Prevalence of multiple sclerosis in Asahikawa, a city in northern Japan

Twenty-two years after the first survey, a follow-up study was performed on the prevalence of multiple sclerosis (MS) in Asahikawa, a city in northern Japan. The crude prevalence of MS rose from 2.5/100,000 (in 1975) to 10.2/100,000 (in 2002). The clinical diagnosis was established using the Poser diagnostic criteria, and the degree of physical disability was determined using the Expanded Disability Status Scale (EDSS). The distribution of patients according to the clinical form of MS was 65% with relapsing-remitting MS, 19% with secondary chronic progressive MS and 16% with the primary chronic progressive forms of MS. Symptoms at onset in the present study less often affected optic nerves (3%) than previously reported in Japan and was more like that seen in western MS series. Although prevalence of MS increase four-fold in Japan over the last two decades, it remains uncertain whether this apparent increase is real or reflects better ascertainment.