TechSectors: Device - Spinal Cord Stimulation

MDNG Pain Management, September 2008, Volume 1, Issue 1

In 1967, Shealy and colleagues published the first report on spinal cord stimulation (SCS) in humans. The first spinal cord stimulators were placed intrathecally via open laminotomy.

In 1967, Shealy and colleagues published the first report on spinal cord stimulation (SCS) in humans. The first spinal cord stimulators were placed intrathecally via open laminotomy. This approach led to many complications and ineff ective stimulation and was abandoned when an epidural approach was developed in the 1980s. Because of the simplicity of a SCS trial using epidural electrodes, the SCS gained in popularity and now is widely used to treat many chronic pain conditions.

The mechanism of action of SCS is multifold. One of the major mechanisms responsible seems to be increased dorsal horn inhibitory action of GABA. The dis-inhibition of descending analgesia pathways originating in periaqueductal gray (PAG), induced release of serotonin and substance P, suppression of sympathetic activity via adrenoreceptors, and modulation of adenosine are other mechanisms responsible for SCS action. In patients with cardiac angina, the redistribution of the coronary blood fl ow from regions with normal perfusion in favor of regions with impaired myocardial perfusion is responsible for pain relief. The typical SCS hardware consists of leads, extensions, and an implantable pulse generator (IPG). Before deciding on a permanent implantation, the SCS is tested, during which the leads are placed in the epidural space—usually in thoracic and cervical spine for leg and arm pain coverage, respectively, and most commonly percutaneously under fl uoroscopic guidance in a similar manner as epidural catheters for labor pain. The actual stimulation occurs from electrodes, placed at the distal end of the lead. An electrical field from SCS leads/electrodes reaches the dorsal columns of the spinal cord and modulates its pain transmission. The patient is then discharged home to (try to) assess eff ectiveness of stimulation on his or her pain for several days. If the trial successfully reduces pain, the SCS lead is removed and a permanent SCS lead is placed on separate occasion. The permanent SCS implant can be achieved by placing the percutaneous lead via epidural needle under local anesthesia or “paddle” lead via open laminotomy. The paddle electrodes are larger and can be anchored directly to the dura, potentially minimizing migration and providing better stimulation coverage in some cases. Th e IPG is then placed in a “pocket” underneath the skin in the gluteal or abdominal area, similar to the cardiac pacemaker, and then connected to the SCS lead (or several leads) placed via epidural.

Most of the recently developed IPG’s contain batteries that are rechargeable, with no need to be replaced for many years. Patients using a “remote control” device can easily adjust the stimulation patterns, but for better adjustment, physicians can fi ne-tune by reprograming the IPG. The most common indication for SCS placement in United States today is lumbar radicular pain that failed to respond to medical management. Patients who fail to improve with surgery respond very well to the SCS. Patients with a rare form of chronic pain formerly known as “reflex sympathetic dystrophy”

and now termed “complex regional pain syndrome (CRPS)” can signifi cantly improve with SCS. The best candidates for SCS are patients with upper or lower extremity pain.

Many studies support the use of SCS for cardiac angina and, to a slightly lesser degree, peripheral vascular disease. The best indication for a SCS trial is cardiac angina refractory to pharmacologic and surgical treatments. An increase in exercise capacity, reduction in anginal complaints, decreased use of short-acting nitrates, and improved quality of life has been demonstrated in patients with ischemic heart disease treated with SCS. Th e fear of potential increase in myocardial damage does not seem to be justifi ed, since the SCS does not completely abolish anginal pain; it only raises the anginal threshold and does not seem to have a negative eff ect on left ventricular ejection fraction nor cardiac arrhythmia.

Recently, new indications for spinal cord stimulation and “peripheral nerve” stimulation have been published. With use of similar implantable stimulation systems to SCS, diffi cult cases of peripheral neuropathic pain, such as occipital neuralgia, can be treated well. Early reports are encouraging for the use of stimulating electrodes for the treatment of chronic abdominal and pelvic pain.

Dr. Stojanovic is the co-founder of the Spine and Pain Institute of New England, Co-medical Director of the Cape Cod Hospital Pain Management Program, and Founder and Former Director of Interventional Pain Program at Massachusetts General Hospital and Assistant Professor at Harvard Medical School.