Defining the response to interferon-β in relapsing-remitting multiple sclerosis patients

Objective: Many patients with multiple sclerosis (MS) are currently receiving treatment with interferon (IFN)-beta. Early identification of nonresponder patients is crucial to try different therapeutic approaches. We investigated various criteria of treatment response to assess which criterion better identifies patients with a poor response. Methods. We studied relapsing-remitting MS (RRMS) patients treated with IFN-beta and followed them up for at least 2 years. Expanded Disability Status Score was scored every 3 months and relapses were recorded. We analyzed various criteria based on relapses, disability progression, or both. Results: Three hundred ninety-three patients were included. After 2 years of treatment, we observed a proportion of nonresponders, ranging from 7 to 49% depending on the stringency of the criteria used. Criteria based in disability progression had higher sensitivity, specificity, and accuracy. The hazard ratio for the development of marked disability after 6 years of treatment was 39.6 (95% confidence interval, 16.6-94.4) among the patients who fulfilled the criterion based only in disability progression. Interpretation: Criteria of response to IFN-beta therapy in RRMS using disability progression are more clinically relevant than those based only in relapse rate. This finding may be important for the counseling and care of RRMS patients treated with IFN-beta.