Multiple Sclerosis Subtypes: How the Natural History of Multiple Sclerosis Was Challenged due to Treatment

The clinical course of multiple sclerosis (MS) is heterogeneous, varying between patients as well as over time. Classification criteria define the relapsing and progressive forms of MS as well as active and stable disease. Prior to the advent of disease-modifying therapies (DMTs), the majority of patients developed a secondarily progressive course. Randomized clinical trials, long-term extension trials, and observational trials provide data on the impact of DMTs on relapses and progression; however, use of these currently available studies to assess the effect on MS disease course is limited by duration or selection bias. Further analysis of a large populations of MS patients is needed to ascertain the long-term effects of DMTs on MS clinical course.