Disability accrual in primary-progressive & secondaryprogressive multiple sclerosis.

Background: Some cohort studies have reported similar onset age and disability accrual in primary and secondary progressive MS (PPMS, SPMS); others have reported later onset and faster disability accrual in SPMS. Comparisons are complicated by differences in baseline disability and exposure to disease-modifying therapies (DMT), and by lack of a standardized definition of SPMS. Objective(s): We compared hazards of disability accrual in PPMS and SPMS patients from the MSBase cohort using multivariable Cox models, applying validated diagnostic criteria for SPMS (Lorscheider et al., Brain 2016). Method(s): Inclusion required adult-onset progressive MS; >= 3 recorded Expanded Disability Status Scale (EDSS) scores; and, for SPMS, initial records with EDSS <= 3 to allow objective identification of SPMS conversion. Phenotypes were subgrouped as active (PPMS-A, SPMS-A) if >= 1 progressive-phase relapse was recorded, and inactive (PPMS-N, SPMS-N) otherwise. Disability accrual was defined by sustained EDSS increases confirmed over >= 6 months. Hazard ratios (HR) for disability accrual were obtained using Andersen-Gill Cox models, adjusted for sex and time-varying age, disability, visit frequency, and proportion of time on DMT or immunosuppressive therapy. Sensitivity analyses were performed using (1) PPMS and SPMS diagnosed since 1995, and (2) physician-diagnosed SPMS. Cumulative probability of reaching EDSS >= 7 (wheelchair required) was assessed (Kaplan-Meier). Result(s): 5461 patients were included (1257 PPMS-N; 1308 PPMS-A; 1731 SPMS-N; 1165 SPMS-A). Age at progression onset was older in SPMS than PPMS (47.2 +/- 10.2, vs. 41.5 +/- 10.7 [mean +/- SD]), and in the inactive subgroups of each phenotype. Hazard of disability accrual was decreased in SPMS relative to PPMS (HR 0.85; 95% CI 0.78-0.92); decreased by proportion of time on DMT (HR 0.99 per 10% increment; 0.98-0.99); and higher in males (1.18; 1.12-1.25). Relative to PPMS-N, hazard was decreased in SPMS-A (0.79; 0.71