Correlating Intraoperative Neuromonitoring Patient Specific Responses during Spinal Cord Stimulation with Clinical Outcomes

Introduction: Intraoperative neuromonitoring (IONM) with SCS promotes patient safety and allows determination of laterality of coverage. We explore the relationship between IONM responses and patient specific factors including outcomes.

Methods: We assessed evoked motor responses during standard of care SCS paddle placement (NCT05459324). Tripoles were tested at paddles placed between T6 and T10 depending on the sweet spot from trialing. Maximum percentage change in root mean square (RMS) were determined across 18 muscle groups for SCS currents < 10mA. Numerical Rating Scale (NRS), Beck Depression Inventory (BDI), McGill Pain Questionnaire (MPQ), Oswestry Disability Index (ODI) and Pain Catastrophizing Scale (PCS) were collected pre-operatively and at 3 months. Responders were determined based on 50% pain relief on NRS or achieving minimum clinically important difference (MCID) across NRS or 3 metrics.

Results: We included 18 patients (12F:6M; mean age 56). 8 patients were diagnosed with neuropathic pain, 8 with FBSS, and 2 with CRPS. Nine were deemed responders at 3 months based on 50% reduction in NRS, 16 based on achieving MCID on NRS and 12 based on reaching MCID on 3 or more outcome metrics. In addition to correlation with other outcome metrics, response rate determined by all 3 methods correlated significantly with APD (anterior-posterior diameter at sweet spot of spinal column) (r=-0.5086, 0.5859, 0.520; p=0.0371, 0.0134, 0.0321, respectively). Response based on MCID on NRS correlated with a blinded assessment of degree to which maxRMS covered painful regions (r=-0.5021, p=0.0337). Maximum stimulation amplitude to achieve a response correlated with APD (AP diameter), inter-pedicular distance, body mass index, and dorsal CSF thickness (r=-0.5386, 0.5578, 0.6389, 0.6573; p=0.0211, 0.0200, 0.0058, 0.0041, respectively).

Conclusion : IONM offers an opportunity to assess how patient factors may alter responses to stimulation. Further these factors from MR and body measurements may ultimately affect patient outcomes and should be considered in evaluation.