Disclosures: Dr. Lubenow has consulting agreements with Medtronic, Abbott, Boston Scientific, Inc, Halyard Medical, and Flowonix.

The realm of neuromodulation continues to grow both in its indications for use and the variety of therapies available. Dorsal root ganglion (DRG) stimulation represents a relatively new, more selective method of neuromodulation in the treatment of certain chronic pain states, especially those that respond suboptimally to traditional spinal cord stimulation (SCS). Providers, however, face learning curves with implantation technique, patient selection, and management of complications.

Dorsal root ganglion stimulation represents a relatively new, more selective method of neuromodulation in the treatment of certain chronic pain states, especially those that respond suboptimally to traditional spinal cord stimulation. Providers, however, face learning curves with implantation technique, patient selection, and management of complications.

In response, the Neuromodulation Appropriateness Consensus Committee (NACC) published several documents designed to guide best practices related to neuromodulation.^[1-8] Its most recent publication is a set of guidelines specific to DRG stimulation^[5] that provide pain physicians with a prototypical model on how to rationally incorporate therapies such as SCS and DRG stimulation into clinical practice.

Scientific Rational for DRG Neuromodulation

The DRG houses a group of pseudounipolar afferent neurons, both somatic and sympathetic, residing under the pedicle in the epidural space. Rather than a passive facilitator, the DRG functions as an active relay terminal for all sensory information, blocking, propagating, or filtering action potentials traveling from the periphery to the brain via the spinal cord, including sympathetic information. Furthermore, glial cells in the DRG and spinal cord itself likely play an integral role in synaptic neurotransmission.^[5]

In neuropathic pain states, the DRG contributes to central sensitization by demonstrating hyperexcitability and generating spontaneous, ectopic action potentials from the cell bodies of damaged peripheral nerves. This information is transmitted to wide dynamic range neurons within the dorsal horn of the spinal cord leading to wind up and central sensitization. In addition, abnormal firing of sympathetic neurons within the DRG can propagate a cycle of pathologic autonomic reflex arcs, clinically leading to some of the sudomotor and vasomotor signs seen in pain disorders such as complex regional pain syndrome.^[1],[5] That physiologic foundation has led clinicians to begin using DRG neuromodulation primarily for the treatment of focal neuropathic pain disorders that have an identified pathology as well as for some mixed neuropathic and nociceptive pain states.

Interestingly, the DRG demonstrates a somatosensory distribution that may overlap several dermatomes. In this way, stimulating the DRG located at one level may affect that specific dermatome as well as the levels adjacent to it. This increases the number of lead configurations that may be effective for any given pain pattern.^[5]

DRG’s Benefits Over SCS

Stimulating the DRG rather than the dorsal columns for the treatment of chronic pain confers several important benefits. First, relatively little cerebrospinal fluid surrounds the DRG, resulting in less current dispersion during electrical stimulation. This allows amplitudes typically less than 1 mA and pulse widths of less than 200–300 microseconds to be used effectively (compared with much higher energy requirements seen in conventional SCS), reducing or eliminating the need for recharging of the implantable pulse generator (IPG). Second, this property allows for paresthesia-free stimulation, which most patients prefer, and likely acts by a mechanism distinct from traditional tonic SCS. Third, stimulating the DRG specifically targets the sensory afferent neurons and spares the motor efferent neurons, providing a more specific pattern of neuromodulation compared with SCS.^[5]

Keys to Successful Implantation

The physician implanting SCS stimulators should ideally have undergone training in a recognized, appropriately credentialed, high-volume center and performed a minimum of 10 cases as the primary implanter. This same requirement should ideally be applied to DRG stimulation since DRG implantation is technically more challenging than conventional SCS. In addition, the Food and Drug Administration mandated that providers complete a specific training course sponsored by Abbott and proctored by leaders in the field of neuromodulation prior to implanting in clinical practice.^[9]

Proper epidural needle positioning strongly predicts the ease and accuracy with which pain physicians implant DRG leads. Specifically, the proceduralist should position the needle such that the introducer enters the epidural space near the midline, with insertion of the lead into the dorsal superior aspect of the neural foramen. Most practitioners make superior and inferior S-shaped tension relief loops within the epidural space to buffer against lead migration that may occur with patient movement, rather than using an anchoring device. Additional tension-relief loops should be made in the subcutaneous tissue to further minimize the potential for lead migration. The number of leads indicated will vary by pain pattern; however, the IPG can accommodate a maximum of four leads. Like traditional SCS, NACC recommended creating the IPG pocket in the posterolateral flank or buttock ipsilateral to the needle entry site for the leads.^[5]

If applied thoughtfully, DRG stimulation can positively affect the lives of some of the most challenging patients who present to pain clinics worldwide. However, until recently a coherent framework for how new and existing neuromodulatory therapies might be intelligently implemented into clinical practice did not exist. NACC integrated the best available data with expert consensus distilled into a concise summary of recommendations. In addition to the most recent installation specific to DRG neurostimulation, NACC published several sets of guidelines addressing topics such as prevention and management of infection,^[6] bleeding,^[8] and neurologic injury^[2],[7] related to neuromodulation that can and should be applied to the implantation of DRG stimulators.

The indications for neuromodulation are growing at an incredibly rapid pace, and using the NACC model to implement those therapies represents a significant boon to young and experienced pain physicians alike.

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