Interstitial Lung Disease in Rheumatoid Arthritis: Incidence and Outcomes in Western Australia

AIM: To determine the incidence, risk factors for, and mortality from interstitial lung disease (ILD) in patients with Rheumatoid Arthritis (RA) in Western Australia (WA). METHODS: A retrospective statewide cohort study of ILD in patients with RA (n = 5971) and age/sex matched controls (n = 20 830) hospitalized between 1985 and 2014. ILD was identified based on validated algorithms. ILD incidence (IR) per 1000 person-years (PY), odds ratio (OR) for risk factors and respiratory complications, and mortality rate (MR) per 1000 PY were estimated with 95% confidence intervals (CI). RESULTS: The IR of ILD in patients with RA (RAILD+) was increased (IR ratio 8.02, CI 6.28-10.32) and stable over 30 years. Age (OR 1.02, CI 1.01-1.03), smoking (OR 1.97, CI 1.48-2.63), and scleritis (OR 3.84, CI 1.86-7.94) were independent risk factors for ILD. Pulmonary infections, oxygen dependence, and lung cancer occurred as frequently in RAILD+ and CoILD+ but at higher rates than in participants without ILD in each group. MR for RAILD+ patients was higher than for RA patients not developing ILD (99.9 vs. 50.8; p < 0.01), but lower than for CoILD+ (166.3 vs. 99.9, p < 0.01). CONCLUSION: The incidence of ILD among patients with RA was stably increased over time. ILD increased respiratory morbidity and mortality in both RA and controls. Smoking cessation and early detection could reduce the risk and severity of ILD.