Multiple sclerosis in Iceland: 1. Evidence of a postwar epidemic.

Since 1974 we have attempted to ascertain all cases of MS beginning 1900-1975 in Iceland. As of October 1979 they numbered 168; all but 5 met all diagnostic criteria of the Schumacher Committee. Virtually all cases had been examined by a least one of the authors. Cases were few and sporadic from 1900 to 1922, then increased to a plateau for 1923-44, then again increased in 1945 with an irregular plateau thereafter. Average annual incidence rate for 1945-1954 was 3.2 per 100,000 population, significantly higher than the 1.6 for 1923-1944 or the 1.9 for 1955-1974. Age at onset was significantly decreased for cases with onset 1945-1949 and then sharply increased for those with 1950-1954 onsets. The occurrence of MS in 1945-1954 meets the criteria for a point-source epidemic, whose tail thereafter mérged into what may be "baseline" for Iceland. This postwar epidemic is then similar to that recently described for the Faroe Islands, a land that shares its history, culture, and peoples with Iceland.