French guidelines for neuropathic pain: An update and commentary

Narrative review of the efficacy and safety of the high-concentration (179mg) capsaicin patch in peripheral neuropathic pain with recommendations for clinical practice and future research

High-concentration capsaicin patch (HC capsaicin patch) is a locally acting treatment option for adults with peripheral neuropathic pain (pNeP) of various etiologies. Numerous clinical trials, post hoc analyses, and meta-analyses have investigated the efficacy and tolerability of the HC capsaicin patch. Despite this extensive body of research, a comprehensive narrative review covering publications on different pNeP conditions is lacking. This narrative review aims to fill the gap by analyzing 52 studies, including randomized controlled trials and real-world evidence. The results show that the HC capsaicin patch consistently provides pain relief and improves quality of life for several pNeP conditions, with increasing benefits seen with repeated treatments. It was found to be superior to placebo and comparable to standard care, regardless of the origin of the pain. Early initiation of therapy appears to improve efficacy, although patients with more prolonged pain also benefit. While the exact mechanisms of action are still unclear, there is evidence to suggest a potential benefit from nerve regeneration in some conditions. However, limited information exists regarding the alteration of treatment intervals and the variation in the size of the painful area upon re-treatment. The review also identifies variability in response rates for different types of pNeP and a lack of reliable predictors of treatment success, indicating a need for further research. In conclusion, the HC capsaicin patch is effective and well tolerated across a range of pNeP conditions, with increasing efficacy upon retreatment. It is a valuable treatment option, although more research is needed to refine its clinical use and explore its full therapeutic potential.

Pretreatment TMS-EEG connectivity assessment as a potential predictor of rTMS effectiveness in chronic pain: A feasibility pilot study

OBJECTIVE

Around half of chronic pain patients report pain intensity reduction to high-frequency (10 Hz) repetitive transcranial magnetic stimulation (rTMS) delivered to the primary motor cortex (M1). However, the other half do not respond, making it essential to identify which patients are likely to benefit before starting treatment. Combining TMS with electroencephalogram (TMS-EEG) allows for exploring cortical connectivity, and evaluating this connectivity before administering rTMS may provide insights into which patients are likely to respond favorably to the treatment.

METHODS

Seven chronic pain patients underwent TMS-EEG assessment of M1 before ten daily sessions of 10 Hz rTMS. Pain intensity was measured at baseline and post-treatment, with responders defined as those showing a 30 % reduction on an 11-point numerical rating scale. TMS-evoked potentials were analyzed using the debiased weighted phase lag index to assess connectivity, quantified by phase (connections exceeding the 95 % confidence interval) and space (Euclidean distance between significantly connected EEG channels). Normative connectivity values were also collected from 82 healthy volunteers.

RESULTS

Four patients responded to M1 rTMS, while three did not, with an average pain intensity reduction of 1.4±1.5. TMS-EEG showed low connectivity indices in all responders to rTMS, whereas two non-responders had higher indices, above the 75th percentile of healthy volunteers.

CONCLUSIONS

This pilot feasibility study showed that the use of TMS-EEG informed rTMS is feasible, and proceeding to larger randomized clinical trials will allow to test this approach.

SIGNIFICANCE

Pre-treatment TMS-EEG connectivity measures may identify rTMS responders, optimizing chronic pain management.

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.

Neuropathic pain and its association with intimate partner violence: The patient's perception in contrast to the intimate partner violence scale

INTRODUCTION

The potential contribution of intimate partner violence (IPV) to the development of neuropathic pain (NP) is not fully elucidated. Therefore, this study aimed to describe self-reported IPV in patients with NP undergoing treatment and to associate the findings with the values ​​obtained on the Intimate Partner Violence Scale (EVIPI, from Portuguese Escala de Violência entre Parceiros Íntimos).

METHODS

This study was conducted with a group of patients undergoing treatment for chronic NP. The EVIPI was used to assess exposure to violence. This instrument was administered to participants who had been in an intimate relationship in the last six months.

RESULTS

The study involved 124 participants, of whom 73 (58.9 %) had been in a relationship in the last six months. All selected participants self-declared being in a heterosexual relationship. Among them, 44 (60.3 %) were women, 53 (72.6 %) self-identified as white, and 33 (45.2 %) had incomplete basic education. When asked if they had experienced any form of violence within the intimate relationship in the last six months, 68 (93.2 %) self-reported that they had not. Additionally, 66 (90.4 %) reported that they had not experienced childhood violence. Cross-tabulation between the EVIPI and self-reported exposure to violence did not show a significant association in the three categories of the EVIPI. Despite the lack of statistical significance, among those who denied having suffered violence in childhood, 29 and 19 participants scored positive in the "injury and physical violence" and "behavioral control" categories of the EVIPI, respectively. Among those who denied having suffered IPV, 30 and 19 participants scored positive in the "injury and physical violence" and "behavioral control" categories of the EVIPI, respectively.

CONCLUSIONS

No significant association was found between the markers evaluated; however, there was a gap in understanding the concept of violence, as most participants denied exposure to violence despite the EVIPI results indicating certain levels of exposure.

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.

Small-Fiber Neuropathy: An Etiology-Oriented Review

BACKGROUND

Small-fiber neuropathy (SFN), affecting Aδ or C nerve fibers, is characterized by alterations of pain and temperature sensation, as well as autonomic dysfunction. Its diagnosis may still remain challenging as methods specifically assessing small nerve fibers are not always readily available, and standard techniques for large-fiber neuropathies, such as electroneuromyography, yield negative results. Still, skin biopsy for epidermal innervation and quantitative sensory testing allow for diagnosis in the presence of a congruent clinical picture.

OBJECTIVES

Many different etiologies may underlie small-fiber neuropathy, of which metabolic (diabetes mellitus/impaired glucose tolerance) and idiopathic remain prevalent. The aim of this narrative review is to provide a general picture of SFN while focusing on the different etiologies described in the literature in order to raise awareness of the variegated set of different causes of SFN and promote adequate diagnostic investigation.

METHODS

The term "Small-Fiber Neuropathy" was searched on the PubMed database with its different recognized etiologies: the abstracts of the articles were reviewed and described in the article if relevant for a total of 40 studies.

RESULTS

Many different disorders have been associated with SFN, even though often in the form of case reports or small case series.

CONCLUSIONS

Idiopathic forms of SFN remain the most prevalent in the literature, but association with different disorders (e.g., infectious, autoimmune) should prompt investigation for SFN in the presence of a congruent clinical picture (e.g., pain with neuropathic features).

Navigating neurologic post-COVID-19 conditions in adults: Management strategies for cognitive dysfunction, headaches and neuropathies

This review aims to describe the neurologic post-COVID-19 conditions (PCC, also known as "long COVID"), a complex array of diagnoses that can occur following recovery from acute COVID-19. The review also includes clinical considerations for the recognition, diagnosis and management of neurologic manifestations of PCC. Cognitive impairment ("Brain Fog"), headaches, and neuropathies are specifically reviewed.

E-52862-A selective sigma-1 receptor antagonist, in peripheral neuropathic pain: Two randomized, double-blind, phase 2 studies in patients with chronic postsurgical pain and painful diabetic neuropathy

BACKGROUND

We report the efficacy and safety of E-52862-a selective, sigma-1 receptor antagonist-from phase 2, randomized, proof-of-concept studies in patients with moderate-to-severe, neuropathic, chronic postsurgical pain (CPSP) and painful diabetic neuropathy (PDN).

METHODS

Adult patients (CPSP [N = 116]; PDN [N = 163]) were randomized at a 1:1 ratio to 4 weeks of treatment with E-52862 (CPSP [n = 55]; PDN [n = 85]) or placebo (CPSP [n = 61]; PDN [n = 78]) orally once daily. Pain intensity scores were measured using a numerical pain rating scale from 0 (no pain) to 10 (worst pain imaginable). The primary analysis population comprised patients who received study drug with ≥1 baseline and on-treatment observation (full analysis set).

RESULTS

In CPSP, mean baseline average pain was 6.2 for E-52862 vs. 6.5 for placebo. Week 4 mean change from baseline (CFB) for average pain was -1.6 for E-52862 vs. -0.9 for placebo (least squares mean difference [LSMD]: -0.9; p = 0.029). In PDN, mean baseline average pain was 5.3 for E-52862 vs. 5.4 for placebo. Week 4 mean CFB for average pain was -2.2 for E-52862 vs. -2.1 for placebo (LSMD: -0.1; p = 0.766). Treatment-emergent adverse events (TEAEs) were reported in 90.9% of E-52862-treated patients vs. 76.7% of placebo-treated patients in CPSP and 34.1% vs. 26.9% in PDN. Serious TEAEs occurred in CPSP only: E-52862: 5.5%; placebo: 6.7%.

CONCLUSIONS

E-52862 demonstrated superior relief of CPSP vs. placebo after 4 weeks. Reductions in pain intensity were seen in PDN with E-52862; high placebo response rates may have prevented differentiation between treatments. E-52862 had acceptable tolerability in both populations.

SIGNIFICANCE STATEMENT

These proof-of-concept studies validate the mode of action of E-52862, a selective sigma-1 receptor antagonist. In CPSP, E-52862 resulted in clinically meaningful pain relief. In PDN, reductions in pain intensity were seen with E-52862; high placebo response rates may have prevented differentiation between E-52862 and placebo. These findings are clinically relevant given that neuropathic pain is highly incapacitating, lacking effective treatments and representing a significant unmet medical need, and support further development of sigma-1 receptor antagonists for peripheral neuropathic pain.

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.

Neuromodulation for neuropathic pain

The treatment of neuropathic pain (NeP) often leads to partial or incomplete pain relief, with up to 40 % of patients being pharmaco-resistant. In this chapter the efficacy of neuromodulation techniques in treating NeP is reviewed. It presents a detailed evaluation of the mechanisms of action and evidence supporting the clinical use of the most common approaches like transcutaneous electrical nerve stimulation (TENS), transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (rTMS), deep brain stimulation (DBS), invasive motor cortex stimulation (iMCS), spinal cord stimulation (SCS), dorsal root ganglion stimulation (DRG-S), and peripheral nerve stimulation (PNS). Current literature suggests that motor cortex rTMS is effective for peripheral and central NeP, and TENS for peripheral NeP. Evidence for tDCS is inconclusive. DBS is reserved for research settings due to heterogeneous results, while iMSC has shown efficacy in a small randomized trial in neuropathic pain due to stroke and brachial plexus avulsion. SCS has moderate evidence for painful diabetic neuropathy and failed back surgery syndrome, but trials were not controlled with sham. DRG-S and PNS have shown positive results for complex regional pain syndrome and post-surgical neuropathic pain, respectively. Adverse effects vary, with non-invasive techniques showing local discomfort, dizziness and headache, and DBS and SCS hardware-related issues. To date, non-invasive techniques have been more extensively studied and some are included in international guidelines, while the evidence level for invasive techniques are less robust, potentially suggesting their use in a case-by-case indication considering patient´s preferences, costs and expected benefits.

Clinical pharmacology of neuropathic pain

This chapter aims to review the current pharmacological options for neuropathic pain treatment, their mechanisms of action, and future directions for clinical practice. Achieving pain relief in neuropathic pain conditions remains a challenge in clinical practice. The field of pharmacotherapy for neuropathic pain has encountered significant difficulties in translating substantial advances in our understanding of the underlying pathophysiological mechanisms into clinically effective therapies. This chapter presents the drugs recommended for the pharmacotherapy of neuropathic pain, based on the widely accepted treatment guidelines formulated by the Neuropathic Pain Special Interest Group of the International Association for the Study of Pain. In addition to discussing how the evidence base is created as part of international consortia, the drugs are also examined in terms of their putative molecular mechanisms as well as pharmacological pleiotropy, i.e., their potential unspecific and multi-target effects resulting in modulation of neuronal hyperexcitability. The chapter closes with a discussion of potential future developments in the field.

Exploring the role of Yuxuebi tablet in neuropathic pain with the method of similarity research of drug pharmacological effects based on unsupervised machine learning

Introduction

Having multiple pharmacological effects is a characteristic of Traditional Chinese Medicine (TCM). Currently, there is a lack of suitable methods to explore and discover modern diseases suitable for TCM treatment using this characteristic. Unsupervised machine learning technology is an efficient strategy to predict the pharmacological activity of drugs. This study takes Yuxuebi Tablet (YXB) as the research object. Using the unsupervised machine learning technology of drug cell functional fingerprint similarity research, the potential pharmacological effects of YXB were discovered and verified.

Methods

LC-MS combined with the in vitro intestinal absorption method was used to identify components of YXB that could be absorbed by the intestinal tract of rats. Unsupervised learning hierarchical clustering was used to calculate the degree of similarity of cellular functional fingerprints between these components and 121 marketed Western drugs whose indications are diseases and symptoms that YXB is commonly used to treat. Then, based on the Library of Integrated Network-based Cellular Signatures database, pathway analysis was performed for selected Western drugs with high similarity in cellular functional fingerprints with the components of YXB to discover the potential pharmacological effects of YXB, which were validated by animal experiments.

Results

We identified 40 intestinally absorbed components of YXB. Through predictive studies, we found that they have pharmacological effects very similar to non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids. In addition, we found that they have very similar pharmacological effects to anti-neuropathic pain medications (such as gabapentin, duloxetine, and pethidine) and may inhibit the NF-κB signaling pathway and biological processes related to pain perception. Therefore, YXB may have an antinociceptive effect on neuropathic pain. Finally, we demonstrated that YXB significantly reduced neuropathic pain in a rat model of sciatic nerve chronic constriction injury (CCI). Transcriptome analysis further revealed that YXB regulates the expression of multiple genes involved in nerve injury repair, signal transduction, ion channels, and inflammatory response, with key regulatory targets including Sgk1, Sst, Isl1, and Shh.

Conclusion

This study successfully identified and confirmed the previously unknown pharmacological activity of YXB against neuropathic pain through unsupervised learning prediction and experimental verification.

Topical treatment of chemotherapy-induced peripheral neuropathy (CIPN) with high-concentration (179 mg) capsaicin patch in breast cancer patients - results of the QUCIP study

Background

Chemotherapy-induced peripheral neuropathy (CIPN) following oral or intravenous chemotherapy often results in neuropathic pain, accompanied by symptoms such tingling, burning and hypersensitivity to stimuli, with a notable decline in quality of life (QoL). Effective therapies for CIPN are lacking, with a high demand for analgesics to address this issue. The QUCIP study aimed to assess the effectiveness of high concentration (179 mg) capsaicin patch (HCCP) in alleviating neuropathic pain and associated symptoms in breast cancer patients with confirmed CIPN.

Methods

QUCIP is a prospective, multi-center observational study spanning 36 weeks with up to three HCCP treatments. Initial treatment (visit V0) was followed by two telephone contacts (T1, T2) and subsequent face-to-face visits every 12 weeks or upon retreatment (visits V1-V3). 73 female patients with painful CIPN post neoadjuvant/adjuvant breast cancer therapy were enrolled. Primary endpoint was the reduction of neuropathic pain symptom score (painDETECT®). Secondary endpoints included improvements in CIPN-specific QoL (QLQ-CIPN20), reductions in pain intensity (numeric pain rating scale, NPRS), and achievement of ≥ 30% and ≥ 50% pain reduction.

Results

Median age was 61 years, with 52.0% of patients experiencing peripheral neuropathic pain for > 1 year (> 2 years: 34.2%). The painDETECT® score significantly decreased from baseline (19.71 ± 4.69) to 15.80 ± 6.20 after initial treatment (p < 0.0001) and continued to decrease at follow-up visits. The NPRS indicated significant pain intensity reduction at each time point, particularly pronounced in patients receiving three HCCP treatments. Clinically significant pain relief of ≥ 30% increased from 25.0% at week 4 (T2) to 36.2%, 43.5%, and 40.0% at weeks 12 (V1), 24 (V2), and 36 (V3), respectively. The percentage of patients achieving pain relief of ≥ 50% increased from 14.7% at T2 to 15.5%, 21.7% and 32.5% at V1, V2 and V3, respectively. Patients further reported a significant improvement in their CIPN-related QoL throughout the study. Adverse drug reactions (ADRs) mainly included application site reactions.

Conclusion

In this study, HCCP shows benefit in managing CIPN in real-world settings. The data demonstrate a sustained and progressive reduction in neuropathic pain and symptomatology, confirming the clinical benefit of repeated treatment observed in former clinical trials. HCCP treatment has also the potential to significantly improve the QoL associated with CIPN. The safety profile of HCCP was confirmed, supporting its use in clinical practice.

Peripheral and central neurobiological effects of botulinum toxin A (BoNT/A) in neuropathic pain: a systematic review

ABSTRACT

Botulinum toxin (BoNT), a presynaptic inhibitor of acetylcholine (Ach) release at the neuromuscular junction (NMJ), is a successful and safe drug for the treatment of several neurological disorders. However, a wide and recent literature review has demonstrated that BoNT exerts its effects not only at the "periphery" but also within the central nervous system (CNS). Studies from animal models, in fact, have shown a retrograde transport to the CNS, thus modulating synaptic function. The increasing number of articles reporting efficacy of BoNT on chronic neuropathic pain (CNP), a complex disease of the CNS, demonstrates that the central mechanisms of BoNT are far from being completely elucidated. In this new light, BoNT might interfere with the activity of spinal, brain stem, and cortical circuitry, modulating excitability and the functional organization of CNS in healthy conditions. Botulinum toxins efficacy on CNP is the result of a wide and complex action on many and diverse mechanisms at the basis of the maladaptive plasticity, the core of the pathogenesis of CNP. This systematic review aims to discuss in detail the BoNT's mechanisms and effects on peripheral and central neuroplasticity, at the basis for the clinical efficacy in CNP syndromes.

Bibliometric analysis of functional magnetic resonance imaging studies on chronic pain over the past 20 years

PURPOSE

The utilization of functional magnetic resonance imaging (fMRI) in studying the mechanisms and treatment of chronic pain has gained significant popularity. However, there is currently a dearth of literature conducting bibliometric analysis on fMRI studies focused on chronic pain.

METHODS

All the literature included in this study was obtained from the Science Citation Index Expanded of Web of Science Core Collection. We used CiteSpace and VOSviewer to analyze publications, authors, countries or regions, institutions, journals, references and keywords. Additionally, we evaluated the timeline and burst analysis of keywords, as well as the timeline and burst analysis of references. The search was conducted from 2004 to 2023 and completed within a single day on October 4th, 2023.

RESULTS

A total of 1,327 articles were retrieved. The annual publication shows an overall increasing trend. The United States has the highest number of publications and the main contributing institution is Harvard University. The journal PAIN produces the most articles. In recent years, resting-state fMRI, the prefrontal cortex, nucleus accumbens, thalamus, and migraines have been researched hotspots of fMRI studies on chronic pain.

CONCLUSIONS

This study provides an in-depth perspective on fMRI for chronic pain research, revealing key points, research hotspots and research trends, which offers valuable ideas for future research activities. It concludes with a summary of advances in clinical practice in this area, pointing out the need for critical evaluation of these findings in the light of guidelines and expert recommendations. It is anticipated that further high-quality research outputs will be generated in the future, which will facilitate the utilization of fMRI in clinical decision-making for chronic pain.

Silencing of FTO inhibits oxidative stress to relieve neuropathic pain by m6A modification of GPR177

BACKGROUND

Neuropathic pain (NP) is a challenging health condition owing to its complex nature and associated multiple etiologies. The occurrence of NP involves the abnormal activity of neurons mediated by oxidative stress (OS). Previous research has demonstrated that m6A methylation plays a role in the regulatory pathway of NP. This study aimed to investigate the specific molecular pathways through which m6A methylation modifiers alleviate NP.

METHODS

For this purpose, an NO rat model was developed via spared nerve injury (SNI), followed by quantifying the animal's pain assessment via paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). The OS in SNI rats was evaluated by measuring reactive oxygen species, superoxide dismutase, and catalase (CAT) in spinal cord tissues. Moreover, quantitative-real-time polymerase chain reaction and western blot analysis were employed for detecting fat mass and obesity-associated (FTO) and GPR177 levels, while m6A levels of GPR117 were analyzed via MeRIP.

RESULTS

The results indicated an enhanced OS with highly expressed FTO in spinal cord tissue samples, where knocking down Fto effectively relieved NP and OS in SNI rats. Mechanistic investigations revealed that Fto-mediated reduction of Grp177 m6A modification was involved in the WNT5a/TRPV1 axis-mediated OS remission of NP. Moreover, in vitro experiment results indicated that YTHDF2 was an important m6A methylated reading protein for this process.

CONCLUSIONS

Fto silencing leads to increased m6A methylation of Grp177 through a YTHDF2-dependent mechanism, resulting in decreased Grp177 stability and ultimately reducing NP in rats by OS suppression.

The deep and the deeper: Spinal cord and deep brain stimulation for neuropathic pain

Neuropathic pain occurs in people experiencing lesion or disease affecting the somatosensorial system. It is present in 7 % of the general population and may not fully respond to first- and second-line treatments in up to 40 % of cases. Neuromodulation approaches are often proposed for those not tolerating or not responding to usual pharmacological management. These approaches can be delivered surgically (invasively) or non-invasively. Invasive neuromodulation techniques were the first to be employed in neuropathic pain. Among them is spinal cord stimulation (SCS), which consists of the implantation of epidural electrodes over the spinal cord. It is recommended in some guidelines for peripheral neuropathic pain. While recent studies have called into question its efficacy, others have provided promising data, driven by advances in techniques, battery capabilities, programming algorithms and software developments. Deep brain stimulation (DBS) is another well-stablished neuromodulation therapy routinely used for movement disorders; however, its role in pain management remains limited to specific research centers. This is not only due to variable results in the literature contesting its efficacy, but also because several different brain targets have been explored in small trials, compromising comparisons between these studies. Structures such as the periaqueductal grey, posterior thalamus, anterior cingulate cortex, ventral striatum/anterior limb of the internal capsule and the insula are the main targets described to date in literature. SCS and DBS present diverse rationales for use, mechanistic backgrounds, and varying levels of support from experimental studies. The present review aims to present their methodological details, main mechanisms of action for analgesia and their place in the current body of evidence in the management of patients with neuropathic pain, as well their particularities, effectiveness, safety and limitations.

Effectiveness of Vortioxetine in Patients with Major Depressive Disorder Associated with Chronic Pain: An Observational Study in a Spanish Population

INTRODUCTION

Chronic pain (CP) and depression/anxiety often coexist, worsening each other's symptoms. Treating this comorbidity is challenging. Tricyclic antidepressants and serotonin noradrenaline reuptake inhibitors are the first-line treatment options for this comorbidity, although sometimes they are not effective and/or well tolerated by patients, and there is little clinical evidence that selective serotonin reuptake inhibitors are useful for controlling CP. The antidepressant vortioxetine, with a multimodal mechanism that may help reduce pain, has proven clinical efficacy in patients with major depressive disorder (MDD). This study investigated vortioxetine's effectiveness for MDD and CP in clinical practice.

METHODS

This was a 3-month, multicenter, prospective, open-label, non-interventional pharmacoepidemiologic study. Patients (n = 64) with MDD (9-item Patient Health Questionnaire [PHQ-9] score ≥ 15) and CP (visual analogue scale [VAS] score ≥ 4) were treated with vortioxetine for 3 months (initiated with 10 mg/day, with flexible dosing thereafter [5-20 mg/day]). VAS, Clinical Global Impression (CGI), and Patient Global Impression (PGI) scales were used at baseline and at 1 and 3 months. Brief Pain Inventory (BPI), PHQ-9 scale, and Satisfaction with Medicines Questionnaire (SATMED-Q) were used at baseline and at 3 months. Adverse Events (AEs) were recorded. Descriptive statistics, chi-square tests, and Student's t-tests were used for paired data.

RESULTS

MDD patients showed a statistically significant improvement in VAS from baseline (mean [standard deviation (SD)]: 7.42 [0.69]) to 1 month (mean [SD]: 6.1 [0.81], P < 0.001) and 3 months (mean [SD]: 5.09 [1.26], P < 0.0001). Similarly, BPI and PHQ-9 scores showed significant improvement from baseline (mean [SD]: 6.20 [0.80] and 16.63 [1.47], respectively) to 3 months (mean [SD]: 4.73 [0.98] and 7.30 [2.60], P < 0.0001, respectively). Patients showed clinical improvement with CGI and PGI scales and reported being satisfied with the treatment in the SATMED-Q. A few mild EAs were registered.

CONCLUSION

Vortioxetine can relieve depressive and pain symptoms, with a good safety profile, in patients with MDD and CP.

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.

Pharmacotherapy for osteoarthritis-related pain: current and emerging therapies

INTRODUCTION

Osteoarthritis (OA) related pain has affected millions of people worldwide. However, the current pharmacological options for managing OA-related pain have not achieved a satisfactory effect.

AREAS COVERED

This narrative review provides an overview of the current and emerging drugs for OA-related pain. It covers the drugs' mechanism of action, safety, efficacy, and limitations. The National Library of Medicine (PubMed) database was primarily searched from 2000 to 2024.

EXPERT OPINION

Current treatment options are limited and suboptimal for OA pain management. Topical nonsteroidal anti-inflammatory drugs (NSAIDs) are the recognized and first-line treatment in the management of OA-related pain, and other drugs are inconsistent recommendations by guidelines. Emerging treatment options are promising for OA-related pain, including nerve growth factor (NGF) inhibitors, ion channel inhibitors, and calcitonin gene-related peptide (CGRP) antagonists. Besides, drugs repurposing from antidepressants and antiepileptic analgesics are shedding light on the management of OA-related pain. The management of OA-related pain is challenging as pain is heterogeneous and subjective. A more comprehensive strategy combined with non-pharmacological therapy needs to be considered, and tailored management options to individualized patients.

Research hotspots and trends of complementary and alternative therapy for neuropathic pain: A bibliometric analysis

BACKGROUND

Neuropathic pain (NP) is a common type of pain in clinic. Due to the limited effect of drug treatment, many patients with NP are still troubled by this disease. In recent years, complementary and alternative therapy (CAT) has shown good efficacy in the treatment of NP. As the interest in CAT for NP continues to grow, we conducted a bibliometric study of publications on CAT treatment for NP. The aim of this study is to analyze the development overview, research hotspots and future trends in the field of CAT and NP through bibliometric methodology, so as to provide a reference for subsequent researchers.

METHODS

Publications on CAT in the treatment of NP from 2002 to 2022 were retrieved from the Web of Science Core Collection. Relevant countries, institutions, authors, journals, keywords, and references were analyzed bibliometrically using Microsoft Excel 2021, bibliometric platform, VOSviewer, and CiteSpace.

RESULTS

A total of 898 articles from 46 countries were published in 324 journals, and they were contributed by 4455 authors from 1102 institutions. The most influential country and institution are China (n = 445) and Kyung Hee University (n = 63), respectively. Fang JQ (n = 27) and Evidence-Based Complementary and Alternative Medicine (n = 63) are the author and journal with the most publications in this field. The clinical efficacy, molecular biological mechanisms and safety of CAT for NP are currently hot directions. Low back pain, postherpetic neuralgia, acupuncture, and herbal are the hot topics in CAT and NP in recent years.

CONCLUSION

This study reveals the current status and hotspots of CAT for NP. The study also indicates that the effectiveness and effect mechanism of acupuncture or herbs for treating emotional problems caused by low back pain or postherpetic neuralgia may be a trend for future research.

Finding predictors for successful opioid response in cancer patients: An analysis of data from four randomized controlled trials

CONTEXT

There is no consensus on which "strong" (or step 3 WHO analgesic ladder) opioid to prescribe to a particular patient with cancer-related pain. A better understanding of opioid and patient characteristics on treatment response will contribute to a more personalized opioid treatment.

OBJECTIVES

Assessment of potential predictors for successful opioid treatment response in patients with cancer pain.

METHODS

An international partnership between four cancer pain research groups resulted in a combined individual-level database from four relevant randomized controlled trials (RCTs; n = 881). Together, these RCTs investigated the short-term (1 week) and medium-term (4 or 5 weeks) treatment responses for morphine, buprenorphine, methadone, oxycodone, and fentanyl. Candidate predictors for treatment response were sex, age, pain type, pain duration, depression, anxiety, Karnofsky performance score, opioid type, and use of anti-neuropathic drug.

RESULTS

Opioid type and pain type were found statistically significant predictors of short-term treatment success. Sex, age, pain type, anxiety, and opioid type were statistically, significantly associated with medium-term treatment success. However, these models showed low discriminative power.

CONCLUSION

Fentanyl and methadone, and mixed pain were found to be statistically significant predictors of treatment success in patients with cancer-related pain. With the predictors currently assessed our data did not allow for the creation of a clinical prediction model with good discriminative power. Additional - unrevealed - predictors are necessary to develop a future prediction model.

Comment on: Antiepileptic prescribing to persons living with dementia residing in nursing homes: A tale of two indications

See the Reply by Candon et al.

Beyond trial-and-error: Individualizing therapeutic transcranial neuromodulation for chronic pain

BACKGROUND AND OBJECTIVE

Repetitive transcranial magnetic stimulation (rTMS) applied to the motor cortex provides supplementary relief for some individuals with chronic pain who are refractory to pharmacological treatment. As rTMS slowly enters treatment guidelines for pain relief, its starts to be confronted with challenges long known to pharmacological approaches: efficacy at the group-level does not grant pain relief for a particular patient. In this review, we present and discuss a series of ongoing attempts to overcome this therapeutic challenge in a personalized medicine framework.

DATABASES AND DATA TREATMENT

Relevant scientific publications published in main databases such as PubMed and EMBASE from inception until March 2023 were systematically assessed, as well as a wide number of studies dedicated to the exploration of the mechanistic grounds of rTMS analgesic effects in humans, primates and rodents.

RESULTS

The main strategies reported to personalize cortical neuromodulation are: (i) the use of rTMS to predict individual response to implanted motor cortex stimulation; (ii) modifications of motor cortex stimulation patterns; (iii) stimulation of extra-motor targets; (iv) assessment of individual cortical networks and rhythms to personalize treatment; (v) deep sensory phenotyping; (vi) personalization of location, precision and intensity of motor rTMS. All approaches except (i) have so far low or moderate levels of evidence.

CONCLUSIONS

Although current evidence for most strategies under study remains at best moderate, the multiple mechanisms set up by cortical stimulation are an advantage over single-target 'clean' drugs, as they can influence multiple pathophysiologic paths and offer multiple possibilities of individualization.

SIGNIFICANCE

Non-invasive neuromodulation is on the verge of personalised medicine. Strategies ranging from integration of detailed clinical phenotyping into treatment design to advanced patient neurophysiological characterisation are being actively explored and creating a framework for actual individualisation of care.

The role of N6-methyladenosine modification in rodent models of neuropathic pain: from the mechanism to therapeutic potential

Neuropathic pain (NP) is a common chronic pain condition resulted from lesions or diseases of somatosensory nervous system, but the pathogenesis remains unclear. A growing body of evidence supports the relationship between pathogenesis and N6-methyladenosine (m6A) modifications of RNA. However, studies on the role of m6A modifications in NP are still at an early stage. Elucidating different etiologies is important for understanding the specific pathogenesis of NP. This article provides a comprehensive review on the role of m6A methylation modifications including methyltransferases ("writers"), demethylases ("erasers"), and m6A binding proteins ("readers") in NP models. Further analysis of the pathogenic mechanism relationship between m6A and NP provided novel theoretical and practical significance for clinical treatment of NP.

Motor corticospinal excitability abnormalities differ between distinct chronic low back pain syndromes

OBJECTIVES

It is not known whether cortical plastic changes reported in low-back pain (LBP) are present in all etiologies of LBP. Here we report on the assessment of patients with three LBP conditions: non-specific-LBP (ns-LBP), failed back surgery syndrome (FBSS), and sciatica (Sc).

METHODS

Patients underwent a standardized assessment of clinical pain, conditioned pain modulation (CPM), and measures of motor evoked potential (MEPs)-based motor corticospinal excitability (CE) by transcranial magnetic stimulation, including short interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Comparisons were also made with normative data from sex- and age-matched healthy volunteers.

RESULTS

60 patients (42 women, 55.1±9.1 years old) with LBP were included (20 in each group). Pain intensity was higher in patients with neuropathic pain [FBSS (6.8±1.3), and Sc (6.4±1.4)] than in those with ns-LBP (4.7±1.0, P<0.001). The same was shown for pain interference (5.9±2.0, 5.9±1.8, 3.2±1.9, P<0.001), disability (16.4±3.3, 16.3±4.3, 10.4±4.3, P<0.001), and catastrophism (31.1±12.3, 33.0±10.4, 17.4±10.7, P<0.001) scores for FBSS, Sc, and ns-LBP groups, respectively. Patients with neuropathic pain (FBSS, Sc) had lower CPM (-14.8±1.9, -14.1±16.7, respectively) compared to ns-LBP (-25.4±16.6; P<0.02). 80.0% of the FBSS group had defective ICF compared to the other two groups (52.5% for ns-LBP, P=0.025 and 52.5% for Sc, P=0.046). MEPs (140%-rest motor threshold) were low in 50.0% of patients in the FBSS group compared to 20.0% of ns-LBP (P=0.018) and 15.0% of Sc (P=0.001) groups. Higher MEPs were correlated with mood scores (r=0.489), and with lower neuropathic pain symptom scores(r=-0.415) in FBSS.

CONCLUSIONS

Different types of LBP were associated with different clinical, CPM and CE profiles, which were not uniquely related to the presence of neuropathic pain. These results highlight the need to further characterize patients with LBP in psychophysics and cortical neurophysiology studies.

Brain stimulation for chronic pain management: a narrative review of analgesic mechanisms and clinical evidence

Chronic pain constitutes one of the most common chronic complaints that people experience. According to the International Association for the Study of Pain, chronic pain is defined as pain that persists or recurs longer than 3 months. Chronic pain has a significant impact on individuals' well-being and psychosocial health and the economy of healthcare systems as well. Despite the availability of numerous therapeutic modalities, treatment of chronic pain can be challenging. Only about 30% of individuals with non-cancer chronic pain achieve improvement from standard pharmacological treatment. Therefore, numerous therapeutic approaches were proposed as a potential treatment for chronic pain including non-opioid pharmacological agents, nerve blocks, acupuncture, cannabidiol, stem cells, exosomes, and neurostimulation techniques. Although some neurostimulation methods such as spinal cord stimulation were successfully introduced into clinical practice as a therapy for chronic pain, the current evidence for brain stimulation efficacy in the treatment of chronic pain remains unclear. Hence, this narrative literature review aimed to give an up-to-date overview of brain stimulation methods, including deep brain stimulation, motor cortex stimulation, transcranial direct current stimulation, repetitive transcranial magnetic stimulation, cranial electrotherapy stimulation, and reduced impedance non-invasive cortical electrostimulation as a potential treatment for chronic pain.

Diagnosis and Management of Neuropathic Pain in Spine Diseases

Neuropathic pain is generally defined as a non-physiological pain experience caused by damage to the nervous system. It can occur spontaneously, as a reaction to a given stimulus, or independently of its action, leading to unusual pain sensations usually referred to as firing, burning or throbbing. In the course of spine disorders, pain symptoms commonly occur. According to available epidemiological studies, a neuropathic component of pain is often present in patients with spinal diseases, with a frequency ranging from 36% to 55% of patients. Distinguishing between chronic nociceptive pain and neuropathic pain very often remains a challenge. Consequently, neuropathic pain is often underdiagnosed in patients with spinal diseases. In reference to current guidelines for the treatment of neuropathic pain, gabapentin, serotonin and norepinephrine reuptake inhibitors and tricyclic antidepressants constitute first-line therapeutic agents. However, long-term pharmacologic treatment often leads to developing tolerance and resistance to used medications. Therefore, in recent years, a plethora of therapeutic methods for neuropathic pain have been developed and investigated to improve clinical outcomes. In this review, we briefly summarized current knowledge about the pathophysiology and diagnosis of neuropathic pain. Moreover, we described the most effective treatment approaches for neuropathic pain and discussed their relevance in the treatment of spinal pain.

Normalization of Neuroinflammation: A New Strategy for Treatment of Persistent Pain and Memory/Emotional Deficits in Chronic Pain

Chronic pain, which affects around 1/3 of the world population and is often comorbid with memory deficit and mood depression, is a leading source of suffering and disability. Studies in past decades have shown that hyperexcitability of primary sensory neurons resulting from abnormal expression of ion channels and central sensitization mediated pathological synaptic plasticity, such as long-term potentiation in spinal dorsal horn, underlie the persistent pain. The memory/emotional deficits are associated with impaired synaptic connectivity in hippocampus. Dysregulation of numerous endogenous proteins including receptors and intracellular signaling molecules is involved in the pathological processes. However, increasing knowledge contributes little to clinical treatment. Emerging evidence has demonstrated that the neuroinflammation, characterized by overproduction of pro-inflammatory cytokines and glial activation, is reliably detected in humans and animals with chronic pain, and is sufficient to induce persistent pain and memory/emotional deficits. The abnormal expression of ion channels and pathological synaptic plasticity in spinal dorsal horn and in hippocampus are resulting from neuroinflammation. The neuroinflammation is initiated and maintained by the interactions of circulating monocytes, glial cells and neurons. Obviously, unlike infectious diseases and cancer, which are caused by pathogens or malignant cells, chronic pain is resulting from alterations of cells and molecules which have numerous physiological functions. Therefore, normalization (counterbalance) but not simple inhibition of the neuroinflammation is the right strategy for treating neuronal disorders. Currently, no such agent is available in clinic. While experimental studies have demonstrated that intracellular Mg²⁺ deficiency is a common feature of chronic pain in animal models and supplement Mg²⁺ are capable of normalizing the neuroinflammation, activation of upregulated proteins that promote recovery, such as translocator protein (18k Da) or liver X receptors, has a similar effect. In this article, relevant experimental and clinical evidence is reviewed and discussed.

Diagnosis, Treatment, and Management of Painful Scar: A Narrative Review

Painful scars can develop after surgery or trauma, with symptoms ranging from a minor itch to intractable allodynia. The problem of the painful scar may involve both intraneural and extraneural structures, requiring a systematic approach to diagnosis and treatment of this neuropathic pain condition that can impact quality of life and function profoundly. In this review, we outline the algorithm for the diagnosis, management, medical and surgical treatment of painful scars.