title: Late-onset myasthenia not on the increase: a nationwide register study in Denmark, 1996-2009.
abstract: BACKGROUND
  An increase in late-onset myasthenia gravis (MG) has been reported. There are few large population-based studies over longer periods of time reflecting recent developments in MG incidence.
  
  
  METHODS
  We identified a nationwide cohort of patients with incident myasthenia in Denmark in 1996-2009. We used a validated algorithm to track subjects based on a combination of diagnosis and prescription (pyridostigmine) data from nationwide registers. Patients with myasthenia were classified into early onset (<50 years old) and late onset (50+ years). We calculated incidence rates (IRs) and corresponding 95% confidence intervals.
  
  
  RESULTS
  We identified 693 patients (362 women) with incident MG in the study period corresponding to an IR of 9.2 per million person-years (8.5-9.9). Overall, 207 (29.9%) were classified as early-onset and 486 (70.1%) as late-onset MG. Women predominated in the early-onset group (70.5%), but not in the late-onset group (44.4%). The incidence rate of early-onset MG was 4.2 (3.6-4.8) and late-onset MG 18.9 (17.3-20.7) per million person-years and it did not vary over time in the study period (P-values for trend 0.54 and 0.15, respectively).
  
  
  CONCLUSIONS
  Late-onset MG comprised a large proportion of all incident cases in Denmark, was more common in men than women, and occurred with a stable incidence in the 14-year study period. Therefore, we speculate whether previous reports of a rise in late-onset MG reflect a non-biological phenomenon, that is, a gradual improvement in the diagnosis of MG in this age group in previous years.
authors.affiliation: Department of Neurology, Odense University Hospital, Odense, Denmark.
authors.forename: E G
authors.initials: EG
authors.lastname: Pedersen
authors.forename: J
authors.initials: J
authors.lastname: Hallas
authors.forename: K
authors.initials: K
authors.lastname: Hansen
authors.forename: P E H
authors.initials: PE
authors.lastname: Jensen
authors.forename: D
authors.initials: D
authors.lastname: Gaist
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000175:diagnosis / Q000453:epidemiology*; D012042:Registries