Multiple sclerosis in Iceland, with observations on the alleged epidemic in the Faroe Islands.

The profile of multiple sclerosis (MS) in Iceland based on a total population study from 1900 to 1990 is reviewed. The first survey in the late 1950s was a retrospective one. Since then, there has been a continuous prospective study that extends over a period of 40 years. The incidence of MS, which was 2.5/100,000 in the 1930s, rose to 3.5 to 4.1/100,000 between 1975 and 1990, but the data from the 1930s must be considered unreliable. There was a similar stepwise increase in prevalence from 30 to approximately 100/100,000 in 1990. It is most likely that the changes in prevalence are the result of improved case ascertainment, the growing number of well-trained neurologists in the country, and the greater awareness of the disease due to the activities of the Icelandic MS Society. No local or regional clusters were identified, but from 1900 to 1980 there was a steady and unexpected increase in the number of cases in rural areas, both by date of clinical onset and date of putative disease acquisition. No evidence was found to support the hypothesis that an epidemic of MS had occurred in Iceland following the arrival of British, Canadian, and American troops during the Second World War. The proposed epidemic in the Faroe Islands was also reexamined, in particular because of the identical ethnic, historical, demographic, and geographical similarities with Iceland. The available data are not supportive of that idea.