title: Prevalence of multiple sclerosis in Canada: a systematic review.
abstract: BACKGROUND
  Studies of the prevalence of multiple sclerosis (MS) in Canada have generally been isolated to specific regions. Given the importance of multiple sclerosis as a cause of disability in adults, a comprehensive review of Canadian MS prevalence examining current data, interregional variation, deficiencies in knowledge and frontiers for research is timely.
  
  
  METHODS
  A systematic review of all studies addressing the prevalence of MS in Canada or regions within Canada, published in English or French since 1985, was conducted. Studies were identified using MEDLINE, EMBASE and bibliographic review. Ten studies were evaluated for methodological rigour and a test of heterogeneity across studies was performed and a measure of consistency (I2) estimated.
  
  
  RESULTS
  Studies were generally of high quality. Nine were restricted to regions within Canada and one provided an estimated national prevalence based on self-reported cases. All reported a high prevalence (>50 per 100,000). Latitude and longitude gradients were not striking while assessment of heterogeneity confirmed that regional differences were unlikely to be the result of sampling variability.
  
  
  CONCLUSIONS
  This review confirms Canada as a country of very high MS prevalence and it is the first study to demonstrate that variation in regional estimates represents true differences in prevalence within Canada. Avenues for future MS prevalence research, including adoption of a national MS registry, are proposed.
authors.affiliation: Department of Clinical Neurosciences, Foothills Medical Centre, Calgary, Alberta, Canada.
authors.forename: Alexandre Y
authors.initials: AY
authors.lastname: Poppe
authors.forename: Christina
authors.initials: C
authors.lastname: Wolfson
authors.forename: Bin
authors.initials: B
authors.lastname: Zhu
mesh_terms: D002170:Canada / Q000453:epidemiology; D003081:Cold Climate / Q000009:adverse effects; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D004777:Environment; D005260:Female; D005843:Geography; D006801:Humans; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology*; D015995:Prevalence; D015203:Reproducibility of Results; D015983:Selection Bias