Diagnostic accuracy of shear wave elastography and ultrasound-derived indices in interstitial lung disease: novel insights into connective tissue disease-associated interstitial lung disease and idiopathic pulmonary fibrosis

Abstract Background This study aimed to evaluate the diagnostic accuracy of shear wave elastography (SWE) and ultrasound-derived indices in detecting and distinguishing interstitial lung disease (ILD) subtypes. Methods Sixty patients with connective tissue disease-associated interstitial lung disease (CTD-ILD) and idiopathic pulmonary fibrosis (IPF), and 30 healthy controls underwent comprehensive pulmonary function testing, six-minute walk tests (6MWT), arterial blood gas analysis, and thoracic imaging. Radiological parameters assessed included diaphragmatic thickness and excursion, SWE stiffness values, and computed tomography (CT) scoring. Receiver operating characteristic (ROC) curve analysis was performed to determine the diagnostic performance of each parameter. Results All groups were predominantly female, with no significant sex distribution differences ( p = 0.66). The CTD-ILD group was significantly younger than both the IPF and control groups ( p = 0.003). Both ILD groups demonstrated significantly reduced VC% and FVC% compared to controls ( p < 0.001), with preserved FEV 1 /FVC ratios. Functional capacity was impaired in ILD patients, who showed higher alveolar–arterial gradients, lower oxygen saturations, and shorter 6MWT distances ( p < 0.001). SWE and ultrasound-derived indices revealed high diagnostic performance in detecting diffuse parenchymal lung disease (DP-ILD). The highest accuracy was achieved by TVDE and SWEC (AUC = 1.00), followed by SWEE (AUC = 0.97), DTF (AUC = 0.96), and CT score (AUC = 0.92). Cutoff-based analysis showed DTF < 73.50 yielded 93% sensitivity and 100% specificity, while SWEC > 1.95 and SWEE > 15.75 demonstrated ≥ 97% accuracy across all metrics. Comparison between IPF and CTD-ILD revealed better pulmonary function and longer 6MWT distances in RA-ILD ( p < 0.05), while diaphragmatic excursion was greater in IPF ( p < 0.05). However, gas exchange and SWE indices showed no significant intergroup differences. MDE and TVDE offered modest discriminatory value (AUCs 0.71 and 0.69, respectively), with cutoff optimization necessary for balancing sensitivity and specificity. Correlations revealed that higher SWEC and SWEE values were strongly linked to worse pulmonary function, gas exchange, exercise tolerance, diaphragmatic dysfunction, and more extensive fibrosis. Conclusion In this single-center study, SWE and ultrasound-derived indices demonstrated excellent diagnostic performance for detecting ILD and showed strong correlations with clinical, functional, and radiological measures, supporting their potential as non-invasive adjunctive tools. However, their ability to differentiate CTD-ILD from IPF remained limited. Given the relatively small sample size and single-center design, these findings should be considered preliminary and require validation in larger, multicenter prospective studies before routine clinical implementation.