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