Q. What is a neurostimulation system?A. Neurostimulation systems generally consist of three parts: 1. Electrical leads – slender insulated wires tipped by electrical contacts – that tunnel beneath the skin to deliver mild electric current to specific areas, generally along the spine or neck. 2. An impulse generator. During a trial treatment for a number of days, an external version is worn atop the skin. If a patient proceeds to a permanent implant, the surgeon or physician creates a small pocket in the fleshy area of the upper hip, abdomen, or above the chest wall, and secures the pulse generator there. About the size of a stopwatch, it may be rechargeable (which involves wearing a coupling device over the implant every few days) or not (which would need replacement when the charge is depleted after several years).3. A patient controller. This handheld remote control allows patients to switch between previously set stimulation parameters that were programmed during a visit after the implant procedure.
The nerve-stimulation components employed by neurostimulation systems resemble technologies previously developed for cochlear implants or heart pacemakers.
Q. What are neurostimulation systems used for?A. Certain types of chronic pain, such as neuropathic pain arising from damaged or diseased nerves, or pain that includes a neuropathic component, can be lessened in some patients through use of neurostimulation systems. Neurostimulation has also been applied to chronic pain arising from ischemic conditions – chronic pain associated with insufficient flow of oxygenated blood – such as peripheral vascular disease and chronic angina pectoris that does not respond sufficiently to pain medicine.
The NACC issued recommendations regarding consideration of neurostimulation in a number of indications, while pointing out that screening for candidacy is the most important factor in order to take into account a patient’s overall condition and realistic expectations for treatment. Conditions and recommendations discussed by the panel included: • Failed back surgery syndrome (post-lamindectomy syndrome) – after conservative medical management of at least three to six months proves inadequate or yields unmanageable side effects, but before repeat back surgery if the patient is neurologically stable• Complex regional pain syndrome – with pain of at least three months’ duration or severe, rapidly progressing disease that is not responding to more conservative measures and only after obtaining informed consent, a psychological screening and successful trial stimulation• Certain types of chronic back or neck pain, including radicular pain (radiating from a nerve root), such as sciatica • Chronic neuropathic pain or pain that includes a neuropathic component (“mixed” pain) – after failure of conservative medical management for at least three to six months, but before consideration of long-acting opioid maintenance therapy• Other types of chronic neuropathic pain – to consider on an individualized basis in HIV neuropathy and with caution due to increased infection risk in diabetic painful peripheral neuropathy• Visceral pain – on a case-by-case basis• Raynaud’s syndrome and other painful ischemic vascular disorders – in the first 12 weeks of symptoms • Refractory angina pectoris – evidence shows neurostimulation may be of some benefit to manage pain• Demyelinating diseases such as multiple sclerosis – a physician should consider if the potential benefits outweigh the risks and MRI-compatible components are available that will meet the patient’s needs for periodic imaging studies• Post-cancer-treatment pain – for pain arising from nervous tissue damage caused by tumor growth or treatment in patients who have an expected survival of at least 12 months
Q. What is chronic pain?A. Chronic pain, by definition, lasts beyond three to six months, and serves no protective purpose. Unmanaged chronic pain burdens society with costs of ongoing medical visits and medication, increased dependence, and decreased productivity. In the U.S., the Institute of Medicine estimates that nearly 100 million Americans have chronic pain, with annual costs totaling about $635 million.
Q. Which medical specialists practice neurostimulation?A. Neurostimulation devices may be implanted by neurosurgeons, pain physicians, urologists, rehabilitation physicians, or similar practitioners. To achieve best outcomes, they may work with other specialists such as neurologists, psychiatrists, psychologists, gastrointestinal or colorectal specialists, primary care physicians, and physical therapists.
Q. How does neurostimulation work?A. Neurostimulation may be thought of as rebalancing activity of neural circuits. It is believed that the stimulation may override transmission of some pain signals as well as triggering release of natural pain-relieving substances.
Electrical contacts are placed in the epidural space above the spinal column, or in areas where they can stimulate peripheral nerve fibers beyond the central nervous system, such as across the lower back.
Future systems under development may involve micro-neurostimulation implants that function wirelessly.
Q. What improvements may be made to neurostimulation?A. In addition to having practitioners track and monitor procedure results, as recommended by the NACC, and meet minimal training standards, anticipated improvements include continued miniaturization of components, customization to various end-uses, wireless operation, new patterns of stimulation and potential new target areas – such as a pain-pathway gateway known as the dorsal root ganglion – as well as improved access by patients who may benefit. Current multi-center randomized controlled clinical trials and device performance registries will influence future directions.
Importantly, time-to-referral has been reported to have a major impact on outcomes, with a 93 percent success rate if the patient had less than three years elapse between an initial back surgery and a spinal cord stimulator implant, but only a 9 percent success rate with a delay of more than 12 years. Therefore, broader awareness among patients and referring physicians could also result in more benefits being realized more widely, which will be important as an aging population lives longer with chronic conditions.
Q. What are the main risks or complications?A. While serious complications such as spinal cord injury are rare and parallel those of other surgical procedures, lead breakage or migration and similar device complications that require revision have been historically reported to range from 30-40 percent. The NACC notes that in such established device-based therapies as cardiovascular–defibrillator implantation and total hip replacement, complication rates dropped with increasing practitioner experience.
Hardware failure rates noted in the published NACC recommendations include:• Lead migration in spinal cord stimulation – 10-25 percent; less often, dislodgement, fracture, high impedance, or extension disconnection have been reported• Battery failure – 1.6 percent; primarily due to programming issues and depletion
Biologic complications may include:• Infection at the implant site – 4-10 percent (the NACC presents a risk-reduction plan to minimize such complications through patient instruction and steps taken before and after the implant procedure)• Fluid pooling near the pulse generator (seroma) – 2.5 percent, generally treated with device removal• Epidermal or subcutaneous hematoma – 0.3 percent; presenting a risk of spinal cord lesion that could cause permanent neurological deficit• Dural puncture – 0.3 percent; may cause headache• Pain over the pulse generator site• Nerve damage including spinal cord injury and paralysis (reported rarely)
Physiologic complications may include:• Uncomfortable intensity, character, or pattern of stimulation when changes in position lead to movement of the electrode in the epidural space with respect to the spinal cord, or because of changes in tissue impedance around the electrodes; later systems and those under development are designed to respond to positional changes or not cause any tingling in the area covered• Stimulation tolerance in which pulse amplitude must be increased to achieve the same pain-relief over time or leading to a loss of efficacy; based on early reports, the NACC believes frequency manipulation may become a method to prevent this
Q. What is a successful trial stimulation?A. The NACC recommends that a successful trial should at least be a 30 percent reduction in both frequency and intensity of migraine pain, in keeping with International Headache Society assessment of clinical relevance; and a 50 percent reduction in other pain complaints, along with better sleep and some improved function, such as increased activity or need for less aid in activities of daily living
Q. Where is more information available?A. For patients, your provider is your front-line source of information relevant to you and your condition. For additional background information about conditions and therapies, the International Neuromodulation Society (INS) provides handouts and online content, as well as references to further resources, at http://www.neuromodulation.com/for-patients. Practitioners and referrers may find additional information throughout the site at http://www.neuromodulation.com/, and also at the INS biennial World Congress and related meetings listed at http://www.neuromodulation.com/events, and in articles and meeting abstracts in the INS official journal, Neuromodulation: Technology at the Neural Interface.