An Observational Electrophysiologic Study for Optimizing Targeting of Monopolar Lumbar Spinal Foraminal Neural Structures: Would Spinal Transforaminal Stimulation Be a More Appropriate Classification?

INTRODUCTION

The dorsal root ganglion (DRG) is an important target for treating chronic refractory pain. However, determining the optimal electrode location for DRG stimulation remains challenging. Conventionally, the ganglion is targeted within the infrapedicular zone of the neuro-foramen for DRG stimulation using radiological imaging. However, clinical experience suggests that optimal focal pain paresthesia stimulation coverage (PPC) often occurs at sites other than directly over the ganglion, indicating that periganglionic neural structures also may play a role as therapeutic targets.

MATERIALS AND

METHODS

Electro-stimulation mapping (ESM) was performed in seven subjects who had previously been implanted with transforaminal spinal cord stimulation (SCS) leads for focal neuropathic lower trunk and limb pain; 12 octapolar transforaminal SCS leads, programmed for monopolar stimulation across multiple lumbar spine levels, were evaluated. At each electrode, stimulation amplitudes were assessed for sensory perception, optimal comfortable stimulation, and uncomfortable stimulation. Using standard radiologic techniques, 288 paresthesia mappings were anatomically related to the spinal pedicles, and categorized into intraspinal, foraminal, and extraforaminal zones to determine optimal pain-paresthesia coverage (PPC) electrode proximity to the putative DRG location.

RESULTS

Optimal focal PPC performance occurred within the conventional radiographic ganglion region in only 25% of electrodes, whereas 75% of electrodes having optimal PPC performance were located outside the defined foraminal zone. ESM also delineated the physiologic and biophysical boundaries of the neuro-foramen that were not reliably identifiable on the anteroposterior projection alone.

CONCLUSIONS

Optimal PPC is not consistently achieved by stimulating directly within the presumed DRG zone and may engage different mechanisms of action across the DRG and adjacent neural structures. Our findings highlight the importance of precise electrode localization, support further comparison of PPC-based targeting with on-label DRG stimulation therapy, and justify the broader term spinal transforaminal stimulation to describe stimulation delivered to these neural targets.