Dorsal Root Ganglion (DRG) Stimulation

The dorsal root ganglion is a cluster of cell bodies of the nerves that travel from the extremities into the brain. This collection of cell bodies forms a bulge within the nerve just before or as it enters the spinal canal. The cell bodies can be looked at as the processing units of the nerves.

Nerves transmit signals from the extremities to the spinal cord. A sensation received at a nerve terminal transmits the signal along the axon to the nerve ending to the spinal cord. These nerves typically connect, or synapse, in the dorsal horn of the spinal cord. The input is processed and the nerve messages are then sent up the spinal cord to the brain.

We now know that within the DRG the cell bodies communicate and can downregulate (slow down) or up regulate (speed up) the nerve transmission. This ‘processing unit’ of the nerves prior to the entrance is an optimal place to intervene with the transmission of pain from the extremities or nerves along the trunk to the brain.

DRG Stimulation, has demonstrated superior pain relief when compared to traditional SCS for treating CRPS and post-surgical nerve pain (the FDA clinical trial, ACCURATE Study, showed that electrically stimulating the ganglion offers patients better and more targeted pain relief from Complex Regional Pain Syndrome).

In traditional SCS, electrical stimulation is provided by a battery-powered pulse generator connected to implanted lead wires placed approximately to the posterior portion of the spinal cord known as the dorsal columns. The dorsal columns are comprised of sensory nerve fibers that transmit only position and fine touch sensation separate from pain to the brain. Stimulating these fibers causes a constant tingling sensation known as a paresthesia in the region of the body that the fibers are transmitting sensation from. By creating a paresthesia in a painful area, pain signaling can be masked and reduced, leading to pain relief.

While this was the earliest form of neuromodulation used to treat chronic pain, it had its shortcomings. First, most patients are not comfortable with the constant tingling sensation SCS creates. Second, tolerance to the stimulation builds over time with loss of efficacy within 1-3 years in many cases. As a result, newer forms of paresthesia-free SCS were introduced with better results, including Burst DR-SCS and High frequency SCS. However, limitations in pain coverage and efficacy with certain conditions like axial low back pain and joint pain remain.

To address these shortcomings, DRG-S was developed as a novel therapy that differs from traditional SCS in its location and use of paresthesia-free stimulation. The dorsal root ganglion (DRG) is a relatively small structure composed of cell bodies of the sensory portion of each spinal nerve, located adjacent to the spinal cord at every spinal level on both the right and left sides. All incoming sensory signals traveling to the spine pass through here. In contrast to SCS, stimulation at this site can target every type of sensory nerve. This gives the advantage of stimulating pain-transmitting nerves directly to block and disrupt pain signaling. In addition, fine touch and other types of sensory nerves can be stimulated to mask and reduce pain signaling indirectly in the spinal cord through a variety of mechanisms, some that are similar to SCS.

Unique anatomical features of the DRG also make it optimal for neuromodulation therapy:

1. All sensory nerve cell bodies at a given spinal level are housed here, allowing for focal stimulation to cover a specific body region, resulting in better and more precise pain coverage.

2. There is a minimal barrier of connective tissue and fluid surrounding the DRG compared to the spinal cord, which allows for much closer lead wire placement to the target nerve tissue. Therefore, significantly lower electrical stimulation is needed to reach the nerves compared to SCS, resulting in potentially less collateral damage to surrounding tissue.

3. The DRG is an immobile structure situated in a bony case outside of the spinal canal. Unlike the spinal cord, it is not prone to shifting and movement, meaning the lead wires remain in the same position relative to the nerve tissue. The amount of stimulation that reaches the nerves and the precise location it is directed towards remain stable, resulting in less fluctuation of pain relief than SCS.

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As with SCS, electrical stimulation is provided by a battery-powered pulse generator connected to implanted lead wires placed approximate to the DRG structure. Depending on the location and area of pain, up to 4 leads may be placed at different spinal levels and/or on both sides of the spine to cover the painful region involved.

To learn more about DRG-S technology and the DRG-S trial and implant procedures, watch this video:[TY2] 

 [TY1]Label the lead wire and electrodes, the DRG, the spinal nerve, the spinal cord and canal, and the vertebrae

 [TY2]I put a placeholder here to link to an instructional video. I think better to describe the procedure and more detail about the basic science behind it with illustrative video.

The placement of the electrical field at the DRG allows us to apply electrical energy to directly modulate pain fibers and also activate pain-relieving nerves to block pain.

From a basic science level, there are special characteristics about the DRG that makes it so appealing as a target. In the natural state, the DRG can serve as a ‘filter’ of sensory input. Thus, the DRG already serves as a ‘gatekeeper’ for sensation from the external environment, and our body, to the central nervous system. Applying stimulation to this site increases this filtering ability to decrease the amount of pain signals that pass through the gate in addition to other distinct mechanisms.

An additional effect of DRG-S is to activate nerve fiber lines as well. So, at the settings used, we can activate the nerve fibers that our body naturally has to block pain. This can be thought of as the way a pacemaker is able to make the heart beat at a certain rhythm. But rather than activating cardiac fibers, we are activating inhibitory fibers.

There are several types of sensory nerves. Aδ and C fibers are the smallest nerve fibers that transmit pain but are also responsible for sending light touch related sensations. These fibers surround our hair follicles and use endorphins as a messenger to transmit signals. Endorphins are inhibitory and act on our body’s opioid receptors to block pain.  We currently have several research projects running to try to prove this is part of the mechanism of how DRG-S works.

After a patient decides to proceed with a DRG stimulator, there are several steps which must be completed. As with a traditional stimulator, there is first a 7-day trial period with the device. The leads are placed through the skin over the target levels. This trial period involves no incisions and the generator is taped to the skin on the outside of the body. An Apple device is provided to the patient and it is used to communicate with the device through an app. All patients are required to have a psychological clearance performed, a MRSA nasal swab, a medical clearance, among other paperwork.  Click here for our pre-DRG-S Trial forms.

After the trial, you will return to the office and the leads are removed. The lead removal is a relatively benign and performed in the exam room. At that time, you will decide whether or not to proceed with the implant of the device.

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