A spinal cord stimulator (SCS) or dorsal column stimulator (DCS) is a type of implantable

neuromodulation Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a sec ...

device (sometimes called a "pain pacemaker") that is used to send electrical signals to select areas of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

(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. There are also spinal cord stimulators under research and development that could enable patients with

spinal cord injury A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. It is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions. Symptoms of ...

to walk again via epidural electrical stimulation (EES).

Medical uses

The most common use of SCS is

failed back surgery syndrome Failed back syndrome (abbreviated as FBS) is a condition characterized by chronic pain following back surgeries. The term "post-laminectomy syndrome" is sometimes used by doctors to indicate the same condition as failed back syndrome. Many fac ...

(FBSS) in the United States and peripheral ischemic pain in Europe. As of 2014 the FDA had approved SCS as a treatment for FBSS, chronic pain,

complex regional pain syndrome Complex regional pain syndrome (CRPS type 1 and type 2), sometimes referred to by the hyponyms reflex sympathetic dystrophy (RSD) or reflex neurovascular dystrophy (RND), is a rare and severe form of neuroinflammatory and dysautonomic disorder ...

, 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 Psychological evaluation is a method to assess an individual's behavior, personality, cognitive abilities, and several other domains. A common reason for a psychological evaluation is to identify psychological factors that may be inhibiting ''a p ...

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.

Contraindications

SCS may be contraindicated in people who have

coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a thrombus, blood clot. It results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The process of co ...

related disorders, or are on anticoagulant therapy. Other contraindications include local and systemic infection,

pacemakers A pacemaker, also known as an artificial cardiac pacemaker, is an implanted medical device that generates electrical pulses delivered by electrodes to one or more of the chambers of the heart. Each pulse causes the targeted chamber(s) to co ...

, 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,

haematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...

s (subcutaneous or epidural),

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

(CSF) leak, post dural puncture headache, discomfort at pulse generator site,

seroma A seroma is a pocket of clear serous fluid (filtered blood plasma). They may sometimes develop in the body after surgery, particularly after breast surgery, abdominal surgery, and reconstructive surgery. They can be diagnosed by physical sign ...

and transient

paraplegia Paraplegia, or paraparesis, is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek () "half-stricken". It is usually caused by spinal cord injury or a congenital condition that affects the neura ...

. Some people find the tingling sensation caused by older model SCS 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 central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

. The mechanism of analgesia when SCS is applied in

neuropathic Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...

pain states may be very different from that involved in analgesia due to limb ischemia. In neuropathic pain states, experimental evidence shows 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 GABA (gamma-aminobutyric acid, γ-aminobutyric acid) is the chief inhibitory neurotransmitter in the developmentally mature mammalian central nervous system. Its principal role is reducing neuronal excitability throughout the nervous system. GA ...

release,

serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...

, and perhaps suppression of levels of some excitatory amino acids, including

glutamate Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...

and

aspartate Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids, i.e., the building blocks of protein ...

. 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 The sympathetic nervous system (SNS or SANS, sympathetic autonomic nervous system, to differentiate it from the somatic nervous system) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous sy ...

, although

vasodilation Vasodilation, also known as vasorelaxation, is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. Blood vessel wa ...

is another possibility. It is also probable that a combination of the two above mentioned mechanisms is involved.

Surgical procedure

Spinal cord stimulators are placed in two different stages: a trial stage followed by a final implantation stage. First, the skin is prepped and draped utilizing sterile technique. The

epidural space In anatomy, the epidural space is the potential space between the dura mater and vertebrae ( spine). The anatomy term "epidural space" has its origin in the Ancient Greek language; , "on, upon" + dura mater also known as "epidural cavity", "e ...

is accessed with loss of resistance technique using a 14-gauge

Tuohy needle A Tuohy (/tOO-ee/) needle is a hollow hypodermic needle, very slightly curved at the end, suitable for inserting epidural catheters. Epidural needle Literally, an epidural Epidural administration (from Ancient Greek ἐπί, "upon" + '' ...

. The lead is fed through carefully with fluoroscopic guidance to the appropriate spinal level. This process is repeated to place another lead adjacent to the first.

Fluoroscopy Fluoroscopy (), informally referred to as "fluoro", is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope () allows a surgeon to see t ...

is used often during the procedure to identify proper placement of the SCS leads. The lead placement depends on the patient's pain location. Based on previous studies, the lead placement for patients with low back pain is typically T9 to T10. The device technician will then turn on the stimulation, typically starting at a very low frequency. The patient is prompted to describe the sensation perceived by activation of the leads, and the technician will calibrate the SCS to achieve the maximum paresthesia coverage of the patient's targeted pain area. Finally, the leads are anchored externally to reduce risk of lead migration, the site is cleaned, and a clean dressing is applied. Once the patient has recovered from the procedure, the device is once again tested and programmed.

Patient screening

Patients who are candidates for stimulator placement should be screened for contraindications and comorbidities. The following should be considered prior to stimulator trial: * Risk of bleeding – Spinal cord stimulator trial and implant have been identified as procedures with high risk of serious intraspinal bleeding, which can cause permanent neurologic damage. Appropriate planning for discontinuation and reinstitution of anti-platelet and anticoagulant medications is necessary prior to placement of a stimulator. * Psychological evaluation – Depression, anxiety, somatization, and hypochondriasis are associated with worse outcomes for spinal cord stimulators. Experts recommend psychological evaluation prior to placement. A diagnosis with a psychiatric disorder is not a strict contraindication to stimulator placement. However, treatment of the disorder prior to consideration of a trial placement is indicated. * Delayed placement – Stimulators may have poor efficacy if placed many years after onset of chronic pain. One review of 400 cases found a success rate of only 9% for patients with stimulator placed over 15 years after onset of pain compared with nearly 85% for patients who received stimulators within two years of pain onset. * Technical difficulty – Variations in anatomy, whether congenital or acquired, may preclude successful placement in certain individuals. Imaging of the spine is necessary to guide selection of candidates for whom spine surgery is more appropriate than stimulator placement.

Trial period

In order to assess the efficacy of the spinal cord stimulator before implantation, a trial must be performed. This trial begins with placement of temporary leads into the epidural space and connected percutaneously to an external generator. The trial typically lasts 3–7 days followed by a 2-week reprieve before SCD implantation to ensure that there is no infection from the trial. Successful trial is defined by at least 50% reduction in pain and 80% paresthesia overlap of the original area of pain. If a patient has sudden changes in their pain, then further investigation is needed for possible lead migration or stimulator malfunction.

History

Electrotherapy of pain by neurostimulation began shortly after Melzack and

Wall A wall is a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or serves a decorative purpose. There are various types of walls, including border barriers between countries, brick wal ...

proposed the

gate control theory The gate control theory of pain asserts that non-painful input closes the nerve "gates" to painful input, which prevents pain sensation from traveling to the central nervous system. The gate control theory of pain describes how non-painful sensati ...

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. At this time neurostimulation for the treatment of pain is used with

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

stimulation, spinal cord stimulation,

deep brain stimulation Deep brain stimulation (DBS) is a type of neurostimulation therapy in which an implantable pulse generator is stereotactic surgery, surgically implanted subcutaneous tissue, below the skin of the chest and connected by Lead (electronics), leads ...

, and

motor cortex The motor cortex is the region of the cerebral cortex involved in the planning, motor control, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...

stimulation.

Research

SCS has been studied in people with Parkinson's disease and

angina pectoris Angina, also known as angina pectoris, is chest pain or pressure, usually caused by insufficient blood flow to the heart muscle (myocardium). It is most commonly a symptom of coronary artery disease. Angina is typically the result of part ...

. 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. SCS is being studied to treat spinal cord injury. In August 2018, The European Commission's Horizon 2020

Future and Emerging Technologies Horizon Europe is a seven-year European Union scientific research initiative to help develop a sustainable and livable society in Europe. It is the ninth of the Framework Programmes for Research and Technological Development (FP9), and the succe ...

program announced a $3.5 million funding grant for the four-nation project team that is building a prototype of an implant designed to 'rewire' the spinal cord. In September 2018,

Mayo Clinic Mayo Clinic () is a Nonprofit organization, private American Academic health science centre, academic Medical centers in the United States, medical center focused on integrated health care, healthcare, Mayo Clinic College of Medicine and Science ...

and

UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California, United States. Its academic roots were established in 1881 as a normal school then known as the southern branch of the C ...

reported that spinal cord stimulation supported with physical therapy can help people with paralysis to regain their ability to stand and walk with assistance. In December 2019, the first double blinded, randomized controlled pivotal study in the history of spinal cord stimulation was published in ''Lancet Neurology''.Long-term safety and efficacy of closed-loop spinal cord stimulation to treat chronic back and leg pain (Evoke): a double-blind, randomized, controlled trial. https://doi.org/10.1016/S1474-4422(19)30414-4

References

{{DEFAULTSORT:Spinal Cord Stimulator Implants (medicine) Neural engineering Neurosurgery Neurotechnology Pain management