Assessing Functional Decline in Neurological Diseases Clinical Trials: Duration of Follow-Up - The Case of Multiple Sclerosis

Background: The main objective in the treatment of multiple sclerosis is to prevent or postpone the long-term disability caused by the disease, which in most cases occurs over years. However, most randomized clinical trials (RCTs) assessing the efficacy and safety of disease-modifying drugs have been designed to measure the short-term efficacy of disease-modifying drugs (up to 2-4 years) in reducing relapse rate and disease activity at magnetic resonance imaging (MRI). Summary: In this chapter we will discuss how drug efficacy in reducing short-term relapse rate and MRI activity impact on delaying the accumulation of long-term disability, and we will summarize the available literature on the long-term efficacy of the drugs as assessed by the few long-term observational and long-term extension RCTs on available drugs, focusing on interferon-β treatment as the one with a more extensive literature. Key Messages: Additional long-term observational studies and long-term extension of follow-up periods for patients included in RCTs are needed to explore the long-term efficacy of available drugs which are known to be effective at the short-term level.