# Dorsal Root Ganglion Stimulation

## Introduction

Dorsal root ganglion (DRG) stimulation represents a targeted approach to neuromodulation that addresses a key limitation of traditional spinal cord stimulation: the difficulty in treating focal, discrete neuropathic pain in specific dermatomes, particularly in the lower extremities, groin, and perineum. FDA-approved in 2016 following the landmark ACCURATE trial, DRG stimulation has established itself as a first-line neuromodulation option for conditions such as complex regional pain syndrome (CRPS) and post-surgical neuropathic pain affecting the distal extremities.

## Anatomy and Physiology of the DRG

### Location and Structure

The DRG is located within the intervertebral foramen, typically sitting in its dorsal-superior aspect. It contains the cell bodies of primary afferent sensory neurons -- the A-beta, A-delta, and C fibers that carry sensory information from the periphery to the spinal cord. The DRG is enclosed by a thin connective tissue capsule but lacks a complete blood-nerve barrier, which makes it more accessible to both chemical mediators and electrical stimulation than structures within the central nervous system. Structurally, the DRG is pseudounipolar: each neuron has a single axon that bifurcates into a peripheral branch (coming from the body's tissues) and a central branch (entering the spinal cord via the dorsal root).

### Role in Pain Processing

The DRG is not merely a passive relay station. In chronic pain states, DRG neurons become active participants in pain amplification. They exhibit increased excitability and spontaneous firing, upregulation of voltage-gated sodium channels (Nav1.7, Nav1.8, Nav1.9), enhanced expression of TRPV1 receptors and neuropeptides (substance P, CGRP), cross-excitation between adjacent neurons within the ganglion through ephaptic coupling, and satellite glial cell activation with release of pro-inflammatory cytokines. These pathological changes make the DRG both a contributor to chronic pain and a logical therapeutic target for neuromodulation.

<image>Detailed anatomical illustration of a transverse section through a lumbar intervertebral foramen showing the dorsal root ganglion location, depicting the DRG as an ovoid structure in the dorsal-superior aspect of the neural foramen, with the dorsal root entering the spinal cord posteriorly and the ventral root exiting anteriorly, labeled surrounding structures including the pedicles above and below, the facet joint posteriorly, the disc anteriorly, the epidural space, and the thecal sac, with a magnified inset showing the cellular architecture of the DRG including pseudounipolar neuron cell bodies of varying sizes, satellite glial cells surrounding the neurons, and the fenestrated capillary network</image>

## Mechanism of Action

### How DRG Stimulation Differs from SCS

Traditional SCS activates dorsal column fibers broadly, while DRG stimulation acts directly on primary afferent cell bodies. The DRG's location within the bony foramen creates a natural compartment that limits current spread, enabling highly targeted stimulation. The thin cerebrospinal fluid layer surrounding the DRG is minimal compared to the dorsal epidural space, which dramatically reduces the positional variability that plagues traditional SCS. Because DRG stimulation modulates pain at the first-order neuron level, it intervenes before nociceptive signals undergo the complex processing that occurs in the dorsal horn.

### Proposed Mechanisms

Several mechanisms have been proposed. The DRG cell body sits at a T-junction where action potentials can be blocked or attenuated, and stimulation may enhance this natural filtering function. Stimulation also decreases the abnormal spontaneous firing of sensitized DRG neurons, modulates satellite glial cell activity to reduce neuroinflammation at the ganglion level, and activates A-beta fibers at the ganglion to provide segmental inhibition -- essentially a gate mechanism operating at the DRG itself.

## Advantages for Focal Neuropathic Pain

### Targeted Dermatomal Coverage

DRG stimulation provides highly specific stimulation confined to one or two dermatomes. This specificity is especially valuable for anatomical regions that traditional SCS covers poorly. The foot and ankle (L4-S1 DRG) are difficult to cover with dorsal column stimulation because sacral fibers are organized medially within the dorsal columns. The groin and inguinal region (T12-L1 DRG) can be targeted for conditions like post-herniorrhaphy pain and ilioinguinal neuralgia. The knee (L3-L4 DRG) can be addressed for post-surgical neuropathic pain, and the hand and wrist (C6-C8 DRG) for CRPS of the upper extremity.

| Target Region | DRG Level | Condition | Why Traditional SCS is Limited |
|--------------|-----------|-----------|-------------------------------|
| Foot and ankle | L4-S1 | CRPS, post-surgical neuropathic pain | Sacral fibers organized medially in dorsal columns |
| Groin/inguinal | T12-L1 | Post-herniorrhaphy pain, ilioinguinal neuralgia | Difficult to isolate without extraneous stimulation |
| Knee | L3-L4 | Post-surgical neuropathic pain | Overlapping dermatomes, positional variability |
| Hand and wrist | C6-C8 | CRPS of upper extremity | Cervical SCS coverage inconsistent for distal hand |

### Positional Stability

Because the DRG is surrounded by bone and bathed in minimal CSF, stimulation intensity remains remarkably stable regardless of body position. Patients report consistent therapy whether they are sitting, standing, lying down, or physically active. This is a major practical advantage over traditional SCS, where changes in CSF dynamics with positional shifts cause fluctuating stimulation intensity that patients find unpredictable and sometimes distressing.

## The ACCURATE Trial

### Study Design

The ACCURATE trial was a prospective, multicenter, randomized controlled trial comparing DRG stimulation to traditional SCS in 152 patients with CRPS type I or II or causalgia affecting the lower extremities. Patients were randomized 1:1 to DRG stimulation (Proclaim DRG system) or traditional dorsal column SCS. The primary endpoint was a composite of safety and efficacy at 3 months, with long-term follow-up extending to 12 months.

### Key Results

At 3 months, 81.2% of DRG patients achieved treatment success compared to 55.7% in the SCS group (p < 0.001), demonstrating statistical superiority. The DRG group achieved significantly greater NRS pain reduction at all time points. The most pronounced difference appeared in the foot pain subgroup, where 85.7% of DRG patients were responders versus 57.9% in the SCS group -- highlighting DRG's particular advantage for distal extremity pain. The DRG group also reported significantly fewer extraneous stimulation events outside the painful area, and showed significantly greater improvements in mood and quality of life.

### Limitations

The control arm used traditional tonic SCS rather than HF10 or burst stimulation, so how DRG stimulation compares to newer SCS waveforms remains unknown. The study population was limited to CRPS and causalgia, and generalizing the findings to other neuropathic conditions requires additional evidence. Long-term data beyond 12 months from the trial itself is limited, though registry data continues to accumulate.

## Surgical Technique

### Lead Placement

DRG lead placement is performed in an operating room or fluoroscopy suite under local anesthesia with sedation. The patient is positioned prone on a radiolucent table. Epidural access is obtained via a 14-gauge Tuohy needle at the level below the target DRG (for example, L4-L5 entry for the L4 DRG). A specialized curved-tip lead is advanced through the needle into the epidural space and, under fluoroscopic guidance, steered from the midline into the ipsilateral neural foramen. The lead tip is positioned at the dorsal-superior aspect of the target foramen, overlying the DRG.

### Fluoroscopic Confirmation

On the AP view, the lead tip should be at or just past the medial border of the pedicle, within the foramen. On the lateral view, the tip should be in the dorsal-superior quadrant of the foramen, at the junction of the medial and lateral thirds. Impedance testing (typically 500-1500 ohms) confirms electrode contact with tissue. Low-amplitude stimulation testing (0.1-0.5 mA) should produce concordant paresthesia in the target dermatome.

### Trial and Permanent Implant

A trial period of 7-10 days with externalized leads is identical in concept to SCS trials. If the trial achieves 50% or greater pain relief, the patient proceeds to permanent implant with IPG placement in the posterior flank or gluteal region. Anchoring is particularly critical for DRG leads because the precision required for foramen positioning means that even 1-2 mm of migration can result in loss of therapeutic effect.

<image>Fluoroscopic imaging composite showing DRG lead placement — left panel showing an AP view of the lumbar spine with a curved lead entering the epidural space at L5-S1 and navigating into the left L5 neural foramen with the four electrode contacts positioned over the DRG at the medial aspect of the pedicle, and right panel showing a lateral view of the same lead with the tip in the dorsal-superior quadrant of the L5 foramen, with anatomical landmarks including the pedicles, vertebral body, facet joints, and foramen boundaries labeled, and a schematic overlay indicating the DRG position within the foramen</image>

## Programming Considerations

### Parameter Settings

DRG stimulation uses significantly lower frequencies than high-frequency SCS -- typically 20-40 Hz -- with pulse widths of 200-400 microseconds. Amplitudes are very low, typically 0.1-1.0 mA, much lower than traditional SCS because the electrode sits in close proximity to its neural target. Stimulation can be delivered at perception or subperception levels.

### Unique Programming Features

The confined anatomical space and proximity to the DRG result in markedly lower energy consumption compared to SCS, which translates to longer battery life. The focal stimulation field means that reprogramming can precisely adjust therapy across the four electrode contacts to optimize dermatomal coverage. Unlike SCS, DRG stimulation rarely requires positional programming adjustments. Up to four leads can be placed simultaneously to cover multiple dermatomes.

## Complications

Lead migration or fracture occurs at lower overall rates than with SCS because the bony foramen provides mechanical confinement, but even minor migration is clinically significant given the precision required. Dural puncture is a risk during foramen navigation, particularly at sacral levels. If the lead migrates ventrally toward the ventral root, motor stimulation may occur and repositioning is needed. Infection rates are similar to SCS at 3-5%. Transient radicular irritation during or after lead placement is usually self-limiting.

## Clinical Pearls

DRG stimulation should be considered first-line for focal neuropathic pain affecting the foot, groin, or discrete dermatomes where traditional SCS provides inconsistent coverage. The ACCURATE trial established superiority over traditional SCS for lower extremity CRPS, but head-to-head comparisons with newer SCS waveforms (HF10, burst) are still needed. Positional stability is one of the most clinically meaningful advantages, and patients with active lifestyles or those who experience positional pain variability with SCS may benefit from conversion to DRG stimulation. Lead placement requires a higher technical skill level than standard SCS due to the precision needed for foramen navigation, and proficiency develops with experience and dedicated training. Programming should always start at the lowest effective amplitude to maximize battery life and minimize unwanted stimulation of adjacent structures.

## References

1. Deer TR, Levy RM, Kramer J, et al. Dorsal root ganglion stimulation yielded higher treatment success rate for complex regional pain syndrome and causalgia at 3 months: A randomized comparative trial. *Pain*. 2017;158(4):669-681.
2. Kramer J, Liem L, Russo M, Smet I, Van Buyten JP, Huygen F. Lack of body positional effects on paresthesias when stimulating the dorsal root ganglion (DRG) in the treatment of chronic pain. *Neuromodulation*. 2015;18(1):50-57.
3. Liem L, Russo M, Huygen FJ, et al. A multicenter, prospective trial to assess the safety and performance of the spinal modulation dorsal root ganglion neurostimulator system in the treatment of chronic pain. *Neuromodulation*. 2013;16(5):471-482.
4. Deer TR, Pope JE, Lamer TJ, et al. The Neuromodulation Appropriateness Consensus Committee on best practices for dorsal root ganglion stimulation. *Neuromodulation*. 2019;22(1):1-35.