title: Identifying patients with myasthenia for epidemiological research by linkage of automated registers.
abstract: BACKGROUND
  We validated a new method of identifying patients with incident myasthenia in automated Danish registers for the purpose of conducting epidemiological studies of the disorder.
  
  
  METHODS
  For residents of a Danish county (population 484,862) in 1993-2008, we identified any hospital contacts coded for myasthenia in a nationwide patient register and any prescriptions for pyridostigmine in the county prescription register. Results from an acetylcholine receptor antibody register were linked to the data. We verified the diagnosis by a review of medical records.
  
  
  RESULTS
  Subjects identified in the Patient Register (n = 83) were comparable with individuals found in the Prescription Register (n = 89) with regard to age and gender, but were more often seropositive (83.1 vs. 74.2%). Seropositivity increased to 91.6% by restricting the data to individuals recorded in both Patient and Prescription Registers (n = 71). We found that for subjects identified in both Patient and Prescription Registers the positive predictive value of the register diagnosis was 92.9% (95% confidence interval, CI, 84.3-97.7), the false-positive rate was low (2.8%), and the sensitivity was acceptable (81.2%; 95% CI 71.2-88.8).
  
  
  CONCLUSIONS
  Our data indicate that this novel approach of combining diagnosis register and prescription register information provides a feasible and valid method to trace incident myasthenia patients for population-based epidemiological studies.
authors: Department of Neurology, Odense University Hospital, Odense, Denmark.
authors: Emil Greve
authors: EG
authors: Pedersen
authors: Jesper
authors: J
authors: Hallas
authors: Klaus
authors: K
authors: Hansen
authors: Poul Erik Hyldgaard
authors: PE
authors: Jensen
authors: David
authors: D
authors: Gaist
mesh_terms: D000328:Adult; D000368:Aged; D003718:Denmark / Q000453:epidemiology; D011307:Drug Prescriptions; D005260:Female; D006761:Hospitals; D006801:Humans; D008297:Male; D008499:Medical Records / Q000592:standards*; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D017891:Pharmacoepidemiology; D012042:Registries / Q000592:standards*