Spinal Cord Stimulation Attenuates Below-Level Mechanical Hypersensitivity in Rats After Thoracic Spinal Cord Injury

Characterization of preclinical models to investigate spinal cord stimulation for neuropathic pain: a systematic review and meta-analysis

Despite advancements in preclinical and clinical spinal cord stimulation (SCS) research, the mechanisms of SCS action remain unclear. This may result from challenges in translatability of findings between species. Our systematic review (PROSPERO: CRD42023457443) aimed to comprehensively characterize the important translational components of preclinical SCS models, including stimulating elements and stimulation specifications. Databases (Embase, PubMed, Web of Science, and WikiStim) were searched on October 5, 2023, identifying 78 studies meeting the search criteria. We conducted a post hoc meta-analysis, including subgroup analyses and meta-regression, to assess SCS efficacy on mechanical hypersensitivity in rats subjected to neuropathic pain. Although monopolar electrodes were predominantly used as stimulating elements until 2013, quadripolar paddle and cylindrical leads gained recent popularity. Most research was conducted using 50 Hz and 200 µs stimulation. Motor threshold (MT) estimation was the predominant strategy to determine SCS intensity, which was set to 71.9% of MT on average. Our analysis revealed a large effect size for SCS (Hedge g = 1.13, 95% CI: [0.93, 1.32]) with similar magnitudes of effect between conventional (≤100 Hz) and nonconventional SCS paradigms while sham SCS had nonsignificant effect size. In addition, different stimulation intensity, frequency, and electrode design did not affect effect size. The risk of bias was assessed using Systematic Review Centre for Laboratory animal Experimentation criteria and was unclear, and only the frequency subgroup analysis showed publication bias. In summary, our review characterizes the critical components of preclinical SCS models and provides recommendations to improve reproducibility and translatability, thereby advancing the scientific foundation for SCS research.

Intraspinal microstimulation of the ventral horn has therapeutically relevant cross-modal effects on nociception

Electrical stimulation of spinal networks below a spinal cord injury is a promising approach to restore functions compromised by inadequate and/or inappropriate neural drive. The most translationally successful examples are paradigms intended to increase neural transmission in weakened yet spared descending motor pathways and spinal motoneurons rendered dormant after being severed from their inputs by lesion. Less well understood is whether spinal stimulation is also capable of reducing neural transmission in pathways made pathologically overactive by spinal cord injury. Debilitating spasms, spasticity and neuropathic pain are all common manifestations of hyperexcitable spinal responses to sensory feedback. Whereas spasms and spasticity can often be managed pharmacologically, spinal cord injury-related neuropathic pain is notoriously medically refractory. Interestingly, however, spinal stimulation is a clinically available option for ameliorating neuropathic pain arising from aetiologies other than spinal cord injury, and the limited evidence available to date suggests that it holds considerable promise for reducing spinal cord injury-related neuropathic pain, as well. Spinal stimulation for pain amelioration has traditionally been assumed to modulate sensorimotor networks overlapping with those engaged by spinal stimulation for rehabilitation of movement impairments. Thus, we hypothesize that spinal stimulation intended to increase the ability to move voluntarily may simultaneously reduce transmission in spinal pain pathways. To test this hypothesis, we coupled a rat model of incomplete thoracic spinal cord injury, which results in moderate to severe bilateral movement impairments and spinal cord injury-related neuropathic pain, with in vivo electrophysiological measures of neural transmission in networks of spinal neurons integral to the development and persistence of the neuropathic pain state. We find that when intraspinal microstimulation is delivered to the ventral horn with the intent of enhancing voluntary movement, transmission through nociceptive specific and wide dynamic range neurons is significantly depressed in response to pain-related sensory feedback. By comparison, spinal responsiveness to non-pain-related sensory feedback is largely preserved. These results suggest that spinal stimulation paradigms could be intentionally designed to afford multi-modal therapeutic benefits, directly addressing the diverse, intersectional rehabilitation goals of people living with spinal cord injury.

Fully Implantable Neurostimulation System for Long-Term Behavioral Animal Study

Spinal cord stimulation (SCS) is an emerging therapeutic option for patients with neuropathic pain due to spinal cord injury (SCI). Numerous studies on pain relief effects with SCS have been conducted and demonstrated promising results while the mechanisms of analgesic effect during SCS remain unclear. However, an experimental system that enables large-scale long-term animal studies is still an unmet need for those mechanistic studies. This study proposed a fully wireless neurostimulation system that can efficiently support a long-term animal study for neuropathic pain relief. The developed system consists of an implantable stimulator, an animal cage with an external charging coil, and a wireless communication interface. The proposed device has the feature of remotely controlling stimulation parameters via radio-frequency (RF) communication and wirelessly charging via magnetic induction in freely moving rats. Users can program stimulation parameters such as pulse width, intensity, and duration through an interface on a computer. The stimulator was packaged with biocompatible epoxy to ensure long-term durability under in vivo conditions. Animal experiments using SCI rats were conducted to demonstrate the functionality of the device, including long-term usability and therapeutic effects. The developed system can be tailored to individual user needs with commercially available components, thus providing a cost-effective solution for large-scale long-term animal studies on neuropathic pain relief.

Differential target multiplexed spinal cord stimulation using a paddle-type lead placed at the appropriate site for neuropathic pain after spinal cord injury in patients with past spinal surgical histories: study protocol for an exploratory clinical trial

BACKGROUND

Neuropathic pain after spinal cord injury (SCI), both traumatic and non-traumatic, is refractory to various treatments. Spinal cord stimulation (SCS) is one of the neuromodulation therapies for neuropathic pain, although SCS has insufficient efficacy for neuropathic pain after SCI. The reasons are presumed to be inappropriate locations of SCS leads and conventional tonic stimulation itself does not have a sufficient analgesic effect for the pain. In patients with past spinal surgical histories, the cylinder-type leads are likely to be placed on the caudal side of the SCI because of surgical adhesions. Differential target multiplexed (DTM) stimulation is one of the latest new stimulation patterns that is superior to conventional stimulation.

METHODS

A single-center, open-label, randomized, two-way crossover trial is planned to investigate the efficacy of SCS using DTM stimulation placing a paddle lead at the appropriate site for neuropathic pain after SCI in patients with spinal surgical histories. The paddle-type lead delivers energy more efficiently than a cylinder-type lead. This study consists of two steps: SCS trial (first step) and SCS system implantation (second step). The primary outcome is rates of achieving pain improvement with more than 33% reduction 3 months after SCS system implantation. The secondary outcomes are to be evaluated as follows: (1) effectiveness of DTM and tonic stimulations during the SCS trial; (2) changes of assessment items from 1 to 24 months; (3) relationships between the result of the SCS trial and the effects 3 months after SCS system implantation; (4) preoperative factors associated with a long-term effect, defined as continuing for more than 12 months; and (5) whether gait function improves from 1 to 24 months.

DISCUSSION

A paddle-type lead placed on the rostral side of SCI and using DTM stimulation may provide significant pain relief for patients with intractable neuropathic pain after SCI in patients with past spinal surgical histories.

TRIAL REGISTRATION

Japan Registry of Clinical Trials (jRCT) jRCT 1042220093. Registered on 21 November 2022, and last modified on 6 January 2023. jRCT is approved as a member of the Primary Registry Network of WHO ICTRP.

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

Background

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

Methods

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

Results

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

Conclusion

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

Motor-targeted spinal stimulation promotes concurrent rebalancing of pathologic nociceptive transmission in chronic spinal cord injury

Electrical stimulation of spinal networks below a spinal cord injury (SCI) is a promising approach to restore functions compromised by inadequate excitatory neural drive. The most translationally successful examples are paradigms intended to increase neural transmission in weakened yet spared motor pathways and spinal motor networks rendered dormant after being severed from their inputs by lesion. Less well understood is whether spinal stimulation is also capable of reducing neural transmission in pathways made pathologically overactive by SCI. Debilitating spasms, spasticity, and neuropathic pain are all common manifestations of hyperexcitable spinal responses to sensory feedback. But whereas spasms and spasticity can often be managed pharmacologically, SCI-related neuropathic pain is notoriously medically refractory. Interestingly, however, spinal stimulation is a clinically available option for ameliorating neuropathic pain arising from etiologies other than SCI, and it has traditionally been assumed to modulate sensorimotor networks overlapping with those engaged by spinal stimulation for motor rehabilitation. Thus, we reasoned that spinal stimulation intended to increase transmission in motor pathways may simultaneously reduce transmission in spinal pain pathways. Using a well-validated pre-clinical model of SCI that results in severe bilateral motor impairments and SCI-related neuropathic pain, we show that the responsiveness of neurons integral to the development and persistence of the neuropathic pain state can be enduringly reduced by motor-targeted spinal stimulation while preserving spinal responses to non-pain-related sensory feedback. These results suggest that spinal stimulation paradigms could be intentionally designed to afford multi-modal therapeutic benefits, directly addressing the diverse, intersectional rehabilitation goals of people living with SCI.

Steering Toward Normative Wide-Dynamic-Range Neuron Activity in Nerve-Injured Rats With Closed-Loop Peripheral Nerve Stimulation

OBJECTIVES

Chronic pain is primarily treated with pharmaceuticals, but the effects remain unsatisfactory. A promising alternative therapy is peripheral nerve stimulation (PNS), but it has been associated with suboptimal efficacy because its modulation mechanisms are not clear and the current therapies are primarily open loop (ie, manually adjusting the stimulation parameters). In this study, we developed a proof-of-concept computational modeling as the first step toward implementing closed-loop PNS in future biological studies. When developing new pain therapies, a useful pain biomarker is the wide-dynamic-range (WDR) neuron activity in the dorsal horn. In healthy animals, the WDR neuron activity occurs in a stereotyped manner; however, this response profile can vary widely after nerve injury to create a chronic pain condition. We hypothesized that if injury-induced changes of neuronal response can be normalized to resemble those of a healthy condition, the pathological aspects of pain may be treated while maintaining protective physiological nociception.

MATERIALS AND METHODS

Using an in vivo electrophysiology data set of WDR neuron recordings obtained in nerve-injured rats and naïve rats, we constructed sets of linear phenomenologic models of WDR firing rate during windup stimulation for both conditions. Then, we applied robust control systems techniques to identify a closed-loop PNS controller, which can drive the dynamics of WDR neuron response in neuropathic pain model into ranges associated with normal physiological pain.

RESULTS

The sets of identified linear models can accurately predict, in silico, nonlinear neural responses to electrical stimulation of the peripheral nerve. In addition, we showed that continuous closed-loop control of PNS can be used to normalize WDR neuron firing responses in three injured cases.

CONCLUSIONS

In this proof-of-concept study, we show how tractable, linear mathematical models of pain-related neurotransmission can be used to inform the development of closed-loop PNS. This new application of robust control to neurotechnology may also be expanded and applied across other neuromodulation applications.

Spinal cord stimulation in patients suffering from chronic pain after surgery for spinal intradural tumors: A case report and literature summary

BACKGROUND

The prevalence of pain after treatment of a spinal intradural tumor is remarkably high, approximately up to 40% of the patients suffer from central neuropathic pain. Publications on spinal cord stimulation (SCS) and its effect on pain caused by intradural spinal tumors are rare. We discuss the case of a patient suffering from chronic pain after removal of a Th7 level meningioma who was successfully treated with SCS and give an overview of the literature.

METHODS

MEDLINE database was searched for neuropathic pain and intradural tumors.

RESULTS

The initial search identified 35 articles, including hand-searched manuscripts. Six articles were included for analysis.

CASE REPORT

A 57-year-old female suffers from neuropathic pain in both legs after surgical removal of a Th7 level intradural meningioma. Postoperative magnetic resonance imaging shows no gross abnormalities, although she developed chronic pain in both legs. Pain in combination with side effects of analgesic intake are too disabling to have decent quality of life. A successful implantation of SCS is achieved at Th5 level as a treatment for the central neuropathic pain, and, at 36 months follow-up, there is significant pain relief and almost complete discontinuation of analgesics.

DISCUSSION

Central pain from spinal intradural tumors may have a different mechanism of origin than pain seen after an acute spinal cord injury (SCI). However, the basic principles of neuromodulation are the same in both etiologies, as for successful stimulation intact pathways in the spinal cord are necessary. The efficacy of SCS as treatment in intradural spinal tumors is rarely described as only a handful of case reports are published. Interestingly, the case reports show that stimulation both above and below the lesion can be effective. In patients with incomplete SCI or intradural tumor resection stimulation below the lesion could be considered and tried in a trial setting before definitive implantation.

Spinal stimulation for motor rehabilitation immediately modulates nociceptive transmission

Objective. Spinal cord injury (SCI) often results in debilitating movement impairments and neuropathic pain. Electrical stimulation of spinal neurons holds considerable promise both for enhancing neural transmission in weakened motor pathways and for reducing neural transmission in overactive nociceptive pathways. However, spinal stimulation paradigms currently under development for individuals living with SCI continue overwhelmingly to be developed in the context of motor rehabilitation alone. The objective of this study is to test the hypothesis that motor-targeted spinal stimulation simultaneously modulates spinal nociceptive transmission.Approach. We characterized the neuromodulatory actions of motor-targeted intraspinal microstimulation (ISMS) on the firing dynamics of large populations of discrete nociceptive specific and wide dynamic range (WDR) neurons. Neurons were accessed via dense microelectrode arrays implantedin vivointo lumbar enlargement of rats. Nociceptive and non-nociceptive cutaneous transmission was induced before, during, and after ISMS by mechanically probing the L5 dermatome.Main results. Our primary findings are that (a) sub-motor threshold ISMS delivered to spinal motor pools immediately modulates concurrent nociceptive transmission; (b) the magnitude of anti-nociceptive effects increases with longer durations of ISMS, including robust carryover effects; (c) the majority of all identified nociceptive-specific and WDR neurons exhibit firing rate reductions after only 10 min of ISMS; and (d) ISMS does not increase spinal responsiveness to non-nociceptive cutaneous transmission. These results lead to the conclusion that ISMS parameterized to enhance motor output results in an overall net decrease n spinal nociceptive transmission.Significance. These results suggest that ISMS may hold translational potential for neuropathic pain-related applications and that it may be uniquely suited to delivering multi-modal therapeutic benefits for individuals living with SCI.