Degenerative muscle changes may be associated with changes in muscle mechanical properties. Shear wave elastography (SWE) allows direct quantification of muscle shear modulus (MSM). The aim of this study was to evaluate the feasibility and reliability of SWE in the severely disordered muscle as observed in inclusion body myositis. To explore the clinical relevance of SWE, potential relationships between MSM values and level muscle impairments (weakness and ultrasound-derived muscle thickness and echo intensity) were investigated. SWE was performed in the biceps brachii at 100°, 90°, 70° and 10° elbow flexion in 34 patients with inclusion body myositis. MSM was assessed before and after five passive stretch-shortening cycles at 4°/s from 70° to 10° elbow angle and after three maximal voluntary contractions to evaluate potential effects of muscle pre-conditioning. Intra-class correlation coefficients and standard errors of measurements were >0.83 and <1.74 kPa and >0.64 and <1.89 kPa for within- and between-day values, respectively. No significant effect of passive loading-unloading and maximal voluntary contractions was found (all p values >0.18). MSM correlated to predicted muscle strength (all Spearman correlation coefficients (ρ) > 0.36; all p values < 0.05). A significant correlation was found between muscle echo intensity and muscle shear modulus at 70° only (ρ = 0.38, p <0.05). No correlation was found between muscle thickness and MSM (all ρ values > 0.23 and all p values > 0.25, respectively). Within- and between-day reliability of muscle SWE was satisfactory and moderate, respectively. SWE shows promise for assessing changes in mechanical properties of the severely disordered muscle. Further investigations are required to clarify these findings and to refine their clinical value.
Keywords: Muscle elasticity; Muscle stiffness; Myositis; Neuromuscular disorders; Passive muscle mechanics; Quantitative muscle ultrasound imaging; Shear wave elastography; Skeletal muscle.
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