Case report: Potential physiological sources of the late response in epidural spinal recordings induced by spinal cord stimulation during intraoperative neuromonitoring.

Objective: This study aims to investigate the sources of later response in epidural spinal recordings (ESRs) obtained from implanted leads during spinal cord stimulation, a topic has not been widely studied in previous research. Methods: Two patients with lower back and lower extremity pain underwent SCS implantation with intraoperative neuromonitoring (IONM). The timing of extracted peaks in ESRs and intramuscular electromyography (EMG) recordings were analyzed and compared to a Monte Carlo simulation for synchronization analysis. Results: Our data show that, when using two most caudal electrodes for stimulation, late response in ESRs collected from SCS leads was not synchronized with EMG recordings from lower extremity muscles. However, parts of the late responses were synchronized with EMG recordings from abdominal muscle groups. Conclusions: Late response in ESRs is believed to result from muscle contractions, although the exact sources have not been fully identified. They are likely to originate from muscles near the implanted leads. Significance: This research indicates that components of the late response may originate beyond the abdominal region, potentially offering additional information for current IONM practice. Additionally, understanding the sources of the late response may be useful for emerging clinical applications in neurorehabilitation.