title: Natural history comparisons of primary and secondary progressive multiple sclerosis reveals differences and similarities.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  Although there were some similarities between SPMS and PPMS, the former had a later onset age in our British Columbian MS cohort.
authors.affiliation: Dept. of Medicine (Neurology), rm S178, 2211 Wesbrook Mal, University of British Columbia, Vancouver, BC V6T 2B5, Canada. tremlett@interchange.ubc.ca
authors.forename: Helen
authors.initials: H
authors.lastname: Tremlett
authors.forename: Yinshan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Virginia
authors.initials: V
authors.lastname: Devonshire
mesh_terms: D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D053208:Kaplan-Meier Estimate; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D020528:Multiple Sclerosis, Chronic Progressive / Q000453:epidemiology*; D012720:Severity of Illness Index; D012737:Sex Factors