Managing chronic pain with spinal cord stimulation

Sustainability inspired fabrication of next generation neurostimulation and cardiac rhythm management electrodes via reactive hierarchical surface restructuring

Over the last two decades, platinum group metals (PGMs) and their alloys have dominated as the materials of choice for electrodes in long-term implantable neurostimulation and cardiac rhythm management devices due to their superior conductivity, mechanical and chemical stability, biocompatibility, corrosion resistance, radiopacity, and electrochemical performance. Despite these benefits, PGM manufacturing processes are extremely costly, complex, and challenging with potential health hazards. Additionally, the volatility in PGM prices and their high supply risk, combined with their scarce concentration of approximately 0.01 ppm in the earth's upper crust and limited mining geographical areas, underscores their classification as critical raw materials, thus, their effective recovery or substitution worldwide is of paramount importance. Since postmortem recovery from deceased patients and/or refining of PGMs that are used in the manufacturing of the electrodes and microelectrode arrays is extremely rare, challenging, and highly costly, therefore, substitution of PGM-based electrodes with other biocompatible materials that can yield electrochemical performance values equal or greater than PGMs is the only viable and sustainable solution to reduce and ultimately substitute the use of PGMs in long-term implantable neurostimulation and cardiac rhythm management devices. In this article, we demonstrate for the first time how the novel technique of "reactive hierarchical surface restructuring" can be utilized on titanium-that is widely used in many non-stimulation medical device and implant applications-to manufacture biocompatible, low-cost, sustainable, and high-performing neurostimulation and cardiac rhythm management electrodes. We have shown how the surface of titanium electrodes with extremely poor electrochemical performance undergoes compositional and topographical transformations that result in electrodes with outstanding electrochemical performance.

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

Introduction

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

Methods

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

Results

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

Discussion

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

Efficacy of Neuromodulation Interventions for the Treatment of Sexual Dysfunction: A Systematic Review

OBJECTIVES

The primary aim of this review was to analyze the literature for the efficacy of neuromodulation interventions in treating both male and female sexual dysfunction.

MATERIALS AND METHODS

Studies were identified from PubMed, Scopus, PsychINFO, CINAHL, and Cochrane. Results were synthesized qualitatively without pooling owing to the heterogeneous nature of outcome assessments.

RESULTS

Overall findings from studies generally supported that neuromodulation interventions were associated with improvement in sexual function. Specific domains that improved in male patients included erectile function, desire, and satisfaction, whereas desire, arousal, orgasm, lubrication, quality of "sex life," intercourse capability, and dyspareunia improved in female patients. Male ejaculation, orgasm, and intercourse capability were the only domains that continued to decline after the use of neuromodulation interventions, although this was only reported in one study.

CONCLUSION

Our review suggests that there may be promise and potential utility of neuromodulation in improving sexual dysfunction; however, further research is needed.

Development of antibacterial neural stimulation electrodes via hierarchical surface restructuring and atomic layer deposition

Miniaturization and electrochemical performance enhancement of electrodes and microelectrode arrays in emerging long-term implantable neural stimulation devices improves specificity, functionality, and performance of these devices. However, surgical site and post-implantation infections are amongst the most devastating complications after surgical procedures and implantations. Additionally, with the increased use of antibiotics, the threat of antibiotic resistance is significant and is increasingly being recognized as a global problem. Therefore, the need for alternative strategies to eliminate post-implantation infections and reduce antibiotic use has led to the development of medical devices with antibacterial properties. In this work, we report on the development of electrochemically active antibacterial platinum-iridium electrodes targeted for use in neural stimulation and sensing applications. A two-step development process was used. Electrodes were first restructured using femtosecond laser hierarchical surface restructuring. In the second step of the process, atomic layer deposition was utilized to deposit conformal antibacterial copper oxide thin films on the hierarchical surface structure of the electrodes to impart antibacterial properties to the electrodes with minimal impact on electrochemical performance of the electrodes. Morphological, compositional, and structural properties of the electrodes were studied using multiple modalities of microscopy and spectroscopy. Antibacterial properties of the electrodes were also studied, particularly, the killing effect of the hierarchically restructured antibacterial electrodes on Escherichia coli and Staphylococcus aureus-two common types of bacteria responsible for implant infections.

Low- and high-frequency spinal cord stimulation and arterial blood pressure in patients with chronic pain and hypertension: a retrospective study

PURPOSE

Evidence suggests that traditional low-frequency spinal cord stimulation (LF-SCS) reduces arterial blood pressure (BP) in patients with chronic pain and hypertension independent of improved pain symptoms. However, it remains unclear whether high-frequency spinal cord stimulation (HF-SCS) also lowers BP in chronic pain patients with hypertension. Therefore, in a retrospective study design, we tested the hypothesis that clinic BP would be significantly reduced following implantation of HF-SCS in patients with chronic pain and hypertension.

METHODS

Clinic BP within 3 months before and after surgical implantation of either a LF-SCS or HF-SCS device between 2010 and 2020 were collected from electronic medical records at The University of Kansas Health System (TUKHS).

RESULTS

A total of 132 patients had available records of clinic BP (64 ± 13 years of age). Patients with hypertension (n = 32) demonstrated a significantly greater reduction in systolic BP (-8 ± 12 versus 2 ± 9 mmHg, P < 0.001) following implantation compared with normotensive patients (n = 100). Importantly, the change in BP was inversely related to baseline BP independent of age and sex following implantation of HF-SCS (n = 70, R =  -0.50, P < 0.001) or LF-SCS (n = 62, R =  -0.42, P = 0.001). Higher pain scores before implantation were not associated with reduction in systolic BP (R = 0.10, P = 0.43) or diastolic BP (R =  -0.08, P = 0.53) (n = 69) after implantation.

CONCLUSION

These findings confirm previous studies showing reduced BP following implantation of LF-SCS in patients with chronic pain and hypertension and provide novel data regarding reduced BP following implantation of newer generation HF-SCS devices.

Femtosecond laser hierarchical surface restructuring for next generation neural interfacing electrodes and microelectrode arrays

Long-term implantable neural interfacing devices are able to diagnose, monitor, and treat many cardiac, neurological, retinal and hearing disorders through nerve stimulation, as well as sensing and recording electrical signals to and from neural tissue. To improve specificity, functionality, and performance of these devices, the electrodes and microelectrode arrays-that are the basis of most emerging devices-must be further miniaturized and must possess exceptional electrochemical performance and charge exchange characteristics with neural tissue. In this report, we show for the first time that the electrochemical performance of femtosecond-laser hierarchically-restructured electrodes can be tuned to yield unprecedented performance values that significantly exceed those reported in the literature, e.g. charge storage capacity and specific capacitance were shown to have improved by two orders of magnitude and over 700-fold, respectively, compared to un-restructured electrodes. Additionally, correlation amongst laser parameters, electrochemical performance and surface parameters of the electrodes was established, and while performance metrics exhibit a relatively consistent increasing behavior with laser parameters, surface parameters tend to follow a less predictable trend negating a direct relationship between these surface parameters and performance. To answer the question of what drives such performance and tunability, and whether the widely adopted reasoning of increased surface area and roughening of the electrodes are the key contributors to the observed increase in performance, cross-sectional analysis of the electrodes using focused ion beam shows, for the first time, the existence of subsurface features that may have contributed to the observed electrochemical performance enhancements. This report is the first time that such performance enhancement and tunability are reported for femtosecond-laser hierarchically-restructured electrodes for neural interfacing applications.

Short-Term Spinal Cord Stimulation or Pulsed Radiofrequency for Elderly Patients with Postherpetic Neuralgia: A Prospective Randomized Controlled Trial

Background. Postherpetic neuralgia (PHN) is the most common and severe complication after varicella-zoster infection, especially in elderly patients. PHN is always refractory to treatment. Both pulsed radiofrequency (PRF) and short-term spinal cord stimulation (stSCS) have been used as effective analgesia methods in clinic. However, which technique could provide better pain relief remains unknown. Objectives. This study is aimed at evaluating the efficacy and safety of PRF and stSCS in elderly patients with PHN. Study Design. A prospective, randomized-controlled study. Setting. Department of Pain Management, the Second Affiliated Hospital of Guangzhou Medical University. Methods. A total of 70 elderly patients with PHN were equally randomized to the PRF group or stSCS group. Patients in the PRF group received PRF treatment, while patients in the stSCS group received stSCS treatment. The primary outcome was the effective rate. The secondary outcomes included the Visual Analogue Scale (VAS), the 36-Item Short Form Health Survey Questionnaire (SF-36), and the pregabalin dosage. All outcomes were evaluated at baseline and at different postoperative time points. Results. At 12 months after surgery, the effective rate reached 79.3% in stSCS group, while 42.1% in PRF group. The effective rate was significantly higher in the stSCS group than in the PRF group at 3, 6, and 12 months after surgery. VAS scores decreased significantly at each postoperative time point in both groups ( $P<0.001$ ). The VAS scores were significantly lower in the stSCS group than in the PRF group at 3, 6, and 12 months after surgery. SF-36 scores (bodily pain and the physical role) were significantly improved at each postoperative time point in both groups ( $P<0.001$ ). The SF-36 scores were significantly higher in the stSCS group than in the PRF group at some postoperative time points. The pregabalin dosage was significantly lower in the stSCS group than in the PRF group at 3, 6, and 12 months after surgery. Limitations. A single-center study with a relatively small sample size. Conclusions. Both PRF and stSCS are effective and safe neuromodulation techniques for elderly patients with PHN. However, stSCS could provide better and longer-lasting analgesic effect compared to PRF.

Tuning of motor outputs produced by spinal stimulation during voluntary control of torque directions in monkeys

Spinal stimulation is a promising method to restore motor function after impairment of descending pathways. While paresis, a weakness of voluntary movements driven by surviving descending pathways, can benefit from spinal stimulation, the effects of descending commands on motor outputs produced by spinal stimulation are unclear. Here, we show that descending commands amplify and shape the stimulus-induced muscle responses and torque outputs. During the wrist torque tracking task, spinal stimulation, at a current intensity in the range of balanced excitation and inhibition, over the cervical enlargement facilitated and/or suppressed activities of forelimb muscles. Magnitudes of these effects were dependent on directions of voluntarily produced torque and positively correlated with levels of voluntary muscle activity. Furthermore, the directions of evoked wrist torque corresponded to the directions of voluntarily produced torque. These results suggest that spinal stimulation is beneficial in cases of partial lesion of descending pathways by compensating for reduced descending commands through activation of excitatory and inhibitory synaptic connections to motoneurons.

Superior galvanostatic electrochemical deposition of platinum nanograss provides high performance planar microelectrodes forin vitroneural recording

Objective.Platinum nanograss (Ptng) has been demonstrated as an excellent coating to increase the electrode roughness and reduce the impedance of microelectrodes for neural recording. However, the optimisation of the original potentiostatic electrochemical deposition (PSED) method has been performed by the original group only and noin vitrovalidation of functionality was reported.Approach.This study firstly reinvestigates the use of the PSED method for Ptng coating at different charge densities which highlights non-uniformities in the edges of the microelectrodes for increasing deposition charge densities, leading to a decreased impedance which is in fact an artefact. We then introduce a novel Ptng fabrication method of galvanostatic electrochemical deposition (GSED).Main results.We demonstrate that the GSED deposition method also significantly reduces the electrode impedance, raises the charge storage capacity and provides a significantly more planar electrode surface in comparison to the PSED method with negligible edge effects. In addition, we demonstrate how high-quality neural recordings were performed, for the first time, using the Ptng GSED deposition microelectrodes from human hNT neurons and how spiking and bursting were observed.Significance.Thus, the GSED Ptng deposition method presented here provides an alternative method of microelectrode fabrication for neural applications with excellent impedance and planarity of surface.

Dissociation between reduced pain and arterial blood pressure following epidural spinal cord stimulation in patients with chronic pain: A retrospective study

PURPOSE

Acute pain and resting arterial blood pressure (BP) are positively correlated in patients with chronic pain. However, it remains unclear whether treatment for chronic pain reduces BP. Therefore, in a retrospective study design, we tested the hypothesis that implantation of an epidural spinal cord stimulator (SCS) device to treat chronic pain would significantly reduce clinic pain ratings and BP and that these reductions would be significantly correlated.

METHODS

Pain ratings and BP in medical records were collected before and after surgical implantation of a SCS device at the University of Iowa Hospitals and Clinics between 2008 and 2018 (n = 213).

RESULTS

Reductions in pain rating [6.3 ± 2.0 vs. 5.0 ± 1.9 (scale: 0-10), P < 0.001] and BP [mean arterial pressure (MAP) 95 ± 10 vs. 89 ± 10 mmHg, P < 0.001] were statistically significant within 30 days of SCS. Interestingly, BP returned toward baseline within 60 days following SCS implantation. Multiple linear regression analysis showed that sex (P = 0.007), baseline MAP (P < 0.001), and taking hypertension (HTN) medications (P < 0.001) were significant determinants of change in MAP from baseline (Δ MAP) (model R2 = 0.33). After statistical adjustments, Δ MAP was significantly greater among women than among men ( - 7.2 ± 8.5 vs.  - 3.9 ± 8.5 mmHg, P = 0.007) and among patients taking HTN medications than among those not taking hypertension medications ( - 10.1 ± 8.7 vs.  - 3.9 ± 8.5 mmHg, P < 0.001), despite no group differences in change in pain ratings.

CONCLUSIONS

Together, these findings suggest that SCS for chronic pain independently produces clinically meaningful, albeit transient, reductions in BP and may provide a rationale for studies aimed at reducing HTN medication burden among this patient population.

Epidural electrical stimulation effectively restores locomotion function in rats with complete spinal cord injury

Epidural electrical stimulation can restore limb motor function after spinal cord injury by reactivating the surviving neural circuits. In previous epidural electrical stimulation studies, single electrode sites and continuous tetanic stimulation have often been used. With this stimulation, the body is prone to declines in tolerance and locomotion coordination. In the present study, rat models of complete spinal cord injury were established by vertically cutting the spinal cord at the T8 level to eliminate disturbance from residual nerve fibers, and were then subjected to epidural electrical stimulation. The flexible extradural electrode had good anatomical topology and matched the shape of the spinal canal of the implanted segment. Simultaneously, the electrode stimulation site was able to be accurately applied to the L2–3 and S1 segments of the spinal cord. To evaluate the biocompatibility of the implanted epidural electrical stimulation electrodes, GFAP/Iba-1 double-labeled immunofluorescence staining was performed on the spinal cord below the electrodes at 7 days after the electrode implantation. Immunofluorescence results revealed no significant differences in the numbers or morphologies of microglia and astrocytes in the spinal cord after electrode implantation, and there was no activated Iba-1⁺ cell aggregation, indicating that the implant did not cause an inflammatory response in the spinal cord. Rat gait analysis showed that, at 3 days after surgery, gait became coordinated in rats with spinal cord injury under burst stimulation. The regained locomotion could clearly distinguish the support phase and the swing phase and dynamically adjust with the frequency of stimulus distribution. To evaluate the matching degree between the flexible epidural electrode (including three stimulation contacts), vertebral morphology, and the level of the epidural site of the stimulation electrode, micro-CT was used to scan the thoracolumbar vertebrae of rats before and after electrode implantation. Based on the experimental results of gait recovery using three-site stimulation electrodes at L2–3 and S1 combined with burst stimulation in a rat model of spinal cord injury, epidural electrical stimulation is a promising protocol that needs to be further explored. This study was approved by the Animal Ethics Committee of Chinese PLA General Hospital (approval No. 2019-X15-39) on April 19, 2019.

Peripheral subcutaneous field stimulation for the treatment of spinal cord injury at-level pain: case report, literature review, and 5-year follow-up

Spinal cord injury (SCI) frequently engenders chronic pain which may be classified as occurring above, at, or below the level of injury. Since patients with SCI may have a complex combination of nociceptive and neuropathic pain, pharmacological interventions often fail. Peripheral subcutaneous field stimulation (PSFS) is a novel neuromodulation surgery for pain in which subcutaneous electrodes designed for spinal cord stimulation are placed subcutaneously in a region of pain. We report the case of a 26-year-old man who was an unrestrained driver in a motor vehicle accident and suffered a complete ASIA A spinal cord injury with paraplegia due to a T4 three-column burst fracture. He underwent successful surgical fixation of the fracture (7/27/12) and developed severe at-level SCI-associated pain which failed all conservative measures. After a successful trial, two octrode leads (Abbott Medical, Plano, TX, USA) were placed for PSFS under general anesthesia and were connected to a right flank rechargeable pulse generator (11/6/13). At 60 months postoperative, the patient continues to use the peripheral field stimulation system on a daily basis and reports near complete relief of his at-level spinal cord injury pain. He noted instantaneous relief of his pain once ideal stimulation programming was achieved and has tolerated complete cessation of all narcotic use. His current programming settings are: Frequency of 50 Hz (Hz), Pulse Width of 350 μs (μsec), Amplitude of 0.00 miliamps (mA), Comf of 7.70 mA, and Perc of 4.50 mA. Chronic pain is a challenging and expensive sequela to manage in SCI patients and newer therapies are needed. Our case suggests that SCI at-level pain may respond durably to PSFS and provides the longest published follow-up on a case of PSFS. Peripheral subcutaneous field stimulation remains an investigational treatment for chronic pain syndrome and larger, long-term follow up studies are needed for the FDA and payers to approve this modality.

[Factors of adverse prediction of application of spinal cord stimulation with chronic pain syndrome in patients with critical lower limb ischemia]

AIM

To study the clinical dynamics in the long-term period after spinal cord stimulation (SCS) in patients with chronic pain syndrome and critical lower limb ischemia (CLLI) and to identify factors affecting the prognosis of SCS.

MATERIAL AND METHODS

The clinical dynamics was analyzed in 48 patients with pain syndrome and CLLI 1 year after SCS. Microcirculatory blood flow (MBF) was studied in the affected foot by laser-doppler flowmetry (LDF) (Perfusion Units (PU)) and transcutaneous oximetry (TcpO₂, mmHg.) using an occlusive test before and after SCS. The factors associated with negative clinical dynamics 1 year after SCS were determined.

RESULTS

In 74% of cases, SCS contributes to the improvement of clinical status (reduction of pain syndrome, increase in motor activity, healing of ulcers). After SCS, according to LDF and TcpO₂, the authors observed an increase in MBF and tissue metabolism - from 1.3 (0.7-2.8) to 6.2 (3.8-8.7) PU and from 14.5 (7.5-22.1) to 41.1 (26.4-57.6) mmHg, respectively with normalization of the MBF reserve during the occlusion test. Negative clinical dynamics after SCS is associated with high comorbidity, TcO₂ <10 mmHg and the duration of pain.

CONCLUSION

SCS contributes to the improvement of the clinical status of patients with chronic pain syndrome and CLLI. The negative dynamics is associated with high comorbidity, TcrO₂ <10 mmHg and the duration of pain.

T12 Dorsal Root Ganglion Stimulation to Treat Chronic Low Back Pain: A Case Series

INTRODUCTION

Dorsal root ganglion stimulation (DRG-S) is a neuromodulation technique for treating neuropathic pain syndromes. Research has demonstrated DRG-S to be more effective than conventional SCS in treating RSD/CRPS, particularly of the lower extremities. Results from recent case series and prospective studies suggest that DRG-S may be effective in treatment of pain syndromes considered to have non-neuropathic components and characteristics (e.g. nociceptive). There have been multiple, small studies demonstrating efficacy of DRG-S for axial low back pain. There has, however, been no consensus regarding the best location for DRG lead placement in the treatment of low back pain.

METHODS

Patients presenting with refractory low back pain in a private pain management practice were considered for DRG-S. Patients were provided a trial stimulator prior to potential implantation. Per standard practice, pain intensity, disability, general health status, and quality of life were followed using the visual analog scale (VAS), Oswestry Disability Index, EQ-5D index, and the SF-36 survey, respectively. Data were collected prior to implantation and at variable follow-ups after DRG-S initiation.

RESULTS

Seventeen consecutive patients presented with predominantly axial low back pain with/without a secondary component of lower extremity pain. All were trialed and subsequently implanted for DRG-S. Leads were placed at T12 to target the low back. Stimulation levels were set very low, below that of which patients experienced paresthesias. Last follow-up times averaged 8.3 months. More than half of the patients experienced pain relief ≥80%, with an average low back pain relief of 78% at last follow-up. Additionally, substantial improvements in physical and mental functioning, disability, and quality of life were reported.

CONCLUSIONS

T12 DRG-S can be an effective treatment for chronic axial low back pain. Stimulation results in reduced pain and disability, while improving quality of life. These outcomes can be achieved without paresthesias.

Spinal Cord Stimulation vs Conventional Therapies for the Treatment of Chronic Low Back and Leg Pain: A Systematic Review of Health Care Resource Utilization and Outcomes in the Last Decade

Objective

The purpose of this review is to critically appraise the literature for evidence supporting the health care resource utilization and cost-effectiveness of spinal cord stimulation (SCS) compared with conventional therapies (CTs) for chronic low back and leg pain.

Methods

The PubMed, MEDLINE, Embase, CINAHL, and Rehabilitation & Sports Medicine databases were searched for studies published from January 2008 through October 2018, using the following MeSH terms: “spinal cord stimulation,” “chronic pain,” “back pain,” “patient readmission,” “economics,” and “costs and cost analysis.” Additional sources were added based on bibliographies and consultation with experts. The following data were extracted and analyzed: demographic information, study design, objectives, sample sizes, outcome measures, SCS indications, complications, costs, readmissions, and resource utilization data.

Results

Of 204 studies screened, 11 studies met inclusion criteria, representing 31,439 SCS patients and 299,182 CT patients. The mean age was 53.5 years for SCS and 55.6 years for CT. In eight of 11 studies, SCS was associated with favorable outcomes and found to be more cost-effective than CT for chronic low back pain. Compared with CT, SCS resulted in shorter hospital stays and lower complication rates and health care costs at 90 days. SCS was associated with significant improvement in health-related quality of life, health status, and quality-adjusted life-years.

Conclusions

For the treatment of chronic low back and leg pain, the majority of studies are of fair quality, with level 3 or 4 evidence in support of SCS as potentially more cost-effective than CT, with less resource expenditure but higher complication rates. SCS therapy may yet play a role in mitigating the financial burden associated with chronic low back and leg pain.

Implantable Pulse Generator Site May Be Associated With Spinal Cord Stimulation Revision Surgeries

BACKGROUND

The use of implantable pulse generators (IPG) for spinal cord stimulation (SCS) in patients with chronic pain has been well established. Although IPG-related complications have been reported on, the association between IPG site and SCS complications has not been well studied.

OBJECTIVE

To investigate whether IPG placement site in buttock or flank is associated with SCS complications and, hence, revision surgeries.

METHOD

A retrospective cohort study was performed that included 330 patients (52% female) treated at a single institution who underwent permanent implantation of an SCS system between 2014 and 2018. Patients ranged between 20 and 94 years of age (mean: 57.54 ± 13.25). Statistical analyses were conducted using IBM SPSS Statistics. Tests included independent samples t test, chi-square test, Mann-Whitney U test, Spearman's rank correlation coefficient, and logistic regression.

RESULTS

There was a total of 93 revision surgeries (rate of 28%), where 71 out of 330 patients (rate of 21.5%) had had at least one revision surgery. Univariate tests demonstrated a significant association between IPG site and revision surgeries (p = 0.028 [chi-square test] and p = 0.031 [Mann-Whitney U test]); however, multivariate logistic regression demonstrated that neither IPG site was more likely than the other to require revision surgeries (p = 0.286).

CONCLUSION

Although this study found a significant association between IPG site and revision surgeries, the effect of IPG site was not found to be predictive. The IPG site likely influences whether a patient will require revision surgery, but further investigation is required to establish this association.

Computational Study of the Effect of Electrode Polarity on Neural Activation Related to Paresthesia Coverage in Spinal Cord Stimulation Therapy

OBJECTIVE

Using computer simulation, we investigated the effect of electrode polarity on neural activation in spinal cord stimulation and propose a new strategy to maximize the activating area in the dorsal column (DC) and, thus, paresthesia coverage in clinical practice.

MATERIALS AND METHODS

A new three-dimensional spinal cord model at the T10 vertebral level was developed to simulate neural activation induced by the electric field distribution produced by different typical four-contact electrode polarities in single- and dual-lead stimulation. Our approach consisted of the combination of a finite element model of the spinal cord developed in COMSOL Multiphysics and a nerve fiber model implemented in MATLAB. Five evaluation parameters were evaluated, namely, the recruitment ratio, the perception and discomfort thresholds, and the activating area and depth. The results were compared quantitatively.

RESULTS

The dual-guarded cathode presents the maximum activating area and depth in single- and dual-lead stimulation. However, the lowest value of the ratio between the perception threshold in DC and the perception threshold in the dorsal root (DR) is achieved when the guarded cathode is programmed. Although the two versions of bipolar polarity (namely bipolar 1 and bipolar 2) produce higher activating area and depth than the guarded cathode, they are suitable for producing DR stimulation. Similarly, dual-lead stimulation is likely to activate DR fibers because the electrodes are closer to these fibers.

CONCLUSIONS

The results suggest that the activating area in the DC is maximized by using the dual-guarded cathode both in single- and dual-lead stimulation modes. However, DC nerve fibers are preferentially stimulated when the guarded cathode is used. According to these results, the new electrode programming strategy that we propose for clinical practice first uses the dual-guarded cathode, but, if the DR nerve fibers are activated, it then uses guarded cathode polarity.

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.

Current Status of Neuromodulatory Therapies for Disorders of Consciousness

Treatment for disorders of consciousness (DOCs) is still a Gordian knot. Evidence-based guidelines on the treatment of DOC patients are not currently available, while neuromodulation techniques are seen as a potential treatment. Multiple neuromodulation therapies have been applied. This article reviews the most relevant studies in the literature in order to describe a clear picture of the current state of neuromodulation therapies that could be used to treat DOC patients. Both invasive and non-invasive brain stimulation is discussed. Significant behavioral improvements in prolonged DOCs under neuromodulation therapies are rare. The efficacy of various such therapies remains a matter of debate. Further clinical investigations of existing techniques in larger samples properly controlling for spontaneous recovery are needed, and new approaches are awaited.

Differential expression of voltage-gated sodium channels in afferent neurons renders selective neural block by ionic direct current

The assertion that large-diameter nerve fibers have low thresholds and small-diameter fibers have high thresholds in response to electrical stimulation has been held in a nearly axiomatic regard in the field of neuromodulation and neuroprosthetics. In contrast to the short pulses used to evoke action potentials, long-duration ionic direct current has been shown to block neural activity. We propose that the main determinant of the neural sensitivity to direct current block is not the size of the axon but the types of voltage-gated sodium channels prevalent in its neural membrane. On the basis of the variants of voltage-gated sodium channels expressed in different types of neurons in the peripheral nerves, we hypothesized that the small-diameter nociceptive fibers could be preferentially blocked. We show the results of a computational model and in vivo neurophysiology experiments that offer experimental validation of this novel phenomenon.

Femoral vascular conductance and peroneal muscle sympathetic nerve activity responses to acute epidural spinal cord stimulation in humans

NEW FINDINGS

What is the central question of this research? Does acute spinal cord stimulation increase vascular conductance and decrease muscle sympathetic nerve activity in the lower limbs of humans? What is the main finding and its importance? Acute spinal cord stimulation led to a rapid rise in femoral vascular conductance, and peroneal muscle sympathetic nerve activity demonstrated a delayed reduction that was not associated with the initial increase in femoral vascular conductance. These findings suggest that neural mechanisms in addition to attenuated muscle sympathetic nerve activity might be involved in the initial increase in femoral vascular conductance during acute spinal cord stimulation.

ABSTRACT

Clinical cases have indicated an increase in peripheral blood flow after continuous epidural spinal cord stimulation (SCS) and that reduced muscle sympathetic nerve activity (MSNA) might be a potential mechanism. However, no studies in humans have directly examined the effects of acute SCS (<60 min) on vascular conductance and MSNA. In study 1, we tested the hypothesis that acute SCS (<60 min) of the thoracic spine would lead to increased common femoral vascular conductance, but not brachial vascular conductance, in 11 patients who previously underwent surgical SCS implantation for management of neuropathic pain. Throughout 60 min of SCS, common femoral artery conductance was elevated and significantly different from brachial artery conductance [in millilitres per minute: 15 min, change (Δ) 26 ± 37 versus Δ-2 ± 19%; 30 min, Δ28 ± 45 versus Δ0 ± 26%; 45 min, Δ48 ± 43 versus Δ2 ± 21%; 60 min, Δ36 ± 61 versus Δ1 ± 24%; and 15 min post-SCS, Δ51 ± 64 versus Δ6 ± 33%; P = 0.013]. A similar examination in a patient with cervical SCS revealed minimal changes in vascular conductance. In study 2, we examined whether acute SCS reduces peroneal MSNA in a subset of SCS patients (n = 5). The MSNA burst incidence in response to acute SCS gradually declined and was significantly reduced at 45 and 60 min of SCS (in bursts per 100 heart beats: 15 min, Δ-1 ± 12%; 30 min, Δ-14 ± 12%; 45 min, Δ-19 ± 16%; 60 min, Δ-24 ± 18%; and 15 min post-SCS: Δ-11 ± 7%; P = 0.015). These data demonstrate that acute SCS rapidly increases femoral vascular conductance and reduces peroneal MSNA. The gradual reduction in peroneal MSNA observed during acute SCS suggests that neural mechanisms in addition to attenuated MSNA might be involved in the acute increase in femoral vascular conductance.

Chronic softening spinal cord stimulation arrays

OBJECTIVE

We sought to develop a cervical spinal cord stimulator for the rat that is durable, stable, and does not perturb the underlying spinal cord.

APPROACH

We created a softening spinal cord stimulation (SCS) array made from shape memory polymer (SMP)-based flexible electronics. We developed a new photolithographic process to pattern high surface area titanium nitride (TiN) electrodes onto gold (Au) interconnects. The thiol-ene acrylate polymers are stiff at room temperature and soften following implantation into the body. Durability was measured by the duration the devices produced effective stimulation and by accelerated aging in vitro. Stability was measured by the threshold to provoke an electromyogram (EMG) muscle response and by measuring impedance using electrochemical impedance spectroscopy (EIS). In addition, spinal cord modulation of motor cortex potentials was measured. The spinal column and implanted arrays were imaged with MRI ex vivo, and histology for astrogliosis and immune reaction was performed.

MAIN RESULTS

For durability, the design of the arrays was modified over three generations to create an array that demonstrated activity up to 29 weeks. SCS arrays showed no significant degradation over a simulated 29 week period of accelerated aging. For stability, the threshold for provoking an EMG rose in the first few weeks and then remained stable out to 16 weeks; the impedance showed a similar rise early with stability thereafter. Spinal cord stimulation strongly enhanced motor cortex potentials throughout. Upon explantation, device performance returned to pre-implant levels, indicating that biotic rather than abiotic processes were the cause of changing metrics. MRI and histology showed that softening SCS produced less tissue deformation than Parylene-C arrays. There was no significant astrogliosis or immune reaction to either type of array.

SIGNIFICANCE

Softening SCS arrays meet the needs for research-grade devices in rats and could be developed into human devices in the future.

Incidence and predictive factors of spinal cord stimulation treatment after lumbar spine surgery

Introduction

Spinal cord stimulation (SCS) is recommended for the treatment of postsurgical chronic back and leg pain refractory to other treatments. We wanted to estimate the incidence and predictive factors of SCS treatment in our lumbar surgery cohort.

Patients and methods

Three questionnaires (a self-made questionnaire, the Oswestry Low Back Pain Disability Questionnaire, and the Beck Depression Inventory) were sent to patients aged 18–65 years with no contraindications for the use of SCS, and who had undergone non-traumatic lumbar spine surgery in the Oulu University Hospital between June 2005 and May 2008. Patients who had a daily pain intensity of ≥5/10 with predominant radicular component were interviewed by telephone.

Results

After exclusions, 814 patients remained in this cohort. Of those, 21 patients had received SCS by the end of June 2015. Fifteen (71%) of these received benefit and continued with the treatment. Complications were rare. The number of patients who replied to the postal survey were 537 (66%). Eleven of them had undergone SCS treatment after their reply. Features predicting SCS implantation were daily or continuous pain, higher intensities of pain with predominant radicular pain, more severe pain-related functional disability, a higher prevalence of depressive symptoms, and reduced benefit from pain medication. The mean waiting time was 65 months (26–93 months). One hundred patients were interviewed by telephone. Fourteen seemed to be potential SCS candidates. From the eleven patients who underwent SCS after responding to the survey, two were classified as potential candidates in the phone interview, while nine were other patients. Twelve patients are still waiting for treatment to commence.

Conclusion

In our region, the SCS treatment is used only for very serious pain conditions. Waiting time is too long and it may be the reason why this treatment option is not offered to all candidates.

Presurgical Psychological Assessments as Correlates of Effectiveness of Spinal Cord Stimulation for Chronic Pain Reduction

BACKGROUND

Spinal Cord Stimulator (SCS) is a surgically implanted device for patients with certain types of chronic pain. While some studies show the value of psychological screening of potential SCS candidates, no consensus exists. This single-site study analyzed the association of SCS success with psychological assessments (e.g., Millon Behavioral Medicine Diagnostic), beliefs regarding SCS efficacy, self-reported pain and quality of life (QOL) among patients approved for SCS.

METHODS

Potential SCS candidates (N = 200) were contacted 3-7 years after initial psychological and medical clearance for SCS; 59 consented to a structured telephone interview. Thirty-four of the 59 had received a SCS; 25 had not received a SCS. Of the 34 that had received a SCS, 22 were approved by routine psychological evaluation while 12 went through in-depth psychological testing.

RESULTS

The majority of respondents (62%) reported effective pain reduction, and 64% of SCS recipients reported improved QOL. Younger patients reported higher pre-implantation pain scores, and participants with higher levels of pain preimplantation were more likely say they would undergo the procedure again. Finally, persons reporting preoperative alcohol problems were more likely to report lower levels of post-SCS pain.

CONCLUSION

Predictors of pain relief and QOL following SCS may depend on expectations of the device and on individuals' interpretation of pain or psychosocial health.

Effects of Combined Electrical Stimulation of the Dorsal Column and Dorsal Roots on Wide-Dynamic-Range Neuronal Activity in Nerve-Injured Rats

OBJECTIVES

Electrical stimulation at the dorsal column (DC) and dorsal root (DR) may inhibit spinal wide-dynamic-range (WDR) neuronal activity in nerve-injured rats. The objective of this study was to determine if applying electrical conditioning stimulation (CS) at both sites provides additive or synergistic benefits.

MATERIALS AND METHODS

By conducting in vivo extracellular recordings of WDR neurons in rats that had undergone L5 spinal nerve ligation, we tested whether combining 50 Hz CS at the two sites in either a concurrent (2.5 min) or alternate (5 min) pattern inhibits WDR neuronal activity better than CS at DC alone (5 min). The intensities of CS were determined by recording antidromic compound action potentials to graded stimulation at the DC and DR. We measured the current thresholds that resulted in the first detectable Aα/β waveform (Ab0) and the peak Aα/β waveform (Ab1) to select CS intensity at each site. The same number of electrical pulses and amount of current were delivered in different patterns to allow comparison.

RESULTS

At a moderate intensity of 50% (Ab0 + Ab1), different patterns of CS all attenuated the C-component of WDR neurons in response to graded intracutaneous electrical stimuli (0.1-10 mA, 2 msec) and inhibited windup in response to repetitive noxious stimuli (0.5 Hz). However, the inhibitory effects did not differ significantly between different patterns. At the lower intensity (Ab0), no CS inhibited WDR neurons.

CONCLUSIONS

These findings suggest that combined stimulation of DC and DR may not be superior to DC stimulation alone for inhibition of WDR neurons.

Interventional Therapies for Chronic Low Back Pain: A Focused Review (Efficacy and Outcomes)

CONTEXT

Lower back pain is considered to be one of the most common complaints that brings a patient to a pain specialist. Several modalities in interventional pain management are known to be helpful to a patient with chronic low back pain. Proper diagnosis is required for appropriate intervention to provide optimal benefits. From simple trigger point injections for muscular pain to a highly complex intervention such as a spinal cord stimulator are very effective if chosen properly. The aim of this article is to provide the reader with a comprehensive reading for treatment of lower back pain using interventional modalities.

EVIDENCE ACQUISITION

Extensive search for published literature was carried out online using PubMed, Cochrane database and Embase for the material used in this manuscript. This article describes the most common modalities available to an interventional pain physician along with the most relevant current and past references for the treatment of lower back pain. All the graphics and images were prepared by and belong to the author.

RESULTS

This review article describes the most common modalities available to an interventional pain physician along with the most relevant current and past references for the treatment of lower back pain. All the graphics and images belong to the author. Although it is beyond the scope of this review article to include a very detailed description of each procedure along with complete references, a sincere attempt has been made to comprehensively cover this very complex and perplexing topic.

CONCLUSION

Lower back pain is a major healthcare issue and this review article will help educate the pain practitioners about the current evidence based treatment options.

Nanostructured platinum grass enables superior impedance reduction for neural microelectrodes

Micro-sized electrodes are essential for highly sensitive communication at the neural interface with superior spatial resolution. However, such small electrodes inevitably suffer from high electrical impedance and thus high levels of thermal noise deteriorating the signal to noise ratio. In order to overcome this problem, a nanostructured Pt-coating was introduced as add-on functionalization for impedance reduction of small electrodes. In comparison to platinum black deposition, all used chemicals in the deposition process are free from cytotoxic components. The grass-like nanostructure was found to reduce the impedance by almost two orders of magnitude compared to untreated samples which was lower than what could be achieved with conventional electrode coatings like IrOx or PEDOT. The realization of the Pt-grass coating is performed via a simple electrochemical process which can be applied to virtually any possible electrode type and accordingly shows potential as a universal impedance reduction strategy. Elution tests revealed non-toxicity of the Pt-grass and the coating was found to exhibit strong adhesion to the metallized substrate.

Electrical stimulation of dorsal root entry zone attenuates wide-dynamic-range neuronal activity in rats

OBJECTIVES

Recent clinical studies suggest that neurostimulation at the dorsal root entry zone (DREZ) may alleviate neuropathic pain. However, the mechanisms of action for this therapeutic effect are unclear. Here, we examined whether DREZ stimulation inhibits spinal wide-dynamic-range (WDR) neuronal activity in nerve-injured rats.

MATERIALS AND METHODS

We conducted in vivo extracellular single-unit recordings of WDR neurons in rats after an L5 spinal nerve ligation (SNL) or sham surgery. We set bipolar electrical stimulation (50 Hz, 0.2 msec, 5 min) of the DREZ at the intensity that activated only Aα/β-fibers by measuring the lowest current at which DREZ stimulation evoked a peak antidromic sciatic Aα/β-compound action potential without inducing an Aδ/C-compound action potential (i.e., Ab1).

RESULTS

The elevated spontaneous activity rate of WDR neurons in SNL rats (n = 25; data combined from post-SNL groups at days 14-16 [n = 15] and days 45-75 [n = 10]) was significantly decreased from the prestimulation level (p < 0.01) at 0-15 min and 30-45 min post-stimulation. In both sham-operated (n = 8) and nerve-injured rats, DREZ stimulation attenuated the C-component, but not the A-component, of the WDR neuronal response to graded intracutaneous electrical stimuli (0.1-10 mA, 2 msec) applied to the skin receptive field. Further, DREZ stimulation blocked windup (a form of brief neuronal sensitization) to repetitive noxious stimuli (0.5 Hz) at 0-15 min in all groups (p < 0.05).

CONCLUSIONS

Attenuation of WDR neuronal activity may contribute to DREZ stimulation-induced analgesia. This finding supports the notion that DREZ may be a useful target for neuromodulatory control of pain.

Upper-limb muscle responses to epidural, subdural and intraspinal stimulation of the cervical spinal cord

OBJECTIVE

Electrical stimulation of the spinal cord has potential applications following spinal cord injury for reanimating paralysed limbs and promoting neuroplastic changes that may facilitate motor rehabilitation. Here we systematically compare the efficacy, selectivity and frequency-dependence of different stimulation methods in the cervical enlargement of anaesthetized monkeys.

APPROACH

Stimulating electrodes were positioned at multiple epidural and subdural sites on both dorsal and ventral surfaces, as well as at different depths within the spinal cord. Motor responses were recorded from arm, forearm and hand muscles.

MAIN RESULTS

Stimulation efficacy increased from dorsal to ventral stimulation sites, with the exception of ventral epidural electrodes which had the highest recruitment thresholds. Compared to epidural and intraspinal methods, responses to subdural stimulation were more selective but also more similar between adjacent sites. Trains of stimuli delivered to ventral sites elicited consistent responses at all frequencies whereas from dorsal sites we observed a mixture of short-latency facilitation and long-latency suppression. Finally, paired stimuli delivered to dorsal surface and intraspinal sites exhibited symmetric facilitatory interactions at interstimulus intervals between 2–5 ms whereas on the ventral side interactions tended to be suppressive for near-simultaneous stimuli.

SIGNIFICANCE

We interpret these results in the context of differential activation of afferent and efferent roots and intraspinal circuit elements. In particular, we propose that distinct direct and indirect actions of spinal cord stimulation on motoneurons may be advantageous for different applications, and this should be taken into consideration when designing neuroprostheses for upper-limb function.

Spinal cord stimulation to achieve wound healing in a primary lower limb critical ischaemia referral centre

Critical lower limb ischaemia is a diffuse pathology that could cause claudication, severe ischaemic pain and tissue loss. The common treatment includes modification of risk factors, pharmacological therapy and endovascular or surgical revascularisation of the lower limb to restore a pulsatile flow distally. Spinal cord stimulator is seen as a valid alternative in patients unsuitable for revascularisation after endovascular or surgical revascularisation failure and as adjuvant therapy in the presence of a functioning bypass in patients with extensive tissue loss and gangrene presenting a slow and difficult wound healing. We report our experience on spinal cord stimulation (SCS) indication and implantation in patients with critical lower limb ischaemia, at a high-volume centre for the treatment of peripheral arterial disease.

Spinal cord stimulation for chronic limb ischemia

The treatment of chronic limb ischemia involves the restoration of pulsatile blood flow to the distal extremity. Some patients cannot be treated with endovascular means or with open surgery; some may have medical comorbidities that render them unfit for surgery, while others may have persistent ischemia or pain even in the face of previous attempts at reperfusion. In spinal cord stimulation (SCS), a device with electrodes is implanted in the epidural space to stimulate sensory fibers. This activates cell-signaling molecules that in turn cause the release of vasodilatory molecules, a decrease in vascular resistance, and relaxation of smooth muscle cells. SCS also suppresses sympathetic vasoconstriction and pain transmission. When patient selection is based on microcirculatory parameters, SCS therapy can significantly improve pain relief, halt the progression of ulcers, and potentially achieve limb salvage.

Default mode network functional connectivity altered in failed back surgery syndrome

The purpose of this study was to identify alterations in the default mode network of failed back surgery syndrome patients as compared to healthy subjects. Resting state functional magnetic resonance imaging was conducted at 3 Tesla and data were analyzed with an independent component analysis. Results indicate an overall reduced functional connectivity of the default mode network and recruitment of additional pain modulation brain regions, including dorsolateral prefrontal cortex, insula, and additional sensory motor integration brain regions, including precentral and postcentral gyri, for failed back surgery syndrome patients.

PERSPECTIVE

This article presents alterations in the default mode network of chronic low back pain patients with failed back surgery syndrome as compared to healthy participants.

Neural interfaces for the brain and spinal cord--restoring motor function

Regaining motor function is of high priority to patients with spinal cord injury (SCI). A variety of electronic devices that interface with the brain or spinal cord, which have applications in neural prosthetics and neurorehabilitation, are in development. Owing to our advancing understanding of activity-dependent synaptic plasticity, new technologies to monitor, decode and manipulate neural activity are being translated to patient populations, and have demonstrated clinical efficacy. Brain-machine interfaces that decode motor intentions from cortical signals are enabling patient-driven control of assistive devices such as computers and robotic prostheses, whereas electrical stimulation of the spinal cord and muscles can aid in retraining of motor circuits and improve residual capabilities in patients with SCI. Next-generation interfaces that combine recording and stimulating capabilities in so-called closed-loop devices will further extend the potential for neuroelectronic augmentation of injured motor circuits. Emerging evidence suggests that integration of closed-loop interfaces into intentional motor behaviours has therapeutic benefits that outlast the use of these devices as prostheses. In this Review, we summarize this evidence and propose that several known plasticity mechanisms, operating in a complementary manner, might underlie the therapeutic effects that are achieved by closing the loop between electronic devices and the nervous system.