Dorsal Root Ganglion Stimulation Is Paresthesia-Independent: A Retrospective Study

Blocking Aδ- and C-fiber neural transmission by sub-kilohertz peripheral nerve stimulation

Introduction

We recently showed that sub-kilohertz electrical stimulation of the afferent somata in the dorsal root ganglia (DRG) reversibly blocks afferent transmission. Here, we further investigated whether similar conduction block can be achieved by stimulating the nerve trunk with electrical peripheral nerve stimulation (ePNS).

Methods

We explored the mechanisms and parameters of conduction block by ePNS via ex vivo single-fiber recordings from two somatic (sciatic and saphenous) and one autonomic (vagal) nerves harvested from mice. Action potentials were evoked on one end of the nerve and recorded on the other end from teased nerve filaments, i.e., single-fiber recordings. ePNS was delivered in the middle of the nerve trunk using a glass suction electrode at frequencies of 5, 10, 50, 100, 500, and 1000 Hz.

Results

Suprathreshold ePNS reversibly blocks axonal neural transmission of both thinly myelinated Aδ-fiber axons and unmyelinated C-fiber axons. ePNS leads to a progressive decrease in conduction velocity (CV) until transmission blockage, suggesting activity-dependent conduction slowing. The blocking efficiency is dependent on the axonal conduction velocity, with Aδ-fibers efficiently blocked by 50-1000 Hz stimulation and C-fibers blocked by 10-50 Hz. The corresponding NEURON simulation of action potential transmission indicates that the disrupted transmembrane sodium and potassium concentration gradients underly the transmission block by the ePNS.

Discussion

The current study provides direct evidence of reversible Aδ- and C-fiber transmission blockage by low-frequency (<100 Hz) electrical stimulation of the nerve trunk, a previously overlooked mechanism that can be harnessed to enhance the therapeutic effect of ePNS in treating neurological disorders.

Effectiveness of Dorsal Root Ganglion Stimulation in Chronic Pain Management: A Systematic Review

OBJECTIVE

This systematic review aims to determine the effectiveness of dorsal root ganglion stimulation (DRGS) in chronic pain management.

METHODS

In 2023, a comprehensive systematic review was undertaken utilizing various electronic databases, employing MeSH terms and free search terms tailored to the study's aims. This review included primary research such as cohorts, case-control studies, and clinical trials, all focusing on the efficacy of DRGS in treating various chronic pain conditions. Nonhuman or animal studies were omitted from the selection process. A review of study quality was conducted, followed by a meticulous analysis of the findings to synthesize the evidence. This review represents the most current research, with updates extending to 2024. A total of 400 articles were reviewed. Twenty-nine articles were included in our review after meticulous screening.

RESULTS

Twenty-nine articles published in the last five years meeting selection criteria were identified, encompassing patients with various diagnoses warranting the use of DRGS beyond complex regional pain syndrome. Additionally, the analysis includes different outcome measurement tools, emphasizing improvements in pain management, functionality, and quality of life. Finally, common complications such as surgical site infections and issues with electrodes are highlighted.

CONCLUSIONS

This systematic review affirms the effectiveness of DRGS therapy in managing diverse chronic pain conditions, highlighting improvements in quality of life, functionality, and mood states, making it a viable alternative for patients unresponsive to traditional treatments.

Mechanisms of Action of Dorsal Root Ganglion Stimulation

The dorsal root ganglion (DRG) serves as a pivotal site for managing chronic pain through dorsal root ganglion stimulation (DRG-S). In recent years, the DRG-S has emerged as an attractive modality in the armamentarium of neuromodulation therapy due to its accessibility and efficacy in alleviating chronic pain refractory to conventional treatments. Despite its therapeutic advantages, the precise mechanisms underlying DRG-S-induced analgesia remain elusive, attributed in part to the diverse sensory neuron population within the DRG and its modulation of both peripheral and central sensory processing pathways. Emerging evidence suggests that DRG-S may alleviate pain by several mechanisms, including the reduction of nociceptive signals at the T-junction of sensory neurons, modulation of pain gating pathways within the dorsal horn, and regulation of neuronal excitability within the DRG itself. However, elucidating the full extent of DRG-S mechanisms necessitates further exploration, particularly regarding its supraspinal effects and its interactions with cognitive and affective networks. Understanding these mechanisms is crucial for optimizing neurostimulation technologies and improving clinical outcomes of DRG-S for chronic pain management. This review provides a comprehensive overview of the DRG anatomy, mechanisms of action of the DRG-S, and its significance in neuromodulation therapy for chronic pain.

Best Practices for Dorsal Root Ganglion Stimulation for Chronic Pain: Guidelines from the American Society of Pain and Neuroscience

With continued innovations in neuromodulation comes the need for evolving reviews of best practices. Dorsal root ganglion stimulation (DRG-S) has significantly improved the treatment of complex regional pain syndrome (CRPS), and it has broad applicability across a wide range of other conditions. Through funding and organizational leadership by the American Society for Pain and Neuroscience (ASPN), this best practices consensus document has been developed for the selection, implantation, and use of DRG stimulation for the treatment of chronic pain syndromes. This document is composed of a comprehensive narrative literature review that has been performed regarding the role of the DRG in chronic pain and the clinical evidence for DRG-S as a treatment for multiple pain etiologies. Best practice recommendations encompass safety management, implantation techniques, and mitigation of the potential complications reported in the literature. Looking to the future of neuromodulation, DRG-S holds promise as a robust intervention for otherwise intractable pain.

Blocking peripheral drive from colorectal afferents by subkilohertz dorsal root ganglion stimulation

ABSTRACT

Clinical evidence indicates dorsal root ganglion (DRG) stimulation effectively reduces pain without the need to evoke paresthesia. This paresthesia-free anesthesia by DRG stimulation can be promising to treat pain from the viscera, where paresthesia usually cannot be produced. Here, we explored the mechanisms and parameters for DRG stimulation using an ex vivo preparation with mouse distal colon and rectum (colorectum), pelvic nerve, L6 DRG, and dorsal root in continuity. We conducted single-fiber recordings from split dorsal root filaments and assessed the effect of DRG stimulation on afferent neural transmission. We determined the optimal stimulus pulse width by measuring the chronaxies of DRG stimulation to be below 216 µs, indicating spike initiation likely at attached axons rather than somata. Subkilohertz DRG stimulation significantly attenuates colorectal afferent transmission (10, 50, 100, 500, and 1000 Hz), of which 50 and 100 Hz show superior blocking effects. Synchronized spinal nerve and DRG stimulation reveals a progressive increase in conduction delay by DRG stimulation, suggesting activity-dependent slowing in blocked fibers. Afferents blocked by DRG stimulation show a greater increase in conduction delay than the unblocked counterparts. Midrange frequencies (50-500 Hz) are more efficient at blocking transmission than lower or higher frequencies. In addition, DRG stimulation at 50 and 100 Hz significantly attenuates in vivo visceromotor responses to noxious colorectal balloon distension. This reversible conduction block in C-type and Aδ-type afferents by subkilohertz DRG stimulation likely underlies the paresthesia-free anesthesia by DRG stimulation, thereby offering a promising new approach for managing chronic visceral pain.

Spinal Cord Stimulation as Treatment for Cancer and Chemotherapy-Induced Pain

Neuropathic pain is a rampant disease exacting a significant toll on patients, providers, and health care systems around the globe. Neuromodulation has been successfully employed to treat many indications including failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), phantom limb pain (PLP), radiculopathies, and intractable pelvic pain, among many others. Recent studies have also demonstrated efficacy for cancer-related pain and chemotherapy induced neuropathy with these techniques. Spinal cord stimulation (SCS) is the most commonly employed technique and involves implantation of percutaneous or paddle leads targeting the dorsal columns of the spinal cord with the goal of disrupting the pain signals traveling to the brain. Tonic, high frequency, and burst waveforms have all been shown to reduce pain and disability in chronic pain patients. Closed-loop SCS systems that automatically adjust stimulation parameters based on feedback (such as evoked compound action potentials) are becoming increasingly used to help ease the burden placed on patients to adjust their programming to their pain and position. Additionally, dorsal root ganglion stimulation (DRGS) is a newer technique that allows for dermatomal coverage especially in patients with pain in up to two dermatomes. Regardless of the technique chosen, neuromodulation has been shown to be cost-effective and efficacious and should be given full consideration in patients with chronic pain conditions.

Progress in the efficacy and mechanism of spinal cord stimulation in neuropathological pain

Neuropathic pain (NP) is a long-term recurrent disease caused by somatosensory nervous system injury, with spontaneous pain, hyperalgesia, ectopic pain, and paresthesia as the main clinical manifestations. It adversely affects patients' quality of life. NP treatments often include medication, physical therapy, and invasive therapy; the first two therapies are generally ineffective for some NP patients. These patients sometimes rely on invasive therapy to alleviate pain. Spinal cord stimulation (SCS) is a very effective therapeutic method. SCS is a neuroregulatory method that involves placing the electrodes on the corresponding painful spinal cords. Pain is greatly alleviated after SCS. SCS has been proven to be an effective therapeutic method for the treatment of neurological pain. Furthermore, SCS provides a feasible approach for patients with unsuccessful drug treatment. This paper reviews the relevant literature of spinal cord electrical stimulation, focusing on the mechanism of action, clinical application, clinical efficacy and technical progress of spinal cord electrical stimulation. SCS is widely used in the treatment of NP diseases such as postherpetic neuralgia, back surgery failure syndrome, and phantom limb pain. With advancements in science and technology, tremendous progress has also been made in the spinal cord electrical stimulation method and good momentum has been maintained.

[ANA- 12 inhibits spinal inflammation and alleviates acute and chronic pain in rats by targeted blocking of BDNF/TrkB signaling]

OBJECTIVE

To investigate the inhibitory effect of ANA-12 that blocks brain-derived neurotrophic factor (BDNF)/ tropomyosin receptor kinase B (TrkB) signaling on inflammatory pain in rats and explore the underlying mechanism.

METHODS

Forty-two adult SD rats were randomized into BDNF-induced acute pain group (n=24) and CFA-induced chronic pain group. The former group were randomly divided into 4 subgroups, including a control group, ANA-12 treatment group, BDNF treatment group, and BDNF+ANA-12 treatment group; the latter group were subgrouped into control group, CFA treatment group (CFA) and CFA + ANA-12 treatment group. The effects of ANA-12 treatment on pain behaviors of the rats with BDNF-induced acute pain and CFA-induced chronic inflammatory pain were observed. Western blotting was used to examine TrkB signaling and expressions of microglia marker protein Iba1 and TNF-α in the spinal cord of the rats.

RESULTS

BDNF injection into the subarachnoid space significantly increased the number of spontaneous paw withdrawal of the rats (P < 0.05), which was obviously reduced by ANA-12 treatment (P < 0.05). The rats with intraplantar injection of CFA, showed significantly increased ipsilateral mechanical stimulation sensitivity (P < 0.05), and ANA-12 treatment obviously increased the ipsilateral foot withdrawal threshold (P < 0.05). Treatment with either BDNF or CFA significantly increased the phosphorylation level of TrkB (Y705) in the spinal cord of the rats (P < 0.05), which was significantly lowered by ANA-12 treatment (P < 0.05). Treatment with BDNF and CFA both significantly up-regulated the expressions of Iba1 and TNF-α in the spinal cord (P < 0.05), but ANA-12 significantly reduced their expression levels (P < 0.05).

CONCLUSION

ANA-12 can reduce spinal cord inflammation and relieve acute and chronic pain in rats by targeted blocking of BDNF/TrkB signaling.

Analgesic dorsal root ganglionic field stimulation blocks conduction of afferent impulse trains selectively in nociceptive sensory afferents

Increased excitability of primary sensory neurons after peripheral nerve injury may cause hyperalgesia and allodynia. Dorsal root ganglion field stimulation (GFS) is effective in relieving clinical pain associated with nerve injury and neuropathic pain in animal models. However, its mechanism has not been determined. We examined effects of GFS on transmission of action potentials (APs) from the peripheral to central processes by in vivo single-unit recording from lumbar dorsal roots in sham injured rats and rats with tibial nerve injury (TNI) in fiber types defined by conduction velocity. Transmission of APs directly generated by GFS (20 Hz) in C-type units progressively abated over 20 seconds, whereas GFS-induced Aβ activity persisted unabated, while Aδ showed an intermediate pattern. Activity generated peripherally by electrical stimulation of the sciatic nerve and punctate mechanical stimulation of the receptive field (glabrous skin) was likewise fully blocked by GFS within 20 seconds in C-type units, whereas Aβ units were minimally affected and a subpopulation of Aδ units was blocked. After TNI, the threshold to induce AP firing by punctate mechanical stimulation (von Frey) was reduced, which was reversed to normal during GFS. These results also suggest that C-type fibers, not Aβ, mainly contribute to mechanical and thermal hypersensitivity (von Frey, brush, acetone) after injury. Ganglion field stimulation produces use-dependent blocking of afferent AP trains, consistent with enhanced filtering of APs at the sensory neuron T-junction, particularly in nociceptive units.

Supraspinal Effects of Dorsal Root Ganglion Stimulation in Chronic Pain Patients

OBJECTIVES

Dorsal root ganglion stimulation (DRGS) has become a popular neuromodulatory treatment for neuropathic pain. We used magnetoencephalography (MEG) to investigate potential biomarkers of pain and pain relief, based on the differences in power spectral density (PSD) during varying degrees of pain and how these oscillations change during DRGS-mediated pain relief.

MATERIALS AND METHODS

Thirteen chronic pain patients with implanted dorsal root ganglion stimulators were included in the MEG analysis. MEG Recordings were performed at rest while the stimulator was turned ON or OFF. Numerical rating scale (NRS) scores were also recorded before and after DRGS was turned OFF and ON. Power spectral and source localization analyses were then performed on preprocessed MEG recordings.

RESULTS

With DRGS-OFF, patients in severe pain had significantly increased cortical theta (4-7 Hz) power and decreased cortical alpha (7-13 Hz) power compared to patients reporting less pain. This shift in power toward lower frequencies was contrasted by a shift toward the higher frequency power spectrum (low beta 13-20 Hz activity) during DRGS-mediated pain relief. A significant correlation was found between the increase in low beta activity and the degree of reported pain relief.

CONCLUSION

Our results demonstrate increased low-frequency power spectral activity in chronic pain patients in the absence of stimulation which shifts toward higher frequency power spectrum activity in response to therapeutic DRGS. These cortical changes in response to DRGS provide support for the use of neuroimaging in the search for potential biomarkers of pain.

Dorsal Root Ganglion (DRG) and Chronic Pain

Context

Chronic neuropathic pain is a common condition, and up to 11.9% of the population have been reported to suffer from uncontrolled neuropathic pain. Chronic pain leads to significant morbidity, lowered quality of life, and loss of workdays, and thus carries a significant price tag in healthcare costs and lost productivity. dorsal root ganglia (DRG) stimulation has been recently increasingly reported and shows promising results in the alleviation of chronic pain. This paper reviews the background of DRG stimulation, anatomical, and clinical consideration and reviews the clinical evidence to support its use.

Evidence Acquisition

The DRG span the length of the spinal cord and house the neurons responsible for sensation from the periphery. They may become irritated by direct compression or local inflammation. Glial cells in the DRG respond to nerve injury, producing inflammatory markers and contribute to the development of chronic pain, even after the resolution of the original insult. While the underlying mechanism is still being explored, recent studies explored the efficacy of DRG stimulation and neuromodulation for chronic pain treatment.

Results

Several reported cases and a small number of randomized trials were published in recent years, describing different methods of DRG stimulation and neuromodulation with promising results. Though evidence quality is mostly low, these results provide evidence to support the utilization of this technique.

Conclusions

Chronic neuropathic pain is a common condition and carries significant morbidity and impact on the quality of life. Recent evidence supports the use of DRG neuromodulation as an effective technique to control chronic pain. Though studies are still emerging, the evidence appears to support this technique. Further studies, including large randomized trials evaluating DRG modulation versus other interventional and non-interventional techniques, are needed to further elucidate the efficacy of this method. These studies are also likely to inform the patient selection and the course of treatment.

Spinal cord stimulation in the treatment of peripheral vascular disease: a systematic review - revival of a promising therapeutic option?

INTRODUCTION

Peripheral vascular disease (PVD) is caused by a blood circulation disorder of the arteries and Critical Limb Ischemia (CLI) is the advanced state of PVD. For patients with surgically non-reconstructable CLI, Spinal Cord Stimulation (SCS) appears to be an alternative therapeutic option.

OBJECTIVE

The aim of our study was to investigate the efficacy of SCS in non-reconstructable CLI compared with the conservative treatment and re-appraise the existing literature in light of the recent advances in neuromodulation.

METHODS

We conducted a systematic review based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, using electronic databases and reference lists for article retrieval.

RESULTS

A total of 404 records were identified and finally 6 randomised controlled trials (RCTs), a Cochrane review and a meta-analysis were included in our systematic review. The studies assessed the efficacy of tonic SCS in the treatment of patients with non-reconstructable CLI compared with the conservative treatment. There is moderate to high quality evidence suggesting, that tonic SCS has beneficial effects for patients suffering from non-reconstructable CLI in terms of limb salvage, pain relief, clinical improvement and quality of life. The contradictory conclusions of the two meta-analyses regarding the efficacy of SCS for limb salvage at 12 months refer rather to the magnitude of the beneficial effect than to the effect itself. So far, the current literature provides evidence about the traditional tonic SCS but there is a lack of studies investigating the efficacy of new waveforms in the treatment of non-reconstructable CLI.

CONCLUSION

SCS represents an alternative for PVD patients with non-reconstructable CLI and the existing literature provides encouraging clinical results, that should not be neglected. Instead, they should be re-appraised in light of the recent advances in neuromodulation with the emergence of novel waveform technologies and neuromodulation targets.

Paresthesia-Free Spinal Nerve Root Stimulation for the Treatment of Chronic Neuropathic Pain

OBJECTIVE

Stimulation of the dorsal spinal roots, or spinal nerve root stimulation (SNRS), is a neuromodulation modality that can target pain within specific dermatomal distributions. The use of paresthesia-free stimulation has been described with conventional dorsal column spinal cord stimulation, although has yet to be described for SNRS. This objective of this study was to investigate the efficacy of paresthesia-free high-frequency (1000-1200 Hz) SNRS in the treatment of intractable, dermatomal neuropathic pain.

MATERIALS AND METHODS

A retrospective chart review was performed on 14 patients implanted with SNRS in varying distributions: Ten patients initially received tonic stimulation and crossed over to a paresthesia-free paradigm and four patients received only paresthesia-free stimulation. The primary outcome was reduction in pain severity (visual analog scale [VAS]), measured at baseline and follow-up to 24 months with paresthesia-free stimulation.

RESULTS

All 14 patients who received paresthesia-free stimulation had significant improvement in pain severity at a mean follow-up of 1.39 ± 0.15 years (VAS 7.46 at baseline vs. 3.25 at most recent follow-up, p < 0.001). Ten patients were initially treated with tonic stimulation and crossed over to paresthesia-free stimulation after a mean of 61.7 months. Baseline pain in these crossover patients was significantly improved at last follow-up with tonic stimulation (VAS 7.65 at baseline vs. 2.83 at 48 months, p < 0.001), although all patients developed uncomfortable paresthesias. There was no significant difference in pain severity between patients receiving tonic and paresthesia-free stimulation.

CONCLUSIONS

We present real-world outcomes of patients with intractable dermatomal neuropathic pain treated with paresthesia-free, high-frequency SNRS. We demonstrate its effectiveness in providing pain reduction at a level comparable to tonic SNRS up to 24 months follow-up, without producing uncomfortable paresthesias.

The Rhythmic Finger Focus Hypnotic Technique: Multilevel Application of Ericksonian Utilization

This paper presents a hypnotic technique that starts with a suggested focus on one's fingertips, and movement of the hands in a self-determined rhythm. The technique involves the use of the utilization principle of Milton Erickson in multiple ways. This includes utilizing psychomotor agitation characteristic of psychophysiological arousal, directing it toward movement that generates the sensations upon which to focus. It utilizes the sensitivity of the fingertips, the high degree of representation of the hands in the somatosensory cortex, and the tendency of the brain to orient to novelty to help facilitate focused absorption. It generates counter stimulation for pain management, and emotionally self- soothing tactile sensations. The technique is further designed to activate and utilize prior sensorimotor learning and sensory experiences associated with the hands to access feelings of mastery, creativity, flow, self-efficacy, and other positive emotional experiences. It is hypothesized that multisystem coherence is generated through activating prior positive motor, behavioral and affective experiential learning. It is further hypothesized that the rhythmic movement and sensory input simultaneously generated by and processed in the right and left hemispheres, entrains the hemispheres toward greater sympathetic/parasympathetic balance.