Late-onset and young-onset relapsing-remitting multiple sclerosis: evidence from a retrospective long-term follow-up study

Background and purpose: Late-onset multiple sclerosis (MS) has a prevalence of about 10-20% in natural history MS studies. Few data have been published about the long-term disease trajectory in the cohort of late-onset relapsing-remitting MS (LORRMS). The aim of this study was to identify the risk factors for reaching an Expanded Disability Status Scale (EDSS) score of 6.0 in LORRMS (onset at >40 years of age) and young-onset relapsing-remitting MS (YORRMS) (onset between 18 and 40 years of age).

Methods: Clinical and radiological [magnetic resonance imaging (MRI) of the brain] follow-up data were collected. Disability was assessed by EDSS score. A Cox proportional hazards model was used to evaluate the demographic and clinical predictors of reaching an EDSS score of 6.0 in the two cohorts.

Results: A total of 671 patients with relapsing-remitting MS were enrolled, 143 (21.3%) with LORRMS and 528 (78.7%) with YORRMS. In LORRMS, age at onset was 47.8 ± 5.3 (mean ± SD) years and duration of follow-up was 120.7 ± 52.7 months. In YORRMS, age at onset was 27 ± 2.7 years and duration of follow-up was 149.9 ± 92.7 months. The survival curve analyses showed a higher probability of reaching an EDSS score of 6.0 for LORRMS in a shorter time (months) than for YORRMS (94.2 vs. 103.2 months; log-rank 8.8; P < 0.05). On MRI, YORRMS showed more brain inflammatory features than LORRMS. In the multivariate Cox model, age at onset [Exp(B) value, 6.5; 95% confidence interval, 1.9-22.6; P < 0.001] and male gender [Exp(B) value, 1.7; 95% confidence interval, 1.0-2.8; P < 0.05] were the strongest predictors of reaching an EDSS score of 6.0.

Conclusions: The male population with LORRMS reached severe disability faster than those with YORRMS, even when YORRMS showed more brain inflammatory features on MRI.