High prevalence of multiple sclerosis in Switzerland.

Prevalence of multiple sclerosis (MS) was determined in the Canton of Berne, Switzerland. This canton is a geographically diverse region at 47 degrees northern latitude with 920,000 inhabitants. Epidemiological data were obtained from the case records of the University Department of Neurology, from the Swiss MS Society, from practising neurologists and from regional hospitals. Diagnostic accuracy was ascertained in retrospect, and only those cases fulfilling the criteria proposed by the Poser Committee were included. Of the patients provided by the Swiss MS Society, only those who had been diagnosed by a neurologist were accepted as definite cases. Changes of population due to migration or death were traced at governmental registry offices, and the place of residence was determined. Using the 1,016 cases of definite and probable MS identified, the minimal prevalence rate was 110 MS cases/100,000 inhabitants in the Canton of Berne on January 1, 1986. The increase in MS in this region since the 1950s was due mainly to the increase in life duration of MS patients rather than an increase in incidence rates over the last 20 years.