A man who went to hospital after developing a bizarre rash across his back was found to have reacted to an unexpected ingredient.
The man, aged 72, was discovered to have eaten a meal containing shiitake mushrooms two days prior, which triggered the line-shaped itchy rash across his back, according to a case report in the New England Journal of Medicine.
The itching of the rash was so intense that he couldn't sleep, and was a result of shiitake dermatitis, which occasionally occurs "after consumption of raw or undercooked shiitake mushrooms," the case report reveals.
Shiitake dermatitis is a rare condition that arises in around two percent of people who eat raw or undercooked shiitake mushrooms. Due to the ingredient's prevalence in China and Japan, these countries have the highest rates of shiitake dermatitis.
"Two predominant theories exist [to explain why shiitake dermatitis occurs]," Eglė Janušonytė, co-author of the case report and dermatology resident at Geneva University Hospitals in Geneva, Switzerland, told Newsweek. "The first one suggests a mechanism dependent on a toxic dose. The other, more commonly embraced theory suggests an immune-mediated hypersensitivity reaction to lentinan which is a thermolabile polysaccharide found in the cell wall of raw or undercooked shiitake mushrooms. The activation of interleukin 1 by lentinan induces vasodilation and formation of the rash. Shiitake dermatitis doesn't occur when the ingested mushrooms are thoroughly cooked at temperatures surpassing 145 degrees C [293 degrees F]."
People with shiitake dermatitis may also experience a number of other symptoms, including localized swelling, fever, diarrhea, tingling of the lips and hands/feet, and discomfort swallowing.
This kind of skin reaction may also be a side effect of other conditions, but the man's dietary history strongly indicated that the shiitakes were to blame.
"Flagellate erythema, also known as whiplash lesions in dermatology, can also be caused by other conditions such as dermatomyositis, adult-onset Still disease, and the use of the medication bleomycin, but it is not triggered by the consumption of other foods" Janušonytė said.
The patient was warned against eating undercooked shiitake in the future, and given some medicine to ease the itching while the rash went away on its own.
"While this condition is self-limiting, we have prescribed topical corticosteroids and antihistamines for symptomatic relief. The patient had excellent improvement in the two weeks follow-up with residual hyperpigmented lesions remaining," Janušonytė said.
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