Effects of methotrexate use in a patient with rheumatoid arthritis and multiple sclerosis

Rheumatoid arthritis (RA) and multiple sclerosis (MS) share similar pathophysiologic processes but coexistence of both diseases in the same patient has rarely been described. We describe the case of a 32 year old woman with rheumatoid arthritis treated with 12.5 mg of methotrexate once a week and 1 mg folic acid who developed paresthesias of her upper and lower extremities. Three years later, she acutely developed 6th nerve palsy, gait imbalance and urinary urgency and a diagnosis of multiple sclerosis was made. The use of methotrexate, though effective in controlling her rheumatoid arthritis, did not influence the development or progression of her multiple sclerosis. Although RA and MS may coexist in the same patient, treatment of one disease may have no influence on the clinical course of the other. Thus, the mechanism by which methotrexate suppresses disease activity in RA but not in MS despite both being T-cell mediated autoimmune diseases requires further investigative studies.