title: Characteristics of myasthenia gravis according to onset-age: Japanese nationwide survey.
abstract: 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.
authors: Department of Neurology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. hmurai@neuro.med.kyushu-u.ac.jp
authors: Hiroyuki
authors: H
authors: Murai
authors: Natsumi
authors: N
authors: Yamashita
authors: Makoto
authors: M
authors: Watanabe
authors: Yoshiko
authors: Y
authors: Nomura
authors: Masakatsu
authors: M
authors: Motomura
authors: Hiroaki
authors: H
authors: Yoshikawa
authors: Yosikazu
authors: Y
authors: Nakamura
authors: Naoki
authors: N
authors: Kawaguchi
authors: Hiroshi
authors: H
authors: Onodera
authors: Shigeru
authors: S
authors: Araga
authors: Noriko
authors: N
authors: Isobe
authors: Masaki
authors: M
authors: Nagai
authors: Jun-ichi
authors: J
authors: Kira
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D000375:Aging / Q000502:physiology*; D044466:Asian People / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity / Q000639:trends; D005260:Female; D018740:Genetic Heterogeneity; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000453:epidemiology* / Q000208:ethnology* / Q000235:genetics; D015995:Prevalence; D055815:Young Adult