Multimodal ultrasound for precise quantitative evaluation of diaphragmatic lesions in idiopathic inflammatory...

Idiopathic inflammatory myopathy (IIM) is a systemic autoimmune disorder in which respiratory failure, driven by diaphragmatic dysfunction and interstitial lung disease (ILD), is a leading cause of mortality. This study aimed to evaluate IIM-related diaphragmatic involvement via multimodal ultrasound, integrating high-frequency ultrasound (HFUS), M-mode imaging, and ultrasound viscoelasticity imaging (UVI).

In this study, 93 IIM patients and 51 matched healthy controls (HCs) underwent diaphragmatic multimodal ultrasound assessments, including measurements of thickness, excursion, and viscoelastic properties [shear wave speed (Cs), viscosity index (Vi), and dispersion slope (Disp)]. Multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were conducted to identify independent predictors of IIM and to assess the diagnostic efficacy of distinguishing IIM patients from HCs. Subgroup ROC analysis was performed within the IIM cohort to evaluate parameters for identifying respiratory involvement. Additionally, correlations between ultrasound parameters and clinical indicators (serological markers, antibodies, and ILD status) were analyzed. In total, 17 IIM patients completed post-treatment follow-up ultrasound examinations.

Compared with the HCs, the patients with IIM exhibited a significantly reduced diaphragmatic thickening fraction (DTF) (HC group: 111.8% vs. IIM group: 74.2%, P<0.001), thickness at end-forced inspiration (3.5 vs. 2.6 mm, P<0.001), quiet breathing excursion (22.8 vs. 14.3 mm, P<0.001), and forced breathing excursion (70.5 vs. 44.0 mm, P<0.001), as well as an elevated Cs_mean (3.1 vs. 3.6 m/s, P<0.05) and Disp_mean (3.9 vs. 4.6 m/s/kHz, P<0.05). Thickness at end‑forced inspiration [odds ratio (OR) =0.33; P<0.001] and forced breathing excursion (OR =0.94; P<0.001) were identified as independent diagnostic markers. For discriminating between patients with IIM and HCs, forced breathing excursion demonstrated the best diagnostic performance among the individual parameters [area under the curve (AUC) =0.84, P<0.001], while a combined model integrating thickness, excursion, and viscoelastic parameters achieved superior diagnostic efficacy (AUC =0.89, P<0.001). For identifying respiratory involvement within the IIM cohort, conventional morpho-functional parameters failed (all AUC <0.65), while the Vi_mean showed significant discriminative ability (AUC =0.72, P<0.010), with the combined model achieving excellent performance (AUC =0.88, P<0.001). Correlation analyses revealed that forced breathing excursion was negatively correlated with ILD (r=-0.29). Post-treatment follow-up revealed significant improvement and normalization of diaphragmatic excursion (DE) and DTF (P<0.05), whereas the thick ness parameters remained unchanged (P>0.05). Myoglobin (MB) decreased significantly (P<0.05), while conventional serological markers, including the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and creatine kinase (CK), showed no significant change (P>0.05).

Multimodal ultrasound enables the early detection and quantitative monitoring of diaphragmatic impairment in IIM. Viscoelastic parameters, particularly the Vi, may aid in the identification of patients with respiratory involvement. Diaphragmatic functional parameters (excursion and the DTF) are responsive to treatment and may serve as objective biomarkers for monitoring the therapeutic response, complementing conventional serological assessments.