Shiitake Flagellate Dermatitis

A man in his early 70s presented with a 3-day history of intensely pruritic erythematous papules and papular vesicular eruption arranged in a flagellate pattern on his neck, trunk, (Figure 1), and extremities with no general symptoms. On questioning, he had eaten undercooked shiitake mushrooms 2 days before the onset of the cutaneous lesions. Laboratory investigation was unremarkable. A skin biopsy revealed spongiosis, marked papillary dermal edema, and a dermal perivascular inflammatory infiltrate mainly composed of lymphocytes and eosinophils. A diagnosis of shiitake flagellate dermatitis (SFD) was made. He was treated with oral antihistamines and topical calamine lotion. The eruption resolved completely in about 10 days, only leaving mild hyperpigmentation (Figure 2).Figure 2After treated with oral antihistamines and topical calamine lotion, the eruption of a patient with shiitake flagellate dermatitis resolved in about 10 days, only leaving mild hyperpigmentation.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Shiitake flagellate dermatitis typically occurs about 24 to 48 hours after eating raw or undercooked shiitake mushrooms. The exact pathogenesis of SFD remains unclear. It is more likely a direct toxic reaction to lentinan, an inflammatory polysaccharide found in shiitake mushrooms that is broken down by heat.1Nguyen A.H. Gonzaga M.I. Lim V.M. Adler M.J. Mitkov M.V. Cappel M.A. Clinical features of shiitake dermatitis: a systematic review.Int J Dermatol. 2017; 56: 610-616https://doi.org/10.1111/ijd.13433Crossref PubMed Scopus (27) Google Scholar It is characterized by erythematous linear grouped papules, petechiae, or vesicular lesions resembling scratch or whiplash marks. Some people can develop laboratory abnormalities and reactive airway disease.2Czarnecka A.B. Kreft B. Marsch WCh Flagellate dermatitis after consumption of shiitake mushrooms.Postepy Dermatol Alergol. 2014; 31: 187-190https://doi.org/10.5114/pdia.2014.40929Crossref PubMed Scopus (18) Google Scholar The histological findings are consistent with a hypersensitivity reaction and are nonspecific. These findings should prompt the clinician to look for an exposure to an allergen (contact or ingested), drug, infection, or systemic disorder. The differential diagnosis of SFD also includes dermatographic urticaria, bleomycin therapy, dermatomyositis, adult Still disease, and human immunodeficiency virus with hypereosinophilic syndrome. Shiitake flagellate dermatitis is self-limited, and antihistamines and topical corticosteroids have been used for symptomatic relief. Fully cooking shiitake mushrooms before ingestion usually prevents recurrence. The authors report no competing interests.