title: Increase in incidence of elderly-onset patients with myasthenia gravis in Nagano Prefecture, Japan.
abstract: OBJECTIVE
  In European countries and the United States the incidence of elderly-onset myasthenia gravis (MG) has recently been increasing. To investigate whether the incidence of the elderly-onset MG has increased in Nagano Prefecture of Japan, we divided the patients into young and elderly groups, and retrospectively examined their incidence.
  
  
  METHODS
  On the basis of two-step questionnaires sent to hospitals and the patient list of the intractable disease registration system in Nagano Prefecture we studied 213 MG patients diagnosed between 1982 and 2001. This 20-year period was divided into 4 five-year terms, and the incidence of MG in young- (younger than 65) and elderly-onset (65 or older) groups was investigated separately for each term.
  
  
  RESULTS
  The ratio of the elderly-onset group showed a significantly positive correlation with terms irrespective of associated thymoma (r=0.98, p<0.05). There was a significant difference in the mean onset age among the 4 terms (p<0.005). The standardized incidence of MG gradually increased in both young- and elderly-onset groups as well as in the whole age range. The elderly group showed a particularly high incidence in females (12.01/million/year) and in patients without thymoma (8.78/million/year) in the final five years.
  
  
  CONCLUSIONS
  We confirmed that the incidence of elderly-onset MG has recently been increasing in the Nagano Prefecture. Since the change of the age distribution in this district is almost identical to that of the whole country, the incidence of MG might have been increasing in Japan as a whole, particularly in the elderly population.
authors: Third Department of Medicine, Shinshu University School of Medicine, Asahi, Matsumoto.
authors: Masayuki
authors: M
authors: Matsuda
authors: Naoko
authors: N
authors: Dohi-Iijima
authors: Akinori
authors: A
authors: Nakamura
authors: Yoshiki
authors: Y
authors: Sekijima
authors: Hiroshi
authors: H
authors: Morita
authors: Shigeyuki
authors: S
authors: Matsuzawa
authors: Shun-Ichi
authors: S
authors: Sato
authors: Hiroyuki
authors: H
authors: Yahikozawa
authors: Ken-Ichi
authors: K
authors: Tabata
authors: Sohei
authors: S
authors: Yanagawa
authors: Shu-Ichi
authors: S
authors: Ikeda
mesh_terms: D017677:Age Distribution; D017668:Age of Onset; D000368:Aged; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D009157:Myasthenia Gravis / Q000150:complications / Q000453:epidemiology*; D012189:Retrospective Studies; D012307:Risk Factors; D012424:Rural Population / Q000706:statistics & numerical data*; D017678:Sex Distribution; D011795:Surveys and Questionnaires; D013945:Thymoma / Q000150:complications / Q000453:epidemiology; D013953:Thymus Neoplasms / Q000150:complications / Q000453:epidemiology