Ab0253 Multimodal Ultrasound of Muscle: A Promising Biomarker for Immune-Mediated Necrotizing Myopathy

Background: Immune-mediated necrotizing myopathy (IMNM) [1] is characterized by acute or subacute onset, symmetric distribution, and proximal muscle weakness, with extremely high muscle enzyme serum levels and muscle histopathology showing necrosis or regeneration. Early diagnosis and monitoring disease activity are essential in the clinical management of patients with IMNM. Muscle ultrasound may offer a promising and cost-effective evaluation tool. Objectives: To compare muscle ultrasound parameters (including conventional ultrasound and shear wave elastography) in patients with IMNM and healthy controls and analyze the correlation with disease activity. Methods: 15 patients with IMNM were recruited prospectively from the rheumatology outpatient clinic, and 20 healthy control cohorts were matched based on age and sex. They all underwent muscle ultrasound of the bilateral right rectus femoris (RF) in axial and longitudinal scans and ultrasound parameters were measured. Spearman's test was used to identify the correlations between ultrasound and disease activity measures. Results: The mean age at diagnosis of patients with IMNM was 50.73 (±9.83) years, with a median disease duration of 13 months, of which 66.67% were females. The control participants were close in age and sex. By ultrasound, patients with IMNM had an increased echogenicity of RF compared with healthy controls [mean pixel intensity of 69.88±4.21 in IMNM vs 66.18±2.33 in controls (P = 0.006)]. No significant differences between IMNM and healthy controls were found in fascia thickness, muscle thickness and power Doppler score (all P > 0.05). Shear wave elastography (SWE) measurements (shear wave speed and shear wave dispersion slope) exhibits good repeatability and stability on longitudinal section. The results shows that shear wave speed (1.89 vs 1.97 m/s, P = 0.028) and dispersion slope (8.85 vs. 10.54 [m/s]/kHz, P = 0.002) of IMNM patients were lower than that of the controls (Figure 1). As shown in Table 1, there was a significant correlation between the two SWE parameters and the serum enzyme indices and MMT. A negative correlation trend for an association between SWE and PGA VAS and MDAAT did not reach statistical significance (P > 0.05). Conclusion: Multimodal ultrasound of muscle may be a valuable imaging method for early detection of muscle involvement and evaluation of IMNM disease activity. REFERENCES: [1] Allenbach Y, Benveniste O, Stenzel W, Boyer O. Immune-mediated necrotizing myopathy: clinical features and pathogenesis. Nat Rev Rheumatol. 2020,16(12):689-701. Acknowledgements: This study was supported by the National Natural Science Foundation of China (No. 82071930). Disclosure of Interests: None declared.