Diaphragmatic Ultrasound in Fibrosing Interstitial Lung Disease: A Systematic Review of Current Evidence

Background/Objectives: Fibrosing interstitial lung disease (F-ILD) is associated with progressive respiratory impairment and substantial symptom burden. Diaphragmatic ultrasound (DUS) is a non-invasive method for assessing diaphragmatic structure and function, but its clinical role in F-ILD remains uncertain. This systematic review evaluated the available evidence on DUS in adults with F-ILD. Methods: This systematic review was conducted and reported according to the PRISMA guidelines. MEDLINE, Embase, CINAHL, and the Cochrane Library were searched and observational studies evaluating DUS in adults with F-ILD were included. Risk of bias was assessed using the QUADAS-2, and outcome-level certainty of evidence was evaluated by GRADE framework. Results: Six cross-sectional observational studies involving 232 participants were included. Diaphragmatic excursion (DE) was assessed in all six studies, while diaphragm thickness (DT) and thickening fraction (TF) were evaluated in four. Some studies reported abnormalities in DUS parameters during deep breathing and cross-sectional associations with pulmonary function, exercise capacity, dyspnoea, or radiological severity. Substantial heterogeneity in study populations, ultrasound protocols, and outcome reporting precluded meta-analysis. The certainty of evidence was very low. Conclusions: Current evidence suggests that DUS may detect diaphragmatic abnormalities in patients with F-ILD and may have future complementary value alongside established clinical assessments. However, the evidence is limited, heterogeneous, and of very low certainty and does not establish diagnostic accuracy, prognostic value, or usefulness for longitudinal monitoring. Accordingly, DUS cannot currently be recommended for routine clinical implementation in F-ILD, and prospective longitudinal validation is required.