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Author: Emma Trowbridge, Registrar, Department of Dermatology, Christchurch Hospital, Christchurch, New Zealand, January 2016. Updated by Lauren Thomas, 3rd Year Postgraduate Medical Student, Flinders University, Northern Territory, Australia; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, September 2016.
Shiitake dermatitis is a distinctive rash that can occur following the ingestion of raw or undercooked shiitake mushrooms (Lentinula edodes).
It is characterised by pruritic, erythematous, linear streaks that resemble whiplash marks, hence the name flagellate.
Shiitake dermatitis is also known as flagellate erythema and toxicodermia.
China and Japan have the highest rates of consumption of shiitake mushrooms and the highest prevalence of shiitake dermatitis. It affects about 2% of people that consume the mushrooms raw or only lightly cooked. It has been reported in people of all ages, who are more often male than female.
More cases of shiitake dermatitis are being diagnosed in other countries where the use of shiitake mushrooms is increasing.
Shiitake flagellate dermatitis is a toxic reaction to lentinan, found in fresh, powdered, or lightly cooked shiitake mushrooms. Lentinan is a thermolabile polysaccharide that activates interleukin 1 secretion, leading to vasodilation, haemorrhage and rash.
This hypothesis is supported by the observation that shiitake dermatitis is not seen with the ingestion of thoroughly cooked at a temperature > 145 C.
Flagellate dermatitis does not result from cutaneous contact with the mushrooms.
The flagellate rash of shiitake dermatitis typically appears 24 hours after ingestion of raw or undercooked shiitake mushrooms.
The rash spontaneously resolves within a few weeks.
Shiitake flagellate dermatitis
Some patients with shiitake flagellate dermatitis have other symptoms.
The diagnosis is clinical, based on the characteristic history of recent mushroom ingestion and on the appearance of the rash. There are no specific laboratory findings. Usual tests may include:
Histopathology is nonspecific, demonstrating focal hyperkeratosis, spongiosis, dermal oedema and perivascular lymphocytic infiltrate with eosinophils.
Flagellate erythema is also associated with:
Raw shiitake mushrooms can also rarely induce contact allergic dermatitis in sensitised individuals.
Shiitake flagellate dermatitis is a self-limiting condition. It is unknown if treatment speeds up the resolution of the rash.
There is generally improvement within 2 days and complete resolution after 3 weeks.
Prevent future attacks by ensuring that Shiitake mushrooms are thoroughly cooked before eating.
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