Natural history of secondary-progressive multiple sclerosis

To examine prognosis and risk factors for progression to and from secondary-progressive multiple sclerosis (SPMS).

Patients with definite relapsing-remitting MS (RRMS), onset before July 1988, attending a British-Columbian MS clinic before July 1998, and at least one Expanded Disability Status Scale (EDSS) scores were selected from the population-based database. Time to SPMS (from onset and birth) and the subsequent time to EDSS 8 were examined, as were potential risk factors.

In all, 2484/2837 (87.6%) were relapsing-remitting (RR) at onset, with 1445/2484 (58.2%) reaching SPMS, taking a median 18.9 years (95% CI: 18.2-19.7). Those younger at onset took longer to reach SPMS (P < 0.0005), but did so at a younger age (P < 0.0005). Males reached SPMS more rapidly from onset and at a younger age (P < 0.0005), but were around the same age as females at EDSS 8 (P = 0.975). Characteristics at SPMS onset associated with a longer time from SPMS to EDSS 8 and an older age at EDSS 8 were: longer disease duration (P < 0.02), older age (P < 0.01) and lower EDSS (P < 0.0005). Onset symptoms had little influence on time to SPMS or subsequent progression.

The RR phase lasted on average almost two decades, being shorter for males and those older at onset of MS. However, neither were necessarily unfavorable predictors as those older at onset were typically older at SPMS and eventually males and females reached EDSS 8 at around the same age. A longer RR phase was a favorable predictor of disease progression in SPMS. Furthermore, reaching SPMS at an older age or lower EDSS did not necessarily confer a worse outcome.