Safety and efficacy of spinal cord stimulation for the treatment of chronic pain: a 20-year literature review

Twiddler's Syndrome: A Rare Hardware Complication in Spinal Cord Stimulation

Twiddler's syndrome is an uncommon hardware complication involving the lead and pulse generators in cardiac pacemakers and defibrillators, deep brain stimulators, and vagal nerve stimulators. However, until very recently, it had not been reported in spinal cord stimulation (SCS). Considering the incidence of hardware complications of spinal cord stimulation, there may be an underreporting of Twiddler's syndrome due to lack of awareness. Two cases of Twiddler's syndrome as a hardware complication of SCS were identified between 2005 and 2015. One patient with hardware failure due to Twiddler's syndrome refused to have a revision surgery. The other patient who had a lead migration associated with coiling of the lead and twisting of pulse generator needed a revision surgery. Twiddler's syndrome in patients treated with SCS is an uncommon but important adverse event. Awareness of characteristic presentation and radiologic finding is essential in the identification of Twiddler's syndrome in SCS.

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

BACKGROUND

Traditional spinal cord stimulation (SCS) requires that paresthesia overlaps chronic painful areas. However, the new paradigm high-frequency SCS (HF-SCS) does not rely on paresthesia.

STUDY DESIGN

A review of preclinical and clinical studies regarding the use of paresthesia-free HF-SCS for various chronic pain states.

METHODS

We reviewed available literatures on HF-SCS, including Nevro's paresthesia-free ultra high-frequency 10 kHz therapy (HF10-SCS). Data sources included relevant literature identified through searches of PubMed, MEDLINE/OVID, and SCOPUS, and manual searches of the bibliographies of known primary and review articles.

OUTCOME MEASURES

The primary goal is to describe the present developing conceptions of preclinical mechanisms of HF-SCS and to review clinical efficacy on paresthesia-free HF10-SCS for various chronic pain states.

RESULTS

HF10-SCS offers a novel pain reduction tool without paresthesia for failed back surgery syndrome and chronic axial back pain. Preclinical findings indicate that potential mechanisms of action for paresthesia-free HF-SCS differ from those of traditional SCS.

CONCLUSIONS

To fully understand and utilize paresthesia-free HF-SCS, mechanistic study and translational research will be very important, with increasing collaboration between basic science and clinical communities to design better trials and optimize the therapy based on mechanistic findings from effective preclinical models and approaches. Future research in these vital areas may include preclinical and clinical components conducted in parallel to optimize the potential of this technology.

Wireless Neuromodulation for Chronic Back Pain: Delivery of High-Frequency Dorsal Root Ganglion Stimulation by a Minimally Invasive Technique

Objective

To evaluate the analgesic effect of a dorsal root ganglion (DRG) stimulation technology utilizing high-frequency pulse rates to treat intractable chronic back and leg pain.

Methods

This case study presents the outcomes, with a novel, wireless, minimally invasive miniature neurostimulator system in a case of chronic back pain. The subject was implanted bilaterally with a Freedom 4A quadripolar electrode array at the L2 dorsal root ganglion. Stimulation was applied using 10 kHz pulse rate and 30 μs pulse width. A VAS pain-rating scale, Oswestry Disability Index (ODI), EQ-5D-5L Quality of Life Questionnaire 5 dimensions, and Patients' Global Impression of Change (PGIC) scale were evaluated at 12 weeks and 6 months post implantation.

Results

VAS pain scores for back pain reduced from 91 to 31 mms and 80 to 35 mms for leg pain. Additionally, while stimulation remained paresthesia-free, there were a marked decrease in pain medications and an increase in quality of life. Also, an increase in functionality from crippled to moderate was reported. There were no adverse reactions related to the procedure or device.

Conclusion

The minimally invasive, wireless approach to deliver high-frequency, paresthesia-free DRG stimulation for treatment of chronic back and leg pain associated with FBSS was effective and encouraging.

Neurostimulation Devices for the Treatment of Neurologic Disorders

Rapid advancements in neurostimulation technologies are providing relief to an unprecedented number of patients affected by debilitating neurologic and psychiatric disorders. Neurostimulation therapies include invasive and noninvasive approaches that involve the application of electrical stimulation to drive neural function within a circuit. This review focuses on established invasive electrical stimulation systems used clinically to induce therapeutic neuromodulation of dysfunctional neural circuitry. These implantable neurostimulation systems target specific deep subcortical, cortical, spinal, cranial, and peripheral nerve structures to modulate neuronal activity, providing therapeutic effects for a myriad of neuropsychiatric disorders. Recent advances in neurotechnologies and neuroimaging, along with an increased understanding of neurocircuitry, are factors contributing to the rapid rise in the use of neurostimulation therapies to treat an increasingly wide range of neurologic and psychiatric disorders. Electrical stimulation technologies are evolving after remaining fairly stagnant for the past 30 years, moving toward potential closed-loop therapeutic control systems with the ability to deliver stimulation with higher spatial resolution to provide continuous customized neuromodulation for optimal clinical outcomes. Even so, there is still much to be learned about disease pathogenesis of these neurodegenerative and psychiatric disorders and the latent mechanisms of neurostimulation that provide therapeutic relief. This review provides an overview of the increasingly common stimulation systems, their clinical indications, and enabling technologies.

Explantation Rates and Healthcare Resource Utilization in Spinal Cord Stimulation

OBJECTIVES

Certain patients ultimately undergo explantation of their spinal cord stimulation (SCS) devices. Understanding the predictors and rates of SCS explantation has important implications for healthcare resource utilization (HCRU) and pain management. The present study identifies explant predictors and discerns differences in HCRU for at-risk populations.

METHODS

We designed a large, retrospective analysis using the Truven MarketScan Database. We included all adult patients who underwent a SCS trial from 2007 to 2012. Patients were grouped into cohorts that remained explant-free or underwent explantation over a three-year period, and multivariate models evaluated differences in healthcare resource utilization.

RESULTS

A total of 8727 unique instances of trial implants between 2007 and 2012 were identified. Overall, 805 (9.2%) patients underwent device explantation. One year prior to SCS implantation, the explant cohort had significantly higher median baseline costs ($42,140.3 explant vs. $27,821.7 in non-explant groups; p < 0.0001), total number of pain encounters (180 vs. 103 p < 0.0001), and associated costs ($15,446.9 vs. $9,227.9; p < 0.0001). The explant cohort demonstrated increased use of procedures (19.0 vs. 9.0; p < 0.0001) compared to non-explanted patients. For each month after initial SCS implantation, explanted patients had a slower decrease in total costs (4% vs. 6% in non-explant; p < 0.01). At the month of explant, explant patients were expected to have incurred 2.65 times the total cost compared to the non-explant cohort (CR 2.65, 95% CI [1.83, 3.84]; p < 0.001). Medium volume providers had lower rates of explantation at one-year and three-years compared to low volume providers (p = 0.042). Increased age and Charlson index were independent predictors of explantation during the same periods.

CONCLUSIONS

In this nationwide analysis, we identified that SCS device explantation is correlated with patients who have higher baseline costs, higher total cost post-SCS implantation, and increased use of procedures to control pain. The higher rates of explantation at three-years postimplant among low volume providers suggest that variations in provider experience and approach also contributes to differences in explantation rates.

Interventional Analgesic Management of Lung Cancer Pain

Lung cancer is one of the four most prevalent cancers worldwide. Comprehensive patient care includes not only adherence to clinical guidelines to control and when possible cure the disease but also appropriate symptom control. Pain is one of the most prevalent symptoms in patients diagnosed with lung cancer; it can arise from local invasion of chest structures or metastatic disease invading bones, nerves, or other anatomical structures potentially painful. Pain can also be a consequence of therapeutic approaches like surgery, chemotherapy, or radiotherapy. Conventional medical management of cancer pain includes prescription of opioids and coadjuvants at doses sufficient to control the symptoms without causing severe drug effects. When an adequate pharmacological medical management fails to provide satisfactory analgesia or when it causes limiting side effects, interventional cancer pain techniques may be considered. Interventional pain management is devoted to the use of invasive techniques such as joint injections, nerve blocks and/or neurolysis, neuromodulation, and cement augmentation techniques to provide diagnosis and treatment of pain syndromes resistant to conventional medical management. Advantages of interventional approaches include better analgesic outcomes without experiencing drug-related side effects and potential for opioid reduction thus avoiding central side effects. This review will describe various pain syndromes frequently described in lung cancer patients and those interventional techniques potentially indicated for those cases.

Acute Neuropathic Orchalgia and Scrotalgia After Percutaneous Spinal Cord Stimulator Lead Placement: Two Cases with an Unusual Complication

Spinal cord stimulation is an effective adjunct to the treatment of a variety of chronic pain syndromes. Complications are relatively low in morbidity and are most often secondary to hardware malfunction/malposition. Infection and undesired dysesthesias represent only a minority of complications. Neuropathic orchalgia and scrotalgia after placement of epidural spinal cord stimulator is a previously unreported morbidity. While alarming, this condition is physiologically benign, causing no neurological or urological dysfunction. The two cases we encountered both occurred during uncomplicated percutaneous trial stimulator placement. Corticosteroid treatment and stimulator activation facilitated resolution of the dysesthesia and allowed completion of the trial in one case, while the other case was refractory and resulted in termination of the trial.

Late Spontaneous Migration of a Dorsal Column Stimulator Paddle Lead

The most frequently encountered complication of dorsal column stimulators is lead migration. The vast majority of these events are seen in the first few weeks to months. Late paddle lead migration is a very uncommon occurrence in this setting. We describe a case of a 51-year-old male with a history of reflex sympathetic dystrophy having undergone dorsal column stimulator insertion at the level of C1-C2. A good clinical benefit was appreciated in the postoperative period once the stimulator was turned on. Approximately six months postoperatively, the patient suddenly lost coverage. Radiographic imaging revealed that the lead had migrated caudally to the C3-C4 level. Subsequent revision surgery took place. This description highlights a common complication, but occurring outside the expected time frame after surgery.

Neuroprosthetics in amputee and brain injury rehabilitation

The goals of rehabilitation medicine programs are to promote health, restore functional impairments and improve quality of life. The field of neuroprosthetics has evolved over the last decade given an improved understanding of neuroscience and the incorporation of advanced biotechnology and neuroengineering in the rehabilitation setting to develop adaptable applications to help facilitate recovery for individuals with amputations and brain injury. These applications may include a simple cognitive prosthetics aid for impaired memory in brain-injured individuals to myoelectric prosthetics arms with artificial proprioceptive feedback for those with upper extremity amputations. The integration of neuroprosthetics into the existing framework of current rehabilitation approaches not only improves quality-of-care and outcomes but help broadens current rehabilitation treatment paradigms. Although, we are in the infancy of the understanding the true benefit of neuroprosthetics and its clinical applications in the rehabilitation setting there is tremendous amount of promise for future research and development of tools to help facilitate recovery and improve quality of life in individuals with disabilities.

A review of spinal cord stimulation systems for chronic pain

Spinal cord stimulation (SCS) applications and technologies are fast advancing. New SCS technologies are being used increasingly in the clinical environment, but often there is a lag period between the clinical application and the publishing of high-quality evidence on safety and efficacy. Recent developments will undoubtedly expand the applicability of SCS, allowing more effective and individualized treatment for patients, and may have the potential to salvage patients who have previously failed neuromodulation. Already, high-level evidence exists for the safety, efficacy, and cost-effectiveness (Level I–II) of traditional SCS therapies in the treatment of chronic refractory low back with predominant limb pain (regardless of surgical history). More than half of all patients with chronic painful conditions experience sustained and significant levels of pain reduction following SCS treatment. Although only limited evidence exists for burst stimulation, there is now Level I evidence for both dorsal root ganglion SCS and high-frequency SCS that demonstrates compelling results compared with traditional therapies. The body of evidence built on traditional SCS research may be redundant, with newer iterations of SCS therapies such as dorsal root ganglion SCS, high-frequency SCS, and burst SCS. A number of variables have been identified that can affect SCS efficacy: implanter experience, appropriate patient selection, etiologies of patient pain, existence of comorbidities, including psychiatric illness, smoking status, and delay to SCS implant following pain onset. Overall, scientific literature demonstrates SCS to be a safe, effective, and drug-free treatment option for many chronic pain etiologies.

An overview of treatment approaches for chronic pain management

Pain which persists after healing is expected to have taken place, or which exists in the absence of tissue damage, is termed chronic pain. By definition chronic pain cannot be treated and cured in the conventional biomedical sense; rather, the patient who is suffering from the pain must be given the tools with which their long-term pain can be managed to an acceptable level. This article will provide an overview of treatment approaches available for the management of persistent non-malignant pain. As well as attempting to provide relief from the physical aspects of pain through the judicious use of analgesics, interventions, stimulations, and irritations, it is important to pay equal attention to the psychosocial complaints which almost always accompany long-term pain. The pain clinic offers a biopsychosocial approach to treatment with the multidisciplinary pain management programme; encouraging patients to take control of their pain problem and lead a fulfilling life in spite of the pain.

Advanced Innovations for Pain

Chronic pain represents one of the most important public health problems in terms of both the number of patients afflicted and health care costs. Most patients with chronic pain are treated with medications as the mainstay of therapy, and yet most medically treated patients continue to report ongoing pain. Additionally, adverse effects from pain medications represent a major challenge for clinicians and patients. Spinal cord stimulation and intrathecal drug delivery systems are well-established techniques that have been utilized for over 25 years. Intrathecal drug delivery systems have proven efficacy for a wide variety of intractable pain conditions and fewer adverse effects than systemic medical therapy in patients with refractory cancer-related pain. Spinal cord stimulation is cost-effective and provides improved pain control compared with medical therapy in patients with a variety of refractory pain conditions including complex regional pain syndrome, painful diabetic neuropathy, and chronic radiculopathy. Patients who have intractable pain that has not responded to reasonable attempts at conservative pain care measures should be referred to a qualified interventional pain specialist to determine candidacy for the procedures discussed in this article.

Spinal cord stimulation in the treatment of chronic pain syndromes

AIM

The study objective was to estimate the efficacy of chronic epidural spinal cord stimulation in the treatment of patients with neuropathic pain syndrome.

MATERIAL AND METHODS

A system for chronic spinal cord stimulation (St. Jude) was implanted to 75 patients with neuropathic pain syndrome. Fifty three (70.7%) patients were diagnosed with failed back surgery syndrome (FBSS); 9 (12.0%) patients had complex regional pain syndrome type II; 4 (5.3%) patients had diabetic polyneuropathy of the lower limbs; 3 (4.0%) patients had idiopathic pelvic-perineal pain; 2 (2.7%) patients had spinal stroke pain; 2 (2.7%) patients had postherpetic intercostal neuralgia; 1 (1.3%) patient had stump pain; 1 (1.3%) patient had spinal cord injury pain. The treatment efficacy was evaluated using the visual analog scale (VAS) and DN4 questionnaire. The follow-up period ranged from 6 to 18 months.

RESULTS

136 patients underwent test stimulation at the Center in 2014. A significant reduction in pain was observed in 75 (55.1%) patients. These patients underwent the second stage of surgery that included implantation of permanent electrodes and a generator. The mean VAS score was 6.5 (maximum: 10; minimum: 5) before surgery, 3.2 at discharge, and 3.1 after 3 and 6 months. The VAS score amounted to 3.6 after 12 months. Complications in the form of pain at the generator implantation site and the need for removal of the system occurred in 2 patients (2.6%), electrode migration was observed in 4 (5.3%) cases.

CONCLUSION

Chronic epidural spinal cord stimulation is an effective and safe technique for the treatment of drug-resistant chronic neurogenic pain syndromes.

Review: Bioelectrical mechanisms in spinal cord stimulation

OBJECTIVES

The aim of this review is to make specialists in a variety of disciplines familiar with basic aspects of spinal cord stimulation and the role of mathematical modeling in understanding its mechanisms of action and the solution of basic problems.

METHODS

The paper is divided into five sections. The content of each section also covers aspects of various disciplines. Most aspects are presented in an unusual way, likely resulting in new viewpoints and further developments in the growing field of neuromodulation.

RESULTS

A special, integrating role is the mathematical modeling of spinal cord stimulation and the simulation studies of various aspects, such as the stimulation in axial low-back pain.

CONCLUSIONS

In particular the conclusions from several computer simulation studies are relevant and of interest to specialists in many disciplines.

The Incidence of Spinal Cord Injury in Implantation of Percutaneous and Paddle Electrodes for Spinal Cord Stimulation

OBJECTIVE

Spinal cord stimulation (SCS) has been proven effective for multiple chronic pain syndromes. Over the past 40 years of use, the complication rates of SCS have been well defined in the literature; however, the incidence of one of the most devastating complications, spinal cord injury (SCI), remains largely unknown. The goal of the study was to quantify the incidence of SCI in both percutaneous and paddle electrode implantation.

METHODS

We conducted a retrospective review of the Thomson Reuter's MarketScan database of all patients that underwent percutaneous or paddle SCS implantation from 2000 to 2009. The main outcome measures of the study were the incidence of SCI and spinal hematoma within 30 days following operation.

RESULTS

Overall 8326 patients met inclusion criteria for the study (percutaneous: 5458 vs. paddle: 2868). The overall incidence of SCI was 177 (2.13%) (percutaneous: 128 (2.35%) vs. paddle: 49 (1.71%), p = 0.0556). The overall incidence of spinal hematoma was 59 (0.71%) (percutaneous: 41 (0.75%) vs. paddle: 18 (0.63%), p = 0.5230).

CONCLUSION

Our study shows that the overall incidence of SCI in SCS is low (2.13%), supporting that SCS is a safe procedure. No significant difference was found in the rates of SCI or spinal hematoma between the percutaneous and paddle groups. Further studies are needed to characterize the mechanisms of SCI in SCS and long-term outcomes in these patients.

Spinal cord stimulation for treatment of the pain associated with hereditary multiple osteochondromas

Objective

Hereditary multiple osteochondromas (HMO) usually presents with neoplastic lesions throughout the skeletal system. These lesions frequently cause chronic pain and are conventionally treated with surgical resection and medication. In cases where conventional treatments have failed, spinal cord stimulation (SCS) could be considered as a potential option for pain relief. The objective of this case was to determine if SCS may have a role in treating pain secondary to neoplastic lesions from HMO.

Case presentation

We report a 65-year-old female who previously received both surgical and pharmacological interventions for treating HMO neoplastic pain in the lumbar, pelvis, femur, and tibial regions. These interventions either failed to offer significant pain relief or caused excessive lethargy. A SCS trial was then offered with a dual 16-contact lead trial leading to 70%–80% improvement in pain from baseline and 85% reduction in oxycodone IR intake. This was followed by permanent implantation of two 2×8 contact paddle leads (T7–T8 and T9–T10 interspaces). After 8-week follow-up, settings were further optimized resulting in an additional 30% improvement in pain compared to last visit. At 6-month follow-up, the patient reported continued pain relief.

Conclusion

This case demonstrates the first successful use of SCS to treat both HMO and nonmalignant neoplastic-related pain. The patient reported pain improvement from baseline, reduced pain medication requirements, and subjective improvement in quality of life. Additionally, this case demonstrates the potential advantage of trialing multiple painful areas with a 16-contact lead in order to avoid multiple trials and placement.

Burst and Tonic Spinal Cord Stimulation Differentially Activate GABAergic Mechanisms to Attenuate Pain in a Rat Model of Cervical Radiculopathy

OBJECTIVE

Spinal cord stimulation (SCS) is widely used to treat neuropathic pain. Burst SCS, an alternative mode of stimulation, reduces neuropathic pain without paresthesia. However, the effects and mechanisms of burst SCS have not been compared to conventional tonic SCS in controlled investigations. This study compares the attenuation of spinal neuronal activity and tactile allodynia, and the role of γ-aminobutyric acid (GABA) signaling during burst or tonic SCS in a rat model of cervical radiculopathy.

METHODS

The effects of burst and tonic SCS were compared by recording neuronal firing before and after each mode of stimulation at day 7 following a painful cervical nerve root compression. Neuronal firing was also recorded before and after burst and tonic SCS in the presence of the GABAB receptor antagonist, CGP35348.

RESULTS

Burst and tonic SCS both reduce neuronal firing. The effect of tonic SCS, but not burst SCS, is blocked by CGP35348. In a separate study, spinal cord stimulators were implanted to deliver burst or tonic SCS beginning on day 4 after painful nerve root compression; allodynia and serum GABA concentration were measured through day 14. Burst and tonic SCS both reduce allodynia. Tonic SCS attenuates injury-induced decreases in serum GABA, but GABA remains decreased from baseline during burst SCS.

CONCLUSION AND SIGNIFICANCE

Together, these studies suggest that burst SCS does not act via spinal GABAergic mechanisms, despite its attenuation of spinal hyperexcitability and allodynia similar to that of tonic SCS; understanding other potential spinal inhibitory mechanisms may lead to enhanced analgesia during burst stimulation.

Basic science and clinical management of painful and non-painful chemotherapy-related neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting toxicity of several chemotherapeutics used in the treatment of all the most common malignancies. There are several defined mechanisms of nerve damage that take place along different areas of the peripheral and the central nervous system. Treatment is based on symptom management and there are several classes of medications found to be efficacious in the treatment of neuropathic pain. Neuropathic pain that persists despite appropriate pharmacotherapy may respond to interventional procedures that span a range of invasiveness. The purpose of this review article is to examine the basic science of neuropathy and currently available treatment options in the context of chemotherapy induced peripheral neuropathy.

Clinical and microbiological aspects of biofilm-associated surgical site infections

While microbial biofilms have been recognized as being ubiquitous in nature for the past 40 years, it has only been within the past 20 years that clinical practitioners have realized that biofilm play a significant role in both device-related and tissue-based infections. The global impact of surgical site infections (SSIs) is monumental and as many as 80 % of these infections may involve a microbial biofilm. Recent studies suggest that biofilm- producing organisms play a significant role in persistent skin and soft tissue wound infections in the postoperative surgical patient population. Biofilm, on an organizational level, allows bacteria to survive intrinsic and extrinsic defenses that would inactivate the dispersed (planktonic) bacteria. SSIs associated with biomedical implants are notoriously difficult to eradicate using antibiotic regimens that would typically be effective against the same bacteria growing under planktonic conditions. This biofilm-mediated phenomenon is characterized as antimicrobial recalcitrance, which is associated with the survival of a subset of cells including "persister" cells. The ideal method to manage a biofilm-mediated surgical site wound infection is to prevent it from occurring through rational use of antibiotic prophylaxis, adequate skin antisepsis prior to surgery and use of innovative in-situ irrigation procedures; together with antimicrobial suture technology in an effort to promote wound hygiene at the time of closure; once established, biofilm removal remains a significant clinical problem.

Evaluation of intradural stimulation efficiency and selectivity in a computational model of spinal cord stimulation

Spinal cord stimulation (SCS) is an alternative or adjunct therapy to treat chronic pain, a prevalent and clinically challenging condition. Although SCS has substantial clinical success, the therapy is still prone to failures, including lead breakage, lead migration, and poor pain relief. The goal of this study was to develop a computational model of SCS and use the model to compare activation of neural elements during intradural and extradural electrode placement. We constructed five patient-specific models of SCS. Stimulation thresholds predicted by the model were compared to stimulation thresholds measured intraoperatively, and we used these models to quantify the efficiency and selectivity of intradural and extradural SCS. Intradural placement dramatically increased stimulation efficiency and reduced the power required to stimulate the dorsal columns by more than 90%. Intradural placement also increased selectivity, allowing activation of a greater proportion of dorsal column fibers before spread of activation to dorsal root fibers, as well as more selective activation of individual dermatomes at different lateral deviations from the midline. Further, the results suggest that current electrode designs used for extradural SCS are not optimal for intradural SCS, and a novel azimuthal tripolar design increased stimulation selectivity, even beyond that achieved with an intradural paddle array. Increased stimulation efficiency is expected to increase the battery life of implantable pulse generators, increase the recharge interval of rechargeable implantable pulse generators, and potentially reduce stimulator volume. The greater selectivity of intradural stimulation may improve the success rate of SCS by mitigating the sensitivity of pain relief to malpositioning of the electrode. The outcome of this effort is a better quantitative understanding of how intradural electrode placement can potentially increase the selectivity and efficiency of SCS, which, in turn, provides predictions that can be tested in future clinical studies assessing the potential therapeutic benefits of intradural SCS.

Spinal cord stimulation for neuropathic pain: current perspectives

Neuropathic pain constitutes a significant portion of chronic pain. Patients with neuropathic pain are usually more heavily burdened than patients with nociceptive pain. They suffer more often from insomnia, anxiety, and depression. Moreover, analgesic medication often has an insufficient effect on neuropathic pain. Spinal cord stimulation constitutes a therapy alternative that, to date, remains underused. In the last 10 to 15 years, it has undergone constant technical advancement. This review gives an overview of the present practice of spinal cord stimulation for chronic neuropathic pain and current developments such as high-frequency stimulation and peripheral nerve field stimulation.

Finite-Element Study of the Performance Characteristics of an Intradural Spinal Cord Stimulator

We have used finite-element (FE) modeling to investigate the mechanical compliance, positional stability and contact pressures associated with a novel type of spinal cord stimulator that is placed directly on the pial surface of the spinal cord in order to more selectively activate neural structures for relief of intractable pain. The properties used in the model are those of the actual prototype devices employed in recent in vitro and chronic in vivo tests. The agreement between predictions and experimental observations serves to validate our FE approach, which can now be used to further optimize the device's design and performance.

A system and method to interface with multiple groups of axons in several fascicles of peripheral nerves

BACKGROUND

Several neural interface technologies that stimulate and/or record from groups of axons have been developed. The longitudinal intrafascicular electrode (LIFE) is a fine wire that can provide access to a discrete population of axons within a peripheral nerve fascicle. Some applications require, or would benefit greatly from, technology that could provide access to multiple discrete sites in several fascicles.

NEW METHOD

The distributed intrafascicular multi-electrode (DIME) lead was developed to deploy multiple LIFEs to several fascicles. It consists of several (e.g. six) LIFEs that are coiled and placed in a sheath for strength and durability, with a portion left uncoiled to allow insertion at distinct sites. We have also developed a multi-lead multi-electrode (MLME) management system that includes a set of sheaths and procedures for fabrication and deployment.

RESULTS

A prototype with 3 DIME leads was fabricated and tested in a procedure in a cadaver arm. The leads were successfully routed through skin and connective tissue and the deployment procedures were utilized to insert the LIFEs into fascicles of two nerves.

COMPARISON WITH EXISTING METHOD(S)

Most multi-electrode systems use a single-lead, multi-electrode design. For some applications, this design may be limited by the bulk of the multi-contact array and/or by the spatial distribution of the electrodes.

CONCLUSION

We have designed a system that can be used to access multiple sets of discrete groups of fibers that are spatially distributed in one or more fascicles of peripheral nerves. This system may be useful for neural-enabled prostheses or other applications.

Long-term follow-up of spinal cord stimulation to restore cough in subjects with spinal cord injury

OBJECTIVE

To determine the long-term effects of the cough stimulation system.

DESIGN

Nonrandomized clinical trial of subjects using the study device well beyond the period of close follow-up.

SETTING

Use of the study device in the home setting.

PARTICIPANTS

Subjects (N = 10) implanted with the device for a minimum of 2 years (mean 4.6 ± 0.6 years).

INTERVENTIONS

Application of daily stimulation.

OUTCOME MEASURES

Airway pressure generation and other clinical assessments including ease in raising secretions, life quality, caregiver support, and incidence of respiratory tract infections were measured at 1 year and mean 4.6 years after implantation.

RESULTS

Each subject continued to use the device on a regular basis. During SCS, mean maximum airway pressures were 103.1 ± 20.4 and 107.7 ± 23.0 cm H₂O at the 1-year and mean 4.6-year follow-up points, respectively (P < 0.05 compared with pre-implant and not significantly different (NS) compared with 1-year follow-up). Benchmarks related to ease in raising secretions and improvements in life quality related to respiratory care were maintained at the mean 4.6 year follow-up. The need for trained caregivers to provide other means of secretion management remained significantly below the pre-implant values (P < 0.05). The incidence of acute respiratory tract infections remained low at 0.2 ± 0.1 events/year, which is significantly below the pre-implant value of 1.4 ± 0.3 events/year (P < 0.05).

CONCLUSION

Subjects continued to use the system on a long-term basis beyond the period of close follow-up and to continued derive significant clinical benefits.

Spinal cord stimulation: Background and clinical application

Background Spinal cord stimulation (SCS) is a surgical treatment for chronic neuropathic pain refractory to conventional treatment. SCS treatment consists of one or more leads implanted in the epidural space of the spinal canal, connected to an implantable pulse generator (IPG). Each lead carries a number of contacts capable of delivering a weak electrical current to the spinal cord, evoking a feeling of peripheral paresthesia. With correct indication and if implanted by an experienced implanter, success rates generally are in the range of about 50-75%. Common indications include complex regional pain syndrome (CRPS I), angina pectoris, and radicular pain after failed back surgery syndrome, and the treatment is also used to treat stump pain after amputation, and pain due to peripheral nerve injury, peripheral vascular disease, and diabetic neuropathy. Recommended contraindications for the treatment include pregnancy, coagulopathy, severe addiction to psychoactive substances, and lack of ability to cooperate (e.g. due to active psychosis or cognitive impairment). Most common complications to the treatment include lead migration, lead breakage, infection, pain over the implant, and dural puncture. Despite extensive research in the area, the mechanisms of action are still only partially understood. Methods In this topical review the historical background behind the treatment is described and the current theories on the mechanism of action are presented. The implantation procedure is described in detail and illustrated with a series of intraoperative pictures. Finally, indications for SCS are discussed along with some of the controversies surrounding the therapy. Implications The reader is presented with a broad overview of spinal cord stimulation, including the historical and theoretical background, practical implantation technique, and clinical application.

Closed-loop neurostimulation: the clinical experience

Neurostimulation is now an established therapy for the treatment of movement disorders, pain, and epilepsy. While most neurostimulation systems available today provide stimulation in an open-loop manner (i.e., therapy is delivered according to preprogrammed settings and is unaffected by changes in the patient's clinical symptoms or in the underlying disease), closed-loop neurostimulation systems, which modulate or adapt therapy in response to physiological changes, may provide more effective and efficient therapy. At present, few such systems exist owing to the complexities of designing and implementing implantable closed-loop systems. This review focuses on the clinical experience of four implantable closed-loop neurostimulation systems: positional-adaptive spinal cord stimulation for treatment of pain, responsive cortical stimulation for treatment of epilepsy, closed-loop vagus nerve stimulation for treatment of epilepsy, and concurrent sensing and stimulation for treatment of Parkinson disease. The history that led to the development of the closed-loop systems, the sensing, detection, and stimulation technology that closes the loop, and the clinical experiences are presented.

A Case of Lead Migration Caused by Involuntary Movement in Implanted Spinal Cord Stimulation

Spinal cord stimulation (SCS) is a reliable clinical option for treatment of refractory chronic pain. It is known to be effective method for treating sympathetic pain, failed back surgery syndrome, and complex regional pain syndrome etc. The devices and implantation techniques for SCS are already highly developed and continuously improving, but there are some complications that can not be corrected easily. Lead migration is the most common complication after SCS. It can cause failure of SCS that can make discomfort to patients. Here we describe our experience of lead migration in implanted SCS which was inserted to a patient with complex regional pain syndrome patient.

Utilization of spinal cord stimulation in patients with failed back surgery syndrome

STUDY DESIGN

Retrospective analysis of a population-based insurance claims data set.

OBJECTIVE

To evaluate the use of spinal cord stimulation (SCS) and lumbar reoperation for the treatment of failed back surgery syndrome (FBSS), and examine their associated complications and health care costs.

SUMMARY OF BACKGROUND DATA

FBSS is a major source of chronic neuropathic pain and affects up to 40% of patients who undergo lumbosacral spine surgery for back pain. Thus far, few economic analyses have been performed comparing the various treatments for FBSS, with these studies involving small sample sizes. In addition, the nationwide practices in the use of SCS for FBSS are unknown.

METHODS

The MarketScan data set was used to analyze patients with FBSS who underwent SCS or spinal reoperation between 2000 and 2009. Propensity score methods were used to match patients who underwent SCS with those who underwent lumbar reoperation to examine health care resource utilization. Postoperative complications were analyzed with multivariate logistic regression. Health care use was analyzed using negative binomial and general linear models.

RESULTS

The study cohort included 16,455 patients with FBSS, with 395 undergoing SCS implantation (2.4%). Complication rates at 90 days were significantly lower for SCS than spinal reoperation (P < 0.0001). Also in the matched cohort, hospital stay (P < 0.0001) and associated charges (P = 0.016) were lower for patients with SCS. However outpatient, emergency room, and medication charges were similar between the 2 groups. Overall cost totaling $82,586 at 2 years was slightly higher in the lumbar reoperation group than in the SCS group with total cost of $80,669 (P = 0.88).

CONCLUSION

Although previous studies have demonstrated superior efficacy for the treatment of FBSS, SCS remains underused. Despite no significant decreases in overall health care cost with SCS implantation, because it is associated with decreased complications and improved outcomes, this technology warrants closer consideration for the management of chronic pain in patients with FBSS.

Mechanisms and models of spinal cord stimulation for the treatment of neuropathic pain

Spinal cord stimulation (SCS) is an established and cost-effective therapy for treating severe chronic pain. However, despite over 40 years of clinical practice and the development of novel electrode designs and treatment protocols, increases in clinical success, defined as the proportion of patients that experience 50% or greater self-reported pain relief, have stalled. An incomplete knowledge of the neural circuits and systems underlying chronic pain and the interaction of SCS with these circuits may underlie this plateau in clinical efficacy. This review summarizes prior work and identifies gaps in our knowledge regarding the neural circuits related to pain and SCS in the dorsal horn, supraspinal structures, and the Pain Matrix. In addition, this review discusses and critiques current experimental and computational models used to investigate and optimize SCS. Further research into the interactions between SCS and pain pathways in the nervous system using animal and computational models is a fruitful approach to improve this promising therapy.

Improved Biphasic Pulsing Power Efficiency with Pt-Ir Coated Microelectrodes

Neuromodulation devices such as deep brain stimulators (DBS), spinal cord stimulators (SCS) and cochlear implants (CIs) use electrodes in contact with tissue to deliver electrical pulses to targeted cells. In general, the neuromodulation industry has been evolving towards smaller, less invasive devices. Improving power efficiency of these devices can reduce battery storage requirements. Neuromodulation devices can realize significant power savings if the impedance to charge transfer at the electrode-tissue interface can be reduced. High electrochemical impedance at the surface of stimulation microelectrodes results in larger polarization voltages. Decreasing this polarization voltage response can reduce power required to deliver the current pulse. One approach to doing this is to reduce the electrochemical impedance at the electrode surface. Previously we have reported on a novel electrochemically deposited 60:40% platinum-iridium (Pt-Ir) electrode material that lowered the electrode impedance by two orders of magnitude or more.

This study compares power consumption of an electrochemically deposited Pt-Ir stimulating microelectrode to that of standard Pt-Ir probe microelectrode produced using conventional techniques. Both electrodes were tested using in-vitro in phosphate buffered saline (PBS) solution and in-vivo (live rat) models.

Prevention of percutaneous spinal cord stimulation electrode migration: a 15-year experience

OBJECTIVES

Percutaneous spinal cord stimulation electrodes have a propensity to migrate longitudinally, which is a costly complication that often compromises therapeutic effect. After implementing simple changes to our percutaneous electrode anchoring technique, we no longer encounter this migration. The current retrospective study updates previously reported results.

MATERIALS AND METHODS

We retrospectively examined data in a consecutive series of patients in whom we had secured a new percutaneous electrode by injecting < 0.1 cm(3) of adhesive into the silicone elastomer lead anchor. From 1998 through 2006, we used whichever anchor was supplied with each lead until we observed one case of migration through a short anchor; thereafter, we used a long, tapered anchor exclusively. From 2007 through 2013, we further modified our technique by adding a fascial incision to accommodate the tip of the anchor and by increasing the strength of our suture material.

RESULTS

In the first series of 291 patients, followed through July 2007 (mean 4.75 years, range 1.1-9.0 years), 4 (1.37%) experienced electrode migration requiring surgical revision. Only one lead had moved with respect to its anchor; the other three anchors remained securely bonded to their leads. No migration (0.00%) occurred in the second series of 142 patients, followed through 2013 (mean follow-up 2.86 years, range 0.10-5.45 years).

CONCLUSION

Improvements to our simple, inexpensive technique apparently have eliminated the most common complication of spinal cord stimulation.

Detailed analysis of allergic cutaneous reactions to spinal cord stimulator devices

The use of spinal cord stimulation (SCS) devices to treat chronic, refractory neuropathic pain continues to expand in application. While device-related complications have been well described, inflammatory reactions to the components of these devices remain underreported. In contrast, hypersensitivity reactions associated with other implanted therapies, such as endovascular and cardiac rhythm devices, have been detailed. The purpose of this case series is to describe the clinical presentation and course of inflammatory reactions as well as the histology of these reactions. All patients required removal of the entire device after developing inflammatory reactions over a time course of 1-3 months. Two patients developed a foreign body reaction in the lead insertion wound as well as at the implantable pulse generator site, with histology positive for giant cells. One patient developed an inflammatory dermatitis on the flank and abdomen that resolved with topical hydrocortisone. "In vivo" testing with a lead extension fragment placed in the buttock resulted in a negative reaction followed by successful reimplantation of an SCS device. Inflammatory reactions to SCS devices can manifest as contact dermatitis, granuloma formation, or foreign body reactions with giant cell formation. Tissue diagnosis is essential, and is helpful to differentiate an inflammatory reaction from infection. The role of skin patch testing for 96 hours may not be suited to detect inflammatory giant cell reactions that manifest several weeks post implantation.

Spinal cord stimulation as treatment for complex regional pain syndrome should be considered earlier than last resort therapy

BACKGROUND

Spinal cord stimulation (SCS), by virtue of its historically described up-front costs and level of invasiveness, has been relegated by several complex regional pain syndrome (CRPS) treatment algorithms to a therapy of last resort. Newer information regarding safety, cost, and efficacy leads us to believe that SCS for the treatment of CRPS should be implemented earlier in a treatment algorithm using a more comprehensive approach.

METHODS

We reviewed the literature on pain care algorithmic thinking and applied the safety, appropriateness, fiscal or cost neutrality, and efficacy (S.A.F.E.) principles to establish an appropriate position for SCS in an algorithm of pain care.

RESULTS AND CONCLUSION

Based on literature-contingent considerations of safety, efficacy, cost efficacy, and cost neutrality, we conclude that SCS should not be considered a therapy of last resort for CRPS but rather should be applied earlier (e.g., three months) as soon as more conservative therapies have failed.

Intracranial somatosensory responses with direct spinal cord stimulation in anesthetized sheep

The efficacy of spinal cord stimulators is dependent on the ability of the device to functionally activate targeted structures within the spinal cord, while avoiding activation of near-by non-targeted structures. In theory, these objectives can best be achieved by delivering electrical stimuli directly to the surface of the spinal cord. The current experiments were performed to study the influence of different stimulating electrode positions on patterns of spinal cord electrophysiological activation. A custom-designed spinal cord neurostimulator was used to investigate the effects of lead position and stimulus amplitude on cortical electrophysiological responses to spinal cord stimulation. Brain recordings were obtained from subdural grids placed in four adult sheep. We systematically varied the position of the stimulating lead relative to the spinal cord and the voltage delivered by the device at each position, and then examined how these variables influenced cortical responses. A clear relationship was observed between voltage and electrode position, and the magnitude of high gamma-band oscillations. Direct stimulation of the dorsal column contralateral to the grid required the lowest voltage to evoke brain responses to spinal cord stimulation. Given the lower voltage thresholds associated with direct stimulation of the dorsal column, and its possible impact on the therapeutic window, this intradural modality may have particular clinical advantages over standard epidural techniques now in routine use.

Dorsal paddle leads implant for spinal cord stimulation through laminotomy with midline structures preservation

Background:

Pain relief obtained with spinal cord stimulation (SCS) in failed back surgery syndrome (FBSS) has been shown to be more effective with paddle leads than with percutaneous catheters. A laminectomy is generally required to implant the paddles, but the surgical approach may lead to iatrogenic spinal instability in flexion. In contrast, clinical and experimental data showed that a laminotomy performed through flavectomy and minimal resection of inferior and superior lamina with preservation of the midline ligamentous structures allowed to prevent iatrogenic instability. Aim of the study was to assess degree of instability and pain level in patients operated for SCS through laminectomy or laminotomy with midline structures integrity. The surgical technique is described and our preliminary results are discussed.

Methods:

Nineteen patients with FBSS underwent SCS, 12 through laminectomy and 7 through uni- or bilateral interlaminotomy with supraspinous ligament preservation. Postoperative local pain was evaluated at 15, 30, and 60 days. Static and dynamic X-rays were performed after 2 months.

Results:

The techniques allowed implanting the paddle leads in all cases. No intraoperative complications occurred. Local pain was higher and recovery time was longer in patients with laminectomy. We did not observe radiological signs of postoperative iatrogenic vertebral instability. Nevertheless, two patients who underwent laminectomy showed persistence of local pain after 2 months probably due to pathologic compensatory stability provided by the paraspinal musculature.

Conclusions:

The laminotomy is a minimally invasive approach that ensures rapid recovery after surgery, spinal functional integrity, and complete reversibility. Further studies are needed to confirm our preliminary results.

Dorsal column stimulator applications

Background:

Spinal cord stimulation (SCS) has been used to treat neuropathic pain since 1967. Following that, technological progress, among other advances, helped SCS become an effective tool to reduce pain.

Methods:

This article is a non-systematic review of the mechanism of action, indications, results, programming parameters, complications, and cost-effectiveness of SCS.

Results:

In spite of the existence of several studies that try to prove the mechanism of action of SCS, it still remains unknown. The mechanism of action of SCS would be based on the antidromic activation of the dorsal column fibers, which activate the inhibitory interneurons within the dorsal horn. At present, the indications of SCS are being revised constantly, while new applications are being proposed and researched worldwide. Failed back surgery syndrome (FBSS) is the most common indication for SCS, whereas, the complex regional pain syndrome (CRPS) is the second one. Also, this technique is useful in patients with refractory angina and critical limb ischemia, in whom surgical or endovascular treatment cannot be performed. Further indications may be phantom limb pain, chronic intractable pain located in the head, face, neck, or upper extremities, spinal lumbar stenosis in patients who are not surgical candidates, and others.

Conclusion:

Spinal cord stimulation is a useful tool for neuromodulation, if an accurate patient selection is carried out prior, which should include a trial period. Undoubtedly, this proper selection and a better knowledge of its underlying mechanisms of action, will allow this cutting edge technique to be more acceptable among pain physicians.

Spinal cord stimulation in pain management: a review

Spinal cord stimulation has become a widely used and efficient alternative for the management of refractory chronic pain that is unresponsive to conservative therapies. Technological improvements have been considerable and the current neuromodulation devices are both extremely sophisticated and reliable in obtaining good results for various clinical situations of chronic pain, such as failed back surgery syndrome, complex regional pain syndrome, ischemic and coronary artery disease. This technique is likely to possess a savings in costs compared with alternative therapy strategies despite its high initial cost. Spinal cord stimulation continues to be a valuable tool in the treatment of chronic disabling pain.

Spinal cord stimulation for complex regional pain syndrome: A systematic review of the clinical and cost-effectiveness literature and assessment of prognostic factors

OBJECTIVE

To review the clinical and cost-effectiveness of spinal cord stimulation (SCS) in the management of patients with complex regional pain syndrome (CRPS) and identify the potential predictors of SCS outcome.

DESIGN

Systematic review of the literature and meta-regression.

METHODS

Electronic databases were searched for controlled and uncontrolled studies and economic evaluations relating to the use of SCS in patients with either CRPS type I or II.

RESULTS

One randomised controlled trial, 25 case series and one cost-effectiveness study were included. In the randomised controlled trial in type I CRPS patients, SCS therapy lead to a reduction in pain intensity at 24 months of follow-up (mean change in VAS score -2.0), whereas pain was unchanged in the control group (mean change in VAS score 0.0) (p<0.001). In the case series studies, 67% (95% CI 51%, 84%) of type I and type II CRPS patients implanted with SCS reported pain relief of at least 50% over a median follow-up period of 33 months. No statistically significant predictors of pain relief with SCS were observed in multivariate meta-regression analysis across studies. An economic analysis based on the randomised controlled trial showed a lifetime cost saving of approximately 58,470 (60,800 US dollars) with SCS plus physical therapy compared with physical therapy alone. The mean cost per quality-adjusted life-year at 12-month follow-up was 22,580 (23,480 US dollars).

CONCLUSIONS

SCS appears to be an effective therapy in the management of patients with CRPS type I (Level A evidence) and type II (Level D evidence). Moreover, there is evidence to demonstrate that SCS is a cost-effective treatment for CRPS type I.

Effects of spinal cord stimulation on cortical excitability in patients with chronic neuropathic pain: A pilot study

BACKGROUND

Despite a broad clinical use, the mechanism of action of SCS is poorly understood. Current information suggests that the effects of SCS are mediated by a complex set of interactions at several levels of the nervous system including spinal and supraspinal mechanisms.

AIMS

The study was undertaken to investigate the influence of SCS on distinct parameters of cortical excitability using single- and paired-pulse transcranial magnetic stimulation (TMS).

METHODS

Five patients with chronic neuropathic pain were examined with the SCS stimulator on and off by means of TMS. Pain was assessed using a visual-analogue scale. Electrophysiological and pain parameters of patients during this procedure were compared by means of a linear mixed effect model.

RESULTS

SCS induced a significant modulation of cortical excitability, especially by influencing the parameter "intracortical facilitation" (t=-2.657; df=8; p=0.029). A significant relationship between this parameter and "perceived pain" could be obtained (t=-4.798; df=8; p=0.002).

CONCLUSIONS

These results suggest that SCS is able to influence neurobiological processes at the supraspinal level and that clinical effects of SCS may be at least in part of cortical origin.

Percutaneous electrode placement for spinal cord stimulation in a patient with spinal fusion: a technical report

A spinal cord stimulation (SCS) trial was attempted to alleviate left knee pain in a patient with spinal fusion from T12 to L4. Good paresthesia coverage for the knee pain was attained with SCS. However, while removing the needle used for electrode placement, the needle became fixed in the bony supplementary tissue. Moreover, while attempting to remove the needle using Kelly forceps, the hub of the needle became blocked. Without the hub, we had no choice but to use a pneumatic drill for removing the needle. Accordingly, the supplementary bone tissue was drilled under real-time imaging, using a pneumatic drill with a 3.2-mm drill bit, and another epidural needle was inserted through the hole. We consider that, in patients with spinal fusion, making a borehole with a pneumatic drill for introducing the epidural needle for percutaneous SCS electrode placement may be advisable in order to avoid the above-mentioned difficulties.

Comparison of wire and disc leads to activate the expiratory muscles in dogs

OBJECTIVE

Respiratory complications account for a major cause of morbidity and mortality in subjects with spinal cord injury (SCI) due to paralysis of the expiratory muscles and the consequent inability to generate effective cough. We demonstrated previously that effective cough can be restored in SCI via spinal cord stimulation (SCS) with disc leads positioned on the lower thoracic and upper lumbar spinal cord via laminotomy incisions. In this study, the effectiveness of wire leads, which can be placed using minimally invasive techniques, to activate the expiratory muscles was evaluated.

DESIGN

Animal study.

SETTING

Research laboratory.

ANIMALS

Dogs (n = 8).

INTERVENTIONS

In separate trials, disc and wire leads were inserted onto the dorsal epidural space at the T9, T11, and L1 spinal cord levels. Effects of electrical stimulation with disc, single wire, and two wire leads placed in parallel were compared.

OUTCOME MEASURES

Airway pressure generation following stimulation with disc and various configurations of wire leads were compared.

RESULTS

Several different configurations of wire leads resulted in airway pressures that were similar to those generated with monopolar stimulation with disc leads (MSDLs). For example, combined monopolar stimulation with parallel wire leads at the T9 + T11 and T9 + L1 levels resulted in airway pressures that were 103.5 ± 6.4 and 101.9 ± 7.0%, respectively, of those achieved with MSDL. Bipolar stimulation with parallel wire leads at T9-T11 and T9-L1 resulted in airway pressures that were 94.2 ± 3.4 and 96.8 ± 5.0%, respectively, of the pressures achieved with MSDL. Other wire configurations were also evaluated, but were generally less effective.

CONCLUSION

These results suggest that specific configurations of wire leads, which can be placed via minimally invasive techniques, result in comparable activation of the expiratory muscles compared to disc leads and may be a useful technique to restore cough in persons with SCI.