Back in 1965, Melczak and Wall published their Gate Control Theory, which led to dramatic changes in the medical community’s understanding of pain and, eventually, to the development of new types of treatment for pain. Per the Gate Control Theory, the brain sometimes regulates incoming pain signals from the body, making them seem less intense. Specifically, when there is a large transmission of signals from a neural pathway, the brain automatically decreases the perceived intensity of those signals (i.e., closing the “gate”). This explains why, if you have an injury to your hand, for example, it may help to hold or rub your arm away from the site of the injury. The increase in total nerve signals (rubbing the arm plus the injury) leads the brain to perceive the injury itself as less painful. People often engage in this sort of behavior after an injury without even realizing it. But, perhaps the most important consequence of the Gate Control Theory was the development of neurostimulation technology.

Neurostimulation basics

Neurostimulation involves the delivery of mild electrical pulses to the body to treat pain and other medical conditions. Traditional applications of neurostimulation include transcutaneous electrical nerve stimulation (TENS) units, which deliver stimulation to through the skin to the nerves in a particular region of the body, as well as spinal cord stimulators.

Spinal cord stimulators are implanted devices that consist of a battery connected to one or more leads, which deliver electrical pulses to the dorsal column of the spinal cord. When these traditional devices are operating, the patient feels a tingling sensation known as paresthesia in the targeted body part. For example, if a spinal cord stimulator is positioned to stimulate the part of the spinal cord that gathers pain signals from the legs, the person would feel paresthesia in their legs when the device is on.

In many cases, paresthesia is not a problem. Patients often like it; paresthesia is generally preferable to the pain it is replacing. However, in some cases it can create challenges.

Typically, a spinal cord stimulator is calibrated to deliver a low to moderate level of paresthesia. However, if this calibration is done while the patient is sitting, when the patient changes position (e.g., lying down) the device leads may get closer to the spinal cord, leading to more intense — potentially painful — paresthesia. Patients often turn the device settings down to a lower, less effective level of stimulation to prevent these painful increases in stimulation. This prevents shocks, but at the expense of more effective relief.

Further, certain pain conditions such as complex regional pain syndrome (CRPS) involve sensitization of the nerves, potentially causing even mild paresthesia to increase the pain in the affected body part. For these reasons, paresthesia is increasingly being viewed by pain doctors not as a necessary guide to delivering neurostimulation, but instead as a potentially unwanted byproduct of neurostimulation.

New neurostimulation technologies

Fortunately, several new neurostimulation technologies are being developed to continue to offer the substantial pain relief of spinal cord stimulators but without the potential drawbacks of paresthesia. Many of these devices are still being tested in clinical trials. We are taking part in many of those trials here at Arizona Pain. Other types are already commercially available for appropriate patients.

High-frequency neurostimulation

Traditional stimulators typically deliver stimulation at lower frequencies, such as 100 or 200 times per second. Some newer devices deliver stimulation at high frequencies, such as 10,000 times per second. The high frequency of stimulation leads the patient to not perceive paresthesia, but pain signals are still blocked. We are currently taking part in a study of a high-frequency stimulator designed by Neuros Medical for lower limb amputation pain. We are also participating in a study of a high-frequency neurostimulator created by Nevro Corp for treating non-spinal post-surgical nerve pain.

Burst stimulation

By delivering many pulses of stimulation for very short periods of time (e.g., 1/1000 of a second), it is also possible to block pain without creating paresthesia. Abbott, previously known as St. Jude Medical, developed a device that delivers such “burst” stimulation. We will be taking part in a study of these devices later this year.

Dorsal root ganglion stimulation

Another change in neurostimulation devices is to target a different part of the spinal cord. Normally, the main part of the spinal cord (the dorsal column) is targeted because it gathers pain signals from all parts of the body. A newer approach involves positioning leads to stimulate the smaller branches coming from the dorsal column, called the dorsal root ganglion (DRG). By selecting the specific DRG bundles to target, it’s possible to block pain while delivering very little paresthesia, particularly to non-painful parts of the body. This appears to be helpful for pain conditions such as CRPS. We are taking part in a study with Abbott of DRG stimulation for CRPS of the lower extremities.

Positional neurostimulation

Another way to avoid excessive paresthesia is to make the device automatically adjust stimulation based on the position of the patient’s body. Medtronic’s RestoreSensor device uses an accelerometer in the battery to make such adjustments. For example, if the device sensed the patient lying down, it would automatically reduce the stimulation in order to avoid excessive paresthesia.

Saluda Medical is developing a device that would use the stimulator leads to get feedback directly from the spinal cord about how much of the stimulation was getting through and make millisecond by millisecond adjustments to keep the stimulation at a comfortable level. We will be taking part in a study with Saluda Medical of this device later this year.

These new technologies have the potential to deliver more effective pain relief to certain patients than current devices. If you are interested in learning more about any of these studies and whether you might qualify, you can discuss this study with your pain management providers at Arizona Pain. For additional information about this study, you can contact me directly at TedS@arizonapain.com.

Ted Swing has 13 years of research experience in psychology and pain medicine and four years of teaching experience, has published in top psychology and medical journals, and has presented his research at major conferences. He received his Ph.D. in Social Psychology from Iowa State University and has been the Research Director at Arizona Pain since May 2012.

From the Research Dept.
New Study to Examine the Efficacy of Burst Neurostimulation
By Ted Swing, Ph.D.

One of the frontiers in the treatment of chronic pain is neurostimulation (also called neuromodulation). Neurostimulation involves devices that deliver electrical pulses to alter nerve responses. When used in the brain, this can be used to prevent epileptic seizures or treat Parkinsonâ€s disease. The most common applications of neurostimulation involve the treatment of central or peripheral nerves in order to produce pain relief. The electrical pulses sent by a neurostimulator trigger sensations in nearby nerves that are often felt as a mild tingling or buzzing sensation. This sensation replaces some or all of the pain that would have otherwise been perceived in that nerve.

Spinal Cord Stimulators

The first type of neuromodulation device, developed in 1968, is called a spinal cord stimulator (SCS). Spinal cord stimulators are devices implanted under the skin along the spine. The device consists of a battery and pulse generator, along with electrodes running along the spinal nerves. These electrodes are positioned to stimulate the specific nerves for the area or areas where that patient has pain. These devices have proven effective for many patients and are widely used today for chronic pain that is not adequately relieved by other treatments.

Potentially Unpleasant Stimulation

One of the challenges with spinal cord stimulators is that the intensity of the stimulation felt by the patient can vary, for example by time of day, type of activity or by body position. A particular level of stimulation may provide effective relief when the patient is standing, but then become too intense when they sit down. This intense stimulation could be unpleasant. Alternatively, if the neurostimulator were set to a level that is effective in one body position, it may become insufficient to cover their pain in a new position. Though the stimulation delivered by the device can be adjusted by the patient to prevent periods of unpleasant or insufficient stimulation, it would be preferable if relief could be produced consistently without potential discomfort. Further, for a small percentage of patients, the feeling of neurostimulation in general is considered unpleasant.

Burst Stimulation

One possible solution to these challenges is the use of burst stimulation. Rather than delivering constant pulses of electrical stimulation, burst stimulation would involve very brief pulses of stimulation (for example, a series of five electrical pulses in a row, each lasting 1/1000 of a second). These bursts would be repeated many times each second. Previous research shows that such pulses are too short to felt by the patient, but are capable of producing pain relief. One of the leaders in neurostimulation devices, St. Jude Medical, has begun a study comparing burst stimulation to standard stimulation. This study will determine if the pain relief produced by burst stimulation is as good as or better than standard stimulation.

St. Jude SUNBURST Study

The St. Jude SUNBURST study will include patients with moderate to severe pain in the trunk or limbs that is not adequately relieved by medications or other treatments. These patients must be appropriate candidates for implantation of a neurostimulation device and meet other criteria, including not being pregnant, having cancer, or being immunocompromised. Patients who qualify will have a trial spinal cord stimulator implanted for several days. This will show whether or not neurostimulation is effective in relieving the patientâ€s pain. If it is, then a permanent spinal cord stimulator will be implanted. Patients are then randomly assigned to receive either standard stimulation throughout the study or periods of standard and burst stimulation. The study will then involve at least four follow up visits over the next 24 weeks and then an additional visit every six months until the study is completed. Arizona Pain will be taking part in this study. If you are interested in learning more about this study, you can speak with your pain management providers or contact me directly at TedS@arizonapain.com.

Ted Swing has more than nine years of research experience and four years of teaching experience in psychology, has published in top psychology and medical journals, and has presented his research at major conferences. He received his Ph.D. in Social Psychology from Iowa State University and has been the Research Director at Arizona Pain since May 2012.