Lung function trajectory in progressive fibrosing interstitial lung disease.

Proposed criteria for progressive fibrosing interstitial lung disease (PF-ILD) have been linked to increased mortality risk, but lung function trajectory after satisfying individual criterion remains unknown. Because survival is rarely employed as the primary endpoint in therapeutic trials, identifying PF-ILD criteria that best predict subsequent change in forced vital capacity (FVC) could improve clinical trial design. A retrospective, multi-center longitudinal cohort analysis was performed in consecutive patients with fibrotic connective tissue disease-associated ILD (CTD-ILD), chronic hypersensitivity pneumonitis and idiopathic interstitial pneumonia at three US centers (test cohort) and one UK center (validation cohort). One-year change in FVC after satisfying proposed PF-ILD criteria was estimated using joint modeling. Subgroup analyses were performed to determine whether results varied across key subgroups. One thousand two hundred twenty-seven patients were included, with CTD-ILD predominating. Six of nine PF-ILD criteria were associated with differential one-year change in FVC, with radiologic progression of fibrosis, alone and in combination with other features, associated with the largest subsequent decline in FVC. Findings varied significantly by ILD subtype, with CTD-ILD demonstrating little change in FVC after satisfying most PF-ILD criteria, while other ILDs showed significantly larger changes. Findings did not vary after stratification by radiologic pattern or exposure to immunosuppressant therapy. Near-term change in FVC after satisfying proposed PF-ILD criteria was heterogeneous depending on the criterion assessed and was strongly influenced by ILD subtype. These findings may inform future clinical trial design and suggest ILD subtype should be taken into consideration when applying PF-ILD criteria.