Spinal cord stimulator
|Spinal cord stimulator|
Anterior view X-ray of a spinal cord stimulator (SCS) implanted in the thoracic spine
A Spinal Cord Stimulator (SCS) or Dorsal Column Stimulator (DCS) is a type of implantable neuromodulation device (sometimes called a "pain pacemaker") that is used to send electrical signals to select areas of the spinal cord (dorsal columns) for the treatment of certain pain conditions. SCS is a consideration for people who have a pain condition that has not responded to more conservative therapy.
In the United States Failed Back Surgery Syndrome is the most common use while in Europe the most common use is peripheral ischemia.
As of 2014 the FDA had approved SCS as a treatment for failed back surgery syndrome (FBSS), chronic pain, Complex Regional Pain Syndrome, Intractable angina, as well as visceral abdominal and perineal pain and pain in the extremities from nerve damage.
Once a person has had a psychological evaluation and deemed an appropriate candidate for SCS, a temporary implant is placed, called a trial, to determine the best stimulation pattern, and the person is sent home for three to ten days with an external pulse generator. If pain control and increased activity was achieved, a permanent system, with leads and a pulse generator, is placed.
SCS may be contraindicated in people who have coagulation related disorders, or are on anticoagulant therapy. Other contraindications include local and systemic infection, pacemakers, or those people for whom pre-surgical imaging studies show have anatomy that makes placement difficult, or if concerns arise during psychological evaluation.
Adverse effects and complications
Complications with SCS range from simple easily correctable problems to devastating paralysis, nerve injury and death. In a 7-year follow-up, the overall complication rate was 5-18%. The most common complications include lead migration, lead breakage, and infection. Other complications include rotation of the pulse generator, haematomas (subcutaneous or epidural), cerebrospinal fluid (CSF) leak, post dural puncture headache, discomfort at pulse generator site, seroma and transient paraplegia.
Some people find the tingling sensation caused by SPS to be unpleasant.
The most common hardware related complication is lead migration, in which the implanted electrodes move from their original placement. With this complication, recapturing paraesthesia coverage can be attempted with reprogramming. In circumstances involving major lead migration a reoperation may be required to reset the lead placement. Studies differ greatly in reporting the percentage of people who have lead migration but the majority of studies report in the range of 10-25% of lead migration for spinal cord stimulation.
Mechanism of action
The neurophysiological mechanisms of action of spinal cord stimulation are not completely understood but may involve masking pain sensation with tingling by altering the pain processing of the central nervous system. The mechanism of analgesia when SCS is applied in neuropathic pain states may be very different from that involved in analgesia due to limb ischemia. In neuropathic pain states, experimental evidence show that SCS alters the local neurochemistry in dorsal horn, suppressing the hyperexcitability of the neurons. Specifically, there is some evidence for increased levels of GABA release, serotonin, and perhaps suppression of levels of some excitatory amino acids, including glutamate and aspartate. In the case of ischemic pain, analgesia seems to derive from restoration of the oxygen demand supply. This effect could be mediated by inhibition of the sympathetic system, although vasodilation is another possibility. It is also probable that a combination of the two above mentioned mechanisms is involved.
Electrotherapy of pain by neurostimulation began shortly after Melzack and Wall proposed the gate control theory in 1965. This theory proposed that nerves carrying painful peripheral stimuli and nerves carrying touch and vibratory sensation both terminate in the dorsal horn (the gate) of spinal cord. It was hypothesized that input to the latter could be manipulated to “close the gate” to the former. As an application of the gate control theory, Shealy et al. implanted the first spinal cord stimulator device directly on the dorsal column for the treatment of chronic pain and in 1971, Shimogi and colleagues first reported the analgesic properties of epidural spinal cord stimulation. Since then this technique has undergone numerous technical and clinical developments.
Research on improving the devices and software has included efforts to increasing the battery life, efforts to develop closed loop control, and combining stimulation with implanted drug delivery systems.
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