Flagellate Mushroom Dermatitis

Abstract

A woman in her 50s presented with a 4-day history of a diffuse, progressive, and pruritic rash. She had no known allergies and did not take any medications. She had no exposures to chemicals, detergents, or new personal care products; however, the patient consumed raw shiitake mushrooms several days before symptom onset. An examination revealed dozens of long flagellate streaks composed of red papules distributed across the trunk and extremities (Figure). She denied fever, malaise, or dyspnea. Laboratory results were remarkable for eosinophilia. The findings and history were consistent with flagellate mushroom dermatitis. The patient was treated with topical steroids, oral antihistamines, and raw shiitake mushroom avoidance, and the condition improved without sequelae.Flagellate mushroom dermatitis, also known as shiitake mushroom dermatitis, is thought to be caused by lentinan, a thermolabile toxin in shiitake mushrooms (Lentinula edodes). 1 Proposed pathogenesis includes delayed T-cell-mediated and toxinmediated reactions, as lentinan has T-cell-mediated antitumor properties, inducing vasodilation and hemorrhage reactions that can manifest as skin findings. However, the exact mechanism remains unknown. 2,3 Characteristic linear streaks of small erythematous pruritic papules appear 1 to 2 days following raw mushroom ingestion. It has been hypothesized that the linear pattern is partially produced by scratching; however, this has been disputed, as there are documented cases in which this pattern appears in the absence of scratching. 4 The distribution is commonly on the trunk and extremities. 1 The differential diagnosis for these findings is narrow and includes adult-onset Still disease, dermatomyositis, and flagellate erythema from chemotherapeutic agents, such as bleomycin. 3,4 Diagnosis of flagellate dermatitis is based on history and physical examination findings. Histology results are often nonspecific and may show spongiosis, perivascular lymphocytic and neutrophilic infiltrate, or eosinophils. 1,3 Flagellate mushroom dermatitis is self-limited, although treatment with topical steroids and oral antihistamines can be helpful. Resolution typically occurs within 1 to 8 weeks of mushroom avoidance, and thoroughly cooking mushrooms can prevent this dermatitis. Recognition of this condition may help guide patients to avoid triggers and minimize unnecessary testing.

Intensely itchy linear rash in a patient with Hodgkin’s lymphoma

“…Other causative drugs include peplomycin (an analogue of bleomycin), bendamustine and docetaxel. Consumption of raw or undercooked shiitake mushrooms can also trigger a similar dermatosis termed flagellate dermatitis 5. Flagellate rashes have also been associated with conditions such as dermatomyositis and adult-onset Still’s disease 2 3…”

Error in Corresponding Author’s Address

“…In the Images in Dermatology titled “Flagellate Mushroom Dermatitis,” the corresponding author’s address was listed incorrectly and should be “Oregon Health and Science University, School of Medicine, 3181 SW Sam Jackson Park Rd, Portland, OR 97239-3098.” This article was corrected online on May 18, 2022.…”