Background: Progression of interstitial lung disease in rheumatoid arthritis (RA-ILD) can be assessed using different criteria, including progressive fibrosing ILD (PF-ILD) and ATS/ERS-defined progressive pulmonary fibrosis (PPF). The prognostic value of these criteria has not been compared in RA-ILD.

Objective: Compare incidence of PF-ILD and PPF and their ability to predict mortality in a RA-ILD cohort.

Methods: All RA-ILD patients at our center were eligible for a retrospective cohort study. Occurrence of PF-ILD and PPF were determined using all available lung function tests, HRCT and symptom assessments. Time-dependent effect of PF-ILD and PPF on transplant-free survival was estimated using Kaplan-Meier and Cox proportional hazards models.

Results: Of 87 patients, 46 (53%) were female, mean age was 60.3±15.7 years at RA-ILD diagnosis. Mean FVC was 72% predicted and mean DLCO 54% predicted. Over a median follow-up time of 7.9 years, PF-ILD criteria were met at least once in 64 (74%) patients, PPF criteria at least once in 59 (68%) patients, 46 (53%) died and 2 (2%) underwent lung transplantation. PF-ILD and PPF were associated with similar increases in subsequent risk of death adjusted for age and gender (HR 4.4 (95%CI 2.2-8.7, p<0.01 for PF-ILD, 4.4 (95%CI 2.3-8.5, p<0.01 for PPF).

Conclusion: Progression is common in RA-ILD regardless of definition. PF-ILD and PPF were associated with a similar, greater than four-fold increase in mortality risk.