Prevalence and characteristics of progressive fibrosing interstitial lung disease in a prospective registry

Rationale\r\nProgressive fibrosing interstitial lung disease (PF-ILD) is characterized by progressive \r\nphysiologic, symptomatic, and/or radiographic worsening. The real-world prevalence and \r\ncharacteristics of PF-ILD remain uncertain.\r\n\r\nMethods\r\nPatients were enrolled from the Canadian Registry for Pulmonary Fibrosis between 2015-2020. \r\nPF-ILD was defined as a relative forced vital capacity (FVC) decline ≥10%, death, lung \r\ntransplantation, or any 2 of: relative FVC decline ≥5 and <10%, worsening respiratory \r\nsymptoms, or worsening fibrosis on computed tomography of the chest, all within 24 months of \r\ndiagnosis. Time-to-event analysis compared progression between key diagnostic subgroups.\r\nCharacteristics associated with progression were determined by multivariable regression.\r\n\r\nResults\r\nOf 2,746 patients with fibrotic ILD (mean age 65±12 years, 51% female), 1,376 (50%) met PFILD criteria in the first 24 months of follow-up. PF-ILD occurred in 427 (59%) patients with \r\nidiopathic pulmonary fibrosis (IPF), 125 (58%) with fibrotic hypersensitivity pneumonitis (HP), \r\n281 (51%) with unclassifiable ILD (U-ILD), and 402 (45%) with connective tissue diseaseassociated ILD (CTD-ILD). Compared to IPF, time to progression was similar in patients with \r\nHP (hazard ratio [HR] 0.96, 95% confidence interval, CI 0.79-1.17), but was delayed in patients \r\nwith U-ILD (HR 0.82, 95% CI 0.71-0.96) and CTD-ILD (HR 0.65, 95% CI 0.56-0.74). \r\nBackground treatment varied across diagnostic subtypes with 66% of IPF patients receiving \r\nantifibrotic therapy, while immunomodulatory therapy was utilized in 49%, 61%, and 37% of \r\npatients with CHP, CTD-ILD, and U-ILD respectively. Increasing age, male sex, \r\ngastroesophageal reflux disease, and lower baseline pulmonary function were independently\r\nassociated with progression. \r\n\r\nInterpretation\r\nProgression is common in patients with fibrotic ILD, and is similarly prevalent in HP and IPF. \r\nRoutinely collected variables help identify patients at risk for progression and may guide \r\ntherapeutic strategies