Changes in the clinical phenotypes of multiple sclerosis during the past 50 years in Japan

In order to clarify whether or not marked changes in the social environment during the past 50 years in Japan may have altered the clinical phenotypes of multiple sclerosis (MS), we retrospectively analyzed 143 consecutive pa tients with clinically definite MS who developed the disease between 1950 a nd 1997. Fifty-two patients were classified as Asian type MS showing a sele ctive involvement of the optic nerves and the spinal cord, while 91 patient s were considered to have Western type MS which demonstrated the involvemen t of multiple sites in the central nervous system including the cerebrum, c erebellum and brainstem. The ratio of Asian type versus Western type MS was 1:0.5 in the patients born in the 1920s and 1:1.27, 1:1.64 and 1:1.7 in th ose born in the 1930s, 1940s and 1950s, respectively, and thereafter it inc reased to 1:4.67 in those born in the 1960s and 1:4 in those born after the 1970s. As a result, the proportion of Asian type MS significantly decrease d in the patients born after 1960 as compared with those born from 1930 to 1959 (P=0.0121). In the Asian type MS, the age of onset was significantly h igher in the patients who developed the disease from 1985 to 1997 (42.4+/-1 3.5 years) than in those who developed the disease from 1950 to 1984 (32.3/-12.4 years) (P=0.0149), while in the Western type MS no such change in th e age of onset was observed. These findings suggest that the frequency of A sian type MS has apparently decreased in younger Japanese born after 1960 w hen Japan's rapid economic growth had just started, and environmental facto rs are therefore considered to contribute to determine the clinical phenoty pes of MS in Asians. (C) 1999 Elsevier Science B.V. All rights reserved.