Characteristics of myasthenia gravis according to onset-age: Japanese nationwide survey

Hiroyuki Murai, Natsumi Yamashita, Makoto Watanabe, Yoshiko Nomura, Masakatsu Motomura, Hiroaki Yoshikawa, Yosikazu Nakamura, Naoki Kawaguchi, Hiroshi Onodera, Shigeru Araga, Noriko Isobe, Masaki Nagai, Jun Ichi Kira

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Objective: To clarify the prevalence and clinical characteristics of myasthenia gravis (MG) in Japan. Methods: We performed a nationwide epidemiological survey of MG in Japan. The clinical features were compared among five groups of patients, divided according to onset age. A generalized additive model (GAM) was used to assess the linearity of these relationships. Results: A total of 8542 patients were reported, and detailed data were analyzed for 3141 patients. The estimated number of MG patients in Japan was 15,100, giving a prevalence of 11.8 per 100,000. Elderly-onset MG (≥ 65 years) accounted for 7.3% in 1987 (adjusted for population in 2005), but this had increased to 16.8% in 2006. Infantile-onset MG (0-4 years) accounted for 10.1% in 1987, and was still as high as 7.0% in 2006. The rate of ocular MG was highest (80.6%) in infantile-onset and lowest (26.4%) in early-onset disease, but the rate rose again in the late-onset group. GAM analysis of the ocular form showed a U-shaped curve, with a dip in the 20s. Anti-acetylcholine receptor antibodies were positive in only 50% of infantile-onset, but nearly 90% of elderly-onset patients. GAM analyses assessing the concurrence of thymoma and hyperplasia both showed reversed U-shapes, with peaks in the 50s and 20s-40s, respectively. Conclusions: Persistent high incidence of infantile-onset disease and clinical heterogeneity according to onset age are characteristic features of MG in Japan.

Original languageEnglish
Pages (from-to)97-102
Number of pages6
JournalJournal of the Neurological Sciences
Issue number1-2
Publication statusPublished - Jun 15 2011

All Science Journal Classification (ASJC) codes

  • Neurology
  • Clinical Neurology


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