Impact of csDMARDs vs. b/tsDMARDs on the Prognosis of Rheumatoid Arthritis-Associated Interstitial Lung Disease: A Multicenter, Retrospective Study

Background/Objectives: Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) significantly affects disease prognosis and patient survival. The impact of conventional synthetic DMARDs (csDMARDs) and biologic/targeted synthetic DMARDs (b/tsDMARDs) on RA-ILD prognoses remains unclear. This study aimed to investigate the effects of csDMARDs and b/tsDMARDs on RA-ILD progression and prognosis based on pulmonary function tests (PFTs), high-resolution computed tomography (HRCT), and symptom changes. Methods: This multicenter, retrospective, observational study included patients with RA-ILD at 13 referral hospitals in South Korea. The participants were categorized into csDMARD-only and b/tsDMARD-exposed groups. RA-ILD prognosis was assessed over a 24-month follow-up period using serial PFTs (the forced vital capacity [FVC] and diffusing capacity of the lungs for carbon monoxide [DLCO]), HRCT findings, and clinical symptom changes. Kaplan–Meier survival analyses and Cox proportional hazards models were used to compare disease progression risk while adjusting for baseline lung function, RA disease activity, and glucocorticoid use. Results: Among 127 eligible patients, 22 (17.3%) were exposed to b/tsDMARDs, predominantly abatacept and tocilizumab. During a mean follow-up of 2.8 years, 65 (51.2%) patients experienced RA-ILD progression. A higher baseline Disease Activity Score-28 with erythrocyte sedimentation rate (DAS28-ESR) (adjusted hazard ratio [aHR]: 1.344, 95% confidence interval [CI]: 1.136–1.590, p = 0.001) and initially prescribed prednisone dose (aHR: 1.078, 95% CI: 1.011–1.151, p = 0.023) were significant prognostic factors for ILD progression. No statistically significant difference in progression risk was observed between the csDMARD-only and b/tsDMARD-exposed groups (aHR: 0.937, p = 0.851). Conclusions: The RA-ILD prognosis was more strongly influenced by disease activity, rather than the type of DMARD used. These findings emphasize the importance of maintaining low RA disease activity to improve RA-ILD prognosis.