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The natural history of primary progressive multiple sclerosis

Background: Primary progressive multiple sclerosis (PPMS) carries the worst prognosis of the multiple sclerosis (MS) subtypes and is currently untreatable. A previous analysis of the British Columbia MS database challenged the view that disability progression is rapid in PPMS, but identified few predictors of disease progression. Here, we extend previous analyses in an updated PPMS retrospective cohort study of prevalent cases. Methods: We used Kaplan-Meier survival analyses and Cox regression models to investigate the influence of gender, age at onset, and onset symptoms on time to and age at Expanded Disability Status Scale (EDSS) 6.0 in patients with PPMS. Results: Of 5,779 patients with definite MS, 552 (10%) had PPMS. Median time to EDSS 6.0 was 14.0 years (95% confidence interval [CI] 11.3–16.7), reached at a median age of 58.6 years (95% CI 56.8–60.3). Sensory onset symptoms were associated with a longer time to and an older age at EDSS 6.0 (multivariable hazard ratios 0.55 [95% CI 0.35–0.87] and 0.54 [0.35–0.85]). Younger age at disease onset was associated with a longer time to but a younger age at EDSS 6.0. Gender and other onset symptoms were not associated with these outcomes. Fifty patients with PPMS (9%) fulfilled criteria for benign MS (EDSS ≤3.0 after 10 years' disease duration). Conclusions: We identified 2 predictors of a slower disease progression in primary progressive multiple sclerosis. Sensory onset symptoms were associated with both a longer time to and a higher age at Expanded Disability Status Scale (EDSS) 6.0. A younger age at disease onset was associated with a longer time to EDSS 6.0, but patients with an early disease onset reached EDSS 6.0 at a younger age.