Differential impacts of interstitial lung disease and airway disease on rheumatoid arthritis disease activity and infection

We aimed to distinguish the individual effects of interstitial lung disease (ILD) and airway disease (AD) on rheumatoid arthritis (RA) disease activity and infection. RA patients who underwent chest CT at Kanazawa University Hospital (2011-2021) were investigated. The primary outcome was infection-related hospitalization, and the secondary was RA disease activity (DAS28-CRP, SDAI) at final observation. Of 569 patients, 125 (22.0%) had ILD (ILD +), and 171 (30.1%) had AD (AD +). At first CT: RA disease activity was similar; ILD + received less methotrexate than ILD-; all DMARDs were similar in AD + and AD-. At final observation (mean: 73.9 months): RA disease activity was higher in ILD + and AD + . Analysis of covariance revealed a significant association between final RA disease activity and ILD, but not AD. Kaplan-Meier analysis showed lower infection-free rates in ILD + and AD + . Cox regression analysis with time-dependent covariates showed an association between infection and ILD after 50 months and AD (HR 3.702 and 1.744). RA disease activity was independently associated with ILD, likely due to reduced methotrexate use. ILD after 50 months and AD both increased infection risk independently. Distinguishing ILD from AD is important for selecting safe and effective treatments.