, Volume 235, Issue 4, pp 241-244

Incidence of multiple sclerosis: a periodic or stable phenomenon

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For diseases of unknown aetiology, the question as to whether the incidence is constant or variable is very important. A study on multiple sclerosis in a defined northern area of the German Democratic Republic showed a prevalence of 68.6 and an incidence rate of 3.0. Retrospective and prospective investigations concerning an observation period of 22 years revealed cyclic periods (6–7 years) of high incidence rates (up to 4.5) interrupted by shorter intervals (4–5 years) with low rates (about 1.8). The differences (1963–1968 vs. 1969–1973, 1974–1978 vs. 1979–1983) are significant. In accordance with the findings of Kurtzke et al. on a cyclic outbreak of multiple sclerosis in the Faroes and Iceland, our results are considered to be a consequence of environmental factors, such as epidemic viral infections.