Evolution of small airway involvement in rheumatoid arthritis. A multicenter prospective study.

<bold>Aim:</bold> To evaluate the respiratory evolution of RA bronchiolitis. <bold>Methods:</bold> Observational, multicenter, prospective study. Rheumatoid arthritis (RA) patients without respiratory history were evaluated between Jan 2017-Dec 2023. RA diagnosis was according to ACR/EULAR 2010. Small Airway Involvement (SAI) was defined as a mosaic pattern on HRCT in more than 3 lobes. HRCT, pulmonary function tests (PFTs), and RA activity variables were evaluated at baseline and at 5 year follow-up. Patients were classified into 2 different clusters according to HRCT: "normal” and "SAI". Clinical variables, PFTs, HRCT and evolution were compared between "normal" vs "SAI". <bold>Results:</bold> We included 48 patients, 92% females, mean age (SD) 52.89 years (12.5), 97% had ACPA (+). The median (IQR) of time since RA diagnosis was 48 (45–60) months. 29 (60.4%) had pathological findings on HRCT: 27 (56.2%) had "SAI" and 2 ILD (4.2%). The mean (SD) follow-up time was 107.6 (52.5) months. 93.7% had a normal PFTs. At follow-up, 29 (60.4%) received methotrexate, 3 anti-TNF and 2 JAK-inhibs. The median (IQR) DAS28-ERS was 2.88 (2.23-3.49) and 19/48 (39.5%) were in "RA remission". In the comparative analysis between "normal HRCT" vs "SAI" clusters, we didn't find significant differences in sex, age, smoking status, physical examination, RA activity, use of DMARDs and evolution of PFTs at follow up among other variables. <bold>Conclusions:</bold> We found a high proportion of "SAI" in asymptomatic respiratory RA patients without any other cause to explain it. However, we didn't find significant differences with "normal" RA patients at follow up, suggesting that "SAI" might be an incidental finding on HRCT possibly linked to RA pathogenesis.