Disability and mortality in multiple sclerosis in Western Norway

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Abstract
Continued studies of frequency trends in carefully selected sites around the world can provide clues to the cause of multiple sclerosis (MS). Based on information from three different, semi-independent sources of information, we have examined the temporal trends in the average annual age-adjusted rates of disability pension incidence, mortality, and incidence of MS from 1966 to 1991 in Møre and Romsdal County, Norway. The average annual age-adjusted disability pension incidence rates (1966-68 = 3.62/100,000; 1990-91 = 7.33/100,000), the mortality rates (1966-68 = 0.91/100,000; 1990-91 = 1.88/100,000), and the incidence rates (1966-68 = 4.22/100,000; 1990-91 = 5.02/100,000) all showed a statistically significant increase. The difference in the development of MS-specific disability pension prevalence rates in the county compared to the nation is notable. We consider that the increase in disability pension incidence, mortality, and incidence of MS is of biological significance. Thus three different sources of information corroborate corresponding trends indicating that better case ascertainment and improved diagnostic facilities only partially can explain the reported MS increase in western Norway.