Older Age at Multiple Sclerosis Onset Is an Independent Factor of Poor Prognosis: A Population-Based Cohort Study

BACKGROUND: Late-onset multiple sclerosis (LOMS) frequently features a primary progressive (PP) course, strongly predicting severe disability. In this population-based cohort, we estimated the prognostic role of age at multiple sclerosis (MS) onset, independent of PP course, on disability progression. METHODS: The association of age at disease onset (adult, <50 years [AOMS], vs. late, ≥50 years [LOMS]) and time to Expanded Disability Status Scale (EDSS) score 4 and 6 was estimated by Cox regression modelling. RESULTS: Among 3,597 patients, 245 had LOMS. Relapsing-remitting (RR) disease was less frequent with LOMS than AOMS (51.8 vs. 90.8%, p < 0.0001). PP course, LOMS and male gender predicted short time to EDSS 4 and 6. Worse outcome with LOMS (time to EDSS 4 and 6, HR 2.0 [95% CI 1.7-2.4] and 2.3 [1.9-2.9]) was independent of PP course or male gender. LOMS had greater impact on RR than PP disease (time to EDSS 4 and 6, HR 3.1 [2.3-4.0] and 4.0 [2.9-5.6]). Only LOMS predicted time from EDSS 4 to 6 (p < 0.0001). CONCLUSIONS: Late onset MS was strongly associated with poor prognosis, independent of initial disease course, in predicting the disability progression along time.