Raw shiitake-induced systemic allergic contact dermatitis

It has been reported that ingestion of raw or undercooked shiitake mushrooms is associated with various adverse food reactions. A 58-year-old man presented with pruritic and maculopapular rashes on the trunk and extremities starting 1 day after ingestion of partially uncooked shiitake mushrooms. A probable diagnosis of systemic allergic contact dermatitis was made. Raw and cooked shiitake mushroom-derived allergen extracts were prepared, and patch and intradermal tests with delayed readings were performed. The case showed positive intradermal test results with delayed readings to the raw, but not cooked, extracts. The case suggests that ingestion of uncooked shiitake mushrooms may induce systemic allergic contact dermatitis through type IV hypersensitivity reaction.