Further Features of the Fennoscandian Focus of Multiple Sclerosis

Reassessment of the distribution of multiple sclerosis with the methodology employed in previous work provides strong evidence for a single focus of high-frequency MS in Norway. This focus occupies the eastern mountain plains area of Southern Norway and extends to the coast on both south and east, as well as northward to encompass the entire waist of Norway up to some 64° north latitude. The distributions are very similar for both cumulative death rates (1951–65) and for disability-pensioned cases (1966), when assessed according to residence within the 104 small units comprising Norway, a number which represents the lower limit of unit size for the method used. In combination with the previously described distributions of MS within small units of Sweden and intermediate-sized units of Finland, the Norwegian data provide even stronger evidence for the existence of a single Fennoscandian focus of high-frequency MS, extending from the southern mountain plains of Norway eastward across the inland lake area of southern Sweden, across the Bay of Bothnia to south-western Finland, and thence back to Sweden at Umeå. The combination of separate studies is thought valid in the light of the strong correlations between distributions of MS covering different generations of patients in Denmark, Switzerland, and Norway. The slope of the regression line for these three lands is about the same, and is such as to raise the possibility of the diffusion of MS over time in these countries.