title: A cohort study of interstitial lung diseases in central Denmark.
abstract: BACKGROUND
  Interstitial lung diseases (ILDs) form a heterogeneous group of diseases with varying degrees of inflammation and fibrosis. Epidemiological data based on the current diagnostic criteria are sparse.
  
  
  OBJECTIVE
  To characterize the incidence rate of ILDs and idiopathic pulmonary fibrosis (IPF) in Danish patients diagnosed at a referral hospital, to evaluate disease severity and survival in these ILD patients and to compare the use of the 2001 and 2011 guidelines to diagnosis of IPF.
  
  
  METHODS
  Single-centre, retrospective, observational cohort study including incident patients diagnosed with ILD at Aarhus University Hospital between 2003 and 2009. All diagnoses were re-evaluated according to current diagnostic criteria. Disease severity in IPF was assessed using the GAP index.
  
  
  RESULTS
  The ILD incidence was 4.1 per 100,000 inhabitants/year. IPF was the most common diagnosis (28%) followed by connective tissue disease-related ILD (14%), hypersensitivity pneumonitis (7%) and non-specific interstitial pneumonia (NSIP) (7%). The GAP index was a strong predictor of survival in IPF. Twenty-three patients who had IPF based on the 2001 criteria had a "possible UIP" HRCT pattern but no lung biopsy, and IPF could therefore not be diagnosed based on the 2011 criteria.
  
  
  CONCLUSIONS
  ILD and IPF incidence was 4.1 and 1.3 per 100,000 inhabitants/year. The diagnostic re-evaluation raised the number of IPF diagnoses, but a diagnostic "grey zone" was still evident in patients with UIP features not qualifying the patients to be diagnosed with IPF. The GAP index was valuable as a measure of IPF severity in this cohort.
authors.affiliation: Department of Respiratory Medicine and Allergology, Aarhus University Hospital, Denmark. Electronic address: chahyl@rm.dk.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Hyldgaard
authors.affiliation: Department of Respiratory Medicine and Allergology, Aarhus University Hospital, Denmark.
authors.forename: Ole
authors.initials: O
authors.lastname: Hilberg
authors.affiliation: Actelion Pharmaceuticals Ltd, Allschwil, Switzerland.
authors.forename: Audrey
authors.initials: A
authors.lastname: Muller
authors.affiliation: Department of Respiratory Medicine and Allergology, Aarhus University Hospital, Denmark.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Bendstrup
mesh_terms: D000328:Adult; D000368:Aged; D018893:Bronchoalveolar Lavage; D001999:Bronchoscopy; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D054990:Idiopathic Pulmonary Fibrosis / Q000175:diagnosis / Q000453:epidemiology / Q000601:surgery; D015994:Incidence; D053208:Kaplan-Meier Estimate; D017563:Lung Diseases, Interstitial / Q000175:diagnosis / Q000453:epidemiology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D017410:Practice Guidelines as Topic / Q000592:standards; D011379:Prognosis; D012189:Retrospective Studies; D012720:Severity of Illness Index; D020775:Thoracic Surgery, Video-Assisted / Q000379:methods
keywords: Classification; Diagnosis; Epidemiology; Idiopathic pulmonary fibrosis; Interstitial lung disease