A 60-year follow-up of the incidence and prevalence of multiple sclerosis in Hordaland County, Western Norway.

Objective: Investigate the incidence of multiple sclerosis during 1953-2013 and estimate the prevalence rate of MS on 1 January 2003 and 2013 in Hordaland County, Western Norway.

Methods: All patients with onset of disease in Hordaland 1953-2013 were identified in files from previous studies until 2003 and from patient records at the departments of Neurology, Haukeland University Hospital and Haugesund Hospital during 2003-2013. 1558 patients were assessed and 1402 of these were included, of whom 1035 were alive and living in Hordaland at prevalence day 1 January 2013. Annual incidence rates were calculated for 1953-2013.

Results: On 1 January 2003, the crude prevalence rate was 191/100 000 population and on 1 January 2013, the crude prevalence rate was 211.4 (95% CI 198.3 to 224.2) per 100 000; 270.9 (95% CI 250.6 to 292.3) for women and 151.8 (95% CI 136.8 to 167.9) for men. Prevalence peaked at ages 55-59 years for women and 60-64 years for men. The annual incidence rate increased from 1.9 (95% CI 1.2 to 2.6) per 100 000 during 1953-1957 to 7.2 (95% CI 6.0 to 8.5) during 1978-1982 and to 8.5 (95% CI 7.3 to 9.7) during 2003-2007, thus indicating a stabilising incidence over the past 35 years. The female/male ratio ranged from 1.2:1 to 1.8:1 (p=0.381) during the period.

Conclusions: Stabilising rather than increasing incidence combined with the stable female/male ratio are indicative of non-fluctuating environmental factors in a geographical area otherwise characterised by lack of vitamin D effective sun exposure. The rising prevalence of MS could result from improved survival and follow-up methodology.