Geographic distribution of multiple sclerosis: An update with special reference to Europe and the Mediterranean region

Abstract

The geographic distribution of multiple sclerosis (MS) was last reassessed in 1975 with data from 180 surveys from about the world. Since then there have been an additional 54 for which prevalence rates have been measured or estimated. In broad terms the world-wide distribution of MS still seems best described as comprising three bands or zones of high, medium, and low frequency or risk. For the entire 35 years since World War II, prevalence rates of 30 or more per 100,000 population have defined high frequency, those of 5–29 medium frequency, and those of less than 5 per 100,000 low frequency. High frequency areas are northern and central Europe into the USSR; southern Canada and northern United States; and New Zealand and southern Australia. These regions are bounded by medium frequency areas, which include southern US; southwestern Norway and northern Scandinavia; probably the USSR from the Ural Mountains into Siberia as well as the Ukraine; and the entire Mediterranean basin from Spain around to Israel – possibly including Tunisia. Enna in Sicily with a high rate is an exception. Also of medium frequency are most of Australia and perhaps the mid-portion of South America. One white group of South Africa too has a medium prevalence rate. Low frequency areas include all known parts of Asia and Africa (save as noted above); the Caribbean region to include Mexico, and probably northern South America; and Alaska and Greenland. The high to medium division in southern Europe extends eastward in an irregularly curved line from about 43° north latitude in the west to some 49°–50° north latitude within the USSR west of the Urals. From a large nationwide case-control series, the division between high and medium in the US is at 37° north latitude across most of the country but extending to some 39° in the east.