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Abstract

Shiitake mushroom dermatitis was first described by Nakamura et al in 1977 as a characteristic flagellate rash affecting patients 24-48 hours after ingestion of Shiitake mushrooms. The clinical differential diagnosis of flagellate dermatitis includes bleomycin-induced eruptions, dermatomyositis flagellate erythema, and phytophotodermtatitis. Here, we present the histopathologic findings and  clinicopathologic correlation in a case of Shiitake mushroom dermatitis. An adult woman presented with an acute onset pruritic rash two days after eating Shiitake mushrooms. The eruption consisted of erythematous and edematous linear plaques and macules on the abdomen and proximal thighs. The patient had no recent illness, no travel history, and no relevant medication history. Review of systems was unremarkable, including no fever or myalgia. Laboratory evaluation demonstrated mild neutrophilia with a normal white blood cell count and essentially normal metabolic panel. Biopsies were obtained and histologic sections demonstrated superficial perivascular dermatitis with eosinophils and mild papillary dermal edema. Direct immunofluorescence was negative for IgG, IgA, IgM, and C3. Thorough review of the clinical history and careful correlation with clinical photos in the electronic medical record allowed for accurate diagnosis in this case. The histopathologic manifestation of a systemic induced cutaneous hypersensitivity reaction to an ingested substance is important to bear in mind when considering this reaction pattern. This case highlights instructive histopathologic findings in a case of Shiitake mushroom dermatitis and emphasizes the importance of clinicopathologic correlation.