This systematic review and meta-analysis shows that unclassifiable interstitial lung disease is common but has substantial heterogeneity and inconsistent definitions across interstitial lung disease cohorts. These findings highlight important limitations in multicenter studies of fibrotic interstitial lung disease and the need for a standardized approach to interstitial lung disease diagnostic classification.

BackgroundThe CAnadian REgistry for Pulmonary Fibrosis (CARE-PF) is a multi-center, prospective registry designed to study the natural history of fibrotic interstitial lung disease (ILD) in adults. The aim of this cross-sectional sub-study was to describe the baseline characteristics, risk factors, and comorbidities of patients enrolled in CARE-PF to date.MethodsPatients completed study questionnaires and clinical measurements at enrollment and each follow-up visit. Environmental exposures were assessed by patient self-report and comorbidities by the Charlson Comorbidity Index (CCI). Baseline characteristics, exposures, and comorbidities were described for the overall study population and for incident cases, and were compared across ILD subtypes.ResultsThe full cohort included 1285 patients with ILD (961 incident cases (74.8%)). Diagnoses included connective tissue disease-associated ILD (33.3%), idiopathic pulmonary fibrosis (IPF) (24.7%), unclassifiable ILD (22.3%), chronic hypersensitivity pneumonitis (HP) (7.5%), sarcoidosis (3.2%), non-IPF idiopathic interstitial pneumonias (3.0%, including idiopathic nonspecific interstitial pneumonia (NSIP) in 0.9%), and other ILDs (6.0%). Patient-reported exposures were most frequent amongst chronic HP, but common across all ILD subtypes. The CCI was ≤2 in 81% of patients, with a narrow distribution and range of values.ConclusionsCTD-ILD, IPF, and unclassifiable ILD made up 80% of ILD diagnoses at ILD referral centers in Canada, while idiopathic NSIP was rare when adhering to recommended diagnostic criteria. CCI had a very narrow distribution across our cohort suggesting it may be a poor discriminator in assessing the impact of comorbidities on patients with ILD.

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BACKGROUND: Fibrotic interstitial lung diseases (ILDs) are highly morbid chronic disorders that frequently occur in working age individuals. The goal of this study was to determine workplace productivity loss, its determinants, and its estimated costs in patients with fibrotic ILD. METHODS: Patients with idiopathic pulmonary fibrosis, chronic hypersensitivity pneumonitis, idiopathic nonspecific interstitial pneumonia, or unclassifiable ILD were identified from the six-center Canadian Registry for Pulmonary Fibrosis (CARE-PF). The Work Productivity and Activity Impairment questionnaire was used to determine health-related productivity loss. Independent predictors of low workplace productivity were identified by using multivariate regression. Patient data were compared with Canadian population census data. The average productivity loss (hours per week) and the individual's hourly wage were used to estimate the costs of productivity loss. RESULTS: Of 650 eligible patients, 148 (23%) were employed. Productivity loss was reported by 55% of employed patients with an average productivity loss of 7.8 AE 0.9 h per week (2.3 AE 0.6 h per week related to absenteeism and 5.5 AE 0.6 h per week related to presenteeism). Employment among patients with ILD aged 25 to 54 years was 23% lower than the age-and sex-matched general Canadian population (60% vs 83%; P < .001). Employment among ABBREVIATIONS: CAD = Canadian dollar; CARE-PF = Canadian Registry for Pulmonary Fibrosis; DLCO = diffusing capacity of the lung for carbon monoxide; ILD = interstitial lung disease; IPF = idiopathic pulmonary fibrosis; VAS = visual analog scale; WPAI = work productivity and activity impairment