GEOGRAPHIC DISTRIBUTION OF MULTIPLE SCLEROSIS 135 



Soviet Union. These data (Table V) also clearly indicate a greater fre- 

 quency in the northern regions. Again, geomagnetic latitude is the better 

 parameter if the results plotted in Fig. 6, are superimposed on those in Figs. 

 2-4. 



Predicted Geographic Distribution of Multiple Sclerosis 



To permit comparison between the data represented in the preceding 

 figures and those from future surveys or from other sources, geomagnetic 

 latitudes corresponding to relative prevalences of 0.1 and 0.9 were deter- 

 mined from the sigmoid curve in Fig. 2 and are approximately 38° and 48°, 

 respectively. These geomagnetic coordinates are indicated as isoprevalence 

 lines by solid lines in Fig. 7. For inhabited areas of geomagnetic latitude less 

 than 38° (i.e., the area between the two 0.1 lines), relatively low prevalence 

 ratios of the order of 4—6 per 100,000 population are predicted. North and 

 south of the 0.9 lines in the northern and southern hemispheres, respectively, 

 relatively high prevalence ratios of the order of 40-60 are predicted. A rapid 

 increase of prevalence with increasing geomagnetic latitude is predicted to 

 lie between the 0.1 and 0.9 lines in both hemispheres. 



The predictions from such a map appear to be in reasonably good agree- 

 ment with much of the available data concerning the distribution of multiple 

 sclerosis (Barlow, 1960). The general distribution being relatively common 

 in northern Europe and in northern North America, but relatively uncom- 

 mon in the Orient, South America, Africa, and the tropics appears to be in 

 accord with the map. 



Comparison of Multiple Sclerosis with Hodgkin's Disease 



The geographic distribution of multiple sclerosis has been contrasted with 

 that for Hodgkin's disease on several occasions (Ulett, 1948; Kurland, 1952; 

 McAlpine et al., 1955), since Hodgkin's disease, at least in the United States 

 and Canada, appears to show little geographic variation. It is of interest to 

 compare statistics for the two diseases from the present standpoint. For this 

 purpose, mortality statistics for the two diseases in several localities through- 

 out the world, compiled by McAlpine et al. (1955), are compared 

 in Table VI and are plotted in Fig. 8. The statistics have limitations and may 

 be subject to considerable sampling error since only one year is represented 

 for each locality. Nonetheless, it is apparent that the latitude trend of rela- 

 tive mortality for multiple sclerosis is somewhat similar to that suggested by 

 the prevalence data in Fig. 3. Moreover, there is possibly less scatter of the 

 points about the sigmoid curve (reproduced from the geomagnetic plot of 

 Fig. 2) for the geomagnetic plot than for the geographic plot. For Hodgkin's 



