Pustular flagellate dermatitis after consumption of shiitake mushrooms

Lentinula edodes, or shiitake mushroom (SM), is typically grown in Eastern Asia and used in traditional Asian medicine and cuisine. Recently, SM became popular in Western culture and is now the second most commonly consumed mushroom in the world.1, 2 Although rare, adverse reactions to SM have been previously reported. In mushroom farm workers, contact dermatitis, contact urticaria, rhinitis, and hypersensitivity pneumonitis have been described. In the general population, oral intake of raw SM has been associated with a typical flagellate eruption, known as shiitake dermatitis (SD).3 Shiitake dermatitis, also termed shiitake toxicoderma or flagellate mushroom dermatitis, classically manifests 12 hours to 5 days after the ingestion of SM.1, 4 Since its first description in 1977, SD has been described in approximately 100 patients, predominantly Japanese.3, 5 Recently, a few cases were reported in Europe and in the United States.1 The mechanism underlying SD has not been fully elucidated. Although the eruption is usually considered nonallergic,6 5 cases of SD resulted in positive delayed skin prick testing, suggesting that delayed-type systemic hypersensitivity may be important in its pathogenesis.2, 3, 4, 7, 8, 9 We report the first case of SD in Canada and, to our knowledge, the first case of pustular SD. In our patient, positive delayed skin prick testing to SM was documented.