Clinical Significance of SSEP Amplitude Changes in Spinal Cord Stimulation: Implications for Pain Relief and Patient Outcomes

Introduction: Intraoperative neuromonitoring, comprising electromyography (EMG) and somatosensory evoked potential (SSEP), is pivotal in ensuring accurate lead placement during spinal cord stimulation (SCS) procedures under general anesthesia. Yet, the quantitative relationship between SSEP parameters and SCS outcomes remains underexplored.
This study aimed to discern the association between intraoperative SSEP amplitude alterations preceding and succeeding paddle electrode placement (off vs. on stimulation) and postoperative pain alleviation.

Methods: We conducted a retrospective analysis of 20 patients: 38% diagnosed with chronic regional pain syndrome (CRPS) and 62% with failed back surgery syndrome (FBSS). All underwent thoracic SCS paddle placements accompanied by SSEP and EMG monitoring. A permutation test was used to compare pain relief outcomes between males and females, and between CRPS and FBSS patients. The association between the percentage change in SSEP amplitude prior to and following lead placement and the overall postoperative pain relief was assessed via a Poisson regression model, accounting for pain laterality (bilateral, left, or right) and EMG responses (left, right, bilateral, or absent).

Results: Patients reported an average pain relief of 66.11% (± 32.42) post-SCS. No significant difference in pain relief was observed between males and females (p=0.16) or between CRPS and FBSS patients (p=0.67). The average percentage change in SSEP amplitude was 66.99% (± 17.94), with a reduction exceeding 50% observed in 75% of the cases. EMG recordings indicated action potential activity in the left lower extremity muscles in 58% of cases, right in 17%, bilateral in 8%, and absent in 17%. The Poisson regression model revealed that a more pronounced reduction in SSEP amplitude percentage change correlated with superior pain relief, even when adjusting for pain laterality and EMG responses (coefficient=0.2, p< 0.001).

Conclusion : Substantial reductions in SSEP amplitude following spinal cord stimulation activation are indicative of improved postoperative pain relief, even when accounting for pain laterality and EMG responses.