Shiitake Dermatitis

In the Rapid Review series, I briefly review the key points of a clinical review paper. (Well, this time it is a combination of 3 papers. The topic: Shiitake dermatitis

The papers: 

Mendonça CN, Silva PM, Avelleira JC, Nishimori FS, Cassia Fde F. Shiitake dermatitis. Anais brasileiros de dermatologia. 2015; 90(2):276-8. PMID: 25831007 [free full text]

Stephany MP, Chung S, Handler MZ, Handler NS, Handler GA, Schwartz RA. Shiitake Mushroom Dermatitis: A Review. American journal of clinical dermatology. 2016; 17(5):485-489. PMID: 27566177

Bachmeyer C, Rouff E. Shiitake dermatitis. CMAJ : Canadian Medical Association journal. 2017; 189(11):E439. PMID: 28385716 [free full text]

What is it?

Shiitake dermatitis is an intensely pruritic rash caused by a toxic reaction to lentinan, a component of shiitake mushrooms. It usually develops 1-3 days after eating raw or undercooked shiitake mushrooms. Not everyone who eats raw shiitake mushrooms has this reaction, so there is another currently unknown contributor.

What does the rash look like?

The rash is composed of linearly arranged erythematous papules or papulovesicles that appear over the trunk and extremities. It was thought to look like the linear marks left after flagellation, and hence the name “flagellate dermatitis”. The linear nature is attributed to the Koebner phenomenon. This looks like dermatographism, but it is not consistently produced by scratching. 

What are the other symptoms?

There are none. There are no systemic symptoms and no mucous membrane involvement.

What is the differential diagnosis?

There are medications that also cause flagellate dermatitis, including bleomycin, ACE inhibitors, and diuretics. Adult onset Still’s disease, dermatomyositis, and HIV induced hypereosinophilic syndrome also can have similar appearing rashes.  

How is it treated?

It is a self-resolving condition, although it may last as long as 8 weeks. Manage the pruritis with antihistamines, topical steroids, or oral steroids. (Some sources seem to say that treatment doesn’t help.)

Can it be prevented?

Lentinan is a heat labile protein, and so is destroyed by cooking. You cannot get flagellate dermatitis from properly cooked mushrooms. 

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Other FOAMed

Flagellate dermatitis — when the shiitake hits the fan

Shiitake happens: dermatitis from uncooked mushrooms