Diagnostic performance of lung ultrasound for systemic sclerosis-associated interstitial lung disease: an international cross-sectional study from two tertiary care centers

OBJECTIVE: To assess the diagnostic accuracy of two lung ultrasound (LUS) scores (≥ 10 B-lines and pleural line abnormalities according to Fairchild's criteria) for detecting interstitial lung disease (ILD) in systemic sclerosis (SSc), when applied independently at two referral centers using a shared standardized protocol. Secondary aims included evaluating the diagnostic performance of their combined use and their association with ILD severity. METHODS: This cross-sectional bi-center study included same-day LUS and high-resolution computed tomography (HRCT), using a 14-zone scanning protocol. ILD was defined as ≥ 10% lung involvement on HRCT. The diagnostic performance of each LUS score and their combination was assessed using OR and AND rules (the OR rule indicating positivity for either criterion, and the AND rule requiring both to be positive). Associations with disease severity, based on the Goh classification, were also explored. RESULTS: ILD was present in 68% of the 108 patients included. The ≥ 10 B-lines cut-off showed 90.5% sensitivity and 84.4% specificity (AUC 0.875), while Fairchild's criteria achieved 93.2% sensitivity and 93.8% specificity (AUC 0.935). The OR rule yielded the highest sensitivity (95.9%) and NPV (89.7%), while the AND rule provided the highest specificity (96.9%) and PPV (98.5%). All patients with extensive ILD were positive for both scores. CONCLUSIONS: In this real-life multicenter setting, both LUS scores showed high and complementary diagnostic performance when applied within a standardized protocol. Their consistent association with ILD extent supports their clinical use as non-invasive tools for routine SSc-ILD assessment. Key Points • Lung ultrasound shows high diagnostic accuracy for SSc-ILD across two international referral centres. • A standardized 14-zone protocol supports reproducible LUS performance. • ≥ 10 B-lines and Fairchild's criteria provide complementary diagnostic information. • Combining B-lines and pleural line criteria improves overall diagnostic performance.