Shiitake happens: dermatitis from uncooked mushrooms

February 20, 2016, 12:18 pm




Shiitake dermatitis: the tale of an under-recognised, undercooked fungus. McNally A et al. Med J Aust 2016 Feb 15;204:124-6



Just when you thought it was safe to go back to the farmers’ market . . .

This interesting paper presents a series of 3 cases of flagellate dermatitis following consumption of raw or undercooked shiitake mushrooms. The rashes described were linear, pruritic, and papular, sparing areas such as the mid-back that could not be reached for scratching. All of these factors suggested that lesions were caused by the Koebner phenomenon.

Symptom onset after consuming undercooked shiitake mushrooms is typically 12-48 hours, with duration from days to several weeks. Symptoms resolve spontaneously, and no treatment has been proven effective. The cause is lentinan, a component of shiitake that is heat-labile and denatures at temperatures of 130-145oF . Not everyone is susceptible to shiitake dermatitis — risk factors may include use of ACE-inhibitors or diuretics, exposure to sunlight, and genetic factors. Differential diagnosis includes bleomycin dermatographism, dermatomyositis, adult-onset Still’s disease, and HIV with hypereosinophilic syndrome.

Shiitakes are grown either on logs or on substrate (sterilized sawdust.) Shiitake dermatitis seems to occur only after ingestion of log-grown mushrooms.

This is a fascinating brief paper, with wonderful color photographs of nasty-looking rashes.

Related post:

Flagellate dermatitis — when the shiitake hits the fan

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