Widespread urticaria due to intramuscular interferon beta-1a therapy for multiple sclerosis.

We describe two multiple sclerosis patients who displayed widespread urticaria due to intramuscular interferon beta-1a (INF-β-1a). Clinicians should be aware of this adverse event, since it may be severe and it may lead to the definitive interruption of treatment. Widespread urticaria complicating intramuscular INF-β-1a therapy in multiple sclerosis should be therefore added to the list of dermatological lesions associated with interferon therapy.