Evaluation of connective tissue disease-related interstitial lung disease using ultrasound elastography: a preliminary study

Background: Interstitial lung disease (ILD) is a common pulmonary complication of connective tissue disease (CTD), which can lead to shortened survival. This article explores the ability of shear wave elastography (SWE) to assess lung surface elastic properties and to distinguish healthy lungs from diseased lungs with connective tissue disease-related interstitial lung disease (CTD-ILD). We aimed to determine whether SWE can be used to assess the severity of CTD-ILD. Methods: A total of 65 CTD-ILD patients and 60 healthy volunteers were included for the case group and the control group, respectively. All participants underwent lung ultrasound (count of B-line and measurement of pleural line thickness) and SWE [measurement of Young's modulus (Emean) and shear wave velocity (SMV) (Cmean)] examinations at 50 lung sites. All participants also underwent an examination with high-resolution computed tomography (HRCT) and a pulmonary function test (PFT). For SWE assessment, the Q-box was set to its minimum size (1 mm) and manually placed on the pleural line, rather than inside the lung, to measure the stiffness of the lung surface. The intra- and inter-reliability of SWE measurements of healthy controls (HC), the receiver operating characteristic (ROC) curve for SWE for CTD-ILD, and correlations between different assessment methods were analyzed. Results: Excellent intra- and inter-reliability of SWE measurements on the mid-anterior lung site of HCs (correlation coefficient >0.97; P<0.01) were found. The results of the lung ultrasound of case group participants were significantly higher than those of HCs at each site (P<0.001). The SWE results revealed a significant increase in both Emean and Cmean in CTD-ILD patients (P<0.001) compared with HCs at certain sites (P<0.001). The areas under the curve (AUC) of Emean and Cmean for CTD-ILD were 0.646 and 0.647 (P<0.05), respectively, and the cutoff values for Emean and Cmean to distinguish CTD-ILD from healthy lungs were 15.81 kPa and 2.31 m/s, respectively. There was no significant correlation between the SWE measured values and the number of B-lines, or the HRCT and PFT results, respectively (P>0.05). Conclusions: As a noninvasive ultrasound elastography (UE) technique, SWE may provide a novel method to differentiate CTD-ILD-affected lungs and healthy lungs. It is a reliable way to measure the stiffness of a healthy lung surface in the supine position. However, the ability of SWE to evaluate the severity of CTD-ILD may be limited.