Differences in Use of Disease-Modifying Therapies Between Patients With Late-Onset and Adult-Onset Relapsing-Remitting Multiple Sclerosis

BACKGROUND AND OBJECTIVES: The therapeutic strategy for late-onset multiple sclerosis (LOMS) with a relapsing-remitting onset remains unclear, potentially leading to underexposure to disease-modifying therapies (DMTs) compared with adult-onset multiple sclerosis (AOMS). We investigated the differences in DMT use between LOMS and AOMS within the French MS registry at comparable levels of disease severity. METHODS: This retrospective cohort study used data extracted in December 2024 from the French MS registry on patients with relapsing-remitting onset MS between 1997 and 2023. The primary outcome was the annual probability of receiving a DMT according to age at MS onset, adjusted for disease severity. Secondary outcomes included the annual probability of receiving a highly effective DMT (HEDMT), each DMT separately, having ≥1 EDSS measurement, having ≥1 brain MRI, and DMT initiations and discontinuations. We used a longitudinal logistic model with generalized estimating equations and an inverse-probability-of-censoring weighting. RESULTS: A total of 36,148 were included patients; 26,540 (73.4%) were female, mean age was 33.5 years (SD, 9.7), and 2,308 (6.4%) were aged ≥50 at disease onset. Median follow-up was 10.8 years (interquartile range, 5.6-17.0). Patients with LOMS had a lower annual probability of receiving a DMT compared with patients with AOMS (73.7% vs 83.1%; odds ratio OR, 0.57 95% CI 0.52-0.62). The difference was greater for HEDMT (24.6% vs 44.4%; OR, 0.41 95% CI 0.36-0.46). Patients with LOMS were more likely to receive teriflunomide and less likely to receive fumarates, S1PR modulators, natalizumab, or anti-CD20. Clinical and radiologic follow-up did not differ significantly between patients with LOMS and AOMS. The rate of DMT initiation was lower in patients with LOMS (0.13 vs 0.17 initiation per patient-year). Although the proportions of DMT discontinuation were similar (59.7% vs 60.4%, excluding pregnancy-related discontinuations), these discontinuations were more often attributed to a complete discontinuation strategy (27.9% vs 22.3%) and less often to an escalation strategy (9.2% vs 13.8%) in patients with LOMS. DISCUSSION: At comparable levels of disease severity, patients with LOMS were less likely to be treated with DMTs, particularly HEDMT, than patients with AOMS. This gap was driven both by fewer DMT initiations and more frequent complete discontinuations.