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© 1991 American Academy of Neurology Epidemiologic trends in multiple sclerosis in Møre and Romsdal, NorwayA prevalence/incidence study in a stable populationDepartment of Neurology (Dr. Midgard), Molde County Hospital, Molde, Section for Medical Informatics and Statistics (Trond Riise) and Department of Neurology (Dr. Nyland), University of Bergen, Norway. The western part of Norway has been a low- to medium-frequency area for multiple sclerosis (MS). The prevalence of definite/probable MS on January 1, 1961, was 24.3/100,000 in the county of Møre and Romsdal, western Norway. Based on the same diagnostic criteria, the prevalence of definite/probable MS increased to 75.4/100,000 on January 1, 1985. The average annual incidence rate increased from 1.94/100,000 in the period 1950-1954 to 3.78/100,000 from 1975-1979. Remitting MS in the younger age groups of both sexes increased the most. We consider this increase of MS to be due to alteration in exogenous factors as variation in genetic susceptibility cannot account for the increase in the stable western Norwegian population. The rise in prevalence/incidence over the last 20 to 25 years in western Norway supports the theory that MS is a disease influenced by exogenous factors that show variation over time. Address correspondence and reprint requests to Dr. Rune Midgard, Department of Neurology, Molde County Hospital, Norway. Supported by MS grants from Fritz and Ingrid Nilsen's Legacy, The Odd Fellow Order, and the Norwegian MS Society. Received September 21, 1990. Accepted for publication in final form November 29, 1990.
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