Shiitake mushrooms (Lentinula edodes) are the second most commonly cultivated mushrooms worldwide. These mushrooms are particularly popular in Japan, where they are consumed as normal cuisine. In traditional Asian medicine, shiitake mushrooms are also used as adjunct therapy in the treatment of hypertension, hypercholesterolemia, and various cancers. Partly due to these proposed health benefits, shiitake mushrooms are becoming increasingly available and utilized in the Western world.
Although the pathophysiology remains unclear, the current leading hypothesis is that flagellate mushroom dermatitis is caused by a thermolabile polysaccharide called lentinan, which is found in shiitake mushrooms. Lentinan is thought to activate leukocytes and cause vasodilation. Given the linearly streaked nature of the lesions, an additional trauma-induced mechanism via the Koebner phenomenon has been suggested but remains controversial.
Most cases have been described in Japan, but recently, cases have also been reported in Europe and North America. In all cases, the dermatitis was observed in individuals who consumed raw or undercooked shiitake mushrooms, with the onset of lesions ranging from 12 hours to 5 days after ingestion. In its classic presentation, there is a rapid eruption of erythematous papules and/or vesicles grouped in multiple linear streaks, coalescing in a flagellate pattern, with accompanying pruritus.
Without continued consumption of raw or undercooked shiitake mushrooms, this condition is self-limited, with spontaneous resolution in 1-8 weeks.
T62.0X4A – Toxic effect of ingested mushrooms, undetermined, initial encounter
86505009 – Toxic effect from eating mushrooms
Differential Diagnosis & Pitfalls
- Drug-induced flagellate pigmentation (bendamustine, bleomycin, docetaxel, peplomycin [bleomycin derivative]) – Bleomycin is the most common culprit. Findings mirror those of shiitake mushroom dermatitis, and there is a tendency for prominent post-inflammatory hyperpigmentation.
- Flagellate erythema of dermatomyositis – Pruritic linear and flagellate streaks are seen in a minority of dermatomyositis patients. Prominent brown discoloration is not seen after resolution.
- Adult-onset Still disease – Cutaneous findings comprise an acute reticulate eruption that may exhibit the Koebner phenomenon; grouped papules that form linear and flagellate streaks that persist more chronically.
- Acute contact dermatitis from poison ivy or poison oak
- Phytophotodermatitis – Probe for history of recent exposure to furocoumarin-containing substances. Erythematous lesions typically blister prior to hyperpigmentation.
- Herpes zoster – Consider polymerase chain reaction (PCR)-based testing if suspicious for an atypical presentation.
- Mycosis fungoides
- Post-inflammatory hyperpigmentation – Probe for history of preceding cutaneous inflammation.
- Drug-induced pigmentation (amiodarone, minocycline)