Clinical, Functional, and Radiological Evaluation of Pulmonary Involvement in Patients with Rheumatoid Arthritis

Background: Pulmonary involvement is one of the most serious extra-articular manifestations of rheumatoid arthritis (RA), frequently remaining clinically silent until irreversible lung damage develops. This study aimed to determine the prevalence of high-resolution computed tomography (HRCT)-detected pulmonary involvement in patients with RA; compare the clinical, laboratory, and pulmonary function characteristics of patients with and without pulmonary involvement; and identify factors associated with pulmonary abnormalities. Methods: In this single-center retrospective cross-sectional study, 141 patients fulfilling the 2010 ACR/EULAR classification criteria for RA who had undergone thoracic HRCT were included. Clinical characteristics, laboratory findings, disease activity scores, pulmonary function tests, and HRCT findings were compared between patients with and without pulmonary involvement. Logistic regression analyses were performed to identify independent predictors of pulmonary involvement, and receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic performance of serum uric acid. Results: HRCT identified pulmonary involvement in 33 of 141 patients (23.4%), with nonspecific interstitial pneumonia being the most common radiological pattern (39.4%), followed by usual interstitial pneumonia (24.2%). Patients with pulmonary involvement had significantly higher serum uric acid concentrations (5.65 ± 1.62 vs. 4.51 ± 1.31 mg/dL, p < 0.001), lower serum albumin levels (38.8 ± 4.9 vs. 40.9 ± 3.5 g/L, p = 0.008), higher platelet counts (p = 0.006), and lower forced vital capacity and predicted FEV1 values (p = 0.010 and p = 0.019, respectively). In multivariable logistic regression analysis, serum uric acid remained the only independent predictor of pulmonary involvement (odds ratio, 1.656; 95% confidence interval, 1.187–2.311; p = 0.003). ROC analysis demonstrated acceptable discriminatory performance for serum uric acid (AUC = 0.713), with an optimal cutoff value of >5 mg/dL yielding 68% sensitivity and 70% specificity. Conclusions: Nearly one-quarter of patients with RA demonstrated HRCT-detected pulmonary involvement despite having a similar prevalence of respiratory symptoms. Elevated serum uric acid was independently associated with pulmonary involvement and may represent an inexpensive, readily available biomarker to identify patients who may benefit from targeted pulmonary evaluation. These findings support the integration of simple laboratory markers with clinical assessment to facilitate earlier recognition of RA-associated pulmonary disease.