Chronic Neuropathic Pain: Management Through Neurostimulation

Mayo Clinic offers numerous approaches to managing chronic pain. Refractory neuropathic pain, one of the most intractable and difficult types of pain to treat, often can be reduced or alleviated through neuromodulation or stimulation techniques. Most prominent among them is spinal cord stimulation (SCS), previously called dorsal column stimulation. The goal of SCS and other stimulation techniques for pain such as peripheral nerve stimulation (PNS) is to cover the affected area with pleasant paresthesias (often experienced as light tingling or buzzing). Spinal cord stimulation is most commonly used to treat lower extremity pain from spinal pathology such as recurrent disk herniation or failed back surgery syndrome. Other indications include upper extremity neuropathic pain, phantom limb pain, arachnoiditis, and complex regional pain syndromes I and II.

The American College of Cardiology/American Heart Association now recommends SCS as a treatment for inoperable, stable angina due to ischemia. Mayo Clinic in Rochester, Minnesota, has had extensive experience with this procedure and was part of a clinical trial testing the use of SCS for angina. Mayo Clinic in Phoenix/Scottsdale, Arizona is currently participating in a similar clinical trial. Other new applications of stimulation techniques include treatment of headache, head pain, facial pain, pelvic pain, and, more recently, SCS for low back or axial pain. Mayo Clinic in Jacksonville, Florida was among the first in the nation to use SCS for visceral pain.

Implantation

SCS implantation is an outpatient surgical procedure. Leads (wires) with metallic contact points (electrodes) are positioned in the appropriate epidural space. The electrodes create an electrical field adjacent to the spinal cord that produces the pleasant paresthesias experienced by the patient. The leads are powered by current from a battery-driven implantable pulse generator (IPG). The IPG is connected to the leads by a thin wire. A remote, handheld programmer allows the patient to control the rate and intensity of the pulses.

Placement of the leads and the IPG depends on the source of the pain and the area affected. In PNS, percutaneous leads are implanted near the affected nerve. In SCS, leads are placed in the epidural space near the spinal cord. The leads may be cylindrical or paddle shaped. The advantage of percutaneous leads is that they can be placed with a minimally invasive procedure. The disadvantage is that they may migrate over time and need to be repositioned. Paddle leads in the epidural space are more stable but require a minilaminectomy. Bilateral lower extremity pain, more challenging to treat, may require 2 leads.

A dual-lead spinal cord stimulation system.

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Mayo Clinic is also using tripolar stimulation, which enables deeper penetration of SCS without spreading stimulation to the peripheral nerve roots. As Marc A. Huntoon, MD, an anesthesiologist and head of the Pain Clinic at Mayo Clinic in Minnesota, notes, "Tripolar stimulation enables us to steer the charge. The technology to do that is improving all the time and is going to enhance treatment of lower back pain and possibly lower extremity pain as well. It's an alternative measure to treat patients with a mixed pain syndrome of both low back and leg pain."

The IPG is implanted in the lower abdomen or buttocks or under the clavicle, depending on where the leads are placed. Other sites that can be treated with PNS include the forehead for pain in the ophthalmic branch of the trigeminal nerve, the occipital region for controlling migraine and cluster headache, and other sites in the head and neck area, depending on the source of the pain.

Trial Run

At Mayo Clinic, all SCS candidates undergo a psychological evaluation before surgery. Terrence L. Trentman, MD, an anesthesiologist and head of the Pain Clinic at Mayo Clinic in Arizona explains, "Among our goals are determining whether the patient is cognitively competent to provide informed consent and run the stimulator and identifying undertreated psychological disorders such as depression or anxiety that may accompany long-term pain."

During insertion of the trial leads, the patient is lightly sedated, and an anesthesiologist inserts the leads percutaneously using fluoroscopic guidance. The stimulator is turned on, and the patient provides feedback about the pain coverage. The goal is to cover all of the patient's painful areas with pleasant paresthesias. The leads are then anchored to the skin, and the patient goes home with an external power source for the 3- to 7-day trial.

At the end of the trial, the patient's response is reviewed relative to pain level, improved sleep, increased activity, decreased use of pain medications, and satisfaction with exchanging pain for paresthesias. The standard threshold for permanent implantation is more than 50% improvement across all measures. A successful trial run is the best predictor of long-term success with SCS.

Recent Advances

Mechanical Improvements
Advances in stimulator technology now allow patients more individualized control. They can preprogram the device to turn on and off at a certain time of day and to vary the pattern of stimulation, choosing, for example, to stimulate the thigh while they are sitting or the calf while walking. Batteries generally last 2 to 5 years, depending on use. Long-life rechargeable batteries are also available, although they, too, eventually must be replaced.

Minimally Invasive Peripheral Nerve Stimulation
In 2007, Dr Huntoon pioneered a noninvasive trial technique for stimulating peripheral nerves so that placement percutaneously is possible. As he notes, "In the past, we had to dissect down to the nerve to place the stimulators next to it. This new method uses ultrasound to guide the needle and placement of the leads right next to the target nerve."

Outcomes

Approximately 50% to 70% of patients report at least 50% long-term relief with neuromodulation. Dr Trentman says, "Between 30% and 50% of patients get less than 50% relief. However, patients who have SCS have invariably been through many other treatments, so the success rate should be viewed accordingly."

Outcomes are optimized through a team approach. Salim M. Ghazi, MD, an anesthesiologist and head of the Pain Clinic at Mayo Clinic in Florida, emphasizes that, as is true of all forms of pain management, neurostimulation requires multispecialty coordination. He notes that the concept of teamwork is built into the name of their Independent Multidisciplinary Pain Clinic. Drs Huntoon and Trentman agree, stating that in neurostimulation, "surgical implantation is only 1 aspect of the picture. All patients need physical therapy and counseling before and after treatment."