Pharmacological treatments of neuropathic pain: real-life comparisons using propensity score matching

CADOR (Capsaicin in neuropathic-like pain in digital osteoarthritis) study protocol: a multicentre randomised parallel-group trial

INTRODUCTION

It is common for finger pain in hand osteoarthritis (HOA) to display a neuropathic component. Non-steroidal anti-inflammatory drugs (NSAIDs) and conventional analgesics are not very effective in relieving this neuropathic-like pain. Capsaicin, a compound extracted from chilli peppers, is approved for the management of localised neuropathic pain. However, the effectiveness of an 8% capsaicin transdermal patch has never been tested in HOA patients with neuropathic-like pain in a randomised setting. In this study, we aimed to compare the 60-day (D60) efficacy of a transdermal application of capsaicin 8% versus a control (very low-dose capsaicin at 0.04%) on hand pain in patients with painful digital osteoarthritis with a neuropathic-like pain component.

METHODS AND ANALYSIS

CADOR (CApsaicin in neuropathic-like pain in Digital Osteoarthritis: a Randomised trial) is a multicentre, randomised, controlled, double-blind, two parallel group, phase 3 clinical trial. Eligible patients have HOA according to the American College of Rheumatology criteria and at least Kellgren-Lawrence grade≥2, with neuropathic-like pain ('Douleur neuropathique en 4 questions' (DN4) score≥4/10 and pain intensity≥40/100 mm). At Day 0, 120 patients will be randomised (1:1) to receive a single 30 min topical application of either capsaicin 8% transdermal patch (experimental group) or capsaicin 0.04% transdermal patch (control group). The primary outcome is pain intensity in the fingers over the past 48 hours at Day 60, measured with a Visual Analogue Scale (VAS) ranging from 0 to 100 mm. Secondary outcomes are functional disability, quality of life, anxiety and depression, the patient's global impression of improvement, use of analgesics and NSAIDs and the safety of capsaicin. At visit D60, patients who still have finger pain≥40/100 mm on the VAS will receive, if they wish a single 30 min topical application of capsaicin 8% transdermal patch (not blinded). The efficacy of two transdermal applications of capsaicin (either two applications of 8% patch in the experimental arm or one application of 0.04% and one application of 8% in the control arm) will be assessed on Day 120.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the French Health Authorities (Comité de protection des Personnes SUD EST V and Agence Nationale de Sécurité du Médicament) on 23 May 2024 in accordance with European Regulation n°536/2014 of 16 April 2014 (ref: 2024-511159-16-00) before participant enrolment.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov: NCT06444919.

Trends and hotspots in burns-related pain research: A bibliometric analysis

OBJECTIVE

The aim of this investigation was to conduct a thorough synthesis of the extant scholarly discourse and to delineate the prevailing global trends in the domain of burn pain, employing a bibliometric analysis.

METHODS

A bibliometric analysis was performed utilizing the Web of Science Core Collection database. Articles were selected based on titles or abstracts containing keywords associated with burns and pain. Both quantitative and qualitative methodologies were applied to examine the retrieved data, encompassing an analysis of publication trends, research themes, and collaboration networks.

RESULTS

The number of articles on this topic has been increasing, averaging an annual growth rate of 6.9 % from 1997 to 2023. Contributions have come from 645 institutions across 53 countries, resulting in 446 papers that span areas such as nursing, anesthesia, and immunology. Key journals include Burns, Journal of Burn Care & Research, and Pain. The United States has demonstrated a significant research output in this field, with active international collaboration, notably with Washington University leading in contributions. Patterson DR was the most prolific author in terms of published papers, while Choiniere M was the most frequently co-cited author. The focus of research has shifted from symptom management to exploring pain mechanisms. Current research priorities in burn pain include "quality of life," "music therapy," and "psychological state." Recent analysis has highlighted key areas in neuropathic pain mechanisms, novel analgesic therapies, and specific groups such as pediatric burn patients. Influential studies have advanced our understanding of pathophysiology, while psychological interventions and inflammation are increasingly receiving attention. Emerging topics include non-pharmacological interventions, psychological support, technology in pain assessment and management, quality of life, and personalized pain management.

CONCLUSION

Research on burn pain is advancing rapidly; however, collaboration among countries and institutions remains limited. Increased cooperation and communication across these entities could significantly advance the field in the future. Future research should prioritize placebo-controlled trials of targeted therapeutic drugs and innovative pain management approaches, with a strong emphasis on patient outcomes and quality of life.

METHA-NeP: effectiveness and safety of methadone for neuropathic pain: a controlled randomized trial

ABSTRACT

In this randomized, double-blind, parallel placebo-controlled clinical trial, we evaluated the efficacy of methadone as an add-on therapy for people with chronic neuropathic pain (NP). Eighty-six patients were randomly assigned to receive methadone or placebo for 8 weeks. The primary outcome was the proportion of participants achieving at least 30% pain relief from baseline using a 100-mm pain Visual Analogue Scale. Secondary outcomes included global impression of change, NP symptoms, sleep quality, quality of life, pain interference in daily activities, and mood. A larger number of responders were found in the methadone (68%), compared to the placebo (33%) arm; risk difference 33.6%; 95% confidence interval 13.0%-54.3%; P = 0.003; number needed to treat = 3.0. Methadone reduced pain intensity ( P < 0.001), burning ( P = 0.023), pressing ( P = 0.005), and paroxysmal dimensions ( P = 0.006) of NP. Methadone also improved sleep ( P < 0.001) and increased the patient's global impression of improvement ( P = 0.002). Methadone did not significantly impact quality of life, pain interference, or mood. Treatment-emergent adverse events occurred in all methadone- and in 73% of placebo-treated patients ( P < 0.001). No serious adverse events or deaths occurred. Discontinuation due to adverse events was reported in 2 participants in the methadone and none in the placebo arm. Methadone use as an add-on to an optimized treatment for NP with first- and/or second-line drugs provided superior analgesia, improved sleep, and enhanced global impression of change, without being associated with significant serious adverse effects that would raise safety concerns.

Safety and feasibility of deep brain stimulation of the anterior cingulate and thalamus in chronic refractory neuropathic pain: a pilot and randomized study

BACKGROUND

Deep Brain Stimulation (DBS) of the anterior cingulum has been recently proposed to treat refractory chronic pain but its safety and its efficacy have not been evaluated in controlled conditions. Our objective was to evaluate the respective feasibility and safety of sensory thalamus (Thal-DBS) combined with anterior cingulate (ACC-DBS) DBS in patients suffering from chronic neuropathic pain.

METHODS

We conducted a bicentric study (clinicaltrials.gov NCT03399942) in patients suffering from medically-refractory chronic unilateral neuropathic pain surgically implanted with both unilateral Thal-DBS and bilateral ACC-DBS, to evaluate successively: Thal-DBS only; combined Thal-DBS and ACC-DBS; ACC-DBS "on" and "off" stimulation periods in randomized cross-over double-blinded conditions; and a 1-year open phase. Safety and efficacy were evaluated by repeated neurological examination, psychiatric assessment, comprehensive assessment of cognitive and affective functioning. Changes on pain intensity (Visual Analogic Scale) and quality of life (EQ-5D scale) were used to evaluate DBS efficacy.

RESULTS

All the patients (2 women, 6 men, mean age 52,1) completed the study. Adverse events were: epileptic seizure (2), transient motor or attention (2), persistent gait disturbances (1), sleep disturbances (1). No patient displayed significant cognitive or affective change. Compared to baseline, the quality of life (EQ-5D utility score) was significantly improved during the ACC-DBS "On" stimulation period (p = 0,039) and at the end of the study (p = 0,034).

CONCLUSION

This pilot study confirmed the safety of anterior cingulate DBS alone or in combination with thalamic stimulation and suggested that it might improve quality of life of patients with chronic refractory neuropathic pain.

TRIAL REGISTRATION

The study has been registered on 20,180,117 (clinicaltrials.gov NCT03399942).

The aqueous extract of Armadillidium vulgare Latreille alleviates neuropathic pain via inhibiting neuron-astrocyte crosstalk mediated by the IL-12-IFN-γ-IFNGR-CXCL10 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Armadillidium vulgare Latreille (AV), the dried body of pillbug, was originally described in Shennong's Classic of Materia Medica. As a common analgesic in animal-based traditional Chinese medicine, it is mainly used to relieve pain, promoting diuresis, relieving fatigue and so on. Our work demonstrated that AV could alleviate various types of acute and chronic pain including neuropathic pain (NP). And transcriptome sequencing analysis revealed that AV could suppress CXCL10 to alleviate NP, however, the upstream mechanisms governing CXCL10 synthesis remain vague.

AIM OF THE STUDY

The research's goal was to identify the mechanism via which AV regulates CXCL10 to ameliorate NP.

MATERIALS AND METHODS

Chronic constriction injury (CCI) to the sciatic nerve was used to induce the NP model 14 days following surgery. To identify cell signaling pathways, various approaches were used, including transcriptome sequencing, western blotting, immunofluorescence, as well as ELISA. The in vitro assay involved the cultivation of neuron PC12 cells and astrocyte C6 cells.

RESULTS

Both in vivo and in vitro results demonstrated that IL-12/IL-18 enhanced IFN-γ production in spinal neurons, which acted on IFN-γ receptors on neurons and astrocytes to upregulate CXCL10 expression in these cells, illustrating the pivotal role of IL-12 in the crosstalk between neurons and astrocytes. The role of IL-12 in pain regulation was elucidated for the first time within the nervous system. Additionally, its synergistic interaction with IL-18 on the downstream IFN-γ-CXCL10 pathway dramatically altered the activation of neurons and astrocytes. And AV could suppress CXCL10 to alleviate NP by mediating the IL-12-IFN-γ-IFNGR signaling pathway.

CONCLUSIONS

We explored a new target for NP by regulating neuron-astrocyte crosstalk and provided a theoretical basis for AV in clinical use.

Effects of multiple transcranial magnetic stimulation sessions on pain relief in patients with chronic neuropathic pain: A French cohort study in real-world clinical practice

BACKGROUND

Current clinical trials indicate that repetitive transcranial magnetic stimulation (rTMS) is effective in reducing drug-resistant neuropathic pain (NP). However, there is a lack of studies evaluating the long-term feasibility and clinical efficacy of rTMS in large patient cohorts in real-world conditions.

METHODS

In this retrospective cohort study, we analysed 12 years of clinical data to assess the long-term analgesic effects of 20 Hz rTMS over the primary motor cortex in patients with NP. Subgroup analyses were conducted to identify predictive factors and assess the potential role of epidural motor cortex stimulation (eMCS) as a sustained solution.

RESULTS

In total, 193 patients completed test period of 4 rTMS sessions and 42% of them reported a pain relief (PR) greater than 30%, with concurrent improvement in their most disabling symptom. Iterative rTMS sessions maintained analgesic effects over 10 years in certain patients identified as responders (≥10% PR) without adverse effects. Success probability was higher in patients with central NP compared to peripheral NP (OR = 2.03[1.04;4.00]), and among those with central post-stroke pain, this probability was higher in ischemic versus hemorrhagic strokes (OR = 3.36[1.17;10.05]). PR obtained with iterative rTMS sessions was an excellent predictor of eMCS efficacy.

CONCLUSIONS

While rTMS shows promise as a therapeutic option for some patients with drug-resistant NP, it does not benefit all patients. Efficacy varies by NP aetiology, aiding patient selection. For responders, eMCS may offer a permanent solution. These findings support a tailored approach to rTMS in NP management, while recognizing both its potential and limitations across diverse patient profiles.

SIGNIFICANCE STATEMENT

Multiple rTMS sessions demonstrate long-term efficacy and safety in treating drug-resistant neuropathic pain. Extending session numbers for the test period can enhance responder identification, especially in patients with initial low pain relief. This identification refines patient selection for neurosurgery, reducing non-responders. Central neuropathic pain shows higher success rates than peripheral. For post-stroke central pain, patients with ischemic stroke are more likely to respond than those with hemorrhagic stroke. These results support integrating rTMS into clinical practice for managing neuropathic pain.

Neuropathic pain: Evidence based recommendations

Neuropathic pain continues to be a significant problem that lacks effective solutions for every single patient. In 2015, international guidelines (NeuPSIG) were published, while the French recommendations were updated in 2020. The purpose of this minireview is to provide an update on the process of developing evidence-based recommendations and explore potential changes to the current recommendations. Primary treatments for neuropathic pain include selective serotonin-norepinephrine reuptake inhibitors (SNRIs) such as duloxetine and venlafaxine, gabapentin, tricyclic antidepressants, as well as topical lidocaine and transcutaneous electrical nerve stimulation, which are specifically suggested for focal peripheral neuropathic pain. Pregabalin is a first line treatment according to international guidelines but second-line in the more recent French guidelines, due to lower efficacy seen in more recent studies and misuse risk. Additionally, tramadol, combination therapies, and psychotherapy as adjuncts are proposed second line; high-concentration capsaicin patches, and botulinum toxin A are proposed specifically for focal peripheral neuropathic pain. In cases where primary and secondary treatments prove insufficient, third-line options come into play. These include high-frequency repetitive transcranial magnetic stimulation (rTMS) targeting the motor cortex, spinal cord stimulation, and the use of strong opioids when no alternative is available. To ensure optimal management of neuropathic pain in real-life situations, it is imperative to disseminate these recommendations widely and secure the acceptance of practitioners. By doing so, we can bridge the gap between theory and practice, and enhance the overall care and treatment of individuals suffering from neuropathic pain.

Cannabis oil extracts for chronic pain: what else can be learned from another structured prospective cohort?

Introduction

The use of medicinal cannabis for managing pain expands, although its efficacy and safety have not been fully established through randomized controlled trials.

Objectives

This structured, prospective questionnaire-based cohort was aimed to assess long-term effectiveness and safety of cannabis oil extracts in patients with chronic pain.

Methods

Adult Israeli patients licensed to use cannabis oil extracts for chronic pain were followed prospectively for 6 months. The primary outcome measure was change from baseline in average weekly pain intensity, and secondary outcomes were changes in related symptoms and quality of life, recorded before treatment initiation and 1, 3, and 6 months thereafter. Generalized linear mixed model was used to analyze changes over time. In addition, "responders" (≥30% reduction in weekly pain at any time point) were identified.

Results

The study included 218 patients at baseline, and 188, 154, and 131 at 1, 3, and 6 months, respectively. At 6 months, the mean daily doses of cannabidiol and Δ9-tetrahydrocannabinol were 22.4 ± 24.0 mg and 20.8 ± 30.1 mg, respectively. Pain decreased from 7.9 ± 1.7 at baseline to 6.6 ± 2.2 at 6 months (F(3,450) = 26.22, P < 0.0001). Most secondary parameters also significantly improved. Of the 218 participants, 24% were "responders" but could not be identified by baseline parameters. "Responders" exhibited higher improvement in secondary outcomes. Adverse events were common but mostly nonserious.

Conclusion

This prospective cohort demonstrated a modest overall long-term improvement in chronic pain and related symptoms and a reasonable safety profile with the use of relatively low doses of individually titrated Δ9-tetrahydrocannabinol and cannabidiol.

Astrocyte senescence-like response related to peripheral nerve injury-induced neuropathic pain

BACKGROUND

Peripheral nerve damage causes neuroinflammation, which plays a critical role in establishing and maintaining neuropathic pain (NeP). The mechanisms contributing to neuroinflammation remain poorly elucidated, and pharmacological strategies for NeP are limited. Thus, in this study, we planned to explore the possible link between astrocyte senescence and NeP disorders following chronic sciatic nerve injury.

METHODS

An NeP animal model was established by inducing chronic constrictive injury (CCI) to the sciatic nerve in adult rats. A senolytic drug combination of dasatinib and quercetin was gavaged daily from the first postoperative day until the end of the study. Paw mechanical withdrawal threshold (PMWT) and paw thermal withdrawal latency (PTWL) were evaluated to assess behaviors in response to pain in the experimental rats. Senescence-associated β-galactosidase staining, western blot analysis, and immunofluorescence were applied to examine the levels of proinflammatory factors and severity of the senescence-like response in the spinal cord. Lipopolysaccharide (LPS) was administered to induce senescence of spinal astrocytes in primary cultures in vitro, to explore the potential impacts of senescence on the secretion of proinflammatory factors. Furthermore, single-cell RNA sequencing (scRNA-seq) was conducted to identify senescence-related molecular responses in spinal astrocytes under neuropathic pain.

RESULTS

Following sciatic nerve CCI, rats exhibited reduced PMWT and PTWL, increased levels of spinal proinflammatory factors, and an enhanced degree of senescence in spinal astrocytes. Treatment with dasatinib and quercetin effectively attenuated spinal neuroinflammation and mitigated the hypersensitivities of the rats subjected to sciatic nerve CCI. Mechanistically, the dasatinib-quercetin combination reversed senescence in LPS-stimulated primary cultured astrocytes and decreased the levels of proinflammatory factors. The scRNA-seq data revealed four potential senescence-related genes in the spinal astrocyte population, and the expression of clusterin (CLU) protein was validated via in vitro experiments.

CONCLUSION

The findings indicate the potential role of astrocyte senescence in neuroinflammation following peripheral nerve injury, and suggest that targeting CLU activation in astrocytes might provide a novel therapeutic strategy to treat NeP.

Drosophila pain sensitization and modulation unveiled by a novel pain model and analgesic drugs

In mammals, pain is regulated by the combination of an ascending stimulating and descending inhibitory pain pathway. It remains an intriguing question whether such pain pathways are of ancient origin and conserved in invertebrates. Here we report a new Drosophila pain model and use it to elucidate the pain pathways present in flies. The model employs transgenic flies expressing the human capsaicin receptor TRPV1 in sensory nociceptor neurons, which innervate the whole fly body, including the mouth. Upon capsaicin sipping, the flies abruptly displayed pain-related behaviors such as running away, scurrying around, rubbing vigorously, and pulling at their mouth parts, suggesting that capsaicin stimulated nociceptors in the mouth via activating TRPV1. When reared on capsaicin-containing food, the animals died of starvation, demonstrating the degree of pain experienced. This death rate was reduced by treatment both with NSAIDs and gabapentin, analgesics that inhibit the sensitized ascending pain pathway, and with antidepressants, GABAergic agonists, and morphine, analgesics that strengthen the descending inhibitory pathway. Our results suggest Drosophila to possess intricate pain sensitization and modulation mechanisms similar to mammals, and we propose that this simple, non-invasive feeding assay has utility for high-throughput evaluation and screening of analgesic compounds.

The relevance of real-world data for the evaluation of neuropathic pain treatments

Treatment of neuropathic pain (NP) is challenging. Interest in real-world evidence (RWE) for benefit-risk assessments of NP treatments increases given the paucity of drugs showing efficacy in randomized controlled trials and restricted labels of available medicines. To provide further context, a literature review regarding regulatory use of RWE and a clinical trial registry search for randomized controlled trials over the last 10 years was carried out. Taken together, and especially for available NP treatments, there is increasing support to consider RWE when evaluating their benefit-risk profile. Examples are provided in which RWE could be used effectively for updating the product label and informing treatment recommendations. Collected and analyzed according to state-of-the-art standards, RWE can inform treatment recommendations and product label decisions.

French guidelines for neuropathic pain: An update and commentary

Neuropathic pain remains a significant unmet need. French recommendations were updated in 2020. The goal of this minireview is to provide an update on these published guidelines. Despite newer relevant studies, our proposed algorithm remains relevant. First-line treatments include serotonin-noradrenaline reuptake inhibitors (duloxetine and venlafaxine), gabapentin and tricyclic antidepressants, topical lidocaine and transcutaneous electrical nerve stimulation being specifically proposed for focal peripheral neuropathic pain. Second-line treatments include pregabalin (such position being confirmed by newer studies), tramadol, combinations and psychotherapy as add on, high-concentration capsaicin patches and botulinum toxin A being proposed specifically for focal peripheral neuropathic pain. Third-line treatments include high-frequency repetitive transcranial magnetic stimulation of the motor cortex, spinal cord stimulation and strong opioids (in the lack of alternative). Disseminating these recommendations and ensuring that they are well accepted by French practitioners will be necessary to optimize neuropathic pain management in real life.