Shiitake mushroom dermatitis is an intensely pruritic dermatitis characterized by disseminated 1mm erythematous micropapules seen in a linear grouped arrangement secondary to Koebnerization due to patient scratching. It is caused by the ingestion of shiitake mushrooms

Lentinan is an inflammatory polysaccharide found in shiitake mushrooms that is broken down by heat. When thoroughly cooked, lentinan is inactivated. However, consuming raw or undercooked mushrooms, containing the still-active lentinan, activates a cutaneous inflammatory response.

The characteristic linear rash develops within two days of exposure, and the diagnosis is often clinical, based on history and examination findings. The condition is self-limiting, typically resolving within three weeks, though can recur with repeat exposure. Management is supportive, and treatment with oral corticosteroids is unnecessary.

There have been case reports of shiitake dermatitis presenting with linear collections of vesicles in a dermatomal distribution. Hence, the differential diagnosis includes an atypical presentation of herpes zoster, allergic dermatitis,  Bleomycin ingestion or drug eruption. The presence of fever, lymphadenopathy, or edema should raise suspicion of another diagnosis, including Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS).

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