Electrical Stimulation Of The Spinal Cord And Peripheral Nerves

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Centuries before the nature of electricity was understood, observant people discovered that electrical stimulation (caused by the proximity of electrical eels) relieved pain. When electricity was controlled, healers replaced the eels with hand-cranked generators and continued to practice electrical therapy without understanding how it relieved pain (12). Eventually, in the mid-20th century, Melzack and Wall crafted a gate-control theory of pain that permitted the incorporation of electrical stimulation with modern medicine (13). Now, despite recognition of the shortcomings of this theory, it is known that SCS can effectively relieve pain (14), and multichannel, computerized systems with percutaneous electrodes allow stimulation of the spinal cord, nerve roots, and peripheral nerves simultaneously (see Fig. 6A,B). In a review of experience with SCS during an 18-year period, North et al. found that, at 7-year mean follow-up, 52% of 171 patients with permanent implants reported at least 50% continued pain relief; most also maintained improvements in quality of life and reduced analgesic use (15).

In Europe, SCS is most often used to treat peripheral vascular disease in patients who cannot undergo vascular reconstruction (16,17). In the United States, SCS is used most often to treat other conditions, including radiculopathic pain arising from failed back surgery syndrome (FBSS) (18). North et al. compared reoperation with SCS to treat FBSS using crossover as a primary outcome and found that, at 6-month follow-up,

Fig. 6. (A) Advanced Neuromodulation Systems spinal cord stimulator, pulse generator, and leads. (Image courtesy of Advanced Neuromodulation Systems, Inc., used with permission.) (B) Medtronic Intrel 3 spinal cord stimulator, pulse generator, and leads. (Image courtesy of Medtronic, Inc., used with permission.)

Fig. 6. (A) Advanced Neuromodulation Systems spinal cord stimulator, pulse generator, and leads. (Image courtesy of Advanced Neuromodulation Systems, Inc., used with permission.) (B) Medtronic Intrel 3 spinal cord stimulator, pulse generator, and leads. (Image courtesy of Medtronic, Inc., used with permission.)

67% of the 15 patients randomly selected for reoperation crossed over to SCS vs 17% of the 12 patients who received SCS at the outset (19).

Studies also validated the utility of SCS to treat complex regional pain syndrome (20-22). When Kemler et al. compared standard treatment for this syndrome with SCS, they deemed SCS efficacious in 20 of the 24 SCS subjects and reported significant improvements in the SCS group compared with the 12 controls in the standard treatment group (23).

In additional studies involving neuropathic pain, Harke et al. found that SCS relieved pain in 23 of 28 patients with postherpetic neuralgia and 4 of 4 with acute herpes zoster (24). Katayama et al. found that deep brain stimulation led to pain control in 6 of 10 patients with phantom limb pain, whereas SCS was only efficacious in 6 of 19 patients (25).

SCS is also an effective treatment for angina pectoris (26,27), and the resulting paresthesia does not appear to interfere with signs of a myocardial infarction (28-30). In a study of patients with angina treated by SCS for 6 weeks, the number of daily anginal episodes decreased from an average of 3.7 to 1.4, exercise duration increased, and mean ST segment depression decreased, as did consumption of nitroglycerin (31). Another study that employed Holter monitoring had similar results (32). SCS thus can be considered a treatment for underlying heart disease.

Additional indications for SCS include pain associated with lumbar arachnoid fibrosis (arachnoiditis) (33) and spinal cord lesions with well-circumscribed segmental pain. Peripheral nerve stimulation is used to treat peripheral nerve injury (34), occipital neuralgia (35), incontinence (36), and pelvic and rectal pain.

Implantation of the SCS leads can result in dural puncture or infection (reported rates are 2-20%). If an infection involves deep tissue, the system must be temporarily removed. The mechanical system problems that can occur include electrode migration, connection leaks, or battery failure. Epidural hematoma or abscess, paralysis, and permanent nerve injury are among the rare serious complications of SCS.

SCS success is generally defined as achieving more than 50% pain relief with enhanced quality of life and patient willingness to repeat the procedure; most studies in the past decade reported 55-80% success. Carefully selected patients can safely enjoy the benefits of SCS for years.

SCS is an advanced pain therapy performed only when more conservative treatments fail (37). With improvements in techniques, equipment, and knowledge about which patients will benefit and how best to time the intervention to maximize success, SCS should be able, with even greater success, to treat pain from even more causes (38). To attain this goal, it is important to determine the cause of the inconsistent outcomes reported in the literature and to make the credentialing of implant physicians more rigorous.

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