Mode of action of spinal cord stimulation in neuropathic pain

Comparison of tonic spinal cord stimulation, high-frequency and burst stimulation in patients with complex regional pain syndrome: a double-blind, randomised placebo controlled trial

Background

Complex Regional Pain Syndrome (CRPS) is a disabling disease that is sometimes difficult to treat. Although spinal cord stimulation (SCS) can reduce pain in most patients with CRPS, some do not achieve the desired reduction in pain. Moreover, the pain reduction can diminish over time even after an initially successful period of SCS. Pain reduction can be regained by increasing the SCS frequency, but this has not been investigated in a prospective trial. This study compares pain reduction using five SCS frequencies (standard 40 Hz, 500 Hz, 1200 Hz, burst and placebo stimulation) in patients with CRPS to determine which of the modalities is most effective.

Design

All patients with a confirmed CRPS diagnosis that have unsuccessfully tried all other therapies and are eligible for SCS, can enroll in this trial (primary implantation group). CRPS patients that already receive SCS therapy, or those previously treated with SCS but with loss of therapeutic effect over time, can also participate (re-implantation group). Once all inclusion criteria are met and written informed consent obtained, patients will undergo a baseline assessment (T0). A 2-week trial with SCS is performed and, if successful, a rechargeable internal pulse generator (IPG) is implanted. For the following 3 months the patient will have standard 40 Hz stimulation therapy before a follow-up assessment (T1) is performed. Those who have completed the T1 assessment will enroll in a 10-week crossover period in which the five SCS frequencies are tested in five periods, each frequency lasting for 2 weeks. At the end of the crossover period, the patient will choose which frequency is to be used for stimulation for an additional 3 months, until the T2 assessment.

Discussion

Currently no trials are available that systematically investigate the importance of variation in frequency during SCS in patients with CRPS. Data from this trial will provide better insight as to whether SCS with a higher frequency, or with burst stimulation, results in more effective pain relief.

Trial registration

Current Controlled Trials ISRCTN36655259

Electrical stimulation of low-threshold afferent fibers induces a prolonged synaptic depression in lamina II dorsal horn neurons to high-threshold afferent inputs in mice

Electrical stimulation of low-threshold Aβ-fibers (Aβ-ES) is used clinically to treat neuropathic pain conditions that are refractory to pharmacotherapy. However, it is unclear how Aβ-ES modulates synaptic responses to high-threshold afferent inputs (C-, Aδ-fibers) in superficial dorsal horn. Substantia gelatinosa (SG) (lamina II) neurons are important for relaying and modulating converging spinal nociceptive inputs. We recorded C-fiber-evoked excitatory postsynaptic currents (eEPSCs) in spinal cord slices in response to paired-pulse test stimulation (500 μA, 0.1 millisecond, 400 milliseconds apart). We showed that 50-Hz and 1000-Hz, but not 4-Hz, Aβ-ES (10 μA, 0.1 millisecond, 5 minutes) induced prolonged inhibition of C-fiber eEPSCs in SG neurons in naive mice. Furthermore, 50-Hz Aβ-ES inhibited both monosynaptic and polysynaptic forms of C-fiber eEPSC in naive mice and mice that had undergone spinal nerve ligation (SNL). The paired-pulse ratio (amplitude second eEPSC/first eEPSC) increased only in naive mice after 50-Hz Aβ-ES, suggesting that Aβ-ES may inhibit SG neurons by different mechanisms under naive and nerve-injured conditions. Finally, 50-Hz Aβ-ES inhibited both glutamatergic excitatory and GABAergic inhibitory interneurons, which were identified by fluorescence in vGlut2-Td and glutamic acid decarboxylase-green fluorescent protein transgenic mice after SNL. These findings show that activities in Aβ-fibers lead to frequency-dependent depression of synaptic transmission in SG neurons in response to peripheral noxious inputs. However, 50-Hz Aβ-ES failed to induce cell-type-selective inhibition in SG neurons. The physiologic implication of this novel form of synaptic depression for pain modulation by Aβ-ES warrants further investigation.

Advanced waveforms and frequency with spinal cord stimulation: burst and high-frequency energy delivery

In recent years, software development has been key to the next generation of neuromodulation devices. In this review, we will describe the new strategies for electrical waveform delivery for spinal cord stimulation. A systematic literature review was performed using bibliographic databases, limited to the English language and human data, between 2010 and 2014. The literature search yielded three articles on burst stimulation and four articles on high-frequency stimulation. High-frequency and burst stimulation may offer advantages over tonic stimulation, as data suggest improved patient tolerance, comparable increase in function and possible success with a subset of patients refractory to tonic spinal cord stimulation. High-frequency and burst stimulation are new ways to deliver energy to the spinal cord that may offer advantages over tonic stimulation. These may offer new salvage strategies to mitigate spinal cord stimulation failure and improve cost-effectiveness by reducing explant rate.

Spinal Cord Stimulation for Refractory Neuropathic Pain of Neuralgic Amyotrophy

The aim of this paper was to report the effect of temporary and chronic spinal cord stimulation for refractory neuropathic pain in neuralgic amyotrophy (NA). A 35-year-old female presented with two-months history of a severe, relentless neuropathic pain of the left shoulder, forearm, palm, and fingers. The neuropathic pain was refractory to various medical treatments, including nonsteroidal anti-inflammatory drugs, opiates, epidural and stellate ganglion blocks, and typically unrelenting. The diagnosis of NA was made with the characteristic clinical history and magnetic resonance imaging. The patient underwent a temporary spinal cord stimulation to achieve an adequate pain relief because her pain was notoriously difficult to control and lasted longer than the average duration (about 4 weeks on average) of a painful phase of NA. Permanent stimulation was given with paddle lead. The neuropathic pain in her NA persisted and she continued using the spinal cord stimulation with 12 months after development of NA. The temporary spinal cord stimulation was effective in a patient with an extraordinary prolonged, acute painful phase of NA attack, and the subsequent chronic stimulation was also useful in achieving an adequate analgesia during the chronic phase of NA.

The role of the dorsolateral funiculi in the pain relieving effect of spinal cord stimulation: a study in a rat model of neuropathic pain

Activation of the dorsal columns is relayed to supraspinal centers, involved in pain modulation, probably via the descending fibers in the dorsolateral funiculi (DLF). The present study examines the role of the DLF in the attenuation of pain-related signs by spinal cord stimulation (SCS). Several groups of rats were subjected to nerve injury and to chronic bilateral DLF lesions at C5-7 level. In each animal, two sets of miniature electrodes were implanted, a caudal system placed in the dorsal epidural space at low thoracic level and another implanted over the dorsal column nuclei, rostral to the lesions. Stimulation (50 Hz, 0.2 ms; 70 % of motor threshold) was applied for 5 min via either of the electrodes. Behavioral tests were used to assess the effects of SCS on the nerve injury-induced mechanical and cold hypersensitivity and heat hyperalgesia. Prior to application of SCS, antagonists to either of GABAA or B, 5-HT1 or 1-2 or α/β-adrenergic receptors were injected i.p. Both stimulations produced comparable decreases (80-90 % of the control) of neuropathic manifestations in rats with intact spinal cords. DLF lesions attenuated the effects of both types of stimulation by about 50 %. Pretreatment with receptor antagonists differentially counteracted the effects of rostral and caudal stimulation; the inhibition with rostral stimulation generally being more prominently influenced. These results provide further support to the notion of important involvement of brainstem pain modulating centers in the effects of SCS. A major component of the inhibitory spinal-supraspinal-spinal loop is mediated by fibers running in the DLF.

[Spinal cord stimulation and failed back surgery syndrome. Clinical results with laminectomy electrodes]

INTRODUCTION

Spinal cord stimulation is a widely-accepted technique in the treatment of back pain resulting from failed back surgery. Classically, stimulation has been carried out with percutaneous electrodes implanted under local anaesthesia and sedation. However, the ease of migration and the difficulty of reproducing electrical paresthesias in large areas with such electrodes has led to increasing use of surgical plate leads, which have the disadvantage of the need for general anaesthesia and a laminectomy for implantation.

OBJECTIVES

Our objective was to report the clinical results, technical details, advantages and benefits of laminectomy lead placement under epidural anaesthesia in failed back surgery syndrome cases.

MATERIAL AND METHODS

Spinal cord stimulation was performed in a total of 119 patients (52 men and 67 women), aged between 31 and 73 years (average, 47.3). Epidural anaesthesia was induced with ropivacaine. In all cases we inserted the octapolar or 16-polar lead in the epidural space through a small laminectomy. The final position of the leads was the vertebral level that provided coverage of the patient's pain. The electrodes were connected at dual-channel or rechargeable pulse generators.

RESULTS

After a mean follow-up of 4.7 years, the results in terms of improvement of the previous painful situation was satisfactory, with an analgesia level of 58% of axial pain and 60% of radicular pain in more than 70% of cases. None of the patients said that the surgery stage was painful or unpleasant. No serious complications were included in the group, but in 6 cases the system had to be explanted because of ineffectiveness or intolerance of long-term neurostimulation.

CONCLUSIONS

This study, with a significant number of patients, used epidural anaesthesia for spinal cord stimulation of lead implants by laminectomy in failed back surgery syndromes. The technique seems to be safe and effective.

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.

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.

Mechanism of dorsal column stimulation to treat neuropathic but not nociceptive pain: analysis with a computational model

OBJECTIVE

Stimulation of axons within the dorsal columns of the human spinal cord has become a widely used therapy to treat refractory neuropathic pain. The mechanisms have yet to be fully elucidated and may even be contrary to standard "gate control theory." Our hypothesis is that a computational model provides a plausible description of the mechanism by which dorsal column stimulation (DCS) inhibits wide dynamic range (WDR) cell output in a neuropathic model but not in a nociceptive pain model.

MATERIALS AND METHODS

We created a computational model of the human spinal cord involving approximately 360,000 individual neurons and dendritic processing of some 60 million synapses--the most elaborate dynamic computational model of the human spinal cord to date. Neuropathic and nociceptive "pain" signals were created by activating topographically isolated regions of excitatory interneurons and high-threshold nociceptive fiber inputs, driving analogous regions of WDR neurons. Dorsal column fiber activity was then added at clinically relevant levels (e.g., Aβ firing rate between 0 and 110 Hz by using a 210-μsec pulse width, 50-150 Hz frequency, at 1-3 V amplitude).

RESULTS

Analysis of the nociceptive pain, neuropathic pain, and modulated circuits shows that, in contradiction to gate control theory, 1) nociceptive and neuropathic pain signaling must be distinct, and 2) DCS neuromodulation predominantly affects the neuropathic signal only, inhibiting centrally sensitized pathological neuron groups and ultimately the WDR pain transmission cells.

CONCLUSION

We offer a different set of necessary premises than gate control theory to explain neuropathic pain inhibition and the relative lack of nociceptive pain inhibition by using retrograde DCS. Hypotheses regarding not only the pain relief mechanisms of DCS were made but also regarding the circuitry of pain itself, both nociceptive and neuropathic. These hypotheses and further use of the model may lead to novel stimulation paradigms.

Spinal cord stimulation reduces mechanical hyperalgesia and glial cell activation in animals with neuropathic pain

BACKGROUND

Spinal cord stimulation (SCS) is commonly used for neuropathic pain; the optimal variables and mechanisms of action are unclear. We tested whether modulation of SCS variables improved analgesia in animals with neuropathic pain by comparing 6-hour vs 30-minute duration and 50%, 75%, or 90% motor threshold (MT) intensity (amplitude). Furthermore, we examined whether maximally effective SCS reduced glial activation in the spinal cord in neuropathic animals.

METHODS

Sprague-Dawley rats received the spared nerve injury model and were implanted with an epidural SCS lead. Animals were tested for mechanical withdrawal threshold of the paw before and 2 weeks after spared nerve injury, before and after SCS daily for 4 days, and 1, 4, and 9 days after SCS. Spinal cords were examined for the effects of SCS on glial cell activation.

RESULTS

The mechanical withdrawal threshold decreased, and glial immunoreactivity increased 2 weeks after spared nerve injury. For duration, 6-hour SCS significantly increased the mechanical withdrawal threshold when compared with 30-minute SCS or sham SCS; 30-minute SCS was greater than sham SCS. For intensity (amplitude), 90% MT SCS significantly increased the withdrawal threshold when compared with 75% MT SCS, 50% MT SCS, and sham SCS. Both 4 and 60 Hz SCS decreased glial activation (GFAP, MCP-1, and OX-42) in the spinal cord dorsal horn when compared with sham.

CONCLUSIONS

Six-hour duration SCS with 90% MT showed the largest increase in mechanical withdrawal threshold, suggesting that the variables of stimulation are important for clinical effectiveness. One potential mechanism for SCS may be to reduce glial activation at the level of the spinal cord.

Comparison of intensity-dependent inhibition of spinal wide-dynamic range neurons by dorsal column and peripheral nerve stimulation in a rat model of neuropathic pain

BACKGROUND

Spinal cord stimulation (SCS) and peripheral nerve stimulation (PNS) are thought to reduce pain by activating a sufficient number of large myelinated (Aβ) fibres, which in turn initiate spinal segmental mechanisms of analgesia. However, the volume of neuronal activity and how this activity is associated with different treatment targets is unclear under neuropathic pain conditions.

METHODS

We sought to delineate the intensity-dependent mechanisms of SCS and PNS analgesia by in vivo extracellular recordings from spinal wide-dynamic range neurons in nerve-injured rats. To mimic therapeutic SCS and PNS, we used bipolar needle electrodes and platinum hook electrodes to stimulate the dorsal column and the tibial nerve, respectively. Compound action potentials were recorded to calibrate the amplitude of conditioning stimulation required to activate A-fibres and thus titrate the volume of activation.

RESULTS

Dorsal column stimulation (50 Hz, five intensities) inhibited the windup (a short form of neuronal sensitization) and the C-component response of wide-dynamic range neurons to graded intracutaneous electrical stimuli in an intensity-dependent manner. Tibial nerve stimulation (50 Hz, three intensities) also suppressed the windup in an intensity-dependent fashion but did not affect the acute C-component response.

CONCLUSIONS

SCS and PNS may offer similar inhibition of short-term neuronal sensitization. However, only SCS attenuates spinal transmission of acute noxious inputs under neuropathic pain conditions. Our findings begin to differentiate peripheral from spinal-targeted neuromodulation therapies and may help to select the best stimulation target and optimum therapeutic intensity for pain treatment.

Factors associated with the success of trial spinal cord stimulation in patients with chronic pain from failed back surgery syndrome

OBJECTIVE

Spinal cord stimulation (SCS) is an effective means of treatment of chronic neuropathic pain from failed back surgery syndrome (FBSS). Because the success of trial stimulation is an essential part of SCS, we investigated factors associated with success of trial stimulation.

METHODS

Successful trial stimulation was possible in 26 of 44 patients (63.6%) who underwent insertion of electrodes for the treatment of chronic pain from FBSS. To investigate factors associated with successful trial stimulation, patients were classified into two groups (success and failure in trial). We investigated the following factors : age, sex, predominant pain areas (axial, limb, axial combined with limbs), number of operations, duration of preoperative pain, type of electrode (cylindrical/paddle), predominant type of pain (nociceptive, neuropathic, mixed), degree of sensory loss in painful areas, presence of motor weakness, and preoperative Visual Analogue Scale.

RESULTS

There were no significant differences between the two groups in terms of age, degree of pain, number of operations, and duration of pain (p>0.05). Univariate analysis revealed that the type of electrode and presence of severe sensory deficits were significantly associated with the success of trial stimulation (p<0.05). However, the remaining variable, sex, type of pain, main location of pain, degree of pain duration, degree of sensory loss, and presence of motor weakness, were not associated with the trial success of SCS for FBSS.

CONCLUSION

Trial stimulation with paddle leads was more successful. If severe sensory deficits occur in the painful dermatomes in FBSS, trial stimulation were less effective.

Conventional and kilohertz-frequency spinal cord stimulation produces intensity- and frequency-dependent inhibition of mechanical hypersensitivity in a rat model of neuropathic pain

BACKGROUND

Spinal cord stimulation (SCS) is a useful neuromodulatory technique for treatment of certain neuropathic pain conditions. However, the optimal stimulation parameters remain unclear.

METHODS

In rats after L5 spinal nerve ligation, the authors compared the inhibitory effects on mechanical hypersensitivity from bipolar SCS of different intensities (20, 40, and 80% motor threshold) and frequencies (50, 1 kHz, and 10 kHz). The authors then compared the effects of 1 and 50 Hz dorsal column stimulation at high- and low-stimulus intensities on conduction properties of afferent Aα/β-fibers and spinal wide-dynamic-range neuronal excitability.

RESULTS

Three consecutive daily SCS at different frequencies progressively inhibited mechanical hypersensitivity in an intensity-dependent manner. At 80% motor threshold, the ipsilateral paw withdrawal threshold (% preinjury) increased significantly from pre-SCS measures, beginning with the first day of SCS at the frequencies of 1 kHz (50.2 ± 5.7% from 23.9 ± 2.6%, n = 19, mean ± SEM) and 10 kHz (50.8 ± 4.4% from 27.9 ± 2.3%, n = 17), whereas it was significantly increased beginning on the second day in the 50 Hz group (38.9 ± 4.6% from 23.8 ± 2.1%, n = 17). At high intensity, both 1 and 50 Hz dorsal column stimulation reduced Aα/β-compound action potential size recorded at the sciatic nerve, but only 1 kHz stimulation was partially effective at the lower intensity. The number of actions potentials in C-fiber component of wide-dynamic-range neuronal response to windup-inducing stimulation was significantly decreased after 50 Hz (147.4 ± 23.6 from 228.1 ± 39.0, n = 13), but not 1 kHz (n = 15), dorsal column stimulation.

CONCLUSIONS

Kilohertz SCS attenuated mechanical hypersensitivity in a time course and amplitude that differed from conventional 50 Hz SCS, and may involve different peripheral and spinal segmental mechanisms.

Neural mechanisms of spinal cord stimulation

Neuromodulation, specifically spinal cord stimulation (SCS), relieves pain and improves organ function. This chapter discusses the limited information presently available about the underlying mechanisms that explain the beneficial effects of treating patients with SCS. Where applicable, information is presented about translational research that illustrates the importance of collaboration between clinicians, basic scientists, and engineers. This chapter presents the infant stage of studies that attempt to explain the mechanisms which come into play for treating neuropathic pain, ischemic pain in peripheral vascular disease, and diseases of the visceral organs, specifically the gastrointestinal tract and the heart. The basic science studies will demonstrate how SCS acts on various pain syndromes and diseases via multiple pathways in the central nervous system as well as in somatic structures and visceral organs.

Safe direct current stimulation to expand capabilities of neural prostheses

While effective in treating some neurological disorders, neuroelectric prostheses are fundamentally limited because they must employ charge-balanced stimuli to avoid evolution of irreversible electrochemical reactions and their byproducts at the interface between metal electrodes and body fluids. Charge-balancing is typically achieved by using brief biphasic alternating current (AC) pulses, which typically excite nearby neural tissues but cannot efficiently inhibit them. In contrast, direct current (DC) applied via a metal electrode in contact with body fluids can excite, inhibit and modulate sensitivity of neurons; however, chronic DC stimulation is incompatible with biology because it violates charge injection limits that have long been considered unavoidable. In this paper, we describe the design and fabrication of a Safe DC Stimulator (SDCS) that overcomes this constraint. The SCDS drives DC ionic current into target tissue via salt-bridge micropipette electrodes by switching valves in phase with AC square waves applied to metal electrodes contained within the device. This approach achieves DC ionic flow through tissue while still adhering to charge-balancing constraints at each electrode-saline interface. We show the SDCS's ability to both inhibit and excite neural activity to achieve improved dynamic range during prosthetic stimulation of the vestibular part of the inner ear in chinchillas.

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.

Qualitative exploration of psychological factors associated with spinal cord stimulation outcome

BACKGROUND AND AIM

Spinal cord stimulation (SCS) is a last resort treatment for chronic pain consisting of an implantable pulse generator connected to leads placed in the epidural space of the spinal cord. Effective in reducing chronic pain, however, efficacy has been found to decrease over time. Psychological factors affecting outcome of SCS have been investigated through quantitative methods, but these have failed to provide confident predictors. We aimed to investigate via a qualitative approach, the experience of SCS following 1 year of therapy.

METHODS

Thirteen chronic non-cancer pain participants were interviewed. All participants had been trialled with SCS. The majority had gone on to full implantation with varying degrees of pain relief. Thematic analysis was employed to analyse the data from the interviews.

RESULTS

Interviews resulted in findings that previous quantitative studies had failed to uncover. Two emergent core themes surfaced: 'coping with pain' and 'SCS treatment'. The effect of emotion upon coping was recurrent. Participants divided the SCS experience into information provision, independence and unexpected experiences.

CONCLUSION

The findings provide context for the patients' experience of SCS. This research suggests that improved preparation prior to SCS including information provision, CBT and contact with expert patients may be of value.

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: neurophysiological and neurochemical mechanisms of action

Chronic neuropathic pain can significantly reduce quality of life and place an economic burden on individuals and society. Spinal cord stimulation (SCS) is an alternative approach to the treatment of neuropathic pain when standard pharmacological agents have failed. However, an improved understanding of the mechanisms by which SCS inhibits pain is needed to enhance its clinical utility. This review summarizes important findings from recent studies of SCS in animal models of neuropathic pain, highlights current understanding of the spinal neurophysiological and neurochemical mechanisms by which SCS produces an analgesic effect, and discusses the potential clinical applicability of these findings and future directions for research.

Spinal cord stimulation modulates cerebral function: an fMRI study

INTRODUCTION

Although spinal cord stimulation (SCS) is widely used for chronic neuropathic pain after failed spinal surgery, little is known about the underlying physiological mechanisms. This study aims to investigate the neural substrate underlying short-term (30 s) SCS by means of functional magnetic resonance imaging in 20 patients with failed back surgery syndrome (FBSS).

METHODS

Twenty patients with FBSS, treated with externalized SCS, participated in a blocked functional magnetic resonance imaging design with stimulation and rest phases of 30 s each, repeated eight times in a row. During scanning, patients rated pain intensity over time using an 11-point numerical rating scale with verbal anchors (0 = no pain at all to 10 = worst pain imaginable) by pushing buttons (left hand, lesser pain; right hand, more pain). This scale was back projected to the patients on a flat screen allowing them to manually direct the pain indicator. To increase the signal-to-noise ratio, the 8-min block measurements were repeated three times.

RESULTS

Marked deactivation of the bilateral medial thalamus and its connections to the rostral and caudal cingulate cortex and the insula was found; the study also showed immediate pain relief obtained by short-term SCS correlated negatively with activity in the inferior olivary nucleus, the cerebellum, and the rostral anterior cingulate cortex.

CONCLUSIONS

Results indicate the key role of the medial thalamus as a mediator and the involvement of a corticocerebellar network implicating the modulation and regulation of averse and negative affect related to pain. The observation of a deactivation of the ipsilateral antero-medial thalamus might be used as a region of interest for further response SCS studies.

Spinal cord stimulation in adolescents with complex regional pain syndrome type I (CRPS-I)

Complex regional pain syndrome type I (CRPS-I) is not uncommon in children, particularly in adolescent girls. Most often, the condition involves a foot and is characterized by spontaneous pain, tactile allodynia and dysautonomic signs. There is usually a history of a minor, local trauma but sometimes no reasonable cause can be identified, and there are no signs of persistent tissue injury giving rise to ongoing nociception. Common analgesics are generally of no benefit, and the standard treatment includes sociopsychological support, physiotherapy, tricyclic antidepressants and antiepileptic drugs, sympathetic blocks (SB), and cognitive-behavioural therapy. For a minority of patients who prove to be resistant to such therapies, spinal cord stimulation (SCS) may be tried. The present study comprises seven girls, 11-14 years of age, presenting with severe, incapacitating and therapy-resistant CRPS-I, who were subjected to SCS. In two of them, percutaneous electrode implantation had to be performed in general anaesthesia. Trial stimulation was performed in all, but one. In two cases, it was not possible to produce paraesthesias that entirely covered the pain area. A pain relieving effect of SCS was usually not reported until after 1-2 weeks of trial stimulation. After another 2-6 weeks, pain alleviation was complete in five of the seven patients, one to eight years after the intervention. In one case, a local infection necessitated the removal of the electrode; nevertheless a few days of trial stimulation produced substantial pain relief that still persists. In four patients, the SCS use was gradually diminished and eventually the device could be removed. The favourable outcome in all seven cases with no or minor remaining symptoms and without severe recurrences illustrates that SCS may also be an efficient treatment in paediatric cases with exceptionally therapy resistant forms of CRPS 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.

One-time-implantable spinal cord stimulation system prototype

A prototype of a one-time-implantable spinal cord stimulation (SCS) system using wireless power and data-transmission techniques is presented in this paper. The power of the implant is induced by wireless coil coupling, and duplex amplitude-shift keying-load-shift keying wireless communication is used so that digital packets can be transmitted by the same inductive link. The proposed novel ASK demodulator attains high demodulation performance and small area without using any resistors and capacitors. The proposed SCS system utilizes many power saving schemes to reduce power dissipation (e.g., dual supply voltages on-chip, high-voltage impulse generation using small current, etc.). Meanwhile, the excess energy induced by the coils is stored in a rechargeable battery to extend the implant's operation time so that the number of battery replacement surgeries will be reduced significantly. The system-on-chip (SOC) is physically implemented on silicon and integrated in the implant as the system controller. The fabricated SOC area is 1410 × 1710 μm(2). Compared with existing commercial products, the proposed SCS system attains better flexibility and longer operation time.

Electrical modalities beyond pacing for the treatment of heart failure

In this review, we report on electrical modalities, which do not fit the definition of pacemaker, but increase cardiac performance either by direct application to the heart (e.g., post-extrasystolic potentiation or non-excitatory stimulation) or indirectly through activation of the nervous system (e.g., vagal or sympathetic activation). The physiological background of the possible mechanisms of these electrical modalities and their potential application to treat heart failure are discussed.

Pain mechanisms: a commentary on concepts and issues

This commentary on ideas about neural mechanisms underlying pain is aimed at providing perspective for a reader who does not work in the field of mammalian somatic sensation. It is not a comprehensive review of the literature. The organization is historical to chronicle the evolution of ideas. The aim is to call attention to source of concepts and how various ideas have fared over time. One difficulty in relating concepts about pain is that the term is used to refer to human and animal reactions ranging from protective spinal reflexes to complex affective behaviors. As a result, the spectrum of "pain"-related neural organization extends to operation of multiple neuronal arrangements. Thinking about pain has shadowed progress in understanding biological mechanisms, in particular the manner of function of nervous systems. This essay concentrates on the evolution of information and concepts from the early 19th century to the present. Topics include the assumptions underlying currently active theories about pain mechanisms. At the end, brief consideration is given to present-day issues, e.g., chronic pain, central pain, and the view of pain as an emotion rather than a sensation. The conceptual progression shows that current controversies have old roots and that failed percepts often resurface after seemingly having been put to rest by argument and evidence.

Spinal cord stimulation as a novel approach to the treatment of refractory neuropathic mediastinal pain

Spinal cord stimulation (SCS) offers new hope for patients with neuropathic pain. SCS "neuromodulates" the transmission and response to "painful" stimuli. The efficacy of SCS has been established in the treatment of a variety of neuropathic pain conditions and more recently in refractory angina pectoris, peripheral vascular disease, and failed back surgery syndrome. Recent publications suggest that visceral pain could be successfully treated with SCS. We report the first successful use of a spinal cord stimulator in the treatment of refractory neuropathic mediastinal, esophageal, and anterior neck pain following esophagogastrectomy.

Nociceptive behavior in animal models for peripheral neuropathy: spinal and supraspinal mechanisms

Since the initial description by Wall [Wall, P.D., 1967. The laminar organization of dorsal horn and effects of descending impulses. J. Neurophysiol. 188, 403-423] of tonic descending inhibitory control of dorsal horn neurons, several studies have aimed to characterize the role of various brain centers in the control of nociceptive input to the spinal cord. The role of brainstem centers in pain inhibition has been well documented over the past four decades. Lesion to peripheral nerves results in hypersensitivity to mild tactile or cold stimuli (allodynia) and exaggerated response to nociceptive stimuli (hyperalgesia), both considered as cardinal signs of neuropathic pain. The increased interest in animal models for peripheral neuropathy has raised several questions concerning the rostral conduction of the neuropathic manifestations and the role of supraspinal centers, especially brainstem, in the inhibitory control or in the abnormal contribution to the maintenance and facilitation of neuropathic-like behavior. This review aims to summarize the data on the ascending and descending modulation of neuropathic manifestations and discusses the recent experimental data on the role of supraspinal centers in the control of neuropathic pain. In particular, the review emphasizes the importance of the reciprocal interconnections between the analgesic areas of the brainstem and the pain-related areas of the forebrain. The latter includes the cerebral limbic areas, the prefrontal cortex, the intralaminar thalamus and the hypothalamus and play a critical role in the control of pain considered as part of an integrated behavior related to emotions and various homeostatic regulations. We finally speculate that neuropathic pain, like extrapyramidal motor syndromes, reflects a disorder in the processing of somatosensory information.

Low frequencies, but not high frequencies of bi-polar spinal cord stimulation reduce cutaneous and muscle hyperalgesia induced by nerve injury

Spinal cord stimulation (SCS) is an established treatment for neuropathic pain. However, SCS is not effective for all the patients and the mechanisms underlying the reduction in pain by SCS are not clearly understood. To elucidate the mechanisms of pain relief by SCS, we utilized the spared nerve injury model. Sprague-Dawley rats were anesthetized, the tibial and common peroneal nerves were tightly ligated, and an epidural SCS lead implanted in the upper lumbar spinal cord. SCS was delivered daily at one of 4 different frequencies (4Hz, 60Hz, 100Hz, and 250Hz) at approximately 85% of motor threshold 2 weeks after nerve injury for 4 days. Mechanical withdrawal threshold of the paw and compression withdrawal threshold of the hamstring muscles were measured before and after SCS on each day. All rats showed a decrease in withdrawal threshold of the paw and the muscle 2 weeks after nerve injury. Treatment with either 4Hz or 60Hz SCS significantly reversed the decreased withdrawal threshold of the paw and muscle. The effect was cumulative with a greater reversal by the fourth treatment when compared to the first treatment. Treatment with 100Hz, 250Hz or sham SCS had no significant effect on the decreased withdrawal threshold of the paw or muscle that normally occurs after nerve injury. In conclusion, SCS at 4Hz and 60Hz was more effective in reducing hyperalgesia than higher frequencies of SCS (100Hz and 250Hz); and repeated treatments result in a cumulative reduction in hyperalgesia.

Spinal GABAergic Transplants Attenuate Mechanical Allodynia in a Rat Model of Neuropathic Pain

Injury to the spinal cord or peripheral nerves can lead to the development of allodynia due to the loss of inhibitory tone involved in spinal sensory function. The potential of intraspinal transplants of GABAergic cells to restore inhibitory tone and thus decrease pain behaviors in a rat model of neuropathic pain was investigated. Allodynia of the left hind paw was induced in rats by unilateral L5- 6 spinal nerve root ligation. Mechanical sensitivity was assessed using von Frey filaments. Postinjury, transgenic fetal green fluorescent protein mouse GABAergic cells or human neural precursor cells (HNPCs) expanded in suspension bioreactors and differentiated into a GABAergic phenotype were transplanted into the spinal cord. Control rats received undifferentiated HNPCs or cell suspension medium only. Animals that received either fetal mouse GABAergic cell or differentiated GABAergic HNPC intraspinal transplants demonstrated a significant increase in paw withdrawal thresholds at 1 week post-transplantation that was sustained for 6 weeks. Transplanted fetal mouse GABAergic cells demonstrated immunoreactivity for glutamic acid decarboxylase and GABA that colocalized with green fluorescent protein. Intraspinally transplanted differentiated GABAergic HNPCs demonstrated immunoreactivity for GABA and beta-III tubulin. In contrast, intraspinal transplantation of undifferentiated HNPCs, which predominantly differentiated into astrocytes, or cell suspension medium did not affect any behavioral recovery. Intraspinally transplanted GABAergic cells can reduce allodynia in a rat model of neuropathic pain. In addition, HNPCs expanded in a standardized fashion in suspension bioreactors and differentiated into a GABAergic phenotype may be an alternative to fetal cells for cell-based therapies to treat chronic pain syndromes.