Central Neuropathic Pain Syndromes

Usefulness of Mirogabalin in Central Neuropathic Pain After Stroke: Post Hoc Analysis of a Phase 3 Study by Stroke Type and Location

INTRODUCTION

Central post-stroke pain (CPSP) is a common type of central neuropathic pain (CNeP) that can occur following the onset of stroke. The oral gabapentinoid mirogabalin besylate (mirogabalin) is a selective α2δ ligand that is effective for the treatment of CNeP, including CPSP. However, it is unknown whether the analgesic effect of mirogabalin on CPSP varies in patients with different background factors.

METHODS

This was a post hoc subgroup analysis of a multinational, open-label, long-term phase 3 study of mirogabalin for the treatment of CNeP conducted between March 2019 and December 2020. Data from patients with CPSP were stratified by type of stroke (ischemic or hemorrhagic), stroke location (thalamus, putamen, brainstem, or other), presence/absence of motor weakness, median time since stroke (≥ 59 or < 59 months), and median duration of CPSP (≥ 55.5 or < 55.5 months). Efficacy was assessed with the short-form McGill Pain Questionnaire (SF-MPQ), and treatment-emergent adverse events (TEAEs) and adverse drug reactions (ADRs) were recorded.

RESULTS

This subanalysis included all 94 patients with CPSP from the phase 3 study; all were Japanese, and the mean age was 65.3 years. The least squares mean change [95% confidence interval] in SF-MPQ visual analog scale (VAS) score from baseline at week 52 (last observation carried forward) was - 17.0 [- 22.1, - 11.9] mm. Among the subgroups, least squares mean changes in SF-MPQ VAS scores were not different. Most TEAEs were mild or moderate; severe TEAEs occurred in six patients (6.4%). Somnolence (25.5%), peripheral edema (13.8%), dizziness (11.7%), and weight gain (6.4%) were the most common ADRs, and the types and frequencies of ADRs were similar among subgroups.

CONCLUSION

Mirogabalin was generally effective and well tolerated in patients with CPSP, regardless of background factors such as stroke type or location, presence/absence of motor weakness, time since stroke, and duration of CPSP.

TRIAL REGISTRATION

Trial registration number NCT03901352.

Influence of sensory retraining on cortical reorganization in peripheral neuropathy: A systematic review

OBJECTIVE

This study systematically reviewed the literature about sensory retraining effect in comparison to other rehabilitative techniques on cortical reorganization in patients with peripheral neuropathic pain. TYPE: Systematic review.

LITERATURE SURVEY

After an electronic search of PubMed, Web of Science, and Embase, risk of bias was assessed using the revised Cochrane risk of bias tool for randomized controlled trials and the ROBINS-1 (Risk of bias in non-randomized studies-of interventions) for non-randomized studies of intervention.

METHODOLOGY

The strength of conclusion was determined using the evidence-based guideline development approach.

SYNTHESIS

Limited evidence indicates a higher increase in cortical inhibition and a higher reduction in cortical activation during a motor task of the affected hemisphere after graded motor imagery compared to wait-list. Higher reductions in map volume (total excitability of the cortical representation) of the affected hemisphere after peripheral electrical stimulation (PES) were observed when compared to transcranial direct current stimulation (tDCS) or to sham treatment with limited evidence. No other differences in cortical excitability and representation of the affected and non-affected hemisphere were observed when comparing mirror therapy with sham therapy or tDCS, PES with sham therapy or tDCS, and graded motor imagery with wait-list.

CONCLUSIONS

Graded motor imagery and PES result in higher cortical excitability reductions of the affected hemisphere compared to wait-list, tDCS and sham treatment, respectively.

Smart Response Biomaterials for Pain Management

The intricate nature of pain classification and mechanism constantly affects the recovery of diseases and the well-being of patients. Key medical challenges persist in devising effective pain management strategies. Therefore, a comprehensive review of relevant methods and research advancements in pain management is conducted. This overview covers the main categorization of pain and its developmental mechanism, followed by a review of pertinent research and techniques for managing pain. These techniques include commonly prescribed medications, invasive procedures, and noninvasive physical therapy methods used in rehabilitation medicine. Additionally, for the first time, a systematic summary of the utilization of responsive biomaterials in pain management is provided, encompassing their response to physical stimuli such as ultrasound, magnetic fields, electric fields, light, and temperature, as well as changes in the physiological environment like reactive oxygen species (ROS) and pH. Even though the application of responsive biomaterials in pain management remains limited and at a fundamental level, recent years have seen the examination and debate of relevant research findings. These profound discussions aim to provide trends and directions for future research in pain management.

In vivo imaging of the neuronal response to spinal cord injury: a narrative review

Deciphering the neuronal response to injury in the spinal cord is essential for exploring treatment strategies for spinal cord injury (SCI). However, this subject has been neglected in part because appropriate tools are lacking. Emerging in vivo imaging and labeling methods offer great potential for observing dynamic neural processes in the central nervous system in conditions of health and disease. This review first discusses in vivo imaging of the mouse spinal cord with a focus on the latest imaging techniques, and then analyzes the dynamic biological response of spinal cord sensory and motor neurons to SCI. We then summarize and compare the techniques behind these studies and clarify the advantages of in vivo imaging compared with traditional neuroscience examinations. Finally, we identify the challenges and possible solutions for spinal cord neuron imaging.

Pharmacological and Non-pharmacological Approaches for the Management of Neuropathic Pain in Multiple Sclerosis

Multiple sclerosis is a chronic inflammatory disease that affects the central nervous system and can cause various types of pain including ongoing extremity pain, Lhermitte's phenomenon, trigeminal neuralgia, and mixed pain. Neuropathic pain is a major concern for individuals with multiple sclerosis as it is directly linked to myelin damage in the central nervous system and the management of neuropathic pain in multiple sclerosis is challenging as the options available have limited efficacy and can cause unpleasant side effects. The literature search was conducted across two databases, PubMed, and Google Scholar. Eligible studies included clinical trials, observational studies, meta-analyses, systematic reviews, and narrative reviews. The objective of this article is to provide an overview of literature on pharmacological and non-pharmacological strategies employed in the management of neuropathic pain in multiple sclerosis. Pharmacological options include cannabinoids, muscle relaxants (tizanidine, baclofen, dantrolene), anticonvulsants (benzodiazepines, gabapentin, phenytoin, carbamazepine, lamotrigine), antidepressants (duloxetine, venlafaxine, tricyclic antidepressants), opioids (naltrexone), and botulinum toxin variants, which have evidence from various clinical trials. Non-pharmacological approaches for trigeminal neuralgia may include neurosurgical methods. Non-invasive methods, physical therapy, and psychotherapy (cognitive behavioral therapy, acceptance and commitment therapy and mindfulness-based stress reduction) may be recommended for patients with neuropathic pain in multiple sclerosis. The choice of treatment depends on the severity and type of pain as well as other factors, such as patient preferences and comorbidities. There is a pressing need for healthcare professionals and researchers to prioritize the development of better strategies for managing multiple sclerosis-induced neuropathic pain.

Central neuropathic pain

Central neuropathic pain arises from a lesion or disease of the central somatosensory nervous system such as brain injury, spinal cord injury, stroke, multiple sclerosis or related neuroinflammatory conditions. The incidence of central neuropathic pain differs based on its underlying cause. Individuals with spinal cord injury are at the highest risk; however, central post-stroke pain is the most prevalent form of central neuropathic pain worldwide. The mechanisms that underlie central neuropathic pain are not fully understood, but the pathophysiology likely involves intricate interactions and maladaptive plasticity within spinal circuits and brain circuits associated with nociception and antinociception coupled with neuronal hyperexcitability. Modulation of neuronal activity, neuron-glia and neuro-immune interactions and targeting pain-related alterations in brain connectivity, represent potential therapeutic approaches. Current evidence-based pharmacological treatments include antidepressants and gabapentinoids as first-line options. Non-pharmacological pain management options include self-management strategies, exercise and neuromodulation. A comprehensive pain history and clinical examination form the foundation of central neuropathic pain classification, identification of potential risk factors and stratification of patients for clinical trials. Advanced neurophysiological and neuroimaging techniques hold promise to improve the understanding of mechanisms that underlie central neuropathic pain and as predictive biomarkers of treatment outcome.

Research progress of plant-derived natural alkaloids in central nervous system diseases

Central nervous system (CNS) disease is one of the most important causes of human death. Because of their complex pathogenesis, more and more attention has been paid to them. At present, drug treatment of the CNS is the main means; however, most drugs only relieve symptoms, and some have certain toxicity and side effects. Natural compounds derived from plants can provide safer and more effective alternatives. Alkaloids are common nitrogenous basic organic compounds found in nature, which exist widely in many kinds of plants and have unique application value in modern medicine. For example, Galantamine and Huperzine A from medicinal plants are widely used drugs on the market to treat Alzheimer's disease. Therefore, the main purpose of this review is to provide the available information on natural alkaloids with the activity of treating central nervous system diseases in order to explore the trends and perspectives for the further study of central nervous system drugs. In this paper, 120 alkaloids with the potential effect of treating central nervous system diseases are summarized from the aspects of sources, structure types, mechanism of action and structure-activity relationship.

Neuropathic Pain in the Emergency Setting: Diagnosis and Management

Neuropathic pain, traditionally considered a chronic condition, is increasingly encountered in the emergency department (ED), accounting for approximately 20% of patients presenting with pain. Understanding the physiology and key clinical presentations of neuropathic pain is crucial for ED physicians to provide optimal treatment. While diagnosing neuropathic pain can be challenging, emphasis should be placed on obtaining a comprehensive medical history and conducting a thorough clinical examination. Patients often describe neuropathic pain as a burning or shock-like sensation, leading them to seek care in the ED after ineffective relief from common analgesics such as paracetamol and NSAIDs. Collaboration between emergency medicine specialists, neurologists, and pain management experts can contribute to the development of evidence-based guidelines specifically tailored for the emergency department setting. This article provides a concise overview of the common clinical manifestations of neuropathic pain that may prompt patients to seek emergency care.

A Nutritional Supplement as Adjuvant of Gabapentinoids for Adults with Neuropathic Pain following Spinal Cord Injury and Stroke: Preliminary Results

Gabapentinoids are first choice drugs for central neuropathic pain (CNP) despite limited evidence of efficacy and side effects affecting therapy outcomes. Nutraceuticals could improve their efficacy and tolerability. Our aim is to investigate the effect of NACVAN®, in addition to gabapentinoids, on pain symptomatology in CNP patients. The effect of 6 weeks of treatment of NACVAN® was preliminary observed among 29 adult inpatients with spinal cord injury (SCI) or stroke-related CNP recruited to the experimental group. Pain intensity, neuropathic pain, and quality-of-life were measured at baseline (T0) and after 3 (T1) and 6 weeks (T2). Change in each outcome over time was assessed through a repeated measures analysis of variance or Wilcoxon matched-pairs test. Preliminary results show a significant reduction in pain intensity (T0 → T1, p = 0.021; T0 → T2, p = 0.011; T1 → T2, p = 0.46), neuropathic symptoms (T0 → T1, p = 0.024; T0 → T2, p = 0.003), and evoked pain (T0 → T2, p = 0.048). There were no significant reductions in other neuropathic pain dimensions and in quality-of-life components. No side-effects were detected. NACVAN® could have a beneficial adjuvant effect when used as an add-on to gabapentinoids in patients suffering from CNP due to SCI or stroke, with no adverse effect. Future analysis on a larger sample, compared with a placebo condition, could confirm these preliminary results.

Aging with spinal cord injury: A narrative review of consequences and challenges

Given the increase in life expectancy, aging with a pre-existing spinal cord injury (SCI) is becoming more common. This condition is challenging as compromised health status and functional independence can worsen. We aimed to provide an updated overview of the consequences of aging with SCI, highlighting the main challenges facing this population in a narrative review of the current literature we retrieved from the PubMed database from 2000 to 2022 on any aspect related to aging in persons with SCI. Here we address adverse circumstances that increase disability and hinder an active lifestyle, such as progressive physical deterioration, secondary health conditions, limitations in personal activity, changes in family and social support structures, aging of caregivers, and depletion of economic resources. Favorable changes are also observed, including psychosocial adjustments that improve quality of life. Additionally, various interventions are discussed to promote well-being, health, and social participation. Due to the relevance of this issue, people with SCI and all those who take care of them must have up-to-date information to carry out the necessary measures to promote healthy aging in a more inclusive social environment.

Nutraceuticals for Fibromyalgia and Neuropathic Pain

Both neuropathic pain and fibromyalgia are horrific painful conditions arising due to impairment in the somatosensory nervous system and the musculoskeletal system, respectively. They share some common symptoms like hyperalgesia, allodynia, insomnia, cognitive deficits, and mood disturbances. It is believed that fibromyalgia is the consequence of dysfunction of the central nervous system, autonomic nervous system, imbalance in neurotransmitters, and psychological and emotional stress. Henceforth, these pain syndromes have become a major challenge for healthcare professionals due to their complex etiology and poor availability and effectiveness of the drugs. Notably, the available synthetic drugs possess serious side effects including physical dependence and tolerance. Therefore, researchers are now seeking natural-based therapy for modulating chronic pain conditions. This chapter has been written with the intention of exploring the beneficial effects of various nutraceuticals including herbal dietary supplements in neuropathic pain and fibromyalgia.

Stroke-Induced Central Pain: Overview of the Mechanisms, Management, and Emerging Targets of Central Post-Stroke Pain

The incidence of stroke plays the foremost role in the genesis of central neuropathic pain. Central post-stroke pain (CPSP) is a central pain arising from a vascular lesion in the central nervous system that elicits somatosensory deficits, often contralateral to stroke lesions. It is expressed as continuous or intermittent pain accompanied by sensory abnormalities like dysesthesia and allodynia. CPSP remains de-emphasized due to the variation in onset and diversity in symptoms, besides the difficulty of distinguishing it from other post-stroke pains, often referred to as a diagnosis of exclusion. Spinothalamic dysfunction, disinhibition of the medial thalamus, and neuronal hyperexcitability combined with deafferentation in thalamocortical regions are the mechanisms underlying central pain, which play a significant role in the pathogenesis of CPSP. The treatment regimen for CPSP seems to be perplexed in nature; however, based on available studies, amitriptyline and lamotrigine are denoted as first-line medications and non-pharmacological choices may be accounted for cases intractable to pharmacotherapy. This review attempts to provide an overview of the mechanisms, existing management approaches, and emerging targets of CPSP. A profound understanding of CPSP aids in optimizing the quality of life among stroke sufferers and facilitates further research to develop newer therapeutic agents for managing CPSP.

Long-Term Safety and Efficacy of Mirogabalin for Central Neuropathic Pain: A Multinational, Phase 3, 52-Week, Open-Label Study in Asia

INTRODUCTION

Central neuropathic pain (CNeP) is difficult to treat and has diverse etiology, including spinal cord injury (CNePSCI), Parkinson's disease (CNePPD), and central post-stroke pain (CPSP). The safety and efficacy of mirogabalin have been demonstrated in short-term trials, including patients with CNePSCI. The objective of our study was to confirm the safety/efficacy of mirogabalin in patients with CNePPD and CPSP, and obtain long-term data for CNePSCI.

METHODS

This 52-week, open-label extension of a previous randomized controlled study was conducted across Japan, Korea, and Taiwan. Patients with CNePSCI, CNePPD, or CPSP received twice daily (BID) 5-10 mg mirogabalin for a 4-week titration period, after which the dosage was maintained for 47 weeks at a maximum of 15 mg BID, followed by a 1-week taper period receiving the same dose but only administered once daily. The primary endpoint was safety, assessed primarily by incidence and severity of treatment-emergent adverse events (TEAEs). Efficacy was assessed in a post hoc analysis of data obtained by the short-form McGill Pain Questionnaire (SF-MPQ).

RESULTS

Of the 210 patients enrolled, 106, 94, and 10 had CNePSCI, CPSP, and CNePPD, respectively. The mean overall age of patients was 62.9 years, and most patients were male and of Japanese ethnicity. TEAEs occurred in 84.8% of patients, the most common being somnolence (16.7%), peripheral edema (12.4%), edema (11.4%), nasopharyngitis (11.0%), and dizziness (7.6%). Most TEAEs were mild. Severe and serious TEAEs occurred in 6.2% and 13.3% of patients, respectively. All patient groups experienced reductions in SF-MPQ visual analog scores for pain: mean ± standard deviation changes from baseline at week 52 were -2.3 ± 21.13 mm (CNePSCI), -17.0 ± 24.99 mm (CPSP), and -17.1 ± 35.32 mm (CNePPD).

CONCLUSION

Mirogabalin was generally safe, well tolerated, and effective for treatment of CNeP in this long-term study.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT03901352.

The bidirectional roles of the cGAS-STING pathway in pain processing: Cellular and molecular mechanisms

Pain is a common clinical condition. However, the mechanisms underlying pain are not yet fully understood. It is known that the neuroimmune system plays a critical role in the pathogenesis of pain. Recent studies indicated that the cyclic-GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway can activate the innate immune system by sensing both extrinsic and intrinsic double-stranded DNA in the cytoplasm, which is involved in pain processing. In this review, we summarise (1) the roles of the cGAS-STING pathway in different pain models, (2) the effect of the cGAS-STING pathway in different cells during pain regulation, and (3) the downstream molecular mechanisms of the cGAS-STING pathway in pain regulation. This review provides evidence that the cGAS-STING pathway has pro- and anti-nociceptive effects in pain models. It has different functions in neuron, microglia, macrophage, and T cells. Its downstream molecules include IFN-I, NF-κB, NLRP3, and eIF2α. The bidirectional roles of the cGAS-STING pathway in pain processing are mediated by regulating nociceptive neuronal sensitivity and neuroinflammatory responses. However, their effects in special brain regions, activation of astrocytes, and the different phases of pain require further exploration.

Fabry Disease and Central Nervous System Involvement: From Big to Small, from Brain to Synapse

Fabry disease (FD) is an X-linked lysosomal storage disorder (LSD) secondary to mutations in the GLA gene that causes dysfunctional activity of lysosomal hydrolase α-galactosidase A and results in the accumulation of globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3). The endothelial accumulation of these substrates results in injury to multiple organs, mainly the kidney, heart, brain and peripheral nervous system. The literature on FD and central nervous system involvement is scarce when focusing on alterations beyond cerebrovascular disease and is nearly absent in regard to synaptic dysfunction. In spite of that, reports have provided evidence for the CNS’ clinical implications in FD, including Parkinson’s disease, neuropsychiatric disorders and executive dysfunction. We aim to review these topics based on the current available scientific literature.

Tachykinin receptor 3 in the lateral habenula alleviates pain and anxiety comorbidity in mice

The coexistence of chronic pain and anxiety is a common clinical phenomenon. Here, the role of tachykinin receptor 3 (NK3R) in the lateral habenula (LHb) in trigeminal neuralgia and in pain-associated anxiety was systematically investigated. First, electrophysiological recording showed that bilateral LHb neurons are hyperactive in a mouse model of trigeminal neuralgia made by partial transection of the infraorbital nerve (pT-ION). Chemicogenetic activation of bilateral LHb glutamatergic neurons in naive mice induced orofacial allodynia and anxiety-like behaviors, and pharmacological activation of NK3R in the LHb attenuated allodynia and anxiety-like behaviors induced by pT-ION. Electrophysiological recording showed that pharmacological activation of NK3R suppressed the abnormal excitation of LHb neurons. In parallel, pharmacological inhibition of NK3R induced orofacial allodynia and anxiety-like behavior in naive mice. The electrophysiological recording showed that pharmacological inhibition of NK3R activates LHb neurons. Neurokinin B (NKB) is an endogenous high-affinity ligand of NK3R, which binds NK3R and activates it to perform physiological functions, and further neuron projection tracing showed that the front section of the periaqueductal gray (fPAG) projects NKB-positive nerve fibers to the LHb. Optogenetics combined with electrophysiology recordings characterize the functional connections in this fPAG ^NKB → LHb pathway. In addition, electrophysiological recording showed that NKB-positive neurons in the fPAG were more active than NKB-negative neurons in pT-ION mice. Finally, inhibition of NKB release from the fPAG reversed the analgesic and anxiolytic effects of LHb Tacr3 overexpression in pT-ION mice, indicating that fPAG ^NKB → LHb regulates orofacial allodynia and pain-induced anxious behaviors. These findings for NK3R suggest the cellular mechanism behind pT-ION in the LHb and suggest that the fPAG ^NKB → LHb circuit is involved in pain and anxiety comorbidity. This previously unrecognized pathway might provide a potential approach for relieving the pain and anxiety associated with trigeminal neuralgia by targeting NK3R.

Role of Sensory Pathway Injury in Central Post-Stroke Pain: A Narrative Review of Its Pathogenetic Mechanism

Central post-stroke pain (CPSP) is a severe chronic neuropathic pain syndrome that is a direct result of cerebrovascular lesions affecting the central somatosensory system. The pathogenesis of this condition remains unclear owing to its extensive clinical manifestations. Nevertheless, clinical and animal experiments have allowed a comprehensive understanding of the mechanisms underlying CPSP occurrence, based on which different theoretical hypotheses have been proposed. We reviewed and collected the literature and on the mechanisms of CPSP by searching the English literature in PubMed and EMBASE databases for the period 2002-2022. Recent studies have reported that CPSP occurrence is mainly due to post-stroke nerve injury and microglial activation, with an inflammatory response leading to central sensitization and de-inhibition. In addition to the primary injury at the stroke site, peripheral nerves, spinal cord, and brain regions outside the stroke site are involved in the occurrence and development of CPSP. In the present study, we reviewed the mechanism of action of CPSP from both clinical studies and basic research based on its sensory pathway. Through this review, we hope to increase the understanding of the mechanism of CPSP.

Review of the Treatments for Central Neuropathic Pain

Central neuropathic pain (CNP) affects millions worldwide, with an estimated prevalence of around 10% globally. Although there are a wide variety of treatment options available, due to the complex and multidimensional nature in which CNP arises and presents symptomatically, many patients still experience painful symptoms. Pharmaceutical, surgical, non-invasive, cognitive and combination treatment options offer a generalized starting point for alleviating symptoms; however, a more customized approach may provide greater benefit. Here, we comment on the current treatment options that exist for CNP and further suggest the need for additional research regarding the use of biomarkers to help individualize treatment options for patients.

Atypical painful stroke presentations: A review

Stroke is a leading cause of death and disability. Some patients may present with atypical symptoms. One of the very rare presentations of stroke is initial neurogenic pain. Rare painful presentations include, amongst others, acute trigeminal neuralgia, atypical facial pain, hemi-sensory pain, and episodic pain. Based on the available literature, the pain at presentation may be episodic, transient, or persistent, and it may herald other debilitating stroke symptoms such as hemiparesis. Pain quality is often described as burning; less often as sharp. Patients often have accompanying focal symptoms and findings on neurological examination. However, in several of the reviewed cases, these were discrete or non-existent. In patients with pain located in the trunk and/or extremities, lesions may involve the thalamus, lateral medulla oblongata, insula, or parietal lobe. In patients with atypical facial or orbital pain (including the burning "salt and pepper" sensation), the stroke lesions are typically located in the pons. In this narrative review, we included studies/case series of patients who had pain at the time of onset, shortly before or within 24 h of stroke symptoms (on the day of admission). Cases with pain related to aortic or cervical vessel dissection, cerebral venous sinus thrombosis, subarachnoid hemorrhage, reversible cerebral vasoconstriction syndrome, and CNS vasculitis were excluded. With this review, we aim to summarize the current knowledge on stroke presenting with acute pain.

Pharmacotherapies for Central Post-Stroke Pain: A Systematic Review and Network Meta-Analysis

Background

Central post-stroke pain (CPSP) is a common condition. Several pharmacotherapies have been applied in practice. However, the comparative effectiveness among these pharmacotherapies is unknown.

Aim

The aim of this study is to study the comparative effectiveness among differential pharmacotherapies for CPSP through a network meta-analysis.

Methods

We searched MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Science from inception to 30 March 2022, without any language restriction. Two reviewers independently screened the retrieved articles, extracted data, and evaluated the risk of bias (RoB). The outcome of interest of the study was the change in the scores of pain intensity scales. We estimated standard mean differences (SMDs) between treatments and calculated corresponding 95% CIs.

Results

Thirteen randomized controlled trials (529 participants) were included after a screen of 1774 articles. Compared with placebo, pamidronate (SMD -2.43, 95% CI -3.54 to -1.31; P − score = 0.93), prednisone (SMD -2.38, 95% CI -3.09 to -1.67; P − score = 0.92), levetiracetam (SMD -2.11, 95% CI -2.97 to -1.26; P − score = 0.87), lamotrigine (SMD -1.39, 95% CI -2.21 to -0.58; P − score = 0.73), etanercept (SMD -0.92, 95% CI -1.8 to -0.03; P − score = 0.59), and pregabalin (SMD -0.46, 95% CI -0.71 to -0.22; P − score = 0.41) had significantly better treatment effect. Pamidronate, prednisone, and levetiracetam ranked as the first three most effective treatments. In subgroup analyses, prednisone, levetiracetam, lamotrigine, and pregabalin were more effective than placebo as oral pharmacotherapies, while etanercept was more effective than placebo as injectable pharmacotherapy.

Conclusions

Our study confirmed that pamidronate, prednisone, and guideline-recommended anticonvulsants were effective for reducing pain intensity for CPSP. Pamidronate and prednisone showed better effect than other pharmacotherapies, which warrants further investigation.

Spinal cord stimulator for the treatment of central neuropathic pain secondary to cervical syringomyelia: illustrative case

BACKGROUND

Central neuropathic pain (CNP) of the cervical and/or thoracic spinal cord has many etiologies, both natural and iatrogenic. Frequently, CNP is medically refractory and requires surgical treatment to modulate the perception of pain. Spinal cord stimulation is a modality commonly used in adults to treat this type of refractory pain; however, it is rarely used in the pediatric population.

OBSERVATIONS

The authors reported a case involving a common pediatric condition, Chiari malformation type I with syrinx, that led to a debilitating complex regional pain syndrome. The associated life-altering pain was successfully alleviated following placement of a spinal cord stimulator.

LESSONS

CNP, or the syndromic manifestations of the pain (complex regional pain syndrome), can alter an individual's life in dramatic ways. Spinal cord stimulator placement in carefully selected pediatric patients should be considered in these difficult pain treatment paradigms.

Central Neuropathic Pain Syndromes: Current and Emerging Pharmacological Strategies

Central neuropathic pain is caused by a disease or lesion of the brain or spinal cord. It is difficult to predict which patients will develop central pain syndromes after a central nervous system injury, but depending on the etiology, lifetime prevalence may be greater than 50%. The resulting pain is often highly distressing and difficult to treat, with no specific treatment guidelines currently available. This narrative review discusses mechanisms contributing to central neuropathic pain, and focuses on pharmacological approaches for managing common central neuropathic pain conditions such as central post-stroke pain, spinal cord injury-related pain, and multiple sclerosis-related neuropathic pain. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, and gabapentinoids have some evidence for efficacy in central neuropathic pain. Medications from other pharmacologic classes may also provide pain relief, but current evidence is limited. Certain non-pharmacologic approaches, neuromodulation in particular, may be helpful in refractory cases. Emerging data suggest that modulating the primary afferent input may open new horizons for the treatment of central neuropathic pain. For most patients, effective treatment will likely require a multimodal therapy approach.

Physiotherapy interventions may relieve pain in individuals with central neuropathic pain: a systematic review and meta-analysis of randomised controlled trials

Objectives:

To evaluate the effectiveness of any form of physiotherapy intervention for the management of central neuropathic pain (cNeP) due to any underlying cause.

Methods:

Multiple databases were searched from inception until August 2021. Randomised controlled trials evaluating physiotherapy interventions compared to a control condition on pain among people with cNeP were included. Methodological quality and the quality of evidence were assessed using the Physiotherapy Evidence Database Scale and the Grading of Recommendations, Assessment, Development, and Evaluation tool, respectively.

Results:

The searches yielded 2661 studies, of which 23 randomised controlled trials met the inclusion criteria and were included in the meta-analyses. Meta-analyses of trials examining non-invasive neurostimulation revealed significant reductions in pain severity due to spinal cord injury (SCI; standardised mean difference (SMD): −0.59 (95% confidence interval [CI]: −1.07, −0.11), p = 0.02) and phantom limb pain (weighted mean difference (WMD): −1.57 (95% CI: −2.85, −0.29), p = 0.02). The pooled analyses of trials utilising acupuncture, transcutaneous electrical nerve stimulation (TENS), and mirror therapy showed significant reductions in pain severity among individuals with stroke (WMD: −1.46 (95% CI: −1.97, −0.94), p < 0.001), multiple sclerosis (SMD: −0.32 (95% CI: −0.57, −0.06), p = 0.01), and phantom limb pain (SMD: −0.74 (95% CI: −1.36, −0.11), p = 0.02), respectively. Exercise was also found to significantly reduce pain among people with multiple sclerosis (SMD: −1.58 (95% CI: −2.85, −0.30), p = 0.02).

Conclusion:

Evidence supports the use of non-invasive neurostimulation for the treatment of pain secondary to SCI and phantom limb pain. Beneficial pain management outcomes were also identified for acupuncture in stroke, TENS in multiple sclerosis, and mirror therapy in phantom limb pain.

Effect Of Mental Imagery And Physical Exercise On Musculoskeletal Pain And Quality Of Life Among Office Workers: A Commentary

Background — Musculoskeletal pain is one of the most common problem among office workers. The main reason is related to the long time spent sitting and the associated lack of physical activity. Musculoskeletal pain can affect not only their work-related performance, but also their personal performance and quality of life. Research has mainly focused on the effects of physical activity in managing musculoskeletal pain in office workers, while research is sparse pertaining to the possible role of mental imagery on reducing musculoskeletal pain in office workers. While mental imagery has only a minor effect on pain modulation in healthy individuals, its effect appears to be more pronounced in those with chronic pain. Aim — This commentary attempts to present beneficial mental imagery techniques that can be used solely or in combination with physical exercise in an office-based setting to improve musculoskeletal pain to enhance work performance and quality of life among office workers.

Non-opioid pharmacologic treatment of chronic spinal cord injury-related pain

Purpose: Spinal cord injury-related pain is often a severe debilitating condition that adversely affects the patient's physical health, psychological wellbeing and quality of life. Opioid medications have historically been prescribed to this population with great frequency. As opioid abuse disorder becomes an ever-worsening public health issue, more attention must be placed upon non-opioid options. This paper reviews non-opioid medications to be considered when treating spinal cord injury-related pain. The pertinent literature is reviewed, and the advantages and pitfalls of various medication options are discussed in the complicated context of the individual with a spinal cord injury.Methods: Peer-reviewed journal articles and medication package insert data are reviewed.Results:. The non-opioid medications with the greatest evidence for efficacy in the treatment of chronic spinal cord injury-related pain are drawn from the antiepileptic drug and antidepressant categories though the specific selection must be nuanced to the particular individual patient. More research is required to understand the role of calcitonin, lithium, and marijuana in treating spinal cord injury-related pain.Conclusions: The complex clinical situation of each individual patient must be weighed against the risks and benefits of each medication, as reviewed in this paper, to determine the ideal treatment strategy for chronic spinal cord injury-related pain.

Endogenous Opioid Dynorphin Is a Potential Link between Traumatic Brain Injury, Chronic Pain, and Substance Use Disorder

Traumatic brain injury (TBI) is a serious public health problem associated with numerous physical and neuropsychiatric comorbidities. Chronic pain is prevalent and interferes with post-injury functioning and quality of life, whereas substance use disorder (SUD) is the third most common neuropsychiatric diagnosis after TBI. Neither of these conditions has a clear mechanistic explanation based on the known pathophysiology of TBI. Dynorphin is an endogenous opioid neuropeptide that is significantly dysregulated after TBI. Both dynorphin and its primary receptor, the ĸ-opioid receptor (KOR), are implicated in the neuropathology of chronic pain and SUD. Here, we review the known roles of dynorphin and KORs in chronic pain and SUDs. We synthesize this information with our current understanding of TBI and highlight potential mechanistic parallels between and across conditions that suggest a role for dynorphin in long-term sequelae after TBI. In pain studies, dynorphin/KOR activation has either antinociceptive or pro-nociceptive effects, and there are similarities between the signaling pathways influenced by dynorphin and those underlying development of chronic pain. Moreover, the dynorphin/KOR system is considered a key regulator of the negative affective state that characterizes drug withdrawal and protracted abstinence in SUD, and molecular and neurochemical changes observed during the development of SUD are mirrored by the pathophysiology of TBI. We conclude by proposing hypotheses and directions for future research aimed at elucidating the potential role of dynorphin/KOR in chronic pain and/or SUD after TBI.

Analgesic Effect of Bumetanide on Neuropathic Pain in Patients With Spinal Cord Injury

Introduction

The current study evaluated the analgesic effects of bumetanide as an adjunctive in the management of neuropathic pain following Spinal Cord Injury (SCI). The peripheral expression of Na-K-Cl Cotransporter-1 (NKCC1) and K-Cl Cotransporter-2 (KCC2) genes in polymorphonuclear lymphocytes (PMLs) was assessed as a possible biomarker indicating central mechanisms underlying the observed response.

Methods

Through an open-label, single-arm, pilot trial of bumetanide (2 mg/d), an add-on treatment was conducted on 14 SCI patients for 19 weeks. This study consisted of 3 phases: pre-treatment (1 month), titration (3 weeks), and active treatment (4 months). Ultimately, 9 patients completed the study. The primary outcome variables were the endpoint pain score using the Numeric Rating Scale (NRS), and also the short-form of the McGill pain questionnaire. Secondary endpoints included the short-form of the health survey that assesses the quality of life. Blood samples were collected and used for determining the expression of NKCC1 and KCC2 genes in transcription and translation levels.

Results

Bumetanide treatment significantly decreased average pain intensity according to the NRS and the short-form of the McGill pain questionnaire scores. Baseline expression of KCC2 protein was low between groups and increased significantly following treatment (P<0.05). In the current study, pain improvement was accompanied by the greater mean change from the baseline (improvement) for the overall quality of life.

Conclusion

These data highlighted the analgesic effect of bumetanide on neuropathic pain and indicated the potential role of the upregulation of KCC2 protein and involvement of GABAergic disinhibition in producing neuropathic pain.

Intrathecal Baclofen Monotherapy and Polyanalgesia for Treating Chronic Pain in Patients with Severe Spasticity

PURPOSE OF REVIEW

Intrathecal drug delivery is a well evidenced strategy for the treatment of many chronic pain syndromes. While opioids, anesthetics, and ziconotide are the most commonly used agents, intrathecal baclofen (ITB), which is indicated to treat spasticity, is also thought to have some analgesic properties that are poorly understood. These analgesic benefits have been reported with ITB use in treating patients with central neurological disorders who suffer from severe spasticity and chronic pain. Our review aims to characterize ITB's effects on pain, function, and quality of life in patients with severe spasticity. We performed a systematic review based on the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines. The primary outcome parameters were analgesic relief and functional improvements. Secondarily, quality of life and adverse effects were also recorded.

RECENT FINDINGS

After an initial survey identified 393 studies, 20 studies met final inclusion criteria. Of these, 16 utilized ITB monotherapy and 4 utilized ITB polyanalgesia. Overall, there was a paucity of high-powered studies. Mean titrated ITB doses ranged from 140 to 627.9 μg daily. Nineteen studies reported improved pain and spasticity. Seven studies reported improved functional outcomes and quality of life. Our results show that ITB may be an effective agent in treatingfor the treatment of chronic pain in patients with severe spasticity independent of its spasmolytic effects. Although this evidence was largely derived from studies lacking clearly defined outcomes of pain relief, ITB is reasonable to consider for concurrent spasticity and pain management. Well-designed studies are still needed to characterize ITB's analgesic efficacy when used in patients with severe spasticity.

Mechanisms of ATP release in pain: role of pannexin and connexin channels

Pain is a physiological response to bodily damage and serves as a warning of potential threat. Pain can also transform from an acute response to noxious stimuli to a chronic condition with notable emotional and psychological components that requires treatment. Indeed, the management of chronic pain is currently an important unmet societal need. Several reports have implicated the release of the neurotransmitter adenosine triphosphate (ATP) and subsequent activation of purinergic receptors in distinct pain etiologies. Purinergic receptors are broadly expressed in peripheral neurons and the spinal cord; thus, purinergic signaling in sensory neurons or in spinal circuits may be critical for pain processing. Nevertheless, an outstanding question remains: what are the mechanisms of ATP release that initiate nociceptive signaling? Connexin and pannexin channels are established conduits of ATP release and have been suggested to play important roles in a variety of pathologies, including several models of pain. As such, these large-pore channels represent a new and exciting putative pharmacological target for pain treatment. Herein, we will review the current evidence for a role of connexin and pannexin channels in ATP release during nociceptive signaling, such as neuropathic and inflammatory pain. Collectively, these studies provide compelling evidence for an important role of connexins and pannexins in pain processing.

Approach to Neuropathic Pain

Neuropathic pain is a common chief complaint encountered by neurologists and primary care providers. It is caused by disorders involving the somatosensory nervous system. The clinical evaluation of neuropathic pain is challenging and requires a multifaceted systematic approach with an emphasis on a thorough history and physical examination to identify characteristic signs and symptoms. Ancillary laboratory investigations, targeted imaging, and electrodiagnostic studies further help identify underlying etiologies to guide specific treatments. Management of neuropathic pain encompasses treating the underlying pathology as well as symptomatic control with nonpharmacological, pharmacological, and interventional therapies. Here, we present an approach to help evaluate patients with neuropathic pain.

Are Symptoms of Spasticity, Pain, and Fatigue Related in People With Stroke?

PURPOSE

The purpose of this study was to determine whether symptoms of spasticity, pain, and fatigue are correlated in people with stroke.

DESIGN

A longitudinal-correlation, mixed-method design was used.

METHODS

Spasticity, pain, and fatigue symptoms were explored in 22 patients with stroke admitted to three different rehabilitation units certified by the Commission on Accreditation of Rehabilitation Facilities. Data were obtained upon admission, postdischarge, and 1 month after discharge. Demographics, numeric ratings, and a semistructured interview were used to determine associations over time.

RESULTS

Symptoms of spasticity, pain, and fatigue were quite variable. Fatigue was more likely to impair recovery. Spasticity appears to contain pain experiences. Pain does not appear to be a major factor over time.

CONCLUSIONS

In this sample of patients with stroke, symptoms of spasticity, pain, and fatigue were correlated.

CLINICAL RELEVANCE

In managing poststroke spasticity, pain, and fatigue, nurses should recognize that these symptoms are correlated.

[Neuropathic pain syndromes in patients with multiple sclerosis]

Among the numerous pain syndromes (PS) of various localizations and types, observed in patients with multiple sclerosis (MS), the greatest attention of researchers is attracted by neuropathic PS. Neuropathic PS are often present already in the early stage of MS, significantly reduce the quality of life, hinder the social adaptation of patients, poorly respond to therapy. Central neuropathic PS, which pathogenesis is closely related with plaques in the central nervous system, are most common in patients with MS. Diagnostics of neuropathic PS in MS is based mainly on typical clinical symptoms; MRI and neurophysiological methods data are of secondary importance. This review focuses on modern concepts of three main neuropathic PS in MS: ongoing extremity pain, trigeminal neuralgia and Lhermitte's sign. Clinical symptoms of neuropathic PS, current ideas about their pathogenetic mechanisms, MRI and neurophysiological techniques data and the existing approaches to conservative therapy and surgical treatment based on randomized trials data are presented.

Co-Players in Chronic Pain: Neuroinflammation and the Tryptophan-Kynurenine Metabolic Pathway

Chronic pain is an unpleasant sensory and emotional experience that persists or recurs more than three months and may extend beyond the expected time of healing. Recently, nociplastic pain has been introduced as a descriptor of the mechanism of pain, which is due to the disturbance of neural processing without actual or potential tissue damage, appearing to replace a concept of psychogenic pain. An interdisciplinary task force of the International Association for the Study of Pain (IASP) compiled a systematic classification of clinical conditions associated with chronic pain, which was published in 2018 and will officially come into effect in 2022 in the 11th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) by the World Health Organization. ICD-11 offers the option for recording the presence of psychological or social factors in chronic pain; however, cognitive, emotional, and social dimensions in the pathogenesis of chronic pain are missing. Earlier pain disorder was defined as a condition with chronic pain associated with psychological factors, but it was replaced with somatic symptom disorder with predominant pain in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) in 2013. Recently clinical nosology is trending toward highlighting neurological pathology of chronic pain, discounting psychological or social factors in the pathogenesis of pain. This review article discusses components of the pain pathway, the component-based mechanisms of pain, central and peripheral sensitization, roles of chronic inflammation, and the involvement of tryptophan-kynurenine pathway metabolites, exploring the participation of psychosocial and behavioral factors in central sensitization of diseases progressing into the development of chronic pain, comorbid diseases that commonly present a symptom of chronic pain, and psychiatric disorders that manifest chronic pain without obvious actual or potential tissue damage.

Tetrodotoxin, a Potential Drug for Neuropathic and Cancer Pain Relief?

Tetrodotoxin (TTX) is a potent neurotoxin found mainly in puffer fish and other marine and terrestrial animals. TTX blocks voltage-gated sodium channels (VGSCs) which are typically classified as TTX-sensitive or TTX-resistant channels. VGSCs play a key role in pain signaling and some TTX-sensitive VGSCs are highly expressed by adult primary sensory neurons. During pathological pain conditions, such as neuropathic pain, upregulation of some TTX-sensitive VGSCs, including the massive re-expression of the embryonic VGSC subtype Na_V1.3 in adult primary sensory neurons, contribute to painful hypersensitization. In addition, people with loss-of-function mutations in the VGSC subtype Na_V1.7 present congenital insensitive to pain. TTX displays a prominent analgesic effect in several models of neuropathic pain in rodents. According to this promising preclinical evidence, TTX is currently under clinical development for chemo-therapy-induced neuropathic pain and cancer-related pain. This review focuses primarily on the preclinical and clinical evidence that support a potential analgesic role for TTX in these pain states. In addition, we also analyze the main toxic effects that this neurotoxin produces when it is administered at therapeutic doses, and the therapeutic potential to alleviate neuropathic pain of other natural toxins that selectively block TTX-sensitive VGSCs.

Pathophysiology of neuropathic pain

Background: Neuropathic pain is notoriously difficult to manage properly, not only because of its varied nature and the absence of objective diagnostic tools but also because of extensive reciprocal neuronal interactive pathogenic mechanism from the molecular level to patient’s own psychophysical characteristics. This paper briefly reviews the pathophysiology of neuropathic pain to the level of clinicians’ interest and its potential in clinical practiceCurrent Concepts: Recent research progress now allows us to obtain a bird view of neuropathic pain pathophysiology: peripheral and central sensitization. For peripheral sensitization, a local inflammatory milieu of the injured nerve primarily drives sequential phenotypic changes, which are critical and shared by both neuropathic and inflammatory pain. Central sensitization is led either by the hyperexcitability of the second-order afferent neuron itself or loss of physiological inhibitory control of the transmission of pain signal to the higher nervous system. Peripheral and central sensitization work synergistically but can also introduce neuropathic pain alone.Discussion and Conclusion: The cause of neuropathic pain is diverse, and understanding of its pathophysiology is still insufficient to realize a mechanism-based approach to clinical phenotypes or therapeutic applications. In dealing with chronic neuropathic pain, it is highly desirable to assess key aspects of a patient’s pain based on a plausible mechanism and select the best management method accordingly.

Etiology and epidemiology of neuropathic pain

Background: Neuropathic pain is defined as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system either at the peripheral or central level. In most cases, neuropathic pain is associated with poor general health and has a problem of suboptimal response to medical treatment. This review will discuss the neurologic and non-neurologic conditions that cause neuropathic pain and the results of epidemiologic studies on neuropathic pain.Current Concepts: Epidemiology would be a useful clinical tool for designing management and prevention strategies for various neuropathic pain syndromes. Validated neuropathic pain screening questionnaires are widely used as useful tools for the epidemiologic study of neuropathic pain. There are also validated Korean versions of these questionnaires. The overall prevalence of neuropathic pain was estimated at 6.9-10%. Common neuropathic pain syndromes include diabetic neuropathy, herpes zoster, and trigeminal neuralgia. In addition, neuropathic pain can also occur in central nervous system disorders such as spinal cord injury or stroke, and other conditions like cancerous diseases, intervertebral disc disease, and joint diseases.Discussion and Conclusion: Neuropathic pain does not respond well to medical treatment, which leaves both patients and physicians are less satisfied with such treatments. Therefore, physicians must identify the causes of the pain, explain them to the patient, and proceed with the treatment together with patients.

Activation of CamKIIα expressing neurons on ventrolateral periaqueductal gray improves behavioral hypersensitivity and thalamic discharge in a trigeminal neuralgia rat model

BACKGROUND

Preceding studies have reported the association of chronic neuropathic orofacial pain with altered ongoing function in the ventrolateral periaqueductal gray (vlPAG). However, its role in trigeminal neuralgia (TN) lacks attention. We here reported the aspect that vlPAG neurons play in TN nociceptive processing by employing excitatory neuron-specific optogenetic approaches.

METHODS

TN was generated via unilateral infraorbital nerve chronic constriction in Sprague Dawley rats which induced mechanical and thermal pain sensitivity in air puff and acetone test, respectively. Channelrhodopsin conjugated virus with CamKIIα promoter was used to specifically activate the excitatory vlPAG neuronal population by optogenetic stimulation and in vivo microdialysis was done to determine its effect on the excitatory-inhibitory balance. In vivo extracellular recordings from ventral posteromedial (VPM) thalamus were assessed in response to vlPAG optogenetic stimulation. Depending on the experimental terms, unpaired student's t test and two-way analysis of variance (ANOVA) were used for statistical analysis.

RESULTS

We observed that optogenetic activation of vlPAG subgroup neurons markedly improved pain hypersensitivity in reflexive behavior tests which was also evident on microdialysis analysis with increase glutamate concentration during stimulation period. Decreased mean firing and burst rates were evident in VPM thalamic electrophysiological recordings during the stimulation period. Overall, our results suggest the optogenetic activation of vlPAG excitatory neurons in a TN rat model has pain ameliorating effect.

CONCLUSIONS

This article presents the prospect of pain modulation in trigeminal pain pathway via optogenetic activation of vlPAG excitatory neurons in rat model. This outlook could potentially assist vlPAG insight and its optogenetic approach in trigeminal neuropathic pain which aid clinicians endeavoring towards enhanced pain relief therapy in trigeminal neuralgia patients.

The NLRP3 inflammasome: an emerging therapeutic target for chronic pain

Chronic pain affects the life quality of the suffering patients and posts heavy problems to the health care system. Conventional medications are usually insufficient for chronic pain management and oftentimes results in many adverse effects. The NLRP3 inflammasome controls the processing of proinflammatory cytokine interleukin 1β (IL-1β) and is implicated in a variety of disease conditions. Recently, growing number of evidence suggests that NLRP3 inflammasome is dysregulated under chronic pain condition and contributes to pathogenesis of chronic pain. This review provides an up-to-date summary of the recent findings of the involvement of NLRP3 inflammasome in chronic pain and discussed the expression and regulation of NLRP3 inflammasome-related signaling components in chronic pain conditions. This review also summarized the successful therapeutic approaches that target against NLRP3 inflammasome for chronic pain treatment.

Dexmedetomidine alleviated neuropathic pain in dorsal root ganglion neurons by inhibition of anaerobic glycolysis activity and enhancement of ROS tolerance

Neuropathic pain is a kind of chronic pain that is triggered or caused primarily by damage to the nervous system and neurological dysfunction. It’s known that dexmedetomidine is a new type of highly selective alpha2-adrenoceptor agonist with sedation, anti-anxiety, analgesic and other effects. However, the function and mechanism of dexmedetomidine on neuropathic pain are not clear. Rat DRG neurons were isolated and identified using immunofluorescence assay. Following treatment with H₂O₂, dexmedetomidine or ROS inhibitor (NAC), the apoptosis and ROS levels were examined by flow cytometery; apoptosis- and anaerobic glycolysis-related proteins were determined by Western blot assay; glucose consumption, pyruvic acid, lactic acid and ATP/ADP ratios were also measured. The results revealed that dexmedetomidine inhibited H₂O₂-induced apoptosis and reactive oxygen species (ROS) in rat DRG neurons and in addition, dexmedetomidine down-regulated the expression levels of anaerobic glycolysis-related proteins, significantly reduced glucose, pyruvic acid and lactic acid levels. It also increased the ATP/ADP ratio in H₂O₂-treated rat dorsal root ganglion (DRG) neurons. Moreover, we also demonstrated that ROS inhibitor (NAC) also inhibited H₂O₂-induced apoptosis and anaerobic glycolysis in rat DRG neurons. In conclusion, dexmedetomidine suppressed H₂O₂-induced apoptosis and anaerobic glycolysis activity by inhibiting ROS, in rat DRG neurons. Therefore, dexmedetomidine might play a pivotal role in neuropathic pain by the inhibition of ROS.

Burst spinal cord stimulation for central neuropathic pain: Two case reports

INTRODUCTION

Central neuropathic pain can result from any type of injury to the central nervous system. Treatment of central neuropathic pain is very challenging. Recently, a novel stimulation paradigm, called burst stimulation, has been presented as an excellent alternative in a group of patients with intractable central neuropathic pain. We report 2 cases where burst spinal cord stimulation (SCS) was applied in patients with neuropathic pain due to spinal cord injury (SCI) or traumatic brain injury.

PATIENT CONCERNS

A 52-year-old man who underwent posterolateral fusion surgery for a T12 bursting fracture after a fall 11 years prior developed disabling pain in the anterolateral part of his right thigh. His neuropathic pain following SCI was refractory to various treatment modalities. A 65-year-old man had complained of intractable, cold, throbbing, and shooting pain mainly in his left lower limb during rehabilitation since undergoing a craniotomy 9 years prior for multiple brain injuries caused by a motorcycle accident.

DIAGNOSIS

Both of these 2 cases were diagnosed with central neuropathic pain syndrome caused by SCI or traumatic brain injury.

INTERVENTIONS

Burst SCS were proposed to alleviate the significant refractory pains that were resistant to various medications and stimulation was delivered to the patient in an alternating pattern between traditional tonic and burst waveforms.

CONCLUSION

The efficacy of burst SCS in central neuropathic pain is desirable considering the severity of pain in such patients, the refractory nature of their pain, and the paucity of alternative therapeutic options.

Efficacy evaluation of neurofeedback applied for treatment of central neuropathic pain using machine learning

Brain-computer interface (BCI) is believed to be the translator of brain signals into actions based on the model, built on the machine learning (ML) algorithms, incorporated in it. This study reports on the performance of various ML algorithms in evaluating efficacy of neurofeedback applied for treatment of central neuropathic pain (CNP). In the first phase of this study, we applied different ML algorithms for classification of electroencephalography (EEG) patterns, associated with CNP, obtained from three groups of participants, during imagined movement of their limbs, named as able-bodied (AB), paraplegic patients with (PWP) and without (PNP) neuropathic pain. In the second phase, we tested the accuracy of BCI-classifier by applying new EEG data obtained from PWP participants who have completed neurofeedback training provided for the management of pain. Support vector Machine (SVM) algorithm gained higher accuracy, with all groups, than the other classifiers. However, the highest classification accuracy of 99 ± 0.49% was obtained with the right hand motor imagery of (AB vs PWP) group and 61 electrodes. In Conclusion, SVM based BCI-classifier achieved high accuracy in evaluating efficacy of neurofeedback applied for treatment of CNP. Results of this study show that the accuracy of BCI changes with ML algorithm, electrodes combinations, and training data set.

miR-223 Inhibits the Polarization and Recruitment of Macrophages via NLRP3/IL-1β Pathway to Meliorate Neuropathic Pain

Background

miRNA is an essential factor in neuropathic pain. However, the underlying mechanism of miRNA in neuropathic pain remains unclear.

Objective

To explore the potential role of miR-223 in neuropathic pain in a mice model of chronic sciatic nerve injury.

Methods

Mice were divided into the sham group, CCI group, CCI + Lenti-vector group, and CCI + Lenti-miR-223 group. Flow cytometry was used to detect the neuronal apoptosis and the proportion of M1/M2 macrophages in each group. Western blot was used to detect the protein expression levels of ASC, caspase-1, IL-1β, and IL-18 in each group. Luciferase activity assay detects the binding of miR-223 and NLRP3. Macrophage chemotaxis experiments verified the anti-inflammatory effect of miR-223 in vitro.

Results

The overexpression of miR-233 significantly reduced the neuropathic pain caused by CCI and reduced the apoptosis and inflammatory factor expression. miR-223 inhibits the expression of NLRP3 by directly binding to the 3'-untranslated region. Overexpression of miR-223 reduces the protein levels of NLRP3, ASC, caspase-1, IL-1β, and IL-18 in the spinal cord of CCI mice, increases the proportion of M2-type macrophages, and reduces the proportion of M1-type macrophages.

Conclusion

miR-223 may facilitate the development of neuropathic pain in CCI mice by inhibiting NLRP3-mediated neuroinflammation.

A mini-review: Bridging the gap between autism spectrum disorder and pain comorbidities

Background

Pain is a complex neurobiological response with a multitude of causes; however, patients with autism spectrum disorder (ASD) often report chronic pain with no known etiology. Recent research has been aimed toward identifying the causal mechanisms of pain in mouse and human models of ASD. In recent years, efforts have been made to better document and explore secondary phenotypes observed in ASD patients in the clinic. As new sequencing studies have become more powered with larger cohorts within ASD, specific genes and their variants are often left uncharacterized or validated. In this review we highlight ASD risk genes often presented with pain comorbidities.

Aims

This mini-review bridges the gap between two fields of literature, neurodevelopmental disorders and pain research. We discuss the importance of the genetic landscape of ASD and its links to pain phenotypes.

Results

Among the numerous genes implicated in ASD, few have been implicated with varying severities of pain comorbidity. Mutations in these genes, such as SCN9A, SHANK3, and CNTNAP2, lead to altered neuronal function that produce different responses to pain, shown in both mouse and human models.

Conclusion

There is a necessity to use new technologies to advance the current understanding of ASD risk genes and their contributions to pain. Secondly, there is a need to power future ASD risk genes associated with pain with their own cohort, because a better understanding is needed of this subpopulation.

Dihydromyricetin attenuates neuropathic pain via enhancing the transition from M1 to M2 phenotype polarization by potentially elevating ALDH2 activity in vitro and vivo

Background

Treatment for neuropathic pain as a refractory disease remains unsatisfactory and represents a significant clinical challenge. A highly effective drug is thus urgently needed for neuropathic pain treatment. Dihydromyricetin (DMY) is a flavonoid with a wide range of biological activities. The purpose of this research is to explore the effects of DMY on neuropathic pain and the underlying mechanism of its effect.

Methods

The effect of DMY was investigated in BV-2 cells and lipopolysaccharide (LPS)-induced BV-2 cells. A neuropathic pain model was established via spared nerve injury (SNI) surgery in mice, and the protein expression level was detected via Western blot assay. The percent of M1 and M2 phenotype polarization cells were detected via flow cytometry assay. Immunochemical staining assay was also performed to measure the marker levels of the M1 and M2 phenotype polarization cells and aldehyde dehydrogenase 2 (ALDH2) level, and mechanical pain sensitivity was evaluated via measurement of the mechanical withdrawal threshold.

Results

We found that DMY promoted the transition from M1 to M2 polarization and upregulated the ALDH2 level in vitro and vitro. ALDA-1, an ALDH2 agonist, promoted the switching from M1 to M2 polarization in vivo and vitro. DMY alleviated pain hypersensitivity induced by SNI via enhancing M2 phenotype polarization by elevating ALDH2 activity in mice. After DMY- or ALDA-1-microglia were injected into SNI-induced pain hypersensitive mice, the mechanical withdrawal threshold was increased significantly when compared with the SNI group.

Conclusions

Our data demonstrated that DMY alleviated neuropathic pain via enhancing the polarization transition from the M1 to M2 phenotype by potentially elevating ALDH2 activity in vitro and vivo. DMY- or ALDA-1-microglia may have alleviative effects on neuropathic pain. The findings herein provide a promising avenue for neuropathic pain treatment, suggesting a new target, ALDH2, in the treatment of neuropathic pain.

Preliminary study of analgesic effect of bumetanide on neuropathic pain in patients with spinal cord injury

BACKGROUND/OBJECTIVE

The current study evaluated the analgesic effects of bumetanide as an adjunctive treatment in managing neuropathic pain following spinal cord injury. The peripheral expression level of Na-K-Cl-cotransporter-1 (NKCC1) and K-Cl-cotransporter-2 (KCC2) genes in polymorphonuclear lymphocytes (PMLs) assessed as a possible biomarker indicating central underlying mechanisms.

METHODS

This open-label, single-arm, pilot trial of bumetanide (2 mg/day) is an add-on treatment conducted in 14 SCI patients for 19 weeks. The whole duration consisted of three phases: pre-treatment (1 month), titration (3 weeks), and active treatment (4 months). Ultimately, nine patients completed the study. The primary outcome variables were the endpoint pain score measured by the numeric rating scale (NRS), and the short-form McGill Pain Questionnaire. Secondary endpoints included the Short-Form Health Survey that measures the quality of life. Blood samples were collected and used for determining the expression of NKCC1 and KCC2 genes in transcription and translation levels.

RESULTS

Bumetanide treatment significantly reduced average pain intensity according to the NRS and the short form of the McGill Pain Questionnaire scores. The baseline expression of KCC2 protein was low between groups and increased significantly following treatment (P < 0.05). Through the current study, pain improvement accompanied by the more significant mean change from the baseline for the overall quality of life.

CONCLUSION

These data might be a piece of preliminary evidence for the analgesic effect of bumetanide on neuropathic pain and could support the potential role of the upregulation of KCC2 protein and involvement of GABAergic disinhibition in producing neuropathic pain.