A 28-year-old man presented with pruritic papules and target-shaped plaques of 2 days’ duration along the extensor surface of the arms (Fig. 1). There were no mucosal lesions. He denied systemic symptoms and confirmed that he had not taken any new drugs. Physical examination showed a scaling, erythematous, circinate plaque on the left forearm (Fig. 2) that, according to the patient, had grown centrifugally over the past 3 weeks, coinciding with the acquisition of a new guinea pig.
Histologic examination of the circinate lesion and a target-shaped plaque confirmed erythema multiforme secondary to tinea corporis. The causative agent was identified as Trichophyton mentagrophytes var. erinacei based on macroscopic and microscopic phenotypic characterization of the culture isolates. The lesions resolved after 4 weeks of treatment with oral prednisone (0.5mg/kg/d) and topical and oral terbinafine.
Erythema multiforme is a mucocutaneous immune reaction that mainly occurs in response to infection by herpes simplex virus or Mycoplasma pneumoniae. It is rarely associated with dermatophyte fungal infections and can be considered an id reaction induced by the release of fungal antigens at a distant site. Dermatophytosis due to T. mentagrophytes var. erinacei is rare in men and generally occurs after direct contact with hedgehogs, and less frequently, other pets, such as guinea pigs, cats, and dogs.
