Arthritis during interferon beta-1b treatment in multiple sclerosis.

Interferon beta (IFN-beta) is the most widely prescribed disease-modifying drug for multiple sclerosis (MS). Therapy with IFN-beta may be associated with a number of adverse reactions The development or exacerbation of other autoimmune diseases is a rare but reported side effect of IFN-beta therapy. In this case report, we present clinical and laboratory findings of two MS patients who developed arthritis during IFN-beta1b treatment, probably of autoimmune origin.