Shiitake Dermatitis Diagnosed After 16 Years!

Shiitake dermatitis is a condition that commonly occurs in Asian countries and has been recently reported in Europe. We report a case diagnosed after a 16-year history of an intermittent flagellate eruption.

A 45-year-old European man presented with a 16-year history of an intermittent eruption. He described a pruritic outbreak mainly on his trunk, with an associated strange, warm sensation. The eruption lasted approximately 1 week and was not helped by antihistamines. He denied any obvious precipitants and was taking no medication.

On examination, we found grouped, crisscrossed, linear, wheallike lesions, especially over the central back (Figure 1 and Figure 2). He was not dermatographic, and the eruption was not reproducible.

Blood tests revealed eosinophilia during the time that the eruption was present, but findings were normal in between eruptions. All other test results were normal. Further questioning revealed an interest in Asian food and cooking, including shiitake mushrooms. Previous episodes occurred after visits to hotels and restaurants where shiitake mushrooms may have been consumed. The diagnosis of shiitake dermatitis was confirmed with an oral challenge of half-cooked shiitake mushrooms. Thirty-six hours after ingestion of the mushrooms, the patient developed the eruption.

Shiitake dermatitis or toxicoderma is a condition that occurs after the ingestion of raw or half-cooked shiitake mushrooms (Lentinus edodes). First reported in 1977 by Nakamura,¹ it is common in Japan and China, but it has recently been reported in England.² The clinical features are linear groups of pruritic erythematous papules or flagellate dermatitis normally occurring up to 48 hours after mushroom ingestion.

The exact pathogenicity of shiitake flagellate dermatitis is still uncertain. Findings of skinprick and patch testing with mushroom extract are negative; therefore, it is unlikely to be a type I or IV allergy.^{3 - 4} Interestingly, 44% of patients also have dermatitis of the face, neck, and hands, and a role for a photosensitizing agent has been queried, although this circumstance did not apply to our patient.⁵ Nakamura³ suggests a form of koebnerization, although the eruption is not reproducible on scratching. It has also been suggested that shiitake dermatitis is caused by a toxic reaction to the polysaccharide lentinan. The beneficial effects of shiitake mushrooms, including reduced blood pressure and lower serum cholesterol levels, are also due to lentinan.³ Hanada and Hashimoto⁵ postulate that lentinan induces interleukin 1 secretion, which produces vasodilation and thus hemorrhage and eruption.

The eruption is similar to that of bleomycin-induced flagellate dermatitis. The sulfur component has been implicated in pathogenesis. As with shiitake dermatitis, in bleomycin dermatitis, the eruption is not reproduced with scratching despite fresh lesions occurring.⁶

Our patient did not link his episodic eruption with the eating of shiitake mushrooms owing to the time lag between ingestion and symptoms. Also, the mushrooms did not always cause a reaction; lentinan is thermolabile and can be destroyed with thorough cooking. The popularity of Asian cuisine has increased worldwide, and this case highlights the importance of recognizing an unusual disease, which may occur for many years before presentation.

Correspondence: Dr Garg, Dermatology Department, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, England (seema.garg@sth.nhs.uk).

Financial Disclosure: None reported.