The IASP classification of chronic pain for ICD-11: chronic neuropathic pain

Pain-on-a-Chip: A microfluidic device for neuron differentiation and functional discrimination in animal models of chronic pain

Chronic pain is a global health issue that is poorly understood and challenging to treat. Improving pain classification and treatment requires new strategies that objectively discriminate between pain conditions and minimise subjectivity associated with the perception of pain. To address this, we have developed a microfluidic biosensor - termed 'pain-on-a-chip' - that leverages recent advancements in biocompatible microfluidic technology with on-chip differentiation of nociceptor-like cells, enabling small sample volumes to be used. Following neuronal differentiation, we used on-chip live cell Ca2+ imaging to functionally validate the system. This includes characterising excitation responses in cells challenged with microfluidic perfusion of known nociceptive stimuli and biological fluids collected from different preclinical pain models. Our results demonstrate that this platform has the potential to discriminate between serum samples from distinct chronic pain models. This system has potential as an objective, and minimally invasive method for distinguishing between different subtypes of chronic pain.

Default mode network-basal ganglia network connectivity predicts the transition to postherpetic neuralgia

Background

Neuroimaging studies have revealed aberrant network functional connectivity in postherpetic neuralgia (PHN) patients. However, there is a lack of knowledge regarding the relationship between the brain network connectivity during the acute period and disease prognosis.

Objective

The purpose of this study was to detect characteristic network connectivity in the process of herpes zoster (HZ) pain chronification and to identify whether abnormal network connectivity in the acute period can predict the outcome of patients with HZ.

Methods

In this cross-sectional study, 31 patients with PHN, 33 with recuperation from herpes zoster (RHZ), and 28 with acute herpes zoster (AHZ) were recruited and underwent resting-state functional magnetic resonance imaging (fMRI). We investigated the differences in the connectivity of four resting-state networks (RSN) among the three groups. Receiver operating characteristic (ROC) curve analysis was performed to identify whether abnormal network connectivity in the acute period could predict the outcome of patients with HZ.

Results

First, we found within-basal ganglia network (BGN) and default mode network (DMN)-BGN connectivity differences, with PHN patients showing increased DMN-BGN connectivity compared to AHZ and RHZ patients, while RHZ patients showing increased within-BGN connectivity compared to AHZ and PHN patients. Moreover, DMN-BGN connectivity was associated with the ID pain score in patients with AHZ. Finally, the DMN-BGN connectivity of AHZ patients could predict the outcome of HZ patients with sensitivity and specificity of 77.8 % and 63.2 %, respectively.

Conclusions

Our results provide evidence that DMN-BGN connectivity during the acute period confers a risk for the development of chronic pain and can act as a neuroimaging biomarker to predict the outcome of patients with HZ.

An overview of the non-procedural treatment options for peripheral neuropathic pain

Peripheral neuropathic pain is common in patients with peripheral nerve injury and can significantly impact both their function and quality of life. There is a wide variety of non-interventional treatment approaches, including pharmacologic therapy, physical/occupational therapy, modalities (therapeutic, mechanical, thermal, etc.), psychology, and lifestyle modification. First line pharmacologic therapy for peripheral neuropathic pain includes gabapentinoids, tricyclic antidepressants, and serotonin-norepinephrine reuptake inhibitors. Other classes of medications, such as topical treatments, opioids, and cannabinoids, have more limited usefulness in treatment but remain part of a treatment regimen. Physical and occupational therapy, psychological interventions, and lifestyle medicine are important adjuncts in the treatment and prevention of future peripheral neuropathic pain. The strength of the evidence supporting each intervention varies, with that for pharmacologic intervention being the strongest. A combination of these options tailored to the individual needs of the patient likely will result in the best treatment outcome for peripheral neuropathic pain.

Association Between Non-spinal Comorbid Medical Conditions and Neuropathic Low Back Pain. - A Further Unravelling of Pain Complexities in the Context of Back Pain

Study DesignProspective cohort study.ObjectiveUnderstanding the complex nature of low back pain (LBP) is crucial for effective management. The PainDETECT questionnaire is a tool that distinguishes between neuropathic (NeP) and nociceptive (NoP) low back pain. Traditionally NeP and NoP have been primarily attributed to patho-anatomical abnormalities within the lumbar spine. However, increasing evidence points to multifaceted involvement, encompassing a range of physical, biomechanical, chemical, and psychosocial factors. The study aimed to determine the independent relationship between NeP as assessed by the PainDETECT questionnaire and non-spinal comorbid medical conditions.MethodsA prospective cohort study was conducted involving 400 patients suffering from chronic LBP (>6months), aged >18 years, who complete the PainDETECT questionnaire and provided responses regarding the presence of any comorbid conditions. A binary logistic regression model was used to analyse the confounding status of comorbid medical conditions and pain severity measured by NRS to determine independent relationships between specific conditions and neuropathic pain.ResultsThe study included 143 and 257 patients suffering from NeP and NoP, respectively. The NeP group had a 38% higher mean numerical rating scale score compared to the NoP group (8.10 ± 1.55 vs 5.86± 2.26, P < 0.001). The odds of developing NeP were 2.9 Exp(B) = 2.844, 95%C.I. [1.426-5.670], P < 0.01), 2.7 (Exp(B) = 2.726, 95%C.I. [1.183-6.283], P < 0.05) and 2.8 (Exp(B) = 2.847, 95%C.I. [1.473-5.503], P < 0.05) times higher in patients suffering from gastrointestinal conditions, rheumatoid arthritis, and depression, respectively.ConclusionNeP as determined by the PainDETECT questionnaire, is associated with gastrointestinal conditions, rheumatoid arthritis, and depression. This pioneering study has shed light on the potential involvement of the gut microbiome as a common factor connecting non-spinal comorbidities and NeP. These findings underscore the importance of formulating personalized management plans tailored to individual pain and medical profiles, rather than relying on a blanket approach to pain management.

Inhibition of S100A4 decreases neurotoxic astrocyte reactivity and attenuates neuropathic pain via the TLR4/NF-κB pathway in a rat model of spinal nerve ligation

S100A4 participates in inflammation and immune reactions in the central nervous system and is involved in the pathogenesis of multiple neurological disorders. It can affect the functions of astrocytes, microglia, infiltrating cells and neurons and further modulates neuronal plasticity and survival in the central nervous system. However, its impact on astrocyte phenotypes and neuropathic pain and the intrinsic mechanisms involved remain poorly understood. Here, we showed that S100A4 was markedly upregulated after spinal nerve ligation and was mainly expressed in neurons in the spinal dorsal horn. Transcriptional inhibition of S100A4 with niclosamide attenuated neuropathic pain after surgery. We found that astrocytes differentiated into C3-positive reactive populations, so-called neurotoxic (A1) astrocytes and identified differentially expressed genes and specific molecular expression signatures after ligation. Neurotoxic astrocyte reactivity is regulated by exogenous S100A4 in vitro, and targeted inhibition of S100A4 suppresses neurotoxic astrocyte proliferation in rats. Finally, we reported that TLR4/NF-κB signaling pathway is a downstream of S100A4 activation, and that specific depletion this pathway suppresses deleterious A1 astrocyte activation and further attenuates the development and maintenance of neuropathic pain after spinal nerve ligation. Thus, S100A4 in neurons plays a key role in neurotoxic astrocyte reactivity and can be targeted for treatment to prevent and alleviate neuropathic pain.

Modified Feature Selection for Improved Classification of Resting-State Raw EEG Signals in Chronic Knee Pain

OBJECTIVE

Diagnosing pain in research and clinical practices still relies on self-report. This study aims to develop an automatic approach that works on resting-state raw EEG data for chronic knee pain prediction.

METHOD

A new feature selection algorithm called "modified Sequential Floating Forward Selection" (mSFFS) is proposed. The improved feature selection scheme can better avoid local minima andexplore alternative search routes.

RESULTS

The feature selection obtained by mSFFS displays better class separability as indicated by the Bhattacharyya distance measures and better visualization results. It also outperforms selections generated by other benchmark methods, boosting the test accuracy to 97.5%.

CONCLUSION

The improved feature selection searches out a compact, effective subset of connectivity features that produces competitive performance on chronic knee pain prediction.

SIGNIFICANCE

We have shown that an automatic approach can be employed to find a compact connectivity feature set that effectively predicts chronic knee pain from EEG. It may shed light on the research of chronic pains and lead to future clinical solutions for diagnosis and treatment.

Pharmacotherapy and non-invasive neuromodulation for neuropathic pain: a systematic review and meta-analysis

BACKGROUND

There remains a substantial unmet need for effective and safe treatments for neuropathic pain. The Neuropathic Pain Special Interest Group aimed to update treatment recommendations, published in 2015, on the basis of new evidence from randomised controlled trials, emerging neuromodulation techniques, and advances in evidence synthesis.

METHODS

For this systematic review and meta-analysis, we searched Embase, PubMed, the International Clinical Trials Registry, and ClinicalTrials.gov from data inception for neuromodulation trials and from Jan 1, 2013, for pharmacological interventions until Feb 12, 2024. We included double-blind, randomised, placebo-controlled trials that evaluated pharmacological and neuromodulation treatments administered for at least 3 weeks, or if there was at least 3 weeks of follow-up, and which included at least ten participants per group. Trials included participants of any age with neuropathic pain, defined by the International Association for the Study of Pain. We excluded trials with enriched enrolment randomised withdrawal designs and those with participants with mixed aetiologies (ie, neuropathic and non-neuropathic pain) and conditions such as complex regional pain syndrome, low back pain without radicular pain, fibromyalgia, and idiopathic orofacial pain. We extracted summary data in duplicate from published reports, with discrepancies reconciled by a third independent reviewer on the platform Covidence. The primary efficacy outcome was the proportion of responders (50% or 30% reduction in baseline pain intensity or moderate pain relief). The primary safety outcome was the number of participants who withdrew from the treatment owing to adverse events. We calculated a risk difference for each comparison and did a random-effects meta-analysis. Risk differences were used to calculate the number needed to treat (NNT) and the number needed to harm (NNH) for each treatment. Risk of bias was assessed by use of the Cochrane risk of bias tool 2 and certainty of evidence assessed by use of GRADE. Recommendations were based on evidence of efficacy, adverse events, accessibility, and cost, and feedback from engaged lived experience partners. This study is registered on PROSPERO, CRD42023389375.

FINDINGS

We identified 313 trials (284 pharmacological and 29 neuromodulation studies) for inclusion in the meta-analysis. Across all studies, 48 789 adult participants were randomly assigned to trial groups (20 611 female and 25 078 male participants, where sex was reported). Estimates for the primary efficacy and safety outcomes were tricyclic antidepressants (TCAs) NNT=4·6 (95% CI 3·2-7·7), NNH=17·1 (11·4-33·6; moderate certainty of evidence), α2δ-ligands NNT=8·9 (7·4-11·10), NNH=26·2 (20·4-36·5; moderate certainty of evidence), serotonin and norepinephrine reuptake inhibitors (SNRIs) NNT=7·4 (5·6-10·9), NNH=13·9 (10·9-19·0; moderate certainty of evidence), botulinum toxin (BTX-A) NNT=2·7 (1·8-9·61), NNH=216·3 (23·5-∞; moderate certainty of evidence), capsaicin 8% patches NNT=13·2 (7·6-50·8), NNH=1129·3 (135·7-∞; moderate certainty of evidence), opioids NNT=5·9 (4·1-10·7), NNH=15·4 (10·8-24·0; low certainty of evidence), repetitive transcranial magnetic stimulation (rTMS) NNT=4·2 (2·3-28·3), NNH=651·6 (34·7-∞; low certainty of evidence), capsaicin cream NNT=6·1 (3·1-∞), NNH=18·6 (10·6-77·1; very low certainty of evidence), lidocaine 5% plasters NNT=14·5 (7·8-108·2), NNH=178·0 (23·9-∞; very low certainty of evidence). The findings provided the basis for a strong recommendation for use of TCAs, α2δ-ligands, and SNRIs as first-line treatments; a weak recommendation for capsaicin 8% patches, capsaicin cream, and lidocaine 5% plasters as second-line recommendation; and a weak recommendation for BTX-A, rTMS, and opioids as third-line treatments for neuropathic pain.

INTERPRETATION

Our results support a revision of the Neuropathic Pain Special Interest Group recommendations for the treatment of neuropathic pain. Treatment outcomes are modest and for some treatments uncertainty remains. Further large placebo-controlled or sham-controlled trials done over clinically relevant timeframes are needed.

FUNDING

NeuPSIG and ERA-NET Neuron.

Clinical Benefits of Ibuprofen Arginine: A Narrative Review

Ibuprofen arginine (IBA) combines well-established analgesic and anti-inflammatory properties with enhanced pharmacokinetics. The addition of arginine significantly improves solubility and absorption, leading to a faster onset of action compared to conventional ibuprofen. Clinical studies consistently demonstrate that IBA achieves meaningful pain relief within a shorter timeframe while maintaining a favorable safety profile. IBA's rapid action is particularly valuable in managing acute exacerbations of chronic pain and preventing central sensitization, thus improving patient comfort, adherence, and overall quality of life. By addressing both the inflammatory and nociceptive components of pain, IBA offers an effective and well-tolerated alternative in multimodal pain management strategies. This review explores the clinical benefits of IBA in pain management among various clinical settings.

Estradiol is Pro-Nociceptive and Associated with a Small-Fiber Neuropathy Among Premenopausal Women with Sickle Cell Disease

Vaso-occlusive crisis (VOC) pain episodes often occur with menses and concurrent hormonal contraceptive use may reduce their frequency. This study tested the hypothesis that among women with sickle cell disease (SCD), sex hormones are associated with pain detection thresholds. Women with SCD aged minimum 18 years with regular menses, and without acute illnesses, pregnancy, oophorectomy, or hormonal contraceptive use within three months prior were included. Pain detection thresholds for heat (HPT) and pressure (PPT), and serum estradiol, progesterone and testosterone were measured at follicular and luteal phases. The Adult Sickle Cell Quality-of-Life Measurement Information System assessed quality-of-life and VOC frequency and severity scores. Generalized linear mixed models were performed, including the day of the cycle standardized by cycle length. Among 125 participants, neither the day nor phase of the menstrual cycle was associated with PPT or HPT. In multivariate analyses, worse VOC scores (β = 1.7) and severe genotype (β = -46.0) were associated with higher and lower trapezius PPT, respectively. Older age was associated with lower forearm HPT (β = -0.1). Among leg measurements, ovulatory cycles (β = -1.1) and hydroxyurea use (β = -1.2) were associated with lower HPT, while worse VOC scores (β = 0.1) were associated with higher HPT. Higher estradiol was associated with lower HPT at the leg (β = -0.02), with an interaction with the cycle day (β = 0.001) predicting lower thresholds earlier in the cycle for the same estradiol level. Estradiol is associated with a time-varying, length-dependent small-fiber neuropathy among SCD women; and may be a potential therapeutic target and biomarker for SCD pain.

Diosmetin Attenuates Painful Symptoms Caused by Antineoplastics Paclitaxel and Anastrozole in Mice

Cancer patients often experience painful symptoms as an adverse effect resulting from various factors, including antineoplastic therapy. Paclitaxel is a chemotherapeutic agent used to treat solid tumours and, unfortunately, causes acute and chronic peripheral neuropathic pain in patients. Anastrozole is an antineoplastic used to treat hormone receptor-positive breast cancer and causes musculoskeletal pain symptoms. The therapies used to control these pain symptoms have limited efficacy and cause adverse effects, highlighting the importance of finding new treatments. Diosmetin is a flavonoid that has shown efficacy in neuropathic, nociplastic, and inflammatory pain models. Therefore, we verified the antinociceptive effects of diosmetin on nociceptive parameters induced by paclitaxel and anastrozole. We investigated the effects of diosmetin (0.015, 0.15 and 1.5 mg/kg; oral route (p.o.)) on nociceptive parameters (mechanical and cold allodynia and pain affective‑motivational behaviour) induced by a single and repeated paclitaxel (1 mg/kg, intraperitoneal (i.p.)) administrations, as well as on the pain-like symptoms (mechanical allodynia, muscle strength, and pain affective‑motivational behaviour) of a single administration of anastrozole (0.2 mg/kg, p.o.) and the combination of both antineoplastics in mice. Diosmetin reduced the nociceptive parameters induced by paclitaxel and anastrozole. In addition, we observed that anastrozole exacerbated the mechanical allodynia induced by paclitaxel, an effect that was also reversed by diosmetin. These results suggest that diosmetin may be an effective therapeutic alternative for the treatment of painful symptoms caused by antineoplastic drugs, such as paclitaxel and anastrozole.

Protein Kinases as Mediators for miRNA Modulation of Neuropathic Pain

Neuropathic pain is a chronic condition resulting from injury or dysfunction in the somatosensory nervous system, which leads to persistent pain and a significant impairment of quality of life. Research has highlighted the complex molecular mechanisms that underlie neuropathic pain and has begun to delineate the roles of microRNAs (miRNAs) in modulating pain pathways. miRNAs, which are small non-coding RNAs that regulate gene expression post-transcriptionally, have been shown to influence key cellular processes, including neuroinflammation, neuronal excitability, and synaptic plasticity. These processes contribute to the persistence of neuropathic pain, and miRNAs have emerged as critical regulators of pain behaviors by modulating signaling pathways that control pain sensitivity. miRNAs can influence neuropathic pain by targeting genes that encode protein kinases involved in pain signaling. This review focuses on miRNAs that have been demonstrated to modulate neuropathic pain behavior through their effects on protein kinases or their immediate upstream regulators. The relationship between miRNAs and neuropathic pain behaviors is characterized as either an upregulation or a downregulation of miRNA levels that leads to a reduction in neuropathic pain. In the case of miRNA upregulation resulting in an alleviation of neuropathic pain behaviors, protein kinases exhibit a positive correlation with neuropathic pain, whereas decreased protein kinase levels correlate with diminished neuropathic pain behaviors. The only exception is GRK2, which shows an inverse correlation with neuropathic pain. In the case of miRNA downregulation resulting in a reduction in neuropathic pain behaviors, protein kinases display mixed relationships to neuropathic pain, with some kinases exhibiting positive correlation, while others exhibit negative correlation. By exploring how protein kinases mediate miRNA modulation of neuropathic pain, valuable insight may be gained into the pathophysiology of neuropathic pain, offering potential therapeutic targets for developing more effective strategies for pain management.

Temporal lobe dysfunction for comorbid depressive symptoms in postherpetic neuralgia patients

Depression often occurs concurrently with postherpetic neuralgia (PHN), yet the neural mechanism underlying pain-depression comorbidity remains poorly understood. For this observational study, we recruited 17 depressed PHN patients, 19 non-depressed PHN patients, and 34 healthy controls (HCs) for resting-state functional MRI scans. We firstly investigated the differences in fractional amplitude of low-frequency fluctuation and regional homogeneity values among the three groups to identify a characteristic brain signal of pain-depression comorbidity. Abnormal voxel-wised functional connectivity was then compared across groups and correlated with clinical variables in each group. One-way analysis of covariance results revealed the fractional amplitude of low-frequency fluctuation values differences in the right temporal lobe (TL) and its voxel-wised connectivity with the inferior frontal gyrus (IFG) among three groups. Furthermore, the TL-IFG connectivity was positively associated with the positive emotional scores and life quality scores among depressed PHN patients, but not non-depressed PHN patients and HCs. In summary, these findings highlighted the TL dysfunction in pain-depression comorbidity among PHN population and may offer heuristic cues for central therapeutic targets that could disrupt the pain-depression vicious circle.

Innovative "Three-in-One" Method for Intervention of Lower Limb Neuropathic Pain: Retrospective Case Series Study

Purpose

Minimally invasive intervention therapy anterior cutaneous branch of the femoral nerve for refractory neuropathic pain in the inner thigh area typically requires punctures at multiple sites to target the three nerves of the obturator nerve cutaneous branch, anterior cutaneous branch of the femoral nerve, and infrapatellar branch of the saphenous nerve. Clinical practice has demonstrated that the innovative "three-in-one" technique allows for simultaneous targeting of the three cutaneous nerves from a single entry point, effectively treating inner thigh pain. Moreover, this approach can also be used for local anaesthesia in shallow surgical procedures in the inner thigh area. We hope to promote this puncture technique among pain physicians.

Patients and Methods

Clinical data of 8 patients with localized pain in the inner thigh from the Pain Department of Taihe Hospital, Shiyan City, Hubei Medical College, from April 2023 to September 2024 were collected. All the patients experienced pain in the cutaneous branch of the obturator nerve, the anterior branch of medial femoral cutaneous nerve, and the infrapatellar branch of the saphenous nerve. The "three-in-one" approach was used for nerve block and radiofrequency puncture.

Results

After the "three-in-one" approach, the 8 patients showed varying degrees of improvement in their Numeric Rating Scale (NRS) scores. The patients were satisfied with the treatment method and efficacy, and no complications, such as nerve damage, occurred during the operation.

Conclusion

The "three-in-one" approach is a potentially effective method for treating pain in the inner lower limb area, significantly reducing the damage caused by multiple puncture and providing ideas for more minimally invasive treatment of other areas; this approach meets expectations for more minimally invasive treatment.

Evaluating the efficacy of transcranial direct current stimulation (tDCS) in managing neuropathic pain-induced emotional consequences: Insights from animal models

Neuropathic pain is a global health concern due to its severity and its detrimental impact on patients' quality of life. It is primarily characterized by sensory alterations, most commonly hyperalgesia and allodynia. As the disease progresses, patients with neuropathic pain develop co-occurring emotional disorders, such as anxiety and depression, which further complicate therapeutic management. While pharmacotherapy remains the first-line treatment, limitations in its efficacy and the prevalence of side effects often leave patients with insufficient pain relief. Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, has recently emerged as a promising alternative for chronic pain management. This review provides an overview of preclinical studies examining the effects of tDCS in rodent models of neuropathic pain. It specifically highlights the potential of tDCS to modulate the emotional-affective component of pain, with a focus on identifying optimal cortical targets for stimulation to enhance the translational application of tDCS in managing pain-related emotional disorders.

Experimentally induced pain and paresthesia respond differently to parameter changes of cuff-based compression in pain-free young individuals

Neuropathic pain is a significant therapeutic challenge due to the co-occurrence with other neurological symptoms such as paresthesia. Human-based models such as cuff algometry can enhance our understanding of pain-paresthesia relationships. This experiment aimed to characterize (psychophysically) pain and paresthesia evoked by stimuli of different temporal and intensity parameters and to demonstrate the reliability of experimental induction of these two symptoms using cuff algometry. Forty participants, aged 18-35, were exposed to mechanical pressure stimuli at three intensities (100, 150, 200 mmHg) and three durations (90, 120, 150 s). Skin Conductance (SC) was continuously monitored, and participants rated pain and paresthesia in real-time using a computerized visual analog scale. The General Linear Model analysis revealed significant differences in paresthesia across all durations (p<0.01), but not all intensities, as paresthesia did not increase from 150 to 200 mmHg (p>0.05). Conversely, pain responses showed significant differences across all pressure intensities (p<0.05) but not durations, as pain did not increase from 90 to 120 and from 120 to 150 s (p>0.05). No interaction effects were found for either symptom. SC analysis showed no significant main or interaction effects. Intraclass correlation coefficients (ICCs) indicated moderate to excellent reliability for pain and paresthesia induction across different durations and intensities (ICC: 0.51-0.91), while SC showed poor to good reliability (ICC: 0.17-0.79). In conclusion, computerized cuff algometry seems to be an effective and reliable method for simultaneously inducing and assessing pain and paresthesia, revealing that these symptoms follow different patterns based on pressure duration and intensity. PERSPECTIVE: This study demonstrates that pain and paresthesia respond differently to varying intensities and durations of mechanical pressure, revealing their distinct psychophysical characteristics. This model can advance the understanding of neuropathic conditions and aid the development of more targeted therapeutic approaches for both pain and paresthesia.

Adverse events, including fractures, among older patients receiving mirogabalin versus pregabalin: A retrospective cohort study using a large claims database in Japan

BACKGROUND

Mirogabalin has a mechanism similar to that of pregabalin in the treatment of neuropathic pain. However, it remains unclear whether these drugs differ in terms of serious side effects, such as fall-related fractures, in older patients. This study aimed to investigate whether mirogabalin is associated with a decrease in adverse events, including fall-related fractures, compared with pregabalin.

METHODS

We performed a retrospective cohort study using the DeSC database, a large administrative claims database in Japan. This study included 130,244 patients ≥65 years taking mirogabalin or pregabalin between April 2019 and May 2021. The primary outcome was defined as the occurrence of fractures or switching to other medications and was compared between those receiving mirogabalin and pregabalin using Kaplan-Meier curves and multivariable Cox proportional hazards models. A sensitivity analysis was performed regarding patients who received mirogabalin or pregabalin without other analgesic medications at the initial dose.

RESULTS

During a median follow-up of 2.8 months, 29,686 (22.8%) and 100,558 (77.2%) received mirogabalin and pregabalin, respectively. The rates of the outcome in the mirogabalin and pregabalin groups were 50.1 and 42.8 per 100 person-years. Cox regression analysis showed that mirogabalin was associated with a lower risk of the outcome (hazard ratio, 0.93; 95% confidence interval, 0.87-1.00). However, sensitivity analysis did not demonstrate a difference in the outcome between the mirogabalin and pregabalin groups without other analgesic medications (hazard ratio, 0.93; 95% confidence interval, 0.86-1.01).

CONCLUSIONS

Our analyses suggest that the outcome may be less likely in the mirogabalin group; however, the difference appears to be clinically insignificant. Further studies are warranted to confirm these findings.

Molecule-rich solutions for achieving novel non-opioid analgesics

Despite their efficacy, opioids have long been associated with risks of addiction, tolerance, and dependence, leaving an unmet clinical need for pain treatment. Efforts have been devoted to developing novel classes of pain-relieving medication that outperform current options in terms of pain relief, side-effect profiles, and potential for abuse, but with limited success. Recent advances in the neurobiology of pain have shed light on the potential of targeting non-opioid receptors involved in pain processing. In this review, we identify avenues, ranging from molecular-based approaches to molecule-rich solutions, for effectively identifying non-opioid analgesics free from the side effects associated with opioids.

Inhibition of SARM1 Reduces Neuropathic Pain in a Spared Nerve Injury Rodent Model

INTRODUCTION/AIMS

The function of the sterile alpha and toll/interleukin receptor motif-containing protein 1 (SARM1) in neuropathic pain development has not yet been established. This protein has a central role in regulating axon degeneration and its depletion delays this process. This study aims to demonstrate the effects of SARM1 deletion on the development of neuropathic pain.

METHODS

Thirty-two wild-type (WT) or SARM1 knockout (KO) rats underwent spared nerve injury (SNI) or sham surgery. Mechanical allodynia was assessed by electronic Von Frey and cold hyperalgesia by the acetone test. Nociception was evaluated at the baseline, Day-1, Day-2, Week-1, Week-2, Week-3, and Week-4 time points. Nerve sections were examined by immunohistochemistry (IHC).

RESULTS

WT Injury rats were more sensitive to pain than WT Sham at all postoperative time points, validating the pain model. Injured SARM1 KO rats only demonstrated a difference in mechanical or cold nociception from KO Sham at Week 3. Injured KO rats demonstrated a clear trend of decreased sensitivity compared to WT Injury nociception, reaching significance at Week 4 (p = 0.044). Injured KO rats showed attenuated sensitivity to cold allodynia relative to WT at Week 2 (p = 0.019). IHC revealed decreased macrophages in spared sural nerves of injured KO animals at 2 and 4 weeks, and the proximal portion of tibial/peroneal nerves at Week 2.

DISCUSSION

This study demonstrates that SARM1 KO rats are less sensitive to mechanical and cold nociception than WT rats in an SNI model with decreased inflammatory response. Given these results, inhibition of SARM1 should be further investigated in the treatment of neuropathic pain.

Gut microbiome and serum metabolites in neuropathic pain: The PPARα perspective

Neuropathic pain (NP) is a chronic disease state centred on neuroinflammation with a high prevalence and limited effective treatment options. Peroxisome proliferator-activated receptor α (PPARα) has emerged as a promising target for NP management due to its anti-inflammatory properties. Recent evidence highlights the critical role of the gut microbiome and its metabolites in NP pathogenesis. This study aimed to investigate whether PPARα modulates the development and alleviation of NP by influencing gut microbial communities and serum metabolites. 16S rDNA sequencing and liquid chromatography-mass spectrometry (LC-MS/MS) untargeted metabolomics analyses performed 14 days after the establishment of a chronic constriction injury (CCI) pain model in C57BL/6 J mice showed significant changes in gut microbial and metabolite levels in CCI mice. Intraperitoneal injection of the PPARα agonist GW7647 (5 mg/kg) significantly attenuated mechanical allodynia and thermal hyperalgesia in CCI mice, whereas injection of the PPARα antagonist GW6471 (20 mg/kg) produced the opposite effect. Immunofluorescence analysis revealed that GW7647 effectively suppressed microglial activation. Additionally, PPARα agonist and antagonist treatments markedly altered the composition and abundance of intestinal microbial communities in CCI mice. Further serum LC-MS/MS analysis identified 258 potential serum metabolic biomarkers, many of which correlated with changes in gut microbial composition. These findings demonstrate that PPARα influences serum metabolite profiles by modulating gut microbiota composition, which subsequently affects NP progression. This study provides novel insights into the mechanisms underlying NP and suggests potential therapeutic avenues targeting PPARα and gut microbiota.

Fear of movement in patients after lumbar spine fusion and an analysis of factors: a cross-sectional study

BACKGROUND

Numerous studies have confirmed the significant benefits of exercise rehabilitation in both preoperative and postoperative treatment of lumbar disc herniation. However, there is a prevalent fear or avoidance of exercise among patients with chronic low back pain prior to surgery, while research on exercise fear after lumbar fusion remains insufficient. This study aims to investigate the incidence and severity of exercise fear in patients with chronic low back pain and leg pain following lumbar fusion surgery, as well as analyze its underlying mechanism and associated risk factors.

METHODS

A cross-sectional study was conducted on patients undergoing posterior lumbar fusion for lumbar disc herniation between May 2023 and January 2024. The Tampa Motor Phobia Scale (TSK-17) was utilized to assess motor fear among participants. Additionally, clinical and imaging risk factors were analyzed through multivariate regression analysis to determine relevant influencing factors.

RESULTS

Following strict inclusion and exclusion criteria, a total of 178 patients who underwent posterior lumbar fusion were included in this study, comprising 104 males (58.4%). Kinesiophobia was defined as a TSK-17 score ≥ 37, which identified 65.2% (116/178) of the screened patients exhibiting motor phobia. Multivariate regression analysis revealed that motor phobia was strongly associated with age, higher levels of pain intensity, elevated Beck Depression Inventory (BDI) scores, lower General Self-Efficacy Scale (GSES) scores, increased number of surgical levels involved during operation, greater amount of postoperative incision drainage, higher degree of nerve root compression observed on preoperative lumbar MRI scans, as well as smaller area occupied by the paravertebral muscles in the lumbar region.

CONCLUSION

This study has identified a significantly high incidence of postoperative exercise fear in patients undergoing posterior lumbar fusion, along with potential risk factors. Therefore, it is crucial for clinicians to closely evaluate and monitor these patients in order to develop appropriate strategies for postoperative exercise rehabilitation.

Focus on P2X7R in microglia: its mechanism of action and therapeutic prospects in various neuropathic pain models

Neuropathic pain (NP) is a common symptom of many diseases and is caused by direct or indirect damage to the nervous system. Tricyclic antidepressants and serotonin-norepinephrine reuptake inhibitors are typical drugs used in clinical practice to suppress pain. However, these drugs have drawbacks, including a short duration of action, a limited analgesic effect, and possible dependence and side effects. Therefore, developing more effective NP treatment strategies has become a priority in medical research and has attracted much research attention. P2X7 receptor (P2X7R) is a non-selective cation channel activated by adenosine triphosphate and is mainly expressed in microglia in the central nervous system. Microglial P2X7R plays an important role in pain regulation, suggesting that it could be a potential target for drug development. This review comprehensively and objectively discussed the latest research progress of P2X7R, including its structural characteristics, functional properties, relationship with microglial activation and polarization, mechanism of action, and potential therapeutic strategies in multiple NP models. This study aimed to provide in-depth insights into the association between P2X7R and NP and explore the mechanism of action of P2X7R in the pathological process of NP and the translational potential and clinical application prospects of P2X7R antagonists in pain treatment, providing a scientific basis for the precise treatment of NP.

Mourning for Silence: Bereavement and Tinnitus-A Perspective

Tinnitus is defined as the conscious awareness of a tonal or composite noise for which there is no identifiable corresponding external acoustic source, which becomes tinnitus disorder when the phantom sound is associated with suffering and/or disability. There is only limited knowledge about the time course of tinnitus disorder. Bereavement science has identified four different trajectories: resilience, recovery, chronic, and delayed. The question arises whether these four trajectories exist in tinnitus as well if one considers tinnitus as the loss of silence (at will). To verify whether these four trajectories exist, short-term tinnitus progression was analyzed retrospectively using an Ecological Momentary Assessment (EMA) approach, extracting the data from patients who started using the TrackYourTinnitus (TYT) app (version 1, Ulm University, 2013) from the start of their tinnitus perception. Four patients were identified retrospectively via the TYT app with acute tinnitus, and the bereavement trajectories were reconstructed based on EMA. In conclusion, this perspective suggests that the four known bereavement trajectories may exist in tinnitus, and prospective evaluations of larger samples are warranted to confirm or disprove this analogy between bereavement and tinnitus, in which tinnitus is conceived as the loss of (controllable) silence.

Autoreactive IgG levels and Fc receptor γ subunit upregulation drive mechanical allodynia after nerve constriction or crush injury

B cells contribute to the development of pain after sciatic nerve chronic constriction injury (CCI) via binding of immunoglobulin G (IgG) to Fc gamma receptors (FcγRs) in the lumbar dorsal root ganglia (DRG) and spinal cord. Yet the contribution of B cells to pain after different types of peripheral nerve injury is uncertain. Using male and female mice, we demonstrate a divergent role for B cell-IgG-FcγR signaling underlying mechanical allodynia between CCI, nerve crush (NC), spared nerve injury (SNI), and spinal nerve ligation (SNL). Depletion (monoclonal anti-CD20) or genetic deletion (muMT mice) of B cells prevented development of allodynia following NC and CCI, but not SNI or SNL. In apparent contradiction, circulating levels of autoreactive IgG and circulating immune complexes were increased in all models, though more prominent following NC and CCI. Passive transfer of IgG from SNI donor mice induced allodynia in CCI muMT recipient mice, demonstrating that IgG secreted after SNI is pronociceptive. To investigate why pronociceptive IgG did not contribute to mechanical allodynia after SNI, we evaluated levels of the Fc receptor γ subunit. SNI or SNL did not increase γ subunit levels in the DRG and spinal cord, whereas CCI and NC did, in agreement with B cell-dependent allodynia in these models. Together, the results suggest that traumatic peripheral nerve injury drives secretion of autoreactive IgG from B cells. However, levels of cognate FcγRs are increased following sciatic nerve constriction and crush, but not transection, to differentially regulate pain through the B cell-IgG-FcγR axis.

The Role of Exercise on Glial Cell Activity in Neuropathic Pain Management

Chronic pain is a widespread global health problem with profound socioeconomic implications, affecting millions of people of all ages. Glial cells (GCs) in pain pathways play essential roles in the processing of pain signals. Dysregulation of GC activity contributes to chronic pain states, making them targets for therapeutic interventions. Non-pharmacological approaches, such as exercise, are strongly recommended for effective pain management. This review examines the link between exercise, regular physical activity (PA), and glial cell-mediated pain processing, highlighting its potential as a strategy for managing chronic pain. Exercise not only improves overall health and quality of life but also influences the function of GCs. Recent research highlights the ability of exercise to mitigate neuroinflammatory responses and modulate the activity of GCs by reducing the activation of microglia and astrocytes, as well as modulating the expression biomarkers, thereby attenuating pain hypersensitivity. Here, we summarize new insights into the role of exercise as a non-pharmacological intervention for the relief of chronic pain.

The basolateral amygdala-anterior cingulate cortex circuit contributes to postherpetic neuralgia-anxiety comorbidity

Background: Postherpetic neuralgia (PHN) causes chronic pain and emotional dysfunction, but its underlying mechanisms are unknown. Methods: We first compared the structural and functional magnetic resonance imaging (MRI) of PHN-anxiety patients with healthy controls (HCs). Then, we created a PHN comorbid anxiety-like model by injecting resiniferatoxin (RTX) intraperitoneally and used Fos-CreER::Ai9 mice to validate brain regions with volume differences in MRI. Furthermore, we combined behavioral experiments with electrophysiology, viral tracing, in vivo fiber-photometry, optogenetics, and chemogenetics, to analyze the role of the basolateral amygdala (BLA)-anterior cingulate cortex (ACC) circuit in PHN comorbid anxiety-like mice multi-dimensionally. Results: According to neuroimages, patients with PHN-anxiety comorbidity have decreased amygdala volume and decreased functional connection (FC) of the BLA and ACC. Furthermore, we created a PHN comorbid anxiety-like model by injection of RTX intraperitoneally, and these mice showed dysesthesia and anxiety-like behaviors 3 weeks after RTX injection. Then, we discovered that BLA and ACC were related to PHN comorbid anxiety-like behaviors using Fos-CreER::Ai9 mice. Immunohistochemistry and electrophysiology revealed enhanced activation of BLA glutamatergic (BLAGlu) neurons in PHN comorbid anxiety-like mice. Opto/chemogenetic activating BLAGlu neurons aggravated pain threshold in PHN comorbid anxiety-like mice. Inhibiting BLAGlu alleviates mechanical nociception, thermal hyperalgesia, and anxiety-like behavior. Moreover, the elevated excitability of BLAGlu neurons resulted in increased excitatory inputs to the ACC. Selective activation or inhibition of the BLAGlu-ACC pathway exacerbated or alleviated the pain and anxiety behavior, respectively. Conclusion: Findings in this study will provide new insight for understanding the central pathomechanism underlying PHN-anxiety comorbidity, as well as serve as solid theoretical underpinnings for the management of PHN.

Trends in Mixed Pain Research Over Three Decades (1993-2024): A Bibliometric Analysis

BACKGROUND

The term "mixed pain" is frequently used in clinical practice to describe the coexistence of nociceptive, neuropathic, and nociplastic pain mechanisms. However, its inconsistent use and lack of a formal definition warrant further investigation. This bibliometric analysis aims to explore publication trends, research networks, and key themes in mixed pain literature.

METHODS

A bibliometric analysis was conducted using the Web of Science Core Collection. The search was performed in February 2024, with journal rankings obtained from Journal Citation Reports™ 2022 (Clarivate Analytics). Extracted data included publication trends, citation analysis, co-authorship networks, and keyword mapping.

RESULTS

A total of 229 publications were identified, demonstrating an increasing trend in both publication volume and citations. Most studies were published in high-ranking Q1 journals as research (77%) and review articles (19%). The USA (21%), Italy (15%), and Germany (12%) were the leading contributors, yet global collaboration was weak, with limited co-authorship connections except within the USA. The keyword analysis revealed five major research clusters, with "neuropathic pain," "management," and "quality of life" emerging as central themes.

CONCLUSIONS

Despite the progressive increase in mixed pain articles in highly ranked journals, this bibliometric analysis highlighted the absence of a well-structured collaborative network among authors and a lack of clear connections between keywords. Given the critical clinical implications of mixed pain, further high-quality studies on this topic and enhanced international collaborations are recommended.

A neuropathic pain scale is effective in identifying neuropathic pain

OBJECTIVE

To explore the application value of a Neuropathic Pain Questionnaire (NPQ) in screening for neuropathic pain (NP).

METHODS

Using a prospective study approach, patients with chronic pain treated and hospitalized in Quanzhou First Hospital between September 2020 and December 2023 were chosen as study subjects. Participants were screened using NPQ and then divided into a neuropathic pain group (NP group) and a non-neuropathic pain group (NNP group) based on NPQ's results. The baseline demographic data and disease causes were evaluated using Cronbach's alpha coefficient and Guttman split-half coefficient to assess internal consistency. A receiver operating characteristic (ROC) curve was plotted, and the area under curve (AUC), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were assessed.

RESULTS

A total of of 121 patients were included, with 61 cases in the NP group and 60 cases in NNP group. There were no substantial differences between the NP group and the NNP group in terms of age, gender, education level, payment method of medical treatment, pain duration, average pain duration, or level of pain (all P > 0.05). The NP group had a substantially higher NPQ score (8.67±1.21) than the NNP group (6.31±1.34) (P < 0.05). The primary causes of NP in the NP group were postherpetic neuralgia (26.23%), diabetic neuropathy (21.31%), and central post-stroke pain (18.03%). The NPQ demonstrated strong reliability, with a Cronbach's alpha coefficient of 0.843 and a Guttman split-half coefficient of 0.822. The ROC analysis showed an AUC of 0.907 (95% CI, 0.853-0.961), with a sensitivity of 86.90%, specificity of 78.30%, PPV of 80.30%, and NPV of 85.45%.

CONCLUSION

NPQ is a reliable and effective tool for identifying neuropathic pain. Its high sensitivity and specificity, coupled with strong diagnostic performance, suggest that it can be used as a screening tool for neuropathic pain.

Chronic postsurgical pain in the ICD-11: implications for anaesthesiology and pain medicine

Chronic postsurgical pain (CPSP) is associated with reduced health-related quality of life and disability. In some patients, it can result in long-term opioid use even after minor surgery. Epidemiological studies have reported highly varying rates of CPSP, largely because researchers have used different definitions with self-defined cut-offs for pain scores. With the introduction of the 11th revision of the World Health Organisation International Classification of Diseases and Related Health Problems (ICD-11), chronic pain is now recognised as an entity of its own, its biopsychosocial nature is emphasised, and its definition is standardised. Compared with the ICD-11 definition, the prevalence of CPSP might have been overestimated in previous studies. The ICD-11 provides a multifactorial assessment of pain severity, referring to pain intensity, pain-related interference, and pain-related distress, which cover the biopsychosocial aspects of chronic pain. These three scores can be added as extension codes to any pain diagnosis. Harmonisation of the CPSP criteria within the different coding levels of the ICD-11 might improve discrimination of CPSP from other chronic pain conditions not induced by surgery. Although neuropathic CPSP increases pain severity and requires alternative therapeutic approaches to nociceptive pain, a specific code to differentiate between neuropathic and non-neuropathic CPSP is not available. For clinical practice and research, the evidence-based ICD-11 definition, which provides clear-cut diagnostic criteria, should generally be used instead of pain scores alone. This will improve the comparability of data, form the basis for future diagnostic and therapeutic approaches, and facilitate communication.

Local Structural Indices Changes During Different Periods of Postherpetic Neuralgia: A Graphical Study in Structural Covariance Networks

Purpose

In this study, we aim to explore the changes in network graph theory indices of structural covariance networks (SCNs) in PHN patients with different disease durations.

Patients and Methods

High-resolution T1 magnetic resonance images were collected from 109 subjects. We constructed SCNs based on cortical thickness data and analyzed the changes in global and regional network measures of PHN patients and herpes zoster (HZ) patients, and get hubs of each group.

Results

(1) PHN patients with a disease duration >6 months had reduced global efficiency (P=0.035) and increased characteristic shortest path length (P=0.028). (2) Nodal efficiency of the right pars opercularis was greater in both HZ and PHN patients with a disease duration of 1 to 3 months (P<0.001); in PHN patients with a disease duration > 6 months, the nodal degree of the left pars triangularis and nodal efficiency of the right middle temporal gyrus were greater (P<0.001). (3) The right supramarginal gyrus was the common hub of healthy controls (HCs) and HZ patients, the right pars opercularis was the common hub of HZ patients and PHN patients with a disease duration of 1 to 3 months, and the bilateral superior frontal gyrus was the common hub of HZ patients and PHN patients with a disease duration >6 months.

Conclusion

There have changes in SCN indices in PHN patients with different disease durations. PHN patients with a disease duration >6 months had increased SCN integration and diminished information transfer capability between nodes, which complemented the topological properties of previous PHN networks. Eglobal and Lp can be considered as potential imaging markers for future clinical restaging of PHN.

The "brain-gut" mechanism of postherpetic neuralgia: a mini-review

Postherpetic neuralgia (PHN), a representative type of neuropathic pain, has attracted much research on its diagnosis and therapy at the molecular level. Interestingly, this study based on the brain-gut axis provided a novel point of view to interpret the mechanism of PHN. Past neuroanatomical and neuroimaging studies of pain suggest that the prefrontal cortex, anterior cingulate cortex, amygdala, and other regions of the brain may play crucial roles in the descending inhibition of PHN. Dominant bacterial species in patients with PHN, such as Lactobacillus, generate short-chain fatty acids, including butyrate. Evidence indicates that disturbance of some metabolites (such as butyrate) is closely related to the development of hyperalgesia. In addition, tryptophan and 5-HT in the intestinal tract act as neurotransmitters that regulate the descending transmission of neuropathic pain signals. Concurrently, the enteric nervous system establishes close connections with the central nervous system through the vagus nerve and other pathways. This review aims to investigate and elucidate the molecular mechanisms associated with PHN, focusing on the interplay among PHN, the gut microbiota, and relevant metabolites while scrutinizing its pathogenesis.

Pathways to a diagnosis of trigeminal neuralgia: a qualitative study of patients' experiences

BACKGROUND

Trigeminal Neuralgia (TN) is a rare disorder which causes episodes of intense facial pain and has been described as the 'suicide disease'. Hence, prompt diagnosis and timely initiation of treatment is vital. However, delays to diagnosis and high rates of misdiagnosis are common, particularly within primary care. To date, most research has focused upon treatment options rather than improving diagnostic experiences. This study sought to explore patients' experiences of the events leading up to their TN diagnosis and their views about the care and support they received when they were diagnosed to provide recommendations for improving the TN diagnostic pathway.

METHODS

This was a qualitative, exploratory study using in-depth interviews. Interviews were conducted with (n = 25) UK-based people with TN recruited via online forums. Data were analysed thematically.

RESULTS

Following the onset of their TN pain, most participants described an arduous and uncertain journey to diagnosis, with many encountering significant delays, misdiagnoses and receiving inappropriate referrals and treatment. As a consequence, participants reported experiencing profound distress, anxiety, depression and, in extreme cases, suicidal ideation; some also described drug and alcohol misuse during this time. Most participants conveyed relief upon finally receiving a diagnosis. However, this was often by eclipsed by what they saw as poor and insensitive communication and inadequate information provisioning.

CONCLUSIONS

The present study highlights the importance of developing bespoke training for primary care and other professionals to facilitate timely recognition of TN symptomatology and ensure that they deliver a TN diagnosis in clear, sensitive and empathetic ways.

Histone deacetylases: the critical enzymes for microglial activation involved in neuropathic pain

Neuropathic pain is a common health problem in clinical practice that can be caused by many different factors, including infection, ischemia, trauma, diabetes mellitus, nerve compression, autoimmune disorders, cancer, trigeminal neuralgia, and abuse of certain drugs. This type of pain can persistently affect patients for a long time, even after the rehabilitation of their damaged tissues. Researchers have identified the crucial role of microglial activation in the pathogenesis of neuropathic pain. Furthermore, emerging evidence has shown that the expression and/or activities of different histone deacetylases (HDACs) can modulate microglial function and neuropathic pain. In this review, we will summarize and discuss the functions and mechanisms of HDACs in microglial activation and neuropathic pain development. Additionally, we will also list the emerging HDAC inhibitors or activators that may contribute to therapeutic advancement in alleviating neuropathic pain.

Neuropathic pain management: a focused review of current treatments and novel data from main ongoing clinical trials

INTRODUCTION

Neuropathic pain (NP) remains a significant challenge in clinical practice, requiring a sophisticated pharmacotherapeutic strategy for effective symptom management. This review provides a comprehensive analysis of the current pharmacological treatments for NP, focusing on their efficacy, mechanism of action, and therapeutic potential. Additionally, it evaluates ongoing clinical trials investigating novel drugs and therapeutic approaches, highlighting emerging trends and future directions in NP management.

AREAS COVERED

This review examines first- to third-line therapeutic modalities for NP, critically analyzing their efficacy, safety profiles, and clinical applications. It also includes an overview of ongoing clinical trials exploring innovative pharmacological therapies. A thorough literature review was conducted using the MEDLINE database without temporal limitations, offering a detailed assessment of established and emerging treatments.

EXPERT OPINION

While current pharmacological options offer significant symptom relief, their overall effectiveness in managing NP remains limited, highlighting the need for further therapeutic advancements. Staying informed about emerging therapies and clinical trials is vital to enhancing patient care and quality of life. The future of NP management lies in optimizing individualized treatment strategies, refining therapeutic approaches, and fostering interdisciplinary collaboration. Close monitoring of outcomes and continued research are essential for advancing understanding and improving the precision of NP therapies.

Effect of pain neuroscience education+ (PNE+) in people with different mechanisms of chronic pain: A systematic review and meta-analysis

BACKGROUND

Chronic pain poses a multifaceted and prevalent challenge that significantly affects an individual's quality of life. Sensory mechanisms, behavioural components (kinesiophobia and catastrophising), and social factors can influence pain perception in both younger and older populations. Moreover, the mechanisms underlying these altered pain phenotypes require further investigation in order to plan appropriate treatment. While Pain Neuroscience Education (PNE) has proven effective in managing chronic pain and previous research has been conducted on PNE physiotherapeutic techniques, there remains insufficient evidence on the efficacy of these adjunctive treatments.

OBJECTIVE

The objective of the present systematic review and meta-analysis was to evaluate the evidence for the efficacy of PNE + PT (PNE+) on pain as a primary outcome and 12 other psychosocial variables as secondary outcomes in patients with different pain mechanisms, and whether PNE+ could be applied to painful diabetic neuropathy.

METHODS

A thorough literature search was conducted in the database Scopus, MEDLINE/PubMed, ScienceDirect, CINAHL, and Web of Science, using keywords like "Pain Neuroscience Education", and "Chronic Pain" from 2010 to 2024 based on inclusion and exclusion criteria. Twenty of the 2558 studies that underwent screening qualified for a meta-analysis and 24 of them for a systematic review. Cochrane Risk of Bias 2 was used to assess the quality of the studies. Forest plots were generated using the Revman 5.3 software.

RESULTS

Studies that predominantly addressed central sensitization and neuropathic pain demonstrated moderate-to good-quality evidence. The review findings indicate that PNE+ is effective in reducing experienced pain intensity and experienced pain interference on the Visual Analogue Scale (VAS: SMD -0.70, 95% CI -1.26 to -0.14), Numerical Pain Rating Scale (NPRS SMD -1.71, 95% CI -2.34 to -1.08), reduced kinesiophobia (Tampa scale of Kinesiophobia: SMD -5.29, 95% CI -7.33 to -3.25), and catastrophizing (pain catastrophizing scale: -3.82, 95% CI -6.44 to -1.21).

CONCLUSION

PNE + has been found to be an effective intervention for reducing perceived pain experience, pain interference and other psychosocial variables in the management of chronic pain with different pain mechanisms. Most studies have focused on central sensitization, urging future research to explore PNE+ efficacy in neuropathic pain, such as painful diabetic neuropathy.

PROSPERO REGISTRATION NUMBER

CRD42023451101.

How does chronic psychosocial distress induce pain? Focus on neuroinflammation and neuroplasticity changes

Chronic primary pain including fibromyalgia for the musculoskeletal system persists for more than 3 months. Its etiological factors and the pathophysiological mechanisms are not known, and therefore, there is no satisfactory therapy, it is an unmet medical need condition. The only etiological and aggravating factor is chronic psychosocial distress, which is known to cause neuroimmune and endocrine changes both in the periphery and the central nervous system. In this short review, we introduce our research perspective by summarizing the recent literature on the interactions between chronic pain, stress, and commonly co-morbid mood disorders. Immune activation, autoimmunity, neuro-immune-vascular crosstalks and neuroinflammation play roles in the pathophysiology of these conditions. Data on stress-induced neuroplasticity changes at cellular and molecular levels were also collected in relation to chronic primary pain both from clinical studies and animal experiments of translational relevance. Understanding these mechanisms could help to identify novel therapeutic targets for chronic primary pain including fibromyalgia.

A patient and public involvement study to explore patient perspectives on the efficacy of treatments for pain and numbness derived from ossification of posterior longitudinal ligament of the spine

BACKGROUND

Chronic pain and numbness are common complaints in patients with ossification of the posterior longitudinal ligament of the spine (OPLL). However, it is unclear whether the current treatments are effective in patients with OPLL in terms of improving pain and numbness.

METHODS

A cross-sectional survey of patients with OPLL was conducted to determine patient satisfaction with surgery and drug therapy for pain and numbness, and its association with health-related quality of life. The survey was conducted by a patient association and its members, and anonymized data were analyzed by physicians. Comparisons between groups were made using T-tests or Kruskal-Wallis and Steel-Dwass tests, chi-square tests, and Fisher's exact tests.

RESULTS

Data from 121 patients with OPLL (age 69 ± 11 years, 69 males; 43 females; and 7 unknown) who completed a mailed questionnaire were analyzed. Of the 93 patients with a history of surgery for OPLL, 24% and 18% reported much improvement in pain and numbness, respectively. After surgery, 42% and 48% reported some improvement, and 34% and 34% reported no improvement, respectively. Patients whose numbness did not improve with surgery had a significantly poorer health-related quality of life than those who did. Of the 78 patients who received medication, only 2% reported "much improvement," 64% reported "some improvement," and 31% reported "no improvement at all." Compared to patients with OPLL only in the cervical spine, those with diffuse-type OPLL showed poorer improvement in numbness after surgery and poorer quality of life.

CONCLUSIONS

The majority of patients with OPLL belonging to the association were unsatisfied with surgery and pharmacotherapy in terms of pain and numbness improvement, indicating that there is an unmet medical need for more effective treatment for chronic pain and numbness in patients with OPLL.

LRP1-mediated p-tau propagation contributes to cognitive impairment after chronic neuropathic pain in rats

Trigeminal neuralgia (TN) is a prevalent chronic neuropathic pain syndrome characterized by severe pain, often accompanied by cognitive dysfunction and cerebral degeneration. However, its mechanisms remain poorly understood. Hyperphosphorylation of tau protein (p-tau) is often seen in neurodegenerative disorders such as Alzheimer's disease (AD). LRP1 expression on brain neurons and microglial cells is believed to facilitate the propagation of p-tau. We established a TN rat model via infraorbital nerve chronic constrictive injury (ION-CCI). Once the model was established, we investigated the association between p-tau and cognitive impairment in TN rats by evaluating behavioral and degenerative markers. During the initial phase, we noted an increase in p-tau level in the prefrontal cortex and hippocampal tissues of TN rats. The accompanied impaired learning and memory abilities suggested cognitive dysfunction. Blocking p-tau synthesis by orally administering a protein phosphatase and by injecting adenoviral vectors targeting LRP1 into the lateral ventricle of rats ameliorated cognitive impairment. This suggests that cognitive decline in TN rats is linked to elevated p-tau levels. Our findings show that LRP1-mediated p-tau propagation may drive cognitive impairment associated with neuropathic pain in TN rats.

Implications of nociceptor receptors and immune modulation: emerging therapeutic targets for autoimmune diseases

Chronic painful autoimmune disorders such as multiple sclerosis (MS), inflammatory bowel disease (IBD), and rheumatoid arthritis (RA) induce significant discomfort. They are defined by persistent inflammation and immune-mediated tissue injury. The activation and sensitisation of nociceptors, mutated in various disorders, are fundamental components contributing to the pain experienced in these conditions. Recent discoveries indicate that immunological mediators and nociceptive receptors interact functionally within peripheral and central sensitisation pathways, amplifying chronic pain. This research examines the involvement of nociceptors in rheumatoid arthritis, multiple sclerosis, and inflammatory bowel disease. It explores how immune cells and pro-inflammatory cytokines induce, sensitise and regulate various nociceptive receptors (P2X, TRPA1 and TRPV1). Finally, we address possible future directions with respect to the treatment of long-lasting effects on immunity, and what new drug targets could be pursued as well, in order to counteract such either neuro-immune interactions in conditions involving the immunological system. By studying nociceptive mechanisms across autoimmune illnesses, we want to identify shared pathways and activation of nociceptors specific to individual diseases. This will shed insight on potential therapies for managing pain associated with autoimmune diseases.

Identifying neural circuitry abnormalities in neuropathic pain with transcranial magnetic stimulation and electroencephalogram co-registration

Non-invasive brain stimulation (NIBS) technology such as transcranial magnetic stimulation (TMS) represents a promising treatment for neuropathic pain. However, neural circuitries underlying analgesia remain to be established, which is largely limiting treatment responses. Using TMS and electroencephalogram co-registration (TMS-EEG), this study quantified the circuitry abnormalities in neuropathic pain and their associations with pain symptoms. A group of 21 neuropathic pain individuals and 21 healthy controls were assessed with TMS-EEG delivering to the primary motor cortex (M1). With source modelling, local current density and current propagation were analysed with significant current density (SCD) and scattering (SCS) respectively. The SCS and SCD data converged on higher activities in neuropathic pain individuals than healthy controls, within the emotional affective (perigenual anterior cingulate cortex, pgACC), sensory nociceptive (primary somatosensory cortex, S1), and the attentional cognitive (anterior insula, aINS; supracallosal anterior cingulate cortex, scACC) structures of pain. Moreover, current propagation to the pgACC was associated with lower pain-related negative emotions, while current propagation to the aINS with higher pain-related negative emotions. Using concurrent TMS-EEG, our data identified abnormal pain circuitries that could be utilised to improve treatment efficacy with brain stimulation technologies.

Cognitive Decline in Patients With Trigeminal Neuralgia: A Resting-State fMRI Study

OBJECTIVE

This study utilized functional magnetic resonance imaging (fMRI) data to investigate cognitive function changes in trigeminal neuralgia (TN) patients and healthy controls (HCs), and to elucidate the potential mechanism.

MATERIALS AND METHODS

The cognitive function of 34 patients with TN and 30 HCs was evaluated. Afterward, we calculated the amplitude of low-frequency fluctuations (ALFFs), regional homogeneity (ReHo), and degree centrality (DC). These metrics were correlated with cognitive performance using the Spearman correlation analysis.

RESULTS

Patients with TN exhibited diminished cognitive performance compared to HCs. Increased mean ALFF (mALFF) levels were detected in the right temporal pole, superior temporal gyrus, and right insula in individuals with TN. These increases were negatively correlated with cognitive function. In contrast, decreased mALFF values were observed in the right lingual gyrus, bilateral calcarine, and left middle occipital gyrus, which were associated with improved cognitive function. Increased DC values were found in various areas, such as the right temporal pole, superior temporal gyrus, right opercular inferior frontal gyrus, bilateral medial superior frontal gyrus, left supplementary motor area, left anterior cingulum, and right middle cingulum in individuals with TN. These values negatively correlated with cognitive performance.

CONCLUSION

TN patients exhibited impairments in multiple cognitive areas, such as attention, memory, executive function, visual perception and executive ability, information processing speed, and motor speed. The metrics ALFF and DC exhibited alterations in TN patients, suggesting that cognitive impairments may be linked to decreased functional activity in specific brain regions. Concurrently, certain cerebral regions may exhibit increased functional activity as a compensatory response to cognitive deficits. These findings hold significant theoretical value and clinical application potential, providing novel methodologies and perspectives for early diagnosis, personalized treatment, and efficacy evaluation. Such advancements are poised to enhance the overall treatment outcomes and quality of life for TN patients.

Noradrenergic Locus Coeruleus-CA3 Activation Alleviates Neuropathic Pain and Anxiety- and Depression-Like Behaviors by Suppressing Microglial Neuroinflammation in SNI Mice

OBJECTIVE

Neuropathic pain (NP) arises from neuroimmune interactions following nerve injury and is often accompanied by anxiety and depression. The aim of the study is to evaluate the effects of the noradrenergic locus coeruleus (LC), a key regulator of pain and emotional states, projects extensively to the hippocampus.

METHOD

We investigated the effects of chronic NP on LC integrity and its projections to the hippocampal CA3 region in spared nerve injury (SNI) mice with behavioral tests, immunohistochemistry, neurochemical analyses, and Gq-DREADD.

RESULTS

Chronic NP induced LC neuronal loss, reduced hippocampal norepinephrine (NE) release, and triggered microglial activation and neuroinflammation in CA3. Selective activation of LC-CA3 noradrenergic neurons using Gq-DREADD chemogenetics alleviated NP and comorbid anxiety- and depression-like behaviors. This intervention suppressed microglial activation, decreased proinflammatory cytokines (TNF-α and IL-1β), and restored NE levels in CA3.

CONCLUSION

Our findings highlighted the therapeutic potential of targeting LC-CA3 projections to mitigate chronic NP and its neuropsychiatric comorbidities via modulation of hippocampal neuroinflammation.

Signs of hyperpathia in chronic peripheral neuropathic pain

BACKGROUND

Neuropathic pain is pain due to a disease or lesion of the somatosensory system, and can be either spontaneous, evoked or both. Hyperpathia is a type of evoked pain defined by IASP as 'a painful syndrome characterized by an abnormally painful reaction to a stimulus, especially a repetitive stimulus, as well as an increased threshold'. The literature is sparse, and definitions are unclear and inconsistent.

METHODS

The aim of this study was to examine for the presence of mechanical hyperpathia in a heterogeneous group of patients with peripheral neuropathic pain and correlate signs of hyperpathia with other sensory signs. Patients were examined with graded pinprick stimuli to obtain a stimulus-response curve and repetitive pinprick stimuli to assess increase in pain over time and aftersensations. Then, patients were grouped based on the likelihood of having mechanical hyperpathia with either a steep stimulus-response curve or a steep curve on the repetitive pinprick test and results were correlated to mechanical detection and pain thresholds and other outcomes from a full quantitative sensory testing.

RESULTS

We included 124 patients with documented peripheral neuropathic pain. Patients with a steep stimulus-response curve did not overlap with patients with a steep curve on the repetitive pinprick test and both groups more often had decreased rather than increased detection and pain thresholds.

CONCLUSIONS

Our study questions the concept of hyperpathia and suggests that more studies are needed to identify which symptoms and signs group together and might form a syndrome.

SIGNIFICANCE STATEMENT

Hyperpathia is a syndrome of evoked pain. It is poorly defined and little is known about its clinical presentation. Since it is part of pain symptomatology it is important to have a clear definition and understand the pathophysiology behind. This study explored signs of hyperpathia in a heterogeneous group of patients with peripheral neuropathic pain. We used stimulus-response function and repetitive pinprick stimulation to group patients based on the IASP definition. More studies are needed to understand how symptoms and signs coincide.

A discrete choice experiment: Understanding patient preferences for managing chronic non-cancer pain

BACKGROUND

The management of chronic non-cancer pain (CNCP) is complex. Concerns about adverse effects associated with opioid pain medications and a lack of funding for holistic programs present challenges for decision-making among clinicians and patients. Discrete choice experiments (DCE) are one way of assessing and valuing patient treatment preferences.

METHOD

DCE attributes and levels were generated through qualitative research and included number of medicines, side effects from medicines, pain interference, care management, risk of addiction, activity goals, preferred source of information on pain management and willingness to pay. The survey was administered to participants with CNCP recruited through an existing cohort study (n = 442) and a sample of people living with CNCP recruited through Australia's leading pain advocacy body (Painaustralia) (n = 256).

RESULTS

The median age of participants was 58 years (SD 12.0), the majority were female. The analysis revealed two latent demographic classes: a younger group with higher levels of private health insurance and an older group with lower levels of private health insurance coverage. There were notable differences in preference. The younger cohort exhibited a greater willingness-to-pay to reduce pain interference, whereas the older group prioritized GP management, preferred more medicines and expressed fewer addiction concerns.

CONCLUSION

Patients' treatment preferences diverged based on age and insurance status, underscoring the importance of understanding patient perspectives in treatment communication and care coordination. These findings provide insight into patient decision-making, which is important for promoting access to quality healthcare and engagement with evidence-based treatment of CNCP.

SIGNIFICANCE STATEMENT

A discrete choice experiment identified two groups: younger, with more private insurance, and older, with less private health insurance, each with unique pain management preferences. Clinicians should be aware that age and private health insurance may have an impact on a patient's preferences for CNCP management.

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.

Barriers and new opportunities in developing effective therapies for diabetic neuropathy: International expert consensus recommendations

BACKGROUND

Diabetic neuropathy (DN) affects up to half of individuals with type 1 and type 2 diabetes. Despite evidence that improving metabolic and cardiovascular health can slow its progression, DN remains a significant clinical challenge due to the lack of disease-modifying therapies and effective pain management strategies. This consensus aimed to identify gaps and recommend strategies to address these challenges.

METHOD

A workshop, initiated by Steno Diabetes Centre Copenhagen and the Danish Diabetes and Endocrinology Academy, conducted a gap analysis based on insights from clinical studies, observational cohorts, and clinical practice. Online invitations targeted experienced clinicians, researchers, and drug developers committed to improving DN treatment through innovative clinical trials. Thirty-five participants from six countries reached consensus via a Delphi process on key steps to advance DN therapy.

RESULT

Four critical barriers and needs were addressed: (1) Translating bench research to clinical practice, (2) Enhancing clinical trial design, (3) Improving outcome measures, and (4) Identifying effective treatments for painful DN.

CONCLUSION

Successful interventional trials require robust outcome measures to capture clinically meaningful changes in DN phenotypes, providing the basis for developing effective, disease-modifying treatments.

Trigeminal Neuralgia Treatment via Piezosurgical Enlargement of the Mental Foramen

Background: This article and the novel surgical approach described here were inspired by the ideas and observations of the late professors T. Pawela and J. Wnukiewicz. The authors present the medical history and unique surgical treatment of four patients with trigeminal neuralgia, who, despite pharmacological treatment and numerous specialists being involved in the treatment process, continued suffering. Our belief is that the direct cause of the symptoms is a narrow mental foramen, which compresses the mental nerve. It can be easily verified by local anesthesia administration to verify the trigger point, and by analyzing CBCT scans with a special emphasis on the diameter of both mental foramina. Methods: Surgical decompression by narrow mental foramen enlargement was conducted with a piezosurgical device. In this procedure, a rectangle of cortical bone is gently and precisely cut around the mental foramen and then into smaller pieces. This technique enables its easy and safe removal. Then, the mental nerve is left loose, uncompressed. Results: All four patients reported immediate recovery, their pain attacks stopped, and their quality of life improved significantly. One patient reported temporal hypoesthesia that lasted 5 months post-op. About 2 years post-op, another patient reported rare recurrences of pain, although much less severe than before surgery. Conclusions: This type of treatment may be considered when trigeminal neuralgia cannot be classified as classic or as secondary and is unresponsive to pharmacological treatment. A piezosurgical device seems to be the safest option in terms of potential damage to the nerve. Further research should include a larger sample of patients and focus on analyzing the mental foramina diameter of patients with idiopathic trigeminal neuralgia.

Analgesic effect of microneedle with 3-acetylaconitine for neuropathic pain

Neuropathic pain is a worldwide problem that causes physical and psychological pain to many patients. 3-acetylaconitine (AAC) is a kind of non-narcotic analgesic with long-lasting action, non-tolerant and non-addiction. However, it has some cardiac toxicity and can easily cause toxic organ damage. To solve these problems, dissolvable microneedle (MN) patches were prepared and delivered subcutaneously through the skin barrier. The results showed that the solid dispersion made with AAC and polyvinyl pyrrolidone (PVP) effectively changed the solubility of AAC and improved its bioavailability. The MN shape was conical and the bending forces of AAC/PVP-MN were all approximately 1.2 N/needle, which was enough to penetrate the stratum corneum of the skin. Through the use of the neuropathic pain model (spared nerve injury) test, it was found that the soluble MN mediated AAC hypodermic delivery provided effective analgesic activity. Compared with the model group, AAC/PVP-MN could increase mechanical pain threshold and hind legs load-bearing capacity, reduce the inflammation in the body, and have certain protective effect to spinal cord neurons. This study provided an idea for the clinical treatment of neuropathic pain and also a new approach for the safe use of toxic drugs with a narrow range.

Relationship Between Chronic Pain and Breast Cancer: Insight From Genetic Correlation Analyses and 2-Sample Mendelian Randomization

OBJECTIVE

To evaluate potential genetic causal relationships between chronic pain subtypes like migraine and multi-site chronic pain (MCP) and their impact on breast cancer occurrence and survival rates.

BACKGROUND

The association between chronic pain and breast cancer was reported before, yet the causal nature between them remained uncertain.

METHODS

Data on chronic pain and breast cancer were sourced from publicly available European genome-wide association study (GWAS) datasets. Genetic association between chronic pain and breast cancer phenotypes was assessed using linkage disequilibrium genetic correlation (LDSC). Colocalization analysis further identified potential shared causal variation. Based on Inverse variance weighted method, 2-sample Mendelian Randomization (MR) was conducted to investigate causal associations between migraine, MCP, and breast cancer or breast cancer survival. Sensitive analysis was conducted to ensure the absence of heterogeneity and horizontal pleiotropy.

RESULTS

LDSC demonstrated significant genetic correlations between migraine and both estrogen receptor-negative (ER-) and overall breast cancer, while also revealing a notable genetic association between MCP and ER- and ER+ breast cancer, as well as overall breast cancer. Through colocalization analysis, potential involvement of rs2183271, located in MLLT10 gene, in regulating MCP and ER+ breast cancer was identified. MR analysis revealed the association between migraine and elevated risk of ER- breast cancer (IVW, P = 4.95 × 10-3). Cochran's Q test ensured the absence of heterogeneity and MR-PRESSO global test, MR-Egger intercept test ensured the absence of horizontal pleiotropy.

CONCLUSION

Our results provided new insights into the role of migraine and MCP in breast cancer, paving the way for targeted preventive strategies and future investigations.

CD28 Superfamily Costimulatory Molecules in Chronic Pain: Focus on Immunomodulation

Chronic pain has substantial effects on patients' quality of life and psychological well-being. It does not respond satisfactorily to available medicinal therapeutics because its mechanism remains unclear. Recent studies have shown a strong relationship between chronic pain and immunomodulation. As important members of the immune response, CD28 superfamily costimulatory molecules were demonstrated to have an analgesic effect on chronic pain. Based on research on the role of these molecules in chronic pain, new and highly effective analgesic medicines are anticipated that could be used in combination with some previous analgesic medicines to reduce substance abuse and side effects. This review of the literature will examine the pain-regulating mechanisms of CD28 superfamily costimulatory molecules, focusing on immunomodulation. In addition, this review will discuss the potential and difficulties of developing novel analgesic medicines targeting CD28 superfamily costimulatory molecules.