Prior to the availability of the approved disease-modifying therapies, studies indicated that 50% of those diagnosed with relapsing-remitting MS (RRMS) would transition to secondary-progressive MS (SPMS) within 10 years, and 90% would transition within 25 years. While MS experts agree that the medications have an impact on disease progression, it is too soon to tell the extent to which the disease-modifying treatments alter or delay the transition to SPMS.