Prevalence of multiple sclerosis in Västerbotten County in northern Sweden.

Objective: To estimate the prevalence and clinical characteristics of multiple sclerosis (MS) in Västerbotten County in northern Sweden.
Methods: Individuals with MS were identified from several sources. A follow-up interview and/or examination was performed in 94% of cases still living in the area during 1997-99. Onset adjusted prevalence and a definition of onset symptoms were applied.
Results: A total of 313 cases were identified, resulting in an onset adjusted crude prevalence of MS for January 1990 of 125/105 (95% confidence interval (CI): 112-140). Female predominance was evident (163/105 (95% CI: 142-187) vs 86/105 (95% CI: 71-104)). Diagnostic coding registers were the most important source for identification of cases.
Conclusions: The crude prevalence of MS in Västerbotten was higher than previous reports from other major areas in Scandinavia. The adjusted prevalence was significantly higher when compared with a previous study from Göteborg, south-western Sweden. The methodology used in this study gives a high degree of case ascertainment and increases the comparability of multiple sclerosis epidemiological studies.