Therapy Habituation at 12 Months: Spinal Cord Stimulation Versus Dorsal Root Ganglion Stimulation for Complex Regional Pain Syndrome Type I and II

10. Complex regional pain syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) is a clinical disorder that can develop following surgery or trauma. Based on the most prominent underlying pathophysiological mechanisms, CRPS can be classified into different subtypes, namely inflammatory, nociplastic/neuropathic, vasomotor, and motor. Depending on the subtype, personalized treatment can be applied. If conservative treatments are insufficient or ineffective, more invasive treatments may be recommended. This article provides an overview of the most recent insights into CRPS and discusses the most common invasive treatments.

METHODS

The literature regarding interventional treatments for CRPS has been systematically reviewed and summarized.

RESULTS

Bisphosphonates are effective in treating the inflammatory subtype, while ketamine can provide pain relief for the nociplastic/neuropathic subtype. Sympathetic blocks are effective in addressing vasomotor disturbances. For patients with refractory symptoms, neurostimulation is a viable option due to its multimechanistic properties for all subtypes. End-of-line motor disturbances may benefit from intrathecal baclofen.

CONCLUSIONS

CRPS is a debilitating condition with an unpredictable course. The effectiveness of treatment varies from patient to patient. When conservative approaches prove insufficient, gradual progression to invasive treatments based on the underlying subtype is recommended.

Occipital nerve stimulation for cluster headache: lessons to learn from the 'voltage tuners'

BACKGROUND

Cluster headache (CH) is a significant health concern due to its major socioeconomic consequences and most patients being refractory to conventional strategies. For treatment resistant CH, occipital nerve stimulation (ONS) is considered an effective treatment option. Whereas most patients do not adjust the amplitude of the ONS system, a subset changes the amplitude on a regular basis using their remote control, and are therefore referred to as 'voltage tuners'. Anxiety and self-control are thought to be central themes to this behavior. Research on this voltage tuning behavior could provide new insights in the use of ONS as acute attack treatment. To date, voltage tuning has not been assessed for CH. Hence this is a unique study aiming to investigate the occurrence and efficacy of voltage tuning in patients with CH and ONS.

METHODS

For this analysis, patients with CH who received ONS from 2020-2024, at our university medical center, were included. All patients underwent bilateral ONS implantation. Data on attack frequency, intensity and duration were collected retrospectively. Outcomes on the response, frequency, moment during the day, duration, rationale, sensation, average increase in amplitude, and efficacy of voltage tuning were collected with prospective interviews.

RESULTS

Thirty-three patients (M = 20) (42 ± 12.7 years) were included in the current analysis. At 1y follow-up, an overall response rate of 70% (23/33) was found for ONS. In total, 48% (18/33) of patients were defined as voltage tuners. Voltage tuning was performed with an average increase in amplitude of 92 (20-360)%, a frequency of 1-20 times/month and duration of 20 minutes-48 hours. Sensations of voltage tuning were described as "tingling" and/or "pinching". The rationale for voltage tuning in patients varied from prevention and ceasing to lowering the intensity and enhance control of CH attack.

CONCLUSIONS

Outcomes show that voltage tuning may cease and/or terminate CH attacks and therefore raise interests in the use of ONS as acute attack treatment for patients with resistant CH treated with ONS. Future research on the occurrence and potential of voltage tuning will provide valuable insights for achieving optimal efficacy of ONS and quality of life in patients with CH.

Electrical neuromodulation for the treatment of chronic pain: derivation of the intrinsic barriers, outcomes and considerations of the sustainability of implantable spinal cord stimulation therapies

INTRODUCTION

For over 60 years, spinal cord stimulation has endured as a therapy through innovation and novel developments. Current practice of neuromodulation requires proper patient selection, risk mitigation and use of innovation. However, there are tangible and intangible challenges in physiology, clinical science and within society.

AREAS COVERED

We provide a narrative discussion regarding novel topics in the field especially over the last decade. We highlight the challenges in the patient care setting including selection, as well as economic and socioeconomic challenges. Physician training challenges in neuromodulation is explored as well as other factors related to the use of neuromodulation such as novel indications and economics. We also discuss the concepts of technology and healthcare data.

EXPERT OPINION

Patient safety and durable outcomes are the mainstay goal for neuromodulation. Substantial work is needed to assimilate data for larger and more relevant studies reflecting a population. Big data and global interconnectivity efforts provide substantial opportunity to reinvent our scientific approach, data analysis and its management to maximize outcomes and minimize risk. As improvements in data analysis become the standard of innovation and physician training meets demand, we expect to see an expansion of novel indications and its use in broader cohorts.

Research hotspots and trends of spinal cord stimulation for neuropathic pain: a bibliometric analysis from 2004 to 2023

The purpose of this study is to systematically analyze the development trend, research hotspots, and future development direction on the treatment of neuropathic pain (NP) with spinal cord stimulation through bibliometric method. We extracted the literature related to the treatment of NP with spinal cord stimulation from January 2004 to December 2023 from the Web of Science database. As a result, a total of 264 articles were retrieved. By analyzing the annual published articles, authors, countries, institutions, journals, co-cited literature, and keywords, we found that the count of publication in this field has been experiencing an overall growth, and the publications within the past 5 years accounted for 42% of the total output. Experts from the United States and the UK have made significant contributions in this field and established a stable collaborative team, initially establishing an international cooperation network. Pain is the frequently cited journal in this field. The study on spinal cord stimulation therapy for NP especially the study on spinal cord stimulation therapy for back surgery failure syndrome (FBSS) and its potential mechanisms are the research hotspots in this field, while the study on novel paradigms such as high-frequency spinal cord stimulation and spinal cord burst stimulation represents the future development directions. In short, spinal cord stimulation has been an effective treatment method for NP. The novel paradigms of spinal cord stimulation are the key point of future research in this field.

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.

A Narrative Review of the Dorsal Root Ganglia and Spinal Cord Mechanisms of Action of Neuromodulation Therapies in Neuropathic Pain

Neuropathic pain arises from injuries to the nervous system in diseases such as diabetes, infections, toxicity, and traumas. The underlying mechanism of neuropathic pain involves peripheral and central pathological modifications. Peripheral mechanisms entail nerve damage, leading to neuronal hypersensitivity and ectopic action potentials. Central sensitization involves a neuropathological process with increased responsiveness of the nociceptive neurons in the central nervous system (CNS) to their normal or subthreshold input due to persistent stimuli, leading to sustained electrical discharge, synaptic plasticity, and aberrant processing in the CNS. Current treatments, both pharmacological and non-pharmacological, aim to alleviate symptoms but often face challenges due to the complexity of neuropathic pain. Neuromodulation is emerging as an important therapeutic approach for the treatment of neuropathic pain in patients unresponsive to common therapies, by promoting the normalization of neuronal and/or glial activity and by targeting cerebral cortical regions, spinal cord, dorsal root ganglia, and nerve endings. Having a better understanding of the efficacy, adverse events and applicability of neuromodulation through pre-clinical studies is of great importance. Unveiling the mechanisms and characteristics of neuromodulation to manage neuropathic pain is essential to understand how to use it. In the present article, we review the current understanding supporting dorsal root ganglia and spinal cord neuromodulation as a therapeutic approach for neuropathic pain.

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Neuromodulation and Habituation: A Literature Review and Conceptional Analysis of Sustaining Therapeutic Efficacy and Mitigating Habituation

Spinal cord stimulation (SCS) is a therapeutic modality for the treatment of various chronic pain conditions that has rapidly evolved over the past 50 years. Unfortunately, over time, patients implanted with SCS undergo a habituation phenomenon leading to decreased pain relief. Consequently, the discovery of new stimulation waveforms and SCS applications has been shown to prolong efficacy and reduce explantation rates. This article explores various SCS waveforms, their applications, and proposes a graded approach to habituation mitigation. We suspect the neural habituation phenomenon parallels that seen in pharmacology. Consequently, we urge further exploration of the early introduction of these stimulation strategies to abate spinal cord stimulation habituation.

Disease applications of spinal cord stimulation: Chronic nonmalignant pain

Neuropathic pain is a chronic condition representing a significant burden for society. It is estimated 1 out of 10 people over the age of 30 that in the US have been diagnosed with neuropathic pain. Most of the available treatments for neuropathic pain have moderate efficacy over time which limit their use; therefore, other therapeutic approaches are needed for patients. Spinal cord stimulation is an established and cost-effective modality for treating severe chronic pain. In this article we will review the current approved indications for the use of spinal cord stimulation in the US and the novel therapeutic options which are now available using this therapy.

Complex Regional Pain Syndrome: Evidence-Based Advances in Concepts and Treatments

PURPOSE OF REVIEW

This review presents the most current information about the epidemiology of complex regional pain syndrome (CRPS), classification and diagnostic criteria, childhood CRPS, subtypes, pathophysiology, conventional and less conventional treatments, and preventive strategies.

RECENT FINDINGS

CRPS is a painful disorder with multifactorial pathophysiology. The data describe sensitization of the central and peripheral nervous systems, inflammation, possible genetic factors, sympatho-afferent coupling, autoimmunity, and mental health factors as contributors to the syndrome. In addition to conventional subtypes (type I and type II), cluster analyses have uncovered other proposed subtypes. Prevalence of CRPS is approximately 1.2%, female gender is consistently associated with a higher risk of development, and substantial physical, emotional, and financial costs can result from the syndrome. Children with CRPS seem to benefit from multifaceted physical therapy leading to a high percentage of symptom-free patients. The best available evidence along with standard clinical practice supports pharmacological agents, physical and occupational therapy, sympathetic blocks for engaging physical restoration, steroids for acute CRPS, neuromodulation, ketamine, and intrathecal baclofen as therapeutic approaches. There are many emerging treatments that can be considered as a part of individualized, patient-centered care. Vitamin C may be preventive. CRPS can lead to progressively painful sensory and vascular changes, edema, limb weakness, and trophic disturbances, all of which substantially erode healthy living. Despite some progress in research, more comprehensive basic science investigation is needed to clarify the molecular mechanisms of the disease so that targeted treatments can be developed for better outcomes. Incorporating a variety of standard therapies with different modes of action may offer the most effective analgesia. Introducing less conventional approaches may also be helpful when traditional treatments fail to provide sufficient improvement.

Long-term analgesic effect of trans-spinal direct current stimulation compared to non-invasive motor cortex stimulation in complex regional pain syndrome

The aim of the present study was to compare the analgesic effect of motor cortex stimulation using high-frequency repetitive transcranial magnetic stimulation or transcranial direct current stimulation and transcutaneous spinal direct current stimulation in patients with complex regional pain syndrome. Thirty-three patients with complex regional pain syndrome were randomized to one of the three treatment groups (repetitive transcranial magnetic stimulation, n = 11; transcranial direct current stimulation, n = 10; transcutaneous spinal direct current stimulation, n = 12) and received a series of 12 sessions of stimulation for 3 weeks (induction phase) and 11 sessions for 4 months (maintenance therapy). The primary end-point was the mean pain intensity assessed weekly with a visual numerical scale during the month prior to treatment (baseline), the 5-month stimulation period and 1 month after the treatment. The weekly visual numerical scale pain score was significantly reduced at all time points compared to baseline in the transcutaneous spinal direct current stimulation group, at the last two time points in the repetitive transcranial magnetic stimulation group (end of the 5-month stimulation period and 1 month later), but at no time point in the transcranial direct current stimulation group. A significant pain relief was observed at the end of induction phase using transcutaneous spinal direct current stimulation compared to repetitive transcranial magnetic stimulation (P = 0.008) and to transcranial direct current stimulation (P = 0.003). In this trial, transcutaneous spinal direct current stimulation was more efficient to relieve pain in patients with complex regional pain syndrome compared to motor cortex stimulation techniques (repetitive transcranial magnetic stimulation, transcranial direct current stimulation). This efficacy was found during the induction phase and was maintained thereafter. This study warrants further investigation to confirm the potentiality of transcutaneous spinal direct current stimulation as a therapeutic option in complex regional pain syndrome.

Research hotspots and trends on spinal cord stimulation for pain treatment: a two-decade bibliometric analysis

Background

Chronic pain poses a significant social burden. Spinal cord stimulation (SCS) is considered to be the most promising treatment for refractory pain. The aim of this study was to summarize the current research hotspots on SCS for pain treatment during the past two decades and to predict the future research trends by bibliometric analysis.

Methods

The literature over the last two decades (2002-2022) which was related to SCS in pain treatment was obtained from the Web of Science Core Collection. Bibliometric analyses were conducted based on the following aspects: (1) Annual publication and citation trends; (2) Annual publication changes of different publication types; (3) Publications and citations/co-citations of different country/institution/journal/author; (4) Citations/co-citation and citation burst analysis of different literature; and (5) Co-occurrence, cluster, thematic map, trend topics, and citation burst analysis of different keywords. (6) Comparison between the United States and Europe. All analyses were performed on CiteSpace, VOSviewer, and R bibliometrix package.

Results

A total of 1,392 articles were included in this study, with an increasing number of publications and citations year by year. The most highly published type of literature was clinical trial. United States was the country with the most publications and citations; Johns Hopkins University was the institution with the most publications; NEUROMODULATION published the most papers; the most published author was Linderoth B; and the most cited paper was published in the PAIN by Kumar K in 2007. The most frequently occurring keywords were "spinal cord stimulation," "neuropathic pain," and "chronic pain," etc.

Conclusion

The positive effect of SCS on pain treatment has continued to arouse the enthusiasm of researchers in this field. Future research should focus on the development of new technologies, innovative applications, and clinical trials for SCS. This study might facilitate researchers to comprehensively understand the overall perspective, research hotspots, and future development trends in this field, as well as seek collaboration with other researchers.

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.

Dorsal root ganglion stimulation for the treatment of joint pain with predominantly nociceptive characteristics: A case series

INTRODUCTION

Dorsal root ganglion stimulation (DRG-S) has recently emerged as a novel therapy in neuromodulation that demonstrated a higher rate of success than spinal cord stimulation (SCS) in a prospective, head-to-head randomized comparative trial to treat complex regional pain syndrome (CRPS) and causalgia. In contrast to SCS, DRG-S also shows promise in treating conditions that are not purely neuropathic such as axial low back pain, which has a prominent nociplastic pain component. It is not known to what extent the effectiveness of DRG-S for such indications is due to effective treatment of the neuropathic pain component versus the effects of DRG-S on mechanical pain. Although rarely studied, reporting outcomes of DRG-S to treat predominantly mechanical/nociceptive pain may help point toward expanding the utility of this therapy. Here, we present five cases of refractory mechanical pain treated with DRG-S.

METHODS

A retrospective analysis of all patients who underwent a successful DRG-S trial and implant between September 2017 and September 2021 at our institute was performed. Patients who had intractable joint pain without strong evidence of neuropathic pain were included in this case series. The Budapest criteria for CRPS, the Douleur Neuropathique 4 Questions (DN4) survey, or a definable nerve injury were used to determine the presence of neuropathic pain. Baseline assessments for pain (Numeric Rating Scale [NRS]), function (Oswestry Disability Index [ODI]), quality of life (EuroQol-5 Dimension [EQ-5D]), and other applicable joint surveys were extracted from pre-trial baseline and follow-up appointments.

RESULTS

Five patients were identified and included. Patient diagnoses consisted of refractory joint pain of the hip, knee, or ankle. Mean NRS pain scores improved by 74% from 9.2 at baseline to 2.4 at the last follow-up (mean = 28 months post-implant). From baseline to the last follow-up, mean ODI scores improved by 65% from 66 to 23 and EQ-5D scores more than doubled from an average of 0.371 to 0.797.

CONCLUSION

This clinical report illustrates the potential utility DRG-S has in treating pain that clinically presents as predominantly refractory mechanical joint pain without a significant neuropathic component. The physiological reasons for our observations may be that DRG-S is able to directly influence the conduction of nociceptive signaling at the DRG and within the spinal cord. Further investigations are warranted to determine if DRG-S is a potential treatment option for chronic mechanical pain.

Long-term safety of spinal cord stimulation systems in a prospective, global registry of patients with chronic pain

Aim: The availability of long-term (>2 years) safety outcomes of spinal cord stimulation (SCS) remains limited. We evaluated safety in a global SCS registry for chronic pain. Methods: Participants were prospectively enrolled globally at 79 implanting centers and followed out to 3 years after device implantation. Results: Of 1881 participants enrolled, 1289 received a permanent SCS implant (1776 completed trial). The annualized rate of device explant was 3.5% (all causes), and 1.1% due to inadequate pain relief. Total incidence of device explantation >3 years was 7.6% (n = 98). Of these, 32 subjects (2.5%) indicated inadequate pain relief as cause for removal. Implant site infection (11 events) was the most common device-related serious adverse event (<1%). Conclusion: This prospective, global, real-world study demonstrates a high-level of safety for SCS with low rate of explant/serious adverse events. Clinical Trial Registration: NCT01719055 (ClinicalTrials.gov).

Methods and system for recording human physiological signals from implantable leads during spinal cord stimulation

Objectives

This article presents a method-including hardware configuration, sampling rate, filtering settings, and other data analysis techniques-to measure evoked compound action potentials (ECAPs) during spinal cord stimulation (SCS) in humans with externalized percutaneous electrodes. The goal is to provide a robust and standardized protocol for measuring ECAPs on the non-stimulation contacts and to demonstrate how measured signals depend on hardware and processing decisions.

Methods

Two participants were implanted with percutaneous leads for the treatment of chronic pain with externalized leads during a trial period for stimulation and recording. The leads were connected to a Neuralynx ATLAS system allowing us to simultaneously stimulate and record through selected electrodes. We examined different hardware settings, such as online filters and sampling rate, as well as processing techniques, such as stimulation artifact removal and offline filters, and measured the effects on the ECAPs metrics: the first negative peak (N1) time and peak-valley amplitude.

Results

For accurate measurements of ECAPs, the hardware sampling rate should be least at 8 kHz and should use a high pass filter with a low cutoff frequency, such as 0.1 Hz, to eliminate baseline drift and saturation (railing). Stimulation artifact removal can use a double exponential or a second-order polynomial. The polynomial fit is 6.4 times faster on average in computation time than the double exponential, while the resulting ECAPs' N1 time and peak-valley amplitude are similar between the two. If the baseline raw measurement drifts with stimulation, a median filter with a 100-ms window or a high pass filter with an 80-Hz cutoff frequency preserves the ECAPs.

Conclusions

This work is the first comprehensive analysis of hardware and processing variations on the observed ECAPs from SCS leads. It sets recommendations to properly record and process ECAPs from the non-stimulation contacts on the implantable leads.

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.

Stimulation holiday rescues analgesia after habituation and loss of efficacy from 10-kilohertz dorsal column spinal cord stimulation

INTRODUCTION

Habituation and loss of efficacy from spinal cord stimulation are commonly reported. This retrospective analysis investigated rescue of analgesia from spinal cord stimulation failure after implementing a strategy called a stimulation holiday, during which spinal cord stimulation is interrupted for a defined period and subsequently restarted.

METHODS

A 6-year review (June 1, 2016-May 13, 2022) from a tertiary care center was conducted on patients who underwent 10 kHz frequency dorsal column spinal cord stimulation for ≥3 months, experienced loss of efficacy (≤30% pain relief or patient self-report of lack of meaningful pain relief), subsequently underwent a stimulation holiday, and then restarted spinal cord stimulation. The primary outcome was comparison of pain relief and responder rate (≥50% relief in pain intensity) before and after stimulation holiday.

RESULTS

Of 212 patients, 40 (18.9%) experienced loss of efficacy at a mean follow-up period of 452.7±326.4 days after stimulator implantation and underwent stimulation holiday. Pain relief was significantly higher 1 month after stimulation holiday (39.4%±28.6%) compared with before stimulation holiday (8.7%±13.0%; mean difference 30.6%, 95% CI 21.9% to 39.3%, paired t-test p<0.001). A significantly higher responder rate (≥50% relief in pain intensity) was identified after stimulation holiday (57.5%) compared with before stimulation holiday (0%; Fisher's exact test p<0.001). Associations of superior pain relief and responder rate remained significant at 3 and 6 months after stimulation holiday.

DISCUSSION

Patients who experience loss of efficacy from spinal cord stimulation habituation could attempt a stimulation holiday rather than abandon therapy. Rescue of analgesia may be achieved after implementing a stimulation holiday and restarting spinal cord stimulation.

Frequency dependency of therapeutic efficacy in dorsal root ganglion stimulation for neuropathic pain

Background

The influence of the stimulation frequency on the outcomes of dorsal root ganglion stimulation (DRG-S) to treat pain is not well understood. It is assumed that specific neural components dedicated to different tasks in the DRG can be preferably influenced at specific frequencies. The identification of frequencies designed for the type of pain and the ratio of neuropathic versus nociceptive pain might improve overall pain control and open new indications in DRG-S.

Method

We report on a randomized double-blind clinical trial with a crossover design. Patients with a permanent DRG-S system underwent phases of stimulation with 20 Hz, 40 Hz, 60 Hz, 80 Hz, and sham in a randomized order. Each phase lasted for 4 days and was followed by a 2-day washout period. Pain intensity and quality of life were assessed with visual analog scale (VAS), McGill Pain Questionnaire (MPQ), EQ-5D, and Beck Depression Inventory (BDI). Analgesics intake was assessed.

Results

Overall 19 patients were included in the study. CRPS was the most frequent pain etiology (7). Five patients had a PainDetect score of 12 or lower at baseline. The mean VAS before the system was implanted was 8.6 and 3.9 at the baseline. Pain intensity was reduced to 3.7 by the stimulation with 20 Hz but increased with higher frequencies reaching 5.8 at 80 Hz. A significant difference among the groups was shown over all variables examined (VAS, MPQ, EQ-5D, BDI). The best results were seen at 20 Hz for all variables, including the smallest increase in pain medication consumption.

Conclusions

The choice of the stimulation frequency shows a clear influence on pain reduction and quality of life. Lower stimulation frequencies seem to be most effective in neuropathic pain. Further studies are required to determine whether specific frequencies should be preferred based on the condition treated.

The Challenge of Converting "Failed Spinal Cord Stimulation Syndrome" Back to Clinical Success, Using SCS Reprogramming as Salvage Therapy, through Neurostimulation Adapters Combined with 3D-Computerized Pain Mapping Assessment: A Real Life Retrospective Study

While paresthesia-based Spinal Cord Stimulation (SCS) has been proven effective as treatment for chronic neuropathic pain, its initial benefits may lead to the development of "Failed SCS Syndrome' (FSCSS) defined as decrease over time related to Loss of Efficacy (LoE) with or without Loss of Coverage (LoC). Development of technologies associating new paresthesia-free stimulation waveforms and implanted pulse generator adapters provide opportunities to manage patients with LoE. The main goal of our study was to investigate salvage procedures, through neurostimulation adapters, in patients already implanted with SCS and experiencing LoE. We retrospectively analyzed a cohort of patients who were offered new SCS programs/waveforms through an implanted adapter between 2018 and 2021. Patients were evaluated before and at 1-, 3-, 6- and 12-month follow-ups. Outcomes included pain intensity rating with a Visual Analog Scale (VAS), pain/coverage mappings and stimulation preferences. Last follow-up evaluations (N = 27) showed significant improvement in VAS (p = 0.0001), ODI (p = 0.021) and quality of life (p = 0.023). In the 11/27 patients with LoC, SCS efficacy on pain intensity (36.89%) was accompanied via paresthesia coverage recovery (55.57%) and pain surface decrease (47.01%). At 12-month follow-up, 81.3% preferred to keep tonic stimulation in their waveform portfolio. SCS conversion using adapters appears promising as a salvage solution, with an emphasis on paresthesia recapturing enabled via spatial retargeting. In light of these results, adapters could be integrated in SCS rescue algorithms or should be considered in SCS rescue.

Dorsal Root Ganglion Stimulation for Lower Extremity Neuropathic Pain Syndromes: An Evidence-Based Literature Review

Dorsal root ganglion stimulation (DRG-S) is a form of selective neuromodulation therapy that targets the dorsal root ganglion. DRG-S offers analgesia in a variety of chronic pain conditions and is approved for treatment of complex regional pain syndrome (CRPS) by the US Food and Drug Administration (FDA). There has been increasing utilization of DRG-S to treat various neuropathic pain syndromes of the lower extremity, although evidence remains limited to one randomized controlled trial and 39 observational studies. In this review, we appraised the current evidence for DRG-S in the treatment of lower extremity neuropathic pain using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) criteria. The primary outcome was change in pain intensity after DRG-S compared to baseline. We stratified presentation of results based of type of neuropathy (CRPS, painful diabetic neuropathy, mononeuropathy, polyneuropathy) as well as location of neuropathy (hip, knee, foot). Future powered randomized controlled trials with homogeneous participants are warranted.

Light-stimulus intensity modulates startle reflex habituation in larval zebrafish

The startle reflex in larval zebrafish describes a C-bend of the body occurring in response to sudden, unexpected, stimuli of different sensory modalities. Alterations in the startle reflex habituation (SRH) have been reported in various human and animal models of neurological and psychiatric conditions and are hence considered an important behavioural marker of neurophysiological function. The amplitude, offset and decay constant of the auditory SRH in larval zebrafish have recently been characterised, revealing that the measures are affected by variation in vibratory frequency, intensity, and interstimulus-interval. Currently, no study provides a model-based analysis of the effect of physical properties of light stimuli on the visual SRH. This study assessed the effect of incremental light-stimulus intensity on the SRH of larval zebrafish through a repeated-measures design. Their total locomotor responses were normalised for the time factor, based on the behaviour of a (non-stimulated) control group. A linear regression indicated that light intensity positively predicts locomotor responses due to larger SRH decay constants and offsets. The conclusions of this study provide important insights as to the effect of light properties on the SRH in larval zebrafish. Our methodology and findings constitute a relevant reference framework for further investigation in translational neurophysiological research.

Long-Term Outcome of Spinal Cord Stimulation in Complex Regional Pain Syndrome

BACKGROUND

Spinal cord stimulation (SCS) is an effective treatment in chronic neuropathic pain, but its efficacy in complex regional pain syndrome (CRPS) needs to be proven.

OBJECTIVE

To study the outcome of SCS in CRPS as measured by trial success, explantation rate, complications, and changes in opioid and neuropathic pain medication use over a 4-yr follow-up.

METHODS

We retrospectively reviewed all medical records of 35 consecutive CRPS patients who underwent SCS trials at 2 hospitals during January 1998 to December 2016. The purchase data of opioids and neuropathic pain medication during January 1995 to March 2016 were retrieved from national registries.

RESULTS

Based on a 1-wk trial, permanent SCS was implanted in 27 (77%) patients. During the median follow-up of 8 yr, 8 (30%) SCS devices were explanted, of which 7 were because of inefficient pain relief. Complications leading to revision occurred in 17 (63%) patients: 8 electrode migrations or stimulation to the wrong area, 1 deep infection, 9 hardware malfunctions, 2 pulse generator discomforts, and 2 SCS replacements. None of the 6 patients using strong opioids discontinued their use during the 2-yr follow-up. The mean opioid dose increased nonsignificantly both in patients with SCS in permanent use (53 ± 150 morphine milligram equivalents morphine milligram equivalent (MME)/day to 120 ± 240 MME/day) and in patients who had SCS explanted (27 ± 72 MME/day to 57 ± 66 MME/day).

CONCLUSION

Despite the fact that CRPS patients were not able to discontinue or reduce their strong opioid or neuropathic pain medication use, 70% continued to use their SCS device during a median 8-yr follow-up.

Dorsal Root Ganglion Stimulation for the Treatment of Non-Complex Regional Pain Syndrome Related Chronic Pain Syndromes: A Systematic Review

BACKGROUND

While the majority of indications and approvals for dorsal root ganglion stimulation (DRGS) are for the refractory management of complex regional pain syndrome (CRPS), emerging evidence has suggested that DRGS may be favorably used for a plethora of other chronic pain phenomena. Consequently, we aimed to characterize the use and efficacy of DRGS for these non-CRPS-related chronic pain syndromes.

MATERIALS AND METHODS

A systematic review of clinical studies demonstrating the use of DRGS for non-CRPS-related chronic pain syndromes. The literature search was performed using PubMed, Cochrane Library, and CINAHL plus across August and September 2020.

RESULTS

A total of 28 reports comprising 354 total patients were included in the analysis. Of the chronic pain syndromes presented, axial low back pain, chronic pelvic and groin pain, other peripheral neuropathies, and studies with multiple concomitant pain syndromes, a majority demonstrated >50% mean pain reduction at the time of last follow-up following DRGS. Physical function, quality of life (QOL), and lesser pain medication usage also were repeatedly reported to be significantly improved.

CONCLUSIONS

DRGS continues to lack supportive evidence from well designed, high level studies and recommendations from consensus committee experts. However, we present repeated and consistent evidence from lower level studies showing success with the use of DRGS for various non-CRPS chronic pain syndromes in reducing pain along with increasing function and QOL from one week to three years. Due to such low-level, high bias evidence, we strongly encourage the continuation of high-level studies in order to provide a stronger foundation for the use of DRGS in non-CRPS chronic pain patients. However, it may be reasonable and appropriate to evaluate patients for DRGS candidacy on a case-by-case basis particularly if they manifest focal pain syndromes refractory to noninterventional measures and may not be ideal candidates for other forms of neuromodulation.

A model-based quantification of startle reflex habituation in larval zebrafish

Zebrafish is an established animal model for the reproduction and study of neurobiological pathogenesis of human neurological conditions. The 'startle reflex' in zebrafish larvae is an evolutionarily preserved defence response, manifesting as a quick body-bend in reaction to sudden sensory stimuli. Changes in startle reflex habituation characterise several neuropsychiatric disorders and hence represent an informative index of neurophysiological health. This study aimed at establishing a simple and reliable experimental protocol for the quantification of startle reflex response and habituation. The fish were stimulated with 20 repeated pulses of specific vibratory frequency, acoustic intensity/power, light-intensity and interstimulus-interval, in three separate studies. The cumulative distance travelled, namely the sum of the distance travelled (mm) during all 20 stimuli, was computed as a group-level description for all the experimental conditions in each study. Additionally, by the use of bootstrapping, the data was fitted to a model of habituation with a first-order exponential representing the decay of locomotor distance travelled over repeated stimulation. Our results suggest that startle habituation is a stereotypic first-order process with a decay constant ranging from 1 to 2 stimuli. Habituation memory lasts no more than 5 min, as manifested by the locomotor activity recovering to baseline levels. We further observed significant effects of vibratory frequency, acoustic intensity/power and interstimulus-interval on the amplitude, offset, decay constant and cumulative distance travelled. Instead, the intensity of the flashed light did not contribute to significant behavioural variations. The findings provide novel insights as to the influence of different stimuli parameters on the startle reflex habituation and constitute a helpful reference framework for further investigation.

Electroacupuncture Alleviates Mechanical Allodynia of a Rat Model of CRPS-I and Modulates Gene Expression Profiles in Dorsal Root Ganglia

Complex regional pain syndrome type-I (CRPS-I) is chronic neurological disorder accompanied with devastating pain. Most conventional medical treatments lack effectiveness, making CRPS-I a challenging clinical condition. Electroacupuncture (EA) showed effectiveness in alleviating the pain symptoms of CRPS-I patients. However, the molecular mechanisms underlying EA's therapeutic effect are still not well-understood. Here, we established the rat chronic post-ischemic pain (CPIP) model to mimic CRPS-I and performed repetitive EA on bilateral hind limbs of the CPIP model rats. We then performed RNA-sequencing (RNA-Seq) to study the differences in gene expression, gene networks, and molecular pathways in ipsilateral DRGs innervating the hind limb of the CPIP model rats with and without repetitive EA treatment. Our results found that repetitive EA treatment significantly alleviated mechanical allodynia in bilateral hind limbs of CPIP model rats. RNA-Seq analysis indicated that EA modulated the expression of multiple genes and gene networks in the DRGs of CPIP model rats. Further bioinformatics analysis identified the up-regulation of an array of genes involved in biological process such as neutrophil chemotaxis and immune response in the DRGs of CPIP model rats after EA treatment. Thus, these results suggest that EA may alleviate pain response in CPIP model rats via regulating multiple genes. Our work may help to further advance the understandings of the molecular mechanisms underlying EA's therapeutic effects on CRPS-I and help to identify novel targets for CRPS-I treatment.

Complex regional pain syndrome: An updated comprehensive review

Complex regional pain syndrome (CRPS) is a complex disorder that can have a significant impact on the quality of life of a person with this syndrome. The diagnosis and treatment of CRPS are often difficult as there is no one confirmatory test and no one definitive treatment. Currently, the most widely accepted clinical diagnostic criteria are the Budapest criteria, which were developed by expert consensus. Though no one single treatment has been found to be universally effective, early detection and an interdisciplinary approach to treatment appear to be key in treating CRPS. This review aims to present up-to-date clinical information regarding the diagnosis and management of CRPS and highlight the potential issues with diagnosis in the neurological population. Ultimately, more research is needed to identify the exact etiology of CRPS in order to help target appropriate therapies. In addition, more randomized controlled trials need to be performed in order to test new therapies or combinations of therapies, including pharmacological, interventional, and behavioral therapies, to determine the best treatment options for this potentially debilitating disorder.

1.2 kHz High-Frequency Stimulation as a Rescue Therapy in Patients With Chronic Pain Refractory to Conventional Spinal Cord Stimulation

OBJECTIVES

We aimed to investigate the efficacy of new subperception stimulation paradigms including 1.2 kHz-high-frequency stimulation (HFS) and advanced-HFS field-shaping algorithm (dorsal horn HFS [DHHFS]) in refractory cases which initially benefited from conventional spinal cord stimulation (SCS) and lost the effect throughout time.

MATERIALS AND METHODS

In the context of a rescue-therapy, patients underwent externalization of the implanted SCS-leads and were tested with multiple combinations of new SCS paradigms. Pain intensity was analyzed using the numeric rating scale (NRS), and data were collected preoperatively and at multiple postoperative follow-ups.

RESULTS

Thirty-seven patients underwent externalization of the leads. Mean preoperative NRS-score was 8.1/10 points (SD ± 0.9) for the ON-stimulation period. Patients received a combination of either tonic, burst and 1.2 kHz-HFS, or burst and 1.2 kHz-HFS, DHHFS, or 1.2 kHz-HFS and DHHFS, or 1.2 kHz-HFS alone. The mean postoperative NRS-score after the testing-phase was 3.8/10 points (SD ± 2.5), showing a 48.0% mean reduction (p < 0.001). In total, 29 patients reported a significant reduction above 50% in NRS-scores and therefore were reimplanted with new generators that could deliver the new paradigms. Eight patients underwent full SCS-system explantation. The patients who continued with the new paradigms (n = 29) reported mean NRS-scores of 3.5/10 points (SD ± 1.7) 12 months postoperatively, still showing a significant reduction of 43.3% when compared to preoperative scores (p < 0.001).

CONCLUSION

Rescue-therapy with combination of multiple waveforms, including tonic, burst, 1.2 kHz-HFS, and DHHFS, was associated with a significant pain relief in patients with failed conventional SCS. This approach is a safe and efficient and should be considered before explantation of the SCS-system.

The Pathways and Processes Underlying Spinal Transmission of Low Back Pain: Observations From Dorsal Root Ganglion Stimulation Treatment

BACKGROUND

Dorsal root ganglion stimulation (DRG-S) is a novel approach to treat chronic pain. Lead placement at L2 has been reported to be an effective treatment for axial low back pain (LBP) primarily of discogenic etiology. We have recently shown, in a diverse cohort including cases of multilevel instrumentation following extensive prior back surgeries, that DRG-S lead placement at T12 is another promising target. Local effects at the T12 DRG, alone, are insufficient to explain these results.

MATERIALS AND METHODS

We performed a literature review to explore the mechanisms of LBP relief with T12 DRG-S.

FINDINGS

Branches of individual spinal nerve roots innervate facet joints and posterior spinal structures, while the discs and anterior vertebrae are carried via L2, and converge in the dorsal horn (DH) of the spinal cord at T8-T9. The T12 nerve root contains cutaneous afferents from the low back and enters the DH of the spinal cord at T10. Low back Aδ and C-fibers then ascend via Lissauer's tract (LT) to T8-T9, converging with other low back afferents. DRG-S at T12, then, results in inhibition of the converged low back fibers via endorphin-mediated and GABAergic frequency-dependent mechanisms. Therefore, T12 lead placement may be the optimal location for DRG-S to treat LBP.