Peripheral Nerve Stimulation

Published on 24/02/2015 by admin

Filed under Anesthesiology

Last modified 24/02/2015

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 1089 times

Chapter 16 Peripheral Nerve Stimulation

Chapter Overview

Chapter Synopsis: Electrical stimulation of a peripheral nerve (PNS) can be used to treat neuropathic pain, ideally that arises from a single nerve and often follows peripheral nerve damage. This chapter considers the issues relevant to successful PNS. The conditions most amenable to PNS include occipital neuralgia, peripheral neuropathic pain, and trigeminal branch pain. With a more regional subcutaneous stimulation, PNS can affect lower back pain and migraine headache. Similar to spinal cord stimulation, our understanding of the mechanism behind PNS is rooted in Melzack and Wall’s gate control theory of pain: stimulation of large-diameter fibers decreases the pain signaling from small-fiber neurons. Other hypotheses suggest that PNS may result in peripheral nerve block or other peripheral changes in action potential kinetics to suppress pain. PNS was traditionally delivered with a cuff electrode wrapped around the target nerve, but this can lead to perineural fibrosis. Today, plate or wire electrodes are more commonly implanted, either surgically or percutaneously. An implantable pulse generator is commonly implanted in the abdominal wall or gluteal region. With surgical implantation, a piece of fascia may be implanted between the electrode and the nerve itself, fulfilling a role analogous to the dura mater in implantation of a spinal cord stimulator. Percutaneous implantation carries its own set of considerations. More recently, the leadless bionic neuron (BION) system has been developed with an eye toward PNS.

Important Points:

Clinical Pearls:

Clinical Pitfalls:

Introduction

Peripheral nerve stimulation (PNS) has been recognized as a treatment modality for peripheral neuropathic pain beginning with Wall and Sweet’s original description in 1967.1 By inserting percutaneous needle electrodes into their own infraorbital regions, these authors were able to test the effects of stimulation on peripheral nerves. Through stimulation with square-wave pulses at 100 Hz and with a pulse width of 100 msec, they were able to induce diminished sensation to pin prick in the area of the stimulation. This led the way to investigations of PNS as a modality for treating neuropathic pain.

The last two decades have seen an increased interest in the use of PNS with application to occipital neuralgia, facial pain, and complex regional pain syndrome.2 In addition to targeting defined peripheral nerves, clinicians are also applying the techniques of PNS to subcutaneous and regional stimulation.3,4 This has led to a number of trials assessing the efficacy of PNS for a wide array of conditions, including lower back pain, postherniorrhaphy inguinal pain, sacral pain, and migraine headaches.5

Basic Science

Our understanding of the mechanism underlying PNS is still being developed. One hypothesis for achieving pain control with PNS involves the gate control theory of pain management proposed by Melzack and Wall in 1965.6 In their initial description of the gate theory, the authors postulated that large- and small-diameter fibers both send input to inhibitory neurons within the substantia gelatinosa. They theorized that small-diameter fibers provided inhibitory input to the substantia gelatinosa and the large-diameter fibers provided excitatory input. The summation of these inputs modulated the overall inhibitory connections from the substantia gelatinosa neurons to the dorsal horn transmission (T) cells, the projections of which formed the anterolateral system. In accordance with this theory, an increase in large-diameter afferent input would lead to increased inhibitory output from the substantia gelatinosa and consequently decreased transmission of nociceptive input to suprasegmental centers. Thus neurostimulation of peripheral nerves through its effect on the lowest threshold large-diameter fibers would act to “close the gate,” effectively inhibiting the transmission of small-diameter pain fibers. Although the gate control theory provides a framework for understanding the mechanism of PNS, the specifics have been challenged.7

Other investigators have shown additional mechanisms that may contribute to the potential efficacy of PNS. Campbell and Taub8 explored the mechanism of PNS through transcutaneous nerve stimulation of the median nerve. The authors stimulated the median nerve proximally with a 100-Hz, 1-msec stimulus. They found that the response elicited depended on the stimulus amplitude. At 10 V to 12 V touch threshold was elevated. With increased voltage pain thresholds were also elevated, and at intensities of 50 V analgesia was elicited. In addition, the development of analgesia was correlated with the loss of the Aδ portion of the compound action potential, suggesting that peripheral nerve transmission block may underlie the suppression of pain by PNS.

Ignelzi and Nyquist9 further explored the mechanism of PNS by placing cuff PNS electrodes around the sural and superficial radial nerves of cats. They found that, with stimulation, all of the components of the compound action potential were affected, although the Aδ fiber peak was more affected following neurostimulation than were the Aα or Aβ peaks. The changes were represented by either a reduction in amplitude or an increase in the latency of these waves. These findings also support the involvement of a more peripheral mechanism underlying the analgesic effect of PNS.

Indications/Contraindications

Indications

PNS is usually indicated for patients with peripheral neuropathic pain that can be attributed to a single peripheral nerve.10 Candidates for PNS should have undergone multimodal therapy, including medical management, anesthetic blockade, and physical therapy. As with patients who are being evaluated for spinal cord stimulation, neuropsychological testing can be valuable. In addition, before permanent implantation of the internal pulse generator, patients should have undergone a successful trial of stimulation with a predetermined therapeutic benefit.

More recent studies of subcutaneous target stimulation (STS) and regional stimulation have broadened the traditional inclusion criteria of neuropathic pain attributable to a single peripheral nerve.11 Retrospective case series of subcutaneous stimulation applied to painful areas has demonstrated therapeutic benefit for lower back pain, neck pain, inguinal pain, and others. However, the longer-term efficacy for this application is unknown.