Increased prevalence, incidence, and female predominance of multiple sclerosis in northern Japan.

OBJECTIVE

To carry out the third epidemiologic surveillance of multiple sclerosis (MS) in Tokachi province, on the northernmost island of Japan, and to compare the results of the present survey on the prevalence, incidence, and characteristics of MS and neuromyelitis optica (NMO) with those of previous surveys performed in 2001 and 2006.

METHODS

A data processing sheet was sent to all MS-related institutions in Tokachi province, and all sheets were collected in March 2011. The criteria of Poser were used for diagnosing MS and the criteria proposed by Wingerchuk for diagnosing NMO. We then compared the results of the present survey with those of previous surveys performed in 2001 and 2006 in the same community.

RESULTS

Fifty-seven patients diagnosed with MS according to the criteria of Poser were identified. The prevalence was 16.2/100,000 in 2011, which was higher than in the previous studies. The female/male ratio of MS was 2.63, 2.75, and 3.38 in 2001, 2006, and 2011, respectively. Three patients fulfilled the criteria for diagnosis of NMO in 2011; the prevalence of NMO was 0.9/100,000.

CONCLUSIONS

The results of this study suggest that the prevalence and the female predominance of MS have been increasing, due to an increase in the incidence after 1990, and that the prevalence of NMO is relatively low in northern Japan.