Neuromodulation

Overview

Neuromodulation is the process whereby an implantable device is used to reversibly alter the activity of the nervous system. This may be accomplished using small doses of medications or a weak electrical current. By altering the activity of certain pathways in the nervous system, pain may be immediately and dramatically relieved.

Spinal Cord Stimulation

Spinal cord stimulation is a technique that has been used to successfully relieve pain for over 40 years in many thousands of patients. During this outpatient procedure, a small electrode is placed in the epidural space adjacent to the spinal cord. No incisions are required and only local anesthetic is required. Once in position, the electrode generates a weak electrical current that interrupts the transmission of pain at a spinal cord level. It is safe, effective, well-tolerated, and can be used to treat many different types of chronic pain, including abdominal and pelvic pain.

Figure 1. X-ray showing a spinal cord stimulator electrode in position in the thoracic spine.

Sacral Nerve Stimulation

Sacral nerve stimulation is a technique related to spinal cord stimulation, except that the electrodes are placed along the sacral nerves in their spinal foraminae, rather than along the spinal cord. As for spinal cord stimulation, this is an outpatient procedure that requires local anesthetic only but no incisions. Once in position, the electrodes generate a weak electrical current that interrupts the transmission of pain at a sacral nerve level. It is safe, effective, well-tolerated, and can be used to treat many different types of chronic pelvic pain. Some of the most notoriously difficult pelvic pain syndromes that are refractory to all other treatments may be effectively treated with sacral nerve stimulation. Proctalgia, vulvodynia, and interstitial cystitis are such examples.

Figure 2. X-ray showing sacral nerve stimulator electrodes in position in the sacral spine.

Figure 3. X-ray showing sacral nerve stimulator electrodes in position in the sacral spine.

Peripheral Nerve Stimulation

Peripheral nerve stimulation is a technique in which an electrode is surgically placed adjacent to a peripheral nerve. A weak electrical current then inhibits the transmission of painful impulses with that nerve, relieving pain within the sensory distribution of that nerve. This technique is sometimes used to treat pain syndromes that are not amenable to treatment with other stimulation procedures.

Figure 4. Intraoperative photograph showing a stimulator electrode being positioned adjacent to a peripheral nerve.

Intraspinal Nerve Root Stimulation

Intraspinal nerve root stimulation is a technique related to spinal cord stimulation, except that the electrodes are placed along the nerve rootlets in the spinal canal, rather than over the spinal cord itself. As for spinal cord stimulation, this is an outpatient procedure that requires local anesthetic and no incisions. Once in position, the electrodes generate a weak electrical current that interrupts the transmission of pain at a spinal nerve root level. It is used to treat some of the more focal abdominopelvic pain syndromes, such as pain following inguinal hernia repair.

Figure 5. X-ray showing intraspinal nerve root stimulator electrodes in position in the thoracolumbar spine.

Spinal Infusion Pump

Spinal infusion pumps enable the constant administration of miniscule amounts of potent medications to the spinal cord and nerve roots. The system consists of a programmable pump that contains a reservoir of medication, and a spinal catheter to deliver it to the spinal canal. This type of device is appropriate for patients who require large daily doses of narcotics to treat their chronic pain syndrome. Generally, patients will be considered for an infusion pump if they have exhausted all other reasonable treatment options, including neurostimulation.

These systems can provide remarkable pain relief, even when all other therapies have failed. Though effective, these systems are a bit complex, requiring periodic refills of medication and vigilance by the patient to make sure the medication does not run out. When the medication runs out, or the system malfunctions, then the patient may go into drug withdrawal. Despite their limitations, spinal infusion pumps enable even the most seemingly hopeless patients transcend the grip of chronic pain misery, obtain pain relief, and begin to live their lives again.

Figure 6. Spinal infusion pump.

Figure 7. X-ray showing a spinal infusion pump (P) in position in the abdominal wall, with the tip of the intraspinal catheter (C) at the level of T11.

References

Cameron T. Safety and efficacy of spinal cord stimulation for the treatment of chronic pain: a 20-year literature review. J Neurosurg (Spine 3) 2004;100:254-67.

Feler CA, Whitworth LA, Fernandez J. Sacral neuromodulation for chronic pain conditions. Anesthesiology Clin N Am 2003;21:785-95.

Weiner RL. Peripheral nerve neurostimulation. Neurosurg Clin N Am 2003;14:401-8.

Aló KM, Holsheimer J. New trends in neuromodulation for the management of neuropathic pain. Neurosurgery 2002;50:690-704.

Bennett G, Serafini M, Burchiel K, Buchser E, Classen A, Deer T, Du Pen S, Ferrante FM, Hassenbusch SJ, Lou L, Maeyaert J, Penn R, Portenoy RK, Rauck R, Willis KD, Yaksh T. Evidence-based review of the literature on intrathecal delivery of pain medication. 2000;20:S12-36.