Natural history comparisons of primary and secondary progressive multiple sclerosis reveals differences and...

Similarities in the onset age of progression in secondary-progressive (SP) and primary-progressive multiple sclerosis (PPMS) have been previously reported. However, with longer follow-up, more relapsing-remitting (RRMS) patients reach SPMS, such that the baseline characteristics, including age at progression may shift. We aimed to examine how this phenomenon impacts on demographic and clinical comparisons made between PP and SPMS.

Patients with definite MS, onset by July 1988 and > or = 1 Expanded Disability Status Scale (EDSS) score were selected from the British Columbia-wide MS database (n = 2837). Of these, 353 (12.4 %) had PPMS and 1445/2484 (58.2 %) of the RRMS population reached SPMS at study close (July 2003). Females predominated in the SPMS population regardless of follow-up time (p < or = 0.032). From Kaplan-Meier analysis (all RR, SP and PP patients considered), the estimated median onset age of progression was greater in SPMS (49.0 years; 95 % CI: 48.3-49.7) than PPMS (41.0 years; 95 % CI: 39.7-42.4), p < 0.0005. If the RR patients (who had not developed SPMS) were excluded, median age of onset of SPMS was still greater (43.1 years (95 % CI: 42.3-43.9, p < 0.0005).

Although there were some similarities between SPMS and PPMS, the former had a later onset age in our British Columbian MS cohort.