Diagnostic Dilemmas in Dermatopathology: Three Challenging Cases

The presentation highlighted three challenging dermatopathology cases that illustrated how difficult it can be to reach a specific diagnosis when clinical and histologic findings overlap. The first case was a 64-year-old man with chronic erythroderma and severe pruritus whose repeated biopsies initially showed only spongiotic and psoriasiform spongiotic dermatitis, raising concern for cutaneous T-cell lymphoma. After multiple biopsies, CD30 positivity, atypical epidermotropic lymphocytes, and limited blood flow abnormalities supported erythrodermic mycosis fungoides with large-cell transformation, and he improved markedly on extracorporeal photopheresis. The speaker emphasized that CTCL may require repeated biopsies, can mimic eczema or drug eruption, and that CD30 positivity has a broad differential. The second case involved a 68-year-old woman with fever, severe arthralgias, weight loss, and pink-to-violet lesions over joints. Biopsies showed palisaded granulomatous dermatitis with leukocytoclastic vasculitis and prominent neutrophils, leading to consideration of atypical Sweet syndrome, adult-onset Still disease, and ultimately reactive granulomatous dermatitis/palisaded neutrophilic granulomatous dermatitis. The discussion focused on its systemic associations with autoimmune disease, malignancy, and infection, and the need for broad workup and follow-up. The third case was a man with aggressive chronic lymphocytic leukemia who developed recurrent pruritic nodules, bullae, and episodic morbilliform eruptions. Biopsies showed eosinophilic spongiosis, subepidermal blistering, dermal eosinophilia, and possible flame figures, with negative direct immunofluorescence, favoring eosinophilic dermatosis of hematologic malignancy over bullous pemphigoid, arthropod bite reaction, or Wells syndrome. Overall, the talk stressed diagnostic uncertainty, the value of repeat sampling, and the importance of correlating pathology with clinical context.