Unique Characteristics of the Dorsal Root Ganglion as a Target for Neuromodulation

Abstract

Objective: The dorsal root ganglion (DRG) is a novel target for neuromodulation, and DRG stimulation is proving to be a viable option in the treatment of chronic intractable neuropathic pain. Although the overall principle of conventional spinal cord stimulation (SCS) and DRG stimulation-in which an electric field is applied to a neural target with the intent of affecting neural pathways to decrease pain perception-is similar, there are significant differences in the anatomy and physiology of the DRG that make it an ideal target for neuromodulation and may account for the superior outcomes observed in the treatment of certain chronic neuropathic pain states. This review highlights the anatomy of the DRG, its function in maintaining homeostasis and its role in neuropathic pain, and the unique value of DRG as a target in neuromodulation for pain.

Methods: A narrative literature review was performed.

Results: Overall, the DRG is a critical structure in sensory transduction and modulation, including pain transmission and the maintenance of persistent neuropathic pain states. Unique characteristics including selective somatic organization, specialized membrane characteristics, and accessible and consistent location make the DRG an ideal target for neuromodulation. Because DRG stimulation directly recruits the somata of primary sensory neurons and harnesses the filtering capacity of the pseudounipolar neural architecture, it is differentiated from SCS, peripheral nerve stimulation, and other neuromodulation options.

Conclusions: There are several advantages to targeting the DRG, including lower energy usage, more focused and posture-independent stimulation, reduced paresthesia, and improved clinical outcomes.

Keywords: Chronic Pain; DRG Stimulation; Dorsal Root Ganglion Stimulation; Neuromodulation; Neuropathic Pain; Neurostimulation; Pain Management; Spinal Cord Stimulation.

Figure 1

A schematic diagram showing the expanse of the primary sensory neuron (middle) and its terminations (left). The locations of dorsal root ganglia (DRGs) in the lumbar and sacral spine are illustrated (right); note the utility of vertebral pedicles as landmarks at lumbar levels and the greater variability of DRG location at sacral levels.

Figure 2

The narrow, flexible dorsal root ganglion (DRG) stimulation lead is maneuvered via an epidural needle into the vertebral foramen to appose the DRG. An S-shaped strain relief loop is placed in the epidural space, and tissue anchors (not pictured) are employed.

Figure 3

Sagittal schematics showing the location of the dorsal root ganglion (DRG) and proximal nerve roots in the spinal foramen (left) and a representation of the many intraforaminal ligaments (right). The DRG stimulation lead is inserted dorsally to lie closely along the DRG.

Figure 4

In an animal model of neuropathic pain induced via experimental spinal nerve axotomy injury, ectopic activity was recorded at dorsal root fibers before entry into the spinal cord (represented by the “R” symbol and two activity traces). 1) Transection of the spinal nerve distal to the dorsal root ganglion (DRG), analogous to the clinical removal of a neuroma, did not prevent the ectopic neural activity from entering the spinal cord. 2) Transection proximal to the DRG did, however, stop all ectopic activity from reaching the recording electrode.