High-Density Electromyography Biomarkers for Detecting and Monitoring of Spastic Muscles During Passive Stretch

Spasticity is one of the most common symptoms that stroke patients develop after the incident. It not only leads to impaired motor control and pain but also lowers the quality of life for stroke patients. Botulinum toxin (BoNT) injection has been used as a first-line treatment for spasticity, which helps to reduce muscle tone. While the Modified Ashworth Scale (MAS) is the current clinical gold standard in evaluating spasticity, it can be affected by low inter-rater reliability. This study aims to evaluate the efficacy of high-density surface electromyography (HD-sEMG) in the passive stretch reflex pre- and post-BoNT injection as a biomarker for spasticity detection and monitoring. Ten stroke participants were recruited in this study, and the root mean squared (RMS) envelope signal and the slope between fast passive extension (FPE) and slow passive extension (SPE) were calculated. The results show that all participants have Peak RMS Envelope and Slope features lower Post-BoNT injection compared to Pre-BoNT injection (SPE: p=0.03938; FPE: p=0.00119; Slope: p=0.00143 while only five out of ten participants have their MAS Score reduce after BoNT injection (p=0.02386). These results suggest that EMG-derived features from spastic muscles may be an appropriate and quantitative alternative to the MAS score as well as a quantitative metric for detecting spasticity.