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Background: Acral lesions may represent the best/only skin lesions to biopsy in patients suspected to have dermatomyositis (DM). However, histopathologic features of acral DM skin lesions are poorly characterized., Methods: We reviewed 50 acral biopsies from 46 DM patients and assessed numerous histopathologic features. The majority of biopsies (42/50; 84%) were sampled from either Gottron papules or signs. We compared histopathologic features in acral biopsies to those in 197 non-acral DM skin biopsies. We also compared histopathologic features in acral biopsies based on the presence of various clinical features., Results: Interface dermatitis, dyskeratotic keratinocytes, and superficial perivascular inflammation were common in DM acral biopsies. However, the absence of > 1 hallmark histopathologic feature (interface dermatitis, dyskeratosis, dermal mucin) was relatively common (56%). The presence of all three hallmark histopathologic features was significantly more likely in non-acral compared with acral DM biopsies (68% vs. 44%; p = 0.0021). The hallmark histopathologic feature most commonly lacking in acral compared with non-acral biopsies was increased dermal mucin. Histopathologic features in acral biopsies did not significantly differ based on acral location, DM subtype, therapeutic regimen, or myositis-associated/myositis-specific antibody status., Conclusions: Pathologists should recognize that acral biopsies in DM patients may lack hallmark histopathologic features commonly seen in biopsies from non-acral locations., (© 2025 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Aim: Post-radiation angiosarcoma is an iatrogenic event seen in the setting of breast cancer treatment. Histopathologically, there are morphologic variants of angiosarcoma that mimic benign entities, including the capillary lobule variant of post-radiation angiosarcoma. We present the largest case series to date of this histopathologic variant of post-radiation angiosarcoma., Methods and Results: Cases of the capillary lobule variant of post-radiation angiosarcoma from institutional/consultation archives from 2008 to June 2022 were reviewed. For inclusion, tumors had to occur in irradiated skin and exhibit a multi-lobular proliferation of tightly packed capillary-like vessels, as previously described in this variant. Prior ancillary studies were also reviewed. Eight cases met the criteria. All occurred in women treated with radiation for breast cancer (median age 75 years). All cases had similar findings, including a multi-lobular proliferation of tightly packed vessels, infiltrative cords, and atypical single endothelial cells. A conventional angiosarcoma pattern was also seen in five cases. All cases tested were positive for vascular markers (CD31, CD34, and/or ERG) and MYC. MYC amplification was shown by FISH in all cases tested. Smooth muscle actin (SMA) was positive in pericytes in the capillary lobules in all five cases tested and areas of conventional angiosarcoma in two of three cases., Conclusions: The capillary lobule variant of angiosarcoma is a rare and therefore potentially under-recognized variant of post-radiation angiosarcoma. The lobular architecture and SMA positivity may mimic benign vascular proliferations. Careful attention to histopathologic features and ancillary tests may facilitate accurate diagnosis., (© 2022 The Authors. Journal of Cutaneous Pathology published by John Wiley & Sons Ltd.)

Acral melanocytic neoplasms often pose diagnostic difficulty. Preferentially expressed antigen in melanoma (PRAME) expression and loss of p16 expression have diagnostic utility in melanocytic tumors. We examined PRAME and p16 expression in 30 acral melanocytic neoplasms (n = 11 nevi; n = 2 dysplastic nevi; n = 7 Spitz nevi; n = 10 acral melanomas). PRAME was scored as % positive nuclei: negative = 0%; 1% to 25% = 1+; 25% to 50% = 2+; 50% to 75% = 3+, or positive: 75% to 100% = 4+. p16 expression was defined as retained (homogeneous or checkerboard) or lost (complete or partial/regionally). PRAME expression was negative in all benign, dysplastic, and Spitz nevi. Conversely, all acral melanomas were diffusely (4+) positive for PRAME expression. p16 expression was retained in all benign acral nevi (8/11 homogeneous, 3/11 checkerboard), completely lost in one dysplastic nevus, and retained in all acral Spitz nevi (3/7 homogeneous, 4/7 checkerboard). p16 was retained in five of 10 acral melanomas (3/10 homogeneous; 2/10 checkerboard), and negative in five of 10 acral melanomas (absent in 3/10, partially lost in 2/10). Our data suggest that 4+ PRAME expression is highly sensitive and specific in the setting of acral melanomas and is a more predictive diagnostic tool compared with p16 immunohistochemistry., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Dermatologists play an important role in diagnosing and managing hospitalized patients with cutaneous abnormalities. Skin biopsies remain an indispensable tool for aiding dermatologists in accurate diagnosis and treatment. We aimed to determine the range of conditions, and the most common conditions, prompting skin biopsy by dermatology hospital consultation (HCON) services to aid in evaluation of hospitalized patients., Methods: All hospitalized patients seen by a single tertiary care center dermatology HCON service between 2015 and 2018 who had associated skin biopsies were identified. Histologic features and clinical diagnoses of each patient were classified into 13 histologic reaction pattern categories., Results: Eight hundred and thirty one inpatients evaluated by our dermatology HCON service had 914 skin biopsies. The most frequent diagnostic categories prompting biopsy were vasculopathic (17.6%), interface dermatitis (16.5%), infectious (12.6%), and spongiotic dermatitis (10.9%). The most frequent diagnostic categories included drug reaction (13.2%), leukocytoclastic vasculitis (8.5%), skin cancer (5.4%), graft-vs-host disease (3.5%), connective tissue disease (3.3%), and calciphylaxis (3.0%)., Conclusion: Our study suggests a variety of serious diseases affecting inpatients prompts biopsy by dermatology consultation services. Educational curricula for dermatology and pathology residents, fellows, and staff designed with these data may enhance knowledge that improves the quality of inpatient dermatology care., (© 2019 The Authors. Journal of Cutaneous Pathology published by John Wiley & Sons Ltd.)

Background: Direct immunofluorescence (DIF) panels (IgG, IgA, IgM, C3 and fibrinogen) are ordered for clinically suspected vasculitis, with frequently negative results., Methods: Cases submitted for DIF and histology (2010-2014) with "vasculitis" in the clinical data were examined, and the electronic medical record reviewed for clinical suspicion of Henoch-Schönlein purpura (HSP). Peri/intravascular IgA was considered positive, other reactants non-specific and no immunoreactivity negative., Results: Vasculitis was the given indication for 20% (258/1318) of DIF studies. HSP was clinically suspected in 36% (95/258). In this setting, leukocytoclastic vasculitis (LCV) was common (66%, 63/95) and DIF was positive in 43% (27/63). One hundred percentage of DIF+ had LCV+. In cases without HSP suspicion, 26% (42/163) were LCV+ and <1% DIF+. Of the 258 cases, LCV+ greatly enriched for DIF+ (105/258 LCV+ with 28/105 [27%] DIF+), captured 100% of HSP and included cases with non-specific DIF/etiologic findings. In LCV cases, DIF positivity was not seen, HSP was not diagnosed and non-specific DIF findings were common., Conclusions: LCV is an H&E-based histopathologic diagnosis that can have positive, negative and non-specific DIF results that are rarely contributory except in the setting of HSP, where DIF is best utilized with IgA as the sole immunoreactant. H&E-based triage of DIF orders is recommended., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

A neutrophil-predominant inflammatory infiltrate in a cutaneous biopsy can be associated with a broad spectrum of diseases. Here we describe three cases showing a neutrophil-predominant dermal infiltrate admixed with abundant acellular bodies surrounded by capsule-like vacuolated spaces, which strikingly mimicked Cryptococcus. Two cases occurred within the settings of underlying hematologic malignancies; the third case was associated with immune dysregulation. Two patients were acutely ill in the medical intensive care unit. Fungal work-up, including cultures and multiple stains were negative. Because of clinical deterioration in these patients, transmission electron microscopy was pursued to definitively rule out fungal infection. In both cases, characteristics most compatible with autolysing human cells, not Cryptococcus, were identified. Chemotherapy and high-dose steroids were given, but both patients eventually succumbed to their diseases. To the best of our knowledge, these represent the first reported cases of autolysing human cells mimicking Cryptococcus organisms within neutrophilic infiltrates. They highlight the therapeutic dilemmas arising with histopathologic mimics, as well as the importance of thorough investigation to distinguish mimickers from true infectious organisms. We believe recognition of this microscopic pitfall will be useful to dermatopathologists faced with similar findings in the future, and may prevent unnecessary delay of appropriate therapy in acutely ill patients., (Copyright © 2012 John Wiley & Sons A/S.)

Background: Secondary angiosarcoma and benign but microscopically atypical vascular proliferations (herein referred to as atypical vascular lesion or AVL) are rare consequences of radiation therapy and/or chronic lymphedema most commonly seen in breast cancer patients. Differentiating angiosarcoma from AVL can be difficult due to overlapping clinical and microscopic features. Recently, amplification of MYC has been associated with 55-100% of secondary angiosarcomas but is reportedly absent in AVL. We examined a series of secondary angiosarcoma and AVL for MYC amplification by fluorescence in situ hybridization (FISH) and expression by immunohistochemistry to investigate the diagnostic utility for discriminating angiosarcoma from AVL., Methods: Cases of secondary angiosarcoma (n = 8) and AVL (n = 4) were retrieved from our archives and examined by FISH and immunohistochemistry., Results: All angiosarcoma cases (8/8 = 100%) demonstrated high-level MYC amplification by FISH, whereas all AVLs (0/4 = 0%) were negative for MYC amplification. Additionally, all angiosarcoma cases (8/8 = 100%) demonstrated nuclear positivity for MYC, whereas all AVLs (0/4 = 0%) were negative., Conclusion: Amplification of MYC and nuclear expression of MYC is present in secondary angiosarcoma but not AVL. These ancillary tests can be useful to distinguish angiosarcoma from AVL in difficult cases., (Copyright © 2011 John Wiley & Sons A/S.)