Spider bite-induced erythema multiforme.

Erythema multiforme (EM) is an immune-mediated mucocutaneous eruption characterized by symmetrically distributed, polymorphic targetoid lesions, mostly on the distal parts of the extremities. It occurs mostly in the setting of an infection in certain predisposed individuals. A 30-year-old pregnant woman was presented with a necrotic erythematous lesion on her right thigh following a spider bite. As she was pregnant for 16 weeks, no systemic medication was given. On the 8th day of the spider bite an erythematous vesicular and targetoid rash was seen on the distal parts of her extremities. Based on the clinical and histopathological findings, lesions were diagnosed as EM. She had not used any medication for 4 months and she gave no prior history of herpetic infection. So her EM lesions were thought to be an ID reaction most probably due to the spider bite. As far as we know, this is the first reported case of EM induced by a spider bite.