Spinal cord stimulation (SCS) or electrical stimulation in the epidural space of the spinal canal has been used for more than 50 years to treat chronic pain by modulating the activity of the spinal cord or spinal cord roots. While originally conceived out of gate theory, the precise effects of spinal cord stimulation are still an active area of research. Certainly there are multiple factors contributing to this unchanged responder rate including diagnosis, psychosocial factors, comorbidities, and implementation gaps, but a major technical hurdle remains personalizing therapy to engage in the precise pain circuits for each individual patient in anatomic location and over time. The delivery of spinal cord stimulation varies significantly with changes in position due to the movement of the spinal cord and its associated nerve roots. Existing spinal cord stimulation platforms rely on tonic stimulation with minimal adjustment with movements of the spinal cord or any adjustment due to changing physiology. Tonic stimulation assumes a stationary system that does not account for short or long-term effects of plasticity or movement. However, the effect of stimulation on the circuits of the spinal cord as with all stimulation of the nervous system can be measured through an event-related potential (ERP) synchronized to stimulation pulses, called the evoked compound action potential (ECAP). As an evoked-response, it is clear that ECAPs may provide a more dynamic insight into the underlying electrophysiologic system underlying the anatomic pathways of chronic pain, and some reports have correlated ECAPs to measures of pain relief, which is difficult to disassociate in patients with stable patterns of pain. The spatial variance of ECAP may imply that spinal cord stimulation for the purposes of pain relief is not homologous to features available in the ECAP signal but could be accessible in the variability of ECAP signal. Similarly, very little experimental evidence exists to incorporate the complex role of pain processing and valuation systems into a model of ECAP electrophysiology. Namely, the correlation between top-down control and higher-order (cognitive/mood) circuit interactions with ECAP features and chronic pain. Understanding the electrophysiology of evoked responses in the spinal cord in the competitive market of non-opioid pain relief should be grounded in basic pain phenotype modeling. This proposal represents the first step in that pathway by studying the feasibility of capturing ECAPs during clinical externalization while collecting the necessary data for behavioral modeling for future causal analysis with ECAP features. This protocol establishes the first step towards closed-loop stimulation through open-loop measurement and stimulation during an existing clinical paradigm. This study aims to understand the feasibility of implementing ECAP during the externalization period of a clinical trial while simultaneously providing clinical feedback for optimal settings discovered during testing.
The purpose of this study will be to investigate the optimization of spinal cord stimulation with ECAPs in patients with spinal cord implants.