Brain activity modifications following spinal cord stimulation for chronic neuropathic pain: A systematic review

EEG-Based Cortical Alterations in Individuals With Chronic Knee Pain Secondary to Osteoarthritis: A Cross-sectional Investigation

Chronic painful knee osteoarthritis (OA) is a disabling physical health condition. Alterations in brain responses to arthritic changes in the knee may explain persistent pain. This study investigated source localized, resting-state electroencephalography activity and functional connectivity in people with knee OA, compared to healthy controls. Adults aged 44 to 85 years with knee OA (n = 37) and healthy control (n = 39) were recruited. Resting-state electroencephalography was collected for 10 minutes and decomposed into infraslow frequency (ISF) to gamma frequency bands. Standard low-resolution electromagnetic brain tomography statistical nonparametric maps were conducted, current densities of regions of interest were compared between groups and correlation analyses were performed between electroencephalography (EEG) measures and clinical pain and functional outcomes in the knee OA group. Standard low-resolution electromagnetic brain tomography nonparametric maps revealed higher (P = .006) gamma band activity over the right insula (RIns) in the knee OA group. A significant (P < .0001) reduction in ISF band activity at the pregenual anterior cingulate cortex, whereas higher theta, alpha, beta, and gamma band activity at the dorsal anterior cingulate cortex, pregenual anterior cingulate cortex, the somatosensory cortex, and RIns in the knee OA group were identified. ISF activity of the dorsal anterior cingulate cortex was positively correlated with pain measures and psychological distress scores. Theta and alpha activity of RIns were negatively correlated with pain interference. In conclusion, aberrations in infraslow and faster frequency EEG oscillations at sensory discriminative, motivational-affective, and descending inhibitory cortical regions were demonstrated in people with chronic painful knee OA. Moreover, EEG oscillations were correlated with pain and functional outcome measures. PERSPECTIVE: This study confirms alterations in the rsEEG oscillations and its relationship with pain experience in people with knee OA. The study provides potential cortical targets and the EEG frequency bands for neuromodulatory interventions for managing chronic pain experience in knee OA.

Optimizing Preoperative Chronic Pain Management in Elective Spine Surgery Patients: A Narrative Review of Outcomes with Opioid and Adjuvant Pain Therapies

» Chronic preoperative opioid use negatively affects outcomes after spine surgery, with increased complications and reoperations, longer hospital stays, decreased return-to-work rates, worse patient-reported outcomes, and a higher risk of continued opioid use postoperatively.» The definition of chronic opioid use is not consistent across studies, and a more specific and consistent definition will aid in stratifying patients and understanding their risk of inferior outcomes.» Preoperative weaning periods and maximum dose thresholds are being established, which may increase the likelihood of achieving a meaningful improvement after surgery, although higher level evidence studies are needed.» Spinal cord stimulators and intrathecal drug delivery devices are increasingly used to manage chronic back pain and are equivalent or perhaps even superior to opioid treatment, although few studies exist examining how patients with these devices do after subsequent spine surgery.» Further investigation is needed to determine whether a true mechanistic explanation exists for spine-related analgesia related to spinal cord stimulators and intrathecal drug delivery devices.

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.

Immediate Effects of Anti-Spastic Epidural Cervical Spinal Cord Stimulation on Functional Connectivity of the Central Motor System in Patients with Stroke- and Traumatic Brain Injury-Induced Spasticity: A Pilot Resting-State Functional Magnetic Resonance Imaging Study

OBJECTIVE

Spinal cord stimulation (SCS) is one approach to the potential improvement of patients with post-stroke or post-traumatic spasticity. However, little is known about whether and how such interventions alter supraspinal neural systems involved in the pathogenesis of spasticity. This pilot study investigated whether epidural spinal cord stimulation at the level of the C3-C5 cervical segments, aimed at reducing spasticity, alters the patterns of functional connectivity of the brain.

METHODS

Eight patients with spasticity in the right limbs as a result of left cerebral hemisphere damage (due to hemorrhagic and ischemic stroke or traumatic and anoxic brain injury) were assessed with fMRI immediately before and immediately after short-term (1 to 6 days) test cervical epidural SCS therapy. Eight demographically and clinically comparable patients with spasticity in the right extremities due to a left hemisphere ischemic stroke and brain injury who received conventional therapy were examined as a control group. All patients also had paresis of one or two limbs and hyperreflexia.

RESULTS

After the SCS therapy, there were three main findings: (1) higher functional connectivity of the brainstem to the right premotor cortex and changes in functional connectivity between cortical motor areas, (2) increased functional connectivity between the right and left lateral nodes of the sensorimotor network, and (3) a positive correlation between decreased spasticity in the right leg and increased functional connectivity within the right hemisphere sensorimotor cortex. All these changes in functional connectivity occurred with a statistically significant decrease in spasticity, as assessed using the modified Ashworth scale. The control group showed no decrease in spasticity or increase in functional connectivity in any of the seeds of interest. On the contrary, a decrease in functional connectivity of the brainstem and right postcentral gyrus was observed in this group during the observation period.

CONCLUSIONS

We were thus able to detect intrinsic brain connectivity rearrangements that occurred during spasticity mitigation following short epidural SCS therapy.

SIGNIFICANCE

The clinical results obtained confirmed the efficacy of short-term anti-spastic SCS therapy. The obtained data on functional rearrangements of the central motor system may shed light on the mechanism of antispastic action of this procedure.

BurstDR spinal cord stimulation rebalances pain input and pain suppression in the brain in chronic neuropathic pain

OBJECTIVE

Chronic pain is processed by at least three well-known pathways, two pain provoking pathways including a medial 'suffering' and lateral 'painfulness' pathway. A third descending pain pathway modulates pain but is predominantly inhibitory. Chronic pain can be seen as an imbalance between the two pain-provoking and the pain inhibitory pathways. If this assumption is correct, then the imbalance between pain input and pain suppression should reverse and normalize in response to successful, i.e., pain reducing burstDR spinal cord stimulation, one of the current treatment options for neuropathic pain.

MATERIALS AND METHODS

Fifteen patients, who received spinal cord stimulation for failed back surgery were included in this study, using source localized electrical brain activity and connectivity recording via EEG to identify the purported imbalance.

RESULTS

BurstDR spinal cord stimulation induces a significant change in EEG activity in both the left and right somatosensory cortex (SSC) for both θ and γ oscillations. In the dorsal anterior cingulate cortex (dACC), we observed a significant drop in both α and β oscillations. This reduction is accompanied by a change in pain intensity and suffering. BurstDR spinal cord stimulation is also associated with a reduction in θ at the pregenual anterior cingulate cortex (pgACC). Analyzing effective connectivity indicates that for the θ band, more information is sent from the pgACC to the left and right SSC. For α, increased information is sent from the pgACC to the dACC and both the left and right SSC. This is associated with a reduced θ-γ coupling in the SSC and reduced α-β coupling in dACC.

CONCLUSION

This study suggests that chronic pain is indeed an imbalance between the ascending and descending pathways in the brain and that burst spinal cord stimulation can normalize this imbalance in the brain.

Case report: Utilizing diffusion-weighted MRI on a patient with chronic low back pain treated with spinal cord stimulation

Diffusion-weighted magnetic resonance imaging (dwMRI) has increasingly demonstrated greater utility in analyzing neuronal microstructure. In patients with chronic low back pain (cLBP), using dwMRI to observe neuronal microstructure can lead to non-invasive biomarkers which could provide clinicians with an objective quantitative prognostic tool. In this case report, we investigated dwMRI for the development of non-invasive biomarkers by conducting a region-based analysis of a 55-year-old male patient with failed back surgery syndrome (FBSS) treated with spinal cord stimulation (SCS). We hypothesized that dwMRI could safely generate quantitative data reflecting cerebral microstructural alterations driven by neuromodulation. Neuroimaging was performed at 6- and 12- months post-SCS implantation. The quantitative maps generated included diffusion tensor imaging (DTI) parameters; fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD) computed from whole brain tractography. To examine specific areas of the brain, 44 regions of interest (ROIs), collectively representing the pain NeuroMatrix, were extracted and registered to the patient's diffusion space. Average diffusion indices were calculated from the ROIs at both 6- and 12- months. Regions with >10% relative change in at least 3 of the 4 maps were reported. Using this selection criterion, 8 ROIs demonstrated over 10% relative changes. These ROIs were mainly located in the insular gyri. In addition to the quantitative data, a series of questionnaires were administered during the 6- and 12-month visits to assess pain intensity, functional disability, and quality of life. Overall improvements were observed in these components, with the Pain Catastrophizing Scale (PCS) displaying the greatest change. Lastly, we demonstrated the safety of dwMRI for a patient with SCS. In summary, the results from the case report prompt further investigation in applying dwMRI in a larger cohort to better correlate the influence of SCS with brain microstructural alterations, supporting the utility of dwMRI to generate non-invasive biomarkers for prognostication.

Does spinal cord stimulation improve gait in Parkinson's disease: A comprehensive review

INTRODUCTION

Axial disability, including gait disturbances, is common in Parkinson's disease (PD), especially in advanced stages. Epidural spinal cord stimulation (SCS) has been investigated as a treatment option for gait disorders in PD. Here, we review the literature on SCS in PD and evaluate its efficacy, optimal stimulation parameters, optimal electrode locations, possible effects of concurrent deep brain stimulation, and possible working mechanisms on gait.

METHODS

Databases were searched for human studies involving PD patients who received an epidural SCS intervention and who had at least one gait-related outcome measure. The included reports were reviewed with respect to design and outcomes. Additionally, the possible mechanisms of action underlying SCS were reviewed.

RESULTS

Out of 433 records identified, 25 unique studies with in total 103 participants were included. Most studies included only a few participants. The gait disorders of most PD patients with concurrent pain complaints, mostly low back pain, improved with SCS in almost all cases, regardless of stimulation parameters or electrode location. Higher-frequency stimulation (>200 Hz) seemed to be more effective in pain-free PD patients, but the results were inconsistent. Heterogeneity in outcome measures and follow-up times hindered comparability.

CONCLUSIONS

SCS may improve gait in PD patients with neuropathic pain, but its efficacy in pain-free patients remains uncertain due to a lack of thorough double-blind studies. Apart from a well-powered, controlled, double-blind study design, future studies could further explore the initial hints that higher-frequency stimulation (>200 Hz) might be the best approach to improve gait outcomes in pain-free patients.

Heterogeneous Cortical Effects of Spinal Cord Stimulation

OBJECTIVES

The understanding of the cortical effects of spinal cord stimulation (SCS) remains limited. Multiple studies have investigated the effects of SCS in resting-state electroencephalography. However, owing to the large variation in reported outcomes, we aimed to describe the differential cortical responses between two types of SCS and between responders and nonresponders using magnetoencephalography (MEG).

MATERIALS AND METHODS

We conducted 5-minute resting-state MEG recordings in 25 patients with chronic pain with active SCS in three sessions, each after a one-week exposure to tonic, burst, or sham SCS. We extracted six spectral features from the measured neurophysiological signals: the alpha peak frequency; alpha power ratio (power 7-9 Hz/power 9-11 Hz); and average power in the theta (4-7.5 Hz), alpha (8-12.5 Hz), beta (13-30 Hz), and low-gamma (30.5-60 Hz) frequency bands. We compared these features (using nonparametric permutation t-tests) for MEG sensor and cortical map effects across stimulation paradigms, between participants who reported low (< 5, responders) vs high (≥ 5, nonresponders) pain scores, and in three representative participants.

RESULTS

We found statistically significant (p < 0.05, false discovery rate corrected) increased MEG sensor signal power below 3 Hz in response to burst SCS compared with tonic and sham SCS. We did not find statistically significant differences (all p > 0.05) between the power spectra of responders and nonresponders. Our data did not show statistically significant differences in the spectral features of interest among the three stimulation paradigms or between responders and nonresponders. These results were confirmed by the MEG cortical maps. However, we did identify certain trends in the MEG source maps for all comparisons and several features, with substantial variation across participants.

CONCLUSIONS

The considerable variation in cortical responses to the various SCS treatment options necessitates studies with sample sizes larger than commonly reported in the field and more personalized treatment plans. Studies with a finer stratification between responders and nonresponders are required to advance the knowledge on SCS treatment effects.

A Review of Effects of Spinal Cord Stimulation on Spectral Features in Resting-State Electroencephalography

BACKGROUND

Spinal cord stimulation (SCS) is an effective therapy for patients with refractory chronic pain syndromes. Although studies have shown that SCS has both spinal and supraspinal effects, the current understanding of cortical effects is still limited. Neuroimaging techniques, such as magnetoencephalography (MEG) and electroencephalography (EEG), combined here as M/EEG, can reveal modulations in ongoing resting-state cortical activity. We aim to provide an overview of available literature on resting-state M/EEG in patients with chronic pain who have been treated with SCS.

MATERIALS AND METHODS

We searched multiple online data bases for studies on SCS, chronic pain, and resting-state M/EEG. Primary outcome measures were changes in spectral features, combined with brain regions in which these changes occurred.

RESULTS

We included eight studies reporting various SCS paradigms (tonic, burst, high-dose, and high-frequency stimulation) and revealing heterogeneity in outcome parameters. We summarized changes in cortical activity in various frequency bands: theta (4-7 Hz), alpha (7-12 Hz), beta (13-30 Hz), and gamma (30-44 Hz). In multiple studies, the somatosensory cortex showed modulation of cortical activity under tonic, burst, and high-frequency stimulation. Changes in connectivity were found in the dorsal anterior cingulate cortex, dorsolateral prefrontal cortex, and parahippocampus.

CONCLUSIONS

The large heterogeneity observed in outcome measures is probably caused by the large variety in study designs, stimulation paradigms, and spectral features studied. Paresthesia-free paradigms have been compared with tonic stimulation in multiple studies. These studies suggest modulation of medial, lateral, and descending pathways for paresthesia-free stimulation, whereas tonic stimulation predominantly modulates lateral and descending pathways. Moreover, multiple studies have reported an increased alpha peak frequency, increased alpha power, and/or decreased theta power when SCS was compared with baseline, indicating modulation of thalamocortical pathways. Further studies with well-defined groups of responders and nonresponders to SCS are recommended to independently study the cortical effects of pain relief and SCS.

Spinal cord stimulation to treat meralgia paresthetica. Is it feasible? A case report

Meralgia paresthetica is a neurological disorder caused by a neuropathy of the lateral femoral cutaneous nerve. Its aetiology can be spontaneous or iatrogenic. It is characterized by pain, paresthesia, and numbness in the anterolateral aspect of the thigh. Diagnosis is based on clinical examination, although image and neurophysiological tests can be useful as well. Despite conservative measures use to be effective in most of patients, refractory cases can benefit from alternative treatments. Available surgical procedures are: nerve decompression (neurolysis) or section (neurectomy) and radiofrequency ablation. We present a case of refractory meralgia paresthetica where spinal cord stimulation was used as a possible effective technique in pain relief and to avoid the neurectomy of the lateral femoral cutaneous nerve.

The Roles of Imaging Biomarkers in the Management of Chronic Neuropathic Pain

Chronic neuropathic pain (CNP) affects around 10% of the general population and has a significant social, emotional, and economic impact. Current diagnosis techniques rely mainly on patient-reported outcomes and symptoms, which leads to significant diagnostic heterogeneity and subsequent challenges in management and assessment of outcomes. As such, it is necessary to review the approach to a pathology that occurs so frequently, with such burdensome and complex implications. Recent research has shown that imaging methods can detect subtle neuroplastic changes in the central and peripheral nervous system, which can be correlated with neuropathic symptoms and may serve as potential markers. The aim of this paper is to review available imaging methods used for diagnosing and assessing therapeutic efficacy in CNP for both the preclinical and clinical setting. Of course, further research is required to standardize and improve detection accuracy, but available data indicate that imaging is a valuable tool that can impact the management of CNP.

Activity-dependent plasticity and spinal cord stimulation for motor recovery following spinal cord injury

Spinal cord injuries lead to permanent physical impairment despite most often being anatomically incomplete disruptions of the spinal cord. Remaining connections between the brain and spinal cord create the potential for inducing neural plasticity to improve sensorimotor function, even many years after injury. This narrative review provides an overview of the current evidence for spontaneous motor recovery, activity-dependent plasticity, and interventions for restoring motor control to residual brain and spinal cord networks via spinal cord stimulation. In addition to open-loop spinal cord stimulation to promote long-term neuroplasticity, we also review a more targeted approach: closed-loop stimulation. Lastly, we review mechanisms of spinal cord neuromodulation to promote sensorimotor recovery, with the goal of advancing the field of rehabilitation for physical impairments following spinal cord injury.

Tonic, Burst, and Burst-Cycle Spinal Cord Stimulation Lead to Differential Brain Activation Patterns as Detected by Functional Magnetic Resonance Imaging

OBJECTIVE

The objective of this preclinical study was to examine the responses of the brain to noxious stimulation in the presence and absence of different modes of spinal cord stimulation (SCS) using blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD-fMRI).

MATERIALS AND METHODS

Sprague-Dawley rats were randomized to groups based on the mode of SCS delivered which included tonic stimulation (n = 27), burst stimulation (n = 30), and burst-cycle stimulation (n = 29). The control (sham) group (n = 28) received no SCS. The SCS electrode was inserted between T10 and T12 spinal levels prior to fMRI session. The experimental protocol for fMRI acquisition consisted of an initial noxious stimulation phase, a treatment phase wherein the SCS was turned on concurrently with noxious stimulation, and a residual effect phase wherein the noxious stimulation alone was turned on. The responses were statistically analyzed through paired t-test and the results were presented as z-scores for the quantitative analysis of the fMRI data.

RESULTS

The treatment with different SCS modes attenuated the BOLD brain responses to noxious hindlimb stimulation. The tonic, burst, and burst-cycle SCS treatment attenuated BOLD responses in the caudate putamen (CPu), insula (In), and secondary somatosensory cortex (S2). There was little to no corresponding change in sham control in these three regions. The burst and burst-cycle SCS demonstrated greater attenuation of BOLD signals in CPu, In, and S2 compared to tonic stimulation.

CONCLUSION

The high-resolution fMRI study using a rat model demonstrated the potential of different SCS modes to act on several pain-matrix-related regions of the brain in response to noxious stimulation. The burst and burst-cycle SCS exhibited greater brain activity reduction in response to noxious hindlimb stimulation in the caudate putamen, insula, and secondary somatosensory cortex compared to tonic stimulation.

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

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

Modulation of the Somatosensory Evoked Potential by Attention and Spinal Cord Stimulation

Introduction: Spinal Cord Stimulation (SCS) is a last-resort treatment for patients with intractable chronic pain in whom pharmacological and other treatments have failed. Conventional tonic SCS is accompanied by tingling sensations. More recent stimulation protocols like burst SCS are not sensed by the patient while providing similar levels of pain relief. It has been previously reported that conventional tonic SCS can attenuate sensory-discriminative processing in several brain areas, but that burst SCS might have additional effects on the medial, motivational-affective pain system. In this explorative study we assessed the influence of attention on the somatosensory evoked brain responses under conventional tonic SCS as well as burst SCS regime.

Methods: Twelve chronic pain patients with an implanted SCS device had 2-weeks evaluation periods with three different SCS settings (conventional tonic SCS, burst SCS, and sham SCS). At the end of each period, an electro-encephalography (EEG) measurement was done, at which patients received transcutaneous electrical pulses at the tibial nerve to induce somatosensory evoked potentials (SEP). SEP data was acquired while patients were attending the applied pulses and while they were mind wandering. The effects of attention as well as SCS regimes on the SEP were analyzed by comparing amplitudes of early and late latencies at the vertex as well as brain activity at full cortical maps.

Results: Pain relief obtained by the various SCS settings varied largely among patients. Early SEP responses were not significantly affected by attention nor SCS settings (i.e., burst, tonic, and sham). However, late SEP responses (P300) were reduced with tonic and burst SCS: conventional tonic SCS reduced P300 brain activity in the unattended condition, while burst SCS reduced P300 brain activity in both attended and unattended conditions.

Conclusion: Burst spinal cord stimulation for the treatment of chronic pain seems to reduce cortical attention that is or can be directed to somatosensory stimuli to a larger extent than conventional spinal cord stimulation treatment. This is a first step in understanding why in selected chronic pain patients burst SCS is more effective than tonic SCS and how neuroimaging could assist in personalizing SCS treatment.

Effects of Chronic Pain Treatment on Altered Functional and Metabolic Activities in the Brain: A Systematic Review and Meta-Analysis of Functional Neuroimaging Studies

Previous studies have identified altered brain changes in chronic pain patients, however, it remains unclear whether these changes are reversible. We summarized the neural and molecular changes in patients with chronic pain and employed a meta-analysis approach to quantify the changes. We included 75 studies and 11 of these 75 studies were included in the activation likelihood estimation (ALE) analysis. In the 62 functional magnetic resonance imaging (fMRI) studies, the primary somatosensory and motor cortex (SI and MI), thalamus, insula, and anterior cingulate cortex (ACC) showed significantly decreased activity after the treatments compared to baseline. In the 13 positron emission tomography (PET) studies, the SI, MI, thalamus, and insula showed significantly increased glucose uptake, blood flow, and opioid-receptor binding potentials after the treatments compared to baseline. A meta-analysis of fMRI studies in patients with chronic pain, during pain-related tasks, showed a significant deactivation likelihood cluster in the left medial posterior thalamus. Further studies are warranted to understand brain reorganization in patients with chronic pain compared to the normal state, in terms of its relationship with symptom reduction and baseline conditions.

Exploration of the Supraspinal Hypotheses about Spinal Cord Stimulation and Dorsal Root Ganglion Stimulation: A Systematic Review

Despite the established efficacy and effectiveness of Spinal Cord Stimulation (SCS), there is still no consensus on the supraspinal mechanisms of action of this therapy. The purpose of this study was to systematically review previously raised hypotheses concerning supraspinal mechanisms of action of SCS based on human, animal and computational studies. Searches were conducted using four electronic databases (PubMed, EMBASE, SCOPUS and Web of Science), backward reference searching and consultation with experts. The study protocol was registered prior to initiation of the review process (PROSPERO CRD42020161531). A total of 54 publications were included, 21 of which were animal studies, and 33 were human studies. The supraspinal hypotheses (n = 69) identified from the included studies could be categorized into six groups concerning the proposed supraspinal hypothesis, namely descending pathways (n = 24); ascending medial pathway (n = 13); ascending lateral pathway (n = 10); affective/motivational influences (n = 8); spinal–cerebral (thalamic)-loop (n = 3) and miscellaneous (n = 11). Scientific support is provided for the hypotheses identified. Modulation of the descending nociceptive inhibitory pathways, medial and lateral pathways were the most frequently reported hypotheses about the supraspinal mechanisms of action of SCS. These hypotheses were mainly supported by studies with a high or moderate confidence in the body of evidence.

Metabolic Imaging of Pain Matrix Using 18 F Fluoro-deoxyglucose Positron Emission Tomography/Computed Tomography for Patients Undergoing L2 Dorsal Root Ganglion Stimulation for Low Back Pain

INTRODUCTION

Nociceptive signals from lumbar intervertebral discs ascend in the sympathetic chain via the L2 dorsal root ganglion (L2 DRG), a potential target for discogenic low back pain in neuromodulation. Positron Emission Tomography/Computed Tomography (PET-CT) measures functional changes in the brain metabolic activity, identified by the changes in the regional cerebral blood flow (rCBF) as determined by the changes of F-18 Fluoro-deoxyglucose (¹⁸ F FDG) tracer within brain tissues.

METHODS AND MATERIALS

Nine patients were recruited to explore the changes in PET-CT imaging at baseline and four-weeks post implantation of bilateral L2 DRG neurostimulation leads and implantable pulse generator (IPG). PET-CT scans were performed 30 min following an IV injection of 250±10% MBq of ¹⁸ F FDG tracer. Fifteen frames were acquired in 15 min. PET list-mode raw data were reconstructed and normalized appropriately to a brain anatomical atlas.

RESULTS

Nine patients were recruited to the study, where PET-CT imaging data for five patients were analyzed. The right and left insular cortex, primary and secondary somato-sensory cortices, prefrontal cortex, anterior cingulate cortex, thalamus, amygdala, hippocampus and the midline periaqueductal areas, were assessed for any changes in the metabolic activity. A total of 85 pain matrix regions were delineated SUV (standardized uptake value)_MAX , SUV _MEAN  ± SD, and SUV_PEAK were calculated for each of these regions of the brain and were compared pre- and post-L2 DRG stimulation. Sixty-one of the 85 matrices showed an increase in metabolic activity whereas 24 matrices showed a reduction in metabolic activity.

CONCLUSION

This is the first ever study reporting the changes in cerebral metabolic activity and multi-frame static brain ¹⁸ F FDG PET imaging after L2 DRG stimulation for discogenic low back pain. Predominantly an increased metabolic activity in nociceptive brain matrices are seen with an increased in F¹⁸ F FDG uptake following L2 DRG stimulation.

Physiological Measures of Acute and Chronic Pain within Different Subject Groups: A Systematic Review

Results

The methods' heart rate variability and electroencephalogram show clear and consistent results as acute pain assessment. Magnetic resonance imaging can measure chronic pain. Ordered by invasiveness and vulnerability, a trend shows that the invasive methods are used more with less vulnerable subjects. Only instruments used for skin conductance and automatic facial recognition have a lower-than-average technological maturity.

Conclusions

Some pain assessment methods show good and consistent results and have high technological maturity; however, using them as pain assessment for persons with ID is uncommon. Since this addition can ameliorate caregiving, more research of assessment methods should occur.

Biomarker Optimization of Spinal Cord Stimulation Therapies

OBJECTIVES

We are in the process of designing and testing an intradural stimulation device that will shorten the distance between the location of the electrode array and the targeted neural tissue, thus improving the efficacy of electrical current delivery. Identifying a biomarker that accurately reflects the response to this intervention is highly valued because of the potential to optimize interventional parameters or predict a response before it is clinically measurable. In this report, we summarize the findings pertaining to the study of biomarkers so that we and others will have an up-to-date reference that critically evaluates the current approaches and select one or several for testing during the development of our device.

MATERIALS AND METHODS

We have conducted a broad survey of the existing literature to catalogue the biomarkers that could be coupled to intradural spinal cord stimulation. We describe in detail some of the most promising biomarkers, existing limitations, and suitability to managing chronic pain.

RESULTS

Chronic, intractable pain is an all-encompassing condition that is incurable. Many treatments for managing chronic pain are nonspecific in action and intermittently administered; therefore, patients are particularly susceptible to large fluctuations in pain control over the course of a day. The absence of a reliable biomarker challenges assessment of therapeutic efficacy and contributes to either incomplete and inconsistent pain relief or, alternatively, intolerable side effects. Fluctuations in metabolites or inflammatory markers, signals captured during dynamic imaging, and genomics will likely have a role in governing how a device is modulated.

CONCLUSIONS

Efforts to identify one or more biomarkers are well underway with some preliminary evidence supporting their efficacy. This has far-reaching implications, including improved outcomes, fewer adverse events, harmonization of treatment and individuals, performance gains, and cost savings. We anticipate that novel biomarkers will be used widely to manage chronic pain.

Effects of spinal cord stimulation on voxel-based brain morphometry in patients with failed back surgery syndrome

OBJECTIVE

Despite the clinical effectiveness of Spinal Cord Stimulation (SCS), potential structural brain modifications have not been explored. Our aim was to identify structural volumetric changes during subsensory SCS, in patients with Failed Back Surgery Syndrome (FBSS).

METHODS

In this cohort study, twenty-two FBSS patients underwent a magnetic resonance imaging protocol before SCS and 3 months after SCS. Clinical parameters were correlated with volumetric changes, calculated with voxel-based morphometry.

RESULTS

After 3 months, a significant volume decrease was found in the inferior frontal gyrus, precuneus, cerebellar posterior lobe and middle temporal gyrus. Significant increases were found in the inferior temporal gyrus, precentral gyrus and the middle frontal gyrus after SCS. Additionally, significant increases in volume of superior frontal and parietal white matter and a significant decrease in volume of white matter underlying the premotor/middle frontal gyrus were revealed after SCS. A significant correlation was highlighted between white matter volume underlying premotor/middle frontal gyrus and leg pain relief.

CONCLUSIONS

This study revealed for the first time that SCS is able to induce volumetric changes in gray and white matter, suggesting the reversibility of brain alterations after chronic pain treatment.

SIGNIFICANCE

Volumetric brain alterations are observable after 3 months of subsensory SCS in FBSS patients.

Persistent pain induces mood problems and memory loss by the involvement of cytokines, growth factors, and supraspinal glial cells

Lesions of peripheral nerves lead to pain, hyperalgesia, and psychological comorbidities. However, the relationship between mood disorders and neuropathic pain is unclear, as well as the underlying mechanisms related to these disorders. Therefore, we investigated if nerve injury induces depression, anxiety, and cognitive impairment and if there were changes in cytokines, growth factors, and glial cell activation in cortical sites involved in processing pain and mood in animals with nerve injury. Nerve injury was induced by partial sciatic nerve ligation (PSNL) in male Swiss mice and compared to sham-operated animals. Nociceptive behavioral tests to mechanical and thermal (heat and cold) stimuli confirmed the development of hyperalgesia. We further examined mood disorders and memory behaviors. We show nerve injury induces a decrease in mechanical withdrawal thresholds and thermal latency to heat and cold. We also show that nerve injury causes depressive-like and anxiety-like behaviors as well as impairment in short-term memory in mice. There were increases in proinflammatory cytokines as well as Brain-Derived Neurotrophic Factor (BDNF) in the injured nerve. In the spinal cord, there were increases in both pro and anti-inflammatory cytokines, as well as of BDNF and Nerve Growth Factor (NGF). Further, in our data was a decrease in the density of microglia and astrocytes in the hippocampus and increased microglial density in the prefrontal cortex, areas associated with neuropathic pain conditions.

The Evolution of Neuromodulation in the Treatment of Chronic Pain: Forward-Looking Perspectives

Background

The field of neuromodulation is continually evolving, with the past decade showing significant advancement in the therapeutic efficacy of neuromodulation procedures. The continued evolution of neuromodulation technology brings with it the promise of addressing the needs of both patients and physicians, as current technology improves and clinical applications expand.

Design

This review highlights the current state of the art of neuromodulation for treating chronic pain, describes key areas of development including stimulation patterns and neural targets, expanding indications and applications, feedback-controlled systems, noninvasive approaches, and biomarkers for neuromodulation and technology miniaturization.

Results and Conclusions

The field of neuromodulation is undergoing a renaissance of technology development with potential for profoundly improving the care of chronic pain patients. New and emerging targets like the dorsal root ganglion, as well as high-frequency and patterned stimulation methodologies such as burst stimulation, are paving the way for better clinical outcomes. As we look forward to the future, neural sensing, novel target-specific stimulation patterns, and approaches combining neuromodulation therapies are likely to significantly impact how neuromodulation is used. Moreover, select biomarkers may influence and guide the use of neuromodulation and help objectively demonstrate efficacy and outcomes.

Percutaneous Peripheral Nerve Stimulation for Chronic Low Back Pain: Prospective Case Series With 1 Year of Sustained Relief Following Short-Term Implant

INTRODUCTION

Percutaneous peripheral nerve stimulation (PNS) provides an opportunity to relieve chronic low back pain and reduce opioid analgesic consumption as an alternative to radiofrequency ablation and permanently implanted neurostimulation systems. Traditionally, the use of neurostimulation earlier in the treatment continuum has been limited by its associated risk, invasiveness, and cost.

METHODS

Percutaneous PNS leads (SPRINT MicroLead) were placed bilaterally to target the medial branches of the dorsal rami nerves under image guidance. The percutaneous leads were connected to miniature wearable stimulators (SPRINT PNS System) for the 1-month therapy period, after which the leads were removed. Pain and disability were assessed long-term up to 12 months after lead removal.

RESULTS

Substantial, clinically significant reductions in average pain intensity (≥50% reduction as measured by the Brief Pain Inventory Short Form) were experienced by a majority of subjects (67%) at end of treatment compared to baseline (average 80% reduction among responders; P < 0.05, analysis of variance; n = 9). Twelve months after the end of PNS treatment, a majority of subjects who completed the long-term follow-up visits experienced sustained, clinically significant reductions in pain and/or disability (67%, n = 6; average 63% reduction in pain intensity and 32-point reduction in disability among responders). No serious or unanticipated adverse events were reported.

CONCLUSIONS

This study challenges the long-held notion that a positive trial of PNS should be followed by a permanent implant in responders. Percutaneous PNS may serve as an effective neurostimulation therapy for patients with chronic low back pain and should be considered earlier in the treatment continuum as a motor-sparing means of avoiding opioids, denervation, and permanently implanted neurostimulation systems.

The influence of High Dose Spinal Cord Stimulation on the descending pain modulatory system in patients with failed back surgery syndrome

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For the first time, the influence of HD-SCS on the descending pathways was tested.

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rsfMRI and functional connectivity were used to evaluate this a priori hypothesis.

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HD-SCS does influence the descending pain modulatory system.

Spinal Cord Stimulation for Freezing of Gait: From Bench to Bedside

Spinal cord stimulation (SCS) has been used for the treatment of chronic pain for nearly five decades. With a high degree of efficacy and a low incidence of adverse events, it is now considered to be a suitable therapeutic alternative in most guidelines. Experimental studies suggest that SCS may also be used as a therapy for motor and gait dysfunction in parkinsonian states. The most common and disabling gait dysfunction in patients with Parkinson's disease (PD) is freezing of gait (FoG). We review the evolution of SCS for gait disorders from bench to bedside and discuss potential mechanisms of action, neural substrates, and clinical outcomes.

Effects of spinal cord stimulation on heart rate variability in patients with Failed Back Surgery Syndrome

Background

Building on the recent finding that chronic pain patients with impaired functioning of the descending nociceptive inhibitory system (DNIS) present lower resting heart rate variability (HRV), this study aims to investigate the impact of Spinal Cord Stimulation (SCS) on HRV in patients with Failed Back Surgery Syndrome (FBSS). More precisely, we hypothesize that SCS influences the DNIS, with increased parasympathetic tone as a consequence, as measurable by HRV analysis.

Methods

Twenty-two patients diagnosed with FBSS and treated with SCS participated in this study. HRV was measured with a 2-lead ECG registration tool during on and off states of SCS. HRV analysis for time, frequency, time-frequency and nonlinear domain parameters was based on a 5-minute recording segment.

Results

The mean heart rate and low frequency power were significantly lower when SCS was activated. HRV, absolute and normalized high frequency power significantly increased during SCS compared to without SCS. The ratio of low frequency/high frequency ratios, as parameter for global sympathetic-parasympathetic equilibrium, significantly decreased when SCS was activated.

Conclusions

When SCS is switched off, patients with FBSS present relatively stronger sympathetic tone and weaker parasympathetic activity. Activation of the SCS, possibly via stimulation of the DNIS, restores this disbalance of autonomic activity.

Observations of Autonomic Variability Following Central Neuromodulation for Chronic Neuropathic Pain in Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) persons with chronic neuropathic pain (NP) demonstrate maladaptive autonomic profiles compared to SCI counterparts without NP (SCI - NP) or able-bodied (AB) controls. These aberrations may be secondary to maladaptive neuroplasticity in the shared circuitry of the pain neuromatrix-central autonomic network interface (PNM-CAN). In this study, we explored the proposed PNM-CAN mechanism in SCI + NP and AB cohorts following centrally-directed neuromodulation to assess if the PNM and CAN are capable of being differentially modulated.

MATERIALS AND METHODS

Central neuromodulation was administered via breathing-controlled electrical stimulation (BreEStim), previously evidenced to operate at the PNM. To quantify CAN activity, conventional heart rate variability (HRV) recordings were used to gather time and frequency domain parameters of autonomic modulation. SCI + NP (n = 10) and AB (n = 13) cohorts received null and active BreEStim randomly in crossover fashion. HRV data were gathered pretest and 30 minutes posttest. Pain modulation was quantified at both time-points by visual analog scale (VAS) for SCI + NP persons and electrical detection and pain threshold levels (EDT, EPT) for AB persons.

RESULTS

Following active BreEStim only, SCI + NP persons demonstrated increased parasympathetic tone (increased NN50, p = 0.03, and pNN50, p = 0.02, HRV parameters). This parasympathetic restoration was associated with analgesia (VAS reduction, p < 0.01). Similarly, AB persons demonstrated increased noxious tolerance (increased EPT, p = 0.03, with preserved EDL, p = 0.78) only following active BreEStim. However, this increased pain threshold was not associated with autonomic changes.

CONCLUSIONS

Central modulation targeting the PNM produced autonomic changes in SCI + NP persons but not AB persons. These findings suggest that AB persons exhibit intact CAN mechanisms capable of compensating for PNM aberrations or simply that SCI + NP persons exhibit altered PNM-CAN machinery altogether. Our collective findings confirm the interconnectedness and maladaptive plasticity of PNM-CAN machinery in SCI + NP persons and suggest that the PNM and CAN circuitry can be differentially modulated.

Predictive Factors Associated with Pain Relief of Spinal Cord Stimulation for Central Post-stroke Pain

The efficacy and predictive factors associated with successful spinal cord stimulation (SCS) for central post-stroke pain (CPSP) have yet to be definitively established. Thus, this study evaluated the rates of pain relief found after more than 12 months and the predictive factors associated with the success of SCS for CPSP. The degree of pain after SCS in 18 patients with CPSP was assessed using the Visual Analog Scale preoperatively, at 1, 6 and 12 months after surgery, and at the time of the last follow-up. After calculating the percentage of pain relief (PPR), patients were separated into two groups. The first group exhibited continuing PPR ≥30% at more than 12 months (effect group) while the second group exhibited successful/unsuccessful trials followed by decreasing PPR <30% within 12 months (no effect group). Pain relief for more than 12 months was achieved in eight out of 18 (44.4%) patients during the 67.3 ± 35.5 month follow-up period. Statistically significant differences were found for both the age and stroke location during comparisons of the preoperative characteristics between the two groups. There was a significantly younger mean age for the effect versus the no effect group. Patients with stoke in non-thalamus were significantly enriched in effect group compared with those with stoke in thalamus. Multivariable analysis using these two factors found no statistical differences, suggesting that these two factors might possibly exhibit the same behaviors for the SCS effect. These results suggest that SCS may be able to provide pain relief in young, non-thalamus stroke patients with CPSP.

Magnetic Resonance Imaging Exploration of the Human Brain During 10 kHz Spinal Cord Stimulation for Failed Back Surgery Syndrome: A Resting State Functional Magnetic Resonance Imaging Study

INTRODUCTION

Apart from the clinical efficacy of high frequency spinal cord stimulation at 10 kHz, the underlying mechanism of action remains unclear. In parallel with spinal or segmental theories, supraspinal hypotheses have been recently proposed. In order to unveil hidden altered brain connectome patterns, a resting state functional magnetic resonance imaging (rsfMRI) protocol was performed in subjects routinely treated for back and/or leg pain with high-frequency spinal cord stimulation (HF-SCS) HF-SCS at 10 kHz.

METHODS

RsfMRI imaging was obtained from ten patients with failed back surgery syndrome who were eligible for HF-SCS at 10 kHz. Specifically-chosen regions of interest with different connectivity networks have been investigated over time. Baseline measurements were compared with measurements after 1 month and 3 months of HF-SCS at 10 kHz. Additionally, clinical parameters on pain intensity, central sensitization, pain catastrophizing, and sleep quality were correlated with the functional connectivity strengths.

RESULTS

The study results demonstrate an increased connectivity over time between the anterior insula (affective salience network) and regions of the frontoparietal network and the central executive network. After 3 months of HF-SCS, the increased strength in functional connectivity between the left dorsolateral prefrontal cortex and the right anterior insula was significantly correlated with the minimum clinically important difference (MCID) value of the Pittsburgh sleep quality index.

CONCLUSION

These findings support the hypothesis that HF-SCS at 10 kHz might influence the salience network and therefore also the emotional awareness of pain.

Supraspinal Mechanisms of Spinal Cord Stimulation for Modulation of Pain: Five Decades of Research and Prospects for the Future

The field of spinal cord stimulation is expanding rapidly, with new waveform paradigms asserting supraspinal sites of action. The scope of treatment applications is also broadening from chronic pain to include cerebral ischemia, dystonia, tremor, multiple sclerosis, Parkinson disease, neuropsychiatric disorders, memory, addiction, cognitive function, and other neurologic diseases. The role of neurostimulation as an alternative strategy to opioids for chronic pain treatment is under robust discussion in both scientific and public forums. An understanding of the supraspinal mechanisms underlying the beneficial effects of spinal cord stimulation will aid in the appropriate application and development of optimal stimulation strategies for modulating pain signaling pathways. In this review, the authors focus on clinical and preclinical studies that indicate the role of supraspinal mechanisms in spinal cord stimulation-induced pain inhibition, and explore directions for future investigations.

Tonic spinal cord stimulation as therapeutic option in Parkinson disease with axial symptoms: Effects on walking and quality of life

Spinal cord stimulation (SCS) is an effective surgical therapy used for the treatment of chronic neuropathic pain. Tonic SCS is safe and improve not only gait disorders, motor symptoms, but also quality of life in Parkinson patients even with dopa-resistant symptoms with or without associated deep brain stimulation.

Spinal Cord Stimulation 50 Years Later: Clinical Outcomes of Spinal Cord Stimulation Based on Randomized Clinical Trials-A Systematic Review

To assess the efficacy of spinal cord stimulation (SCS) for each indication, one must critically assess each specific clinical outcome to identify outcomes that benefit from SCS therapy. To date, a comprehensive review of clinically relevant outcome-specific evidence regarding SCS has not been published. We aimed to assess all randomized controlled trials from the world literature for the purpose of evaluating the clinical outcome-specific efficacy of SCS for the following outcomes: perceived pain relief or change pain score, quality of life, functional status, psychological impact, analgesic medication utilization, patient satisfaction, and health care cost and utilization. Interventions were SCS, without limitation to the type of controls or the type of SCS in the active arms. For each study analyzed, a quality assessment was performed using a validated scale that assesses reporting, external validity, bias, confounding, and power. Each outcome was assessed specific to its indication, and the primary measure of each abovementioned outcome was a summary of the level of evidence. Twenty-one randomized controlled trials were analyzed (7 for trunk and limb pain, inclusive of failed back surgery syndrome; 8 for refractory angina pectoris; 1 for cardiac X syndrome; 3 for critical limb ischemia; 2 for complex regional pain syndrome; and 2 for painful diabetic neuropathy). Evidence assessments for each outcome for each indication were depicted in tabular format. Outcome-specific evidence scores were established for each of the abovementioned indications, providing both physicians and patients with a summary of evidence to assist in choosing the optimal evidence-based intervention. The evidence presented herein has broad applicability as it encompasses a breadth of patient populations, variations of SCS therapy, and comparable controls that, together, reflect comprehensive clinical decision making.

Mechanisms of spinal cord stimulation for the treatment of pain: Still in the dark after 50 years

Background and Objective

Despite the value of spinal cord stimulation (SCS) in treating some patients with focal neuropathic pain, technological advances in stimulator design and treatment protocols have not correlated with significant improvements in clinical outcomes. This may be because incomplete understanding of the mechanisms underlying SCS precludes improvement in clinical efficacy. In this brief review, we (a) review phenomenological effects of SCS, (b) review the literature on proposed spinal sites of action of SCS and (c) propose a novel hypothesis of mechanism of action.

Results

Dorsal columns, dorsal roots and dorsal horns have each been proposed as spinal sites of action of SCS. We suggest that evidence in favour of the dorsal columns or dorsal roots as the primary mediators of SCS is weak and propose that the dorsal horn is the crucial site of action. Furthermore, we hypothesize that, based on their location, and neurochemical and morphological properties, dorsal horn islet cells may mediate the effects of SCS.

Conclusions

The precise spinal mechanisms of action of SCS are still unknown. Dorsal horn islet cells have properties that position them to play a key role in analgesic effects of electrical stimulation. Understanding the mechanisms responsible for positive SCS effects are needed for successful translation into clinical dividends.

Significance

We review possible spinal mechanisms of action of spinal cord stimulation for neuropathic pain, proposing that direct modulation of dorsal horn neurons is crucial. We suggest that mechanistic insights are needed for translation into more favourable clinical outcomes.

Effects of Tonic Spinal Cord Stimulation on Sensory Perception in Chronic Pain Patients: A Systematic Review

OBJECTIVES

Even if spinal cord stimulation (SCS) is widely used and effective in treating intractable chronic neuropathic pain conditions, little is known about its possible impacts on sensory perception. Quantitative sensory testing (QST) is a useful tool to assess this issue. The aim of this study was to review the impact of tonic SCS on somatosensory perception quantified by QST in chronic pain patients.

MATERIALS AND METHODS

Relevant articles and abstracts were searched in all languages from CINAHL, Cochrane, Embase, MEDLINE, and Web of Knowledge data bases. Data were extracted and included studies were assessed for risk of bias.

RESULTS

Out of 5610 records, 15 peer-reviewed articles were eligible and included. The results are heterogeneous due to inadequate comparability among studies for populations (a total of 224 patients diagnosed with more than 13 chronic pain conditions), QST parameters (22 measured with 25 different devices) and experimental procedures (study design, comparator, evaluation time, and area tested). The wide variety of studies, designs, populations, and measures included in this review did not lead to strong evidence on how conventional ("tonic") SCS affects sensory processing in patients with chronic pain.

CONCLUSIONS

The data available tend to suggest that conventional SCS does not interfere with perception of external stimuli. New studies that follow a standardized procedure and consider the possible influence of sensory profile, after-effect bias, and confounding factors are required to confirm this observation. Moreover, the impact on sensory perception of other SCS modalities and alternative electrical neuromodulation therapies could also be explored.

Functional magnetic resonance imaging: cerebral function alterations in subthreshold and suprathreshold spinal cord stimulation

Background and purpose

Failed back surgery syndrome (FBSS) is a common and devastating chronic neuropathic pain disorder. Conventional spinal cord stimulation (SCS) applies electrical suprathreshold pulses to the spinal cord at a frequency of 40-60 Hz and relieves pain in FBSS patients. During the last decade, two major changes have emerged in the techniques of stimulating the spinal cord: paresthesia-free or subthreshold stimulation and administration of higher frequency or higher amounts of energy to the spinal cord. Despite the positive clinical results, the mechanism of action remains unclear. A functional MRI (fMRI) study was conducted to investigate the brain alterations during subthreshold and suprathreshold stimulation at different frequencies.

Methods

Ten subjects with FBSS, treated with externalized SCS, received randomly four different stimulation frequencies (4 Hz, 60 Hz, 500 Hz, and 1 kHz) during four consecutive days. At every frequency, the patient underwent sub- and suprathreshold stimulation. Cerebral activity was monitored and assessed using fMRI.

Results

Suprathreshold stimulation is generally accompanied with more activity than sub-threshold SCS. Suprathreshold SCS resulted in increased bilateral activation of the frontal cortex, thalamus, pre- and postcentral gyri, basal ganglia, cingulate gyrus, insula, thalamus, and claustrum. We observed deactivation of the bilateral parahippocampus, amygdala, precuneus, posterior cingulate gyrus, postcentral gyrus, and unilateral superior temporal gyrus.

Conclusion

Suprathreshold stimulation resulted in greater activity (both activation and deactivation) of the frontal brain regions; the sensory, limbic, and motor cortices; and the diencephalon in comparison with subthreshold stimulation. Each type of frequency at suprathreshold stimulation was characterized by an individual activation pattern.

The effects of transcranial direct current stimulation on metabolite changes at the anterior cingulate cortex in neuropathic pain: a pilot study

Background

Neuropathic pain (NP) in individuals with spinal cord injury (SCI) is both common and highly refractory to treatment. Primary motor cortex stimulation can relieve pain by interrupting the transmission of noxious information of descending pain modulatory systems including the anterior cingulate cortex (ACC). Previous research has shown that transcranial direct current stimulation (tDCS) can produce pain relief in individuals with NP. However, the underlying mechanisms for these effects are not yet understood. Research findings suggest the possibility that changes in brain metabolite concentrations produced by tDCS might explain some of these effects. For example, previous research has shown that SCI-related NP is associated with elevated levels of glutamine combined glutamate (Glx) per creatine (Glx/Cr). In addition, decreased N-acetylaspartate (NAA) has been observed in the ACC in individuals with chronic pain.

Methods

We used magnetic resonance spectroscopy (MRS) to study changes in NAA and Glx levels in the ACC after tDCS treatment. Ten patients with SCI with NP were given five daily anodal tDCS sessions, and an MRS evaluation was performed before and after treatment.

Results

The results showed treatment-related reductions in pain, and increases in both Glx/Cr and NAA/Cr in the ACC. The observed increase in NAA/Cr is consistent with the possibility that tDCS improves the descending pain modulation system by increasing the neuronal activity in the ACC.

Conclusion

The findings suggest the possibility that tDCS’s beneficial effects on neuropathic pain may be due, at least in part, to the changes it produces in Glx/Cr and NAA/Cr levels in the ACC. Additional research with larger samples sizes and a control group to evaluate this possibility is warranted.

Long-term Effect and Predictive Factors of Motor Cortex and Spinal Cord Stimulation for Chronic Neuropathic Pain

The long-term effects of motor cortex stimulation (MCS) and spinal cord stimulation (SCS) remain unknown. To identify the long-term effects after MCS or SCS and determine any associated predictive factors for the outcomes. Fifty patients underwent MCS (n = 15) or SCS (n = 35) for chronic neuropathic pain. The degree of pain was assessed preoperatively, at 1, 6, and 12 months after surgery, and during the time of the last follow-up using Visual Analog Scale (VAS). Percentage of pain relief (PPR) was calculated, with “long-term effect” defined as PPR ≥ 30% and the presence of continued pain relief over 12 months. Outcomes were classified into excellent (PPR ≥ 70%) and good (PPR 30–69%) sub-categories. Long-term effects of MCS and SCS were observed in 53.3% and 57.1% of the patients, respectively. There were no predictive factors of long-term effects identified for any of the various preoperative conditions. However, the VAS at 1 month after surgery was significantly associated with the long-term effects in both MCS and SCS. All patients with an excellent outcome at 1 month after the surgery continued to exhibit these effects. In contrast, patients with the good outcome at 1 month exhibited a significant decrease in the effects at 6 months after surgery. The long-term effects of MCS and SCS were approximately 50% during the more than 8.5 and 3.5 years of follow-up, respectively. The VAS at 1 month after surgery may be a postoperative predictor of the long-term effects for both MCS and SCS.

Effects of spinal cord stimulation on postural control in Parkinson's disease patients with freezing of gait

Freezing of gait (FoG) in Parkinson’s disease (PD) is an incapacitating transient phenomenon, followed by continuous postural disorders. Spinal cord stimulation (SCS) is a promising intervention for FoG in patients with PD, however, its effects on distinct domains of postural control is not well known. The aim of this study is to assess the effects of SCS on FoG and distinct domains of postural control. Four patients with FoG were implanted with SCS systems in the upper thoracic spine. Anticipatory postural adjustment (APA), reactive postural responses, gait and FoG were biomechanically assessed. In general, the results showed that SCS improved FoG and APA. However, SCS failed to improve reactive postural responses. SCS seems to influence cortical motor circuits, involving the supplementary motor area. On the other hand, reactive posture control to external perturbation that mainly relies on neuronal circuitries involving the brainstem and spinal cord, is less influenced by SCS.

Sub-paresthesia spinal cord stimulation reverses thermal hyperalgesia and modulates low frequency EEG in a rat model of neuropathic pain

Paresthesia, a common feature of epidural spinal cord stimulation (SCS) for pain management, presents a challenge to the double-blind study design. Although sub-paresthesia SCS has been shown to be effective in alleviating pain, empirical criteria for sub-paresthesia SCS have not been established and its basic mechanisms of action at supraspinal levels are unknown. We tested our hypothesis that sub-paresthesia SCS attenuates behavioral signs of neuropathic pain in a rat model, and modulates pain-related theta (4–8 Hz) power of the electroencephalogram (EEG), a previously validated correlate of spontaneous pain in rodent models. Results show that sub-paresthesia SCS attenuates thermal hyperalgesia and power amplitude in the 3–4 Hz range, consistent with clinical data showing significant yet modest analgesic effects of sub-paresthesia SCS in humans. Therefore, we present evidence for anti-nociceptive effects of sub-paresthesia SCS in a rat model of neuropathic pain and further validate EEG theta power as a reliable ‘biosignature’ of spontaneous pain.

Spinal Cord Stimulation: Clinical Efficacy and Potential Mechanisms

Spinal cord stimulation (SCS) is a minimally invasive therapy used for the treatment of chronic neuropathic pain. SCS is a safe and effective alternative to medications such as opioids, and multiple randomized controlled studies have demonstrated efficacy for difficult-to-treat neuropathic conditions such as failed back surgery syndrome. Conventional SCS is believed mediate pain relief via activation of dorsal column Aβ fibers, resulting in variable effects on sensory and pain thresholds, and measurable alterations in higher order cortical processing. Although potentiation of inhibition, as suggested by Wall and Melzack's gate control theory, continues to be the leading explanatory model, other segmental and supraspinal mechanisms have been described. Novel, non-standard, stimulation waveforms such as high-frequency and burst have been shown in some studies to be clinically superior to conventional SCS, however their mechanisms of action remain to be determined. Additional studies are needed, both mechanistic and clinical, to better understand optimal stimulation strategies for different neuropathic conditions, improve patient selection and optimize efficacy.

Burst or High-Frequency (10 kHz) Spinal Cord Stimulation in Failed Back Surgery Syndrome Patients With Predominant Back Pain: One Year Comparative Data

OBJECTIVES

Burst and 10 kHz spinal cord stimulation (SCS) demonstrated improvement for failed back surgery syndrome (FBSS) with predominant, refractory back pain. Here, we report the long-term follow-up of a previously published study comparing the safety and efficacy of burst vs. 10 kHz SCS for predominant back pain (70% of global pain) of FBSS patients.

METHODS

This comparative, observational study extended the follow-up period up to 20 months evaluating both SCS modalities. Pain intensity (visual analog scale [VAS_B , VAS_L ]), functional capacity (Pittsburgh Sleep Quality Index [PSQI]; depression (Beck Depression Inventory [BDI]), stimulation parameters and hardware and/or stimulation associated adverse events were recorded and analyzed over time.

RESULTS

Overall VAS_B (t_1,12  = 66.76, p < 0.001) and VAS_L (t_1,12  = 4.763, p < 0.049; p < 0.001) declined over time. Burst significantly decreased VAS_B by 87.5% (±17.7) (mean 8 ± 0.76 to 1 ± 1.41; t₁ =12.3, p < 0.001), and 10 kHz significant decreased VAS_B by 54.9% (±44) (mean 8 ± 0.63 to 3.5 ± 3.27; t₁ =3.09, p = 0.027). No significant differences for between SCS types were revealed (t₁ =1.75, p = 0.13). VAS_L was significantly suppressed for burst (burst: 3.6 ± 1.59 to 1.5 ± 1.06; t₁  = 3.32, p = 0.013). A significant effect of time was found for functional outcome with no significant differences between SCS types (PSQI: t_1,12  = 8.8, p = 0.012; and BDI: t₁  = 53.3, p < 0.001). No stimulation/hardware-related complications occurred.

DISCUSSION

Long-term data of this comparative study suggests that burst responsiveness was superior to 10 kHz in our small-scale cohort, thus a larger, randomized-controlled comparative study design is highly recommended.