[ARTICLE] Quantifying spasticity in individual muscles using shear wave elastography – Full Text

Abstract

Spasticity is common following stroke; however, high subject variability and unreliable measurement techniques limit research and treatment advances. Our objective was to investigate the use of shear wave elastography (SWE) to characterize the spastic reflex in the biceps brachii during passive elbow extension in an individual with spasticity. The patient was a 42-year-old right-hand-dominant male with history of right middle cerebral artery-distribution ischemic infarction causing spastic left hemiparesis. We compared Fugl-Meyer scores (numerical evaluation of motor function, sensation, motion, and pain), Modified Ashworth scores (most commonly used clinical assessment of spasticity), and SWE measures of bilateral biceps brachii during passive elbow extension. We detected a catch that featured markedly increased stiffness of the brachialis muscle during several trials of the contralateral limb, especially at higher extension velocities. SWE was able to detect velocity-related increases in stiffness with extension of the contralateral limb, likely indicative of the spastic reflex. This study offers optimism that SWE can provide a rapid, real-time, quantitative technique that is readily accessible to clinicians for evaluating spasticity.

Introduction

An estimated 795,000 Americans experience stroke every year [1], and stroke incidence is expected to increase as the population ages [2]. It is estimated that the prevalence of spasticity after stroke ranges from 18% to 39% [3], [4] and [5], and spasticity-associated functional limitations create significant burdens on survivors and caregivers [6]. Health care costs for individuals with stroke who develop spasticity are estimated to be fourfold higher than those without spasticity [7]. However, high subject variability and indeterminate measurement techniques limit research investigation and treatment advances [8] and [9].

Though classically considered to have increased stiffness resulting solely from the over-active velocity-dependent stretch reflex, chronically spastic muscles associated with stroke appear to also have increased nonreflex stiffness when compared to the side of the body ipsilateral to the lesioned hemisphere, as well as healthy controls [9] and [10]. Clinically, spasticity is diagnosed and monitored using the 5-point Modified Ashworth Scale (MAS): a simple technique that requires no equipment, though is subjective, qualitative, and varies widely with muscle groups [11] and [12]. Though the precise mechanism behind spasticity is not known, we now recognize a variety of biomechanical changes within skeletal muscle connective tissue that likely limit the effectiveness of a simplistic tool, such as the MAS, for evaluating spasticity in chronic stroke [13] and [14]. Electromyography or biomechanical measures may offer more reliable, quantitative information, though are impractical for routine clinical use [14], [15] and [16]. Furthermore, elevated muscle tone in persons with spasticity may not be related to activation of the muscle groups in question [17] and [18].

A variety of imaging-based elastography techniques have emerged with great promise for skeletal muscle evaluation, including ultrasound elastography and magnetic resonance elastography [18], [19], [20], [21] and [22]. Strain elastography, a qualitative measure of relative stiffness, is also available but offers little advantage over the MAS, as neither offers a quantitative, objective measure [21], [23] and [24]. The two quantitative imaging modalities, magnetic resonance elastography and ultrasound shear wave elastography (SWE), show good agreement in both phantoms and tissues, though SWE is especially promising for its flexibility, accessibility, and real-time results [25], [26] and [27]. For this reason, SWE may be uniquely suited for evaluating pathologic alterations in stiffness of individual muscles, especially for quantifying spasticity [18], [28], [29], [30] and [31].

This study evaluated the feasibility of using SWE to characterize the spastic reflex during passive elbow extension in an individual with spasticity caused by stroke. We hypothesized that SWE would capture heightened skeletal muscle stiffness, representing the spastic reflex, during passive elbow range of motion.

Continue —> Quantifying spasticity in individual muscles using shear wave elastography

Fig. 1. Shear wave speeds, ultrasound images, and elastograms for 60°/s ipsilateral elbow extension trials. (A) Ipsilateral biceps; (B) ipsilateral brachialis; (C) ultrasound images and elastograms from trial 1 with sample regions of interest demonstrated in the first panel.

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