Lower muscle stiffness assessed with supersonic shear imaging is associated with more severe muscle impairments in patients with sporadic inclusion body myositis


Supersonic shear imaging (SSI) is a recently developed technique for noninvasive assessment of tissue stiffness. In muscle, mechanical properties may be affected by multiscale structural alterations induced by disease processes. However, muscle SSI data in patients with neuromuscular disorders are particularly scarce. In this pilot study, we aimed to evaluate potential relationship between the severity of muscle weakness and passive muscle stiffness in patients with inclusion body myositis (IBM). Twenty-three patients (61% men, age = 65.7 ± 8.9 years; BMI = 25.0 ± 3.9 kg·m−2; inclusion body myositis weakness composite index = 62.5 ± 23.5) volunteered to participate in this study. Muscle shear modulus was assessed in the short head of the right biceps brachii with the elbow flexed at 80, 90, 110 and 170°. SSI was performed with an Aixplorer coupled with a SL 15-4 probe (Supersonic Imagine, Aix-en–Provence, France). Shear modulus measurements were measured before and after a conditioning of 5 cycles at 4°/s. Elbow flexion maximal voluntary isometric strength was assessed at 90° using an isokinetic dynamometer and expressed as percentage of predicted values. Shear modulus was 6.5 ± 1.1, 7.2 ± 1.4, 8.3 ± 1.8, and 20.6 ± 6.6 kPa at 80, 90, 110 and 170°, respectively. Muscle shear modulus was significantly increased at all angles (all P < 0.05) and no significant effect of conditioning was found (P = 0.51). Elbow flexion strength was 26.0 ± 12.9 Nm i.e. 50.4 ± 21.1% of predicted values. Shear modulus was linearly related to elbow flexion strength at all tested angles (R = 0.59; R = 0.77; R = 0.76; R = 0.56 at 80, 90, 110 and 170°, respectively; all P < 0.001). In conclusion, lower passive muscle stiffness assessed by SSI was associated with more severe muscle weakness in patients with IBM. Further investigations including the quantification of muscle degenerating processes (e.g. fibrosis, fatty infiltration) are required to clarify mechanisms underlying these findings.

Neuromuscular Disorders