Thoracic ultrasound finding interstitial lung disease in systemic lupus erythematosus: a diagnostic test accuracy study

Abstract Objectives Interstitial lung diseases (ILDs) are frequent and clinically important in systemic lupus erythematosus (SLE) but diagnosis of ILD can be challenging. Thoracic ultrasound (TUS) shows promise in detecting ILD, hence, we aimed to evaluate the utility of TUS to identify ILD in SLE. Methods Patients fulfilling the EULAR/ACR 2019 SLE classification criteria were invited. Participants were assessed for ILD by means of chest high-resolution computed tomography scans and pulmonary function tests and diagnosed at a multidisciplinary discussion, according to reference standards, independent of TUS. TUS evaluated the presence of B-lines and pleural abnormalities, blinded to status of ILD. The ability of B-lines to identify ILD using a prespecified threshold of ≥ 10 B-lines was analysed using diagnostic test accuracy measures. Further, we explored the diagnostic performance of B-lines and pleural abnormalities to identify ILD across various scenarios. Results Among 185 patients with SLE ILD were present in 22 (12%). With the predefined threshold of ≥ 10 B-lines we found a modest diagnostic test accuracy as 14 of 22 ILD cases were classified as abnormal TUS, with diagnostic odds ratio of 10.7 (3.2-32.3), sensitivity of 64% (41% to 83%) and negative predictive value 97% (90% to 98%). In exploratory analyses, excluding participants with certain characteristics possibly affecting the TUS from the analyses improved the performance of TUS and pleural abnormalities were associated with ILD. Conclusion In SLE TUS focusing on the presence of B-lines demonstrated modest but statistically significant diagnostic test accuracy for detecting ILD. Pleural abnormalities were significantly associated to ILD.