The prevalence of neuropathic pain: clinical evaluation compared with screening tools in a community population

Peripheral magnetic stimulation for chronic peripheral neuropathic pain: A systematic review and meta-analysis

OBJECTIVES

To provide a systematic review of the literature on the effects of peripheral magnetic stimulation (PMS) in the treatment of chronic peripheral neuropathic pain.

METHODS

A systematic search of MEDLINE, EMBASE, CENTRAL, CINHAL, Web of Science, and ProQuest was conducted from inception to July 2023 to identify studies of any design published in English language that enrolled adult patients (≥18 years) that received PMS for treatment of a chronic peripheral neuropathic pain disorder (pain > 3 months).

RESULTS

Twenty-three studies were identified which included 15 randomized controlled trials (RCTs), five case series, two case reports, and one non-randomized trial. PMS regimens varied across studies and ranged from 5 to 240 min per session over 1 day to 1 year of treatment. Results across included studies were mixed, with some studies suggesting benefits while others showing no significant differences. Of nine placebo-controlled RCTs, four reported statistically significant findings in favor of PMS use. In the meta-analysis, PMS significantly reduced pain scores compared to control within 0-1 month of use (mean difference -1.64 on a 0-10 numeric rating scale, 95% confidence interval -2.73 to -0.56, p = 0.003, I2 = 94%, 7 studies [264 participants], very low quality of evidence), but not at the 1-3 months and >3 months of PMS use (very low and low quality of evidence, respectively). Minimal to no adverse effects were reported with PMS use.

DISCUSSION

There is limited and low-quality evidence to make definitive recommendations on PMS usage, however, the available data is encouraging, especially for short-term applications of this novel modality. Large high-quality randomized controlled trials are required to establish definitive efficacy and safety effects of PMS.

In vitro models for neuropathic pain phenotypic screening in brain therapeutics

The discovery of brain therapeutics faces a significant challenge due to the low translatability of preclinical results into clinical success. To address this gap, several efforts have been made to obtain more translatable neuronal models for phenotypic screening. These models allow the selection of active compounds without predetermined knowledge of drug targets. In this review, we present an overview of various existing models within the field, examining their strengths and limitations, particularly in the context of neuropathic pain research. We illustrate the usefulness of these models through a comparative review in three crucial areas: i) the development of novel phenotypic screening strategies specifically for neuropathic pain, ii) the validation of the models for both primary and secondary screening assays, and iii) the use of the models in target deconvolution processes.

Ultramicronized N-palmitoylethanolamine Contributes to Morphine Efficacy Against Neuropathic Pain: Implication of Mast Cells and Glia

BACKGROUND

In the current management of neuropathic pain, in addition to antidepressants and anticonvulsants, the use of opioids is wide, despite their related and well-known issues.

OBJECTIVE

N-palmitoylethanolamine (PEA), a natural fatty-acid ethanolamide whose anti-inflammatory, neuroprotective, immune-modulating and anti-hyperalgesic activities are known, represents a promising candidate to modulate and/or potentiate the action of opioids.

METHODS

This study was designed to evaluate if the preemptive and morphine concomitant administration of ultramicronized PEA, according to fixed or increasing doses of both compounds, delays the onset of morphine tolerance and improves its analgesic efficacy in the chronic constriction injury (CCI) model of neuropathic pain in rats.

RESULTS

Behavioral experiments showed that the preemptive and co-administration of ultramicronized PEA significantly decreased the effective dose of morphine and delayed the onset of morphine tolerance. The activation of spinal microglia and astrocytes, commonly occurring both on opioid treatment and neuropathic pain, was investigated through GFAP and Iba-1 immunofluorescence. Both biomarkers were found to be increased in CCI untreated or morphine treated animals in a PEA-sensitive manner. The increased density of endoneural mast cells within the sciatic nerve of morphine-treated and untreated CCI rats was significantly reduced by ultramicronized PEA. The decrease of mast cell degranulation, evaluated in terms of reduced plasma levels of histamine and N-methyl-histamine metabolite, was mainly observed at intermediate-high doses of ultramicronized PEA, with or without morphine.

CONCLUSION

Overall, these results show that the administration of ultramicronized PEA in CCI rats according to the study design fully fulfilled the hypotheses of this study.

Schwann Cell-Derived Exosomal Vesicles: A Promising Therapy for the Injured Spinal Cord

Exosomes are nanoscale-sized membrane vesicles released by cells into their extracellular milieu. Within these nanovesicles reside a multitude of bioactive molecules, which orchestrate essential biological processes, including cell differentiation, proliferation, and survival, in the recipient cells. These bioactive properties of exosomes render them a promising choice for therapeutic use in the realm of tissue regeneration and repair. Exosomes possess notable positive attributes, including a high bioavailability, inherent safety, and stability, as well as the capacity to be functionalized so that drugs or biological agents can be encapsulated within them or to have their surface modified with ligands and receptors to imbue them with selective cell or tissue targeting. Remarkably, their small size and capacity for receptor-mediated transcytosis enable exosomes to cross the blood-brain barrier (BBB) and access the central nervous system (CNS). Unlike cell-based therapies, exosomes present fewer ethical constraints in their collection and direct use as a therapeutic approach in the human body. These advantageous qualities underscore the vast potential of exosomes as a treatment option for neurological injuries and diseases, setting them apart from other cell-based biological agents. Considering the therapeutic potential of exosomes, the current review seeks to specifically examine an area of investigation that encompasses the development of Schwann cell (SC)-derived exosomal vesicles (SCEVs) as an approach to spinal cord injury (SCI) protection and repair. SCs, the myelinating glia of the peripheral nervous system, have a long history of demonstrated benefit in repair of the injured spinal cord and peripheral nerves when transplanted, including their recent advancement to clinical investigations for feasibility and safety in humans. This review delves into the potential of utilizing SCEVs as a therapy for SCI, explores promising engineering strategies to customize SCEVs for specific actions, and examines how SCEVs may offer unique clinical advantages over SC transplantation for repair of the injured spinal cord.

Multimodal non-invasive non-pharmacological therapies for chronic pain: mechanisms and progress

BACKGROUND

Chronic pain conditions impose significant burdens worldwide. Pharmacological treatments like opioids have limitations. Non-invasive non-pharmacological therapies (NINPT) encompass diverse interventions including physical, psychological, complementary and alternative approaches, and other innovative techniques that provide analgesic options for chronic pain without medications.

MAIN BODY

This review elucidates the mechanisms of major NINPT modalities and synthesizes evidence for their clinical potential across chronic pain populations. NINPT leverages peripheral, spinal, and supraspinal mechanisms to restore normal pain processing and limit central sensitization. However, heterogeneity in treatment protocols and individual responses warrants optimization through precision medicine approaches.

CONCLUSION

Future adoption of NINPT requires addressing limitations in standardization and accessibility as well as synergistic combination with emerging therapies. Overall, this review highlights the promise of NINPT as a valuable complementary option ready for integration into contemporary pain medicine paradigms to improve patient care and outcomes.

Investigating the potential of GalR2 as a drug target for neuropathic pain

Neuropathic pain is a chronic and debilitating condition characterised by episodes of hyperalgesia and allodynia. It occurs following nerve damage from disease, inflammation or injury and currently impacts up to 17% of the UK population. Existing therapies lack efficacy and have deleterious side effects that can be severely limiting. Galanin receptor 2 (GalR2) is a G-protein coupled receptor (GPCR) implicated in the control and processing of painful stimuli. Within the nervous system it is expressed in key tissues involved in these actions such as dorsal root ganglia (DRG) and the dorsal horn of the spinal cord. Stimulation of GalR2 is widely reported to have a role in the attenuation of inflammatory and neuropathic pain. Several studies have indicated GalR2 as a possible drug target, highlighting the potential of specific GalR2 agonists to both provide efficacy and to address the side-effect profiles of current pain therapies in clinical use. A strong biological target for drug discovery will be well validated with regards to its role in the relevant disease pathology. Ideally there will be good translational models, sensitive probes, selective and appropriate molecular tools, translational biomarkers, a clearly defined patient population and strong opportunities for commercialisation. Before GalR2 can be considered as a drug target suitable for investment, key questions need to be asked regarding its expression profile, receptor signalling and ligand interactions. This article aims to critically review the available literature and determine the current strength of hypothesis of GalR2 as a target for the treatment of neuropathic pain.

Cross-sectional study examining the epidemiology of chronic pain in Nepal

Introduction

The World Health Organization recognizes chronic pain as a global public health concern; however, there is a bias towards research conducted in relatively affluent nations. There is a dearth of large-scale epidemiological studies in Nepal using rigorously validated, cross-culturally adapted instruments.

Objectives

The aim of this study was to examine the prevalence of both chronic pain and chronic pain of predominantly neuropathic origin and their associations with a range of sociodemographic and psychosocial characteristics.

Methods

We conducted a cross-sectional study of adults (≥18 years) in all households in Ranipani, Baluwa Village Development Committee, Nepal. All adults (n = 887) were approached, and those consenting, who met the inclusion criteria (n = 520, 58.6%), participated. Questionnaires validated in Nepali were used to examine several constructs: demographics; chronic pain; neuropathic pain; pain catastrophizing; resilience, pain intensity; pain interference; sleep disturbance; and depression.

Results

The point prevalence of chronic pain was 53.3% (n = 277). The point prevalence of chronic pain of predominantly neuropathic origin was 12.7% (n = 66). Chronic pain was associated with female gender, older age, and manual labour occupations. Using standardized scoring techniques, compared with available population estimates from other countries, those with chronic pain were associated with lower pain intensity and resilience scores and higher pain catastrophizing, pain interference, and depression scores.

Conclusion

These findings are broadly comparable to epidemiological studies from other countries, and these indicate areas for targeting interventions (eg, occupational and mental health). For comparison, more data are needed, from larger population samples in this region.

Epidemiology of neuropathic pain: an analysis of prevalence and associated factors in UK Biobank

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An analysis of UK Biobank participants who completed a detailed pain questionnaire identified factors associated with neuropathic pain (NeuP) vs no chronic pain and non-NeuP and estimated the prevalence of NeuP.

Introduction:

Previous epidemiological studies of neuropathic pain have reported a range of prevalences and factors associated with the disorder.

Objectives:

This study aimed to verify these characteristics in a large UK cohort.

Methods:

A cross-sectional analysis was conducted of 148,828 UK Biobank participants who completed a detailed questionnaire on chronic pain. The Douleur Neuropathique en Quatre Questions (DN4) was used to distinguish between neuropathic pain (NeuP) and non-neuropathic pain (non-NeuP) in participants with pain of at least 3 months' duration. Participants were also identified with less than 3 months' pain or without pain (NoCP). Multivariable regression was used to identify factors associated with NeuP compared with non-NeuP and NoCP, respectively.

Results:

Chronic pain was present in 76,095 participants (51.1%). The overall prevalence of NeuP was 9.2%. Neuropathic pain was significantly associated with worse health-related quality of life, having a manual or personal service type occupation, and younger age compared with NoCP. As expected, NeuP was associated with diabetes and neuropathy, but also other pains (pelvic, postsurgical, and migraine) and musculoskeletal disorders (rheumatoid arthritis, osteoarthritis, and fibromyalgia). In addition, NeuP was associated with pain in the limbs and greater pain intensity and higher body mass index compared with non-NeuP. Female sex was associated with NeuP when compared with NoCP, whereas male sex was associated with NeuP when compared with non-NeuP.

Conclusion:

This is the largest epidemiological study of neuropathic pain to date. The results confirm that the disorder is common in a population of middle- to older-aged people with mixed aetiologies and is associated with a higher health impact than non-neuropathic pain.

Pain and aging: A unique challenge in neuroinflammation and behavior

Chronic pain is one of the most common, costly, and potentially debilitating health issues facing older adults, with attributable costs exceeding $600 billion annually. The prevalence of pain in humans increases with advancing age. Yet, the contributions of sex differences, age-related chronic inflammation, and changes in neuroplasticity to the overall experience of pain are less clear, given that opposing processes in aging interact. This review article examines and summarizes pre-clinical research and clinical data on chronic pain among older adults to identify knowledge gaps and provide the base for future research and clinical practice. We provide evidence to suggest that neurodegenerative conditions engender a loss of neural plasticity involved in pain response, whereas low-grade inflammation in aging increases CNS sensitization but decreases PNS sensitivity. Insights from preclinical studies are needed to answer mechanistic questions. However, the selection of appropriate aging models presents a challenge that has resulted in conflicting data regarding pain processing and behavioral outcomes that are difficult to translate to humans.

The Role of microRNAs in Regulating Cancer Cell Response to Oxaliplatin-Containing Regimens

Oxaliplatin (cyclohexane-1,2-diamine; oxalate; platinum [2+]) is a third-generation chemotherapeutic drug with anticancer effects. Oxaliplatin has a role in the treatment of several cancers. It is one of the few drugs which can eliminate the neoplastic cells of colorectal cancer. Also, it has an influential role in breast cancer, lung cancer, bladder cancer, prostate cancer, and gastric cancer. Although oxaliplatin has many beneficial effects in cancer treatment, resistance to this drug is in the way to cure neoplastic cells and reduce treatment efficacy. microRNAs are a subtype of small noncoding RNAs with ∼22 nucleotides that exist among species. They have diverse roles in physiological processes, including cellular proliferation and cell death. Moreover, miRNAs have essential roles in resistance to cancer treatment and can strengthen sensitivity to chemotherapeutic drugs and regimens. In colorectal cancer, the co-treatment of oxaliplatin with anti-miR-19a can partially reverse the oxaliplatin resistance through the upregulation of phosphatase and tensin homolog (PTEN). Moreover, by preventing the spread of gastric cancer cells and downregulating glypican-3 (GPC3), MiR-4510 may modify immunosuppressive signals in the tumor microenvironment. Treatment with oxaliplatin may develop into a specialized therapeutic drug for patients with miR-4510 inhibition and glypican-3-expressing gastric cancer. Eventually, miR-122 upregulation or Wnt/β-catenin signaling suppression boosted the death of HCC cells and made them more sensitive to oxaliplatin. Herein, we have reviewed the role of microRNAs in regulating cancer cells' response to oxaliplatin, with particular attention to gastrointestinal cancers. We also discussed the role of these noncoding RNAs in the pathophysiology of oxaliplatin-induced neuropathic pain.

The Identification of Human Translational Biomarkers of Neuropathic Pain and Cross-Species Validation Using an Animal Model

Neuropathic pain is a common chronic condition, which remains poorly understood. Many patients receiving treatment continue to experience severe pain, due to limited diagnostic/treatment management programmes. The development of objective clinical diagnostic/treatment strategies requires identification of robust biomarkers of neuropathic pain. To this end, we looked to identify biomarkers of chronic neuropathic pain by assessing gene expression profiles in an animal model of neuropathic pain, and differential gene expression in patients to determine the potential translatability. We demonstrated cross-species validation of several genes including those identified through bioinformatic analysis by assessing their expression in blood samples from neuropathic pain patients, according to conservative assessments of significance measured using Bonferroni-corrected p-values. These include CASP5 (p = 0.00226), CASP8 (p = 0.00587), CASP9 (p = 2.09 × 10^-9), FPR2 (p = 0.00278), SH3BGRL3 (p = 0.00633), and TMEM88 (p = 0.00038). A ROC analysis revealed several combinations of genes to show high levels of discriminatory power in the comparison of neuropathic pain patients and control participants, of which the combination SH3BGRL3, TMEM88, and CASP9 achieved the highest level (AUROC = 0.923). The CASP9 gene was found to be common in five combinations of three genes revealing the highest levels of discriminatory power. In contrast, the gene combination PLAC8, ROMO1, and A3GALT2 showed the highest levels of discriminatory power in the comparison of neuropathic pain and nociceptive pain (AUROC = 0.919), when patients were grouped by S-LANSS scores. Molecules that demonstrate an active role in neuropathic pain have the potential to be developed into a biological measure for objective diagnostic tests, or as novel drug targets for improved pain management.

Glutamatergic systems in neuropathic pain and emerging non-opioid therapies

Neuropathic pain, a disease of the somatosensory nervous system, afflicts many individuals and adequate management with current pharmacotherapies remains elusive. The glutamatergic system of neurons, receptors and transporters are intimately involved in pain but, to date, there have been few drugs developed that therapeutically modulate this system. Glutamate transporters, or excitatory amino acid transporters (EAATs), remove excess glutamate around pain transmitting neurons to decrease nociception suggesting that the modulation of glutamate transporters may represent a novel approach to the treatment of pain. This review highlights and summarizes (1) the physiology of the glutamatergic system in neuropathic pain, (2) the preclinical evidence for dysregulation of glutamate transport in animal pain models, and (3) emerging novel therapies that modulate glutamate transporters. Successful drug discovery requires continuous focus on basic and translational methods to fully elucidate the etiologies of this disease to enable the development of targeted therapies. Increasing the efficacy of astrocytic EAATs may serve as a new way to successfully treat those suffering from this devastating disease.

The Roles of Imaging Biomarkers in the Management of Chronic Neuropathic Pain

Chronic neuropathic pain (CNP) affects around 10% of the general population and has a significant social, emotional, and economic impact. Current diagnosis techniques rely mainly on patient-reported outcomes and symptoms, which leads to significant diagnostic heterogeneity and subsequent challenges in management and assessment of outcomes. As such, it is necessary to review the approach to a pathology that occurs so frequently, with such burdensome and complex implications. Recent research has shown that imaging methods can detect subtle neuroplastic changes in the central and peripheral nervous system, which can be correlated with neuropathic symptoms and may serve as potential markers. The aim of this paper is to review available imaging methods used for diagnosing and assessing therapeutic efficacy in CNP for both the preclinical and clinical setting. Of course, further research is required to standardize and improve detection accuracy, but available data indicate that imaging is a valuable tool that can impact the management of CNP.

Prevalence and Determinants of Chronic Pain Post-COVID; Cross-Sectional Study

Introduction: Chronic pain is increasingly recognized as part of long COVID syndrome, mainly in the form of myalgias. However, chronic pain has several forms, and according to our clinical experience, COVID-19 survivors suffer from numerous painful syndromes, other than myalgias. The aim of our study was to estimate the prevalence of chronic pain, describe the commonest painful syndromes and identify pain determinants in a random population of COVID-19 survivors. Methods: This was a cross-sectional study conducted at the Medical School, University of Cyprus. A random population of 90 COVID-19 survivors was recruited. Demographic and COVID-19 related clinical characteristics were recorded. The painDETECT and DN4 questionnaires were used to evaluate the painful syndromes. Results: The prevalence of chronic pain was estimated to be 63.3%. The most common site of pain was low back (37.8%), followed by joints (28.9%) and neck (12.2%). Patients with chronic pain compared to subjects without pain were older (50.5 ± 15.9 versus 42.2 ± 12.6, p = 0.011) and more likely to be female (71.9% versus 45.5%, p = 0.013). One in six subjects (16.7%) reported new-onset pain post COVID-19. The prevalence of neuropathic pain was estimated to be 24.4%. After adjusting for age and gender, headache during COVID-19 was a statistically significant predictor of neuropathic pain, increasing 4.9 times (95% 1.4–16.6, p = 0.011) the odds of neuropathic pain. Conclusion: Chronic pain—especially neuropathic—is widely prevalent in COVID-19 survivors. One in six subjects will develop new-onset pain that will persist beyond the acute phase of the disease and, therefore, should be considered a symptom of long COVID syndrome.

Pro-inflammatory cytokines and leukocyte integrins associated with chronic neuropathic pain in traumatic and inflammatory neuropathies: Initial observations and hypotheses

Leukocyte infiltration and persistence within peripheral nerves have been implicated in chronic nociception pathogenesis in murine peripheral neuropathy models. Endoneurial cytokine and chemokine expression contribute to leukocyte infiltration and maintenance of a pro-inflammatory state that delays peripheral nerve recovery and promotes chronic pain behaviors in these mice. However, there has been a failure to translate murine model data into safe and effective treatments for chronic neuropathic pain in peripheral neuropathy patients, or develop reliable biomarkers that may help diagnose or determine treatment responses in affected patients. Initial work showed that persistent sciatic nerve CD11b+ CD45+ leukocyte infiltration was associated with disease severity in three mouse models of inflammatory and traumatic peripheral neuropathies, implying a direct contributing role in disease pathogenesis. In support of this, CD11b+ leukocytes were also seen in the sural nerve biopsies of chronic neuropathic pain patients with three different peripheral neuropathies. Systemic CD11b antagonism using a validated function-neutralizing monoclonal antibody effectively treated chronic nociception following unilateral sciatic nerve crush injury (a representative traumatic neuropathy model associated with axonal degeneration and increased blood-nerve barrier permeability) and does not cause drug addiction behaviors in adult mice. These data suggest that CD11b could be an effective molecular target for chronic neuropathic pain treatment in inflammatory and traumatic peripheral neuropathies. Despite known murine peripheral neuropathy model limitations, our initial work suggests that early expression of pro-inflammatory cytokines, such as tissue inhibitor of metalloproteinases-1 may predict subsequent chronic nociception development following unilateral sciatic nerve crush injury. Studies aligning animal model investigation with observational data from well-characterized human peripheral neuropathies, including transcriptomics and proteomics, as well as animal model studies using a human clinical trial design should foster the identification of clinically relevant biomarkers and effective targeted treatments with limited addiction potential for chronic neuropathic pain in peripheral neuropathy patients.

Essential Oils and Neuropathic Pain

Neuropathic pain is one of the most prominent chronic pain syndromes, affecting almost 10% of the United States population. While there are a variety of established pharmacologic and non-pharmacologic treatment options, including tricyclic antidepressants (TCAs), serotonin-noradrenaline reuptake inhibitors, anticonvulsants, trigger point injections, and spinal cord stimulators, many patients continue to have chronic pain or suboptimal symptom control. This has led to an increased interest in alternative solutions for neuropathic pain such as nutritional supplements and essential oils. In this review, we explore the literature on the most commonly cited essential oils, including lavender, bergamot, rosemary, nutmeg, Billy goat weed, and eucalyptus. However, the literature is limited and largely comprised of preclinical animal models and a few experimental studies, some of which were poorly designed and did not clearly isolate the effects of the essential oil treatment. Additionally, no standardized method of dosing or route of administration has been established. Further randomized control studies isolating the active components of various essential oils are needed to provide conclusive evidence on the use of essential oils for neuropathic pain. In this review, we explore the basis behind some of the essential oils of interest to patients with neuropathic pain seen in rheumatology clinics.

Systematic Review of Voltage-Gated Calcium Channel α2δ Subunit Ligands for the Treatment of Chronic Neuropathic Pain and Insight into Structure-Activity Relationship (SAR) by Pharmacophore Modeling

BACKGROUND

Neuropathic pain (NP) is a complex symptom related to the nerve damage. The discovery of new drugs for treating chronic NP has been continuing for several decades, while more progress is still needed to be made because of the unsatisfactory efficacy and the side effects of the currently available drugs. Among all the approved drugs for chronic NP, voltage-gated calcium channel (VGCC) α2δ subunit ligands, also known as gabapentinoids, are among the first-line treatment and represent a class of efficacious and relatively safe therapeutic agents. However, new strategies are still needed to be explored due to the unsatisfied response rate.

OBJECTIVES

To review the latest status of the discovery and development of gabapentinoids for the treatment of chronic NP by covering both the marketed and the preclinical/clinical ones. To analyze the structure-activity relationship (SAR) of gabapentinoids to facilitate the future design of structurally novel therapeutic agents targeting VGCC α2δ subunit.

METHODS

We searched PubMed Central, Embase, Cochrane Library, Web of Science, Scopus and Espacenet for the literature and patents of diabetic peripheral neuropathic pain, postherpetic neuralgia, fibromyalgia, voltage-gated calcium channel α2δ subunit and related therapeutic agents from incipient to June 10, 2021. The SAR of gabapentinoids were analyzed by pharmacophore modeling using Phase module in Schrödinger suite.

RESULTS

A variety of gabapentinoids were identified as VGCC α2δ ligands that have ever been under development for the treatment of chronic NP. Among them, four gabapentinoids are marketed, one is at the active late clinical trials, and eight have been discontinued. Pharmacophore models were generated by using Phase module in Schrödinger suite, and common pharmacophores were predicted based on pharmacophoric features and analyzed.

CONCLUSION

The latest progress of the discovery and development of gabapentinoids for the treatment of chronic NP was reviewed. Moreover, the structure-activity relationship (SAR) of gabapentinoids is analyzed by pharmacophore modeling, which will be valuable for the future design of structurally novel therapeutic agents targeting VGCC α2δ subunit.

Efficacy and Safety of Ketamine in the Treatment of Neuropathic Pain: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Purpose

Ketamine is a N-methyl-D-aspartate (NMDA) antagonist with strong analgesic properties. Its addition to the treatment of neuropathic pain may reduce pain intensity and improve overall quality of life. A systematic review and meta-analysis of randomized controlled trials was performed to investigate the addition of ketamine to the treatment of patients with neuropathic pain.

Patients and Methods

GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach was used to rate the overall certainty of the evidence for each outcome. Eighteen (18) randomized controlled trials including 706 participants were included for further analysis.

Results

Ketamine addition to standard treatment of neuropathic pain (NP) resulted in a statistically significant reduction of pain intensity at one week after the end of treatment with ketamine (MD −2.14, 95% CI −2.65 to −1.63; p<0.00001) and after 30 days after the end of treatment with ketamine (MD −1.68, 95% CI −2.25 to −1.12; p<0.00001) and a statistically significant increase in discomfort (RR 4.06; 95% CI 1.18 to 13.95; p=0.03), and psychedelic effects (RR 4.94; 95% CI 2.76 to 8.84; p<0.00001).

Conclusion

There is a statistically significant pain reduction by adding ketamine to the treatment of chronic NP when compared to the standard treatment. However, such pain reduction comes at the expense of adverse outcomes, especially psychedelic effects related to the administration of ketamine. However, the overall quality of certainty of evidence is low due to the clinical heterogeneity among the intervention characteristics of the trials analyzed (different administration routes, dosing regimen, therapy durations, different clinical characteristics of the population investigated). Future large multi-centered trials are necessary to confirm or not the results of the present review.

Asprosin, a novel therapeutic candidate for painful neuropathy: an experimental study in mice

Recent studies indicate presence of a strong link between adipokines and neuropathic pain. However, the effects of asprosin, a novel adipokine, on neuropathic pain have not been studied in animal models.Mouse models were employed to investigate the antinociceptive effectiveness of asprosin in the treatment of three types of neuropathic pain, with metabolic (streptozocin/STZ), toxic (oxaliplatin/OXA), and traumatic (sciatic nerve ligation/CCI [chronic constriction nerve injury]) etiologies, respectively. Changes in nociceptive behaviors were assessed relative to controls using thermal (the hot plate and cold plate tests, at 50 °C and 4 °C respectively) and mechanical pain (von Frey test) tests after intraperitoneal (i.p.) administration of asprosin (10 µg/kg) and gabapentin (50 mg/kg) in several times intervals. Besides, possible effect of asprosin on the motor coordination of mice was assessed with a rotarod test. Serum level of asprosin was quantified by ELISA.In neuropathic pain models (STZ, OXA, and CCI), asprosin administration significantly reduced both mechanical and thermal hypersensitivity, indicating that it exhibits a clear-cut antihypersensitivity effect in the analyzed neuropathic pain models. The most effective time of asprosin on pain threshold was observed 60 min after its injection. Also, asprosin displayed no notable effect on the motor activity. Asprosin levels were significantly lower in neuropathic pain compared to healthy group (p < 0.05).The results yielded by the present study suggest that asprosin exhibits an analgesic effect in the neuropathic pain models and may have clinical utility in alleviating chronic pain associated with disease and injury originating from peripheral structures.

Inhibiting spinal secretory phospholipase A2 after painful nerve root injury attenuates established pain and spinal neuronal hyperexcitability by altering spinal glutamatergic signaling

Neuropathic injury is accompanied by chronic inflammation contributing to the onset and maintenance of pain after an initial insult. In addition to their roles in promoting immune cell activation, inflammatory mediators like secretory phospholipase A₂ (sPLA₂) modulate nociceptive and excitatory neuronal signaling during the initiation of pain through hydrolytic activity. Despite having a known role in glial activation and cytokine release, it is unknown if sPLA₂ contributes to the maintenance of painful neuropathy and spinal hyperexcitability later after neural injury. Using a well-established model of painful nerve root compression, this study investigated if inhibiting spinal sPLA₂ 7 days after painful injury modulates the behavioral sensitivity and/or spinal dorsal horn excitability that is typically evident. The effects of sPLA₂ inhibition on altered spinal glutamatergic signaling was also probed by measuring spinal intracellular glutamate levels and spinal glutamate transporter (GLAST and GLT1) and receptor (mGluR5, GluR1, and NR1) expression. Spinal sPLA₂ inhibition at day 7 abolishes behavioral sensitivity, reduces both evoked and spontaneous neuronal firing in the spinal cord, and restores the distribution of neuronal phenotypes to those of control conditions. Inhibiting spinal sPLA₂ also increases intracellular glutamate concentrations and restores spinal expression of GLAST, GLT1, mGluR5, and GluR1 to uninjured expression with no effect on NR1. These findings establish a role for spinal sPLA₂ in maintaining pain and central sensitization after neural injury and suggest this may be via exacerbating glutamate excitotoxicity in the spinal cord.

Effects of repetitive transcranial magnetic stimulation on neuropathic pain: A systematic review and meta-analysis

Neuropathic pain (NP) is a chronic pain condition caused by lesion or disease of the somatosensory nervous system. Repetitive transcranial magnetic stimulation (rTMS) is a neuroregulatory tool that uses pulsed magnetic fields to modulate the cerebral cortex. This review aimed to ascertain the therapeutic effect of rTMS on NP and potential factors regulating the therapeutic effect of rTMS. Database search included Web of Science, Embase, Pubmed, and Cochrane Library from inception to July 2021. Eligible studies included randomized controlled studies of the analgesic effects of rTMS in patients with NP. Thirty-eight studies were included. Random effect analysis showed effect sizes of -0.66 (95 % CI, -0.87 to -0.46), indicating that real rTMS was better than sham condition in reducing pain (P < 0.001). This comprehensive review indicated that stimulation frequency, intervention site, and location of lesion were important factors affecting the therapeutic effect. The findings of this study may guide clinical decisions and future research.

The Calcium Channel α2δ1 Subunit: Interactional Targets in Primary Sensory Neurons and Role in Neuropathic Pain

Neuropathic pain is mainly triggered after nerve injury and associated with plasticity of the nociceptive pathway in primary sensory neurons. Currently, the treatment remains a challenge. In order to identify specific therapeutic targets, it is necessary to clarify the underlying mechanisms of neuropathic pain. It is well established that primary sensory neuron sensitization (peripheral sensitization) is one of the main components of neuropathic pain. Calcium channels act as key mediators in peripheral sensitization. As the target of gabapentin, the calcium channel subunit α2δ1 (Cavα2δ1) is a potential entry point in neuropathic pain research. Numerous studies have demonstrated that the upstream and downstream targets of Cavα2δ1 of the peripheral primary neurons, including thrombospondins, N-methyl-D-aspartate receptors, transient receptor potential ankyrin 1 (TRPA1), transient receptor potential vanilloid family 1 (TRPV1), and protein kinase C (PKC), are involved in neuropathic pain. Thus, we reviewed and discussed the role of Cavα2δ1 and the associated signaling axis in neuropathic pain conditions.

The Kynurenine Pathway as a Potential Target for Neuropathic Pain Therapy Design: From Basic Research to Clinical Perspectives

Accumulating evidence suggests the key role of the kynurenine pathway (KP) of the tryptophan metabolism in the pathogenesis of several diseases. Despite extensive research aimed at clarifying the mechanisms underlying the development and maintenance of neuropathic pain, the roles of KP metabolites in this process are still not fully known. Although the function of the peripheral KP has been known for several years, it has only recently been acknowledged that its metabolites within the central nervous system have remarkable consequences related to physiology and behavior. Both the products and metabolites of the KP are involved in the pathogenesis of pain conditions. Apart from the neuroactive properties of kynurenines, the KP regulates several neurotransmitter systems in direct or indirect ways. Some neuroactive metabolites are known to have neuroprotective properties (kynurenic acid, nicotinamide adenine dinucleotide cofactor), while others are toxic (3-hydroxykynurenine, quinolinic acid). Numerous animal models show that modulation of the KP may turn out to be a viable target for the treatment of diseases. Importantly, some compounds that affect KP enzymes are currently described to possess analgesic properties. Additionally, kynurenine metabolites may be useful for assessing response to therapy or as biomarkers in therapeutic monitoring. The following review describes the molecular site of action and changes in the levels of metabolites of the kynurenine pathway in the pathogenesis of various conditions, with a particular emphasis on their involvement in neuropathy. Moreover, the potential clinical implications of KP modulation in chronic pain therapy as well as the directions of new research initiatives are discussed.

Validation of the Nepali Version of the Self-reported Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS) in Adults With Chronic Pain and Predominantly Low-literacy Levels

Neuropathic pain research and clinical care is limited in low- and middle-income countries with high prevalence of chronic pain such as Nepal. We translated and cross-culturally adapted the Self-report version of the Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS)-a commonly used, reliable and valid instrument to screen for pain of predominantly neuropathic origin (POPNO)-into Nepali (S-LANSS-NP) and validated it using recommended guidelines. We recruited 30 patients with chronic pain in an outpatient setting for cognitive debriefing and recruited 287 individuals with chronic pain via door-to-door interviews for validation. For known-group validity, we hypothesized that the POPNO group would report significantly more pain intensity and pain interference than the chronic pain group without POPNO using a cut-off score of ≥10/24. The S-LANSS-NP was comprehensible based on the ease of understanding the questionnaire and lack of missing responses. The validation sample consisted of predominantly low-levels of literacy (81% had 5 years or less education); 23% were classified as having POPNO. Internal consistency was good (alpha = .80). Known-group validity was supported (chronic pain with POPNO reported significantly greater pain intensity than those without). The S-LANSS-NP is a comprehensible, unidimensional, internally consistent, and valid instrument to screen POPNO in individuals with chronic pain with predominantly low-levels of literacy for clinical and research use. PERSPECTIVE: This paper shows that the Nepali version of the S-LANSS is comprehensible, reliable and valid in adults with chronic pain and predominantly low-levels of literacy in rural Nepal. The study could potentially develop research and clinical care of neuropathic pain in this resource-limited setting where chronic pain is a significant problem.

Novel RET agonist for the treatment of experimental neuropathies

The glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) alleviate symptoms of experimental neuropathy, protect and stimulate regeneration of sensory neurons in animal models of neuropathic pain, and restore their functional activity. However, clinical development of GFL proteins is complicated by their poor pharmacokinetic properties and multiple effects mediated by several receptors. Previously, we have identified a small molecule that selectively activates the major signal transduction unit of the GFL receptor complex, receptor tyrosine kinase RET, as an alternative to GFLs, for the treatment of neuropathic pain. We then introduced a series of chemical changes to improve the biological activity of these compounds and tested an optimized compound named BT44 in a panel of biological assays. BT44 efficiently and selectively stimulated the GFL receptor RET and activated the intracellular mitogene-activated protein kinase/extracellular signal-regulated kinase pathway in immortalized cells. In cultured sensory neurons, BT44 stimulated neurite outgrowth with an efficacy comparable to that of GFLs. BT44 alleviated mechanical hypersensitivity in surgery- and diabetes-induced rat models of neuropathic pain. In addition, BT44 normalized, to a certain degree, the expression of nociception-related neuronal markers which were altered by spinal nerve ligation, the neuropathy model used in this study. Our results suggest that the GFL mimetic BT44 is a promising new lead for the development of novel disease-modifying agents for the treatment of neuropathy and neuropathic pain.

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.

Modulation of Pathological Pain by Epidermal Growth Factor Receptor

Chronic pain has been widely recognized as a major public health problem that impacts multiple aspects of patient quality of life. Unfortunately, chronic pain is often resistant to conventional analgesics, which are further limited by their various side effects. New therapeutic strategies and targets are needed to better serve the millions of people suffering from this devastating disease. To this end, recent clinical and preclinical studies have implicated the epidermal growth factor receptor signaling pathway in chronic pain states. EGFR is one of four members of the ErbB family of receptor tyrosine kinases that have key roles in development and the progression of many cancers. EGFR functions by activating many intracellular signaling pathways following binding of various ligands to the receptor. Several of these signaling pathways, such as phosphatidylinositol 3-kinase, are known mediators of pain. EGFR inhibitors are known for their use as cancer therapeutics but given recent evidence in pilot clinical and preclinical investigations, may have clinical use for treating chronic pain. Here, we review the clinical and preclinical evidence implicating EGFR in pathological pain states and provide an overview of EGFR signaling highlighting how EGFR and its ligands drive pain hypersensitivity and interact with important pain pathways such as the opioid system.

A review of the StimRouter® peripheral neuromodulation system for chronic pain management

The StimRouter® peripheral nerve stimulation system created by Bioness, Inc., (CA, USA) is US FDA-approved for the treatment of peripheral mononeuropathy refractory to conservative medical management. StimRouter is a minimally invasive system that utilizes a subcutaneously implanted lead with integrated anchor and electrodes, and an external pulse generator to produce peripheral neuromodulation and achieve pain relief. Multiple published clinical trials reviewed here have shown the StimRouter system to have a high margin of safety, differentiating it from other existing peripheral neuromodulation systems requiring open surgical electrode placement and implantable pulse generators. These studies have also shown the StimRouter system to be efficacious in the treatment of multiple peripheral mononeuropathies; improving patient pain, activity levels and quality of life. StimRouter represents a feasible option for management of chronic peripheral mononeuropathy.

Development of a common peroneal nerve injury model in domestic swine for the study of translational neuropathic pain treatments

OBJECTIVE

To date, muscular and bone pain have been studied in domestic swine models, but the only neuropathic pain model described in swine is a mixed neuritis model. Common peroneal nerve injury (CPNI) neuropathic pain models have been utilized in both mice and rats.

METHODS

The authors developed a swine surgical CPNI model of neuropathic pain. Behavioral outcomes were validated with von Frey filament testing, thermal sensitivity assessments, and social and motor scoring. Demyelination of the nerve was confirmed through standard histological assessment. The contralateral nerve served as the control.

RESULTS

CPNI induced mechanical and thermal allodynia (p < 0.001 [n = 10] and p < 0.05 [n = 4], respectively) and increased pain behavior, i.e., guarding of the painful leg (n = 12). Myelin protein zero (P0) staining revealed demyelination of the ligated nerve upstream of the ligation site.

CONCLUSIONS

In a neuropathic pain model in domestic swine, the authors demonstrated that CPNI induces demyelination of the common peroneal nerve, which the authors hypothesize is responsible for the resulting allodynic pain behavior. As the anatomical features of domestic swine resemble those of humans more closely than previously used rat and mouse models, utilizing this swine model, which is to the authors' knowledge the first of its kind, will aid in the translation of experimental treatments to clinical trials.

Differential effects of epidermal growth factor receptor inhibitors in a single patient with neuropathic pain

Neuropathic pain (NP) represents an unmet medical need, where analgesic responses to different epidermal growth factor receptor inhibitors (EGFR-Is) have been described. The human EGFR family of receptors consists of four members (human epidermal growth factor receptor, HER 1-4), signalling via different homodimer and heterodimer combinations. A 52-year-old man was treated with the EGFR-I cetuximab in a trial of severe NP. Pain scores decreased dramatically after blinded cetuximab, but not after placebo. On pain recurrence after the trial, he was prescribed the oral EGFR-Is erlotinib, gefitinib, and lapatinib without relief. However, treatment with the pan-HER-inhibitor afatinib was effective. After 4 years on afatinib, pain control remains excellent with manageable side effects. This is the first reported observation of differential effects of EGFR-Is on NP in the same patient and the first report describing NP relief with afatinib. Further understanding of the underlying pathophysiology could lead to development of EGFR-Is specifically targeting NP.

Patient-reported outcomes in those consuming medical cannabis: a prospective longitudinal observational study in chronic pain patients

PURPOSE

We investigated patients with chronic pain seeking medical cannabis. We assessed their demographics, patterns of cannabis use, and the long-term effectiveness of cannabis on their pain and functional domains.

METHODS

This observational study enrolled patients between 8 September 2015 and 31 July 2018 from community-based cannabis clinics in Ontario, Canada. In addition to collecting demographic information, the primary outcomes studied were pain intensity and pain-related interference scores assessed at baseline, three, six, and 12 months. Using validated questionnaires, we also assessed anxiety, depression, quality of life (QoL), general health symptoms, neuropathic pain, self-reported opioid consumption, and adverse events.

RESULTS

Of the 1,000 patients consented, 757 (76%) participated at one or more of the study time points. At six and 12 months, 230 (30.4%) and 104 (13.7%) of participants were followed up, respectively. Most participants were female (62%), Caucasian (91%), and sought cannabis for pain relief (88%). Time was a significant factor associated with improvement in pain intensity (P < 0.001), pain-related interference scores (P < 0.001), QoL (P < 0.001), and general health symptoms (P < 0.001). Female sex was significantly associated with worse outcomes than male sex including pain intensity (P < 0.001) and pain-related interference (P < 0.001). The proportion of individuals who reported using opioids decreased by half, from 40.8% at baseline to 23.9% at 12 months.

CONCLUSION

Despite significant challenges to collecting long-term observational data on patients who attempted a trial of cannabis products, approximately one-third of patients in the cohort remained on medical cannabis for six months. In this cohort, pain intensity and pain-related interference scores were reduced and QoL and general health symptoms scores were improved compared with baseline.

Prevalence and associated factors of painful diabetic peripheral neuropathy among diabetic patients on follow up at Jimma University Medical Center

BACKGROUND

Despite having significant impact on the patient's quality of life, painful diabetic peripheral neuropathy (PDPN) is usually underdiagnosed. Screening for PDPN in patients with diabetes is needed in order to get timely identification and management. Hence, the purpose of this study was to assess the prevalence and determinants of PDPN among diabetes patients attending outpatient at Jimma University Medical Center from September 1 November 10, 2019.

METHODS

Hospital based cross-sectional study was conducted and douleur neuropathique-4 was used to identify the presence of PDPN. Data were collected using pretested structured questionnaire and entered into EPI data 3.1 and exported to SPSS version 20 for analysis. Both bivariate and multivariate binary logistic regression was employed to identify factors associated with PDPN. Variable having a p value of <0.25 in the bivariate model were considered as candidates for multivariable regression. Adjusted odds ratios were calculated at 95%CI and considered significant with a p value of <0.05.

RESULTS

A total of 366 diabetic patients were enrolled into the study and their mean duration of diabetes was 6.8 ± 5.3 years. The study finding showed that the prevalence of PDPN was 14.5%. According to the multivariate logistic regression analysis smoking [current smoker(AOR = 6.17; 95%CI:2.25,16.86),former smoker(AOR = 3.22;95%CI:1.29,8.03)],diabetes duration[5 to 10 years (AOR = 3.32;95%CI:1.29,8.53), ≥ 10 years (AOR = 8.86;95% CI: 3.49,22.5)] and comorbid hypertension [AOR = 2.54; 95%CI:1.17,5.49] were independent predictors of PDPN among study participants.

CONCLUSION

The overall prevalence of PDPN in this study was 14.5% and it was significantly associated with smoking, comorbid hypertension and diabetes duration of above 5 years. Early detection and appropriate interventions are important for high risk patients identified in the current study.

Neuropathic Pain after Adolescent Idiopathic Scoliosis Correction Surgery

Study Design

Prospective study.

Purpose

To investigate the prevalence and the associated risk factors of chronic neuropathic pain symptoms using painDETECT questionnaire in adolescent idiopathic scoliosis (AIS) patients who underwent posterior spinal fusion (PSF) surgery.

Overview of Literature

Post-lumbar surgery syndrome is a disease entity that describes neuropathic pain following spinal surgery. However, few studies have investigated the prevalence and risk factors for neuropathic pain in pediatric population undergoing corrective spinal surgery.

Methods

Forty AIS patients were recruited. Demographic, preoperative, and postoperative data were recorded. The magnitude and characteristics of postoperative pain were assessed using the painDETECT questionnaire through telephone enquiries at intervals of 2, 6, 12, and 24 weeks. Statistical analyses were followed by Pearson correlation test to determine the relationship between pain scores at 6, 12, and 24 weeks with the risk factors.

Results

Based on the painDETECT questionnaire, 90% of the patients had nociceptive pain, and 10% had a possible neuropathic pain component at 2 weeks postoperatively as per a mean painDETECT score of 7.1±4.5. Assessments at 6, 12, and 24 weeks showed that no patients had neuropathic pain with painDETECT scores of 4.4±3.2, 2.9±2.9, and 1.5±2.0, respectively. There was a significant correlation between total postoperative morphine use during 48 hours after the surgery and a tendency to develop neuropathic pain (p=0.022).

Conclusions

Chronic neuropathic pain was uncommon in AIS patients who had undergone PSF surgery. Higher opioid consumption will increase the possibility of developing chronic neuropathic pain.

Glial cell line-derived neurotrophic factors (GFLs) and small molecules targeting RET receptor for the treatment of pain and Parkinson's disease

Rearranged during transfection (RET), in complex with glial cell line-derived (GDNF) family receptor alpha (GFRα), is the canonical signaling receptor for GDNF family ligands (GFLs) expressed in both central and peripheral parts of the nervous system and also in non-neuronal tissues. RET-dependent signaling elicited by GFLs has an important role in the development, maintenance and survival of dopamine and sensory neurons. Both Parkinson's disease and neuropathic pain are devastating disorders without an available cure, and at the moment are only treated symptomatically. GFLs have been studied extensively in animal models of Parkinson's disease and neuropathic pain with remarkable outcomes. However, clinical trials with recombinant or viral vector-encoded GFL proteins have produced inconclusive results. GFL proteins are not drug-like; they have poor pharmacokinetic properties and activate multiple receptors. Targeting RET and/or GFRα with small molecules may resolve the problems associated with using GFLs as drugs and can result in the development of therapeutics for disease-modifying treatments against Parkinson's disease and neuropathic pain.

RET Receptor Tyrosine Kinase: Role in Neurodegeneration, Obesity, and Cancer

Rearranged during transfection (RET) is the tyrosine kinase receptor that under normal circumstances interacts with ligand at the cell surface and mediates various essential roles in a variety of cellular processes such as proliferation, differentiation, survival, migration, and metabolism. RET plays a pivotal role in the development of both peripheral and central nervous systems. RET is expressed from early stages of embryogenesis and remains expressed throughout all life stages. Mutations either activating or inhibiting RET result in several aggressive diseases, namely cancer and Hirschsprung disease. However, the physiological ligand-dependent activation of RET receptor is important for the survival and maintenance of several neuronal populations, appetite, and weight gain control, thus providing an opportunity for the development of disease-modifying therapeutics against neurodegeneration and obesity. In this review, we describe the structure of RET, its signaling, and its role in both normal conditions as well as in several disorders. We highlight the differences in the signaling and outcomes of constitutive and ligand-induced RET activation. Finally, we review the data on recently developed small molecular weight RET agonists and their potential for the treatment of various diseases.

Gamma Knife central lateral thalamotomy for the treatment of neuropathic pain

OBJECTIVE

The goal of this study was to assess the safety and efficacy of stereotactic central lateral thalamotomy with Gamma Knife radiosurgery in patients with neuropathic pain.

METHODS

Clinical and radiosurgical data were prospectively collected and analyzed in patients with neuropathic pain who underwent Gamma Knife central lateral thalamotomy. The safety and efficacy of the lesioning procedure were evaluated by neurological examination and standardized scales for pain intensity and health-related quality of life. Visual analog scale (VAS) for pain, McGill Pain Questionnaire (MPQ), EuroQol-5 dimensions (EQ-5D), and the 36-Item Short Form Health Survey, version 2 (SF-36v2) were measured during baseline and postoperative follow-up evaluations at 3, 6, 12, 24, and 36 months.

RESULTS

Eight patients with neuropathic pain underwent Gamma Knife central lateral thalamotomy. Four patients suffered from trigeminal deafferentation pain, 2 from brachial plexus injury, 1 from central poststroke facial neuropathic pain, and 1 from postherpetic neuralgia. No lesioning-related adverse effect was recorded during the follow-up periods. All patients had pain reduction following thalamotomy. The mean follow-up time was 24 months. At the last follow-up visits, 5 patients reported ≥ 50% VAS pain reduction. The overall mean VAS pain score was 9.4 (range 8-10) before radiosurgery. After 1 year, the mean VAS pain score decreased significantly, from 9.4 (range 8-10) to 5.5 (mean -41.33%, p = 0.01). MPQ scores significantly decreased (mean -22.18%, p = 0.014). Statistically significant improvements of the SF-36v2 quality of life survey (mean +48.16%, p = 0.012) and EQ-5D (+45.16%, p = 0.012) were observed. At 2 years after radiosurgery, the VAS pain score remained significantly reduced to a mean value of 5.5 (p = 0.027). Statistically significant improvements were also observed for the MPQ (mean -16.05%, p = 0.034); the EQ-5D (mean +35.48%, p = 0.028); and the SF-36v2 (mean +35.84%, p = 0.043). At the last follow-up visits, pain had recurred in 2 patients, who were suffering from central poststroke neuropathic pain and brachial plexus injury, respectively.

CONCLUSIONS

Safe, nonpharmacological therapies are imperative for the management of refectory chronic pain conditions. The present series demonstrates that Gamma Knife central lateral thalamotomy is safe and potentially effective in the long term for relieving chronic neuropathic pain refractory to pharmacotherapy and for restoring quality of life.

Function and Mechanisms of Truncated BDNF Receptor TrkB.T1 in Neuropathic Pain

Brain-derived neurotrophic factor (BDNF), a major focus for regenerative therapeutics, has been lauded for its pro-survival characteristics and involvement in both development and recovery of function within the central nervous system (CNS). However, studies of tyrosine receptor kinase B (TrkB), a major receptor for BDNF, indicate that certain effects of the TrkB receptor in response to disease or injury may be maladaptive. More specifically, imbalance among TrkB receptor isoforms appears to contribute to aberrant signaling and hyperpathic pain. A truncated isoform of the receptor, TrkB.T1, lacks the intracellular kinase domain of the full length receptor and is up-regulated in multiple CNS injury models. Such up-regulation is associated with hyperpathic pain, and TrkB.T1 inhibition reduces neuropathic pain in various experimental paradigms. Deletion of TrkB.T1 also limits astrocyte changes in vitro, including proliferation, migration, and activation. Mechanistically, TrkB.T1 is believed to act through release of intracellular calcium in astrocytes, as well as through interactions with neurotrophins, leading to cell cycle activation. Together, these studies support a potential role for astrocytic TrkB.T1 in hyperpathic pain and suggest that targeted strategies directed at this receptor may have therapeutic potential.

In Vitro and In Vivo Effects of Flavonoids on Peripheral Neuropathic Pain

Neuropathic pain is a common symptom and is associated with an impaired quality of life. It is caused by the lesion or disease of the somatosensory system. Neuropathic pain syndromes can be subdivided into two categories: central and peripheral neuropathic pain. The present review highlights the peripheral neuropathic models, including spared nerve injury, spinal nerve ligation, partial sciatic nerve injury, diabetes-induced neuropathy, chemotherapy-induced neuropathy, chronic constriction injury, and related conditions. The drugs which are currently used to attenuate peripheral neuropathy, such as antidepressants, anticonvulsants, baclofen, and clonidine, are associated with adverse side effects. These negative side effects necessitate the investigation of alternative therapeutics for treating neuropathic pain conditions. Flavonoids have been reported to alleviate neuropathic pain in murine models. The present review elucidates that several flavonoids attenuate different peripheral neuropathic pain conditions at behavioral, electrophysiological, biochemical and molecular biological levels in different murine models. Therefore, the flavonoids hold future promise and can be effectively used in treating or mitigating peripheral neuropathic conditions. Thus, future studies should focus on the structure-activity relationships among different categories of flavonoids and develop therapeutic products that enhance their antineuropathic effects.

Mechanisms for Reducing Neuropathic Pain

Injury typically results in the development of neuropathic pain, but the pain normally decreases and disappears in paralleled with wound healing. The pain results from cells resident at, and recruited to, the injury site releasing pro-inflammatory cytokines and other mediators leading to the development of pro-inflammatory environment and causing nociceptive neurons to develop chronic ectopic electrical activity, which underlies neuropathic pain. The pain decreases as some of the cells that induce pro-inflammation, changing their phenotype leading to the blocking the release of pro-inflammatory mediators while releasing anti-inflammatory mediators, and blocking nociceptive neuron chronic spontaneous electrical activity. Often, despite apparent wound healing, the neuropathic pain becomes chronic. This raises the question of how chronic pain can be eliminated. While many of the cells and mediators contributing to the development and maintenance of neuropathic pain are known, a better understanding is required of how the injury site environment can be controlled to permanently eliminate the pro-inflammatory environment and silence the chronically electrically active nociceptive neurons. This paper examines how methods that can promote the transition of the pro-inflammatory injury site to an anti-inflammatory state, by changing the composition of local cell types, modifying the activity of pro- and anti-inflammatory receptors, inducing the release of anti-inflammatory mediators, and silencing the chronically electrically active nociceptive neurons. It also examines the hypothesis that factors released from platelet-rich plasma applied to chronic pain sites can permanently eliminate chronic inflammation and its associated chronic pain.

Cdk5-Dependent Phosphorylation of CaV3.2 T-Type Channels: Possible Role in Nerve Ligation-Induced Neuropathic Allodynia and the Compound Action Potential in Primary Afferent C Fibers

Voltage-gated T-type Ca²⁺ (Ca_V3) channels regulate diverse physiological events, including neuronal excitability, and have been linked to several pathological conditions such as absence epilepsy, cardiovascular diseases, and neuropathic pain. It is also acknowledged that calcium/calmodulin-dependent protein kinase II and protein kinases A and C regulate the activity of T-type channels. Interestingly, peripheral nerve injury induces tactile allodynia and upregulates Ca_V3.2 channels and cyclin-dependent kinase 5 (Cdk5) in dorsal root ganglia (DRG) and spinal dorsal horn. Here, we report that recombinant Ca_V3.2 channels expressed in HEK293 cells are regulatory targets of Cdk5. Site-directed mutagenesis showed that the relevant sites for this regulation are residues S561 and S1987. We also found that Cdk5 may regulate Ca_V3.2 channel functional expression in rats with mechanical allodynia induced by spinal nerve ligation (SNL). Consequently, the Cdk5 inhibitor olomoucine affected the compound action potential recorded in the spinal nerves, as well as the paw withdrawal threshold. Likewise, Cdk5 expression was upregulated after SNL in the DRG. These findings unveil a novel mechanism for how phosphorylation may regulate Ca_V3.2 channels and suggest that increased channel activity by Cdk5-mediated phosphorylation after SNL contributes nerve injury-induced tactile allodynia.SIGNIFICANCE STATEMENT Neuropathic pain is a current public health challenge. It can develop as a result of injury or nerve illness. It is acknowledged that the expression of various ion channels can be altered in neuropathic pain, including T-type Ca²⁺ channels that are expressed in sensory neurons, where they play a role in the regulation of cellular excitability. The present work shows that the exacerbated expression of Cdk5 in a preclinical model of neuropathic pain increases the functional expression of Ca_V3.2 channels. This finding is relevant for the understanding of the molecular pathophysiology of the disease. Additionally, this work may have a substantial translational impact, since it describes a novel molecular pathway that could represent an interesting therapeutic alternative for neuropathic pain.

Sensitivities to Thermal and Mechanical Stimuli: Adults With Sickle Cell Disease Compared to Healthy, Pain-Free African American Controls

Evidence supports^, but is inconclusive that sensitization contributes to chronic pain in some adults with sickle cell disease (SCD). We determined the prevalence of pain sensitization among adults with SCD pain compared with pain-free healthy adults. In a cross sectional, single session study of 186 African American outpatients with SCD pain (age 18-74 years, 59% female) and 124 healthy age, gender, and race matched control subjects (age 18-69 years, 49% female), we compared responses to standard thermal (Medoc TSA II) and mechanical stimuli (von Frey filaments). Although we observed no significant differences in thermal thresholds between controls and patients, patients with SCD had lower pain thresholds to mechanical stimuli and reported higher pain intensity scores to all thermal and mechanical stimuli at a non-painful body site. Compared with controls, about twice as many patients with SCD showed sensitization: 12% versus 23% at the anterior forearm site (P = .02), and 16% versus 32% across 3 tested sites (P = .004). Among patients with SCD, 18% exhibited some element of central sensitization. Findings indicate that persistent allodynia and hyperalgesia can be part of the SCD pain experience and should be considered when selecting therapies for SCD pain. PERSPECTIVE: Compared with matched healthy controls, quantitative sensory testing in adults with pain and sickle cell disease (SCD) demonstrates higher prevalence of sensitization, including central sensitization. The findings of allodynia and hyperalgesia may indicate neuropathic pain and could contribute to a paradigm shift in assessment and treatment of SCD pain.

Injury-Induced Effectors of Neuropathic Pain

Injuries typically result in the development of neuropathic pain, which decreases in parallel with wound healing. However, the pain may remain after the injury appears to have healed, which is generally associated with an ongoing underlying pro-inflammatory state. Injury induces many cells to release factors that contribute to the development of a pro-inflammatory state, which is considered an essential first step towards wound healing. However, pain elimination requires a transition of the injury site from pro- to anti-inflammatory. Therefore, developing techniques that eliminate chronic pain require an understanding of the cells resident at and recruited to injury sites, the factors they release, that promote a pro-inflammatory state, and promote the subsequent transition of that site to be anti-inflammatory. Although a relatively large number of cells, factors, and gene expression changes are involved in these processes, it may be possible to control a relatively small number of them leading to the reduction and elimination of chronic neuropathic pain. This first of two papers examines the roles of the most salient cells and mediators associated with the development and maintenance of chronic neuropathic pain. The following paper examines the cells and mediators involved in reducing and eliminating chronic neuropathic pain.

Prospective case series on the use of peripheral nerve stimulation for focal mononeuropathy treatment

Aim: This case series looks at outcomes in 39 patients implanted using the Bioness Stimrouter system on various isolated mononeuropathies. Patients & methods: A case series of 39 patients with a total of 42 implants were enrolled starting August 2017 at various pain management centers. Results: Of 39 patients studied, 78% of the participants noticed an improvement in their pain. There was a 71% reduction in pain scores with the average preprocedure score of 8 improving to 2 post-implant. Participants noted on average a 72% improvement in activity with the greatest observed in the brachial plexus (80%) and suprascapular nerve (80%) and smallest in the intercostal nerve (40%). Approximately 89% of those implanted with a peripheral nerve stimulator experienced a greater than 50% reduction in opioid consumption. Conclusion: Peripheral nerve stimulators are a new, minimally invasive neuromodulation modality that shows promising early results in our 39-patient case series.

[The use of analgesics and risk of self-medication in an urban population sample: cross-sectional study]

BACKGROUND AND OBJECTIVES

There are few data in the literature characterizing the pattern of analgesic use in Latin American countries, including Brazil. Little is known about the undertreatment of pain and its influence on the habit of self-medication with analgesics. The aim of this study is to define the pattern of analgesic use among chronic pain patients and its potential association with self-medication with analgesics.

METHOD

Cross-sectional observational study with an urban population sample. Chronic pain was defined as a pain lasting for at least 90 days. The study was approved by the Research Ethics Committee of the institution.

RESULTS

416 subjects were included; 45.7% (n=190) had chronic pain, with females (72.3%; p=0.04) being the most affected. Self-medication with analgesics is practiced by 78.4% of patients with chronic pain. The most common current analgesic treatment consists of non-steroidal anti-inflammatory drugs (dipyrone and acetaminophen). Weak opioids are rarely used and only 2.6% of subjects with chronic pain were taking these analgesics. None of the subjects were taking potent opioids.

CONCLUSIONS

The practice of self-medication with analgesics is frequent among patients with chronic pain, which may be due to the underprescription of more potent analgesics, such as opioids. It can also be said that, given the data presented, there is no crisis of recreational opioid use in the studied population.