Patterns and predictors of transition between multiple sclerosis phenotypes: A longitudinal analysis.

BACKGROUND: Multiple sclerosis (MS) phenotype transitions are challenging to characterize. Our understanding of their predictors is also limited. OBJECTIVE: To investigate the transition between relapsing-remitting MS (RRMS) and secondary progressive MS (SPMS) within the Comprehensive Longitudinal Investigation of MS at the Brigham and Women's Hospital (CLIMB) study. METHODS: This retrospective study included adult people with MS having ≥10-year follow-up data who were classified as RRMS, primary progressive MS, and SPMS (active SPMS [aSPMS]: with relapse; nonrelapsing SPMS [nrSPMS]: no relapses within 2-year pre-index). Demographics, disability scores, and transition predictors were assessed. RESULTS: Ninety-seven of 565 people with RRMS (17.2%) transitioned to SPMS, of whom 92.8% (n = 90/97) were classified as nrSPMS by the final visit. People with RRMS who transitioned to nrSPMS were older (mean age, 53.1 vs. 45.4 years; P < 0.001) and took longer time to transition (mean, 13.0 vs. 7.8 years; P < 0.001) than those who transitioned to aSPMS. Older age at MS onset and a high number of disease-modifying therapy switches were significantly associated with a shorter time-to-nrSPMS transition (P ≤ 0.001). CONCLUSION: This study provides a comprehensive characterization of MS phenotype transitions, that may enhance clinical decision-making and therapeutic targeting of underlying pathophysiology driving disability in progressive MS.