Spinal Cord Stimulation for Treating Chronic Pain: Reviewing Preclinical and Clinical Data on Paresthesia-Free High-Frequency Therapy

Long-Term Efficacy and Safety of High-Frequency Spinal Stimulation for Chronic Pain: A Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

The aim of our meta-analysis was to systematically assess the enduring effectiveness and safety of high-frequency spinal stimulation (HF-SCS) in the management of chronic pain.

METHODS

We developed a comprehensive literature search strategy to identify clinical trials investigating the efficacy of high-frequency spinal stimulation for chronic pain. The search was conducted in multiple databases, including Web of Science, Cochrane, PubMed, and Embase, covering the period from 2004 to 2023. The inclusion and exclusion criteria established for this study were applied to screen the eligible literature by carefully reviewing abstracts and, when necessary, examining the full text of selected articles. To assess the quality of the included studies, we utilized the Risk of Bias assessment tool provided by the Cochrane Collaboration. The PRISMA method was followed for the selection of articles, and the quality of the articles was evaluated using the risk assessment table for bias provided by the Cochrane Collaboration. Meta-analysis of the selected studies was performed using Review Manager 5.4 and STATA 16.0. Effect sizes for continuous data were reported as mean differences (MD) or standardized mean differences (SMD), while categorical data were analyzed using relative risks (RR).

RESULTS

According to our predefined literature screening criteria, a total of seven English-language randomized controlled trials (RCTs) were included in the meta-analysis. The findings from the meta-analysis demonstrated that HF-SCS exhibited superior efficacy in the long-term treatment of chronic pain when compared with the control group (RR=2.44, 95% CI: 1.20-4.96, P =0.01). Furthermore, HF-SCS demonstrated a statistically significant improvement in the Oswestry Disability Index score (mean difference MD=3.77, 95% CI: 1.17-6.38, P =0.005). However, for pain assessment (standardized mean difference SMD=-0.59, 95% CI: -1.28 to 0.10, P =0.09), Patient Global Impression of Improvement (PGI-I) score (MD=0.11, 95% CI: -0.66 to 0.88, P =0.78 for 6 months; MD=0.02, 95% CI: -0.42 to 0.43, P =0.97 for 12 mo), Clinical Global Impression of Improvement (CGI-I) score (MD=-0.58, 95% CI: -1.62 to 0.43, P =0.27 for 6 mo; MD=-0.23, 95% CI: -0.94 to 0.48, P =0.52 for 12 mo), and occurrence of adverse effects (odds ratio [OR]=0.77, 95% CI: 0.23-2.59, P =0.67), HF-SCS did not show statistically sufficient effects compared with the control group.

CONCLUSIONS

The findings from our comprehensive review and meta-analysis offer encouraging data about the prolonged efficacy and safety of HF-SCS in chronic pain management on some but not all outcomes. Recognizing the constraints of the existing evidence is crucial. Additional clinical trials, meticulously planned and stringent, are essential to bolster the current body of evidence and reach more conclusive findings.

Frequency-Dependent Neural Modulation of Dorsal Horn Neurons by Kilohertz Spinal Cord Stimulation in Rats

Kilohertz high-frequency spinal cord stimulation (kHF-SCS) is a rapidly advancing neuromodulatory technique in the clinical management of chronic pain. However, the precise cellular mechanisms underlying kHF-SCS-induced paresthesia-free pain relief, as well as the neural responses within spinal pain circuits, remain largely unexplored. In this study, using a novel preparation, we investigated the impact of varying kilohertz frequency SCS on dorsal horn neuron activation. Employing calcium imaging on isolated spinal cord slices, we found that extracellular electric fields at kilohertz frequencies (1, 3, 5, 8, and 10 kHz) induce distinct patterns of activation in dorsal horn neurons. Notably, as the frequency of extracellular electric fields increased, there was a clear and significant monotonic escalation in neuronal activity. This phenomenon was observed not only in superficial dorsal horn neurons, but also in those located deeper within the dorsal horn. Our study demonstrates the unique patterns of dorsal horn neuron activation in response to varying kilohertz frequencies of extracellular electric fields, and we contribute to a deeper understanding of how kHF-SCS induces paresthesia-free pain relief. Furthermore, our study highlights the potential for kHF-SCS to modulate sensory information processing within spinal pain circuits. These insights pave the way for future research aimed at optimizing kHF-SCS parameters and refining its therapeutic applications in the clinical management of chronic pain.

High-Frequency Spinal Stimulation Suppresses Microglial Kaiso-P2X7 Receptor Axis-Induced Inflammation to Alleviate Neuropathic Pain in Rats

OBJECTIVE

Neuropathic pain poses a persistent challenge in clinical management. Neuromodulation has emerged as a last-resort therapy. Conventional spinal cord stimulation (Con SCS) often causes abnormal sensations and provides short analgesia, whereas high-frequency spinal cord stimulation (HF SCS) is a newer therapy that effectively alleviates pain without paresthesia. However, the modes of action of 10kHz HF SCS (HF10 SCS) in pain relief remain unclear. To bridge this knowledge gap, we employed preclinical models that mimic certain features of clinical SCS to explore the underlying mechanisms of HF10 SCS. Addressing these issues would provide the scientific basis for improving and evaluating the effectiveness, reliability, and practicality of different frequency SCS in clinical settings.

METHODS

We established a preclinical SCS model to examine its effects in a neuropathic pain rat model. We conducted bulk and single-cell RNA sequencing in the spinal dorsal horn (SDH) to examine cellular and molecular changes under different treatments. We employed genetic manipulations through intrathecal injection of a lentiviral system to explore the SCS-mediated signaling axis in pain. Various behavioral tests were performed to evaluate pain conditions under different treatments.

RESULTS

We found that HF10 SCS significantly reduces immune responses in the SDH by inactivating the Kaiso-P2X7R pathological axis in microglia, promoting long-lasting pain relief. Targeting Kaiso-P2X7R in microglia dramatically improved efficacy of Con SCS treatment, leading to reduced neuroinflammation and long-lasting pain relief.

INTERPRETATION

HF10 SCS could improve the immunopathologic state in the SDH, extending its benefits beyond symptom relief. Targeting the Kaiso-P2X7R axis may enhance Con SCS therapy and offer a new strategy for pain management. ANN NEUROL 2024;95:966-983.

Spinal Cord Stimulation Waveforms for the Treatment of Chronic Pain

PURPOSE OF REVIEW

Since the advent of spinal cord stimulation (SCS), advances in technology have allowed for improvement and treatment of various conditions, especially chronic pain. Additionally, as the system has developed, the ability to provide different stimulation waveforms for patients to treat different conditions has improved. The purpose and objective of the paper is to discuss basics of waveforms and present the most up-to-date literature and research studies on the different types of waveforms that currently exist. During our literature search, we came across over sixty articles that discuss the various waveforms we intend to evaluate.

RECENT FINDINGS

There are several publications on several waveforms used in clinical practice, but to our knowledge, this is the only educational document teaching on waveforms which provides essential knowledge. There is a gap of knowledge related to understanding wave forms and how they work.

10 kHz stimulation as rescue therapy for spinal cord stimulation trial failure or loss of efficacy: A retrospective study

INTRODUCTION

Spinal cord stimulation (SCS) is currently used for the management of pain of different origin, and since its inception, many waveforms have been developed. Some patients experience no pain relief already during SCS trial, while other patients go through a loss of efficacy due to habituation after a variable period of satisfying pain control. Our retrospective study represents the first report exploring the potential role of 10 kHz stimulation as rescue therapy for patients who did not benefit not only from conventional stimulation but even from other waveforms during SCS trial or follow-up.

METHODS

This study was conducted in Germany; we retrospectively enrolled patients with no pain relief during SCS trial or with loss of efficacy of other waveforms over time; and we recorded visual analogic scale (VAS), Oswestry Disability Index (ODI), and daily opioid consumption expressed as morphine milligram equivalents (MME), right before and 12 months after the switching to 10 kHz simulation.

RESULTS

The rate of successful switching to 10 kHz stimulation was comparable in patients enrolled during the SCS trial and during the follow-up (43% vs. 40%, respectively); notably, the highest rate of failed rescue was recorded in case of persistent spinal pain syndrome (PSPS) II. Patients who responded to the switching showed a significant improvement in VAS and ODI after 12 months of treatment compared to baseline (3.6 ± 1.0 vs. 8.2 ± 0.9, p < 0.00001 and 34.0 ± 7.8 vs. 64.3 ± 8.7, p < 0.0001, respectively), whereas there was no reduction in the consumption of opioids in terms of MME (3 (0-16) vs. 5 (0-8.75), p = 0.1003).

CONCLUSIONS

Rescue therapy with 10 kHz stimulation could be an important strategy to avoid SCS explant in both patients non-responsive during trial or experiencing a loss of efficacy during the years with other waveforms.

Bioelectronic Medicine: a multidisciplinary roadmap from biophysics to precision therapies

Bioelectronic Medicine stands as an emerging field that rapidly evolves and offers distinctive clinical benefits, alongside unique challenges. It consists of the modulation of the nervous system by precise delivery of electrical current for the treatment of clinical conditions, such as post-stroke movement recovery or drug-resistant disorders. The unquestionable clinical impact of Bioelectronic Medicine is underscored by the successful translation to humans in the last decades, and the long list of preclinical studies. Given the emergency of accelerating the progress in new neuromodulation treatments (i.e., drug-resistant hypertension, autoimmune and degenerative diseases), collaboration between multiple fields is imperative. This work intends to foster multidisciplinary work and bring together different fields to provide the fundamental basis underlying Bioelectronic Medicine. In this review we will go from the biophysics of the cell membrane, which we consider the inner core of neuromodulation, to patient care. We will discuss the recently discovered mechanism of neurotransmission switching and how it will impact neuromodulation design, and we will provide an update on neuronal and glial basis in health and disease. The advances in biomedical technology have facilitated the collection of large amounts of data, thereby introducing new challenges in data analysis. We will discuss the current approaches and challenges in high throughput data analysis, encompassing big data, networks, artificial intelligence, and internet of things. Emphasis will be placed on understanding the electrochemical properties of neural interfaces, along with the integration of biocompatible and reliable materials and compliance with biomedical regulations for translational applications. Preclinical validation is foundational to the translational process, and we will discuss the critical aspects of such animal studies. Finally, we will focus on the patient point-of-care and challenges in neuromodulation as the ultimate goal of bioelectronic medicine. This review is a call to scientists from different fields to work together with a common endeavor: accelerate the decoding and modulation of the nervous system in a new era of therapeutic possibilities.

Evaluating the Effects of Pulsed Electrical Stimulation on the Mechanical Behavior and Microstructure of Medulla Oblongata Tissues

The development of remote surgery hinges on comprehending the mechanical properties of the tissue at the surgical site. Understanding the mechanical behavior of the medulla oblongata tissue is instrumental for precisely determining the remote surgery implementation site. Additionally, exploring this tissue's response under electric fields can inform the creation of electrical stimulation therapy regimens. This could potentially reduce the extent of medulla oblongata tissue damage from mechanical compression. Various types of pulsed electric fields were integrated into a custom-built indentation device for this study. Experimental findings suggested that applying pulsed electric fields amplified the shear modulus of the medulla oblongata tissue. In the electric field, the elasticity and viscosity of the tissue increased. The most significant influence was noted from the low-frequency pulsed electric field, while the burst pulsed electric field had a minimal impact. At the microstructural scale, the application of an electric field led to the concentration of myelin in areas distant from the surface layer in the medulla oblongata, and the orderly structure of proteoglycans became disordered. The alterations observed in the myelin and proteoglycans under an electric field were considered to be the fundamental causes of the changes in the mechanical behavior of the medulla oblongata tissue. Moreover, cell polarization and extracellular matrix cavitation were observed, with transmission electron microscopy results pointing to laminar separation within the myelin at the ultrastructure scale. This study thoroughly explored the impact of electric field application on the mechanical behavior and microstructure of the medulla oblongata tissue, delving into the underlying mechanisms. This investigation delved into the changes and mechanisms in the mechanical behavior and microstructure of medulla oblongata tissue under the influence of electric fields. Furthermore, this study could serve as a reference for the development of electrical stimulation regimens in the central nervous system. The acquired mechanical behavior data could provide valuable baseline information to aid in the evolution of remote surgery techniques involving the medulla oblongata tissue.

Neuromodulation Techniques in Chronic Refractory Coccydynia: A Narrative Review

Refractory coccydynia is a condition characterized by severe coccygeal pain and poses a challenging management dilemma for clinicians. Advancements in neuromodulation (NM) technology have provided benefits to people experiencing chronic pain that is resistant to standard treatments. This review aims to summarize the spectrum of current NM techniques employed in the treatment of refractory coccydynia along with their effectiveness. A review of studies in the scientific literature from 2012 to 2023 was conducted, revealing a limited number of case reports. Although the available evidence at this time suggests significant pain relief with the utilization of NM techniques, the limited scope and nature of the studies reviewed emphasize the need for large-scale, rigorous, high-level research in this domain in order to establish a comprehensive understanding of the role of NM and its effectiveness in the management of intractable coccydynia.

Spinal Cord Stimulation for Painful Diabetic Neuropathy

Spinal cord stimulation (SCS) technology has been recently approved by the US Food and Drug Administration (FDA) for painful diabetic neuropathy (PDN). The treatment involves surgical implantation of electrodes and a power source that delivers electrical current to the spinal cord. This treatment decreases the perception of pain in many chronic pain conditions, such as PDN. The number of patients with PDN treated with SCS and the amount of data describing their outcomes is expected to increase given four factors: (1) the large number of patients with this diagnosis, (2) the poor results that have been obtained for pain relief with pharmacotherapy and noninvasive non-pharmacotherapy, (3) the results to date with investigational SCS technology, and (4) the recent FDA approval of systems that deliver this treatment. Whereas traditional SCS replaces pain with paresthesias, a new form of SCS, called high-frequency 10-kHz SCS, first used for pain in 2015, can relieve PDN pain without causing paresthesias, although not all patients experience pain relief by SCS. This article describes (1) an overview of SCS technology, (2) the use of SCS for diseases other than diabetes, (3) the use of SCS for PDN, (4) a comparison of high-frequency 10-kHz and traditional SCS for PDN, (5) other SCS technology for PDN, (6) deployment of SCS systems, (7) barriers to the use of SCS for PDN, (8) risks of SCS technology, (9) current recommendations for using SCS for PDN, and (10) future developments in SCS.

Selective Infrared Neural Inhibition Can Be Reproduced by Resistive Heating

OBJECTIVES

Small-diameter afferent axons carry various sensory signals that are critical for vital physiological conditions but sometimes contribute to pathologies. Infrared (IR) neural inhibition (INI) can induce selective heat block of small-diameter axons, which holds potential for translational applications such as pain management. Previous research suggested that IR-heating-induced acceleration of voltage-gated potassium channel kinetics is the mechanism for INI. Therefore, we hypothesized that other heating methods, such as resistive heating (RH) in a cuff, could reproduce the selective inhibition observed in INI.

MATERIALS AND METHODS

We conducted ex vivo nerve-heating experiments on pleural-abdominal connective nerves of Aplysia californica using both IR and RH. We fabricated a transparent silicone nerve cuff for simultaneous IR heating, RH, and temperature measurements. Temperature elevations (ΔT) on the nerve surface were recorded for both heating modalities, which were tested over a range of power levels that cover a similar ΔT range. We recorded electrically evoked compound action potentials (CAPs) and segmented them into fast and slow subcomponents on the basis of conduction velocity differences between the large and small-diameter axonal subpopulations. We calculated the normalized inhibition strength and inhibition selectivity index on the basis of the rectified area under the curve of each subpopulation.

RESULTS

INI and RH showed a similar selective inhibition effect on CAP subcomponents for slow-conducting axons, confirmed by the inhibition probability vs ΔT dose-response curve based on approximately 2000 CAP measurements. The inhibition selectivity indexes of the two heating modalities were similar across six nerves. RH only required half the total electrical power required by INI to achieve a similar ΔT.

SIGNIFICANCE

We show that selective INI can be reproduced by other heating modalities such as RH. RH, because of its high energy efficiency and simple design, can be a good candidate for future implantable neural interface designs.

Should we Oppose or Combine Waveforms for Spinal Cord Stimulation in PSPS-T2 Patients? A Prospective Randomized Crossover Trial (MULTIWAVE Study)

Refractory persistent spinal pain syndrome after surgery (PSPS-T2) can be successfully addressed by spinal cord stimulation (SCS). While conventional stimulation generates paresthesia, recent systems enable the delivery of paresthesia-free stimulation. Studies have claimed non-inferiority/superiority of selected paresthesia-free stimulation compared with paresthesia-based stimulation, but the comparative efficacy between different waveforms still needs to be determined in a given patient. We designed a randomized controlled 3-month crossover trial to compare pain relief of paresthesia-based stimulation versus high frequency versus burst in 28 PSPS-T2 patients implanted with multiwave SCS systems. Our secondary objectives were to determine the efficacy of these 3 waveforms on pain surface, quality of life, functional capacity, psychological distress, and validated composite multidimensional clinical response index to provide holistic comparisons at 3-, 6-, 9-, and 15-month post-randomization. The preferred stimulation modality was documented during the follow-up periods. No difference between the waveforms was observed in this study (P = .08). SCS led to significant pain relief, quality of life improvement, improvement of multidimensional clinical response index, and of all other clinical outcomes at all follow-up visits. Forty-four percent of the patients chose to keep the paresthesia-based stimulation modality after the 15-month follow-up period. By giving the possibility to switch and/or to combine several waveforms, the overall rate of SCS responders further increased with 25%. In this study, high frequency or burst do not appear superior to paresthesia-based stimulation, wherefore paresthesia-based stimulation should still be considered as a valid option. However, combining paresthesia-based stimulation with paresthesia-free stimulation, through personalized multiwave therapy, might significantly improve SCS responses. PERSPECTIVE: This article assesses clinical SCS efficacy on pain relief, by comparing paresthesia-based stimulation and paresthesia-free stimulation (including high frequency and burst) modalities in patient presenting with PSPS-T2. Switching and/or combining waveforms contribute to increasing the global SCS responders rate.

Novel Pulsed Ultrahigh-frequency Spinal Cord Stimulation Inhibits Mechanical Hypersensitivity and Brain Neuronal Activity in Rats after Nerve Injury

BACKGROUND

Spinal cord stimulation (SCS) is an important pain treatment modality. This study hypothesized that a novel pulsed ultrahigh-frequency spinal cord stimulation (pUHF-SCS) could safely and effectively inhibit spared nerve injury-induced neuropathic pain in rats.

METHODS

Epidural pUHF-SCS (± 3V, 2-Hz pulses comprising 500-kHz biphasic sinewaves) was implanted at the thoracic vertebrae (T9 to T11). Local field brain potentials after hind paw stimulation were recorded. Analgesia was evaluated by von Frey-evoked allodynia and acetone-induced cold allodynia.

RESULTS

The mechanical withdrawal threshold of the injured paw was 0.91 ± 0.28 g lower than that of the sham surgery (24.9 ± 1.2 g). Applying 5-, 10-, or 20-min pUHF-SCS five times every 2 days significantly increased the paw withdrawal threshold to 13.3 ± 6.5, 18.5 ± 3.6, and 21.0 ± 2.8 g at 5 h post-SCS, respectively (P = 0.0002, < 0.0001, and < 0.0001; n = 6 per group) and to 6.1 ± 2.5, 8.2 ± 2.7, and 14.3 ± 5.9 g on the second day, respectively (P = 0.123, 0.013, and < 0.0001). Acetone-induced paw response numbers decreased from pre-SCS (41 ± 12) to 24 ± 12 and 28 ± 10 (P = 0.006 and 0.027; n = 9) at 1 and 5 h after three rounds of 20-min pUHF-SCS, respectively. The areas under the curve from the C component of the evoked potentials at the left primary somatosensory and anterior cingulate cortices were significantly decreased from pre-SCS (101.3 ± 58.3 and 86.9 ± 25.5, respectively) to 39.7 ± 40.3 and 36.3 ± 20.7 (P = 0.021, and 0.003; n = 5) at 60 min post-SCS, respectively. The intensity thresholds for pUHF-SCS to induce brain and sciatic nerve activations were much higher than the therapeutic intensities and thresholds of conventional low-frequency SCS.

CONCLUSIONS

Pulsed ultrahigh-frequency spinal cord stimulation inhibited neuropathic pain-related behavior and paw stimulation evoked brain activation through mechanisms distinct from low-frequency SCS.

EDITOR’S PERSPECTIVE

Use of spinal cord stimulation in treatment of intractable headache diseases

Headache diseases remain one of the leading causes of disability in the world. With the development of neuromodulation strategies, high cervical spinal cord stimulation (hcSCS) targeting the trigeminocervical complex has been deployed to treat refractory headache diseases. In this article, we review the proposed mechanism behind hcSCS stimulation, and the various studies that have been described for the successful use of this treatment strategy in patients with chronic migraine, cluster headache, and other trigeminal autonomic cephalalgias.

A Novel, Paresthesia-Free Spinal Cord Stimulation Waveform for Chronic Neuropathic Low Back Pain: Six-Month Results of a Prospective, Single-Arm, Dose-Response Study

OBJECTIVES

The aim of this prospective, single-blinded, dose-response study was to evaluate the safety and efficacy of a novel, paresthesia-free (subperception) spinal cord stimulation (SCS) waveform designed to target dorsal horn dendrites for the treatment of chronic neuropathic low back pain (LBP).

MATERIALS AND METHODS

Twenty-seven participants with chronic neuropathic LBP were implanted with a commercial SCS system after a successful trial of SCS therapy. Devices were programmed to deliver the investigative waveform (100 Hz, 1000 μs, T9/T10 bipole) at descending stimulation perception threshold amplitudes (80%, 60%, 40%). Programs were evaluated at six, ten, and 14 weeks, after which participants selected their preferred program, with more follow-up at 26 weeks (primary outcomes). Participants were blinded to the nature of the programming. Pain score (visual analog scale [VAS]), Brief Pain Inventory (BPI), quality of life (EQ-5D-5L), and health status (36-Item Short Form [SF-36]) were measured at baseline and follow-ups. Responder rate, treatment satisfaction, clinician global impression of change, and adverse events (AEs) also were evaluated.

RESULTS

Mean (± SD) baseline VAS was 72.5 ± 11.2 mm. At 26 weeks (n = 26), mean change from baseline in VAS was -51.7 mm (95% CI, -60.7 to -42.7; p < 0.001), with 76.9% of participants reporting ≥50% VAS reduction, and 46.2% reporting ≥80% VAS reduction. BPI, EQ-5D-5L, and SF-36 scores were all statistically significantly improved at 26 weeks (p < 0.001), and 100% of participants were satisfied with their treatment. There were no unanticipated AEs related to the study intervention, device, or procedures.

CONCLUSIONS

This novel, paresthesia-free stimulation waveform may be a safe and effective option for patients with chronic neuropathic LBP eligible for SCS therapy and is deliverable by all current commercial SCS systems.

CLINICAL TRIAL REGISTRATION

This study is registered on anzctr.org.au with identifier ACTRN12618000647235.

An optimization framework for targeted spinal cord stimulation

Objective. Spinal cord stimulation (SCS) is a common neurostimulation therapy to manage chronic pain. Technological advances have produced new neurostimulation systems with expanded capabilities in an attempt to improve the clinical outcomes associated with SCS. However, these expanded capabilities have dramatically increased the number of possible stimulation parameters and made it intractable to efficiently explore this large parameter space within the context of standard clinical programming procedures. Therefore, in this study, we developed an optimization approach to define the optimal current amplitudes or fractions across individual contacts in an SCS electrode array(s).Approach. We developed an analytic method using the Lagrange multiplier method along with smoothing approximations. To test our optimization framework, we used a hybrid computational modeling approach that consisted of a finite element method model and multi-compartment models of axons and cells within the spinal cord. Moreover, we extended our approach to multi-objective optimization to explore the trade-off between activating regions of interest (ROIs) and regions of avoidance (ROAs).Main results. For simple ROIs, our framework suggested optimized configurations that resembled simple bipolar configurations. However, when we considered multi-objective optimization, our framework suggested nontrivial stimulation configurations that could be selected from Pareto fronts to target multiple ROIs or avoid ROAs.Significance. We developed an optimization framework for targeted SCS. Our method is analytic, which allows for the fast calculation of optimal solutions. For the first time, we provided a multi-objective approach for selective SCS. Through this approach, we were able to show that novel configurations can provide neural recruitment profiles that are not possible with conventional stimulation configurations (e.g. bipolar stimulation). Most importantly, once integrated with computational models that account for sources of interpatient variability (e.g. anatomy, electrode placement), our optimization framework can be utilized to provide stimulation settings tailored to the needs of individual patients.

Publication Rates and Characteristics of Clinical Trials in Deep Brain and Responsive Neurostimulation

INTRODUCTION

Prompt dissemination of clinical trial results is essential for ensuring the safety and efficacy of intracranial neurostimulation treatments, including deep brain stimulation (DBS) and responsive neurostimulation (RNS). However, the frequency and completeness of results publication, and reasons for reporting delays, are unknown. Moreover, the patient populations, targeted anatomical locations, and stimulation parameters should be clearly reported for both reproducibility and to identify lacunae in trial design. Here, we examine DBS and RNS trials from 1997 to 2022, chart their characteristics, and examine rates and predictors of results reporting.

METHODS

Trials were identified using ClinicalTrials.gov. Associated publications were identified using ClinicalTrials.gov and PubMed.gov. Pearson's χ2 tests were used to assess differences in trial characteristics between published and unpublished trials.

RESULTS

Across 449 trials, representing a cumulative cohort of 42,769 patient interventions, there were 37 therapeutic indications and 44 stimulation targets. The most common indication and target were Parkinson's disease (40.55%) and the subthalamic nucleus (35.88%), respectively. Only 0.89% of trials were in pediatric patients (11.58% were mixed pediatric and adult). Explored targets represented 75% of potential basal ganglia targets but only 29% of potential thalamic targets. Allowing a 1-year grace period after trial completion, 34/169 (20.12%) had results reported on ClinicalTrials.gov, and 107/169 (63.31%) were published. ∼80% of published trials included details about stimulation parameters used. Published and unpublished trials did not significantly differ by trial characteristics.

CONCLUSION

We highlight key knowledge and performance gaps in DBS and RNS trial research. Over one-third of trials remain unpublished >1 year after completion; pediatric trials are scarce; most of the thalamus remains unexplored; about one-in-five trials fail to report stimulation parameters; and movement disorders comprise the most studied indications.

On temporal scale-free non-periodic stimulation and its mechanisms as an infinite improbability drive of the brain's functional connectogram

Rationalized development of electrical stimulation (ES) therapy is of paramount importance. Not only it will foster new techniques and technologies with increased levels of safety, efficacy, and efficiency, but it will also facilitate the translation from basic research to clinical practice. For such endeavor, design of new technologies must dialogue with state-of-the-art neuroscientific knowledge. By its turn, neuroscience is transitioning-a movement started a couple of decades earlier-into adopting a new conceptual framework for brain architecture, in which time and thus temporal patterns plays a central role in the neuronal representation of sampled data from the world. This article discusses how neuroscience has evolved to understand the importance of brain rhythms in the overall functional architecture of the nervous system and, consequently, that neuromodulation research should embrace this new conceptual framework. Based on such support, we revisit the literature on standard (fixed-frequency pulsatile stimuli) and mostly non-standard patterns of ES to put forward our own rationale on how temporally complex stimulation schemes may impact neuromodulation strategies. We then proceed to present a low frequency, on average (thus low energy), scale-free temporally randomized ES pattern for the treatment of experimental epilepsy, devised by our group and termed NPS (Non-periodic Stimulation). The approach has been shown to have robust anticonvulsant effects in different animal models of acute and chronic seizures (displaying dysfunctional hyperexcitable tissue), while also preserving neural function. In our understanding, accumulated mechanistic evidence suggests such a beneficial mechanism of action may be due to the natural-like characteristic of a scale-free temporal pattern that may robustly compete with aberrant epileptiform activity for the recruitment of neural circuits. Delivering temporally patterned or random stimuli within specific phases of the underlying oscillations (i.e., those involved in the communication within and across brain regions) could both potentiate and disrupt the formation of neuronal assemblies with random probability. The usage of infinite improbability drive here is obviously a reference to the "The Hitchhiker's Guide to the Galaxy" comedy science fiction classic, written by Douglas Adams. The parallel is that dynamically driving brain functional connectogram, through neuromodulation, in a manner that would not favor any specific neuronal assembly and/or circuit, could re-stabilize a system that is transitioning to fall under the control of a single attractor. We conclude by discussing future avenues of investigation and their potentially disruptive impact on neurotechnology, with a particular interest in NPS implications in neural plasticity, motor rehabilitation, and its potential for clinical translation.

Narrative review of current neuromodulation modalities for spinal cord injury

Neuromodulation is a developing field of medicine that includes a vast array of minimally invasive and non-invasive therapies including transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), vagus nerve stimulation (VNS), peripheral nerve stimulation, and spinal cord stimulation (SCS). Although the current literature surrounding the use of neuromodulation in managing chronic pain is abundant, there is an insufficient amount of evidence specifically regarding neuromodulation in patients with spinal cord injury (SCI). Given the pain and functional deficits that these patients face, that are not amenable to other forms conservative therapy, the purpose of this narrative review is to examine and assess the use of various neuromodulation modalities to manage pain and restore function in the SCI population. Currently, high-frequency spinal cord stimulation (HF-SCS) and burst spinal cord stimulation (B-SCS) have been shown to have the most promising effect in improving pain intensity and frequency. Additionally, dorsal root ganglion stimulation (DRG-S) and TMS have been shown to effectively increase motor responses and improve limb strength. Although these modalities carry the potential to enhance overall functionality and improve a patient's degree of disability, there is a lack of long-term, randomized-controlled trials in the current space. Additional research is warranted to further support the clinical use of these emerging modalities to provide improved pain management, increased level of function, and ultimately an overall better quality of life in the SCI population.

Combination therapy with simultaneous delivery of spinal cord stimulation modalities: COMBO randomized controlled trial

Aim: The Combining Mechanisms for Better Outcomes randomized controlled trial assessed the effectiveness of various spinal cord stimulation (SCS) modalities for chronic pain. Specifically, combination therapy (simultaneous use of customized sub-perception field and paresthesia-based SCS) versus monotherapy (paresthesia-based SCS) was evaluated. Methods: Participants were prospectively enrolled (key inclusion criterion: chronic pain for ≥6 months). Primary end point was the proportion with ≥50% pain reduction without increased opioids at the 3-month follow-up. Patients were followed for 2 years. Results: The primary end point was met (n = 89; p < 0.0001) in 88% of patients in the combination-therapy arm (n = 36/41) and 71% in the monotherapy arm (n = 34/48). Responder rates at 1 and 2 years (with available SCS modalities) were 84% and 85%, respectively. Sustained functional outcomes improvement was observed out to 2 years. Conclusion: SCS-based combination therapy can improve outcomes in patients with chronic pain. Clinical Trial Registration: NCT03689920 (ClinicalTrials.gov), Combining Mechanisms for Better Outcomes (COMBO).

Impact of spinal cord stimulation on sick leave and disability pension in patients with chronic neuropathic pain: a real-world evidence study in Sweden

ABSTRACT

Current research indicates that spinal cord stimulation (SCS) has a positive short-term impact on outcomes, such as quality of life, pain, and productivity in patients with chronic neuropathic pain. However, there is a need for studies on larger population samples. This study used data from Swedish national registers to analyze change and predictors of sick leave and disability pension 2 years before and after SCS treatment. Patients with SCS implanted between 2006 and 2017, and a reference group consisting of 5 individuals matched to each SCS patient without replacement with respect to age, sex, and region of residence, were included. A difference-in-difference approach was used to compare the average change (2 years after treatment vs 2 years before treatment) in net disability days and indirect cost related to disability days for the SCS group, compared with the average change for the reference group. The results showed that SCS treatment in Sweden is associated with a decrease of 21 disability days and consequent decrease in indirect cost of €4127 in working age patients. Large work loss prior to index date was also demonstrated (average 214 days before 1 year), indicating a significant burden on the patient, employers, and the society at large. The number of disability days varied considerably depending on age, sex, socioeconomic variables, and comorbidities; however, the effect of SCS seemed to have little association with patient characteristics. This economic benefit needs to be considered, as well as the clinical outcome, when evaluating the full societal value of SCS.

Advances in Pain Medicine: a Review of New Technologies

Purpose of Review

This narrative review highlights the interventional musculoskeletal techniques that have evolved in recent years.

Recent Findings

The recent progress in pain medicine technologies presented here represents the ideal treatment of the pain patient which is to provide personalized care. Advances in pain physiology research and pain management technologies support each other concurrently.

Summary

As new technologies give rise to new perspectives and understanding of pain, new research inspires the development of new technologies

Novel Therapies for the Treatment of Neuropathic Pain: Potential and Pitfalls

Neuropathic pain affects more than one million people across the globe. The quality of life of people suffering from neuropathic pain has been considerably declining due to the unavailability of appropriate therapeutics. Currently, available treatment options can only treat patients symptomatically, but they are associated with severe adverse side effects and the development of tolerance over prolonged use. In the past decade, researchers were able to gain a better understanding of the mechanisms involved in neuropathic pain; thus, continuous efforts are evident, aiming to develop novel interventions with better efficacy instead of symptomatic treatment. The current review discusses the latest interventional strategies used in the treatment and management of neuropathic pain. This review also provides insights into the present scenario of pain research, particularly various interventional techniques such as spinal cord stimulation, steroid injection, neural blockade, transcranial/epidural stimulation, deep brain stimulation, percutaneous electrical nerve stimulation, neuroablative procedures, opto/chemogenetics, gene therapy, etc. In a nutshell, most of the above techniques are at preclinical stage and facing difficulty in translation to clinical studies due to the non-availability of appropriate methodologies. Therefore, continuing research on these interventional strategies may help in the development of promising novel therapies that can improve the quality of life of patients suffering from neuropathic 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.

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.

Neural Substrates of Transcutaneous Spinal Cord Stimulation: Neuromodulation across Multiple Segments of the Spinal Cord

Transcutaneous spinal cord stimulation (tSCS) has the potential to promote improved sensorimotor rehabilitation by modulating the circuitry of the spinal cord non-invasively. Little is currently known about how cervical or lumbar tSCS influences the excitability of spinal and corticospinal networks, or whether the synergistic effects of multi-segmental tSCS occur between remote segments of the spinal cord. The aim of this review is to describe the emergence and development of tSCS as a novel method to modulate the spinal cord, while highlighting the effectiveness of tSCS in improving sensorimotor recovery after spinal cord injury. This review underscores the ability of single-site tSCS to alter excitability across multiple segments of the spinal cord, while multiple sites of tSCS converge to facilitate spinal reflex and corticospinal networks. Finally, the potential and current limitations for engaging cervical and lumbar spinal cord networks through tSCS to enhance the effectiveness of rehabilitation interventions are discussed. Further mechanistic work is needed in order to optimize targeted rehabilitation strategies and improve clinical outcomes.

Successful application of spinal cord stimulation in a patient with refractory bilateral meralgia paresthetica

We present a 38-year-old morbidly obese male who presented with functionally limiting bilateral anterior thigh pain consistent with meralgia paresthetica. His symptoms had been unresponsive to conservative measures which included physical therapy, oral medications and multiple nerve blocks. Patient underwent a trial of spinal cord stimulation (SCS), experiencing 70% of pain relief. He then underwent permanent SCS implant. At subsequent follow-ups 3 and 6 months later, he continued to report 70% improvement of his pain, as well as improved function and quality of life. To our knowledge, this is only the second reported case of successful treatment of meralgia paresthetica with SCS, and the first in a morbidly obese patient.

Comparison of Paresthesia Mapping With Anatomic Placement in Burst Spinal Cord Stimulation: Long-Term Results of the Prospective, Multicenter, Randomized, Double-Blind, Crossover CRISP Study

OBJECTIVES

Spinal cord stimulation (SCS) is an effective therapy for chronic intractable pain. Conventional SCS involves electrode placement based on intraoperative paresthesia mapping; however, newer paradigms like burst may allow for anatomic placement of leads. Here, for the first time, we report the one-year safety and efficacy of burst SCS delivered using a lead placed with conventional, paresthesia mapping, or anatomic placement approach in subjects with chronic low back pain (CLBP).

MATERIALS AND METHODS

Subjects with CLBP were implanted with two leads. The first lead was placed to cross the T8/T9 disc and active contacts for this lead were chosen through paresthesia mapping. The second lead was placed at the T9/T10 spinal anatomic landmark. Subjects initially underwent a four-week, double-blinded, crossover trial with a two-week testing period with burst SCS delivered through each lead in a random order. At the end of trial period, subjects expressed their preference for one of the two leads. Subsequently, subjects received burst SCS with the preferred lead and were followed up at 3, 6, and 12 months. Pain intensity (visual analog scale), quality-of-life (EuroQol-5D instrument), and disability (Oswestry Disability Index) were evaluated at baseline and follow-up.

RESULTS

Forty-three subjects successfully completed the trial. Twenty-one preferred the paresthesia mapping lead and 21 preferred the anatomic placement lead. Anatomic placement lead was activated in one subject who had no preference. The pain scores (for back and leg) significantly improved from baseline for both lead placement groups at all follow-up time points, with no significant between-group differences.

CONCLUSIONS

This study demonstrated that equivalent clinical benefits could be achieved with burst SCS using either paresthesia mapping or anatomic landmark-based approaches for lead placement. Nonparesthesia-based approaches, such as anatomic landmark-based lead placement investigated here, have the potential to simplify implantation of SCS and improve current surgical practice.

High-frequency spinal cord stimulation produces long-lasting analgesic effects by restoring lysosomal function and autophagic flux in the spinal dorsal horn

High-frequency spinal cord stimulation (HF-SCS) has been established as an effective therapy for neuropathic pain. However, the analgesic mechanisms involved in HF-SCS remain to be clarified. In our study, adult rat neuropathic pain was induced by spinal nerve ligation. Two days after modeling, the rats were subjected to 4 hours of HF-SCS (motor threshold 50%, frequency 10,000 Hz, and pulse width 0.024 ms) in the dorsal horn of the spinal cord. The results revealed that the tactile allodynia of spinal nerve-injured rats was markedly alleviated by HF-SCS, and the effects were sustained for 3 hours after the stimulation had ceased. HF-SCS restored lysosomal function, increased the levels of lysosome-associated membrane protein 2 (LAMP2) and the mature form of cathepsin D (matu-CTSD), and alleviated the abnormally elevated levels of microtubule-associated protein 1A/B-light chain 3 (LC3)-II and sequestosome 1 (P62) in spinal nerve-injured rats. HF-SCS also mostly restored the immunoreactivity of LAMP2, which was localized in neurons in the superficial layers of the spinal dorsal horn in spinal nerve-injured rats. In addition, intraperitoneal administration of 15 mg/kg chloroquine for 60 minutes reversed the expression of the aforementioned proteins and shortened the timing of the analgesic effects of HF-SCS. These findings suggest that HF-SCS may exhibit long-lasting analgesic effects on neuropathic pain in rats through improving lysosomal dysfunction and alleviating autophagic flux. This study was approved by the Laboratory Animal Ethics Committee of China Medical University, Shenyang, China (approval No. 2017PS196K) on March 1, 2017.

Effects of Noninvasive Low-Intensity Focus Ultrasound Neuromodulation on Spinal Cord Neurocircuits In Vivo

Although neurocircuits can be activated by focused ultrasound stimulation, it is unclear whether this is also true for spinal cord neurocircuits. In this study, we used low-intensity focused ultrasound (LIFU) to stimulate lumbar 4–lumbar 5 (L4–L5) segments of the spinal cord of normal Sprague Dawley rats with a clapper. The activation of the spinal cord neurocircuits enhanced soleus muscle contraction as measured by electromyography (EMG). Neuronal activation and injury were assessed by EMG, western blotting (WB), immunofluorescence, hematoxylin and eosin (H&E) staining, Nissl staining, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry (IHC), somatosensory evoked potentials (SEPs), motor evoked potentials (MEPs), and the Basso–Beattie–Bresnahan locomotor rating scale. When the LIFU intensity was more than 0.5 MPa, LIFU stimulation induced soleus muscle contraction and increased the EMG amplitudes (P < 0.05) and the number of c-fos- and GAD65-positive cells (P < 0.05). When the LIFU intensity was 3.0 MPa, the LIFU stimulation led to spinal cord damage and decreased SEP amplitudes for electrophysiological assessment (P < 0.05); this resulted in coagulation necrosis, structural destruction, neuronal loss in the dorsal horn by H&E and Nissl staining, and increased expression of GFAP, IL-1β, TNF-α, and caspase-3 by IHC, ELISA, and WB (P < 0.05). These results show that LIFU can activate spinal cord neurocircuits and that LIFU stimulation with an irradiation intensity ≤1.5 MPa is a safe neurostimulation method for the spinal cord.

A narrative review and future considerations of spinal cord stimulation, dorsal root ganglion stimulation and peripheral nerve stimulation

PURPOSE OF REVIEW

In recent years, neuromodulation has experienced a renaissance. Novel waveforms and anatomic targets show potential improvements in therapy that may signify substantial benefits. New innovations in peripheral nerve stimulation and dorsal root ganglion stimulation have shown prospective evidence and sustainability of results. Sub-perception physiologic bursting, high-frequency stimulation and feedback loop mechanisms provide significant benefits over traditional tonic spinal cords stimulation (SCS) in peer reviewed investigations. We reviewed the themes associated with novel technology in the context of historical stalwart publications.

RECENT FINDINGS

New innovations have led to better nerve targeting, improvements in disease-based treatment, and opioid alternatives for those in chronic pain. In addition, new neural targets from both structural and cellular perspectives have changed the field of Neurostimulation.

SUMMARY

For many years, tonic SCS was representative of neuromodulation, but as this review examines, the progression of the field in the past decade has reshaped patient options.

Tissue Temperature Increases by a 10 kHz Spinal Cord Stimulation System: Phantom and Bioheat Model

OBJECTIVE

A recently introduced Spinal Cord Stimulation (SCS) system operates at 10 kHz, faster than conventional SCS systems, resulting in significantly more power delivered to tissues. Using a SCS heat phantom and bioheat multi-physics model, we characterized tissue temperature increases by this 10 kHz system. We also evaluated its Implanted Pulse Generator (IPG) output compliance and the role of impedance in temperature increases.

MATERIALS AND METHODS

The 10 kHz SCS system output was characterized under resistive loads (1-10 KΩ). Separately, fiber optic temperature probes quantified temperature increases (ΔTs) around the SCS lead in specially developed heat phantoms. The role of stimulation Level (1-7; ideal pulse peak-to-peak of 1-7mA) was considered, specifically in the context of stimulation current Root Mean Square (RMS). Data from the heat phantom were verified with the SCS heat-transfer models. A custom high-bandwidth stimulator provided 10 kHz pulses and sinusoidal stimulation for control experiments.

RESULTS

The 10 kHz SCS system delivers 10 kHz biphasic pulses (30-20-30 μs). Voltage compliance was 15.6V. Even below voltage compliance, IPG bandwidth attenuated pulse waveform, limiting applied RMS. Temperature increased supralinearly with stimulation Level in a manner predicted by applied RMS. ΔT increases with Level and impedance until stimulator compliance was reached. Therefore, IPG bandwidth and compliance dampen peak heating. Nonetheless, temperature increases predicted by bioheat multi-physic models (ΔT = 0.64°C and 1.42°C respectively at Level 4 and 7 at the cervical segment; ΔT = 0.68°C and 1.72°C respectively at Level 4 and 7 at the thoracic spinal cord)-within ranges previously reported to effect neurophysiology.

CONCLUSIONS

Heating of spinal tissues by this 10 kHz SCS system theoretically increases quickly with stimulation level and load impedance, while dampened by IPG pulse bandwidth and voltage compliance limitations. If validated in vivo as a mechanism of kHz SCS, bioheat models informed by IPG limitations allow prediction and optimization of temperature changes.

The Immediate and Short-Term Effects of Transcutaneous Spinal Cord Stimulation and Peripheral Nerve Stimulation on Corticospinal Excitability

Rehabilitative interventions involving electrical stimulation show promise for neuroplastic recovery in people living with Spinal Cord Injury (SCI). However, the understanding of how stimulation interacts with descending and spinal excitability remain unclear. In this study we compared the immediate and short-term (within a few minutes) effects of pairing Transcranial Magnetic Stimulation (TMS) with transcutaneous Spinal Cord stimulation (tSCS) and Peripheral Nerve Stimulation (PNS) on Corticospinal excitability in healthy subjects. Three separate experimental conditions were assessed. In Experiment I, paired associative stimulation (PAS) was applied, involving repeated pairing of single pulses of TMS and tSCS, either arriving simultaneously at the spinal motoneurones (PAS_0ms) or slightly delayed (PAS_5ms). Corticospinal and spinal excitability, and motor performance, were assessed before and after the PAS interventions in 24 subjects. Experiment II compared the immediate effects of tSCS and PNS on corticospinal excitability in 20 subjects. Experiment III compared the immediate effects of tSCS with tSCS delivered at the same stimulation amplitude but modulated with a carrier frequency (in the kHz range) on corticospinal excitability in 10 subjects. Electromyography (EMG) electrodes were placed over the Tibialis Anterior (TA) soleus (SOL) and vastus medialis (VM) muscles and stimulation electrodes (cathodes) were placed on the lumbar spine (tSCS) and lateral to the popliteal fossa (PNS). TMS over the primary motor cortex (M1) was paired with tSCS or PNS to produce Motor Evoked Potentials (MEPs) in the TA and SOL muscles. Simultaneous delivery of repetitive PAS (PAS_0ms) increased corticospinal excitability and H-reflex amplitude at least 5 min after the intervention, and dorsiflexion force was increased in a force-matching task. When comparing effects on descending excitability between tSCS and PNS, a subsequent facilitation in MEPs was observed following tSCS at 30-50 ms which was not present following PNS. To a lesser extent this facilitatory effect was also observed with HF- tSCS at subthreshold currents. Here we have shown that repeated pairing of TMS and tSCS can increase corticospinal excitability when timed to arrive simultaneously at the alpha-motoneurone and can influence functional motor output. These results may be useful in optimizing stimulation parameters for neuroplasticity in people living with SCI.

High-frequency spinal cord stimulation in failed back surgery syndrome patients with predominant low back pain-single-center experience

Treatment of patients with failed back surgery syndrome (FBSS) with predominant low back pain (LBP) remains challenging. High-frequency spinal cord stimulation (HF10 SCS) is believed to achieve significant pain reduction. We aimed to evaluate the real-life efficacy of HF-10 SCS in a tertiary spine center. A prospective observational study of all patients with FBSS and predominant LBP who underwent HF-10 SCS surgery was performed between 2016 and 2018. Patients > 18 years with Visual Analogue Scale (VAS) scores of ≥ 5 for LBP and pain duration > 6 months under stable medication were implanted percutaneous under general anesthesia and a trial phase of 7-14 days was accomplished. Primary end point was a successful trial defined as ≥ 50% VAS score reduction for LBP. Thirty-four of 39 (85%) subjects had a successful trial. Fifty-three percent were female and the mean age was 69 years. Median follow-up lasted for 10 months. Devices were removed after a median of 10 months in 5 cases. Remaining 29 patients stated significant VAS score reduction for LBP from 8.1 to 2.9 and VAS for leg pain from 4.9 to 2.2. Twenty-four percent of all patients were able to discontinue their opioids. Eight of 9 patients (89%) with signs of adjacent disc disease and 7 of 10 (70%) patients with hardware failure were successfully implanted with significant VAS reduction for LBP. HF-10 SCS achieves significant pain reduction in most patients with FBSS and predominant LBP. It might be an efficient alternative to revision surgery.

A Call to Action Toward Optimizing the Electrical Dose Received by Neural Targets in Spinal Cord Stimulation Therapy for Neuropathic Pain

Spinal cord stimulation has seen unprecedented growth in new technology in the 50 years since the first subdural implant. As we continue to grow our understanding of spinal cord stimulation and relevant mechanisms of action, novel questions arise as to electrical dosing optimization. Programming adjustment — dose titration — is often a process of trial and error that can be time-consuming and frustrating for both patient and clinician. In this report, we review the current preclinical and clinical knowledge base in order to provide insights that may be helpful in developing more rational approaches to spinal cord stimulation dosing. We also provide key conclusions that may help in directing future research into electrical dosing, given the advent of newer waveforms outside traditional programming parameters.

Real-World Outcomes Using a Spinal Cord Stimulation Device Capable of Combination Therapy for Chronic Pain: A European, Multicenter Experience

Given the differing mechanisms thought to underlie therapeutic sub- and supra-perception-based neurostimulative modalities, Spinal Cord Stimulation (SCS) systems designed for combined delivery of these approaches may help improve analgesic outcomes and quality of life, and reduce treatment failures. This multicenter, observational case-series evaluated 188 patients with chronic back and/or leg pain implanted with an SCS device capable of sequential or simultaneous delivery of sub-perception and supra-perception stimulation programming (i.e., combination therapy) at 16 in Europe. Following implantation, patients were provided with an array of advanced supra-perception programs (e.g., paresthesia-based SCS using multiple independent current sources), and a custom set of sub-perception programs optimized with specific waveforms and/or field shapes. A mean overall pain score of 7.9 ± 1.7 (Standard Deviation (SD)) was reported pre-trial (Baseline). Overall pain was reduced by 4.4 ± 2.8 points (NRS) at 3-months (n = 117) and at 12 months post-implant (n = 90), respectively (p < 0.0001). Substantial quality-of-life (EQ-5D-5L) improvement as assessed at last follow-up was also observed (n = 60). These results suggest that an implanted SCS device capable of combination therapy, while also enabled with patient-specific waveform optimization and stimulation field targeting capabilities, can enable highly effective pain relief and improve quality of life in patients suffering with chronic pain.

Effects of Dorsal Column Spinal Cord Stimulation on Neuroinflammation: Revisiting Molecular Mechanisms and Clinical Outcomes on Chronic Lumbar/Leg Pain and Failed Back Surgery Syndrome

OBJECTIVE

In this narrative review, we reviewed and discussed current literature describing the molecular mechanisms leading to neuroinflammation and its role in the onset and progression of chronic neuropathic lumbar and leg pain in patients with persistent spinal pain syndrome. In addition, we reviewed the proposed mechanisms and impact of spinal cord stimulation (SCS) on neuroinflammation.

METHODS

A broad search of current literature in PubMed, Embase, Scopus, Cochrane library, Medline/Ovid, and Web of Science was performed using the following terms and their combinations: "biomarkers", "chronic back and leg pain", "cytokines", "neuroinflammation", "spinal cord stimulation (scs)," and "spinal cord modulation". We selected: 1) articles published in the English language between January 2000 and July 2020 2) preclinical and clinical data 3) case reports 4) meta-analysis and systematic reviews and 5) conference abstracts. Manuscripts not disclosing methodology or without full-text availability were excluded.

DISCUSSION

SCS techniques have gradually evolved since inception to include novel methods such as burst-SCS, high frequency SCS, and differential targeted multiplexed SCS. The incidence of chronic pain after spine surgery is highly variable, with at least one third of patients developing persistent spinal pain syndrome. Novel SCS techniques have been associated with improved clinical and functional outcomes thus increasing patient quality of life.

CONCLUSION

Currently, health care providers rely on different options and methods for SCS when treating patients with refractory chronic lumbar pain and persistent spinal pain syndrome. Nevertheless, compelling clinical trials remain necessary to elucidate the long-term benefits and mechanisms of neuromodulation of all different types of SCS.

Management of Chronic and Neuropathic Pain with 10 kHz Spinal Cord Stimulation Technology: Summary of Findings from Preclinical and Clinical Studies

Since the inception of spinal cord stimulation (SCS) in 1967, the technology has evolved dramatically with important advancements in waveforms and frequencies. One such advancement is Nevro’s Senza^® SCS System for HF10, which received Food and Drug and Administration (FDA) approval in 2015. Low-frequency SCS works by activating large-diameter Aβ fibers in the lateral discriminatory pathway (pain location, intensity, quality) at the dorsal column (DC), creating paresthesia-based stimulation at lower-frequencies (30–120 Hz), high-amplitude (3.5–8.5 mA), and longer-duration/pulse-width (100–500 μs). In contrast, high-frequency 10 kHz SCS works with a proposed different mechanism of action that is paresthesia-free with programming at a frequency of 10,000 Hz, low amplitude (1–5 mA), and short-duration/pulse-width (30 μS). This stimulation pattern selectively activates inhibitory interneurons in the dorsal horn (DH) at low stimulation intensities, which do not activate the dorsal column fibers. This ostensibly leads to suppression of hyperexcitable wide dynamic range neurons (WDR), which are sensitized and hyperactive in chronic pain states. It has also been reported to act on the medial pathway (drives attention and pain perception), in addition to the lateral pathways. Other theories include a reversible depolarization blockade, desynchronization of neural signals, membrane integration, glial–neuronal interaction, and induced temporal summation. The body of clinical evidence regarding 10 kHz SCS treatment for chronic back pain and neuropathic pain continues to grow. There is high-quality evidence supporting its use in patients with persistent back and radicular pain, particularly after spinal surgery. High-frequency 10 kHz SCS studies have demonstrated robust statistically and clinically significant superiority in pain control, compared to paresthesia-based SCS, supported by level I clinical evidence. Yet, as the field continues to grow with the technological advancements of multiple waveforms and programming stimulation algorithms, we encourage further research to focus on the ability to modulate pain with precision and efficacy, as the field of neuromodulation continues to adapt to the modern healthcare era.

High-frequency spinal cord stimulation as rescue therapy for chronic pain patients with failure of conventional spinal cord stimulation

BACKGROUND

This study aims to evaluate the efficacy of 10-kHz high-frequency (HF10) devices as a rescue treatment in patients with failure of conventional spinal cord stimulation (SCS) therapy for chronic pain without the need to change the spinal hardware.

METHODS

In this real-world prospective study, patients with neuropathic pain treated with conventional tonic SCS in whom the therapy had failed, either during the trial phase or after a period of optimal functioning, were recruited throughout 2 years for HF10-SCS therapy. Data on analgesia, functionality, analgesics use and treatment safety were collected 12 months after treatment.

RESULTS

Eleven of the 18 (61%) patients included in the study were successfully rescued with HF10-SCS. Of them, 5 out of 12 (45%) were in the trial phase and six out of six (100%) had previously functioning implants. A significant improvement in low-back and limb pain was obtained (p = 0.003 and p = 0.0001, respectively). Treatment success was significantly associated with gender (p = 0.037), weight (p = 0.014), body mass index (BMI) (p = 0.007) and time of rescue (p = 0.015). A linear regression test confirmed a significant association between treatment failure and BMI and gender (p = 0.004).

CONCLUSIONS

Our results suggest that analgesic rescue with HF10-SCS is an effective therapeutic option for non-responders to conventional SCS, although obesity might be a limiting factor for treatment success. Nevertheless, more comprehensive studies are needed to corroborate our findings.

SIGNIFICANCE

This study shows that high-frequency stimulation may be useful in patients with failure of conventional tonic stimulation for chronic pain, both in the trial phase and in previously implanted subjects. The novelty of this study lies in the use of the implanted epidural electrodes, which avoids the need for further surgery. The results in terms of pain control and recovery of functionality are satisfactory. In addition, variables such as male gender and high body mass index could be predictors of therapy failure.

A novel fast-acting sub-perception spinal cord stimulation therapy enables rapid onset of analgesia in patients with chronic pain

Background: Treating chronic pain using sub-perception Spinal Cord Stimulation (SCS) does not elicit paresthesia but is associated with long analgesic 'wash-in' (i.e. duration until maximum pain relief) and prolonged assessment of therapy. We describe the attainment of clinically meaningful and rapid-onset analgesic outcomes using a novel sub-perception SCS approach.Methods: This observational case-series evaluated patients implanted with an SCS device for chronic pain, who underwent re-programming utilizing a new methodology in which paresthesia was used to guide sub-perception stimulation field targeting at specific parameters including charge-balanced symmetrical pulses at 90 Hz (termed Fast-Acting Sub-Perception Therapy, FAST). Pain scores (NRS) were collected as reported per standard-of-care from patient charts.Results: Mean overall pain score at baseline was 8.4 ± 0.2 (n = 41). After activation of FAST, a 7.1-point reduction in overall pain score was (1.3 ± 0.2, p < 0.0001) reported within 11.2 ± 1.9 minutes (n = 34). This decrease in pain score was sustained out to 3-month (1.6 ± 0.3, n = 26) and 6-month follow-up (1.7 ± 0.4, n = 18). At last follow up (mean = 223 ± 132 days), a pain score of 1.6 ± 0.3, n = 30 was determined.Conclusions: After FAST implementation, a profound analgesic response, requiring substantially less energy than conventional sub-perception methodologies, was observed. This rapid analgesic onset achieved with the novel FAST technique suggests the potential for an alternative mechanism of action(s) of sub-perception SCS.

Cervical Electrical Neuromodulation Effectively Enhances Hand Motor Output in Healthy Subjects by Engaging a Use-Dependent Intervention

Electrical enabling motor control (eEmc) through transcutaneous spinal cord stimulation is a non-invasive method that can modify the functional state of the sensory-motor system. We hypothesize that eEmc delivery, together with hand training, improves hand function in healthy subjects more than either intervention alone by inducing plastic changes at spinal and cortical levels. Ten voluntary participants were included in the following three interventions: (i) hand grip training, (ii) eEmc, and (iii) eEmc with hand training. Functional evaluation included the box and blocks test (BBT) and hand grip maximum voluntary contraction (MVC), spinal and cortical motor evoked potential (sMEP and cMEP), and resting motor thresholds (RMT), short interval intracortical inhibition (SICI), and F wave in the abductor pollicis brevis muscle. eEmc combined with hand training retained MVC and increased F wave amplitude and persistency, reduced cortical RMT and facilitated cMEP amplitude. In contrast, eEmc alone only increased F wave amplitude, whereas hand training alone reduced MVC and increased cortical RMT and SICI. In conclusion, eEmc combined with hand grip training enhanced hand motor output and induced plastic changes at spinal and cortical level in healthy subjects when compared to either intervention alone. These data suggest that electrical neuromodulation changes spinal and, perhaps, supraspinal networks to a more malleable state, while a concomitant use-dependent mechanism drives these networks to a higher functional state.

Isotonic ion replacement can lower the threshold for selective infrared neural inhibition

Significance: Infrared (IR) inhibition can selectively block peripheral sensory nerve fibers, a potential treatment for autonomic-dysfunction-related diseases (e.g., neuropathic pain and interstitial cystitis). Lowering the IR inhibition threshold can increase its translational potentials. Aim: Infrared induces inhibition by enhancing potassium channel activation. We hypothesized that the IR dose threshold could be reduced by combining it with isotonic ion replacement. Approach: We tested the IR inhibition threshold on the pleural-abdominal connective of Aplysia californica. Using a customized chamber system, the IR inhibition was applied either in normal saline or in isotonic ion-replaced saline, which could be high glucose saline, high choline saline, or high glucose/high choline saline. Each modified saline was at a subthreshold concentration for inhibiting neural conduction. Results: We showed that isotonically replacing ions in saline with glucose and/or choline can reduce the IR threshold and temperature threshold of neural inhibition. Furthermore, the size selectivity of IR inhibition was preserved when combined with high glucose/high choline saline. Conclusions: The present work of IR inhibition combined with isotonic ion replacement will guide further development of a more effective size-selective IR inhibition modality for future research and translational applications.

Spinal Cord Stimulation Attenuates Below-Level Mechanical Hypersensitivity in Rats After Thoracic Spinal Cord Injury

OBJECTIVES

The burden of pain after spinal cord injury (SCI), which may occur above, at, or below injury level, is high worldwide. Spinal cord stimulation (SCS) is an important neuromodulation pain therapy, but its efficacy in SCI pain remains unclear. In SCI rats, we tested whether conventional SCS (50 Hz, 80% motor threshold [MoT]) and 1200 Hz, low-intensity SCS (40% MoT) inhibit hind paw mechanical hypersensitivity, and whether conventional SCS attenuates evoked responses of wide-dynamic range (WDR) neurons in lumbar spinal cord.

MATERIALS AND METHODS

Male rats underwent a moderate contusive injury at the T9 vertebral level. Six to eight weeks later, SCS or sham stimulation (120 min, n = 10) was delivered through epidural miniature electrodes placed at upper-lumbar spinal cord, with using a crossover design. Mechanical hypersensitivity was examined in awake rats by measuring paw withdrawal threshold (PWT) to stimulation with von Frey filaments. WDR neurons were recorded with in vivo electrophysiologic methods in a separate study of anesthetized rats.

RESULTS

Both conventional SCS and 1200 Hz SCS increased PWTs from prestimulation level in SCI rats, but the effects were modest and short-lived. Sham SCS was not effective. Conventional SCS (10 min) at an intensity that evokes the peak Aα/β waveform of sciatic compound action potential did not inhibit WDR neuronal responses (n = 19) to graded or repeated electrical stimulation that induces windup.

CONCLUSIONS

Conventional SCS and 1200 Hz, low-intensity SCS modestly attenuated below-level mechanical hypersensitivity after SCI. Inhibition of WDR neurons was not associated with pain inhibition from conventional SCS.

Spinal cord stimulation for chronic intractable trunk or limb pain: study protocol for a Chinese multicenter randomized withdrawal trial (CITRIP study)

Background

Although effective results of many studies support the use of spinal cord stimulation in chronic pain patients, no randomized controlled trial has been undertaken in China to date. CITRIP is a multicenter, prospective, randomized, withdrawal study designed to evaluate the clinical effectiveness and safety of spinal cord stimulation plus remote programming management in patients with intractable trunk or limb pain.

Method

Participants will be recruited in approximately 10 centers across China. Eligible participants with intractable trunk or limb and an average visual analog scale (VAS) score ≥ 5 will undergo a spinal cord stimulation test. Participants with VAS score reduction ≥ 50% could move forward to receive implantation of an implanted pulse generator. In the withdrawal period at 3-month follow-up visit, participants randomized to the experimental group (EG) will undergo continuous stimulation while ceasing the stimulation in the control group (CG). The outcome assessment will occur at baseline and at 1, 3 (pre- and post-randomization), and 6 months. The primary outcome is the difference of maximal VAS score between EG and CG in the withdrawal period compared with baseline before the withdrawal period. Additional outcomes include VAS score change at 1-, 3-, and 6-month follow-ups; responder rate (VAS score improving by 50%); achievement rate of a desirable pain state (VAS score ≤ 4); awake times during sleep; Beck Depression Inventory for depression evaluation; short-form 36 for quality of life evaluation; drug usage; and satisfaction rating of the device. Adverse events will be collected. The primary analysis will follow the intention-to-treat principle.

Discussion

The CITRIP study seeks to evaluate the effectiveness and safety of a randomized withdrawal trial of spinal cord stimulation for patients with intractable trunk or limb pain.

Trial registration

ClinicalTrials.gov NCT03858790. Registered on March 1, 2019, retrospectively registered

Clinical Effectiveness and Mechanism of Action of Spinal Cord Stimulation for Treating Chronic Low Back and Lower Extremity Pain: a Systematic Review

PURPOSE OF REVIEW

The purpose of the present systematic review is to provide a current understanding of the mechanism of action and the evidence available to support clinical decision-making. The focus is to summarize randomized controlled trials (RCTs) and nonrandomized or observational studies of spinal cord stimulation in chronic pain to understand clinical effectiveness and the mechanism of action.

RECENT FINDINGS

Several recent studies have demonstrated the benefit of spinal cord stimulation in managing chronic pain. Until recently, the mechanism of action was founded on a central paradigm derived from gate control theory, which is the need to stimulate the dorsal column of the spinal cord to generate paresthesia. The recent development of new therapies that do not rely on paresthesia has left the field without a clear mechanism of action that could serve as a strong foundation to further improve clinical outcomes. Consequently, multiple theories have emerged to explain how electrical pulse applied to the spinal cord could alleviate pain, including activation of specific supraspinal pathways, and segmental modulation of the neurological interaction. Recent systematic reviews also have shown the clinical effectiveness of spinal cord stimulation in managing chronic spinal pain, phantom limb pain, complex regional pain syndrome, and other chronic painful conditions. Spinal cord stimulation for the treatment of chronic pain is rapidly evolving with technology at its forefront. This comprehensive focused review evaluated 11 RCTs and 7 nonrandomized/observational studies which provided levels of evidence ranging from I to II.

Neuromodulation With Burst and Tonic Stimulation Decreases Opioid Consumption: A Post Hoc Analysis of the Success Using Neuromodulation With BURST (SUNBURST) Randomized Controlled Trial

OBJECTIVE

The SUNBURST study was a prospective, multicenter, randomized crossover trial of a single device delivering burst and tonic spinal cord stimulation (SCS) for chronic trunk and/or limb pain. We performed a post hoc analysis of opioid consumption at baseline and after device implantation.

MATERIALS AND METHODS

After implantation, 100 patients were randomized to one mode (tonic or burst) for 12 weeks, and the other mode for the subsequent 12 weeks. After the crossover period (24 weeks), patients chose their preferred mode and were assessed for one year. We analyzed 69 patients who took opioid medication at baseline. The primary endpoint was opioid consumption in morphine milligram equivalents (MMEs) at baseline and 12 months postimplantation. Subgroup analysis included opioid consumption based on Center for Disease Control markers (<50, 50-90, 90-120, >120 MME/day) and stimulation mode preference.

RESULTS

Opioid consumption at 12 months was lower compared to baseline (53.94 vs. 79.19 MME, MD -25.25, 95% CI -43.77 to 6.73, p = 0.008). By 12 months, 11 of 69 patients (15.9%) discontinued all opioid (p = 0.001). Based on CDC dose markers, the proportion of patients taking >120 MME/day decreased by 61.7% at 12 months postintervention compared to baseline (p = 0.043). Forty-five of 69 patients (65.2%) preferred burst SCS while 15 of 69 patients (21.7%) preferred tonic SCS (p < 0.001).

CONCLUSION

A device delivering tonic and burst SCS was associated with decreased opioid consumption after 12 months in patients with chronic trunk and/or limb pain. The proportion of patients reporting the highest opioid intake (>120 MME/day) decreased to a lower CDC dose category by 61.7%, carrying important implications for those at highest risk for opioid-related substance use disorder, overdose, and death.

High-frequency spinal cord stimulation treatment attenuates the increase in spinal glutamate release and spinal miniature excitatory postsynaptic currents in rats with spared nerve injury-induced neuropathic pain

High-frequency spinal cord stimulation (HFSCS) at 10 kHz provides paresthesia-free treatment for chronic pain. However, the underlying mechanisms of its action have not been fully elucidated. The aim of the present study was to investigate the effect of HFSCS treatment on spinal glutamate release and uptake in spared nerve injury (SNI) rats. HFSCS was applied to the T10/T11 spinal cord 3 days after SNI. The concentration of spinal glutamate, glutamate transporter activity and miniature excitatory postsynaptic currents (mEPSCs) from neurons in lamina II were evaluated. HFSCS treatment alleviated SNI pain induced by mechanical and cold allodynia. HFSCS treatment also partially restored altered spinal glutamate uptake activity, the levels of spinal glutamate, and the frequency of mEPSCs following SNI. In conclusion, HFSCS treatment attenuated SNI-induced neuropathic pain and partially restored the altered glutamate uptake after SNI.

Cascade Programming for 10 kHz Spinal Cord Stimulation: A Single Center Case Series of 114 Patients With Neuropathic Back and Leg Pain

OBJECTIVE

Ten kilohertz spinal cord stimulation (SCS) is usually initiated in a single-bipolar configuration over the radiological reference point T9/T10 intervertebral disc space for neuropathic back and leg pain. Cascade is a duty-cycled, multi-bipolar contact configuration across an entire eight-contact lead. Potential advantages by using a broader area of SCS coverage include mitigation against minor lead migration and a reduction in the need for reprogramming. We report here the results of a retrospective case series of 114 patients using Cascade.

MATERIALS AND METHODS

Retrospective data were collected over two years. We selected patients with neuropathic back with or without/leg pain who had a trial of SCS. Pain assessments using Numerical Rating Scales (NRS) and Patient Global Impression of Change (PGIC) scores were collected at baseline, six months, and last follow-up beyond 12 months (mean 15.1 months). Patients were programmed with 10 kHz SCS using Cascade during the trial, which was continued unless reporting inadequate pain relief. Morbidity and deviations from Cascade programming were also obtained.

RESULTS

At six months, 87 of 97 (90.6%) patients with active devices were using Cascade and 58 of 72 (81%) patients at the last follow-up >12 months. There was a significant reduction in back NRS (8.3 vs. 3.9 [p < 0.0001], N = 97) and leg pain (7.53 vs. 3.83 [p < 0.0001], N = 77) at 6 months and last follow-up >12 months back (8.3 vs. 3.95 [p < 0.0001] N = 72), leg (7.53 vs. 3.534 [p < 0.0001], N = 58). The PGIC score was 6 of 7 or all of 7 in 72% of patients (70/97) at six months and in 68% (49/72) of patients at the last follow-up beyond 12 months.

CONCLUSION

Cascade is an effective programming methodology that may have benefits over a single-bipole configuration for 10 kHz SCS, particularly during a trial of stimulation. Results from this study suggest it is a durable program for patients with neuropathic back and leg pain.