Based on the clinical findings, the patient was diagnosed with flagellate shiitake mushroom dermatitis. (Subsequent treponemal and nontreponemal tests were negative for syphilis.)
Shiitake dermatitis is a rare disease that appears in susceptible patients after the consumption of large amounts of raw or undercooked shiitake mushrooms. The eruption is believed to be attributable to either a toxic or hypersensitivity reaction to lentinan, a polysaccharide component found within the mushroom cell wall.1 Shiitake dermatitis is self-limiting and treatment focuses on symptomatic management.
Early recognition and proper counseling should ensure symptomatic relief and prevent future episodes. In addition, anyone preparing shiitake mushrooms should make sure that they are fully cooked before serving or eating them.2
In the case described here, the patient was advised to avoid eating undercooked shiitake mushrooms in the future and he was prescribed topical steroids (mometasone furoate 0.1% cream). The eruption resolved 2 weeks later.
References
1. Nguyen AH, Gonzaga MI, Lim VM, et al. Clinical features of shiitake dermatitis: a systematic review. Int J Dermatol. 2017;56:610-616.
2. Stephany MP, Chung S, Handler MZ, et al. Shiitake mushroom dermatitis: a review. Am J Clin Dermatol. 2016;17:485-489.