Imaging in Systemic Sclerosis-Associated Interstitial Lung Disease: Comparison of Transthoracic Lung Ultrasound and HR Chest CT in Detecting Characteristic Patterns

Background/Objectives: Even today the interstitial lung disease (ILD) is diagnosed by chest high-resolution computed tomography (lung HR-CT). A large amount of data is available about the use-fulness of lung ultrasound (LUS) in ILD. The aim of this study is to evaluate the LUS capacity to discrim-inate different ILD patterns in systemic sclerosis (SSc) patients, such as UIP, NSIP with GGO, and NSIP with GGO and reticulations, and then the possibilityto identify the progressive fibrosing ILD. Methods: All SSc-patients with recent HRCT performed underwent LUS. Results: ILD was observed in 99 (63.5%) patients (25% with UIP pattern, and 75% with NSIP pattern (46 with GGO, 28 with GGO and reticula-tions). By ROC curve analysis, that higher accuracy, sensitivity, and specificity were found for pleural line irregularity (0.68, 95.8%, and 41.5%, p=0.004), pleural line thickness (0.72, 70.8%, and 73.2%, p=0.001), and subpleural cyst (0.68, 58.3%, and 78.9%, p=0.004) to detect UIP pattern. The best performance among LUS signs for NSIP with GGO pattern was observed for B-lines (accuracy: 0.73, sensitivity: 92.9% and specific-ity: 54.3, p=0.0001). LUS signs with higher accuracy, sensitivity, and specificity for NSIP with GGO and reticulations were pleural line irregularity (0.69, 96%, and 42.1%, p=0.002), pleural line thickness (0.69, 65.4%, 72.7%, p=0.002), and B-lines (0.72, 96.2%, 48.8%, p=0.0001). Furthermore, a total number of B-line > 10 maximises LUS performance with 92.3% sensitivity, and an accuracy of 0.83 (p=0.0001) to detect the NSIP pattern, particularly GGO. A sample-restricted analysis (66 SSc patients) evidenced the presence of progressive fibrosing ILD in 77%. By binary regression analysis, that the unique LUS sign associated with progressive fibrosing ILD was the presence of pleural line irregularity (OR: 3.6; 95% CI 1.08-11.9; p= 0.036). Conclusions: Our study demonstrated that the LUS presented a high capacity to discriminate the different patterns of SSc-ILD. Therefore, the hypothesis of using transthoracic LUS as a screening method for the evaluation of the presence of SSc-ILD and to establish the correct timing for the execution of chest HR-CT, in order to avoid patients from excessive exposure to ionising radiation is supported.