The diagnostic utility of lung ultrasound in the assessment of interstitial lung disease associated with rheumatoid arthritis

Background To investigate the diagnostic accuracy of lung ultrasound (LUS) for interstitial lung disease (ILD) in patients with rheumatoid arthritis (RA). Methods This retrospective study included patients over 18 years with RA evaluated at the Department of Rheumatology and Immunology of Shantou Central Hospital. All patients underwent chest high-resolution computed tomography (HRCT) and LUS within one month. The LUS was performed in a total of 50 scanning sites (ScS), and the number of B-lines present in each ScS was counted and summed up as B-lines score. A positive judgement was given on LUS when the B-lines score exceeded 10. The presence and patterns of ILD were defined by HRCT findings. ROC curve analysis was used to calculate the accuracy of LUS to detect ILD. Results A total of 120 RA patients (86 women, with a median age of 56.0 [50.0-64.0] years) were enrolled. Based on the HRCT, 76 patients were found to have radiographic ILD, with 63 exhibiting nonspecific interstitial pneumonia (NSIP) and 13 showing usual interstitial pneumonia (UIP). Sonographic ILD was detected in 76 patients who underwent LUS examination. The concordance rate between two modalities was 83.33% (Kappa value = 0.64, 95% CI 0.50-0.78). The diagnostic sensitivity and specificity of LUS were 86.84% and 77.27%, respectively. The positive predictive value, negative predictive value, a positive likelihood ratio and a negative likelihood ratio were 86.84%, 77.27%, 3.82, and 0.17, respectively. The number of B-lines in RA with ILD and without ILD on HRCT showed a significant difference (34.0 [15.0-96.5] vs. 6.5 [2.5-10.0], P < 0.001). The presence of 12 B-lines on 50 ScS was the optimal cutoff value for detecting RA-ILD (AUC = 0.89, 95% CI 0.82-0.94, sensitivity of 85.53%, specificity of 81.82%, P < 0.001). Conclusions Lung ultrasound is a valuable diagnostic tool for RA-ILD and can be used as a screening method to identify patients who require further evaluation with chest HRCT.