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Sometimes a patient presents with a dermatitis where the biopsy is consistent with an urticarial type dermal hypersensitivity reaction, yet the etiology remains elusive. Then the patient comes back and reports that she found the cause by “Googling” it!

Clinical Case

A healthy 65-year-old woman taking no medication or supplements reported that she noticed an asymptomatic flagellate rash on her abdomen (See figure, next page). The evening prior to the onset of the rash, she said she ate Asian food and assumed she was reacting to something she had eaten. The rash completely subsided within 48 hours. Two weeks later, she ate the same Asian cuisine with four different types of undercooked mushrooms, including shiitake mushrooms, and the rash recurred. She reported that she went on Google and typed in “a rash that looks like you scratched” and determined that it was flagellate dermatitis caused by eating undercooked Shiitake mushrooms.


Shiitake (Lentinus edodes) mushrooms are heavily consumed, especially in Asia. These mushrooms contain a heat labile polysaccharide, lentinan. Lentinan is believed to be anticarcinogenic (adjuvant therapy for colorectal and gastric cancer) and is also used to lower lipids and treat hypertension.1 The dermatitis caused by raw or undercooked shiitake mushrooms is usually pruritic and occurs from 12 to 48 hours after ingestion. The lesions present as urticarial or petechial in a linear or crisscrossed pattern mainly on the trunk; thus the descriptive term: flagellate dermatitis.2,3

Since lentinan is heat-labile, the dermatitis does not occur after eating cooked shiitakes. The flagellate pattern is consistent with the Koebner phenomenon, however our patient denied any pruritus. Drugs reported to cause flagellate dermatitis include bleomycin, ACE inhibitors, and diuretics. Bleomycin produces a form of flagellate-like hyperpigmentation of the skin in eight to 66 percent of those exposed.4 Lesions begin as linear, erythematous, pruritic lesions that are slowly replaced by hyperpigmentation and present hours to weeks after dosing. The eruption usually resolves without treatment over weeks to months.5

Ron Ramirez, JD, MS4 is at the American University of the Caribbean School of Medicine, Sint Maarten, NA. Kathryn Zeoli, MD, FAAD is with the Skin Cancer Treatment Center, Inc., Pembroke Pines, FL, and aVoluntary Assistant Clinical Professor at the University of Miami Dept of Dermatology.

The authors have no relevant conflicts of interest
to disclose.

1. Diaz-Corpas T, Poppe LM, Anders D, Kneitz H, Brocker EB, Benoit S. Dermatitis flagelada tras la ingesta de setas del genero Shiitake. Actas Dermosifiliogr, 2011;102:830-832.

2. Nakamura T. Toxicoderma caused by shiitake (Lentinus edodes). Jpn J Clin Dermatol. 1977; 31:65-8.

3. Boels D et al. Shiitake dermatitis recorded by French Poison Control Center – new case series with clinical observations. Clin Toxicol 2014, Jul;52:625-628.

4. Guillet G et al. Cutaneous pigmented stripes and bleomycin treatment. Arch Dermatol 122:381,1986.

5. Kumar R, Pai V: Bleomycin induced flagellate pigmentation. Indian Pediatr 43:74.

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