The study team compared disability accrual in primary and secondary progressive multiple sclerosis (PPMS, SPMS) in the international MSBase cohort, using multivariable survival models, and applying objective diagnostic criteria for SPMS.
There were 2563 patients with PPMS and 2598 patients with SPMS included in the study. Age at progressive-phase onset was older in SPMS than in PPMS. Hazard of disability accrual was decreased in SPMS versus PPMS, and increased in males. However, patients with PPMS and SPMS reached EDSS ≥ 7 at similar ages.
Disability at progressive-phase onset is greater in SPMS than in PPMS. However, we find that in SPMS the progressive phase has later onset and lower hazard of disability accrual. Wheelchair requirement therefore occurs at similar ages in each phenotype, consistent with convergence toward a partially age-dependent timeline of disability accrual.