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Burst and Dorsal Root Ganglion Stimulation Show Promise in SCS

Source: Pain Medicine News

Brian Dunleavy

NEW YORK—Interventional pain specialists need new tools and targets for spinal cord stimulation (SCS) to improve the overall efficacy of the care they provide. That was the key message of a lecture on the discipline presented during the 68th New York State Society of Anesthesiologists’ PostGraduate Assembly.

Electrical stimulation has been used to treat pain since the 1960s. Approximately 27,000 SCS devices are currently implanted annually in the United States. However, according to Michael L. Weinberger, MD, associate clinical professor of anesthesiology, Columbia University College of Physicians and Surgeons and director, Pain Management Center, NewYork-Presbyterian Hospital/Columbia University Medical Center, in New York City, recent studies suggest that up to 40% of patients who have SCS devices implanted “do not end up having satisfactory pain relief,” and as many as 50% of patients who experience initial pain relief find that their devices lose efficacy over time.

The good news, Dr. Weinberger noted, is that novel approaches already in use in Europe and other parts of the world have shown promise in clinical practice. He presented clinical data on two methods: dorsal root ganglion (DRG) stimulation and burst stimulation.

The DRG, a sensory root that sits in the neural foramen and is surrounded by glial cells, has emerged as a therapeutic target for SCS in recent years. The cells that comprise it are actively involved in signaling in both the central and peripheral nervous systems. The satellite glial cells have receptors for various neuroreactive chemicals that might be released as a result of injury or inflammation, including bradykinin and ATP. It has been demonstrated that the DRG plays an active role in the mechanism of both neuropathic and chronic pain via central sensitization.

“It has been suggested that electrical stimulation of the DRG may alter its sodium, potassium and/or calcium channel gene expression,” Dr. Weinberger told the attendees. “If you have changes in the DRG based on neurofiber injury, we can restore the fibers back to normal via electrical stimulation.”

The value of the DRG as an analgesic target has been confirmed in a rat model (Neuromodulation 2013;16:304-311) and several clinical trials. The rat model found that field stimulation of the DRG directly suppresses excitability of sensory neurons that play a role in the pathogenesis of pain.

Perhaps the most notable clinical trial of DRG stimulation to date is a one-year follow-up study, published in Neuromodulation (2015;18:41-49), involving human subjects with back, neck or foot pain. The authors concluded that DRG stimulation is comparable to “traditional SCS” in terms of pain relief, and that its benefits “may include the ability to achieve precise pain–paresthesia concordance, including in regions that are typically difficult to target with SCS, and to consistently maintain that coverage over time”—even when patients move.

Historically, one of the concerns with SCS is the variability in the amplitude of stimulation resulting from patient movement. Because of the cerebrospinal fluid (CSF) surrounding the spinal cord, any movement by the patient can cause the SCS device lead to move, altering its proximity to the spinal cord. There is no CSF surrounding the DRG, and it is also very difficult to injure or damage the DRG, according to Dr. Weinberger.

“[In these studies] paresthesias were well mapped to where the pain was,” he said.

Burst stimulation consists of intermittent packets of closely spaced, high-frequency stimuli. De Ridder pioneered the approach in New Zealand, where he experimented with 40-Hz burst mode with five spikes at 500 Hz per burst, with a pulse width of 100 msec. In contrast, traditional SCS is delivered in constant or tonic fashion, at a pulse width of 300 to 500 msec. Furthermore, unlike with traditional SCS or DRG stimulation, patients undergoing burst stimulation treatment do not experience paresthesia.

According to Dr. Weinberger, a recent study comparing burst stimulation with traditional SCS in a rat model found that burst stimulation reduced the visceromotor reflexes more than tonic SCS, and that only burst stimulation significantly decreased nociceptive somatic response at low-intensity SCS (Neuromodulation 2014;17:143-151). Based on these findings, the researchers concluded that burst stimulation is more effective than tonic SCS in attenuating visceral nociception, and that burst stimulation has a greater inhibitory effect on neuronal response to noxious somatic stimuli than to noxious visceral stimuli. They also noted that the reduced paresthesia associated with burst stimulation might be due in part to the fact that the approach does not increase spontaneous activity of neurons in the gracile nucleus.

Dr. Weinberger then cited a prospective, randomized, double-blind, placebo-controlled study on the effectiveness of burst stimulation in 20 patients with failed back surgery syndrome (Neuromodulation 2014;17:443-450). Participants were randomized to receive 500-Hz tonic stimulation, burst stimulation or placebo stimulation for one week. For the burst stimulation treatment group, mean numeric rating scale and Short-Form McGill Pain Questionnaire scores were significantly decreased compared with the other treatment groups; these scores did not differ significantly between 500-Hz tonic stimulation and placebo stimulation groups.

“So what are the advantages of burst? No paresthesia, maybe better analgesia,” said Dr. Weinberger.

“Neurostimulation, as it stands, is effective for a small, rather specific patient population,” said Ebby G. Varghese, MD, medical director of the Interventional Pain Medicine Clinic, and assistant professor of clinical physical medicine and rehabilitation, University of Missouri-Columbia, who was not part of the PGA lecture. “Early literature in burst stimulation suggests the quality of the stimulation is improved, a broader area is covered, and the strength of stimulation is not subject to positional variability. DRG stimulation is not subject to the patient’s positional changes either and can be used to target specific painful dermatomes. These options have never been seen before, and the results seen in Europe are promising. If they hold true, [burst and DRG stimulation] will improve patient outcomes [compared with the options] we currently provide.”