Use of lung ultrasound surface wave elastography in patients with interstitial lung disease.

OBJECTIVES

To assess whether lung ultrasound surface wave elastography (LUSWE), a non-invasive measure of lung stiffness, correlates with pulmonary function and high-resolution CT (HRCT) patterns in suspected interstitial lung disease (ILD). We hypothesised that LUSWE-derived lung stiffness would be associated with functional impairment and radiological ILD patterns.

SETTING

Prospective, single-centre pilot study conducted in a tertiary referral ILD unit in Barcelona, Spain.

PARTICIPANTS

68 consecutive patients (41 men and 27 women) with suspected ILD were enrolled between June 2020 and February 2024 and completed LUSWE assessment at diagnosis under clinically stable conditions. Final diagnoses comprised sarcoidosis, idiopathic pulmonary fibrosis, combined pulmonary fibrosis and emphysema, fibrosing ILD, connective tissue disease-related ILD, other ILD and absence of pulmonary disease.

PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was the association between LUSWE velocity and pulmonary function parameters, specifically forced vital capacity (FVC) and diffusing capacity of the lung for carbon monoxide (DLCO). Secondary outcomes included associations with HRCT radiological patterns, fibrosing vs non-fibrosing ILD, usual interstitial pneumonia (UIP)/probable UIP vs other HRCT patterns and quantitative HRCT-derived fibrosis extent.

RESULTS

LUSWE velocity did not significantly correlate with FVC (r=0.23, 95% CI -0.01 to 0.45; p=0.07) or DLCO (r=0.13, 95% CI -0.12 to 0.36; p=0.31). No significant differences in LUSWE velocity were observed across HRCT patterns (Kruskal-Wallis χ²=1.2018; p=0.8778). Exploratory point-by-point analyses showed one significant association between the R2 point and FVC (r=0.33; p=0.0068), but this did not remain significant after correction for multiple comparisons (adjusted p=0.137). LUSWE distributions were similar between fibrosing and non-fibrosing ILD groups (3.35 (IQR 2.87-4.16) vs 3.55 (IQR 2.98-4.17) m/s; p=0.526) and between UIP/probable UIP and other HRCT patterns (3.36 (IQR 2.89-4.21) vs 3.59 (IQR 2.86-4.15) m/s; p=0.876). Quantitative HRCT analyses also showed weak, non-significant correlations between hemithorax-level fibrosis extent and corresponding LUSWE values.

CONCLUSIONS

In this heterogeneous cohort of patients evaluated at diagnosis for suspected ILD, LUSWE was not meaningfully associated with pulmonary function impairment, HRCT patterns or quantitative fibrosis extent. Larger multicentre studies using standardised acquisition protocols and focused on well-defined fibrosing ILD populations with predominant subpleural involvement are needed.