title: Use of variability in national and regional data to estimate the prevalence of lymphangioleiomyomatosis.
abstract: BACKGROUND
  Understanding the true prevalence of lymphangioleiomyomatosis (LAM) is important in estimating disease burden and targeting specific interventions. As with all rare diseases, obtaining reliable epidemiological data is difficult and requires innovative approaches.
  
  
  OBJECTIVE
  To determine the prevalence and incidence of LAM using data from patient organizations in seven countries, and to use the extent to which the prevalence of LAM varies regionally and nationally to determine whether prevalence estimates are related to health-care provision.
  
  
  METHODS
  Numbers of women with LAM were obtained from patient groups and national databases from seven countries (n = 1001). Prevalence was calculated for regions within countries using female population figures from census data. Incidence estimates were calculated for the USA, UK and Switzerland. Regional variation in prevalence and changes in incidence over time were analysed using Poisson regression and linear regression.
  
  
  RESULTS
  Prevalence of LAM in the seven countries ranged from 3.4 to 7.8/million women with significant variation, both between countries and between states in the USA. This variation did not relate to the number of pulmonary specialists in the region nor the percentage of population with health insurance, but suggests a large number of patients remain undiagnosed. The incidence of LAM from 2004 to 2008 ranged from 0.23 to 0.31/million women/per year in the USA, UK and Switzerland.
  
  
  CONCLUSIONS
  Using this method, we have found that the prevalence of LAM is higher than that previously recorded and that many patients with LAM are undiagnosed.
authors.affiliation: Division of Therapeutics and Molecular Medicine and Respiratory Biomedical Research Unit, University of Nottingham, Nottingham, UK.
authors.forename: E C
authors.initials: EC
authors.lastname: Harknett
authors.forename: W Y C
authors.initials: WY
authors.lastname: Chang
authors.forename: S
authors.initials: S
authors.lastname: Byrnes
authors.forename: J
authors.initials: J
authors.lastname: Johnson
authors.forename: R
authors.initials: R
authors.lastname: Lazor
authors.forename: M M
authors.initials: MM
authors.lastname: Cohen
authors.forename: B
authors.initials: B
authors.lastname: Gray
authors.forename: S
authors.initials: S
authors.lastname: Geiling
authors.forename: H
authors.initials: H
authors.lastname: Telford
authors.forename: A E
authors.initials: AE
authors.lastname: Tattersfield
authors.forename: R B
authors.initials: RB
authors.lastname: Hubbard
authors.forename: S R
authors.initials: SR
authors.lastname: Johnson
mesh_terms: D001315:Australia / Q000453:epidemiology; D002170:Canada / Q000453:epidemiology; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D018192:Lymphangioleiomyomatosis / Q000453:epidemiology*; D009520:New Zealand / Q000453:epidemiology; D015995:Prevalence; D012042:Registries / Q000706:statistics & numerical data*; D013557:Switzerland / Q000453:epidemiology; D006113:United Kingdom / Q000453:epidemiology; D014481:United States / Q000453:epidemiology