Neuropathic pain: diagnosis, pathophysiological mechanisms, and treatment. Lancet Neurol. 2010;9:807-819. [PMID: 20650402 DOI: 10.1016/s1474-4422(10)70143-5]

Tapentadol in neuropathic pain cancer patients: a prospective open label study

Many chemotherapy treatments induce peripheral neuropathy (CIPN). These patients often experience neuropathic pain (NP) that reduces the quality of life. The aim of this prospective, open label study was to evaluate the efficacy and tolerability of tapentadol (TP) in patients affected by CIPN. CIPN were consecutively enrolled in a prospective open label study at the Neuro-Oncology Unit of the Regina Elena National Cancer Institute in Rome. During the titration phase, each patient initially received doses of TP 50 mg twice a day. All patients underwent pain intensity (NRS) and DN4. For evaluation of quality of life, patients underwent EORTC QLQ-C30 and EORTC QLQ-CIPN2 QLQ-CIPN20. We enrolled 31 patients, 19 were females with a median age of 60 years. After 3 months of treatment with TP, 22 patients completed the statistical package for social sciences (SPSS). Nineteen patients out of 22 showed a response to treatment (86%). We also observed that TP reduced the NRS and DN4 values from baseline to the last visit in a significant way (p < 0.001, respectively). Seven patients (22.5%) discontinued the TP therapy after the first week of occurrence of side effects. Furthermore, we observed that TP improved also the global health status measured by EORT QLQ-C30. TP is well tolerated and efficacy in the treatment of NP. The important reduction of neuropathic pain, the improvement in NRS and QoL scores after therapy with TP makes it a candidate in the management of patients suffering from neuropathic pain of CIPN also as a first line of therapy.

The Potential Role of Sensory Testing, Skin Biopsy, and Functional Brain Imaging as Biomarkers in Chronic Pain Clinical Trials: IMMPACT Considerations

Valid and reliable biomarkers can play an important role in clinical trials as indicators of biological or pathogenic processes or as a signal of treatment response. Currently, there are no biomarkers for pain qualified by the U.S. Food and Drug Administration or the European Medicines Agency for use in clinical trials. This article summarizes an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting in which 3 potential biomarkers were discussed for use in the development of analgesic treatments: 1) sensory testing, 2) skin punch biopsy, and 3) brain imaging. The empirical evidence supporting the use of these tests is described within the context of the 4 categories of biomarkers: 1) diagnostic, 2) prognostic, 3) predictive, and 4) pharmacodynamic. Although sensory testing, skin punch biopsy, and brain imaging are promising tools for pain in clinical trials, additional evidence is needed to further support and standardize these tests for use as biomarkers in pain clinical trials.

PERSPECTIVE

The applicability of sensory testing, skin biopsy, and brain imaging as diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for use in analgesic treatment trials is considered. Evidence in support of their use and outlining problems is presented, as well as a call for further standardization and demonstrations of validity and reliability.

Assessments of sensory plasticity after spinal cord injury across species

Spinal cord injury (SCI) is a multifaceted phenomenon associated with alterations in both motor function and sensory function. A majority of patients with SCI report sensory disturbances, including not only loss of sensation, but in many cases enhanced abnormal sensation, dysesthesia and pain. Development of therapeutics to treat these abnormal sensory changes require common measurement tools that can enable cross-species translation from animal models to human patients. We review the current literature on translational nociception/pain measurement in SCI and discuss areas for further development. Although a number of tools exist for measuring both segmental and affective sensory changes, we conclude that there is a pressing need for better, integrative measurement of nociception/pain outcomes across species to enhance precise therapeutic innovation for sensory dysfunction in SCI.

The Link between Depression and Chronic Pain: Neural Mechanisms in the Brain

Chronic pain, as a stress state, is one of the critical factors for determining depression, and their coexistence tends to further aggravate the severity of both disorders. Unfortunately, their association remains unclear, which creates a bottleneck problem for managing chronic pain-induced depression. In recent years, studies have found considerable overlaps between pain- and depression-induced neuroplasticity changes and neurobiological mechanism changes. Such overlaps are vital to facilitating the occurrence and development of chronic pain and chronic pain-induced depression. In this review, we summarized the role of neuroplasticity in the occurrence and development of the two disorders in question and explored individualized application strategies of analgesic drugs and antidepressants that have different pharmacological effects in the treatment of chronic pain-induced depression. Therefore, this review may provide new insights into the understanding of association between chronic pain and depression.

Multivariate pattern analysis utilizing structural or functional MRI-In individuals with musculoskeletal pain and healthy controls: A systematic review

OBJECTIVE

The purpose of this systematic review is to systematically review the evidence relating to findings generated by multivariate pattern analysis (MVPA) following structural or functional magnetic resonance imaging (fMRI) to determine if this analysis is able to: a) Discriminate between individuals with musculoskeletal pain and healthy controls, b) Predict pain perception in healthy individuals stimulated with a noxious stimulus compared to those stimulated with a non-noxious stimulus.

METHODS

MEDLINE, CINAHL, Embase, PEDro, Google Scholar, Cochrane library and Web of Science were systematically screened for relevant literature using different combinations of keywords regarding structural and functional MRI analysed with MVPA, both in individuals with musculoskeletal pain and healthy controls. Reference lists of included articles were hand-searched for additional literature. Eligible articles were assessed on risk of bias and reviewed by two independent researchers.

RESULTS

The search query returned 18 articles meeting the inclusion criteria. Methodological quality varied from poor to good. Seven studies investigated the ability of machine-learning algorithms to differentiate patient groups from healthy control participants. Overall, the review demonstrated that MVPA can discriminate between individuals with MSK pain and healthy controls with an overall accuracy ranging from 53% to 94%. Twelve studies utilized healthy control participants (using them as their own controls), during experimental pain paradigms aimed to investigate the ability of machine-learning to differentiate individuals stimulated with noxious stimuli from those stimulated with non-noxious stimuli, with 'pain' detection rates ranging from 60% to 94%. However, significant heterogeneity in patient conditions, study methodology and brain imaging techniques resulted in various findings that make study comparisons and formal conclusions challenging.

CONCLUSION

There is preliminary and emerging evidence that MVPA analyses of structural or functional MRI are able to discriminate between patients and healthy controls, and also discriminate between noxious and non-noxious stimulation. No prospective studies were found in this review to allow determination of the prognostic or diagnostic capabilities or treatment responsiveness of these analyses. Future studies would also benefit from combining various behavioural, genotype and phenotype data into analyses to assist with development of sensitive and specific signatures that could guide future individualized patient treatment options and evaluate how treatments exert their effects.

AMPK activation by peri-sciatic nerve administration of ozone attenuates CCI-induced neuropathic pain in rats

Neuropathic pain is a debilitating clinical condition with few efficacious treatments, warranting development of novel therapeutics. Ozone is widely used as an alternative therapy for many different pain conditions, with exact mechanisms still elusive. In this study, we found that a single peri-sciatic nerve injection of ozone decreased mechanical allodynia and thermal hyperalgesia, and normalized the phosphorylation of protein kinase C γ, N-methyl-D-aspartate receptor, and extracellular signal-regulated kinase in a chronic constriction injury (CCI) model in rat sciatic nerve. Meanwhile, ozone significantly suppressed CCI-induced activation of spinal microglia. More importantly, the anti-nociceptive effect of ozone depended on the activation of 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK), which was proved by the fact that the phosphorylated AMPK level increased during the ozone therapy and AMPK antagonist abolished the effect of ozone in vivo and in vitro. In addition, direct injection of AMPK agonist could replicate the anti-nociceptive effect of ozone in CCI rats. In conclusion, our observations indicate that peri-sciatic nerve injection of ozone activates AMPK to attenuate CCI-induced neuropathic pain.

Psychometric properties of the painDETECT questionnaire in rheumatoid arthritis, psoriatic arthritis and spondyloarthritis: Rasch analysis and test-retest reliability

Background

Pain is inherent in rheumatoid arthritis (RA), psoriatic arthritis (PsA) and spondyloarthritis (SpA) and traditionally considered to be of nociceptive origin. Emerging data suggest a potential role of augmented central pain mechanisms in subsets of patients, thus, valid instruments that can identify underlying pain mechanisms are needed. The painDETECT questionnaire (PDQ) was originally designed to differentiate between pain phenotypes. The objectives were to evaluate the psychometric properties of the PDQ in patients with inflammatory arthritis by applying Rasch analysis and to explore the reliability of pain classification by test-retest.

Methods

For the Rasch analysis 900 questionnaires from patients with RA, PsA and SpA (300 per diagnosis) were extracted from ‘the DANBIO painDETECT study’. The analysis was directed at the seven items assessing somatosensory symptoms and included: 1) the performance of the six-category Likert scale; 2) whether a unidimensional construct was defined; 3) the reliability and precision of estimates. Another group of 30 patients diagnosed with RA, PsA or SpA participated in a test-retest study. Intraclass Correlation Coefficients (ICC) and classification consistency were calculated.

Results

The Rasch analysis revealed: (1) Acceptable psychometric rating scale properties; the frequency distribution peaked in category 0 except for item 5, threshold calibration >10 observations per category, no disorder in the category measures for all items, scale category outfit Mnsq <2.0, small distances (<1.4 logits) between thresholds for category 1, 2 and 3 for all items. (2) The principal component analysis supported unidimensionality; the standardized residuals showed that 53.7% of total variance was explained by the measure and the magnitude of first contrast had an eigenvalue of 1.5, no misfitting items, clinical insignificant different item hierarchies across diagnoses (DIF < 0.5 logits). (3) A targeted item-person map, person and item separation indices of 1.88(reliability = 0.78), and 13.04 (reliability = 0.99). The test-retest revealed: ICC: RA 0.86(0.56–0.96), PsA 0.96(0.74–0.99), SpA 0.93(0.76–98), overall 0.94(0.84–0.98). Classification consistency was: RA 70%, PsA 80%, SpA 90%, overall 80%.

Conclusion

The results support that the PDQ can be used as a classification instrument and assist identification of underlying pain-mechanisms in patients suffering from inflammatory arthritis.

Serotonin-norepinephrine reuptake inhibitors and the influence of binding affinity (Ki) on analgesia

WHAT IS KNOWN AND OBJECTIVE

Serotonin-norepinephrine reuptake inhibitors (SNRIs) are commonly used for various psychiatric conditions and neuropathic pain syndromes. SNRIs inhibit the reuptake of serotonin (5-HT) and norepinephrine (NE); however, NE reuptake inhibition is thought to be the primary mediator for their analgesic effect.

COMMENT

Key differences in pharmacodynamics and receptor affinities exist between SNRIs. The selectivity for each monoamine differs among SNRIs based on the agent's affinity and activity at the monoamine reuptake transporter. We review differences in receptor affinities and monoamine selectivity among SNRIs and the corresponding clinical impact.

WHAT IS NEW AND CONCLUSION

The varying selectivity for 5-HT and NE among the SNRIs may help explain the therapeutic dosing required for neuropathic pain as well as dose-related adverse effects. It is important to understand the pharmacologic differences among SNRIs, in addition to the data from clinical trials, to guide their safe and effective use.

[Polyneuropathy in the elderly]

The peripheral nervous system is subject to changes during the ageing process, e. g. deep tendon reflexes decrease, as does proprioception. Polyneuropathies, on the other hand, need to be distinguished from age-related changes as independent diseases with etiologies similar to those at younger ages. Etiologies includes metabolic disorders, primary inflammatory polyneuropathies, and systemic disorders. Neuropathies associated with diabetes, malignancy, and monoclonal gammopathies appear to be more common in older patients. Using a systematic approach, it is possible to establish a specific diagnosis in the majority of cases. Since polyneuropathies contribute to reduced mobility in the elderly, an assessment of functional skills is mandatory. Polyneuropathy therapy is primarily based on the treatment of underlying conditions and neuropathic pain management. Physiotherapy and rehabilitation target pain relief and maintaining activities of daily living.

Comparison of Ozone and Photo-Biomodulation Therapies on Mental Nerve Injury in Rats

PURPOSE

This study compared photo-biomodulation (PBM) and ozone therapy (OT) for mental nerve injury by counting Schwann cells (SCs) and fasciculated nerve branches and measuring fascicular nerve areas.

MATERIALS AND METHODS

The effects of OT and PBM on mental nerve injury were evaluated. Mental nerves of 27 rats were partly sutured and allocated into 3 groups. Group 1 received no treatment, group 2 received OT, and group 3 received PBM. The number of fascicules beyond nerve branches and the number of SCs before and after nerve injury were evaluated histologically.

RESULTS

A better healing pattern was observed in the treatment groups. The number of SCs was markedly larger in the OT and PBM groups than in the control group.

CONCLUSIONS

Oral and maxillofacial surgeons should be familiar with the differential diagnosis, prevention, and management of neurosensory disturbances. This study provides insights into the management of neurosensory disturbances related to mental nerve injury using OT and PBM. This study clearly suggests that OT and PBM are promising novel methods for the treatment of mental nerve injury.

Transdermal oxycodone patch for the treatment of postherpetic neuralgia: a randomized, double-blind, controlled trial

AIM

To evaluate the efficacy, systemic exposure, safety and tolerability of a transdermal oxycodone patch containing tocopheryl phosphate mixture (TPM) in patients with postherpetic neuralgia (PHN).

PATIENTS & METHODS

The study was a Phase IIa, multicenter, randomized, double-blind, vehicle-controlled crossover study.

RESULTS

While the TPM/oxycodone patch did not significantly improve 'average' Numeric Pain Rating Scale scores versus vehicle patch, patients reporting high levels of paresthesia (n = 9) showed a trend toward improved pain reduction. The TPM/oxycodone patch resulted in a low systemic exposure to oxycodone and was well tolerated.

CONCLUSION

The TPM/oxycodone patch delivered oxycodone to the site of perceived pain in subjects suffering from PHN, but did not provide analgesia for the broad PHN indication.

Prevention of chronic post-surgical pain: the importance of early identification of risk factors

Chronic post-surgical pain (CPSP) is currently an inevitable surgical complication. Despite the advances in surgical techniques and the development of new modalities for pain management, CPSP can affect 15-60% of all surgical patients. The development of chronic pain represents a burden to both the patient and to the community. In order to have a meaningful impact on this debilitating condition it is essential to identify those at risk. Early identification of patients at risk will help to reduce the percentage of patients who go on to develop CPSP. Unfortunately, evidence about any effective actions to reduce this condition is limited. This review will focus on providing context to the challenging problem of CPSP. The possible role of both the surgeon and anesthesiologist in reducing the incidence of this problem will be explored.

Ipsilateral and contralateral sensory changes in healthy subjects after experimentally induced concomitant sensitization and hypoesthesia

BACKGROUND

In unilateral neuropathic pain. e.g. after peripheral nerve injury, both positive and negative sensory signs occur often, accompanied by minor but equally directed contralateral sensory changes. To mimic this feature, we experimentally aimed to induce concomitant c-fibre sensitization and block in healthy subjects and analyzed the bilateral sensory changes by quantitative sensory testing (QST) using the protocol of the German Research Network on Neuropathic Pain.

METHODS

Twenty eight healthy subjects were firstly randomized in 2 groups to receive either topical capsaicin (0.6%, 12 cm², application duration: 15 min.) or a lidocaine/prilocaine patch (25/25 mg, 10 cm², application duration: 60 min.) on the right volar forearm. Secondly, 7-14 days later in the same area either at first capsaicin (for 15 min.) and immediately afterwards local anesthetics (for 60 min.) was applied (Cap/LA), or in inversed order with the same application duration (LA/Cap). Before, after each application and 7-14 days later a QST was performed bilaterally.

STATISTICS

Wilcoxon-test, ANOVA, p < 0.05.

RESULTS

Single application of 0,6% capsaicin induced thermal hypoesthesia, cold hypoalgesia, heat hyperalgesia and tactile allodynia. Lidocaine/prilocaine alone induced thermal and tactile hypoesthesia as well as mechanical and cold hypoalgesia, and a heat hyperalgesia (to a smaller extent). Ipsilaterally both co-applications induced a combination of the above mentioned changes. Significant contralateral sensory changes occurred only after the co-application with concomitant sensitization and hypoesthesia and comprised increased cold (Cap/LA, LA/Cap) and mechanical detection as well as cold pain threshold (LA/Cap).

CONCLUSION

The present experimental model using combined application of capsaicin and LA imitates partly the complex sensory changes observed in patients with unilateral neuropathic pain and might be used as an additional surrogate model. Only the concomitant use both agents in the same area induces both positive and negative sensory signs ipsilaterally as well as parallel contralateral sensory changes (to a lesser extent).

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT01540877 , registered on 23 February 2012.

K+ Channel Modulatory Subunits KChIP and DPP Participate in Kv4-Mediated Mechanical Pain Control

The K⁺ channel pore-forming subunit Kv4.3 is expressed in a subset of nonpeptidergic nociceptors within the dorsal root ganglion (DRG), and knockdown of Kv4.3 selectively induces mechanical hypersensitivity, a major symptom of neuropathic pain. K⁺ channel modulatory subunits KChIP1, KChIP2, and DPP10 are coexpressed in Kv4.3⁺ DRG neurons, but whether they participate in Kv4.3-mediated pain control is unknown. Here, we show the existence of a Kv4.3/KChIP1/KChIP2/DPP10 complex (abbreviated as the Kv4 complex) in the endoplasmic reticulum and cell surface of DRG neurons. After intrathecal injection of a gene-specific antisense oligodeoxynucleotide to knock down the expression of each component in the Kv4 complex, mechanical hypersensitivity develops in the hindlimbs of rats in parallel with a reduction in all components in the lumbar DRGs. Electrophysiological data further indicate that the excitability of nonpeptidergic nociceptors is enhanced. The expression of all Kv4 complex components in DRG neurons is downregulated following spinal nerve ligation (SNL). To rescue Kv4 complex downregulation, cDNA constructs encoding Kv4.3, KChIP1, and DPP10 were transfected into the injured DRGs (defined as DRGs with injured spinal nerves) of living SNL rats. SNL-evoked mechanical hypersensitivity was attenuated, accompanied by a partial recovery of Kv4.3, KChIP1, and DPP10 surface levels in the injured DRGs. By showing an interdependent regulation among components in the Kv4 complex, this study demonstrates that K⁺ channel modulatory subunits KChIP1, KChIP2, and DPP10 participate in Kv4.3-mediated mechanical pain control. Thus, these modulatory subunits could be potential drug targets for neuropathic pain.SIGNIFICANCE STATEMENT Neuropathic pain, a type of moderate to severe chronic pain resulting from nerve injury or disorder, affects 6.9%-10% of the global population. However, less than half of patients report satisfactory pain relief from current treatments. K⁺ channels, which act to reduce nociceptor activity, have been suggested to be novel drug targets for neuropathic pain. This study is the first to show that K⁺ channel modulatory subunits KChIP1, KChIP2, and DPP10 are potential drug targets for neuropathic pain because they form a channel complex with the K⁺ channel pore-forming subunit Kv4.3 in a subset of nociceptors to selectively inhibit mechanical hypersensitivity, a major symptom of neuropathic pain.

Self-Reported Neuropathic Pain Characteristics of Women With Provoked Vulvar Pain: A Preliminary Investigation

BACKGROUND

Provoked vestibulodynia (PVD) is a common chronic genital pain condition affecting approximately 12% of premenopausal women. Although parallels have been drawn between PVD and neuropathic pain (NP), no studies have examined self-reported NP characteristics in PVD.

AIM

To explore pain symptoms that resemble NP reported by those with PVD and compare responses with those with an established NP condition.

METHODS

Women with provoked vulvar pain (PVP; n = 65) completed online questionnaires designed to assess characteristics of NP. Responses were compared with those of women with postherpetic neuralgia (PHN; n = 30).

OUTCOMES

In addition to a range of descriptive questions, participants completed the McGill Pain Questionnaire, the Self-Complete Leeds Assessment of Neuropathic Signs and Symptoms (S-LANSS), the Neuropathic Pain Symptom Inventory (NPSI), and the Pain Quality Assessment Scale (PQAS).

RESULTS

PVP exhibits some neuropathic characteristics, typically evoked pain (as opposed to the more constant pain of PHN) indicative of allodynia and hyperalgesia. Specifically, women with PVP scored, on average, higher than the NP cutoff on the S-LANSS, and there were no significant differences between women with PVP and those with PHN on some NPSI subscales. However, women with PHN reported more NP symptoms on the PQAS, S-LANSS, and other NPSI subscales.

CLINICAL IMPLICATIONS

Validated NP questionnaires could be of particular use for health care professionals who need a more efficient way to assess symptoms of patients with PVP and should be included in future studies investigating the mechanisms and treatment of this pain.

STRENGTHS AND LIMITATIONS

This study takes a unique approach to the examination of PVP by using multiple validated NP measures to compare pain characteristics with those of a group of participants with PHN, an established NP condition. However, it is limited by self-reported data not confirmed with clinical examination, small size of the PHN group, and the severity of the pain experienced in the PVP group.

CONCLUSION

Women with PVP report some symptoms suggestive of NP characteristics, and future research should use NP measures in addition to physical examinations to further investigate the mechanisms that maintain this pain condition. Dargie E, Gilron I, Pukall CF. Self-Reported Neuropathic Pain Characteristics of Women With Provoked Vulvar Pain: A Preliminary Investigation. J Sex Med 2017;14:577-591.

Methylene Blue for the Treatment of Intractable Pain Associated with Oral Mucositis

Oral mucositis is a common and often debilitating complication among cancer patients receiving radiation therapy to the head and neck or chemotherapy agents, or undergoing hematopoietic stem cell transplantation. Pain and decreased oral function associated with oral mucositis may persist long after the conclusion of therapy. Although most patients respond to conservative management, a subset of patients develops intractable pain with severe consequences. For some, the use of total parenteral nutrition with insertion of percutaneous endoscopic gastrostomy feeding tubes is the only alternative. Current recommendations to treat mucositis and its related pain include basic oral care, bland oral rinses, topical anesthetics, and systemic analgesics. We believe that chemical neurolysis of the affected areas with methylene blue used as an oral rinse is a noninvasive, efficient, safe, and cost-effective alternative that can provide prolonged analgesia in patients with intractable pain of oral mucositis. The benefits of this therapy are reflected in its improvement of patients' quality of life by enabling oral feeding and controlling pain. We report a series of 5 consecutive patients with intractable oral mucositis-related pain despite conventional treatment with systemic opiates. All 5 patients responded well to the use of 0.05% methylene blue as mouth rinse, demonstrating sustained analgesia over 3 weeks. The treatment was tolerated well, and overall patient satisfaction was very high. We also observed that methylene blue rinse significantly reduced the total opioid requirement, as demonstrated by reductions in the patients' morphine equivalent daily dose scores after its use. Our case series suggests that 0.5% methylene blue oral rinse therapy is an effective and inexpensive modality that can be used safely to palliate intractable oral pain in patients with mucositis associated with cancer treatment. To our knowledge, this is the first report using this therapy to treat pain from oral mucositis.

A Review on Ubiquitination of Neurotrophin Receptors: Facts and Perspectives

Ubiquitination is a reversible post-translational modification involved in a plethora of different physiological functions. Among the substrates that are ubiquitinated, neurotrophin receptors (TrkA, TrkB, TrkC, and p75^NTR) have been studied recently. TrkA is the most studied receptor in terms of its ubiquitination, and different E3 ubiquitin ligases and deubiquitinases have been implicated in its ubiquitination, whereas not much is known about the other neurotrophin receptors aside from their ubiquitination. Additional studies are needed that focus on the ubiquitination of TrkB, TrkC, and p75^NTR in order to further understand the role of ubiquitination in their physiological and pathological functions. Here we review what is currently known regarding the ubiquitination of neurotrophin receptors and its physiological and pathological relevance.

Symptom profiles in the painDETECT Questionnaire in patients with peripheral neuropathic pain stratified according to sensory loss in quantitative sensory testing

The painDETECT Questionnaire (PDQ) is commonly used as a screening tool to discriminate between neuropathic pain (NP) and nociceptive pain, based on the self-report of symptoms, including pain qualities, numbness, and pain to touch, cold, or heat. However, there are minimal data about whether the PDQ is differentially sensitive to different sensory phenotypes in NP. The aim of the study was to analyze whether the overall PDQ score or its items reflect phenotypes of sensory loss in NP as determined by quantitative sensory testing. An exploratory analysis in the Innovative Medicines Initiative Europain and Neuropain database was performed. Data records of 336 patients identified with NP were grouped into sensory profiles characterized by (1) no loss of sensation, (2) loss of thermal sensation, (3) loss of mechanical sensation, and (4) loss of thermal and mechanical sensation. painDETECT Questionnaire profiles were analyzed in a 2-factor analysis of variance. Patients with loss of thermal sensation (2 and 4) significantly more often reported pain evoked by light touch, and patients with loss of mechanical sensation (3 and 4) significantly more often reported numbness and significantly less often burning sensations and pain evoked by light touch. Although the PDQ was not designed to assess sensory loss, single items reflect thermal and/or mechanical sensory loss at group level, but because of substantial variability, the PDQ does not allow for individual allocation of patients into sensory profiles. It will be useful to develop screening tools according to the current definition of NP.

Nrf2 and NF-κB modulation by Plumbagin attenuates functional, behavioural and biochemical deficits in rat model of neuropathic pain

BACKGROUND

Plumbagin is known to exhibit a broad range of biological activities including anti-cancer, antimicrobial and has been widely used traditionally. Nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) inhibitory and Nuclear factor (erythroid derived-2) like-2 (Nrf2) modulatory activities of Plumbagin have been reported already. In nerve injury model of neuropathy in rats, the role of NF-κB upregulation and declined antioxidant defence has been well recognized. So, we evaluated neuroprotective potential of Plumbagin in chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in male Sprague-Dawley rats.

METHODS

Animals were tested for functional, behavioural and biochemical changes. Various markers associated with oxidative stress and inflammatory changes were assessed in the sciatic nerve and dorsal root ganglion (DRG) of the animals exposed to CCI mediated nerve injury.

RESULTS

CCI induced nerve injury led to long-lasting mechanical hyperalgesia, loss of hind limb function and abnormal pain sensation. Plumbagin treatment (10 and 20mg/kg, po) significantly and dose-dependently reversed mechanical hyperalgesia and other functional deficits. There was a marked increase in NF-κB and reduced Nrf2 levels in sciatic nerve and DRG following nerve injury. Plumbagin strengthened the antioxidant defence by improving Nrf2 levels and checked the neuroinflammation by decreasing NF-κB levels in sciatic nerve and DRG.

CONCLUSIONS

Together, these results suggested that Plumbagin alleviated CCI-induced neuropathic pain via antioxidant and anti-inflammatory mechanisms. Hence, the study suggests that Plumbagin may be useful for the management of trauma-induced neuropathic pain.

Antidepressive and antinociceptive effects of ethanolic extract and fruticuline A from Salvia lachnostachys Benth leaves on rodents

Objectives

This study investigated the antidepressant and antinociceptive effects of ethanolic extract (SLEE) and pure fruticuline A obtained from Salvia lachnostachys leaves on rats and mice.

Methods

In this study, SLEE (100 mg/kg, p.o. route) was evaluated for its effects on spared nerve injury (SNI) in rats. The animals were submitted to mechanical sensitivity, forced swim (FST) and cold sensitivity tests 10 and 15 days after surgery. SLEE (100 mg/kg, p.o.) and fruticuline A (3 mg/kg, p.o.) were also evaluated with respect to nociceptive behavior induced by formalin. In addition, clonidine-induced depressive-like behavior was also analyzed.

Results

The oral administration of SLEE for up to 15 days and the subcutaneous injection of 10 mg/kg of ketamine (positive control) significantly inhibited SNI-induced mechanical hyperalgesia and decreased immobility in the FST. On the 15th day of oral treatment, SLEE prevented the SNI-induced increase in cold sensitivity. In the formalin test, SLEE and fruticuline A significantly reduced the frequency of paw licking during the first and second phases and decreased the formation of edema. In locomotor analysis (open field test without clonidine treatment), SLEE and fruticuline A did not alter the response. SLEE and fruticuline A significantly attenuated clonidine-induced suppression of spontaneous locomotor activity (squares invaded and licking) and emotionality (grooming and freezing) compared with controls, similar to the naive group.

Conclusion

SLEE exhibits antihyperalgesic, antidepressant, and antinociceptive effects, and fruticuline A appears to be at least partly responsible for the effects of SLEE. Together, these results demonstrate the antidepressive effects of SLEE and fruticuline A and indicate that both derivatives obtained from S. lachnostachys act against spontaneous neuropathic pain.

Differential drug effects on spontaneous and evoked pain behavior in a model of trigeminal neuropathic pain

PURPOSE

Baclofen and morphine have shown efficacy against mechanical allodynia after infraorbital nerve chronic constriction injury (IoN-CCI). No drug effects have yet been reported on spontaneous trigeminal neuropathic pain. It has been proposed that the directed face grooming behavior that also develops following IoN-CCI offers a measure of spontaneous trigeminal neuropathic pain.

SUBJECTS AND METHODS

We examined the effects of a continuous 1-week infusion of 30 mg/day carbamazepine (the first-line drug treatment for trigeminal neuralgia), 1.06 mg/day baclofen, 4.18 mg/day clomipramine, and 5 mg/day morphine on spontaneous and mechanically evoked pain behavior (ie, directed face grooming and von Frey testing) in IoN-CCI rats.

RESULTS

Isolated face grooming was significantly reduced in rats receiving carbamazepine and baclofen but not in clomipramine- or morphine-treated rats. All drugs showed significant antiallodynic effects; carbamazepine showed the strongest effects, whereas clomipramine had only minor efficacy.

CONCLUSION

The tested drugs have differential effects in the IoN-CCI model, and different neuropathological mechanisms may underlie the different somatosensory symptoms in this model. A mechanism-based approach may be needed to treat (trigeminal) neuropathic pain. The present data support IoN-CCI as a model of trigeminal neuralgia in which isolated face grooming is used as a measure of spontaneous neuropathic pain.

Down-Regulation of miRNA-128 Contributes to Neuropathic Pain Following Spinal Cord Injury via Activation of P38

Background

Neuropathic pain (NPP) arises from a lesion or dysfunction of the somatosensory nervous system. Recent studies have demonstrated multiple microRNAs (miRNAs) play key roles in NPP development. This study aimed to investigate the effects of miR-128 on microglial cells.

Material/Methods

We established a compressive spinal cord injury (SCI) model and collected the spinal cord segment-derived conditioned medium (CM). We then measured the expression of miR-128 in the murine microglial cell line BV2 treated with CM-SCI or CM obtained from control (CM-NC). Furthermore, lentivirus production of miR-128 and scrambled control were transfected into BV2 cells, which were first treated with CM-SCI or CM-NC. Moreover, the effects of miR-128 on cell viability, M1/M2 microglial gene expression, inflammatory cytokines concentration, and the protein expression of P38 and phosphorylated P38 (P-P38) were investigated.

Results

The expression of miR-128 was downregulated in murine microglial BV2 cells treated with CM-SCI. Overexpression of miR-128 markedly promoted the viability of murine microglial cells. In addition, miR-128 overexpression significantly decreased the expression levels of microglial M1 phenotypic markers CD86 and CD32, and increased the expression levels of M2 phenotypic markers Arg1 and CD206. Furthermore, miR-128 overexpression obviously decreased the concentration of TNF-α, IL-1β, and IL-6. We found that miR-128 overexpression significantly downregulated the expression levels of P38 andP-P38.

Conclusions

Our findings indicate that down-regulation of miR-128 in murine microglial cells may contribute to the development of NPP following SCI via activation of P38. MiR-128 may be a potential intervention target for NPP.

Potential Therapeutic Benefits of Maintaining Mitochondrial Health in Peripheral Neuropathies

Background: Peripheral neuropathies are a group of diseases characterized by malfunctioning of peripheral nervous system. Neuropathic pain, one of the core manifestations of peripheral neuropathy remains as the most severe disabling condition affecting the social and daily routine life of patients suffering from peripheral neuropathy.

Method: The current review is aimed at unfolding the possible role of mitochondrial dysfunction in peripheral nerve damage and to discuss on the probable therapeutic strategies against neuronal mitotoxicity. The article also highlights the therapeutic significance of maintaining a healthy mitochondrial environment in neuronal cells via pharmacological management in context of peripheral neuropathies.

Results: Aberrant cellular signaling coupled with changes in neurotransmission, peripheral and central sensitization are found to be responsible for the pathogenesis of variant toxic neuropathies. Current research reports have indicated the possible involvement of mitochondria mediated redox imbalance as one of the principal causes of neuropathy aetiologies. In addition to imbalance in redox homeostasis, mitochondrial dysfunction is also responsible for alterations in physiological bioenergetic metabolism, apoptosis and autophagy pathways.

Conclusions: In spite of various etiological factors, mitochondrial dysfunction has been found to be a major pathomechanism underlying the neuronal dysfunction associated with peripheral neuropathies. Pharmacological modulation of mitochondria either directly or indirectly is expected to yield therapeutic relief from various primary and secondary mitochondrial diseases.

The role of spinal thrombin through protease-activated receptor 1 in hyperalgesia after neural injury

OBJECTIVE Painful neuropathic injuries induce blood-spinal cord barrier (BSCB) breakdown, allowing pro-inflammatory serum molecules to cross the BSCB, which contributes to nociception. The goal of these studies was to determine whether the blood-borne serine protease thrombin also crosses a permeable BSCB, contributing to nociception through its activation of protease-activated receptor-1 (PAR1). METHODS A 15-minute C-7 nerve root compression, which induces BSCB breakdown and painful behaviors by Day 1, was administered in the rat (n = 10); sham operation (n = 11) and a 3-minute compression (n = 10) that does not induce sensitivity were administered as controls. At Day 1 after root compression, spinal cord tissue was co-immunolabeled for fibrin/fibrinogen, the enzymatic product of thrombin, and IgG, a serum protein, to determine whether thrombin acts in areas of BSCB breakdown. To determine whether spinal thrombin and PAR1 contribute to hyperalgesia after compression, the thrombin inhibitor hirudin and the PAR1 antagonist SCH79797, were separately administered intrathecally before compression injuries (n = 5-7 per group). Rat thrombin was also administered intrathecally with and without SCH79797 (n = 6 per group) to determine whether spinal thrombin induces hypersensitivity in naïve rats through PAR1. RESULTS Spinal fibrin(ogen) was elevated at Day 1 after root compression in regions localized to BSCB breakdown and decreased in those regions by Day 7. Blocking either spinal thrombin or PAR1 completely prevented compression-induced hyperalgesia for 7 days. Intrathecal thrombin induced transient pain that was prevented by blocking spinal PAR1 before its injection. CONCLUSIONS The findings of this study suggest a potent role for spinal thrombin and its activation of PAR1 in pain onset following neuropathic injury.

Anti-nociceptive and anti-inflammatory actions of sulforaphane in chronic constriction injury-induced neuropathic pain mice

Neuropathic pain is still considered as incurable disease as current therapies are not ideal in terms of efficacy and tolerability. It is imperative to search for novel drugs to obtain better treatments. Sulforaphane (SFN), a derivative of glucoraphanin present in cruciferous vegetables, exhibits therapeutic effects on inflammation-related diseases. Since inflammation plays an important role in regulating chronic pain, in the present study, we investigated anti-nociceptive effects of SFN and its underlying mechanisms in a neuropathic pain mouse model, sciatic nerve chronic constriction injury (CCI). SFN (0.1-100 mg/kg) was injected intraperitoneally for 7 days when pain behaviors, including mechanical allodynia and thermal hyperalgesia, reached to the maximum in CCI mice. We observed that SFN dose-dependently attenuated CCI-induced pain behavioral hypersensitivity, accompanied by reduction in pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) and upregulation of an anti-inflammatory cytokine (IL-10). Moreover, SFN counteracted CCI enhancement of COX2 and iNOS in injured nerves, two key enzymes implicated in inflammation and neuropathic pain. Furthermore, pretreatment of naloxone, an antagonist of opioid receptors, significantly blocked SFN attenuation of behavioral hypersensitivity without affecting SFN modulation of inflammatory cytokines in CCI mice. Interestingly, CCI-induced increase in µ-opioid receptors in injured sciatic nerves was further increased by SFN treatment. Taken together, SFN has both anti-nociceptive and anti-inflammatory actions.

Gene expression profile changes in rat dorsal horn after sciatic nerve injury

OBJECTIVE

This study aims to investigate gene expression changes in rat dorsal horns after sciatic nerve injury (SNI).

METHODS

The GSE18803 microarray data collected from young and adult rats were downloaded from GEO. After preprocessing, differentially expressed genes (DEGs) between SNI and sham-operated groups were selected using Limma package, in young and adult group, respectively, followed by Venn analysis. Then, enrichment analyses were performed for these DEGs using DAVID. The STRING database was used to identify protein-protein interactions (PPIs) among these DEGs, and the module network was further extracted using plugin ClusterONE. Finally, protein domain enrichment analysis of DEGs in each module was performed using InterPro database.

RESULTS

Totally, 210 and 50 DEGs were identified in adult and young group, respectively. Among them, 160 were specific in adult group (e.g. CCL2, NF-κB1 and RAC2); 9 were specific in young group (e.g. ILF3 and LYVE1); and 41 were common in both two groups (e.g. FCER1G, C1QA, C1QB and C1QC). The up-regulated DEGs were mostly enriched in immune response-related biological processes, as well as 15 immune- and inflammation-related pathways. Then, two modules were identified in PPI network. CCL2 and NF-κB1 had high connectivity degrees in module 1, and RAC2, FCER1G and CD68 in module 2.

CONCLUSION

CCL2, NF-κB1, RAC2, FCER1G and C1Q may contribute to the generation of neuropathic pain after SNI via immune and defense pathways. Among the five genes, the first three are specific in adult population, while the latter two are age-independent. They all might function through involvement of these immune or inflammatory pathways.

Recent trends in neuropathic pain patents

INTRODUCTION

Neuropathic pain (NP) is one of the most important health problems faced nowadays. NP is a chronic disease that cannot be treated like other pain conditions because it is developed from a nerve injury that evolves into a permanent dysfunction of the central and/or peripheral nervous system. Therefore, it involves the participation of several systems and should be viewed as a multi-factorial disease that needs a whole new pharmacological strategy in order to achieve the desired pain relief. Areas covered: The Espacenet site was used as the main source in order to perform the patent research for NP treatment. This review covers the patents with relevant approaches for NP treatment from 2014 until today. Expert opinion: Our patent research has shown that there is not a consensus approach to treat NP in any of its forms. In our opinion, the approach regarding NP needs to be like cancer's approach. As there are different types of cancer and different ways to treat them, the same needs to be done for NP. Currently, there are several promising targets, which corroborates that this is a wide-open research area. For these reasons, neuropathic pain is a therapeutic field full of potential for innovation.

Feasibility of Topical Applications of Natural High-Concentration Capsaicinoid Solutions in Patients with Peripheral Neuropathic Pain: A Retrospective Analysis

Background. Capsaicin, one of several capsaicinoid compounds, is a potent TRPV1 agonist. Topical application at high concentration (high concentration, >1%) induces a reversible disappearance of epidermal free nerve endings and is used to treat peripheral neuropathic pain (PNP). While the benefit of low-concentration capsaicin remains controversial, the 8%-capsaicin patch (Qutenza®, 2010, Astellas, Netherlands) has shown its effectiveness. This patch is, however, costly and natural high-concentration capsaicinoid solutions may represent a cheaper alternative to pure capsaicin. Methods. In this retrospective study, 149 patients were screened, 132 were included with a diagnosis of neuropathic pain, and eighty-four were retained in the final analyses (median age: 57.5 years [IQR25–75: 44.7–67.1], male/female: 30/54) with PNP who were treated with topical applications of natural high-concentration capsaicinoid solutions (total number of applications: 137). Indications were postsurgical PNP (85.7%) and nonsurgical PNP (14.3%) (posttraumatic, HIV-related, postherpetic, and radicular PNP). Objectives. To assess the feasibility of topical applications of natural high-concentration capsaicinoid solutions for the treatment of PNP. Results. The median treated area was 250 cm² [IQR25–75: 144–531]. The median amount of capsaicinoids was 55.1 mg [IQR25–75: 28.7–76.5] per plaster and the median concentration was 172.3 μg/cm² [IQR25–75: 127.6–255.2]. Most patients had local adverse effects on the day of treatment, such as mild to moderate burning pain and erythema. 13.6–19.4% of the patients experienced severe pain or erythema. Following treatment, 62.5% of patients reported a lower pain intensity or a smaller pain surface, and 35% reported a sustained pain relief lasting for at least 4 weeks. Conclusion. Analgesic topical treatment with natural high-concentration capsaicinoid is feasible and may represent a low cost alternative to alleviate PNP in clinical practice.

Cardamonin attenuates hyperalgesia and allodynia in a mouse model of chronic constriction injury-induced neuropathic pain: Possible involvement of the opioid system

Neuropathic pain arises from the injury of nervous system. The condition is extremely difficult to be treated due to the ineffectiveness and presence of various adverse effects of the currently available drugs. In the present study, we investigated the antiallodynic and antihyperlagesic properties of cardamonin, a naturally occurring chalcone in chronic constriction injury (CCI)-induced neuropathic pain mice model. Our findings showed that single and repeated dose of intra-peritoneal administration of cardamonin (3, 10, 30mg/kg) significantly inhibited (P<0.001) the chronic constriction injury-induced neuropathic pain using the Hargreaves plantar test, Randall-Selitto analgesiometer test, dynamic plantar anesthesiometer test and the cold plate test in comparison with the positive control drug used (amitriptyline hydrochloride, 20mg/kg, i.p.). Pre-treatment with naloxone hydrochloride (1mg/kg, i.p.) and naloxone methiodide (1mg/kg, s.c) significantly reversed the antiallodynic and antihyperalgesic effects of cardamonin in dynamic plantar anesthesiometer test and Hargreaves plantar test, respectively. In conclusion, the current findings demonstrated novel antiallodynic and antihyperalgesic effects of cardamonin through the activation of the opioidergic system both peripherally and centrally and may prove to be a potent lead compound for the development of neuropathic pain drugs in the future.

Biological mechanism of post-herpetic neuralgia: Evidence from multiple patho-psychophysiological measures

BACKGROUND

Post-herpetic neuralgia (PHN), which develops after the resolution of a herpes zoster eruption, is an exceptionally drug-resistant neuropathic pain. The unsatisfactory management of PHN partly results from the difficulty in dissecting out its contributing factors due to the complexity of PHN mechanism.

METHODS

Here, to elaborate our understanding of the PHN mechanism and to establish a basis for effective therapeutic strategies, we comprehensively investigated the contributions of multiple factors to PHN severity.

RESULTS

Based on the comparison of somatosensory detection thresholds (C, Aδ and Aβ fibre thresholds) between affected and unaffected sides, 16 PHN patients with significant sensory deficits and 13 PHN patients without significant sensory deficits were identified and assigned to different groups. The different extents of lesions in the nociceptive system between patients with and without sensory deficits were confirmed using laser-evoked brain responses. Moreover, patients with sensory deficits had more severe pain and psychological disorders, e.g. anxiety and depression. Importantly, chronic pain severity was significantly influenced by various psychophysiological factors (sleep disturbances, psychological disorders and hypothalamic-pituitary-adrenal axis dysfunction) for patients with sensory deficits.

CONCLUSIONS

Our findings demonstrated the contribution of multiple patho-psychophysiological factors to PHN severity, which could help establish a basis for the development of a rational, patient-centred therapeutic strategy.

SIGNIFICANCE

This study revealed the contribution of multiple patho-psychophysiological factors to PHN severity, which expanded our understanding of the underlying PHN mechanism, and helped develop a rational, patient-centred therapeutic strategy targeting towards the corresponding etiology and psychophysiological disorders for individual patient.

Early-onset treadmill training reduces mechanical allodynia and modulates calcitonin gene-related peptide fiber density in lamina III/IV in a mouse model of spinal cord contusion injury

Below-level central neuropathic pain (CNP) affects a large proportion of spinal cord injured individuals. To better define the dynamic changes of the spinal cord neural network contributing to the development of CNP after spinal cord injury (SCI), we characterized the morphological and behavioral correlates of CNP in female C57BL/6 mice after a moderate T11 contusion SCI (50 kdyn) and the influence of moderate physical activity. Compared with sham-operated animals, injured mice developed mechanical allodynia 2 weeks post injury when tested with small-diameter von Frey hair filaments (0.16 g and 0.4 g filament), but presented hyporesponsiveness to noxious mechanical stimuli (1.4 g filament). The mechano-sensory alterations lasted up to 35 days post injury, the longest time point examined. The response latency to heat stimuli already decreased significantly 10 days post injury reaching a plateau 2 weeks later. In contrast, injured mice developed remarkable hyposensitivity to cold stimuli. Animals that underwent moderate treadmill training (2 × 15 minutes; 5 d/wk) showed a significant reduction in the response rate to light mechanical stimuli as early as 6 days after training. Calcitonin gene-related peptide (CGRP) labeling in lamina III-IV of the dorsal horn revealed significant increases in CGRP-labeling density in injured animals compared with sham control animals. Importantly, treadmill training reduced CGRP-labeling density by about 50% (P < 0.01), partially reducing the injury-induced increases. Analysis of IB4-labeled nonpeptidergic sensory fibers revealed no differences between experimental groups. Abnormalities in temperature sensation were not influenced by physical activity. Thus, treadmill training partially resolves signs of below-level CNP after SCI and modulates the density of CGRP-labeled fibers.

Different Phenotyping Approaches Lead to Dissimilar Biologic Profiles in Men With Chronic Fatigue After Radiation Therapy

CONTEXT

Cancer-related fatigue (CRF) persists months after treatment completion. Although a CRF biomarker has not yet been identified, validated self-report questionnaires are used to define and phenotype CRF in the discovery of potential biomarkers.

OBJECTIVES

The purposes of this study are to identify CRF subjects using three well-known CRF phenotyping approaches using validated self-report questionnaires and to compare the biologic profiles that are associated with each CRF phenotype.

METHODS

Fatigue in men with nonmetastatic prostate cancer receiving external beam radiation therapy was measured at baseline (T1), midpoint (T2), end point (T3), and one-year post-external beam radiation therapy (T4) using the Functional Assessment of Cancer Therapy-Fatigue (FACT-F) and Patient Reported Outcomes Measurement Information System-Fatigue. Chronic fatigue (CF) and nonfatigue subjects were grouped based on three commonly used phenotyping approaches: 1) T4 FACT-F <43; 2) T1-T4 decline in FACT-F score ≥3 points; 3) T4 Patient Reported Outcomes Measurement Information System-Fatigue T-score >50. Differential gene expressions using whole-genome microarray analysis were compared in each of the phenotyping criterion.

RESULTS

The study enrolled 43 men, where 34%-38% had CF based on the three phenotyping approaches. Distinct gene expression patterns were observed between CF and nonfatigue subjects in each of the three CRF phenotyping approaches: 1) Approach 1 had the largest number of differentially expressed genes and 2) Approaches 2 and 3 had 40 and 21 differentially expressed genes between the fatigue groups, respectively.

CONCLUSION

The variation in genetic profiles for CRF suggests that phenotypic profiling for CRF should be carefully considered because it directly influences biomarker discovery investigations.

Neuropathic pain may be common in chronic lower limb tendinopathy: a prospective cohort study

BACKGROUND

To identify the prevalence of neuropathic pain, through the use of the painDETECT questionnaire, in a cohort of patients with chronic lower limb tendinopathy conditions.

METHODS

Patients with chronic lower limb tendinopathy conditions treated within a Sport and Exercise Medicine hospital clinic were identified from clinical records. At the time of the clinical consultation, pain and painDETECT scores were recorded.

RESULTS

In total, 282 suitable patients with chronic lower limb tendinopathy conditions were identified who had completed a painDETECT questionnaire. There was a median age of 51.9 years, 35% of patients were male and a median duration of symptoms of 24.0 months. There was a median score of 7.0/10 for self-reported 'average' pain and 8.0/10 for self-reported 'worst' pain. There was a median painDETECT score of 14.0, 28% of respondents scored 19 or higher with painDETECT (neuropathic component to pain may be likely), 29% scored 13-18 (equivocal result) and 43% of respondents scored 12 or less (neuropathic pain component was unlikely).

CONCLUSIONS

This study suggests that neuropathic pain as identified by the painDETECT questionnaire may be common in patients with chronic lower limb tendinopathy conditions. It is unclear if patients with tendinopathy who have neuropathic pain may have poorer outcomes from initial treatments, contributing to the high proportion seen in secondary care. These are results from a single hospital clinic, and comparison with a control group is currently lacking. However, on the results to date, neuropathic pain should be considered in management strategies in patients with chronic tendinopathy.

Histamine H4 receptor agonist-induced relief from painful peripheral neuropathy is mediated by inhibition of spinal neuroinflammation and oxidative stress

BACKGROUND AND PURPOSE

Neuropathic pain is under-treated, with a detrimental effect on quality of life, partly because of low treatment efficacy, but also because pathophysiological mechanisms are not fully elucidated. To clarify the pathobiology of neuropathic pain, we studied the contribution of neuroinflammation and oxidative stress in a model of peripheral neuropathy. We also assessed an innovative treatment for neuropathic pain by investigating the effects of histamine H₄ receptor ligands in this model.

EXPERIMENTAL APPROACH

A peripheral mononeuropathy was induced in mice, by spared nerve injury (SNI). Neuroinflammation and oxidative stress parameters were evaluated by spectrophotometry. The mechanical (von Frey test) and thermal (plantar test) nociceptive thresholds were evaluated.

KEY RESULTS

SNI mice showed increased expression of the pro-inflammatory cytokines IL-1ß and TNF-α, decreased antioxidant enzyme Mn-containing SOD (MnSOD), increased levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), an indicator of oxidative DNA damage, and of PARP, nuclear enzyme activated upon DNA damage. Intrathecal administration of VUF 8430 (H₄ receptor agonist) reversed the mechanical and thermal allodynia and was associated with decreased expression of IL-1ß, TNF-α, 8-OHdG and PARP and with restoration of MnSOD activity in the spinal cord and sciatic nerve. These effects were prevented by JNJ 10191584 (H₄ receptor antagonist).

CONCLUSION AND IMPLICATIONS

In the SNI mouse model of neuropathic pain, neuronal H₄ receptor stimulation counteracts hyperalgesia and reduces neuroinflammation and oxidative stress in the spinal cord and sciatic nerve. Targeting both oxidative stress and pro-neuroinflammatory pathways through H₄ receptor-mediated mechanisms could have promising therapeutic potential for neuropathic pain management.

Dorsal horn interneuron-derived Netrin-4 contributes to spinal sensitization in chronic pain via Unc5B

Hayano et al. show that Netrin-4, which is originally identified as an axon guidance molecule, is capable of enhancing sensitivity to sensory input and can contribute to neuropathic pain. The findings provide evidence for a previously unknown pain-inducing signal from spinal cord interneurons.

Because of the incomplete understanding of the molecular mechanisms that underlie chronic pain, the currently available treatments for this type of pain remain inefficient. In this study, we show that Netrin-4, a member of the axon guidance molecule family, was expressed in dorsal horn inner lamina II excitatory interneurons in the rat spinal cord. A similar expression pattern for Netrin-4 was also observed in human spinal cord. Behavioral analysis revealed that tactile and heat hyperalgesia after peripheral nerve injury or inflammation were abolished in Netrin-4–mutant rats. Transient suppression of Netrin-4 or its receptor Unc5B after injury could also prevent allodynia. Conversely, intrathecal administration of Netrin-4 protein to naive rats enhanced excitatory synaptic transmission in the dorsal horn and induced allodynia, suggesting that Netrin-4 is involved in spinal sensitization. Furthermore, the Unc5B receptor and subsequent activation of the tyrosine phosphatase SHP2 mediated Netrin-4–induced pain signaling in the spinal cord. These results identify Netrin-4 as a novel protein regulating spinal sensitization leading to chronic pain. Our findings provide evidence for the function of Netrin in the adult nervous system, as well as a previously unknown function in inducing pain signals from dorsal horn interneurons.

Gabapentinoids for chronic low back pain: a protocol for systematic review and meta-analysis of randomised controlled trials

INTRODUCTION

Chronic low back pain (CLBP) is a common condition and causes significant pain, distress and disability across the world. It is multifactorial in aetiology and is challenging to manage. Although the underlying mechanism of pain is predominantly non-specific, many argue that there is a substantial neuropathic pain element. Neuropathic pain is more severe, with significant disability. Gabapentinoids, including gabapentin and pregabalin, have proven efficacy in some neuropathic pain conditions. Despite no clear evidence, a substantial population of patients with CLBP are treated with gabapentinoids.

OBJECTIVES

We aim to assess whether the use of gabapentinoids is effective and safe in the treatment of predominant CLBP, by conducting a systematic review and meta-analysis of randomised control trials (RCTs).

METHODOLOGY

We will search the databases of MEDLINE, EMBASE and Cochrane for RCTs published in English language and have used gabapentinoids for the treatment of CLBP. Study selection and data extraction will be performed independently by paired reviewers using structured electronic forms, piloted between pairs of reviewers. The review outcomes will be guided by Initiative on Methods, Measurement and Pain Assessment in Clinical Trials guidelines, with pain relief as the primary outcome. We propose to carry out meta-analysis if there are three or more studies in a particular outcome domain, using a random effects model. Pooled outcomes will be reported as weighted mean differences or standardised mean differences and risk ratios with their corresponding 95% CIs, for continuous outcomes and dichotomous outcomes, respectively. Rating of quality of evidence will be reported using GRADE summary of findings table.

DISCUSSION

The proposed systematic review will be able to provide valuable evidence to help decision-making in the use of gabapentinoids for the treatment of CLBP. This will help advance patient care and potentially highlight limitations in existing evidence to direct future research.

ETHICS AND DISSEMINATION

Being a systematic review, this study would not necessitate ethical review and approval. We plan to report and publish our study findings in a high impact medical journal, with online access.

TRIAL REGISTRATION NUMBER

CRD42016034040.

The 5% Lidocaine-Medicated Plaster: Its Inclusion in International Treatment Guidelines for Treating Localized Neuropathic Pain, and Clinical Evidence Supporting its Use

When peripheral neuropathic pain affects a specific, clearly demarcated area of the body, it may be described as localized neuropathic pain (LNP). Examples include postherpetic neuralgia and painful diabetic neuropathy, as well as post-surgical and post-traumatic pain. These conditions may respond to topical treatment, i.e., pharmaceutical agents acting locally on the peripheral nervous system, and the topical route offers advantages over systemic administration. Notably, only a small fraction of the dose reaches the systemic circulation, thereby reducing the risk of systemic adverse effects, drug–drug interactions and overdose. From the patient’s perspective, the analgesic agent is easily applied to the most painful area(s). The 5% lidocaine-medicated plaster has been used for several years to treat LNP and is registered in approximately 50 countries. Many clinical guidelines recommend this treatment modality as a first-line option for treating LNP, particularly in frail and/or elderly patients and those receiving multiple medications, because the benefit-to-risk ratios are far better than those of systemic analgesics. However, some guidelines make only a weak recommendation for its use. This paper considers the positioning of the 5% lidocaine-medicated plaster in international treatment guidelines and how they may be influenced by the specific criteria used in developing them, such as the methodology employed by randomized, placebo-controlled trials. It then examines the body of evidence supporting use of the plaster in some prevalent LNP conditions. Common themes that emerge from clinical studies are: (1) the excellent tolerability and safety of the plaster, which can increase patients’ adherence to treatment, (2) continued efficacy over long-term treatment, and (3) significant reduction in the size of the painful area. On this basis, it is felt that the 5% lidocaine-medicated plaster should be more strongly recommended for treating LNP, either as one component of a multimodal approach or as monotherapy.

Effect of Botulinum Toxin on Disabling Neuropathic Pain: A Case Presentation Suggesting a New Therapeutic Strategy

This case presentation describes a 47-year-old woman who developed complex regional pain syndrome type II with severe neuropathic pain following iatrogenic transection of the tibial nerve at the ankle. The pain and disability progressively worsened over time, markedly impaired ambulation, and were not relieved despite various analgesic treatments. After injection of botulinum toxin (abobotulinumtoxinA, BoNT-A) in the leg muscles the tendons of which pass through the tarsal tunnel (together with the tibial nerve), her pain decreased and her walking capacity improved. This case suggests a new therapeutic role for botulin toxin in treating peripheral neuropathic pain caused by movement-evoked ectopic potentials.

LEVEL OF EVIDENCE

V.

Fentanyl for neuropathic pain in adults

BACKGROUND

Opioid drugs, including fentanyl, are commonly used to treat neuropathic pain, and are considered effective by some professionals. Most reviews have examined all opioids together. This review sought evidence specifically for fentanyl, at any dose, and by any route of administration. Other opioids are considered in separate reviews.

OBJECTIVES

To assess the analgesic efficacy of fentanyl for chronic neuropathic pain in adults, and the adverse events associated with its use in clinical trials.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and Embase from inception to June 2016, together with the reference lists of retrieved articles, and two online study registries.

SELECTION CRITERIA

We included randomised, double-blind studies of two weeks' duration or longer, comparing fentanyl (in any dose, administered by any route, and in any formulation) with placebo or another active treatment in chronic neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently searched for studies, extracted efficacy and adverse event data, and examined issues of study quality and potential bias. We did not carry out any pooled analyses. We assessed the quality of the evidence using GRADE.

MAIN RESULTS

Only one study met our inclusion criteria. Participants were men and women (mean age 67 years), with postherpetic neuralgia, complex regional pain syndrome, or chronic postoperative pain. They were experiencing inadequate relief from non-opioid analgesics, and had not previously taken opioids for their neuropathic pain. The study used an enriched enrolment randomised withdrawal design. It was adequately blinded, but we judged it at unclear risk of bias for other criteria.Transdermal fentanyl (one-day fentanyl patch) was titrated over 10 to 29 days to establish the maximum tolerated and effective dose (12.5 to 50 µg/h). Participants who achieved a prespecified good level of pain relief with a stable dose of fentanyl, without excessive use of rescue medication or intolerable adverse events ('responders'), were randomised to continue with fentanyl or switch to placebo for 12 weeks, under double-blind conditions. Our prespecified primary outcomes were not appropriate for this study design, but the measures reported do give an indication of the efficacy of fentanyl in this condition.In the titration phase, 1 in 3 participants withdrew because of adverse events or inadequate pain relief, and almost 90% experienced adverse events. Of 258 participants who underwent open-label titration, 163 were 'responders' and entered the randomised withdrawal phase. The number of participants completing the study (and therefore continuing on treatment) without an increase of pain by more than 15/100 was 47/84 (56%) with fentanyl and 28/79 (35%) with placebo. Because only 63% responded sufficiently to enter the randomised withdrawal phase, this implies that only a maximum of 35% of participants entering the study would have had useful pain relief and tolerability with transdermal fentanyl, compared with 22% with placebo. Almost 60% of participants taking fentanyl were 'satisfied' and 'very satisfied' with their treatment at the end of the study, compared with about 40% with placebo. This outcome approximates to our primary outcome of moderate benefit using the Patient Global Impression of Change scale, but the group was enriched for responders and the method of analysis was not clear. The most common adverse events were constipation, nausea, somnolence, and dizziness.There was no information about other types of neuropathic pain, other routes of administration, or comparisons with other treatments.We downgraded the quality of the evidence to very low because there was only one study, with few participants and events, and there was no information about how data from people who withdrew were analysed.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support or refute the suggestion that fentanyl works in any neuropathic pain condition.