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

doi:10.1016/j.jns.2012.08.032

Journal of the Neurological Sciences

Volume 323, Issues 1–2, 15 December 2012, Pages 117-122

https://doi.org/10.1016/j.jns.2012.08.032 Get rights and content

Abstract

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.

Introduction

In most patients with multiple sclerosis (MS), disease onset is in the third or fourth decade of life with its peak in the most economically productive years [1]. The most striking epidemiological characteristic is the apparent uneven distribution of the disease across the world, and the interplay between genes and the geographically determined physical environment are important factors for the different prevalence of MS [2]. Several studies have suggested an increasing prevalence of MS worldwide [3], [4], [5]. Although incidence studies are rarer than prevalence studies, some have shown that the annual MS incidence rates have gradually increased over the last 30 years [3], [6], [7], [8].

MS prevalence had been considered low (0.8–4.0/100,000 persons) in Japan [9]. In 2001, we conducted a survey of the prevalence of MS in Tokachi province and showed that it was not as low as expected in northern Japan (8.6/100,000 persons) [10]. We conducted a second survey in the same province in 2006 and reported that the prevalence of MS was increasing (13.1/100,000 persons) [11]. The proportion of optic-spinal MS (OSMS) is considered to be high in Asia, although we [10] and others [12] reported that this is not the case in northern Japan (3–16%). In 2006, Wingerchuk et al. proposed criteria for the diagnosis of neuromyelitis optica (NMO) [13], and most patients with OSMS have been considered to have NMO. To date, there are no data regarding the prevalence of NMO in Japan.

In this third epidemiologic surveillance of MS in Tokachi province, we investigated whether MS prevalence has increased over the last 10 years. In the present study, we excluded cases of NMO using the criteria of Poser et al. [14], and we surveyed the prevalence of NMO in northern Japan for the first time. In Europe, the female/male MS ratio has been increasing over the last decade [1]. We investigated whether the same tendency can also be seen in northern Japan. However, the incidence rate is a better measure of the risk of MS, because it is independent of survival time, and prevalence can be indicative of several other factors such as diagnostic accuracy and ascertainment probability besides the true frequency of MS [2]. Taken together, we were also able to assess the incidence of MS over the last 30 years.

Section snippets

Study area and study population

This third survey was conducted in Tokachi province located on Hokkaido, the northernmost island of Japan, in March 2011, using the same methods as in the previous studies in 2001 and 2006 [10], [11]. The official population of Tokachi province according to the Government Census Office was 352,353 (169,249 men and 183,104 women) at the end of March 2011. The population in the community decreased by 9,373 from 2001 to 2011 (361,726 in 2001); however, the population has stabilized between 350,000

Prevalence

On the prevalence day (March 31, 2011), 60 patients (47 female and 13 male) residing in the study area, were included in the study as they exhibited clinically definite or laboratory-supported definite MS according to the criteria of Poser et al. [14]. Of these 60 patients, 50 were diagnosed by one of the authors (H.H.). In the previous two studies [10], [11], the crude prevalence of MS was calculated at this stage 8.6/100,000 persons in 2001 and 13.1/100,000 persons in 2006. In the present

Discussion

There have been many reported MS prevalence studies, but it is sometimes difficult to accurately determine the change of prevalence because of migration and population changes. As population size may be an important source of bias, MS studies should investigate populations of comparable size [23]. As a general principle, the use of very large populations provides more precise estimates but is subject to several problems: loss of detail, ethnic heterogeneity, and high cost, as well as difficulty

Conflict of interest

Dr. Houzen has no conflicts of interest to disclose. Dr. Niino receives research support from Grants-in-Aid for Scientific Research from the Ministry of Health, Labor and Welfare of Japan and the National Hospital Organization of Japan, serves on a scientific advisory board for Biogen Idec, and has received speaker honoraria from Biogen Idec, Bayer Schering Pharma, Asahi Kasei Kuraray Medical Co., Ltd, and Novartis Pharma. Dr. Hirotani has no conflicts of interest to disclose. Dr. Fukazawa

Acknowledgments

We thank the following colleagues for enrolling patients in the study: Dr. Kondo, Department of Neurology, Hokuto Hospital; Dr. Kamaya, Department of Neurology, Obihiro Nishi Hospital; and Dr. Maeda, Department of Medicine, Kurosawa Hospital.

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

Abstract

Objective

Methods

Results

Conclusions

Introduction

Section snippets

Study area and study population

Prevalence

Discussion

Conflict of interest

Acknowledgments

Lancet Neurol

J Neurol Sci

J Neurol Sci

J Neurol Sci

Lancet Neurol

Autoimmun Rev

Lancet Neurol

Epidemiology of multiple sclerosis in Europe: a review

Int Rev Psychiatry

A 50-year follow-up of the incidence of multiple sclerosis in Hordaland County, Norway

Neurology

Incidence and prevalence of multiple sclerosis in Saskatoon, Saskatchewan

Neurology

The rising prevalence and changing age distribution of multiple sclerosis in Manitoba

Neurology

Increasing incidence of multiple sclerosis in the province of Sassari, northern Sardinia

Neuroepidemiology

Possible increasing risk of multiple sclerosis in Catania, Sicily

Neurology

Incidence and prevalence of multiple sclerosis in Olmsted County, Minnesota, 1985–2000

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Prevalence of multiple sclerosis and its north-to-south gradient in Japan

Neuroepidemiology

Increasing prevalence and incidence of multiple sclerosis in northern Japan

Mult Scler