterized by intercellular deposition of IgA that reacts to the glycoprotein desmocollin-1 in the upper layer of the epidermis. Intraepidermal neutrophilic dermatosis is distinguished by the presence of autoantibodies against the desmoglein members of the cadherin superfamily of proteins. Additionally, unlike subcorneal pustular dermatosis, intraepidermal neutrophilic dermatosis autoantibody reactivity occurs in the lower epidermis.⁴

The differential includes dermatitis herpetiformis, which is commonly seen on the elbows, knees, and buttocks, with DIF showing IgA deposition at the dermal papillae. Pemphigus foliaceus is distributed on the scalp, face, and trunk, with DIF showing IgG intercellular deposition. Pustular psoriasis presents as erythematous sterile pustules in a more localized annular pattern. Subcorneal pustular dermatosis (Sneddon-Wilkinson disease) has similar clinical and histological findings to IgA pemphigus; however, DIF is negative.

The Diagnosis: IgA Pemphigus

Histopathology revealed a neutrophilic pustule and vesicle formation underlying the corneal layer (Figure). Direct immunofluorescence (DIF) showed weak positive staining for IgA within the intercellular keratinocyte in the epithelial compartment and a negative pattern with IgG, IgM, C3, and fibrinogen. The patient received a 40-mg intralesional triamcinolone injection and was placed on an oral prednisone 50-mg taper within 5 days. The plaques, bullae, and pustules began to resolve, but the lesions returned 1 day later. Oral prednisone 10 mg daily was initiated for 1 month, which resulted in full resolution of the lesions.

IgA pemphigus is a rare autoimmune disorder characterized by the occurrence of painful pruritic blisters caused by circulating IgA antibodies, which react against keratinocyte cellular components responsible for mediating cell-to-cell adherence.¹ The etiology of IgA pemphigus presently remains elusive, though it has been reported to occur concomitantly with several chronic malignancies and inflammatory conditions. Although its etiology is unknown, IgA pemphigus most commonly is treated with oral dapsone and corticosteroids.²

IgA pemphigus can be divided into 2 primary subtypes: subcorneal pustular dermatosis and intraepidermal neutrophilic dermatosis.^1,3 The former is characterized by intercellular deposition of IgA that reacts to the glycoprotein desmocollin-1 in the upper layer of the epidermis. Intraepidermal neutrophilic dermatosis is distinguished by the presence of autoantibodies against the desmoglein members of the cadherin superfamily of proteins. Additionally, unlike subcorneal pustular dermatosis, intraepidermal neutrophilic dermatosis autoantibody reactivity occurs in the lower epidermis.⁴

The differential includes dermatitis herpetiformis, which is commonly seen on the elbows, knees, and buttocks, with DIF showing IgA deposition at the dermal papillae. Pemphigus foliaceus is distributed on the scalp, face, and trunk, with DIF showing IgG intercellular deposition. Pustular psoriasis presents as erythematous sterile pustules in a more localized annular pattern. Subcorneal pustular dermatosis (Sneddon-Wilkinson disease) has similar clinical and histological findings to IgA pemphigus; however, DIF is negative.

The Diagnosis: IgA Pemphigus

Histopathology revealed a neutrophilic pustule and vesicle formation underlying the corneal layer (Figure). Direct immunofluorescence (DIF) showed weak positive staining for IgA within the intercellular keratinocyte in the epithelial compartment and a negative pattern with IgG, IgM, C3, and fibrinogen. The patient received a 40-mg intralesional triamcinolone injection and was placed on an oral prednisone 50-mg taper within 5 days. The plaques, bullae, and pustules began to resolve, but the lesions returned 1 day later. Oral prednisone 10 mg daily was initiated for 1 month, which resulted in full resolution of the lesions.

IgA pemphigus is a rare autoimmune disorder characterized by the occurrence of painful pruritic blisters caused by circulating IgA antibodies, which react against keratinocyte cellular components responsible for mediating cell-to-cell adherence.¹ The etiology of IgA pemphigus presently remains elusive, though it has been reported to occur concomitantly with several chronic malignancies and inflammatory conditions. Although its etiology is unknown, IgA pemphigus most commonly is treated with oral dapsone and corticosteroids.²

IgA pemphigus can be divided into 2 primary subtypes: subcorneal pustular dermatosis and intraepidermal neutrophilic dermatosis.^1,3 The former is characterized by intercellular deposition of IgA that reacts to the glycoprotein desmocollin-1 in the upper layer of the epidermis. Intraepidermal neutrophilic dermatosis is distinguished by the presence of autoantibodies against the desmoglein members of the cadherin superfamily of proteins. Additionally, unlike subcorneal pustular dermatosis, intraepidermal neutrophilic dermatosis autoantibody reactivity occurs in the lower epidermis.⁴

The differential includes dermatitis herpetiformis, which is commonly seen on the elbows, knees, and buttocks, with DIF showing IgA deposition at the dermal papillae. Pemphigus foliaceus is distributed on the scalp, face, and trunk, with DIF showing IgG intercellular deposition. Pustular psoriasis presents as erythematous sterile pustules in a more localized annular pattern. Subcorneal pustular dermatosis (Sneddon-Wilkinson disease) has similar clinical and histological findings to IgA pemphigus; however, DIF is negative.

Perineuriomas are benign, slow-growing tumors derived from perineurial cells,¹ which form the structurally supportive perineurium that surrounds individual nerve fascicles.^2,3 Perineuriomas are classified into 2 main forms: intraneural or extraneural.⁴ Intraneural perineuriomas are found within the border of the peripheral nerve,⁵ while extraneural perineuriomas usually are found in soft tissue and skin. Extraneural perineuriomas can be further classified into variants based on their histologic appearance, including reticular, sclerosing, and plexiform subtypes. Extraneural perineuriomas usually present on the extremities or trunk of young to middle-aged adults as a well-circumscribed, painless, subcutaneous masses.¹ These tumors are especially unusual in children.⁴ We present 2 extraneural perineurioma cases in children, and we review the pertinent diagnostic features of perineurioma as well as the presentation in the pediatric population.

Case Reports

Patient 1—A 10-year-old boy with a history of cerebral palsy and related comorbidities presented to the clinic for evaluation of a lesion on the thigh with no associated pain, irritation, erythema, or drainage. Physical examination revealed a soft, pedunculated, mobile nodule on the right medial thigh. An elliptical excision was performed. Gross examination demonstrated a 2.0×2.0×1.8-cm polypoid nodule. Histologic examination showed a dermal-based proliferation of bland spindle cells (Figure 1). The cytomorphology was characterized by elongated tapering nuclei and many areas with delicate bipolar cytoplasmic processes. The constituent cells were arranged in a whorled pattern in a variably myxoid to collagenous stroma. The tumor cells were multifocally positive for CD34; focally positive for smooth muscle actin (SMA); and negative for S-100, epithelial membrane antigen (EMA), GLUT1, claudin-1, STAT6, and desmin. Rb protein was intact. The CD34 immunostain highlighted the cytoplasmic processes. Electron microscopy was performed because the immunohistochemical results were nonspecific despite the favorable histologic features for perineurioma and showed pinocytic vesicles with delicate cytoplasmic processes, characteristic of perineurioma (Figure 2). Follow-up visits were related to the management of multiple comorbidities; no known recurrence of the lesion was documented.

Patient 2—A 15-year-old adolescent boy with no notable medical history presented to the pediatric clinic for a bump on the right upper arm of 4 to 5 months’ duration. He did not recall an injury to the area and denied change in size, redness, bruising, or pain of the lesion. Ultrasonography demonstrated a 2.6×2.3×1.3-cm hypoechoic and slightly heterogeneous, well-circumscribed, subcutaneous mass with internal vascularity. The patient was then referred to a pediatric surgeon. The clinical differential included a lipoma, lymphadenopathy, or sebaceous cyst. An excision was performed. Gross inspection demonstrated a 7-g, 2.8×2.6×1.8-cm, homogeneous, tan-pink, rubbery nodule with minimal surrounding soft tissue. Histologic examination showed a bland proliferation of spindle cells with storiform and whorled patterns (Figure 3). No notable nuclear atypia or necrosis was identified. The tumor cells were focally positive for EMA (Figure 4), claudin-1, and CD34 and negative for S-100, SOX10, GLUT1, desmin, STAT6, pankeratin AE1/AE3, and SMA. The diagnosis of perineurioma was rendered. No recurrence of the lesion was appreciated clinically on a 6-month follow-up examination.

Comment

Characteristics of Perineuriomas—On gross evaluation, perineuriomas are firm, gray-white, and well circumscribed but not encapsulated. Histologically, perineuriomas can have a storiform, whorled, or lamellar pattern of spindle cells. Perivascular whorls can be a histologic clue. The spindle cells are bland appearing and typically are elongated and slender but can appear slightly ovoid and plump. The background stroma can be myxoid, collagenous, or mixed. There usually is no atypia, and mitotic figures are rare.^2,3,6,7 Intraneural perineuriomas vary architecturally in that they display a unique onion bulb–like appearance in which whorls of cytoplasmic material of variable sizes surround central axons.³

Diagnosis—The diagnosis of perineuriomas usually requires characteristic immunohistochemical and sometimes ultrastructural features. Perineuriomas are positive for EMA and GLUT1 and variable for CD34.⁶ Approximately 20% to 91% will be positive for claudin-1, a tight junction protein associated with perineuriomas.⁸ Of note, EMA and GLUT1 usually are positive in both neoplastic and nonneoplastic perineurial cells.^9,10 Occasionally, these tumors can be focally positive for SMA and negative for S-100 and glial fibrillary acidic protein. The bipolar, thin, delicate, cytoplasmic processes with long-tapering nuclei may be easier to appreciate on electron microscopy than on conventional light microscopy. In addition, the cells contain pinocytotic vesicles and a discontinuous external lamina, which may be helpful for diagnosis.¹⁰

Genetics—Genetic alterations in perineurioma continue to be elucidated. Although many soft tissue perineuriomas possess deletion of chromosome 22q material, this is not a consistent finding and is not pathognomonic. Notably, the NF2 tumor suppressor gene is found on chromosome 22.¹¹ For the sclerosing variant of perineurioma, rearrangements or deletions of chromosome 10q have been described. A study of 14 soft tissue/extraneural perineuriomas using whole-exome sequencing and single nucleotide polymorphism array showed 6 cases of recurrent chromosome 22q deletions containing the NF2 locus and 4 cases with a previously unreported finding of chromosome 17q deletions containing the NF1 locus that were mutually exclusive events in all but 1 case.¹² Although perineuriomas can harbor NF1 or NF2 mutations, perineuriomas are not considered to be associated with neurofibromatosis type 1 or 2 (NF1 or NF2, respectively). Patients with NF1 or NF2 and perineurioma are exceedingly rare. One pediatric patient with both soft tissue perineurioma and NF1 has been reported in the literature.¹³

Differential Diagnosis—Perineuriomas should be distinguished from other benign neural neoplasms of the skin and soft tissue. Commonly considered in the differential diagnosis is schwannoma and neurofibroma. Schwannomas are encapsulated epineurial nerve sheath tumors comprised of a neoplastic proliferation of Schwann cells. Schwannomas morphologically differ from perineuriomas because of the presence of the hypercellular Antoni A with Verocay bodies and the hypocellular myxoid Antoni B patterns of spindle cells with elongated wavy nuclei and tapered ends. Other features include hyalinized vessels, hemosiderin deposition, cystic degeneration, and/or degenerative atypia.^3,14 Importantly, the constituent cells of schwannomas are positive for S-100 and SOX10 and negative for EMA.³ Neurofibromas consist of fascicles and whorls of Schwann cells in a background myxoid stroma with scattered mast cells, lymphocytes, fibroblasts, and perineurial cells. Similar to schwannomas, neurofibromas also are positive for S-100 and negative for EMA.^3,14 Neurofibromas can have either a somatic or germline mutation of the biallelic NF1 gene on chromosome 17q11.2 with subsequent loss of protein neurofibromin activity.¹⁵ Less common but still a consideration are the hybrid peripheral nerve sheath tumors that may present with a biphasic or intermingled morphology. Combinations include neurofibroma-schwannoma, schwannoma-perineurioma, and neurofibroma-perineurioma. The hybrid schwannoma-perineurioma has a mixture of thin and plump spindle cells with tapered nuclei as well as patchy S-100 positivity corresponding to schwannian areas. Similarly, S-100 will highlight the wavy Schwann cells in neurofibroma-perineurioma as well as CD34-highlighting fibroblasts.^7,15 In both aforementioned hybrid tumors, EMA will be positive in the perineurial areas. Another potential diagnostic consideration that can occur in both pediatric and adult populations is dermatofibrosarcoma protuberans (DFSP), which is comprised of a dermal proliferation of monomorphic fusiform spindle cells. Although both perineuriomas and DFSP can have a storiform architecture, DFSP is more asymmetric and infiltrative. Dermatofibrosarcoma protuberans is recognized in areas of individual adipocyte trapping, referred to as honeycombing. Dermatofibrosarcoma protuberans typically does not express EMA, though the sclerosing variant of DFSP has been reported to sometimes demonstrate focal EMA reactivity.^11,14,16 For morphologically challenging cases, cytogenetic studies will show t(17;22) translocation fusing the COL1A1 and PDGFRB genes.¹⁶ Finally, for subcutaneous or deep-seated tumors, one also may consider other mesenchymal neoplasms, including solitary fibrous tumor, low-grade fibromyxoid sarcoma, or low-grade malignant peripheral nerve sheath tumor (MPNST).¹¹

Management—Perineuriomas are considered benign. The presence of mitotic figures, pleomorphism, and degenerative nuclear atypia akin to ancient change, as seen in ancient schwannoma, does not affect their benign clinical behavior. Treatment of a perineurioma typically is surgical excision with conservative margins and minimal chance of recurrence.^1,11 So-called malignant perineuriomas are better classified as MPNSTs with perineural differentiation or perineurial MPNST. They also are positive for EMA and may be distinguished from perineurioma by the presence of major atypia and an infiltrative growth pattern.^17,18

Considerations in the Pediatric Population—Few pediatric soft tissue perineuriomas have been reported. A clinicopathologic analysis by Hornick and Fletcher¹ of patients with soft tissue perineurioma showed that only 6 of 81 patients were younger than 20 years. The youngest reported case of perineurioma occurred as an extraneural perineurioma on the scalp in an infant.¹⁹ Only 1 soft tissue perineural MPNST has been reported in the pediatric population, arising on the face of an 11-year-old boy. In a case series of 11 pediatric perineuriomas, including extraneural and intraneural, there was no evidence of recurrence or metastasis at follow-up.⁴

Conclusion

Perineuriomas are rare benign peripheral nerve sheath tumors with unique histologic and immunohistochemical features. Soft tissue perineuriomas in the pediatric population are an important diagnostic consideration, especially for the pediatrician or dermatologist when encountering a well-circumscribed nodular soft tissue lesion of the extremity or when encountering a neural-appearing tumor in the subcutaneous tissue.

Acknowledgment—We would like to thank Christopher Fletcher, MD (Boston, Massachusetts), for his expertise in outside consultation for patient 1.

Perineuriomas are benign, slow-growing tumors derived from perineurial cells,¹ which form the structurally supportive perineurium that surrounds individual nerve fascicles.^2,3 Perineuriomas are classified into 2 main forms: intraneural or extraneural.⁴ Intraneural perineuriomas are found within the border of the peripheral nerve,⁵ while extraneural perineuriomas usually are found in soft tissue and skin. Extraneural perineuriomas can be further classified into variants based on their histologic appearance, including reticular, sclerosing, and plexiform subtypes. Extraneural perineuriomas usually present on the extremities or trunk of young to middle-aged adults as a well-circumscribed, painless, subcutaneous masses.¹ These tumors are especially unusual in children.⁴ We present 2 extraneural perineurioma cases in children, and we review the pertinent diagnostic features of perineurioma as well as the presentation in the pediatric population.

Case Reports

Patient 1—A 10-year-old boy with a history of cerebral palsy and related comorbidities presented to the clinic for evaluation of a lesion on the thigh with no associated pain, irritation, erythema, or drainage. Physical examination revealed a soft, pedunculated, mobile nodule on the right medial thigh. An elliptical excision was performed. Gross examination demonstrated a 2.0×2.0×1.8-cm polypoid nodule. Histologic examination showed a dermal-based proliferation of bland spindle cells (Figure 1). The cytomorphology was characterized by elongated tapering nuclei and many areas with delicate bipolar cytoplasmic processes. The constituent cells were arranged in a whorled pattern in a variably myxoid to collagenous stroma. The tumor cells were multifocally positive for CD34; focally positive for smooth muscle actin (SMA); and negative for S-100, epithelial membrane antigen (EMA), GLUT1, claudin-1, STAT6, and desmin. Rb protein was intact. The CD34 immunostain highlighted the cytoplasmic processes. Electron microscopy was performed because the immunohistochemical results were nonspecific despite the favorable histologic features for perineurioma and showed pinocytic vesicles with delicate cytoplasmic processes, characteristic of perineurioma (Figure 2). Follow-up visits were related to the management of multiple comorbidities; no known recurrence of the lesion was documented.

Patient 2—A 15-year-old adolescent boy with no notable medical history presented to the pediatric clinic for a bump on the right upper arm of 4 to 5 months’ duration. He did not recall an injury to the area and denied change in size, redness, bruising, or pain of the lesion. Ultrasonography demonstrated a 2.6×2.3×1.3-cm hypoechoic and slightly heterogeneous, well-circumscribed, subcutaneous mass with internal vascularity. The patient was then referred to a pediatric surgeon. The clinical differential included a lipoma, lymphadenopathy, or sebaceous cyst. An excision was performed. Gross inspection demonstrated a 7-g, 2.8×2.6×1.8-cm, homogeneous, tan-pink, rubbery nodule with minimal surrounding soft tissue. Histologic examination showed a bland proliferation of spindle cells with storiform and whorled patterns (Figure 3). No notable nuclear atypia or necrosis was identified. The tumor cells were focally positive for EMA (Figure 4), claudin-1, and CD34 and negative for S-100, SOX10, GLUT1, desmin, STAT6, pankeratin AE1/AE3, and SMA. The diagnosis of perineurioma was rendered. No recurrence of the lesion was appreciated clinically on a 6-month follow-up examination.

Comment

Characteristics of Perineuriomas—On gross evaluation, perineuriomas are firm, gray-white, and well circumscribed but not encapsulated. Histologically, perineuriomas can have a storiform, whorled, or lamellar pattern of spindle cells. Perivascular whorls can be a histologic clue. The spindle cells are bland appearing and typically are elongated and slender but can appear slightly ovoid and plump. The background stroma can be myxoid, collagenous, or mixed. There usually is no atypia, and mitotic figures are rare.^2,3,6,7 Intraneural perineuriomas vary architecturally in that they display a unique onion bulb–like appearance in which whorls of cytoplasmic material of variable sizes surround central axons.³

Diagnosis—The diagnosis of perineuriomas usually requires characteristic immunohistochemical and sometimes ultrastructural features. Perineuriomas are positive for EMA and GLUT1 and variable for CD34.⁶ Approximately 20% to 91% will be positive for claudin-1, a tight junction protein associated with perineuriomas.⁸ Of note, EMA and GLUT1 usually are positive in both neoplastic and nonneoplastic perineurial cells.^9,10 Occasionally, these tumors can be focally positive for SMA and negative for S-100 and glial fibrillary acidic protein. The bipolar, thin, delicate, cytoplasmic processes with long-tapering nuclei may be easier to appreciate on electron microscopy than on conventional light microscopy. In addition, the cells contain pinocytotic vesicles and a discontinuous external lamina, which may be helpful for diagnosis.¹⁰

Genetics—Genetic alterations in perineurioma continue to be elucidated. Although many soft tissue perineuriomas possess deletion of chromosome 22q material, this is not a consistent finding and is not pathognomonic. Notably, the NF2 tumor suppressor gene is found on chromosome 22.¹¹ For the sclerosing variant of perineurioma, rearrangements or deletions of chromosome 10q have been described. A study of 14 soft tissue/extraneural perineuriomas using whole-exome sequencing and single nucleotide polymorphism array showed 6 cases of recurrent chromosome 22q deletions containing the NF2 locus and 4 cases with a previously unreported finding of chromosome 17q deletions containing the NF1 locus that were mutually exclusive events in all but 1 case.¹² Although perineuriomas can harbor NF1 or NF2 mutations, perineuriomas are not considered to be associated with neurofibromatosis type 1 or 2 (NF1 or NF2, respectively). Patients with NF1 or NF2 and perineurioma are exceedingly rare. One pediatric patient with both soft tissue perineurioma and NF1 has been reported in the literature.¹³

Differential Diagnosis—Perineuriomas should be distinguished from other benign neural neoplasms of the skin and soft tissue. Commonly considered in the differential diagnosis is schwannoma and neurofibroma. Schwannomas are encapsulated epineurial nerve sheath tumors comprised of a neoplastic proliferation of Schwann cells. Schwannomas morphologically differ from perineuriomas because of the presence of the hypercellular Antoni A with Verocay bodies and the hypocellular myxoid Antoni B patterns of spindle cells with elongated wavy nuclei and tapered ends. Other features include hyalinized vessels, hemosiderin deposition, cystic degeneration, and/or degenerative atypia.^3,14 Importantly, the constituent cells of schwannomas are positive for S-100 and SOX10 and negative for EMA.³ Neurofibromas consist of fascicles and whorls of Schwann cells in a background myxoid stroma with scattered mast cells, lymphocytes, fibroblasts, and perineurial cells. Similar to schwannomas, neurofibromas also are positive for S-100 and negative for EMA.^3,14 Neurofibromas can have either a somatic or germline mutation of the biallelic NF1 gene on chromosome 17q11.2 with subsequent loss of protein neurofibromin activity.¹⁵ Less common but still a consideration are the hybrid peripheral nerve sheath tumors that may present with a biphasic or intermingled morphology. Combinations include neurofibroma-schwannoma, schwannoma-perineurioma, and neurofibroma-perineurioma. The hybrid schwannoma-perineurioma has a mixture of thin and plump spindle cells with tapered nuclei as well as patchy S-100 positivity corresponding to schwannian areas. Similarly, S-100 will highlight the wavy Schwann cells in neurofibroma-perineurioma as well as CD34-highlighting fibroblasts.^7,15 In both aforementioned hybrid tumors, EMA will be positive in the perineurial areas. Another potential diagnostic consideration that can occur in both pediatric and adult populations is dermatofibrosarcoma protuberans (DFSP), which is comprised of a dermal proliferation of monomorphic fusiform spindle cells. Although both perineuriomas and DFSP can have a storiform architecture, DFSP is more asymmetric and infiltrative. Dermatofibrosarcoma protuberans is recognized in areas of individual adipocyte trapping, referred to as honeycombing. Dermatofibrosarcoma protuberans typically does not express EMA, though the sclerosing variant of DFSP has been reported to sometimes demonstrate focal EMA reactivity.^11,14,16 For morphologically challenging cases, cytogenetic studies will show t(17;22) translocation fusing the COL1A1 and PDGFRB genes.¹⁶ Finally, for subcutaneous or deep-seated tumors, one also may consider other mesenchymal neoplasms, including solitary fibrous tumor, low-grade fibromyxoid sarcoma, or low-grade malignant peripheral nerve sheath tumor (MPNST).¹¹

Management—Perineuriomas are considered benign. The presence of mitotic figures, pleomorphism, and degenerative nuclear atypia akin to ancient change, as seen in ancient schwannoma, does not affect their benign clinical behavior. Treatment of a perineurioma typically is surgical excision with conservative margins and minimal chance of recurrence.^1,11 So-called malignant perineuriomas are better classified as MPNSTs with perineural differentiation or perineurial MPNST. They also are positive for EMA and may be distinguished from perineurioma by the presence of major atypia and an infiltrative growth pattern.^17,18

Considerations in the Pediatric Population—Few pediatric soft tissue perineuriomas have been reported. A clinicopathologic analysis by Hornick and Fletcher¹ of patients with soft tissue perineurioma showed that only 6 of 81 patients were younger than 20 years. The youngest reported case of perineurioma occurred as an extraneural perineurioma on the scalp in an infant.¹⁹ Only 1 soft tissue perineural MPNST has been reported in the pediatric population, arising on the face of an 11-year-old boy. In a case series of 11 pediatric perineuriomas, including extraneural and intraneural, there was no evidence of recurrence or metastasis at follow-up.⁴

Conclusion

Perineuriomas are rare benign peripheral nerve sheath tumors with unique histologic and immunohistochemical features. Soft tissue perineuriomas in the pediatric population are an important diagnostic consideration, especially for the pediatrician or dermatologist when encountering a well-circumscribed nodular soft tissue lesion of the extremity or when encountering a neural-appearing tumor in the subcutaneous tissue.

Acknowledgment—We would like to thank Christopher Fletcher, MD (Boston, Massachusetts), for his expertise in outside consultation for patient 1.

Perineuriomas are benign, slow-growing tumors derived from perineurial cells,¹ which form the structurally supportive perineurium that surrounds individual nerve fascicles.^2,3 Perineuriomas are classified into 2 main forms: intraneural or extraneural.⁴ Intraneural perineuriomas are found within the border of the peripheral nerve,⁵ while extraneural perineuriomas usually are found in soft tissue and skin. Extraneural perineuriomas can be further classified into variants based on their histologic appearance, including reticular, sclerosing, and plexiform subtypes. Extraneural perineuriomas usually present on the extremities or trunk of young to middle-aged adults as a well-circumscribed, painless, subcutaneous masses.¹ These tumors are especially unusual in children.⁴ We present 2 extraneural perineurioma cases in children, and we review the pertinent diagnostic features of perineurioma as well as the presentation in the pediatric population.

Case Reports

Patient 1—A 10-year-old boy with a history of cerebral palsy and related comorbidities presented to the clinic for evaluation of a lesion on the thigh with no associated pain, irritation, erythema, or drainage. Physical examination revealed a soft, pedunculated, mobile nodule on the right medial thigh. An elliptical excision was performed. Gross examination demonstrated a 2.0×2.0×1.8-cm polypoid nodule. Histologic examination showed a dermal-based proliferation of bland spindle cells (Figure 1). The cytomorphology was characterized by elongated tapering nuclei and many areas with delicate bipolar cytoplasmic processes. The constituent cells were arranged in a whorled pattern in a variably myxoid to collagenous stroma. The tumor cells were multifocally positive for CD34; focally positive for smooth muscle actin (SMA); and negative for S-100, epithelial membrane antigen (EMA), GLUT1, claudin-1, STAT6, and desmin. Rb protein was intact. The CD34 immunostain highlighted the cytoplasmic processes. Electron microscopy was performed because the immunohistochemical results were nonspecific despite the favorable histologic features for perineurioma and showed pinocytic vesicles with delicate cytoplasmic processes, characteristic of perineurioma (Figure 2). Follow-up visits were related to the management of multiple comorbidities; no known recurrence of the lesion was documented.

Patient 2—A 15-year-old adolescent boy with no notable medical history presented to the pediatric clinic for a bump on the right upper arm of 4 to 5 months’ duration. He did not recall an injury to the area and denied change in size, redness, bruising, or pain of the lesion. Ultrasonography demonstrated a 2.6×2.3×1.3-cm hypoechoic and slightly heterogeneous, well-circumscribed, subcutaneous mass with internal vascularity. The patient was then referred to a pediatric surgeon. The clinical differential included a lipoma, lymphadenopathy, or sebaceous cyst. An excision was performed. Gross inspection demonstrated a 7-g, 2.8×2.6×1.8-cm, homogeneous, tan-pink, rubbery nodule with minimal surrounding soft tissue. Histologic examination showed a bland proliferation of spindle cells with storiform and whorled patterns (Figure 3). No notable nuclear atypia or necrosis was identified. The tumor cells were focally positive for EMA (Figure 4), claudin-1, and CD34 and negative for S-100, SOX10, GLUT1, desmin, STAT6, pankeratin AE1/AE3, and SMA. The diagnosis of perineurioma was rendered. No recurrence of the lesion was appreciated clinically on a 6-month follow-up examination.

Comment

Characteristics of Perineuriomas—On gross evaluation, perineuriomas are firm, gray-white, and well circumscribed but not encapsulated. Histologically, perineuriomas can have a storiform, whorled, or lamellar pattern of spindle cells. Perivascular whorls can be a histologic clue. The spindle cells are bland appearing and typically are elongated and slender but can appear slightly ovoid and plump. The background stroma can be myxoid, collagenous, or mixed. There usually is no atypia, and mitotic figures are rare.^2,3,6,7 Intraneural perineuriomas vary architecturally in that they display a unique onion bulb–like appearance in which whorls of cytoplasmic material of variable sizes surround central axons.³

Diagnosis—The diagnosis of perineuriomas usually requires characteristic immunohistochemical and sometimes ultrastructural features. Perineuriomas are positive for EMA and GLUT1 and variable for CD34.⁶ Approximately 20% to 91% will be positive for claudin-1, a tight junction protein associated with perineuriomas.⁸ Of note, EMA and GLUT1 usually are positive in both neoplastic and nonneoplastic perineurial cells.^9,10 Occasionally, these tumors can be focally positive for SMA and negative for S-100 and glial fibrillary acidic protein. The bipolar, thin, delicate, cytoplasmic processes with long-tapering nuclei may be easier to appreciate on electron microscopy than on conventional light microscopy. In addition, the cells contain pinocytotic vesicles and a discontinuous external lamina, which may be helpful for diagnosis.¹⁰

Genetics—Genetic alterations in perineurioma continue to be elucidated. Although many soft tissue perineuriomas possess deletion of chromosome 22q material, this is not a consistent finding and is not pathognomonic. Notably, the NF2 tumor suppressor gene is found on chromosome 22.¹¹ For the sclerosing variant of perineurioma, rearrangements or deletions of chromosome 10q have been described. A study of 14 soft tissue/extraneural perineuriomas using whole-exome sequencing and single nucleotide polymorphism array showed 6 cases of recurrent chromosome 22q deletions containing the NF2 locus and 4 cases with a previously unreported finding of chromosome 17q deletions containing the NF1 locus that were mutually exclusive events in all but 1 case.¹² Although perineuriomas can harbor NF1 or NF2 mutations, perineuriomas are not considered to be associated with neurofibromatosis type 1 or 2 (NF1 or NF2, respectively). Patients with NF1 or NF2 and perineurioma are exceedingly rare. One pediatric patient with both soft tissue perineurioma and NF1 has been reported in the literature.¹³

Differential Diagnosis—Perineuriomas should be distinguished from other benign neural neoplasms of the skin and soft tissue. Commonly considered in the differential diagnosis is schwannoma and neurofibroma. Schwannomas are encapsulated epineurial nerve sheath tumors comprised of a neoplastic proliferation of Schwann cells. Schwannomas morphologically differ from perineuriomas because of the presence of the hypercellular Antoni A with Verocay bodies and the hypocellular myxoid Antoni B patterns of spindle cells with elongated wavy nuclei and tapered ends. Other features include hyalinized vessels, hemosiderin deposition, cystic degeneration, and/or degenerative atypia.^3,14 Importantly, the constituent cells of schwannomas are positive for S-100 and SOX10 and negative for EMA.³ Neurofibromas consist of fascicles and whorls of Schwann cells in a background myxoid stroma with scattered mast cells, lymphocytes, fibroblasts, and perineurial cells. Similar to schwannomas, neurofibromas also are positive for S-100 and negative for EMA.^3,14 Neurofibromas can have either a somatic or germline mutation of the biallelic NF1 gene on chromosome 17q11.2 with subsequent loss of protein neurofibromin activity.¹⁵ Less common but still a consideration are the hybrid peripheral nerve sheath tumors that may present with a biphasic or intermingled morphology. Combinations include neurofibroma-schwannoma, schwannoma-perineurioma, and neurofibroma-perineurioma. The hybrid schwannoma-perineurioma has a mixture of thin and plump spindle cells with tapered nuclei as well as patchy S-100 positivity corresponding to schwannian areas. Similarly, S-100 will highlight the wavy Schwann cells in neurofibroma-perineurioma as well as CD34-highlighting fibroblasts.^7,15 In both aforementioned hybrid tumors, EMA will be positive in the perineurial areas. Another potential diagnostic consideration that can occur in both pediatric and adult populations is dermatofibrosarcoma protuberans (DFSP), which is comprised of a dermal proliferation of monomorphic fusiform spindle cells. Although both perineuriomas and DFSP can have a storiform architecture, DFSP is more asymmetric and infiltrative. Dermatofibrosarcoma protuberans is recognized in areas of individual adipocyte trapping, referred to as honeycombing. Dermatofibrosarcoma protuberans typically does not express EMA, though the sclerosing variant of DFSP has been reported to sometimes demonstrate focal EMA reactivity.^11,14,16 For morphologically challenging cases, cytogenetic studies will show t(17;22) translocation fusing the COL1A1 and PDGFRB genes.¹⁶ Finally, for subcutaneous or deep-seated tumors, one also may consider other mesenchymal neoplasms, including solitary fibrous tumor, low-grade fibromyxoid sarcoma, or low-grade malignant peripheral nerve sheath tumor (MPNST).¹¹

Management—Perineuriomas are considered benign. The presence of mitotic figures, pleomorphism, and degenerative nuclear atypia akin to ancient change, as seen in ancient schwannoma, does not affect their benign clinical behavior. Treatment of a perineurioma typically is surgical excision with conservative margins and minimal chance of recurrence.^1,11 So-called malignant perineuriomas are better classified as MPNSTs with perineural differentiation or perineurial MPNST. They also are positive for EMA and may be distinguished from perineurioma by the presence of major atypia and an infiltrative growth pattern.^17,18

Considerations in the Pediatric Population—Few pediatric soft tissue perineuriomas have been reported. A clinicopathologic analysis by Hornick and Fletcher¹ of patients with soft tissue perineurioma showed that only 6 of 81 patients were younger than 20 years. The youngest reported case of perineurioma occurred as an extraneural perineurioma on the scalp in an infant.¹⁹ Only 1 soft tissue perineural MPNST has been reported in the pediatric population, arising on the face of an 11-year-old boy. In a case series of 11 pediatric perineuriomas, including extraneural and intraneural, there was no evidence of recurrence or metastasis at follow-up.⁴

Conclusion

Perineuriomas are rare benign peripheral nerve sheath tumors with unique histologic and immunohistochemical features. Soft tissue perineuriomas in the pediatric population are an important diagnostic consideration, especially for the pediatrician or dermatologist when encountering a well-circumscribed nodular soft tissue lesion of the extremity or when encountering a neural-appearing tumor in the subcutaneous tissue.

Acknowledgment—We would like to thank Christopher Fletcher, MD (Boston, Massachusetts), for his expertise in outside consultation for patient 1.