How Do Spinal Cord Stimulators Really Work?Spinal cord stimulation (SCS) is used for 1000s of people with chronic, debilitating pain but how it works is still a mystery. Scientists from France conducted a study with 20 pain patients to help unravel the mechanisms behind pain relief with this treatment.
A spinal cord stimulator, also called a dorsal column stimulator, is an implanted electronic device used to help treat chronic pain. They have been used for over 30 years. The device delivers a low level electrical current through wires. The wires are placed in the area near the spinal cord. The device is similar in size to a pacemaker.
The original theory behind how these devices work is called the gate control theory of pain. According to this theory, electrical stimulation generated by the stimulator replaces the pain impulses.
The gate theory suggests that when the electrical stimulation reaches the spinal cord first, the "gate" closes and blocks the pain impulses. As pain lessens, the muscles around the sore area relax, further lessening pain. But studies over the years have shown that this theory only explains some of the pain relief obtained. It probably isn't the only way the stimulator works.
That's where this study comes in. They used the spinal cord stimulator for patients with chronic leg pain after failed back surgery. The experiment was set up so that electrical stimulation was placed ON for one hour and then OFF for one hour.
During those two hours, a set of data was collected including plantar sympathetic skin response (SSR), F-wave, and somatosensory-evoked potentials (P40-SEP) from the tibial nerve. Another group of measurements were taken from the sural nerve including H-reflex of the soleus muscle and nociceptive flexion (RIII) reflex.
Unless you are an expert in electrophysiology, these terms won't mean anything to you. The basic idea is that they are testing nerve transmissions for pain to two nerves in the lower leg (the tibial and sural nerves).
By looking at all the various ways pain can be transmitted, when the patient had pain, and when the pain was gone, they were able to find the pathways pain travel and understand how to turn them off.
It might be helpful to understand who was in this study. As mentioned, all 20 participants had chronic burning or freezing lower leg pain from failed back surgery. Other symptoms included electric shock sensations, pins and needle sensation, tingling or itching, numbness, or increased pain brought on by rubbing the painful area.
Surgeries included disc removal (discectomy), spinal fusion, opening the space around the spinal nerves (foraminotomy), and removing some of the bone from around the spinal cord (laminectomy). All of these procedures are designed to reduce pressure on the nerve tissue (spinal cord or spinal nerve roots).
The group included men and women between the ages of 36 and 66. They all had used a spinal cord stimulator for more than a year with good results. Knowing the unit worked for these patients, the researchers used this experimental design to test different neural pathways. The goal was to find out what was affected (and what wasn't) in bringing about pain relief.
The authors provide a detailed description of each of the neurophysiologic test procedures performed. They also offer analysis of the statistical methods used to make sense of all the data collected.
The important finding from this study was that spinal cord stimulation actually affects not one, but several different neural pathways. By testing different nerve pathways, they found which ones were inhibited or "turned off" to produce pain relief.
The results from this study confirm that spinal cord stimulation can be very helpful for people with chronic leg pain that is caused by changes in normal nerve function. It's likely that patients with just leg pain will benefit more than patients with back and leg pain, especially when the back pain is mechanical in nature, not neurologic.
They can also use this information to test patients who have chronic pain from other neurologic problems. The use of spinal cord stimulation may expand to include patients with nerve pain as well as motor disturbances.
Daniel Ciampi de Andrade, et al. Neurophysiological Assessment of Spinal Cord Stimulation in Failed Back Surgery Syndrome. In PAIN. September 2010. Vol. 150. No. 3. Pp. 485-491.
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