Spinal Cord Stimulation (SCS)

• An introduction to spinal cord stimulation (SCS)
• Common indications for spinal cord stimulation
  • Failed back surgery syndrome (FBSS)
  • Complex regional pain syndrome (CRPS)
  • Angina pectoris
  • Peripheral neuropathy
  • Peripheral vascular disease
  • Post-herpetic neuralgia
  • Visceral pain
• The procedure of spinal cord stimulation
  • Lead insertion and electrode placement
  • Screening trial
  • Generator or radiofrequency implantation
• Benefits of spinal cord stimulation
  • Trial period
  • Reversibility
  • Individual therapy
  • Quality of life
• Complications of spinal cord stimulation
• Availability of spinal cord stimulation
• Cost benefits of spinal cord stimulation
• Conclusion

An introduction to spinal cord stimulation (SCS)

Spinal cord stimulation (SCS) is an emerging, minimally invasive procedure used to treat chronic, refractory, neuropathic pain. Neuropathic pain is one of the most difficult medical conditions to treat; it is not the “normal” pain we associate with stubbing a toe or getting a paper cut – these are called nocioceptive pain. Neuropathic pain is caused by abnormal nerve signalling in the nervous system and, as a result, often does not respond to most pain relief strategies. It is for this reason that SCS is becoming widely accepted for use in multiple areas of neuropathic pain management.
SCS involves the implantation of electrodes into the epidural space near the source of pain. The electrodes, stimulated by an external or internal source, emit a current that stimulates the pain inhibition pathways. SCS does not eliminate pain but creates a numbness, called paraesthesia, in the area. This results in a masking of the pain. Scientists and doctors are still investigating exactly how SCS induces paraesthesia.
SCS is considered a last resort treatment in the management of pain. However, many neurosurgeons believe it should be considered earlier in some situations. As more and more studies are being published on SCS, the procedure is gaining recognition and popularity. The cost benefits and success of the procedure are also being realised.

Common indications for spinal cord stimulation

Failed back surgery syndrome (FBSS)
The most extensively studied use of SCS has been for failed back surgery syndrome (FBSS). FBSS is characterised by persistent back and/or leg pain despite one or more surgeries aimed at correcting an abnormal and painful lumbo-sacral spinal section. FBSS is diagnosed, as the name suggests, when the outcome of such an operation does not succeed in providing any relief. FBSS indicates that there is also no response to the less invasive therapies associated with back pain, such as pain medication, nerve blocks, chiropractic therapy and corticosteroid injections.
PROCESS (prospective randomised controlled multicentre study of patients with failed back surgery syndrome), the first randomised controlled trial to evaluate the cost and effectiveness of SCS for FBSS, reported that SCS significantly improved pain ratings, movement, functional capacity and quality of life. It is thought that SCS will be the most helpful for FBSS if the stimulator is implanted within 3 years of the failed back operation.
More recently, the National Institute for Health Research released the Health Technology Assessment (HTA) for SCS. The assessment confirmed that SCS was associated with a greater reduction in pain and opiate use, a greater improvement in functionality and quality of life compared with conventional pain medication.
People who undergo SCS for FBSS play a large part in making their own treatment successful. It is important to try and become as involved and as knowledgeable in SCS as you can be. By diligently monitoring your pain during the trial and then reporting this to your surgeon, they will have all the information needed to best program your SCS device. Learning how to manage the controls is also very important – the better you can do this, the better you can manage your own pain.
SCS is also indicated in other conditions that involve back pain, including:

• Lumbar spinal stenosis; and
• Pain originating in the cervical spine that is refractory to conventional treatments.

Complex regional pain syndrome (CRPS)
Complex regional pain syndrome (CRPS) or Sudeck’s atrophy is a dysfunction in the sympathetic nervous system. This condition is usually treated using pain medication, physical therapy, sympathetic nerve blocks or transcutaneous electrical nerve stimulation.
SCS has shown promising improvements in quality of life, pain scores and functionality in people with CRPS, compared to those that have not undergone SCS. Compared to physical therapy CRPS patients report a higher perceived global effect after SCS.

Angina pectoris
SCS is fast emerging as an effective treatment of angina pectoris for refractory angina. Refractory angina pectoris is an unrelenting chest pain experienced by people with cardiovascular disease (CAD) that has not responded to other forms of treatment. The increase in treatments and medications for people with CAD has improved life expectancy, but has also given rise to an increased incidence of angina, the symptoms of which are extremely difficult to relieve.
The conventional therapies for the condition include coronary artery bypass graft surgery and coronary revascularisation. After SCS, people with refractory angina commonly report treatment satisfaction, increased exercise capacity, improved pain scores and quality of life. These benefits have been reported to last up to 5 years. Exercise capacity has also been shown to be improved after the implantation.
In the past, SCS has been criticised for treatment of cardiac conditions as it is thought the paraesthesia may mask warning signs of cardiac events, such as a heart attack, but this has not been found to be the case.

Peripheral neuropathy
Peripheral neuropathies such as phantom limb pain, stump pain and diabetic neuropathy have also been treated successfully with SCS. One study has shown that SCS for diabetic neuropathy improves blood glucose control as well as pain relief and exercise tolerance.

Peripheral vascular disease
Peripheral vascular disease results from the narrowing of the arteries in certain limbs, commonly the legs. Peripheral vascular disease is very painful and is thought to have a neuropathic pain component that worsens as the disease progresses. SCS has been used to treat some peripheral vascular diseases and has shown positive results, perhaps most commonly for critical limb ischaemia (CLI).
CLI is a condition in which the blood flow to a limb is obstructed. The obstruction in some cases can be so severe that wounds which do not heal form, and gangrene can occur in the affected limb. SCS is thought to increase blood flow and skin temperature controls, which are thought to be mechanisms that increase the rate of wound healing; enhance the probability for limb survival; and decrease pain for patients with CLI. Patients who have been treated with SCS for CLI have reported an increased health-related quality of life.

Post-herpetic neuralgia
Post-herpetic neuralgia (PHN) is a form of neuropathic pain. It is highly unresponsive to most therapies but has shown positive results when treated with SCS. SCS for PHN is not as extensively studied, although results to date have shown that up to 82% of people who had PHN for up to 2 years received pain relief.

Visceral pain
Visceral pain is a very common type of pain that describes any pain we experience from our internal organs. Some visceral pains are currently being investigated as a candidate for SCS treatment, and so far reports have indicated positive outcomes. To date, the following visceral indications treated successfully with SCS include:

• Pancreatitis;
• Interstitial cystitis;
• Urinary urgency;
• Incontinence;
• Oesophageal pain;
• Irritable bowel syndrome;
• Restriction of blood supply to the intestine;
• Vulvar pain that is refractory to other treatments; and
• Failed abdominal surgery.

It is important to note that results for these conditions have not been studied extensively and need further investigation to be confirmed.

The procedure of spinal cord stimulation

SCS causing paraesthesia by applying an electric current to electrodes placed in the epidural space. The number of electrodes needed and their placement will vary according to the degree of pain experienced by the person. The electrode power is supplied either by an external radiofrequency transmitter or by an implanted battery.
Implantation of a spinal cord stimulator is generally a two stage process: the insertion of the lead or “wires” and electrode placement, followed by the implantation of a permanent pulse generator. These processes are separated by a trial period of 3–8 days.

Lead insertion and electrode placement
During lead insertion, only local anaesthetic is used. This may be daunting for some people but is actually one of the major benefits of SCS. Local anaesthetic enables the person undergoing the implantation to tell the surgeons when they are feeling adequate paraesthesia in the target area, while still being strong enough to prevent muscle spasm and pain. This is an invaluable tool for a successful implantation.
The surgeons can watch the lead insertion by using fluoroscopy. This allows a clear camera view of the spine.
The level of entry into the epidural space will vary depending on the site of pain. The electrodes are placed so that the paraesthesia overlaps the area of pain. During the procedure, the surgeons will employ test stimulation. This should not lead to an unpleasant feeling; if it does, the electrode will be manoeuvred until it is comfortably placed.
The lead is then attached internally to muscles in the surrounding paravertebral area, and connected to an external neurostimulator. At this stage, the lead is only temporary, and remains temporary until after the screening trial.

Screening trial
The screening trial allows the effects of SCS to be experienced before it is made permanent. During the trial period, the stimulator settings are adjusted to suit the level of pain and tolerance to the paraesthesia. The settings can be increased or decreased depending on the individual response to the stimulation.
At least 50% pain relief indicates a successful trial, in which case the stimulator is made permanent. If adequate pain relief is not achieved, a second trial can be considered on a case-by-case basis. After most unsuccessful trials, the system is removed.
Any longer than 8 days is not recommended for the screening period, as this will increase the chances of infection.

Generator or radiofrequency implantation
The choice of whether a radiofrequency system or a totally implantable system is used to supply the power depends on the individual and the type of stimulation needed to give adequate pain relief. The benefit of the totally implantable system placed in a subcutaneous pocket is that it is more aesthetically pleasing, although the system needs to be removed when the battery dies. The radiofrequency system requires no battery, but an antenna and transmitter must be worn.

For more information, see Spinal Cord Stimulation Devices.

Benefits of spinal cord stimulation

Trial period
The trial period is a valuable and unique benefit of SCS. The trial gives the individual a “test run” with the stimulator before having the lead placed permanently. This saves the expense of undergoing a potentially unsuccessful implantation.

Reversibility
The implantation is completely reversible, so the stimulator can be removed if the the pain relief is inadequate or the paraesthesia is intolerable.

Individual therapy
SCS is adapted to the individual, making it an attractive and efficacious option for pain management. The settings on the generator are established during the trial period to match the individual level of pain experienced, and the individual’s lifestyle. The placement of the electrodes is dictated by the individual during the procedure, in order to achieve optimal pain relief and satisfaction from the implantation.

Quality of life
SCS has been extensively studied; the results of many trials and case studies indicate that SCS has a positive effect on pain relief, sleep and movement. SCS provided sustained pain relief, with a large proportion of people reporting satisfaction after the procedure. SCS has been shown to reduce the need for analgesic and narcotic use. A significant proportion of people who undergo SCS are able to return to work.
Improved quality of life is reported by many patients who undergo SCS, with a decrease in the depressive symptoms that often accompany chronic pain and the debilitating effects of living with chronic pain.
Indirectly, SCS may also have a positive effect on neurological functioning due to a decrease in pain medication use and associated side effects. Secondly, the decrease in pain indirectly enhances movement coordination and control.

Complications of spinal cord stimulation

Like any medication has side effects, spinal cord stimulator implantation can also have complications. The complications associated with SCS are common but not major, and are easily reversible with early intervention.
Problems associated with SCS are predominantly technical, involving electrode dislodgement or fracture, failure of the generator, or wiring problems associated with the extension cable.
Infection is a possibility after implantation; infections usually occur in the first three months after implantation, and can be treated quite effectively.
Very rarely, some individuals may experience leakage of the cerebrospinal fluid (CSF). CSF is a fluid that cushions the brain and plays a very important protective role.
Although unlikely, the risk of serious spinal cord or nerve injury are also present, which can lead to paralysis, weakness, numbness and clumsiness below the level of the implant.

Availability of spinal cord stimulation

Many people with chronic pain will not be suitable for selection for SCS. Surgeons assessing the eligibility for implantation must carefully consider:

• The pain reported must be consistent from the individual and physician. For example, if the pain has been inconsistent or abnormal, or if a secondary form of pain is experienced, the person may not be eligible. This is because the secondary pain may be intensified once the predominant pain has been treated.
• Psychological factors that may impede the success of the treatment must be ruled out. For example, people with previous drug abuse or unresolved psychiatric illness are not eligible.
• It is very important to establish the cause and type of pain. SCS is generally not effective in treating nocioceptive pain.
• As there is a significant risk of infection with SCS, people with sepsis or increased risk of sepsis must be strictly excluded.
• People with pacemakers or who require the use of defibrillators, magnetic resonance imaging (MRI), diathermy, ultrasonic equipment or radiation therapy may be unsuitable for SCS.
• The presence of bacteria in the blood (bacteraemia) will make infection after implantation more likely. People with chronic or recurrent infection should not have the procedure.
• People with bleeding disorders, such as haemophilia A or haemophilia B, are ineligible, as it will increase the risk of bleeding into the epidural space.
• People who are hypersensitive to the implant material.

Cost benefits of spinal cord stimulation

At first glance, spinal cord stimulation presents as a costly procedure, and without taking into consideration the long term cost benefits, the immediate costs are beyond what most people would be willing to pay.
After six months, the procedure is still significantly more expensive per individual compared to other conventional treatment methods. However, it is estimated that after two years, the costs of SCS would be equivalent to alternative management. Furthermore, it is expected that after five years SCS may present as the treatment with the greatest cost benefit. This also applies to individuals with refractory angina. Those treated with SCS tend to require less days in hospital than CABG making SCS a less expensive option.
SCS has both direct and indirect cost benefits. Recent studies have concluded that SCS for FBSS not only prevents costs associated with further surgeries and medication, but also increases the proportion of people able to return to work.
The cost benefits do not stop at the individual. SCS is proposed to reduce government healthcare costs. The use of SCS is proposed to increase each year but as yet SCS is not subsidised on the pharmaceutical benefits scheme.

Conclusion

SCS is not a first line treatment. However, in the opinion of many in the field, it should not always be considered a “last resort” either. SCS is a minimally invasive procedure with minimal complications that is developing a large, impressive and promising profile.

For more information, see Spinal Cord Stimulation.

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