Multiple sclerosis in Oslo, Norway: prevalence on 1 January 1995 and incidence over a 25-year period

The Oslo Multiple Sclerosis (MS) Registry was established in 1990, and this is the first report on the prevalence and incidence of MS in the city of O slo, Norway. The prevalence rate of definite MS on 1 January 1995 was 120.4 /10(5). Inclusion of patients of native Norwegian ancestry only and exclusi on of non-Norwegian immigrants yielded a prevalence rate of 136.0/10(5)). A similar prevalence rate (136.5/10(5)) was found when patients and immigran ts from the other Nordic countries (Finland, Sweden, Denmark) were included . Segregation of the native Norwegian patients according to the counties wh ere they were born showed no significant differences except for a dispropor tionate increase of patients born in the inland county of Oppland. A total of 794 cases were resident in Oslo at the time of a diagnosis of de finite MS in the period 1972-99. The crude average annual incidence rate fo r each 5-year period, between 1972 and 1996, increased significantly from 3 .7/10(5) in the 1972-76 to 8.7/10(5) in the 1992-96 period. The increase wa s more marked in relapsing-remitting (RR) than in primary progressive disea se and in female cases.