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Mushroom Misery

Mushroom Misery

Shiitake dermatitis is a big price to pay for the joy of shiitake mushrooms.  The dermatitis consists of intense itching that occurs shortly after ingesting raw or undercooked shiitake mushrooms.  Characteristic of the rash are raised, red streaks which is also called “flagellate erythema” because it literally looks like the sequela of being whipped.  Other than this characteristic appearance, the dietary history is the cue to diagnosis.    

It responds quickly to oral antihistamines and/or steroids.  It is prevented by adequate cooking of the mushrooms.  But some Eastern health supplements may also contain raw shiitake. 

The shiitake mushroom contains lentinan, a sugar molecule called 1,3 beta-glucan.  In mice experiments when its given intravenously it has anti-cancer and anti-viral benefits.  For cancer it disrupts harmful intra-cellular signaling that helps cancer spread.  For viruses it inhibits tissue cells from absorbing the harmful virus.  Given orally to mice it has no benefit.  It also increases the production of an immune molecule called interleukin-1 (IL-1).  It’s the IL-1 that causes vasodilation (dilation of skin capillaries) and rash. 

Q – Tips: Mushrooms

Q – Tips: Mushrooms

Another less common mimic of food allergy is mushroom intolerance.  In this syndrome the deficient enzyme is Trehalase disaccharidase.   Mushrooms contain “double” (di-) sugar (saccharide).   If the sugar isn’t broken down into single sugar (mono-saccharide) it ferments in the colon causing bloating, gas, and diarrhea.  

Shitaki ‘shrooms tasty, but linked to streaky, itchy rash

Shitaki ‘shrooms tasty, but linked to streaky, itchy rash

Now, say that fast three times with your mouth full of mushrooms.  Shitake toxicoderma is a very common dermatitis in Asia, especially, China, Japan and Korea.  However, it is being seen more commonly in the U.S. as the popularity of shitake mushrooms increases.  The rash is fairly unique, consisting of a long linear array of urticaria. The skin looks like it has been whipped with cat-o-nine tails having red raised streaks that are very pruritic. The itchy lines can last for several weeks, and typically occur within a day of eating raw or cooked shitake mushrooms.
The mechanism of rash is felt to be due to Lentinam a polysaccharide found in the mushrooms that has immune-modulating effects. In fact, Lentinan has been used for chemotherapy in the treatment of colon and gastric cancers, It seems that individuals who get the rash have a hyper-immune response. Sun exposure can act as an adjunctive factor. The rash can be treated with steroids, usually topically, but if the problem is severe, oral steroids are used.