title: Prevalence and prognosis of unclassifiable interstitial lung disease.
abstract: The aim of this study was to determine the prevalence, characteristics and outcomes of patients with unclassifiable interstitial lung disease (ILD) and to develop a simple method of predicting disease behaviour. Unclassifiable ILD patients were identified from an ongoing longitudinal cohort. Unclassifiable ILD was diagnosed after a multidisciplinary review did not secure a specific ILD diagnosis. Clinical characteristics and outcomes were compared with idiopathic pulmonary fibrosis (IPF) and non-IPF ILDs. Independent predictors of mortality were determined using Cox proportional-hazards analysis to identify subgroups with distinct disease behaviour. Unclassifiable ILD was diagnosed in 10% of the ILD cohort (132 out of 1370 patients). The most common reason for being unclassifiable was missing histopathological assessment due to a high risk of surgical lung biopsy. Demographic and physiological features of unclassifiable ILD were intermediate between IPF and non-IPF disease controls. Unclassifiable ILD had longer survival rates when compared to IPF on adjusted analysis (hazard ratio 0.62, p = 0.04) and similar survival compared to non-IPF ILDs (hazard ratio 1.54, p = 0.12). Independent predictors of survival in unclassifiable ILD included diffusion capacity of the lung for carbon monoxide (p = 0.001) and a radiological fibrosis score (p = 0.02). Unclassifiable ILD represents approximately 10% of ILD cases and has a heterogeneous clinical course, which can be predicted using clinical and radiological variables.
authors.affiliation: Dept of Medicine, University of British Columbia, Vancouver, BC, Canada. chris.ryerson@hli.ubc.ca
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Ryerson
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Urbania
authors.forename: Luca
authors.initials: L
authors.lastname: Richeldi
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Mooney
authors.forename: Joyce S
authors.initials: JS
authors.lastname: Lee
authors.forename: Kirk D
authors.initials: KD
authors.lastname: Jones
authors.forename: Brett M
authors.initials: BM
authors.lastname: Elicker
authors.forename: Laura L
authors.initials: LL
authors.lastname: Koth
authors.forename: Talmadge E
authors.initials: TE
authors.lastname: King
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Wolters
authors.forename: Harold R
authors.initials: HR
authors.lastname: Collard
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D016022:Case-Control Studies; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D006801:Humans; D054990:Idiopathic Pulmonary Fibrosis / Q000175:diagnosis / Q000453:epidemiology; D053208:Kaplan-Meier Estimate; D008137:Longitudinal Studies; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D017563:Lung Diseases, Interstitial / Q000145:classification / Q000175:diagnosis / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011379:Prognosis; D016016:Proportional Hazards Models; D011653:Pulmonary Diffusing Capacity; D012307:Risk Factors; D012720:Severity of Illness Index; D012907:Smoking / Q000453:epidemiology; D015996:Survival Rate; D014057:Tomography, X-Ray Computed; D014797:Vital Capacity