In February 2016, the U.S. Food and Drug Administration approved a novel treatment for patients with complex regional pain syndrome (CRPS I and II) in the lower extremities. Dorsal root ganglion (DRG) stimulation is an outpatient neuromodulation therapy, similar to traditional spinal cord (SCS) stimulation. Rather than placing the electrodes over the posterior aspect of the spinal cord as in SCS, leads are implanted on the dorsal root ganglion, a cluster of neurons in the posterior root of spinal nerves.
“The dorsal root ganglion represent the sensory gate of the spinal cord,” says Nagy Mekhail, MD, PhD, of Cleveland Clinic’s Department of Pain Management. “Every sensory perception entering the spinal cord must pass through the dorsal root ganglion.” The DRG neurons are capable of modulating all sensations before processing to the spinal cord and other areas of the central nervous system. That makes DRG stimulation a particularly effective therapeutic approach for patients with chronic intractable pain.
Advantages of DRG Stimulation
DRG stimulation features two components that are surgically implanted: A pulse generator, which is placed beneath the skin in the buttocks or abdomen, and up to four leads. The leads are attached to the pulse generator and the tissue near the target treatment area. When activated, the leads send very small electrical impulses to the dorsal root ganglion, thereby blocking the pain stimulant.
Patients first undergo a trial for one week to ensure the therapy is effective. Then, one week to 10 days later, surgeons implant the system under the skin, much like a pacemaker. The implant procedure takes approximately 60 to 90 minutes.
Dr. Mekhail cites four distinct advantages of targeting the dorsal root ganglion for pain relief:
- Directed anatomical targeting – DRG stimulation offers a highly-directed stimulation field, which can limit stimulation to the pain area. In the clinical trial of DRG stimulation for chronic lower limb pain – the ACCURATE Study – 94.5 percent of patients received targeted stimulation in the area of pain without extraneous paresthesia compared to 61.2 percent of patients in the SCS control group.
- Low energy requirements – The dorsal root ganglion is surrounded by a very thin layer of spinal fluid. Because the layer between the stimulator and the dorsal root ganglion cells is so narrow, DRG stimulation uses only about 10 percent of the energy required for traditional SCS. That, in turn, leads to longer-lasting batteries.
- Marginal risk of lead migration – The dorsal root ganglion is tucked in a very small space, reducing the chances of lead migration. Stimulation leads reported less than a 1 percent migration rate in the ACCURATE Study. Traditional SCS reports a 14 percent migration rate. (Washburn, et al., Industry Wide Incidence Rate of SCS Related Complications, NANS 2010.)
- Minimal postural effects – Because the dorsal root ganglion is located in such a small space, and the cerebral spinal fluid in between does not vary with patient’s body position, the pattern of stimulation for DRG is constant regardless of any changes in body position. The patient receives the same stimulation –and pain relief – whether lying down, standing, sitting or walking. Conversely, the pattern of stimulation varies with position in SCS patients.
Dr. Mekhail is one of two pain management physicians at Cleveland Clinic trained to perform the DRG stimulation procedure. Dr. Mekhail functioned as the medical monitor of the FDA sponsored multicenter trial Accurate study. The other is Samuel Samuel, MD, Director of the Pain Management Clinics at Cleveland Clinic Marymount Hospital who participated as investigator in the ACCURATE Study that led to FDA approval of the St. Jude Medical System Axium™ Neurostimulator System for CRPS.
“The results I’ve seen so far are very encouraging, and I am really excited about this procedure,” says Dr. Samuel. During the clinical trial, which ran from September 2014 to July 2015, he handled the first two cases done at Cleveland Clinic. One patient had CRPS II following foot surgery and a subsequent infection. She couldn’t walk and experienced severe pain if someone touched her foot.
“The minute we turned on the DRG stimulation, her pain was 100 percent gone,” says Dr. Samuel. “We could touch and squeeze her foot with absolutely no pain.” The patient received the implant one week after her trial and has remained pain-free ever since. She’s back to her normal life – wearing shoes, walking and working, adds Dr. Samuel.
The FDA has approved DRG stimulation for lower extremity CRPS, which could include neuropathic pain conditions and chronic pain following foot, knee, groin and other surgeries. DRG stimulation is not a replacement for SCS, but rather an alternative in the right clinical scenario. “Certain areas are tough to capture with spinal cord stimulation – the foot, the front of the knee, the groin,” says Dr. Samuel. “DRG stimulation is a new treatment for conditions that are inadequately treated with conventional SCS.”
Dr. Mekhail says one of the best future indications for DRG stimulation is diabetic neuropathy. Over time, high blood sugar can damage the peripheral nerves, particularly in the legs and feet. Patient pain is often managed with medication, which can be costly and may cause multiple side effects. “Using DRG stimulation at the L5 ganglia, we can target both feet and relieve the intractable pain of diabetic neuropathy,” he says.
He also recommends the procedure for patients with CRPS who have had limited or no success with conservative treatment, including physical therapy, medications and sympathetic nerve blocks. “If these treatments have not worked within three to six months, move on,” says Dr. Mekhail. “DRG stimulation can pay for itself over time by saving healthcare costs, and it can provide patients much needed relief.”
DRG Stimulation Study Results
Traditional spinal cord stimulation has been utilized since 1967, and although the technology has evolved, it’s not a panacea for chronic pain patients. “I call it the 50/50 club: All of the studies so far indicate that 50 percent of patients get relief [with SCS] and 50 percent don’t, which is really quite dismal,” says Nagy Mekhail, MD, PhD, of Cleveland Clinic’s Department of Pain Management.
The recently-approved dorsal root ganglion (DRG) stimulation therapy offers hope for improved relief. Dr. Mekhail cites several promising results from the safety and effectiveness trial of DRG stimulation:
- Three months after the implant, 70 percent of participants who received DRG stimulation had greater than 80 percent pain relief, compared to 52 percent of the control group who underwent SCS.
- One year after the implant, 67.3 percent of DRG subjects had greater than 80 percent pain relief, compared to 54 percent of SCS subjects.
- 5 percent of DRG subjects received targeted stimulation in the area of pain without extraneous paresthesia, compared to 61.2 percent of SCS subjects.