Role of diaphragmatic ultrasound in the assessment of disease severity in stable interstitial lung disease patients

Assessment of disease severity in interstitial lung disease (ILD) is usually performed using lung function tests, exercise testing, and chest imaging. Each modality has its own benefits and drawbacks. Ultrasound (USG) examination of the diaphragm is a non-invasive imaging modality that has been found to be effective in evaluating diseases like chronic obstructive pulmonary disease and asthma. However, its role in the assessment of stable ILD has been scarcely evaluated. We conducted a cross-sectional study to evaluate the role of diaphragmatic USG in the assessment of disease severity in 55 stable ILD patients. After clinical evaluation, all patients underwent spirometry [forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC)], high-resolution computed tomography (HRCT) of the thorax and 6-minute walk test as per standard criteria. The Warrick score was calculated using HRCT to quantify the radiological extent of disease. Thereafter, USG was performed, and diaphragmatic excursion (DE) and thickness were measured during both quiet and deep breathing (DB). Dyspnea grade, spirometry values, 6-minute walk distance (6MWD), and the Warrick score were correlated with USG variables to assess for any possible association. The mean age of the patients was 57.6±12.8 years (M:F=1:1). Idiopathic pulmonary fibrosis (n=15) was the most common ILD. The median FVC%, FEV1%, 6MWD, and Warrick score of the patients were 60 (48-74), 68 (53-90), 360 (245-400) m, and 18 (14-22), respectively. Out of 5 USG variables studied, thickening fraction, DE & diaphragmatic thickness (DB) showed statistically significant correlation (p<0.05) with dyspnea grade, FVC, 6MWD, and Warrick score in decreasing order of strength. On logistic regression analysis, FVC was the only factor that independently predicted thickening fraction (adjusted odds ratio: -1.08; 95% confidence interval 1.03-1.13; p=0.003). Diaphragmatic mobility and thickness showed a strong correlation with dyspnea, lung functions, exercise capacity, and radiological extent of disease in ILD patients. USG of the diaphragm can play an effective role in the assessment of disease severity in ILD.