[STUDY] Defining the response to interferon-beta in relapsing-remitting MS 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.""... "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...."