Coexistence of multiple sclerosis (MS) with other autoimmune diseases has been attributed to common background genetic or environmental factors. This study presents development of rheumatoid arthritis (RA) during treatment of MS. The MS was confirmed by the Mc Donald criteria and the diagnosis of RA was confirmed by the ACR/EULAR criteria. A 35 years old women with 9 years of MS who was receiving interferon beta 1-a (INF) for 7 years and who did not respond to conventional therapy of RA over 8 months developed clinical manifestations of RA. But a rapid response was observed after discontinuation of INF. These findings suggest a possible contribution of INF in the development of RA.
Keywords: Coexistence; Interferon beta 1-a; Multiple sclerosis; Rheumatoid arthritis.