Inhibition of Cortical Laser‐Evoked Potentials by Transcutaneous Electrical Nerve Stimulation

Objectives. This study attempts to confirm the hypothesis that transcutaneous electrical stimulation (TENS) of peripheral Aβ fibers inhibits nociceptive processing, by quantifying the change of laser‐evoked potential (LEP) components, using a 980‐nm diode laser. Materials and Methods. Cutaneous heat stimuli were delivered to the dorsum of the right hand in 13 volunteers. LEPs and pain intensity ratings were recorded before, during, and after the use of TENS (110 Hz) at the dorsolateral forearm. Area under the curve (AUC), LEP amplitudes (N2P2), and peak latencies (N2, P2) were calculated. The paired samples t‐test was used for statistical analysis. Results. A significant reduction of LEP amplitudes and AUC was found during and after the use of TENS (p < 0.05). After 10 min of TENS this was associated with a clinically relevant decrease of pain intensity. Conclusions. Our data suggest that TENS inhibits nociceptive processing. Ten minutes of TENS exerts a clinically relevant pain reduction.     

Peripheral Nerve Field Stimulation: Is Age an Indicator of Outcome?

Objective. This study aims to assess peripheral nerve field stimulation as a treatment option for chronic pain and test for indicators of outcome. Materials and Methods. We reviewed all patients permanently implanted with peripheral nerve field stimulators over the past 24 months. A questionnaire was used to assess outcomes. Results. Twenty‐seven questionnaires were sent out and 23/27 responded. A significant average decrease of 4.02 visual analog scale points was observed. The average pain decrease for the low back was 3.77 points and 5.9 for occipital implants. An age effect was detected; younger patients (<60 years) reported an average pain relief of 4.79 points while older patients (>61 years) reported an average pain relief decrement of only 2.83 points. Most patients reported decreases in analgesic use after treatment. Pain relief was significantly and highly correlated with reduced analgesic intake and patient satisfaction. Conclusion. Peripheral nerve field stimulation is a safe, reversible, and effective treatment option for patients with chronic pain, particularly those under 60 years.     

Subcutaneous Peripheral Nerve Stimulation Treatment for Chronic Pelvic Pain

Two cases of chronic pelvic pain of unknown etiology with symptoms referable to the low abdominal wall are presented. These patients are often difficult to manage because of multiple causes and multiple pathways for pain transmission from the pelvis. In these cases, the patients’ complaints were refractory to medication management, as well as diagnostic and therapeutic nerve blockade. After careful evaluation, a successful trial of peripheral nerve stimulation was followed by permanent implantation of low abdominal subcutaneous leads and a pulse generator device. The patients reported excellent relief of their chronic pelvic pain. The use of neuromodulation via peripheral stimulation deserves further investigation as an alternative to spinal cord stimulation for chronic pelvic pain.     

Implantable Peripheral Nerve Stimulation for Trigeminal Neuropathic Pain: A Systematic Review and Meta-Analysis

ObjectivesImplantable peripheral nerve stimulation has been increasingly used to treat neuropathic pain. This neuromodulation strategy may be an alternative option for intractable trigeminal neuropathic pain; however, evidence for this treatment approach remains limited. A systematic review was conducted to identify studies of patients that underwent peripheral nerve stimulation implantation for trigeminal neuropathic pain.Materials and MethodsDatabases including, PubMed, EMBASE, and Cochrane Library were searched up to October 5, 2020. The primary outcomes were changes in pain scores and response rates of neuromodulation therapy. A random effects model was used for meta-analysis. Subgroup analysis was performed to examine the source of heterogeneity.ResultsThirteen studies including 221 participants were evaluated. The estimated response rate of neuromodulation treatment was 61.3% (95% CI: 44.4–75.9%, I² = 70.733%, p < 0.0001) at the last follow-up. The overall reduction in pain scores was 2.363 (95% CI: 1.408–3.319, I² = 85.723%, p < 0.0001). Subgroup analysis further confirmed that stimulation target (peripheral branch vs. trigeminal ganglion vs. trigeminal nerve root) contributed the heterogeneity across enrolled studies. Better clinical outcome was associated with stimulation of the trigeminal peripheral branch (p < 0.0001).ConclusionPeripheral nerve stimulation may be a promising approach in the management of trigeminal neuropathic pain, especially for patients intractable to conventional therapy.     

Peripheral Nerve Stimulation: A Treatment for Chronic Low Back Pain and Failed Back Surgery Syndrome?

Objective. This study aims to evaluate the usefulness of peripheral nerve stimulation as a treatment option for patients with chronic low back pain. Materials and Methods. More than 12 months, we collected data on consecutive patients who had successful trials and were subsequently implanted with octrode percutaneous leads placed subcutaneously within the major area of pain. Eleven patients met diagnostic criteria for failed back surgery syndrome. A questionnaire assessed outcomes including: pain, analgesic use, and patient satisfaction. The response rate was 93% (13/14): average follow‐up time was seven months. Results. There was a significant decrease in pain levels: an average reduction of 3.77 visual analog scale points. Eleven patients (85%) reported successful outcomes and an average pain reduction of 4.18 points but two reported a poor response. Pain relief was highly correlated with reduced analgesia and patient satisfaction. No complications were reported. Conclusion. This study demonstrates a treatment option that is safe, nonpharmacologic, reversible, and effective for patients with chronic low back pain that have exhausted other treatment options.     

Peripheral Nerve Stimulation for Back Pain in Patients With Multiple Myeloma as Bridge Therapy to Radiation Treatment: A Case Series

ObjectivesPatients with spinal lesions or vertebral compression fractures from multiple myeloma often present with back pain that restricts their ability to lie flat and prevents them from undergoing cancer treatment. Temporary, percutaneous peripheral nerve stimulation (PNS) has been described for cancer pain secondary to oncologic surgery or neuropathy/radiculopathy from tumor invasion. The purpose of this case series is to show the use of PNS as an analgesic bridge therapy to treat myeloma-related back pain and allow patients to complete their course of radiation.Materials and MethodsTemporary, percutaneous PNS was placed under fluoroscopic guidance for four patients with unremitting low back pain secondary to myelomatous spinal lesions. Before PNS, the patients had pain refractory to medical management and were unable to tolerate radiation mapping and treatment owing to low back pain while supine. Patients were followed with routine clinic visits to monitor pain and progression through cancer therapy. PNS was removed after approximately 60 days or after completion of radiation.ResultsThis case series presents four successful cases of PNS to treat low back pain from myelomatous spinal lesions and associated vertebral compression fractures. PNS targeted the medial branch nerves to treat both nociceptive and neuropathic low back pain. All four patients successfully completed radiation therapy with PNS in place.ConclusionsPNS can effectively treat low back pain secondary to myeloma-related spinal lesions as a bridge therapy to radiation. The use of PNS is a promising option for back pain from other primary or metastatic tumors. Further research is needed into the use of PNS for cancer-related back pain.     

A Functional Near-infrared Spectroscopy Study to Detect Activation of Somatosensory Cortex by Peripheral Nerve Stimulation

Introduction  Multi-channel near-infrared spectroscopy (NIRS) is a method for non-invasively monitoring of relative concentrations of oxygenated, deoxygenated, and total hemoglobin. This technique has found expanding application in brain mapping and functional imaging. The purpose of this study was to investigate whether activation of somatosensory cortex can be detected without the necessity of the patient’s cooperation in performing a task. Methods  Real-time bilateral parietotemporal cerebral oxygenation was monitored in 12 healthy volunteers. The median nerve at the wrist was electrically stimulated repeatedly at an amplitude below the threshold of discomfort. Interstimulus intervals were randomized between 13 and 31 s to minimize synchronization with respiration or other natural oscillations in cerebral oxygenation. Results  In 8 of the 12 subjects, activation over the contralateral primary somatosensory cortex was detected, correlating significantly with the predicted hemodynamic response function. Conclusions  To our knowledge, this is the first time functional NIRS has been used to detect activation of somatosensory cortex with peripheral nerve stimulation. While the sensitivity for detection of the functional hemodynamic response was inadequate for clinical diagnostics, these findings are uniquely important in critical care imaging in that the regional blood flow and oxygenation changes can be detected without the requirement of a volitional task. This advancement potentially expands the capability of this modality to be used in brain mapping and in the evaluation of patients with impaired cognitive or motor function at the bedside.     

Electrophysiologic Studies of Cervical Vagus Nerve Stimulation in Humans: II. Evoked Potentials

Evidence from studies of experimental animals indicates that electrical stimulation of the vagus nerve not only can alter the EEG but evokes activity in specific brain areas. We report effects of electrical stimulation of the vagus nerve in 9 patients with medically intractable seizures as part of a clinical trial of chronic vagal stimulation for control of epilepsy. The left vagus nerve in the neck was stimulated with a programmable implanted stimulator. Effects of stimulus amplitude, duration, and rate were studied. Noncephalic reference recording of the vagus nerve evoked potential showed some unusual properties: a scalp negative component occurred with a latency of 12 ms, very high amplitude (< or = 60 microV), and widespread scalp distribution. Field distribution studies indicated that this potential was myogenic in origin and generated in the region of the stimulating electrodes in the neck area. Chemically induced muscle paralysis confirmed this observation. Bipolar scalp recording showed several small-amplitude topographically distinct potentials occurring in 30 ms. No effect, either acute or chronic, could be detected on pattern-reversal evoked potentials, auditory brainstem evoked potentials, auditory 40-Hz potentials, or cognitive evoked potentials.     

An Innovative Case Report Detailing the Successful Treatment of Post‐Thoracotomy Syndrome with Peripheral Nerve Field Stimulation

Introduction: The detrimental effects of post‐thoracotomy pain syndrome is experienced worldwide; however, an effective treatment regimen remains elusive. Methods: We report a case of post‐thoracotomy pain syndrome effectively treated with peripheral nerve field stimulation (PNfS). Results: In the presented case, the patient underwent permanent placement of the PSfS device after a successful trial period. Upon follow‐up the patient has reported even better coverage over her painful areas and admits to 80% and higher reductions in her painful symptoms. Conclusion: Although the data are limited, in the aforesaid case report, post‐thoracotomy syndrome was effectively treated with the use of PNfS. This resulted in a significant pain perception reduction, increased quality of life and mobility, as well as decreased usage of oral pain medications. This adds to the accumulating case report and case series data that suggest PNfS is showing great promise as a pain reduction modality. Further, it is minimally invasive, can be trialled prior to implantation, and is reversible. Large prospective studies will be required in the future to further evaluate its efficacy before it can be widely accepted and adopted.