Quantifying changes in material properties of stroke-impaired muscle

Abstract Background Material properties of muscles are clinically important parameters for evaluating altered muscle function. Stroke survivors display motor impairments almost immediately after the vascular event, and then gradually develop altered muscle properties. Little is known about the magnitude of these changes in muscle material properties, specifically stiffness. Previous measures of stiffness are limited to estimates of joint stiffness or groups of muscles. Thus, our aim was to determine changes in passive muscle stiffness and composition by measuring: (1) shear wave speed using shear wave ultrasound elastography and (2) echo intensity of the B-mode ultrasound images of the biceps brachii muscle in individuals who have had a stroke. Methods Shear wave ultrasound elastography and B-mode ultrasound images of the biceps brachii muscle of the paretic and non-paretic limbs of sixteen stroke survivors were captured at rest. Findings Our main results show that shear wave speed and echo intensity of the paretic side were on average 69.5% and 15.5% significantly greater than those of the non-paretic side, respectively. Differences in shear wave speed between the non-paretic and the paretic muscles were strongly correlated with differences in echo intensity, time since stroke, and with Fugl-Meyer scores. Interpretation Muscle stiffness and muscle composition, as indicated by SW speed and echo intensity, may be altered in stroke-impaired muscle at rest. These findings highlight the potential for SW elastography as a tool for both investigating the fundamental mechanisms behind changes in stroke-impaired muscle, and for evaluation of muscle mechanical properties as part of clinical examination.