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01 May 2010
Spinal Cord Stimulation (SCS) is a minimally invasive procedure that involves implanting a device that applies low currents of electrical stimulation to the spinal cord and/or its exiting nerves.
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Spinal cord stimulation is referred to by some pain experts as a “pacemaker for pain”. It works by sending small electrical impulses created by a compact generator through thin leads, or electrical cables, to the spinal cord, where they block pain signals traveling to the brain. Pain is replaced with a mild tingling or a massaging sensation, called paresthesias. A wireless remote control is used to adjust the location and degree of stimulation by selecting pre-programmed settings.
The core technology that is used in today’s SCS systems was developed in the mid-1960s. Melzack and Wall developed the original theory for the mechanism of spinal cord stimulation in 1965 (1). This “gate-control theory” for pain proposes that simultaneously triggered touch and vibratory sensation inhibits pain stimuli sensation due to their shared location in the spinal cord, the dorsal horn nucleus. In essence this theory is the foundation for spinal cord stimulation. An everyday example of this theory is seen when one has a headache. Many people will rub their temples or another area of their head, stimulating the muscles of the head or sensory fibers of the skin. When these areas are stimulated, to some degree they block the sharp pain perceived from an active headache. This is also commonly seen when you accidently bump your knee, elbow, or finger and you rub the associated area inhibiting the acute painful stimuli to the brain.
The first spinal cord stimulators were implanted directly on the dorsal column of the spinal cord of terminal cancer patients by Shealy et al. (2) in 1967. Shortly after, Shimogi et al. were the first to publish the successful implementation of epidural spinal cord stimulation (3), which is a percutaneous, less invasive technique. This avoids the complications of the original open surgery, which includes cerebrospinal fluid leakage, localized fibrosis, and arachnoiditis. Another initial challenge was a limited area covered by the single, or monopolar electrode. SCS leads today have evolved from monopolar (1 active electrode) to bipolar (2 active eletrodes), quadripolar (4 active electrodes), and octapolar (8 active elctrodes) leads.
Since then, SCS has been used in the treatment of cervical and lumbar post-laminectomy syndrome (failed back or neck surgery syndrome), cervical and lumbar radiculitis (neck and back radiating pain), complex regional pain syndromes (CRPS or RSD), intractable pain due to peripheral vascular disease, phantom limb pain, intractable pain due to angina, peripheral neuropathy, post-thoracotomy syndrome, neuropathic extremity pain, chronic visceral pain syndromes, and other pain conditions.
Anatomy
The spinal cord is a bundle of nervous tissue and supporting material that extends from the brain to innervate the rest of the body. The brain and the spinal cord together form the central nervous system (CNS), which sends and receives messages from the body through the peripheral nervous system (PNS).
The spinal cord is contained in the spinal canal formed by the vertebral column. The meninges are a covering consisting of three layers that continues from the cranium to the sacrum and protects the spinal cord and its nerves. The innermost layer, or pia mater, wraps around the brain and spinal cord. The middle layer, or arachnoid mater, is a spider web-like layer. The outermost layer is called the tough dura mater. Between the arachnoid mater and the pia mater is ones cerebral spinal fluid (CSF) which protects and buffers the brain and spinal cord. Outside of the three-layered meninges is the epidural space. The epidural space is a potential space that lies outside of the dura and typically houses protective fatty tissue and blood vessels. The epidural space is where medications are placed for epidural blocks and where the leads are placed for spinal cord stimulation.
The spinal cord normally extends from the foramen magnum, a hole at the bottom of the cranium, to the L1 vertebra in adults. In children the spinal cord ends at L3 and travels upward as they grow older. Nerve roots exit from the back and front of the spinal cord and then join to form the spinal nerves from second cervical nerve root to the fifth sacral nerve root (C2 to S5). The spinal nerves then leave the spinal canal through openings between each vertebra called the intervertebral foramen.
The main functions of the spinal cord are to relay signals from the brain to all muscles for movement, relay signals up from the body for sensory input, and to also coordinate reflexes. Each spinal nerve root supplies sensory innervations to a specific area of skin called a dermatome. Lesions of specific nerve roots result in predictable pattern of signs and symptoms. For instance, a lesion in a lumbar nerve root may cause radiating pain, muscle weakness, numbness, tingling, and/or reflex changes in the legs. This gives physicians a tool for localizing the lesion that is causing the symptoms. Imaging modalities such as MRIs and diagnostic tools like EMGs (electromyography) may be used to assist and confirm a diagnosis.
Live Procedure
In this video, an Arizona Pain Specialist physician performs a minimally invasive procedure for chronic pain. Known as spinal cord stimulation, this procedure is often referred to by experts as the "pacemaker for pain." This patient suffered from chronic pain due to a gunshot wound, where several pieces of shrapnel were still embedded in the patient's back, causing severe left leg pain and low back pain.
Description
SCS is a minimally invasive procedure that is done on an outpatient or short hospital stay basis. There are two steps to the procedure, a trial procedure and a permanent implant. The trial procedure is a brief procedure that is usually done under light sedation. The area where the leads are implanted is numbed with local anesthesia. One or more needles are directed under x-ray guidance into the epidural space, which is the area surrounding the spinal cord and/or nerve roots. The leads are then placed through the needles and are steered to the desired location. The leads are then connected to an external generator. Once the generator is turned on, the impulses are sent with varying intensities to different positions on the leads. The patient will sense paresthesias (tingling and/or buzzing) while a programmer adjusts the settings to provide the “optimal coverage” over the painful areas. These settings are then saved on the remote control so that the patient can adjust the stimulator to best fit their needs. The trial period usually lasts a few days to a week, depending on the effectiveness of the SCS. The goal is to test the stimulator’s effectiveness at relieving pain, increasing normal daily activities, and overall improving quality of life.
If SCS trial period provides sufficient pain relief (usually 50% or greater), then the trial is deemed a success and a permanent implant may be scheduled if the patient desires. The permanent procedure is carried out in similar fashion to the trial procedure. The significant difference is that the generator is implanted, like a pacemaker, in a subcutaneous pocket. Usually the upper, outer quadrant of the buttock is chosen, which results in a largely unrecognizable and comfortable experience. A different type of lead may also be used if your physician believes this will give you better long-term relief. A few small bandages will be applied over the incisions. After the procedure, the patient can usually return home the same or the following day.
Benefits
In general, SCS is much more effective in treating radicular pain, or pain that radiates down one’s arm or leg, than it is at treating axial pain, or pain that is only in the neck or back. One of the first and most frequent uses of SCS has been for the treatment of post-laminectomy syndrome (PLS) which is also called failed back surgery syndrome (FBSS). Post-laminectomy syndrome is recurrent pain, usually involving the lower back and/or legs, following spinal surgery. Imaging must first prove that surgically correctable lesions are absent since PLS is considered a diagnosis of exclusion. A multicenter study confirmed that majority of patients with PLS reported fair to excellent pain relief in both the low back (68.8%) and legs (88.2%) with a spinal cord stimulator device (4). When compared to repeat spine surgery for PLS, spinal cord stimulation was found to be superior for pain relief (5). Spinal cord stimulation is also more effective in providing leg and back pain relief in the setting of neuropathic pain secondary to PLS when compared to conservative medical treatment (6).
Complex regional pain syndrome (CRPS), which is also called reflex sympathetic dystrophy (RSD), is a neuropathic pain syndrome that involves severe pain, swelling, and skin changes. CRPS can be a severe disabling condition and is difficult to treat with most conservative care. CRPS is the second most common indication for spinal cord stimulation in the U.S. Research has shown that SCS provides pain relief in over 73% of CRPS patients, as well as significantly reducing the associated edema (7, 8). In addition, a European study found that, "the functional status and the quality of life could be significantly improved in sympathetically maintained CRPS I" when SCS was combined with physiotherapy (9).
Peripheral vascular disease (PVD), in which narrowing of blood vessels can lead to tissue ischemia, pain, and limb damage, is a serious condition that has the potential to result in debilitating pain or even amputation. A study from the mid 1980s demonstrated that SCS is a "valid alternative treatment for moderate peripheral arterial disorders when direct arterial surgery is not possible or has been unsuccessful" (10). Later in the 1990s, another study found similar results for pain relief (62%) and concluded that SCS is most effective in patients without hypertension (11). SCS has also been utilized for the treatment of intractable pain due to angina, or chest pain. Chronic angina that cannot be adequately controlled by a combination of advanced medical, interventional, and surgical therapies may respond to the effects of spinal cord stimulation. Research has found that SCS "significantly improves exercise capacity and quality of life.” The beneficial effects of SCS for chronic angina "may be related to improved oxygen supply to the heart combined with an analgesic effect" (13). In Europe, SCS has been utilized to a much greater extend for chronic peripheral vascular disease and for chronic angina.
SCS is also an effective therapy for pain syndromes associated with peripheral neuropathies. Peripheral neuropathy is defined as an abnormality of the peripheral nerves. Peripheral nerves transmit pain, sensory, vibratory, and movement signals to the spinal cord. The information is then transmitted to the brain. The most common types of neuropathies are diabetic peripheral neuropathy and idiopathic neuropathy. Spinal cord stimulation has been used to treat many of these painful peripheral neuropathies. Some research indicates that pain associated with diabetic peripheral neuropathy is more responsive to SCS than post-herpetic neuropathy pain (12).
Recently, SCS has been reported to successfully treat visceral, or internal organ, pain. One case reported SCS as a novel treatment of refractory neuropathic mediastinal pain, or pain from the front of the central chest, following surgery (14).
In general, spinal cord stimulation offers many desirable benefits for those with severe debilitating chronic pain. Some of the benefits of SCS include being easily adjustable, testable, reversible and/or removable if necessary. For many pain conditions, SCS can be less invasive and more effective than surgery. Ultimately, SCS may permit an individual to return to their daily activities, enjoy recreational activities, and overall increase quality-of-life with less pain.
Risks
As with any surgical procedure, there are risks, including: infection, bleeding, nerve damage and allergic reaction. In addition, there are specific risks to spinal cord stimulation. These may include: headache possibly from leakage of spinal fluid, bladder problems, scar formation around the electrodes, equipment failure that leads to intermittent or over-stimulation, disconnection, and lead migration, which may require additional procedures to correct. The most common complication is lead migration (leads moving), which usually occurs within a few days after the implantation. Migration happens less in quadripolar leads (11%) than in those with monopolar electrodes (45%) (15). Long-term studies have indicated that SCS may have a diminishing effect over time for patients with complex regional pain syndromes (16). Serious complications can occur with either the SCS trial or permanent placement. Fortunately, complications are usually rare when the implantation is performed properly (17).
References
1) Melzack, R., and Wall, P.D. (1965). Pain mechanisms: a new theory. Science, 150:971–979.
2) Shealy, C.N., Mortimer, J.T., and Resnick, J. Electrical inhibition of pain by stimulation of the dorsal columns: Preliminary reports. J. Int. Anesth. Res. Soc, 46:489–491, 1967.
3) Shimoji K, Higashi H, Kano T, Asai S, Morioka T. Electrical management of intractable pain. (1971) Masui (The Japanese journal of anesthesiology), 20: 444–447.
4) Burchiel KJ, Anderson VC, Brown FD, Fessler RG, Friedman WA, Pelofsky S, Weiner RL, Oakley J, Shatin D. Prospective, multicenter study of spinal cord stimulation for relief of chronic back and extremity pain. Spine 1996; 21:2786-2794.
5) North RB, Ewend MG, Lawton MT, Kidd DH, Piantadosi S. Failed back surgery syndrome: 5-year follow-up after spinal cord stimulator implantation. Neurosurgery 1991;28:692-9.
6) Kumar K, Taylor RS, Jacques L, Eldabe S, Meglio M, Molet J, et al. Spinal cord stimulation versus conventional medical management for neuropathic pain: a multicentre randomised controlled trial in patients with failed back surgery syndrome. Pain 2007;132:179-88.
7) Barolat G, Schwartzmann R, Woo R. Epidural spinal cord stimulation in the management of reflex sympathetic dystrophy. Neurophysiology 1987;50:442-3.
8) Robaina FJ, Rodriguez JL, de Vera JA, Martin MA. Transcutaneous electrical nerve stimulation and spinal cord stimulation for pain relief in reflex sympathetic dystrophy. Stereotact Funct Neurosurg 1989;52:53-62.
9) Harke H, Gretenkort P, Ladleif HU, Rahman S. Spinal cord stimulation in sympathetically maintained complex regional pain syndrome type I with severe disability. A prospective clinical study. Eur J Pain 2005; 9:363-373.
10) Broseta J, Barbera J, de Vera JA, Barcia- Salorio JL, Garcia-March G, González-Darder J, Rovaina F, Joanes V. Spinal cord stimulation in peripheral arterial disease. A cooperative study. J Neurosurg 1986; 64:71-80.
11) Jivegard LE, Augustinsson LE, Holm J, Risberg B, Ortenwall P. Effects of spinal cord stimulation (SCS) in patients with inoperable severe lower limb ischaemia: A prospective randomized controlled study. J Vasc Endovasc Surg 1995; 9:421-425.
12) Kumar K, Toth C, Nath RK. Spinal cord stimulation for chronic pain in peripheral neuropathy. Surg Neurol. 1996 Oct;46(4):363-9.
13) De Jongste MJL, Hautvast RWM, Hillege HL, Lie KI; Working Group on Neuroradiology. Efficacy of spinal cord stimulation as adjuvant therapy for intractable angina pectoris: A prospective, randomized clinical study. J Am Coll Cardiol 1994; 23:1592-1597.
14) Guttman OT, Hammer A, Korsharskyy B. Spinal cord stimulation as a novel approach to the treatment of refractory neuropathic mediastinal pain. Pain Pract. 2009 Jul-Aug;9(4):308-11.
15) Cameron T. Safety and efficacy of spinal cord stimulation for the treatment of chronic pain: a 20-year literature review. J Neurosurg 2004;100:254-67.
16) Kemler MA, de Vet HC, Barendse GA, van den Wildenberg FA, van Kleef M. Effect of spinal cord stimulation for chronic complex regional pain syndrome Type 1: Five-year final follow-up of patients in a randomized controlled trial. J Neurosurg 2008; 108:292-298.
17) Barolat G. Experience with 509 plate-electrodes implanted epidurally from C1 to L1. Stereotact Funct Neurosurg 1993;61:60-79.
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