LAUSR

A 47-year-old man presented to a clinic with a history of recurrent episodes of a generalized, pruritic, and flagellate dermatitis over the trunk and extremities. At the time of consultation, the patient’s eruption had resolved. However, he provided photographs depicting an erythematous, well-demarcated, extensive, pink, scaly, flagellate dermatitis over the arms, legs, trunk, and back (Figs. 1 and 2). The patient described consuming large quantities of shiitake mushrooms (Lentinus edodes) in homemade soup. The episodes of flagellate dermatitis were sporadic and did not occur each time he consumed shiitake mushroom soup. The episode depicted in the photographs appearedwithin 12hoursof consuming themushrooms and lasted approximately 5 days. He tried taking diphenhydramine, which did not seem to have an effect on the extent or duration of the eruption. Therewas no history of bleomycin or docetaxel use, nor did he experience any systemic symptoms.Hisonly othermedicationwas perindopril for hypertension, and there were no known allergies. His father has a history of allergic contact dermatitis, supported by patch testing to several exotic woods. First described in Japan in 1977, shiitake dermatitis (SD) presents with pruritic papules or petechiae partly arranged in a distinctive linear pattern. It may develop in individuals who eat or half-cook shiitake mushrooms (L. edodes), a commonly used ingredient in Asian cuisine. It is thought to represent a toxic irritant dermatitis to shiitake mushrooms. A polysaccharide component of the mushroom, known as lentinan, has been proposed as a causative agent of SD. This is supported by the alteration of lentinan’s molecular structure at high temperatures, which may explain why cooked mushrooms are not typically associated with SD.4 Further, SD-like reactions were reported in 9 of 519 patients in Japan who were treated with lentinan infusions as anticancer therapy. Both prick testing and patch testing are not clinically relevant in the diagnosis of SD. The differential diagnoses of flagellate dermatitis include drug eruptions from docetaxel and bleomycin, dermatomyositis, and adult-onset Still disease, all of which were excluded in this case. The clinical photographs and exposure history in this case were classic for SD (Figs. 1 and 2). The patient was advised to try and prevent recurrence by completely cooking shiitake mushrooms before consumption. Other than proper cooking and avoidance of the proposed polysaccharide toxin, there is no known treatment Figure 1. Flagellate mushroom dermatitis. Note the linear and flagellate erythematous streaks on the back. Figure 2. The right lateral chest wall and abdomen. PEARLS & ZEBRAS