The prevalence of multiple sclerosis in Tayside, Scotland: do latitudinal gradients really exist?

To determine the prevalence of multiple sclerosis (MS) in the Tayside Healt h Board Area, Scotland, we carried out a population-based survey using four intersecting sources (Neurology Department records, a survey of general pr actitioners, Scottish Morbidity Records of discharges from hospitals and vi sual evoked response requests). A two-source capture-recapture model estima ted survey coverage, and direct age-sex standardisation was used to take ac count of different population structures. Comparisons were made between the prevalence in Scotland and that in the rest of the United Kingdom. A total of 727 (definite and probable) and 880 cases (early, probable and possible ) were identified using the criteria of Poser et al. and those of Allison a nd Millar in a population of 395,600 (1995 mid-year estimate). The prevalen ce of MS on 1 September 1996 was 184/100,000 (95% confidence interval 171-1 98) and 222/100,000 (95% confidence interval 210-240), respectively. The tw o-source capture-recapture model estimated that the survey was between 93% and 99% complete. Age-sex standardisation eliminated certain north-south di fferences in prevalence when comparisons were made with previous surveys. D iagnostic misclassification may also have influenced reported prevalence st atistics. The prevalence is similar to that found in revised figures from t he Grampian region in Scotland but significantly higher than recent estimat es from England and Wales. Methodological differences may account for most of the reported differences between north and south, although there is stil l evidence to suggest that MS is more prevalent in northern Great Britain a nd Northern Ireland than in England and Wales.