Widespread maculopapular rash due to intramuscular interferon beta-1a during the treatment of multiple sclerosis.

We describe a 41-year-old woman with multiple sclerosis, who presented erythematous maculopapular rash on the trunk and extremities after the second injection of interferon beta-1a. Histopathologic examination of the lesion revealed lymphocytic exocytosis and perivascular lymphocytic infiltrate in the dermis. Oral antihistamine and topical corticosteroid was started. After improvement of the lesions, the third injection was performed. However, the same reaction occurred. A prick test, which was performed 6 weeks after the eruption, also revealed positive reaction. Although injection-site reactions have been observed with interferon beta-1a, to our knowledge there have been no previous reports of interferon beta-1a-induced widespread cutaneous reaction.