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

J Neurol Sci. 2011 Jun 15;305(1-2):97-102. doi: 10.1016/j.jns.2011.03.004. Epub 2011 Mar 26.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Age of Onset
  • Aged
  • Aging / physiology*
  • Asians / genetics
  • Child
  • Child, Preschool
  • Comorbidity / trends
  • Female
  • Genetic Heterogeneity
  • Humans
  • Infant
  • Infant, Newborn
  • Japan / epidemiology
  • Male
  • Middle Aged
  • Myasthenia Gravis / epidemiology*
  • Myasthenia Gravis / ethnology*
  • Myasthenia Gravis / genetics
  • Prevalence
  • Young Adult