Pharmacologic, Surgical, and Device-Based Cardiac Neuromodulation

The cardiac autonomic nervous system plays a key role in maintaining normal cardiac physiology, and once disrupted, it worsens the cardiac disease states. Neuromodulation therapies have been emerging as new treatment options, and various techniques have been introduced to mitigate autonomic nervous imbalances to help cardiac patients with their disease conditions and symptoms. In this review article, we discuss various neuromodulation techniques used in clinical settings to treat cardiac diseases.

New-Onset Tinnitus After Dorsal Root Ganglion Stimulator Implantation: A Case Report

Dorsal column (dcSCS) and dorsal root ganglion stimulation (DRG-S) complications are similar, typically related to placement and device failure. We present the first case of tinnitus after DRG-S implantation. The patient presented with complex regional pain syndrome (CRPS) type 2. After previous failed treatments, she had a lumbosacral DRG-S trial, which provided relief; however, she briefly noted ringing in her ears. After permanent implantation, she reported persistent, intolerable left-sided tinnitus. Tinnitus can be modulated by secondary somatosensory inputs to the cochlear nucleus from the dcSCS. Therefore, lumbosacral DRG-S stimulating distal sensory neurons leading to tinnitus is a feasible complication.

Effectiveness of combined dorsal root ganglion and spinal cord stimulation: a retrospective, single-centre case series for chronic focal neuropathic pain

OBJECTIVE

This case series retrospectively reviewed the outcomes in patients implanted with combined, synchronous dorsal root ganglion stimulation (DRGS) and spinal cord stimulation (SCS) connected to a single implantable pulse generator (IPG) in a tertiary referral neuromodulation centre in the United Kingdom.

METHODS

Twenty-six patients underwent a trial of DRGS+SCS for treating focal neuropathic pain between January 2016 and December 2019, with a follow-up in February 2022. A Transgrade approach was employed for DRGS. Patients were provided with 3 possible stimulation programs: DRGS-only, SCS-only, or DRGS+SCS. Patients were assessed for pain intensity, patients' global impression of change (PGIC), preferred lead(s) and complications.

RESULTS

Twenty patients were successful and went on for full implantation. The most common diagnosis was Complex Regional Pain Syndrome. After an average of 3.1 years follow-up, 1 patient was lost to follow-up, and 2 were non-responders. Of the remaining 17 patients, 16 (94%) continued to report a PGIC of 7. The average pain intensity at Baseline was 8.5 on an NRS scale of 0-10. At the last follow-up, the average NRS reduction overall was 78.9% with no statistical difference between those preferring DRGS+SCS (n = 9), SCS-only (n = 3) and DRGS-only (n = 5). The combination of DRGS+SCS was preferred by 53% at the last follow-up. There were no serious neurological complications.

CONCLUSIONS

This retrospective case series demonstrates the potential effectiveness of combined DRGS+SCS with sustained analgesia observed at an average follow-up of over 3 years. Implanting combined DRGS+SCS may provide programming flexibility and therapeutic alternatives.

Twiddler's syndrome after dorsal root ganglion stimulation: A case report

Dorsal root ganglion stimulation (DRG-S) is a promising therapy for chronic neuropathic pain, but complications of this therapy are poorly understood. Twiddler's syndrome, a rare complication characterized by lead displacement and coiling of wires, has been reported in other neuromodulation devices, but has not been described in the context of DRG-S. Here, we present a first-of-a-kind case report of Twiddler's syndrome occurring after 8 months of DRG-S. This case report highlights the importance of considering Twiddler's syndrome as a potential complication in patients undergoing DRG-S, especially in those with significant weight loss history.

Interventions for treating pain and disability in adults with complex regional pain syndrome- an overview of systematic reviews

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic pain condition that usually occurs in a limb following trauma or surgery. It is characterised by persisting pain that is disproportionate in magnitude or duration to the typical course of pain after similar injury. There is currently no consensus regarding the optimal management of CRPS, although a broad range of interventions have been described and are commonly used. This is the first update of the original Cochrane review published in Issue 4, 2013.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the efficacy, effectiveness, and safety of any intervention used to reduce pain, disability, or both, in adults with CRPS.

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of Ovid MEDLINE, Ovid Embase, Cochrane Database of Systematic Reviews, CINAHL, PEDro, LILACS and Epistemonikos from inception to October 2022, with no language restrictions. We included systematic reviews of randomised controlled trials that included adults (≥18 years) diagnosed with CRPS, using any diagnostic criteria.  Two overview authors independently assessed eligibility, extracted data, and assessed the quality of the reviews and certainty of the evidence using the AMSTAR 2 and GRADE tools respectively. We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes quality of life, emotional well-being, and participants' ratings of satisfaction or improvement with treatment.  MAIN RESULTS: We included six Cochrane and 13 non-Cochrane systematic reviews in the previous version of this overview and five Cochrane and 12 non-Cochrane reviews in the current version. Using the AMSTAR 2 tool, we judged Cochrane reviews to have higher methodological quality than non-Cochrane reviews. The studies in the included reviews were typically small and mostly at high risk of bias or of low methodological quality. We found no high-certainty evidence for any comparison.  There was low-certainty evidence that bisphosphonates may reduce pain intensity post-intervention (standardised mean difference (SMD) -2.6, 95% confidence interval (CI) -1.8 to -3.4, P = 0.001; I2 = 81%; 4 trials, n = 181) and moderate-certainty evidence that they are probably associated with increased adverse events of any nature (risk ratio (RR) 2.10, 95% CI 1.27 to 3.47; number needed to treat for an additional harmful outcome (NNTH) 4.6, 95% CI 2.4 to 168.0; 4 trials, n = 181).  There was moderate-certainty evidence that lidocaine local anaesthetic sympathetic blockade probably does not reduce pain intensity compared with placebo, and low-certainty evidence that it may not reduce pain intensity compared with ultrasound of the stellate ganglion. No effect size was reported for either comparison. There was low-certainty evidence that topical dimethyl sulfoxide may not reduce pain intensity compared with oral N-acetylcysteine, but no effect size was reported. There was low-certainty evidence that continuous bupivacaine brachial plexus block may reduce pain intensity compared with continuous bupivacaine stellate ganglion block, but no effect size was reported. For a wide range of other commonly used interventions, the certainty in the evidence was very low and provides insufficient evidence to either support or refute their use. Comparisons with low- and very low-certainty evidence should be treated with substantial caution. We did not identify any RCT evidence for routinely used pharmacological interventions for CRPS such as tricyclic antidepressants or opioids.

AUTHORS' CONCLUSIONS

Despite a considerable increase in included evidence compared with the previous version of this overview, we identified no high-certainty evidence for the effectiveness of any therapy for CRPS. Until larger, high-quality trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult. Current non-Cochrane systematic reviews of interventions for CRPS are of low methodological quality and should not be relied upon to provide an accurate and comprehensive summary of the evidence.

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.

Application of Repetitive Transcranial Magnetic Stimulation in Neuropathic Pain: A Narrative Review

Neuropathic pain, affecting 6.9-10% of the general population, has a negative impact on patients' quality of life and potentially leads to functional impairment and disability. Repetitive transcranial magnetic stimulation (rTMS)-a safe, indirect and non-invasive technique-has been increasingly applied for treating neuropathic pain. The mechanism underlying rTMS is not yet well understood, and the analgesic effects of rTMS have been inconsistent with respect to different settings/parameters, causing insufficient evidence to determine its efficacy in patients with neuropathic pain. This narrative review aimed to provide an up-to-date overview of rTMS for treating neuropathic pain as well as to summarize the treatment protocols and related adverse effects from existing clinical trials. Current evidence supports the use of 10 Hz HF-rTMS of the primary motor cortex to reduce neuropathic pain, especially in patients with spinal cord injury, diabetic neuropathy and post-herpetic neuralgia. However, the lack of standardized protocols impedes the universal use of rTMS for neuropathic pain. rTMS was hypothesized to achieve analgesic effects by upregulating the pain threshold, inhibiting pain impulse, modulating the brain cortex, altering imbalanced functional connectivity, regulating neurotrophin and increasing endogenous opioid and anti-inflammatory cytokines. Further studies are warranted to explore the differences in the parameters/settings of rTMS for treating neuropathic pain due to different disease types.

[Post-traumatic pain mononeuropathies]

Neuropathic pain syndrome (NPS) caused by peripheral nerve (PN) injury is a serious clinical problem due to its prevalence, complexity of pathogenesis, significant impact on the quality of life of patients. The issues of epidemiology, pathogenesis and treatment of patients with NBS with PN injury are considered. Modern possibilities of invasive treatment of such patients are discussed.

Modern Principles of Diagnosis and Treatment in Complex Regional Pain Syndrome

BACKGROUND

Background: Complex regional pain syndrome (CRPS) is a relatively common complication, occurring in 5% of cases after injury or surgery, particularly in the limbs. The incidence of CPRS is around 5-26/100 000. The latest revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) now categorizes CRPS as a primary pain condition of multifactorial origin, rather than a disease of the skeletal system or the autonomic nervous system.

METHODS

Method: Based on a selective search of the literature, we summarize current principles for the diagnosis and treatment of CRPS.

RESULTS

Results: Regional findings in CRPS are accompanied by systemic symptoms, especially by neurocognitive disorders of body perception and of symptom processing. The therapeutic focus is shifting from predominantly passive peripheral measures to early active treatments acting both centrally and peripherally. The treatment is centered on physiotherapy and occupational therapy to improve sensory perception, strength, (fine) motor skills, and sensorimotor integration/ body perception. This is supported by stepped psychological interventions to reduce anxiety and avoidance behavior, medication to decrease inflammation and pain, passive physical measures for reduction of edema and of pain, and medical aids to improve functioning in daily life. Interventional procedures should be limited to exceptional cases and only be performed in specialized centers. Spinal cord and dorsal root ganglion stimulation, respectively, are the interventions with the best evidence.

CONCLUSION

Conclusion: The modern principles for the diagnosis and treatment of CRPS consider both, physiological and psychological mechanisms, with the primary goal of restoring function and participation. More research is needed to strengthen the evidence base in this field.

A prospective long-term follow-up of dorsal root ganglion stimulation for the management of chronic intractable pain

ABSTRACT

Initial clinical studies have shown that the stimulation of the dorsal root ganglion (DRG) can significantly reduce chronic intractable pain. However, clinical data on long-term results and complications of these systems are limited. The aim of this prospective study is to report on a single center long-term follow-up of DRG stimulation for intractable chronic pain. Participants were implanted with DRG stimulation devices between 2013 and 2015 with an observation period of 24 months. Patients were contacted again in 2020 for a final follow-up (ie, between 5 and 7 years postimplantation). Forty-two participants were recruited, of whom 32 received the fully implantable pulse generator (IPG). At the final follow-up, 50% (16/32) of participants were still using DRG stimulation. Two participants still had the original IPG and 14 had received a replacement IPG. Pain scores were significantly reduced at 24 months, mean difference 1.7 (95% confidence interval: 0.2-3.3, P = 0.03), and at the last follow-up, mean difference 2.1 (95% confidence interval: 0.3-4, P = 0.03). Significant improvements were observed for health-related quality of life. The findings were generally robust to imputation methods of missing data. Implantable pulse generators of 8 patients were explanted because of dissatisfaction with pain relief. In conclusion, DRG stimulation can provide effective pain relief and improved quality of life in patients suffering with neuropathic pain, although this study had a revision rate of 42% within the first 24 months, and 56% of IPGs that were replaced because of battery depletion had a shorter than expected battery life.

Concept of the Number Needed to Treat for the Analysis of Pain Relief Outcomes in Patients Treated with Spinal Cord Stimulation

In the rapidly evolving field of spinal cord stimulation (SCS), measures of treatment effects are needed to help understand the benefits of new therapies. The present article elaborates the number needed to treat (NNT) concept and applies it to the SCS field. We reviewed the basic theory of the NNT, its calculation method, and its application to historical controlled trials of SCS. We searched the literature for controlled studies with ≥20 implanted SCS patients with chronic axial back and/or leg pain followed for ≥3 months and a reported responder rate defined as ≥50% pain relief. Relevant data necessary to estimate the NNT were extracted from the included articles. In total, 12 of 1616 records were eligible for inclusion. The records reported 10 clinical studies, including 7 randomized controlled trials, 2 randomized crossover trials, and 1 controlled cohort study. The studies investigated traditional SCS and more recently developed SCS modalities, including 10 kHz SCS. In conclusion, the NNT estimate may help SCS stakeholders better understand the effect size difference between compared treatments; however, interpretation of any NNT should take into account its full context. In addition, comparisons across trials of different therapies should be avoided since they are prone to interpretation biases.

Comparison of Spinal Cord Stimulation vs. Dorsal Root Ganglion Stimulation vs. Association of Both in Patients with Refractory Chronic Back and/or Lower Limb Neuropathic Pain: An International, Prospective, Randomized, Double-Blinded, Crossover Trial (BOOST-DRG Study)

While spinal cord stimulation (SCS) is a well-established therapy to address refractory persistent spinal pain syndrome after spinal surgery (PSPS-T2), its lack of spatial selectivity and reported discomfort due to positional effects can be considered as significant limitations. As alternatives, new waveforms, such as burst stimulation and different spatial neural targets, such as dorsal root ganglion stimulation (DRGS), have shown promising results. Comparisons between DRGS and standard SCS, or their combination, have never been studied on the same patients. "BOOST DRG" is the first prospective, randomized, double-blinded, crossover study to compare SCS vs. DRGS vs. SCS+DRGS. Sixty-six PSPS-T2 patients will be recruited internationally in three centers. Before crossing over, patients will receive each stimulation modality for 1 month, using tonic conventional stimulation. After 3 months, stimulation will consist in switching to burst for 1 month, and patients will choose which modality/waveform they receive and will then be reassessed at 6 and 12 months. In addition to our primary outcome based on pain rating, this study is designed to assess quality of life, functional disability, psychological distress, pain surface coverage, global impression of change, medication quantification, adverse events, brain functional imaging and electroencephalography, with the objective being to provide a multidimensional insight based on composite pain assessment.

Dorsal Root Ganglion Stimulation for Chronic Groin Pain: A Review

INTRODUCTION

Chronic neuropathic groin pain develops in a significant number of postsurgical patients; however, multiple etiologies have been identified, and this makes it a challenging condition to treat. While treatment often involves a multimodal approach, advancements in neuromodulation technology, particularly dorsal root ganglion (DRG) stimulation, have benefited patients plagued by chronic pain refractory to standard treatment modalities. Our goal was to provide a definitive source of information for interventional pain physicians regarding groin pain and the use of DRG stimulation for its treatment.

MATERIALS AND METHODS

In this narrative review, we provide an overview of groin pain and discuss potential pain generators. We also outline appropriate treatment options with particular interest on DRG stimulation. Lastly, we provide a narrative review of the published literature regarding DRG stimulation for chronic groin pain from a variety of etiologies.

CONCLUSION

DRG stimulation has emerged as an alternative neuromodulatory technique for patients with chronic groin pain. While previous studies suggest substantial sustained pain relief with DRG stimulation in this patient population, prospective randomized controlled studies are necessary before formal recommendations can be made.

Auricular Vagus Neuromodulation-A Systematic Review on Quality of Evidence and Clinical Effects

Background: The auricular branch of the vagus nerve runs superficially, which makes it a favorable target for non-invasive stimulation techniques to modulate vagal activity. For this reason, there have been many early-stage clinical trials on a diverse range of conditions. These trials often report conflicting results for the same indication. Methods: Using the Cochrane Risk of Bias tool we conducted a systematic review of auricular vagus nerve stimulation (aVNS) randomized controlled trials (RCTs) to identify the factors that led to these conflicting results. The majority of aVNS studies were assessed as having "some" or "high" risk of bias, which makes it difficult to interpret their results in a broader context. Results: There is evidence of a modest decrease in heart rate during higher stimulation dosages, sometimes at above the level of sensory discomfort. Findings on heart rate variability conflict between studies and are hindered by trial design, including inappropriate washout periods, and multiple methods used to quantify heart rate variability. There is early-stage evidence to suggest aVNS may reduce circulating levels and endotoxin-induced levels of inflammatory markers. Studies on epilepsy reached primary endpoints similar to previous RCTs testing implantable vagus nerve stimulation therapy. Preliminary evidence shows that aVNS ameliorated pathological pain but not evoked pain. Discussion: Based on results of the Cochrane analysis we list common improvements for the reporting of results, which can be implemented immediately to improve the quality of evidence. In the long term, existing data from aVNS studies and salient lessons from drug development highlight the need for direct measures of local neural target engagement. Direct measures of neural activity around the electrode will provide data for the optimization of electrode design, placement, and stimulation waveform parameters to improve on-target engagement and minimize off-target activation. Furthermore, direct measures of target engagement, along with consistent evaluation of blinding success, must be used to improve the design of controls-a major source of concern identified in the Cochrane analysis. The need for direct measures of neural target engagement and consistent evaluation of blinding success is applicable to the development of other paresthesia-inducing neuromodulation therapies and their control designs.

Review of complex regional pain syndrome and the role of the neuroimmune axis

Background

Complex regional pain syndrome (CRPS) is a progressive and painful disease of the extremities that is characterized by continuous pain inconsistent with the initial trauma. CRPS is caused by a multi-mechanism process that involves both the peripheral and central nervous system, with a prominent role of inflammation in CRPS pathophysiology. This review examines what is currently known about the CRPS inflammatory and pain mechanisms, as well as the possible impact of neurostimulation therapies on the neuroimmune axis of CRPS.

Study design

A narrative review of preclinical and clinical studies provided an overview of the pain and inflammatory mechanisms in CRPS and addressed the effect of neurostimulation on immunomodulation.

Methods

A systematic literature search was conducted based on the PRISMA guidelines between September 2015 to September 2020. Data sources included relevant literature identified through searches of PubMed, Embase and the Cochrane Database of Systematic Reviews.

Results

Sixteen preclinical and eight clinical studies were reviewed. Preclinical studies identified different mechanisms of pain development in the acute and chronic CRPS phases. Several preclinical and clinical studies investigating inflammatory mechanisms, autoimmunity, and genetic profiles in CRPS, supported a role of neuroinflammation in the pathophysiology of CRPS. The immunomodulatory effects of neurostimulation therapy is still unclear, despite clinical improvement in the CRPS patients.

Conclusions

Increasing evidence supports a role for inflammation and neuroinflammation in CRPS pathophysiology. Preliminary neurostimulation findings, together with the role of (neuro)inflammation in CRPS, seems to provide a compelling rationale for its use in CRPS pain treatment. The possible immunomodulatory effects of neurostimulation opens new therapeutic possibilities, however further research is needed to gain a better understanding of the working mechanisms.

Utility of Electrical Neuromodulation for Treating Chronic Pain Syndromes in the Pediatric Setting: A Systematic Review

OBJECTIVES

Chronic pain syndromes in children can carry significant threats to psychological well-being, opioid overuse, functional impairments, and severe disability. While several high-level studies, almost exclusively in adults, have demonstrated the utility of implantable electrical neuromodulation systems for treating various chronic pain syndromes, there exists a paucity of pediatric-specific evidence. Unfortunately, evidence and practice patterns established from adults may not be fully translatable to children given differences in disease manifestations and anatomical variances.

MATERIALS AND METHODS

We performed a systematic review using conventional PRISMA methodology to identify studies reporting use of implantable electrical neuromodulation systems in children. The primary outcome parameters collected were analgesic relief and functional benefits. Additionally, previous interventions attempted, neuromodulation parameters, and limitations were collected as reported.

RESULTS

A total of 11 studies was identified, which described 19 patients who were refractory to multidisciplinary pain management strategies. The cohort was mostly adolescent (18/19), suffered from CRPS (14/19), and received SCS (17/19). Nearly all patients, both those with CRPS (13/14) and non-CRPS conditions (4/4), reported significant pain relief and functional recovery following neuromodulation. There were no severe complications reported; limitations included suboptimal benefit or loss of analgesia (3/19), lead or device revision (3/19), and subcutaneous infection (1/19), all of which were congruent with adult outcomes.

CONCLUSION

There exist children with chronic pain refractory to standard of care approaches who could be considered for neuromodulation interventions. The existing data, which was limited and from a low tier of evidence, suggest that these interventions are relatively safe and provide meaningful pain reduction and functional improvements. While not previously reported, we recommend careful consideration of the pubertal growth spurt prior to device lead placement-if reasonable and appropriate-given the possibility of inferior lead migration with physiologic growth in patients with SCS devices or foraminal extrusion in patients with dorsal root ganglion stimulation devices.

Effect of Patient Characteristics on Clinical Outcomes More Than 12 Months Following Dorsal Root Ganglion Stimulation Implantation: A Retrospective Review

INTRODUCTION

Dorsal root ganglion (DRG) stimulation is an effective treatment option for lower extremity complex regional pain syndrome and other focal pain conditions. However, the patient characteristics that may predict long-term outcomes have not been defined.

MATERIALS AND METHODS

This was a retrospective observational study that included 93 patients who were implanted with a DRG stimulator at a single private practice institution. A variety of demographic data was collected. Follow-up results were reviewed from multiple time points more than 12 months. Patients were classified as either "responder" or "nonresponder" status using two different thresholds, "greater than or equal to 50% pain relief" and "greater than or equal to 80% pain relief."

RESULTS

A history of prior chronic opioid use was associated with significantly lower rates of responder status based on both a 50% pain relief threshold and 80% pain relief threshold at the one week to one month, three months, and 12-months visits.

CONCLUSIONS

This single-center retrospective study found patients prescribed chronic opioids at the time of DRG stimulator implantation had a higher likelihood of less than 50% pain relief and 80% pain relief at one month, three months, and 12 months follow-up visits.