NeuroStim Pain Relief

Spinal Neurostimulation Devices
For the Relief of Intractable Pain

Courtesy ANS

The successful "intradural" placement of stimulating electrodes was the single key technical advance to demonstrate that spinal electrodes could be safely placed in stable positions and did not have to reside in the subarachnoid space to be effective. It then became apparent, from clinical experience, that the most effective pain relief from spinal neurostimulators was primarily that involving the lower extremities and, to a lesser degree, low back.

The success of the intradural electrodes led to the development of multi-contact catheter and plate electrodes designed to be placed directly into the epidural space. Various designs for epidural neurostimulation have evolved over time.

Multicontact electrodes were developed to allow for greater control of the stimulation patterns. Most of the electrode configurations in the past were either single or double column electrodes. A newer three column configuration (shown to the left) has been of particular interest in it's ability to provide a greater degree of low back pain coverage.

The neurostimulator pioneer company has been Medtronic, Inc. Because they were primarily a cardiac pacemaker company they made a corporate decision a number of years ago to turn their back on their Radiofrequency coupled implanted systems and focus on marketing only internal pulse generators (IPGs). By turning their back on these more compact and more reliable radiofrequency coupled systems Medtronic allowed other companies the opportunity entering into the neurostimulation business.

Shown here is what has been the typical bulky neurostimulator IPG which is similar to those used in cardiac pacemakers. The basic IPGs are powered by internal batteries which require surgery replacement. Typical clinical life in the past was 2-3 years.

The present generation of IPGs now represent a real advance in that they are quite compact and rechargeable from an external source. Shown here is the ANS "Mini Eon" which is presently estimated to have a 8-10 year life expectancy.

The new generation of mini-IPGs are now about the same size of a compact Radio Frequency (RF) receiver (shown here) which have been the most reliable systems over the past 30 years. Because they are activated by an external source the implanted components are inert

This illustration shows a radio-frequency (RF) coupled system where the batteries are in an external pulse generator. The RF receiver, which is about the size of a silver dollar, is placed under the skin and is activated by a small coil placed on the outside of the skin. The coil usually held in place with an adhesive pad. Anterior receiver placement is usually preferred so that the patient can properly place the transmitting external disc.

Courtesy Medtronic

In the illustration to the left a catheter electrode has been inserted through a percutaneously placed needle into the epidural space. This technique, which is performed under local anesthesia with sedation, is typically used as a screening procedure because it is relatively simple to perform. This ease of implantation has unfortunately made PENS electrodes the definitive implant for many pain management specialists (who are not surgeons). PENS systems are notorious for their instability and tendency to migrate following implantation.

In the example shown above PENS electrodes have been placed for long-term stimulation (as a definitive implant). Over a two month period there has been electrode migration causing failure of the neurostimulator requiring revision. This is not an uncommon circumstance. In the author's practice PENS electrodes are used only temporarily for screening purposes and are removed after about a week.

Shown here is a surgically implanted plate electrode into the epidural space. This procedure is typically performed under general anesthesia. Unlike PENS electrodes epidural plate electrodes have a high degree of stability and much less failure. In individuals who have had successful screening and testing the long-term good results are 60-65% on a long-term basis.

One of the more exciting observations, over the years, has been that some patients who have previously been disabled by pain are able to decrease their need for pain medications and are able to markedly increase exercise and activity to the point where the neurostimulator is no longer needed.

The Editor's experience, based on over 1,500 spinal cord neurostimulators implanted for the relief of intractable pain over a 35 year period, has indicated that when patients are carefully screened and the procedure is performed by appropriately trained and experienced specialists that there can, and should be, be a long-term success record. As with all medical devices and as with all surgeries there are potential serious complications and informed consent is important in regard to this. Fortunately, however, with neurostimulators the most likely complication is that of failure of the device itself, something which is typically repairable.