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- Presentation
Dermatopathology Discussion: Clear Cell Tumors, PEComa, and Pemphigus Variants
Description
The discussion reviewed dermatopathology differentials and key diagnostic clues for clear cell tumors and pemphigus variants. A bloody clear cell skin tumor initially suggested metastatic renal cell carcinoma, but other possibilities were considered, including clear cell sarcoma, hidradenoma, melanoma, granular cell tumor, fibrous papule, and PEComa. Immunostains showed glycogen, negative CD10/RCC/PAX8, and strong desmin positivity, supporting PEComa; the speaker noted that PEComas may express melanocytic markers, sometimes S100, and often muscle markers, with behavior-based classification important. The second major topic was pemphigus foliaceus, which presented with scalp scale and nonspecific skin lesions; biopsy showed subcorneal “grains” and features that can mimic Darier disease, but DIF with a chicken-wire pattern confirmed pemphigus foliaceus, an anti-desmoglein 1 disease typically limited to skin without mucosal involvement. Diagnostic limitations of ELISA and DIF were mentioned. Finally, a third case with exophytic lesions, pseudoepitheliomatous hyperplasia, and pus was diagnosed as pemphigus vegetans, emphasizing that pemphigus variants can mimic infection, neoplasia, or other inflammatory dermatoses and may present in scalp, oral, or intertriginous sites.
View moreConclusions
- The clear-cell skin tumor in the first case was favored to be a PEComa rather than renal cell carcinoma, clear cell sarcoma, or melanoma because it showed glycogen-rich clear cells with negative RCC/CD10/PAX8 and positive desmin.
- PEComas are diagnostically tricky because they can express melanocytic and muscle markers in overlapping patterns, and a minority can even be S100 positive.
- A subset of PEComas behave aggressively, so proposed classification systems use size, infiltrative growth, mitotic activity, necrosis, and vascular invasion to stratify risk.
- For pemphigus foliaceus, the key diagnostic clues were superficial acantholysis with corneocytes/grains and confirmatory intercellular “chicken wire” DIF staining, with disease limited to skin because of desmoglein 1 autoimmunity.
- Pemphigus foliaceus can present very variably, including scalp-predominant disease and hyperpigmented or minimally scaly lesions, so clinicopathologic correlation is important.
- Serologic and immunofluorescence tests for pemphigus are helpful but imperfect, with limited sensitivity and substrate-dependent performance.
- Pemphigus vegetans was identified when an exophytic, pus-rich lesion with pseudoepitheliomatous hyperplasia showed DIF features of pemphigus rather than infection or a simple reactive process.
- When confronted with PEH plus pustules, the differential should include halogenoderma, deep fungal infection, granuloma inguinale, leishmaniasis, and pemphigus vegetans.
- Overall, the presentation emphasized that careful histology, targeted immunostains, and direct immunofluorescence are often necessary to separate clinically similar mimics in dermatopathology.
- Folpe AL, Mentzel T, Lehr HA, Fisher C, Balzer BL, Weiss SW. Perivascular epithelioid cell neoplasms of soft tissue and gynecologic origin: a clinicopathologic study of 26 cases and proposal for classification. Am J Surg Pathol. 2005.#10.1097/01.pas.0000173232.22117.37