Multiple sclerosis in Iceland from 1900 to 2000: A total population study.

The epidemiology of multiple sclerosis (MS) in Iceland in1900-2000 is presented. The incidence increased significantly from 2.58×10(5) in 1950 to 5.06×10(5) in 2000 (from 2.71 to 7.03×10(5) for women and from 2.55 to 3.10×10(5) for men) with a yearly increase by a factor of 1.0816 per year for women and 1.01207 per year for men (Poisson regression analysis). Prevalence standardized to the European standard population rose from 29.9×10(5) in 1950 to 131.7×10(5) in 2000. The standardized prevalence was constantly higher amongst women (42.8-181.6×10(5) vs. 16.7-81.5×10(5) for men) with a female to male ratio of 2.6 in 1950 and in 2000. Mean age at onset for all patients increased from 27.8 years in 1950 to 30.7 years in 2000 (from 27.0 to 30.1 years for women and from 28.6 to 32.2 years for men). Children and adolescents (<18 years) were 9.6% of all, of whom 60% were diagnosed after 1970. Mean age of onset for children and adolescents was 14.7 years (9-17 years, 95% CI 4.2 years). The rise in incidence and prevalence can have multiple explanations, including diagnosis of milder forms of MS, increased awareness of MS in the older population, better diagnostic measures and longer survival but the authors find it likely that there has been a true rise in the MS incidence.