Long term clinical outcome of peripheral nerve stimulation in patients with chronic peripheral neuropathic pain

The Neurostimulation Appropriateness Consensus Committee (NACC)®: Recommendations for Spinal Cord Stimulation Long-Term Outcome Optimization and Salvage Therapy

INTRODUCTION

The International Neuromodulation Society (INS) has recognized a need to establish best practices for optimizing implantable devices and salvage when ideal outcomes are not realized. This group has established the Neurostimulation Appropriateness Consensus Committee (NACC)® to offer guidance on matters needed for both our members and the broader community of those affected by neuromodulation devices.

MATERIALS AND METHODS

The executive committee of the INS nominated faculty for this NACC® publication on the basis of expertise, publications, and career work on the issue. In addition, the faculty was chosen in consideration of diversity and inclusion of different career paths and demographic categories. Once chosen, the faculty was asked to grade current evidence and along with expert opinion create consensus recommendations to address the lapses in information on this topic.

RESULTS

The NACC® group established informative and authoritative recommendations on the salvage and optimization of care for those with indwelling devices. The recommendations are based on evidence and expert opinion and will be expected to evolve as new data are generated for each topic.

CONCLUSIONS

NACC® guidance should be considered for any patient with less-than-optimal outcomes with a stimulation device implanted for treating chronic pain. Consideration should be given to these consensus points to salvage a potentially failed device before explant.

Combined optogenetic and electrical stimulation of the sciatic nerve for selective control of sensory fibers

Introduction

Electrical stimulation offers a drug-free alternative for the treatment of many neurological conditions, such as chronic pain. However, it is not easy to selectively activate afferent or efferent fibers of mixed nerves, nor their functional subtypes. Optogenetics overcomes these issues by controlling activity selectively in genetically modified fibers, however the reliability of responses to light are poor compared to electrical stimulation and the high intensities of light required present considerable translational challenges. In this study we employed a combined protocol of optical and electrical stimulation to the sciatic nerve in an optogenetic mouse model to allow for better selectivity, efficiency, and safety to overcome fundamental limitations of electrical-only and optical-only stimulation.

Methods

The sciatic nerve was surgically exposed in anesthetized mice (n = 12) expressing the ChR2-H134R opsin via the parvalbumin promoter. A custom-made peripheral nerve cuff electrode and a 452 nm laser-coupled optical fiber were used to elicit neural activity utilizing optical-only, electrical-only, or combined stimulation. Activation thresholds for the individual and combined responses were measured.

Results

Optically evoked responses had a conduction velocity of 34.3 m/s, consistent with ChR2-H134R expression in proprioceptive and low-threshold mechanoreceptor (Aα/Aβ) fibers which was also confirmed via immunohistochemical methods. Combined stimulation, utilizing a 1 ms near-threshold light pulse followed by an electrical pulse 0.5 ms later, approximately halved the electrical threshold for activation (p = 0.006, n = 5) and resulted in a 5.5 dB increase in the Aα/Aβ hybrid response amplitude compared to the electrical-only response at equivalent electrical levels (p = 0.003, n = 6). As a result, there was a 3.25 dB increase in the therapeutic stimulation window between the Aα/Aβ fiber and myogenic thresholds (p = 0.008, n = 4).

Discussion

The results demonstrate that light can be used to prime the optogenetically modified neural population to reside near threshold, thereby selectively reducing the electrical threshold for neural activation in these fibers. This reduces the amount of light needed for activation for increased safety and reduces potential off-target effects by only stimulating the fibers of interest. Since Aα/Aβ fibers are potential targets for neuromodulation in chronic pain conditions, these findings could be used to develop effective strategies to selectively manipulate pain transmission pathways in the periphery.

Evidence-Based Clinical Guidelines from the American Society of Pain and Neuroscience for the Use of Implantable Peripheral Nerve Stimulation in the Treatment of Chronic Pain

The objective of this peripheral nerve stimulation consensus guideline is to add to the current family of consensus practice guidelines and incorporate a systematic review process. The published literature was searched from relevant electronic databases, including PubMed, Scopus, Cochrane Central Register of Controlled Trials, and Web of Science from database inception to March 29, 2021. Inclusion criteria encompassed studies that described peripheral nerve stimulation in patients in terms of clinical outcomes for various pain conditions, physiological mechanism of action, surgical technique, technique of placement, and adverse events. Twenty randomized controlled trials and 33 prospective observational studies were included in the systematic review process. There is Level I evidence supporting the efficacy of PNS for treatment of chronic migraine headaches via occipital nerve stimulation; chronic hemiplegic shoulder pain via stimulation of nerves innervating the trapezius, supraspinatus, and deltoid muscles; failed back surgery syndrome via subcutaneous peripheral field stimulation; and lower extremity neuropathic and lower extremity post-amputation pain. Evidence from current Level I studies combined with newer technologies facilitating less invasive and easier electrode placement make peripheral nerve stimulation an attractive alternative for managing patients with complex pain disorders. Peripheral nerve stimulation should be used judiciously as an adjunct for chronic and acute postoperative pain following adequate patient screening and positive diagnostic nerve block or stimulation trial.

Peripheral Nerve Stimulation for Chronic Pain: A Systematic Review of Effectiveness and Safety

Peripheral nerve stimulation (PNS) was the first application of neuromodulation. Widespread application of PNS was limited by technical concerns. Recent advances now allow the percutaneous placement of leads with ultrasound or fluoroscopic guidance, while the transcutaneous powering of these leads removes the need for leads to cross major joints. This systematic review was written to assess the current status of high-quality evidence supporting the use of PNS for pain conditions treated by interventional pain physicians. The available literature on PNS, limited to conditions treated by interventional pain physicians, was reviewed and the quality assessed. Literature from 1966 to June 2021 was reviewed. The outcome measures were pain relief and functional improvement. One hundred and two studies were identified. Five randomized controlled trials (RCT) and four observational studies, all case series, met the inclusion criteria. One RCT was of high quality and four were of moderate quality; all four case series were of moderate quality. Three of the RCTs and all four case series evaluated peripheral nerve neuropathic pain. Based upon these studies, there is level II evidence supporting the use of PNS to treat refractory peripheral nerve injury. One moderate-quality RCT evaluated tibial nerve stimulation for pelvic pain, providing level III evidence for this indication. One moderate-quality RCT evaluated surgically placed cylindrical leads for cluster headaches, providing level III evidence for this indication. The evidence suggests that approximately two-thirds of patients with peripheral neuropathic pain will have at least 50% sustained pain relief. Adverse events from PNS are generally minor. A major advantage of PNS over spinal cord stimulation is the absence of any risk of central cord injury. The study was limited by the paucity of literature for some indications. No studies dealt with joint-related osteoarthritic pain.

Peripherally Induced Reconditioning of the Central Nervous System: A Proposed Mechanistic Theory for Sustained Relief of Chronic Pain with Percutaneous Peripheral Nerve Stimulation

Peripheral nerve stimulation (PNS) is an effective tool for the treatment of chronic pain, although its efficacy and utilization have previously been significantly limited by technology. In recent years, purpose-built percutaneous PNS devices have been developed to overcome the limitations of conventional permanently implanted neurostimulation devices. Recent clinical evidence suggests clinically significant and sustained reductions in pain can persist well beyond the PNS treatment period, outcomes that have not previously been observed with conventional permanently implanted neurostimulation devices. This narrative review summarizes mechanistic processes that contribute to chronic pain, and the potential mechanisms by which selective large diameter afferent fiber activation may reverse these changes to induce a prolonged reduction in pain. The interplay of these mechanisms, supported by data in chronic pain states that have been effectively treated with percutaneous PNS, will also be discussed in support of a new theory of pain management in neuromodulation: Peripherally Induced Reconditioning of the Central Nervous System (CNS).

Direct Peripheral Nerve Stimulation for the Treatment of Complex Regional Pain Syndrome: A 30-Year Review

INTRODUCTION

Complex regional pain syndrome (CRPS), formerly known as reflex sympathetic dystrophy (RSD), is a difficult to treat condition characterized by debilitating pain and limitations in functional ability. Neuromodulation, in the form of spinal cord stimulation (SCS) and peripheral nerve stimulation (PNS), have been traditionally used as a treatment for CRPS with variable success.

OBJECTIVE

This chart review describes the use of implantable PNS systems in the treatment of CRPS of the upper and lower extremities spanning nearly three decades.

MATERIALS AND METHODS

A retrospective chart review was performed on 240 patients with PNS implanted between 1990 and 2017 at our institution. Of these, 165 patients were identified who had PNS systems implanted for a diagnosis of CRPS. Patient profile, including baseline characteristics, comorbidities, past/current interventions/medications and targeted nerves, was descriptively summarized through standard summary statistics. Patients' pain scores and opioid consumptions at baseline (preimplant), 1 month, 6 months, and 12 months were collected and compared. Device revisions and explants were summarized, and patient functional outcomes were described.

RESULTS

Pain scores at baseline and at 12-month follow-up were decreased from a mean of 7.4 ± 1.6 to 5.5 ± 2.4 and estimated to be 1.87 (95% CI: [1.29, 2.46], paired t-test p-value <0.001) lower at 12 months. At baseline, 62% of patients were on chronic opioid therapy, compared with 41% at 12 months. Of 126 patients who reported changes in functional status, 64 (51%) reported improvement, 27 (21%) reported worsening, and 35 (28%) did not report any meaningful change. Excluding end-of-life battery replacements, surgical revision occurred in 56 (34%) of patients. Thirteen patients (8%) underwent implantation of a second PNS because of symptomatic expansion outside of the original painful region. Device explant was performed in 32 (19%) of patients. Median length of follow-up was 74 [14, 147] months. Of the 36 patients who continue to follow-up at our institution, 29 (81%) continue to use their PNS.

CONCLUSIONS

We can conclude that PNS is a useful modality to improve function and reduce long-term pain in selected patients suffering from CRPS type I and type II.

Median Nerve Stimulation as a Nonpharmacological Approach to Bypass Analgesic Tolerance to Morphine: A Proof-of-Concept Study in Mice

Analgesic tolerance to opioids contributes to the opioid crisis by increasing the quantity of opioids prescribed and consumed. Thus, there is a need to develop non-opioid-based pain-relieving regimens as well as strategies to circumvent opioid tolerance. Previously, we revealed a non-opioid analgesic mechanism induced by median nerve electrostimulation at the overlaying PC6 (Neiguan) acupoint (MNS-PC6). Here, we further examined the efficacy of MNS-PC6 in morphine-tolerant mice with neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve. Daily treatments of MNS-PC6 (2 Hz, 2 mA), but not electrostimulation at a nonmedian nerve-innervated location, for a week post-CCI induction significantly suppressed established mechanical allodynia in CCI-mice in an orexin-1 (OX₁) and cannabinoid-1 (CB₁) receptor-dependent fashion. This antiallodynic effect induced by repeated MNS-PC6 was comparable to that induced by repeated gabapentin (50 mg/kg, i.p.) or single morphine (10 mg/kg, i.p.) treatments, but without tolerance, unlike repeated morphine-induced analgesia. Furthermore, single and repeated MNS-PC6 treatments remained fully effective in morphine-tolerant CCI-mice, also in an OX₁ and CB₁ receptor-dependent fashion. In CCI-mice receiving escalating doses of morphine for 21 days (10, 20 and 50 mg/kg), single and repeated MNS-PC6 treatments remained fully effective. Therefore, repeated MNS-PC6 treatments induce analgesia without tolerance, and retain efficacy in opioid-tolerant mice via a mechanism that involves OX₁ and CB₁ receptors. This study suggests that MNS-PC6 is an alternative pain management strategy that maybe useful for combatting the opioid epidemic, and opioid-tolerant patients receiving palliative care. PERSPECTIVE: Median nerve stimulation relieves neuropathic pain in mice without tolerance and retains efficacy even in mice with analgesic tolerance to escalating doses of morphine, via an opioid-independent, orexin-endocannabinoid-mediated mechanism. This study provides a proof of concept for utilizing peripheral nerve stimulating devices for pain management in opioid-tolerant patients.

Peripheral Nerve Stimulation of the Brachial Plexus for Chronic Refractory CRPS Pain of the Upper Limb: Description of a New Technique and Case Series

OBJECTIVE

Upper limb complex regional pain syndrome is an important cause of chronic pain, and its treatment is challenging. In this pilot case series, we preliminarily evaluated the feasibility, effectiveness, and safety of a new technique for brachial plexus neuromodulation in the treatment of this disease in patients refractory to conservative treatment.

METHODS

Between 2017 and 2018, 14 patients considered to be refractory to optimized conservative treatment were recruited to this study. In the first stage, patients were trialed for seven days with a new technique of implant of the brachial plexus. Patients with ≥50% pain relief in visual analog scale (VAS) score received a definitive implantation in the second stage. Follow-ups were conducted at pre-implant and 12 months using the Neuropathic Pain Scale, SF-32, and the visual analogic scale for pain.

RESULTS

After the initial trial, 10 patients had a pain reduction of ≥50% and received a permanent implant. At 12-month follow-up, VAS, Neuropathic Pain Scale, SF-12 physical and mental scores improved by 57.4% +/- 10% (P = 0.005), 60.2% +/- 12.9% (P = 0.006), and 21.9% +/- 5.9% (P = 0.015), respectively.

CONCLUSIONS

Our data suggest that this new technique of brachial plexus stimulation may have long-term utility in the treatment of painful upper limb complex regional pain syndrome. New more detailed comprehensive studies should be carried out to confirm our findings in a larger population and to further refine the clinical implementation of this technique.

Refractory neuropathic pain from a median nerve injury: spinal cord or peripheral nerve stimulation? A case report

Spinal cord stimulation (SCS) is the most frequently used neuromodulation technique even for neurogenic pain from a peripheral nerve injury although peripheral nerve stimulation (PNS) has been designed for this purpose. PNS appears less invasive than SCS or deep brain stimulation. It provides greater and specific target coverage and it could be more cost-effective than SCS because low electrical stimulation is exclusively delivered to the precise painful territory. We report a case of excellent result following median nerve stimulation at arm level after SCS failure and a 10-year history of intense pain. PNS would certainly have been considered much earlier if it was accepted and reimbursed by the Belgium National Insurance. PNS is a safe, simple, and efficient technique available for decades but it is still considered as experimental and underemployed. Belgian National Insurance fears an explosion of indications on neuromodulation if PNS was reimbursed. We consider that PNS aside SCS and other neuromodulation techniques should be made available in Belgium in case of peripheral chronic neuropathic pain.

Median nerve stimulation induces analgesia via orexin-initiated endocannabinoid disinhibition in the periaqueductal gray

Adequate pain management remains an unmet medical need. We previously revealed an opioid-independent analgesic mechanism mediated by orexin 1 receptor (OX1R)-initiated 2-arachidonoylglycerol (2-AG) signaling in the ventrolateral periaqueductal gray (vlPAG). Here, we found that low-frequency median nerve stimulation (MNS) through acupuncture needles at the PC6 (Neiguan) acupoint (MNS-PC6) induced an antinociceptive effect that engaged this mechanism. In mice, MNS-PC6 reduced acute thermal nociceptive responses and neuropathy-induced mechanical allodynia, increased the number of c-Fos-immunoreactive hypothalamic orexin neurons, and led to higher orexin A and lower GABA levels in the vlPAG. Such responses were not seen in mice with PC6 needle insertion only or electrical stimulation of the lateral deltoid, a nonmedian nerve-innervated location. Directly stimulating the surgically exposed median nerve also increased vlPAG orexin A levels. MNS-PC6-induced antinociception (MNS-PC6-IA) was prevented by proximal block of the median nerve with lidocaine as well as by systemic or intravlPAG injection of an antagonist of OX1Rs or cannabinoid 1 receptors (CB1Rs) but not by opioid receptor antagonists. Systemic blockade of OX1Rs or CB1Rs also restored vlPAG GABA levels after MNS-PC6. A cannabinoid (2-AG)-dependent mechanism was also implicated by the observations that MNS-PC6-IA was prevented by intravlPAG inhibition of 2-AG synthesis and was attenuated in Cnr1 ^-/- mice. These findings suggest that PC6-targeting low-frequency MNS activates hypothalamic orexin neurons, releasing orexins to induce analgesia through a CB1R-dependent cascade mediated by OX1R-initiated 2-AG retrograde disinhibition in the vlPAG. The opioid-independent characteristic of MNS-PC6-induced analgesia may provide a strategy for pain management in opioid-tolerant patients.

Peripheral Nerve Stimulation of Brachial Plexus Nerve Roots and Supra-Scapular Nerve for Chronic Refractory Neuropathic Pain of the Upper Limb

OBJECTIVES

We report the outcome of a consecutive series of 26 patients suffering from chronic medically-refractory neuropathic pain of the upper limb (including 16 patients with complex regional pain syndrome), topographically limited, treated by brachial plexus (BP) nerve roots or supra-scapular nerve (SSN) peripheral nerve stimulation (PNS).

MATERIALS AND METHODS

The technique consisted in ultrasound-guided percutaneous implantation of a cylindrical lead (Pisces-Quad, Medtronic) close to the SSN or the cervical nerve roots within the BP, depending on the pain topography. All the patients underwent a positive trial stimulation before lead connection to a subcutaneous stimulator. Chronic bipolar stimulation mean parameters were: frequency 55.5 Hertz, voltage 1.17 Volts. The voltage was set below the threshold inducing muscle contractions or paresthesias.

RESULTS

Two patients were lost immediately after surgery. At last follow-up (mean 27.5 months), the 20 patients still using the stimulation experienced a mean pain relief of 67.1%. Seventeen patients were improved ≥50%, including 12 improved ≥70%. In 11 patients with a follow-up >2 years, the mean pain relief was 68%. At last follow-up, respectively, six out of the nine (67%) patients treated by SSN stimulation and 10 out of 17 patients (59%) treated by BP stimulation were improved ≥50%. At last follow-up, 12 out of 20 patients still using the stimulation were very satisfied, six were satisfied, and two were poorly satisfied. Complications were: stimulation intolerance due to shock-like sensations (three cases), superficial infection (1), lead fractures (2), and migration (1).

CONCLUSION

In this pilot study, SSN or BP roots PNS provided a relatively safe, durable and effective option to control upper limb neuropathic pain.

Chronic post-traumatic neuropathic pain of brachial plexus and upper limb: a new technique of peripheral nerve stimulation

The aim of the study was to evaluate the effect on pain relief in patients with peripheral neuropathic pain after brachial plexus injuries using an implanted peripheral nerve stimulator applied directly to the nerve branch involved into the axillary cavity. Seven patients with post-traumatic brachial plexus lesions or distal peripheral nerve complaining of severe intractable chronic pain were enrolled in a single-centre, open-label trial. Conventional drugs and traditional surgical treatment were not effective. Patients underwent careful neurological evaluation, pain questionnaires and quantitative sensory testing (QST). Surgical treatment consists of a new surgical technique: a quadripolar electrode lead was placed directly on the sensory peripheral branch of the main nerve involved, proximally to the site of lesion, into the axillary cavity. To assess the effect, we performed a complete neuroalgological evaluation and QST battery after 1 week and again after 1, 6 and 12 weeks. All patients at baseline experienced severe pain with severe positive phenomena in the median (5) and/or radial (2) territory. After turning on the neuro-stimulator system, all patients experienced pain relief within a few minutes (>75 % and >95 % in most), with long-lasting pain relief with a reduction in mean Numerical Rating Scale (NRS) of 76.2 % after 6 months and of 71.5 % after 12 months. No significant adverse events occurred. We recommend and encourage this surgical technique for safety reasons; complications such as dislocation of electrocatheters are avoided. The peripheral nerve stimulation is effective and in severe neuropathic pain after post-traumatic nerve injuries of the upper limbs.

Predicting outcome in peripheral nerve stimulation for chronic neuropathic pain

OBJECTIVE

The aim of the study was to investigate the predictive value of percutaneous electrical nerve stimulation (PENS) in peripheral nerve stimulation (PNS) for chronic neuropathic pain.

MATERIALS AND METHODS

Twelve patients being evaluated for PNS for chronic neuropathic pain were included in this survey. Stimulation with acupuncture needles was applied with continuous high frequency stimulation. Position, polarity, frequency and amperage threshold of perception, and adverse effects were noted. Additional stimulation side effects were documented. A StimScore was developed to evaluate effects in a standardized manner. This StimScore comprises coverage of the painful area, therapeutic range, and amperage required for successful stimulation. StimScore was determined during PENS, during test stimulation, and under final stimulation.

RESULTS

PNS was well tolerated by all patients. Seven of the 12 patients (58%) were classified as successfully treated, and 5/12 patients (42%) as unsuccessful. The mean overall pain reduction in the first group was 4.0 points (SD = 2.87, P = 0.010) and 2.4 points (SD = 1.29, P = 0.014), respectively, on the visual analogue scale. In the successful stimulation group, a mean StimScore of 13.14 (SD 11.19-15.0) was calculated vs. 10.4 (95% CI 8.52-12.28) in the unsuccessful stimulation group (P = 0.033, 95% CI = 0.265-5.220).

CONCLUSIONS

Predicting response to PNS is crucial to reduce the number of patients implanted in vain. To adopt PENS via electroacupuncture needles as a percutaneous simulation method for PNS seemed to be feasible. The technique presented herein bears the potential to improve patient selection combined with reduced invasiveness. The presented results are encouraging and deliver a starting point for further trials.

Subcutaneous peripheral neurostimulation for the treatment of severe chronic poststernotomy neuralgia

OBJECTIVE

Poststernotomy pain frequently develops after sternotomy in thoracic and cardiovascular surgery, and may affect patients' quality of life. In some cases of severe poststernotomy neuralgia, pharmacologic therapy does not provide adequate relief.

CASE REPORT

We report on a 42- year-old woman who underwent sternotomy for aortic and mitral valve replacement. She developed severe chronic poststernotomy neuralgia that was refractory to medical treatment. After local anesthesia markedly but only transiently alleviated pain, we considered the option of subcutaneous peripheral neurostimulation (SPNS). Plate electrodes were implanted bilaterally in the parasternal region at the site of maximal pain. After a period of test stimulation, the electrodes were connected to a dual-channel implantable pulse generator. SPNS induced paresthesias in the painful area. Revision surgery was necessary twice because of electrode migration. Chronic SPNS markedly alleviated pain (visual-analog scale, VAS, 9/10 preoperatively, 2/10 postoperatively) and allodynia (VAS 9/10 preoperatively, 2/10 postoperatively) at the last available follow-up, 15 months postoperatively.

CONCLUSIONS

SPNS may be a viable treatment option in patients with severe chronic poststernotomy neuralgia.

Recent advances in the treatment of pain

Cancer pain and chronic non-malignant pain can be difficult to manage and may not respond satisfactorily to standard analgesics. Sequential empiric analgesic trials are usually done to manage individual patients. Experimental human pain models have helped to clarify mechanisms of opioid and adjuvant analgesic actions. Combinations of opioids and adjuvant analgesics better relieve pain than either opioids or adjuvant analgesics alone, as demonstrated in randomized controlled trials. The analgesic activity of antidepressants is largely dependent upon norepinephrine reuptake and activation of alpha 2 adrenergic receptors. Corticosteroids reduce postoperative orthopedic incident pain, which may allow patients to ambulate earlier and with less pain. Spinal corticosteroids reduce lower hemibody pain. Gabapentinoids as single high doses reduce postoperative pain and certain acute pain syndromes. Individuals who experience flares of pain while on spinal opioids benefit from intrathecal boluses of levobupivicaine or sublingual ketamine. Interventional approaches to pain management are often necessary due to the limitations of systemic analgesics. Electronics stimulators (peripheral, spinal and motor cortex) improve difficult to manage chronic pain syndromes. Pulsed radiofrequency reduces pain without tissue damage, which could be an advantage over chemical or radiofrequency neurotomy. Botulinum toxin A reduces focal neuropathic pain that is durable. Interventional related successes in relieving pain are operator dependent. Most reported benefits of systemic and regional analgesics and interventional approaches to pain relief are not based on randomized trials and are subject to selection bias, sampling error, and placebo responses, which may over-inflate reported benefits. Randomized controlled trials are needed to confirm reported benefits.