Non-steroidal anti-inflammatory drugs for neuropathic pain: How do we explain continued widespread use?

Chronic pain for rheumatological disorders: Pathophysiology, therapeutics and evidence

Pain is the leading reason people seek orthopedic and rheumatological care. By definition, most pain can be classified as nociceptive, or pain resulting from non-neural tissue injury or potential injury, with between 15% and 50% of individuals suffering from concomitant neuropathic pain or the newest category of pain, nociplastic pain, defined as "pain arising from altered nociception despite no clear evidence of actual or threatened tissue damage, or of a disease or lesion affecting the somatosensory system." Pain classification is important because it affects treatment decisions at all levels of care. Although several instruments can assist with classifying treatment, physician designation is the reference standard. The appropriate treatment of pain should ideally involve multidisciplinary care including physical therapy, psychotherapy and integrative therapies when appropriate, and pharmacotherapy with non-steroidal anti-inflammatory drugs for acute, mechanical pain, membrane stabilizers for neuropathic and nociplastic pain, and serotonin-norepinephrine reuptake inhibitors and tricyclic antidepressants for all types of pain. For nonsurgical interventions, there is evidence to support a small effect for epidural steroid injections for an intermediate-term duration, and conflicting evidence for radiofrequency ablation to provide at least 6months of benefit for facet joint pain, knee osteoarthritis, and sacroiliac joint pain. Since pain and disability represent the top reason for elective surgery, it should be reserved for patients who fail conservative interventions. Risk factors for procedural failure are the same as risk factors for conservative treatment failure and include greater disease burden, psychopathology, opioid use, central sensitization and multiple comorbid pain conditions, poorly controlled preoperative and postoperative pain, and secondary gain.

Non-steroidal anti-inflammatory drugs for pain in hospice/palliative care: an international pharmacovigilance study

OBJECTIVES

To describe the current, real-world use of non-steroidal anti-inflammatory drugs for pain and the associated benefits and harms.

METHODS

A prospective, multicentre, consecutive cohort pharmacovigilance study conducted at 14 sites across Australia, Aotearoa/New Zealand and the UK including hospital, hospice inpatient and outpatient services. Pain scores and harms were graded using the National Cancer Institute Common Terminology Criteria for Adverse Events at baseline, 2 days and 14 days. Ad-hoc safety reporting continued until day 28.

RESULTS

Data were collected from 92 patients between March 2018 and October 2021. Most patients had cancer (91%) and were coprescribed opioids (90%). At 14 days, 83% of patients had benefit from non-steroidal anti-inflammatory drugs and 22% had harm. The most common harms were nausea (8%), vomiting (3%), acute kidney injury (3%) and non-gastrointestinal bleeding (3%); only 2% were severe and no patients ceased their non-steroidal anti-inflammatory drugs due to toxicity. Overall, 65% had benefit without harm and 3% had harm without benefit.

CONCLUSIONS

Most patients benefited from non-steroidal anti-inflammatory drugs with only one in five patients experiencing tolerable harm. This suggests that short-term use of non-steroidal anti-inflammatory drugs in patients receiving palliative care is safer than previously thought and may be underused.

The Pharmacological Treatment of Neuropathic Pain in Children

The International Association for the Study of Pain (IASP) defines neuropathic pain as pain caused by a lesion or disease of the somatosensory nervous system. It is characterized as a clinical condition in which diagnostic studies reveal an underlying cause of an abnormality in the peripheral or central nervous system. Many common causes of neuropathic pain in adults are rare in children. The purpose of this focused narrative review is, to 1) provide an overview of neuropathic pain in children, 2) highlight unique considerations related to the diagnosis and mechanisms of neuropathic pain in children, and 3) perform a comprehensive analysis of the pharmacological treatments available. We emphasize that data for routine use of pharmacological agents in children with neuropathic pain are largely inferred from adult literature with little research performed on pediatric populations, yet have clear evidence of harms to pediatric patients. Based on these findings, we propose risk mitigation strategies such as utilizing topical treatments whenever possible, assessing pain phenotyping to guide drug class choice, and considering pharmaceuticals in the broader context of the multidisciplinary treatment of pediatric pain. Furthermore, we highlight important directions for future research on pediatric neuropathic pain treatment.

Designing a clinical trial of non-steroidal anti-inflammatory drugs for cancer pain: a survey of UK palliative care physicians

OBJECTIVES

Insufficient quality evidence exists to support or refute the use of non-steroidal anti-inflammatory drugs (NSAIDs) in the management of cancer pain. We aimed to determine the most clinically pragmatic design of a future randominsed controlled trial (RCT), based on how NSAIDs are currently used and perceived efficacy.

METHODS

An online survey was distributed to members of the Association for Palliative Medicine of Great Britain and Ireland examining NSAID use, indications and perceived efficacy, as well as duration of respondents' experience in palliative medicine.

RESULTS

23% of 968 members responded. A placebo-controlled trial of NSAIDs as a strong opioid adjunct in cancer-related bone pain was considered the most clinically pragmatic design. Concerning current practice, oral administration was the preferential route (79.4%), dosed regularly (79.5%). Selective cyclooxygenase-2 (COX-2) inhibitors and non-selective COX-2 inhibitors were considered similarly effective by 45% in cancer pain; ibuprofen being the first line oral NSAID of choice (42.6%). Treatment efficacy is generally determined within 1 week (94.3%). On a Likert scale, most physicians consider NSAIDs improve cancer pain either 'sometimes' (57.7%) or 'often' (40%). Years of specialist palliative care experience did not affect perception of efficacy (p=0.353).

CONCLUSIONS

A randomised controlled trial of NSAIDs as opioid adjuncts for cancer-related bone pain would be the most pragmatic design supported by palliative care clinicians to benefit clinical practice.

Novel Drug Targets and Emerging Pharmacotherapies in Neuropathic Pain

Neuropathic pain is a debilitating condition characterized by abnormal signaling within the nervous system, resulting in persistent and often intense sensations of pain. It can arise from various causes, including traumatic nerve injury, neuropathy, and certain diseases. We present an overview of current and emerging pharmacotherapies for neuropathic pain, focusing on novel drug targets and potential therapeutic agents. Current pharmacotherapies, including tricyclic antidepressants, gabapentinoids, and serotonin norepinephrine re-uptake inhibitors, are discussed, as are emerging treatments, such as ambroxol, cannabidiol, and N-acetyl-L-cysteine. Additionally, the article highlights the need for further research in this field to identify new targets and develop more effective and targeted therapies for neuropathic pain management.

Potential Mediators of Oxaliplatin-Induced Peripheral Neuropathy From Adjuvant Therapy in Stage III Colon Cancer: Findings From CALGB (Alliance)/SWOG 80702

PURPOSE

We sought to evaluate the independent and interactive associations of planned treatment duration, celecoxib use, physical activity, body mass index (BMI), diabetes mellitus, and vitamin B6 with oxaliplatin-induced peripheral neuropathy (OIPN) among patients with stage III colon cancer enrolled in a clinical trial.

METHODS

We conducted a prospective, observational study of 2,450 patients with stage III colon cancer enrolled in the CALGB/SWOG 80702 trial, randomly assigned to 6 versus 12 cycles of adjuvant fluorouracil, leucovorin, and oxaliplatin chemotherapy with or without 3 years of celecoxib. OIPN was reported using the Common Terminology Criteria for Adverse Events (CTCAE) during and following completion of chemotherapy and the FACT/GOG-NTX-13 15-17 months after random assignment. Multivariate analyses were adjusted for baseline sociodemographic and clinical factors.

RESULTS

Patients assigned to 12 treatment cycles, relative to 6, were significantly more likely to experience higher-grade CTCAE- and FACT/GOG-NTX-13-reported neuropathy and longer times to resolution, while neither celecoxib nor vitamin B6 intake attenuated OIPN. Exercising ≥ 9 MET-hours per week after treatment relative to < 9 was associated with improvements in FACT/GOG-NTX-13-reported OIPN (adjusted difference in means, 1.47; 95% CI, 0.49 to 2.45; P = .003). Compared with patients with baseline BMIs < 25, those with BMIs ≥ 25 were at significantly greater risk of developing higher-grade CTCAE-reported OIPN during (adjusted odds ratio, 1.18; 95% CI, 1.00 to 1.40; P = .05) and following completion (adjusted odds ratio, 1.23; 95% CI, 1.01 to 1.50; P = .04) of oxaliplatin treatment. Patients with diabetes were significantly more likely to experience worse FACT/GOG-NTX-13-reported neuropathy relative to those without (adjusted difference in means, -2.0; 95% CI, -3.3 to -0.73; P = .002). There were no significant interactions between oxaliplatin treatment duration and any of these potentially modifiable exposures.

CONCLUSION

Lower physical activity, higher BMI, diabetes, and longer planned treatment duration, but not celecoxib use or vitamin B6 intake, may be associated with significantly increased OIPN severity.

Response profile in a rat model of exercise-induced hypoalgesia is associated with duloxetine, pregabalin and diclofenac effect on constriction-induced neuropathy

BACKGROUND

Exercise is a known trigger of the inhibitory pain modulation system and its analgesic effect is termed exercise-induced hypoalgesia (EIH). Previous studies have demonstrated that rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury compared to rats with substantial analgesic response following exercise.

OBJECTIVES

A rat model of EIH as an indicator of the pain inhibitory system's efficiency was used to explore the association between EIH profiles and the effect of pharmacotherapy on rat's neuropathic pain.

METHODS

EIH profiles were assessed by evaluating paw responses to mechanical stimuli before and after exercise on a rotating rod. Rats with a reduction of ≤33% in responses were classified as low EIH and those with ≥67% as high EIH. Low and high EIH rats underwent sciatic nerve chronic constriction injury (CCI). Paw responses to mechanical stimuli were measured at baseline, following CCI, and after treatment with diclofenac, duloxetine or pregabalin. In a different group of low and high EIH rats, EIH was measured before and following treatment with the same medications.

RESULTS

Low EIH rats developed more significant hypersensitivity following CCI. Duloxetine and pregabalin successfully reduced hypersensitivity, although significantly more so in low EIH rats. Diclofenac had limited effects, and only on low EIH rats. Four days of duloxetine administration transformed low EIH rats' profiles to high EIH.

CONCLUSIONS

The findings of this study suggest that EIH profiles in rats can not only predict the development of hypersensitivity following injury but may also support targeted pharmacological treatment.

SIGNIFICANCE

Exercise is a known trigger of the inhibitory pain modulation. Rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury. Pain modulation profiles in rats can also support targeted pharmacological treatment; rats with deficient analgesic response following exercise benefit more from treatment with duloxetine and gabapentin. Treatment with duloxetine can improve pain modulation profile.

Agmatine Administration Effects on Equine Gastric Ulceration and Lameness

Osteoarthritis (OA) accounts for up to 60% of equine lameness. Agmatine, a decarboxylated arginine, may be a viable option for OA management, based on reports of its analgesic properties. Six adult thoroughbred horses, with lameness attributable to thoracic limb OA, received either daily oral phenylbutazone (6.6 mg/kg), agmatine sulfate (25 mg/kg) or a control for 30 days, with 21-day washout periods between treatments. Subjective lameness, thoracic limb ground reaction forces (GRF), plasma agmatine and agmatine metabolite levels were evaluated using an established rubric, a force platform, and mass spectrometry, respectively, before, during and after each treatment period. Gastric ulceration and plasma chemistries were evaluated before and after treatments. Braking GRFs were greater after 14 and 29 days of agmatine compared to phenylbutazone administration. After 14 days of phenylbutazone administration, vertical GRFs were greater than for agmatine or the control. Glandular mucosal ulcer scores were lower after agmatine than phenylbutazone administration. Agmatine plasma levels peaked between 30 and 60 min and were largely undetectable by 24 h after oral administration. In contrast, plasma citric acid levels increased throughout agmatine administration, representing a shift in the metabolomic profile. Agmatine may be a viable option to improve thoracic limb GRFs while reducing the risk of glandular gastric ulceration in horses with OA.

Acupuncture and Moxibustion for Peripheral Neuropathic Pain: A Frequentist Network Meta-Analysis and Cost-Effectiveness Evaluation

Purpose

Acupuncture and moxibustion techniques have been increasingly used to treat peripheral neuropathic pain (PNP). However, there is a paucity of comparative information and cost-effectiveness assessment for techniques on PNP management. Patients and Methods. Randomized controlled trials studying the acupuncture or moxibustion treatments on PNP were identified from electronic databases. The quality of the included studies and the potential risk of bias was evaluated using the ROB 2.0 assessment tool. The primary outcome was at least 20% pain relief. The treatment effects were pooled through a frequentist-based network meta approach. Subsequently, the cost-effectiveness measured by incremental cost per additional responder (ICPR) was calculated.

Results

One three-arm trial and 15 two-arm trials comprising 1308 participants that satisfy the eligibility criteria were identified. Among the included studies, 12.5% were at low risk of bias, 68.75% had some concerns about the risk of bias, and 18.75% were at high risk of bias. The major sources of bias originated from the randomization processes of the studies. The patients were assigned to seven different acupuncture or moxibustion interventions and two pharmaceutical treatments. Except for acupoint injection, all the included acupuncture and moxibustion techniques showed superior improvements in PNP and were more cost-effective as compared to pharmaceutical treatments. Warm needling, fire needling, and moxibustion were the most effective treatments. Fire needling showed the lowest ICPR relative to the nonsteroidal anti-inflammatory drugs in the cost-effectiveness analysis of direct and indirect costs.

Conclusion

Acupuncture and moxibustion techniques are beneficial and cost-effective approaches for easing PNP and hence can be considered for PNP management.

β-elemene relieves neuropathic pain in mice through the regulation on C-X-C motif chemokine receptor 3 and GABAA receptor

β-elemene (Bel) is a sesquiterpene compound has shown potential in the antinociceptive treatment. This study focused on the function of Bel in neuropathic pain relief in mice. A murine model with spared nerve injury (SNI) was established and treated with Bel. The paw withdrawal thresholds in response to mechanical and thermal stimulations were examined using von Frey filaments. The L4-L6 spinal dorsal horn tissue samples were collected for histological examination. Bel treatment reduced the sensitivities of model mice to mechanical and thermal stimulations, and it inhibited activation of microglia and the secretion of inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 in tissues. Bel treatment reduced the expression of nociceptor excitatory NMDAR whereas enhanced the expression of nociceptor inhibitory GABAA receptor to relieve the nociception of mice. CXCR3 was a downstream molecule mediated by Bel. Either overexpression of CXCR3 or downregulation of GABAA receptor in the tissues aggravated the neuropathic pain in SNI mice which was initially relieved by Bel. In conclusion, this study suggested that Bel might serve as a drug for nociception management by inhibiting CXCR3 and upregulating GABAA receptor. This study may offer novel insights into the field of neuropathic pain relief.

Assessment of the Anti-Allodynic and Anti-Hyperalgesic Efficacy of a Glycine Transporter 2 Inhibitor Relative to Pregabalin, Duloxetine and Indomethacin in a Rat Model of Cisplatin-Induced Peripheral Neuropathy

Cisplatin, which is a chemotherapy drug listed on the World Health Organisation's List of Essential Medicines, commonly induces dose-limiting side effects including chemotherapy-induced peripheral neuropathy (CIPN) that has a major negative impact on quality of life in cancer survivors. Although adjuvant drugs including anticonvulsants and antidepressants are used for the relief of CIPN, analgesia is often unsatisfactory. Herein, we used a rat model of CIPN (cisplatin) to assess the effect of a glycine transporter 2 (GlyT2) inhibitor, relative to pregabalin, duloxetine, indomethacin and vehicle. Male Sprague-Dawley rats with cisplatin-induced mechanical allodynia and mechanical hyperalgesia in the bilateral hindpaws received oral bolus doses of the GlyT2 inhibitor (3-30 mg/kg), pregabalin (3-100 mg/kg), duloxetine (3-100 mg/kg), indomethacin (1-10 mg/kg) or vehicle. The GlyT2 inhibitor alleviated both mechanical allodynia and hyperalgesia in the bilateral hindpaws at a dose of 10 mg/kg, but not at higher or lower doses. Pregabalin and indomethacin induced dose-dependent relief of mechanical allodynia but duloxetine lacked efficacy. Pregabalin and duloxetine alleviated mechanical hyperalgesia in the bilateral hindpaws while indomethacin lacked efficacy. The mechanism underpinning pain relief induced by the GlyT2 inhibitor at 10 mg/kg is likely due to increased glycinergic inhibition in the lumbar spinal cord, although the bell-shaped dose-response curve warrants further translational considerations.

Evidence for 5-HT1A receptor-mediated antiallodynic and antihyperalgesic effects of apigenin in mice suffering from mononeuropathy

BACKGROUND AND PURPOSE

Neuropathic pain places a devastating health burden, with very few effective therapies. We investigated the potential antiallodynic and antihyperalgesic effects of apigenin, a natural flavonoid with momoamine oxidase (MAO) inhibitory activity, against neuropathic pain and investigated the mechanism(s).

EXPERIMENTAL APPROACH

The neuropathic pain model was produced by chronic constriction injury of sciatic nerves in male C57BL/6J mice, with pain-related behaviours being assayed by von Frey test and Hargreaves test. In this model the role of 5-HT and 5-HT_1A receptor-related mechanisms were investigated in vivo/in vitro.

KEY RESULTS

Apigenin repeated treatment (p.o., once per day for 2 weeks), in a dose-related manner (3, 10 and 30 mg·kg^-1 ), ameliorated the allodynia and hyperalgesia in chronic nerve constriction injury in mice. These effects seem dependent on neuronal 5-hydroxytryptamine, because (i) the antihyperalgesia and antiallodynia were attenuated by depletion of 5-HT with p-chlorophenylalanine and potentiated by 5-hydroxytryptophan and (ii), apigenin-treated chronic constriction injury mice caused an increased level of spinal 5-HT, associated with diminished MAO activity. In vivo administration, spinally or systematically, of the 5-HT_1A antagonist WAY-100635 inhibited the apigenin-induced antiallodynia and antihyperalgesia. In vitro, apigenin acted as a positive allosteric modulator to increase the efficacy (stimulation of [³⁵ S]GTPγS binding) of the 5-HT_1A agonist 8-OH-DPAT. Apigenin attenuated neuronal changes caused by chronic constriction of the sciatic nerve in mice, without causing a hypertensive crisis.

CONCLUSION AND IMPLICATIONS

Apigenin antiallodynic and antihyperalgesic actions against neuropathic pain crucially involve spinal 5-HT_1A receptors and indicate it could be used to treat neuropathic pain.

Chronic nanocurcumin treatment ameliorates pain-related behavior, improves spatial memory, and reduces hippocampal levels of IL-1β and TNFα in the chronic constriction injury model of neuropathic pain

BACKGROUND

Memory deficit is a common cognitive comorbid in patients with neuropathic pain that need better treatment. Recent research revealed that nanocurcumin has an antinociceptive action and a protective effect against memory disorders, suggesting its possible effectiveness for the treatment of neuropathic pain and its comorbidity.

METHODS

Adult male albino Wistar rats (n = 32) were randomly divided into four experimental groups: CCI+ nanocurcumin, CCI + vehicle, sham + nanocurcumin, and sham + vehicle. Neuropathic pain induced by a chronic constriction injury of the sciatic nerve. Nanocurcumin or vehicle was injected intraperitoneally for 10 days. Behavioral assessment achieved to evaluate pain threshold in the von Frey test and radiant heat test, also spatial learning and memory examined by the Morris water maze (MWM) test. To explore the possible relation, IL-1β, and TNF-α levels of the hippocampus measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our data showed that CCI caused neuropathic pain-related behaviors and spatial learning and memory disorders in rats. Chronic treatment with nanocurcumin significantly increased pain threshold (P < 0.001; F = 27.63, F = 20.58), improved spatial memory (P < 0.01; F = 47.37), and decreased the hippocampal levels of IL-1β (P < 0.001; F = 33.57) and TNF-α (P < 0.01; F = 7.25) in CCI rats.

CONCLUSION

Chronic nanocurcumin can ameliorate pain-related behavior, improve spatial learning and memory deficits, and is associated with the reduction of IL-1β and TNF-α levels in the hippocampus in CCI rats. Nanocurcumin may be potentially providing a therapeutic alternative for the treatment of neuropathic pain and its memory impairment comorbidity.

Effects of the publication of Clinical Guidelines for the Management of Chemotherapy-Induced Peripheral Neuropathy on the Administration Preferences of Oncology Specialists: Japanese Association of Supportive Care in Cancer

OBJECTIVE

We conducted a questionnaire survey of oncology specialists to investigate the frequency of administration of different drugs for the management of chemotherapy-induced peripheral neuropathy in Japan in 2015. Our group published Clinical Guidelines for the Management of Chemotherapy-Induced Peripheral Neuropathy in 2017 (CIPN-GL2017). In these guidelines, we recommended duloxetine only. To verify the effect of the publication of the CIPN-GL2017, we conducted a questionnaire survey in 2019.

METHODS

In 2015 and again in 2019, we investigated the use of vitamin B12, antiepileptic agents, duloxetine, antidepressants other than duloxetine, non-steroidal anti-inflammatory drugs, opioids and the Kampo compound (goshajinkigan) in a questionnaire employing a three-point scale wherein A implies routine or prophylactic administration, B implies occasional administration and C implies infrequent administration.

RESULTS

We sent the questionnaires via email to 971 diplomates of the Subspecialty Board of Japanese Society of Medical Oncology in 2015 and 1239 diplomates in 2019. The administration ratio (A + B) of duloxetine for numbness and pain was 46.8 and 31.7%, respectively, in 2015 and 68.9% (P < 0.01) and 73.1% (P < 0.01) in 2019. In response to the question regarding awareness of the CIPN-GL2017, 53.2% of respondents to the 2019 questionnaire were aware of the CIPN-GL2017. Among the respondents with an awareness of the CIPN-GL2017, the prescription rate of duloxetine (78.3%) for pain was significantly higher than that among respondents without any awareness (67.4%).

CONCLUSIONS

It is possible that the publication of CIPN-GL2017 influenced administration preferences of oncology specialists.

Neuropathic Pain: From Mechanisms to Treatment

Neuropathic pain caused by a lesion or disease of the somatosensory nervous system is a common chronic pain condition with major impact on quality of life. Examples include trigeminal neuralgia, painful polyneuropathy, postherpetic neuralgia, and central poststroke pain. Most patients complain of an ongoing or intermittent spontaneous pain of, for example, burning, pricking, squeezing quality, which may be accompanied by evoked pain, particular to light touch and cold. Ectopic activity in, for example, nerve-end neuroma, compressed nerves or nerve roots, dorsal root ganglia, and the thalamus may in different conditions underlie the spontaneous pain. Evoked pain may spread to neighboring areas, and the underlying pathophysiology involves peripheral and central sensitization. Maladaptive structural changes and a number of cell-cell interactions and molecular signaling underlie the sensitization of nociceptive pathways. These include alteration in ion channels, activation of immune cells, glial-derived mediators, and epigenetic regulation. The major classes of therapeutics include drugs acting on α₂δ subunits of calcium channels, sodium channels, and descending modulatory inhibitory pathways.

5-HT1A receptor-mediated attenuation of heat hyperalgesia and mechanical allodynia by chrysin in mice with experimental mononeuropathy

BACKGROUND

Persistent neuropathic pain poses a health problem, for which effective therapy or antidote is in dire need. This work aimed to investigate the pain-relieving effect of chrysin, a natural flavonoid with monoamine oxidase inhibitory activity, in an experimental model of neuropathic pain and elucidate mechanism(s).

METHODS

Chronic constriction injury (CCI) was produced by loose ligation of sciatic nerve in mice. The pain-related behaviors were examined using von Frey test and Hargreaves test. The serotonin-related mechanisms were investigated by serotonin depletion with p-chlorophenylalanine (PCPA) and antagonist tests in vivo and in vitro.

RESULTS

Repeated treatment of CCI mice with chrysin (orally, two times per day for 2 weeks) ameliorated heat hyperalgesia and mechanical allodynia in a dose-dependent fashion (3-30 mg/kg). The chrysin-triggered pain relief seems serotonergically dependent, since its antihyperalgesic and antiallodynic actions were abolished by chemical depletion of serotonin by PCPA, whereas potentiated by 5-hydroxytryptophan (a precursor of 5-HT). Consistently, chrysin-treated neuropathic mice showed enhanced levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, chrysin-evoked pain relief was preferentially counteracted by 5-HT_1A receptor antagonist WAY-100635 delivered systematically or spinally. In vitro, chrysin (0.1-10 nM) increased the maximum effect (Emax, shown as stimulation of [³⁵S] GTPγS binding) of 8-OH-DPAT, a 5-HT_1A agonist. Beneficially, chrysin was able to correct comorbid behavioral symptoms of depression and anxiety evoked by neuropathic pain, without causing hypertensive crisis (known as 'cheese reaction').

CONCLUSION

These findings confirm the antihyperalgesic and antiallodynic efficacies of chrysin, with spinal 5-HT_1A receptors being critically engaged.

Guideline "diagnosis and non interventional therapy of neuropathic pain" of the German Society of Neurology (deutsche Gesellschaft für Neurologie)

2019 the DGN (Deutsche Gesellschaft für Neurology) published a new guideline on the diagnosis and non-interventional therapy of neuropathic pain of any etiology excluding trigeminal neuralgia and CRPS (complex regional pain syndrome). Neuropathic pain occurs after lesion or damage of the somatosensory system. Besides clinical examination several diagnostic procedures are recommended to assess the function of nociceptive A-delta and C-Fibers (skin biopsy, quantitative sensory testing, Laser-evoked potentials, Pain-evoked potentials, corneal confocal microscopy, axon reflex testing). First line treatment in neuropathic pain is pregabalin, gabapentin, duloxetine and amitriptyline. Second choice drugs are topical capsaicin and lidocaine, which can also be considered as primary treatment in focal neuropathic pain. Opioids are considered as third choice treatment. Botulinum toxin can be considered as a third choice drug for focal limited pain in specialized centers only. Carbamazepine and oxcarbazepine cannot be generally  recommended, but might be helpful in single cases. In Germany, cannabinoids can be prescribed, but only after approval of reimbursement. However, the use is not recommended, and can only be considered as off-label therapy within a multimodal therapy concept.

Serotonergically dependent antihyperalgesic and antiallodynic effects of isoliquiritin in a mouse model of neuropathic pain

Chronic neuropathic pain poses a significant health problem worldwide, for which effective treatment is lacking. The current work aimed to investigate the potential analgesic effect of isoliquiritin, a flavonoid from Glycyrrhiza uralensis, against neuropathic pain and elucidate mechanisms. Male C57BL/6J mice were subjected to chronic constriction injury (CCI) by loose ligation of their sciatic nerves. Following CCI surgery, the neuropathic mice developed pain-like behaviors, as shown by thermal (heat) hyperalgesia in the Hargreaves test and tactile allodynia in the von Frey test. Repetitive treatment of CCI mice with isoliquiritin (p.o., twice per day for two weeks) ameliorated behavioral hyperalgesia to thermal (heat) stimuli and allodynia to tactile stimuli in a dose-dependent fashion (5, 15 and 45 mg/kg). The isoliquiritin-triggered analgesia seems serotonergically dependent, since its antihyperalgesic and antiallodynic actions were totally abolished by chemical depletion of spinal serotonin by p-chlorophenylalanine, whereas potentiated by 5-HTP (a precursor of 5-HT). Consistently, isoliquiritin-treated neuropathic mice showed escalated levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, isoliquiritin-evoked antihyperalgesia and antiallodynia were preferentially counteracted by the 5-HT_1A receptor antagonist WAY-100635 delivered systematically or spinally. Of notable benefit, isoliquiritin was able to correct co-morbid behavioral symptoms of depression and anxiety evoked by neuropathic pain. Collectively, these findings demonstrate, for the first time, the therapeutic efficacy of isoliquiritin on neuropathic hypersensitivity, and this effect is dependent on the spinal serotonergic system and 5-HT_1A receptors.

Isorhynchophylline Exerts Antinociceptive Effects on Behavioral Hyperalgesia and Allodynia in a Mouse Model of Neuropathic Pain: Evidence of a 5-HT1A Receptor-Mediated Mechanism

Chronic neuropathic pain poses a significant health problem, for which effective therapy is lacking. The current work aimed to investigate the potential antinociceptive efficacy of isorhynchophylline, an oxindole alkaloid, against neuropathic pain and elucidate mechanisms. Male C57BL/6J mice were subjected to chronic constriction injury (CCI) by loose ligation of their sciatic nerves. Following CCI surgery, the neuropathic mice developed pain-like behaviors, as shown by thermal hyperalgesia in the Hargreaves test and tactile allodynia in the von Frey test. Repetitive treatment of CCI mice with isorhynchophylline (p.o., twice per day for two weeks) ameliorated behavioral hyperalgesia and allodynia in a dose-dependent fashion (5, 15, and 45 mg/kg). The isorhynchophylline-triggered antinociception seems serotonergically dependent, since its antinociceptive actions on neuropathic hyperalgesia and allodynia were totally abolished by chemical depletion of spinal serotonin by PCPA, whereas potentiated by 5-HTP (a precursor of 5-HT). Consistently, isorhynchophylline-treated neuropathic mice showed escalated levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, the isorhynchophylline-evoked antinociception was preferentially counteracted by co-administration of 5-HT_1A receptor antagonist WAY-100635. In vitro, isorhynchophylline (0.1-10 nM) increased the Emax (stimulation of [³⁵S] GTPγS binding) of 8-OH-DPAT, a 5-HT_1A agonist. Of notable benefit, isorhynchophylline was able to correct co-morbidly behavioral symptoms of depression and anxiety evoked by neuropathic pain. Collectively, these findings confirm, for the first time, the disease-modifying efficacy of isorhynchophylline on neuropathic hypersensitivity, and this effect is dependent on spinal serotonergic system and 5-HT_1A receptors.

Challenges of neuropathic pain: focus on diabetic neuropathy

Neuropathic pain is a frequent condition caused by a lesion or disease of the central or peripheral somatosensory nervous system. A frequent cause of peripheral neuropathic pain is diabetic neuropathy. Its complex pathophysiology is not yet fully elucidated, which contributes to underassessment and undertreatment. A mechanism-based treatment of painful diabetic neuropathy is challenging but phenotype-based stratification might be a way to develop individualized therapeutic concepts. Our goal is to review current knowledge of the pathophysiology of peripheral neuropathic pain, particularly painful diabetic neuropathy. We discuss state-of-the-art clinical assessment, validity of diagnostic and screening tools, and recommendations for the management of diabetic neuropathic pain including approaches towards personalized pain management. We also propose a research agenda for translational research including patient stratification for clinical trials and improved preclinical models in relation to current knowledge of underlying mechanisms.

Synergistic symptom-specific effects of ketorolac-tramadol and ketorolac-pregabalin in a rat model of peripheral neuropathy

BACKGROUND

Although current neuropathic pain treatment guidelines do not recommend the use of nonsteroidal anti-inflammatory drugs (NSAIDs), whether NSAIDs can serve as a useful adjuvant to conventional multimodal therapy remains unclear.

METHODS

The spared nerve injury (SNI) rats rapidly developed profound and long-lasting spontaneous and evoked pain behaviors, including mechanical and cold allodynia of the ipsilateral hind paw. At day 5, we first characterized the nociceptive responses to ketorolac, tramadol, pregabalin, and their combinations.

RESULTS

We found that tramadol and pregabalin exerted dose-dependent analgesic effects on both spontaneous and evoked behaviors. However, ketorolac alone did not suppress any behaviors regardless of the dose. Ketorolac-tramadol and ketorolac-pregabalin produced variable degrees of additive suppression of spontaneous and evoked behavioral responses. Cold allodynia was profoundly diminished after ketorolac was added to ineffective pregabalin or tramadol. Mechanical allodynia was markedly attenuated by ketorolac-pregabalin but less so by ketorolac-tramadol mixtures.

CONCLUSION

Our data demonstrated that an NSAID alone failed to relieve spontaneous or evoked pain behaviors in the rat SNI model, but when combined with a weak opioid and α-2-δ-ligand produced a profound synergistic analgesic effect on cold allodynia and discrepant efficacy for mechanical allodynia and spontaneous pain.

Benzothiophenes as Potent Analgesics Against Neuropathic Pain

Neuropathic pain arises because of neuronal injury. Unlike inflammatory pain which can be managed by classical nonsteroid anti-inflammatory drugs (NSAIDs), neuropathic pain is difficult to treat. The classical NSAIDs work through inhibition of cyclooxygenase 2 (COX2) enzyme. However, COX2 inhibitors are insufficient to treat neuropathic pain. Hence, it becomes important to explore for novel molecules acting through cell surface molecules like ion channels, for the treatment of neuropathic pain. We investigated multiple bromobenzothiophene carboxamides for their efficacy against neuropathic pain. Interestingly, AS6 was found to be very effective in treating neuropathic pain through inhibition of Kv4.3 ion channel. AS6 also reduced the COX2 overexpression associated with neuropathic pain. These results as well as results from our previous study indicate that AS6 can be a potent antinociceptive agent against both inflammatory and neuropathic pain.

Monoamines as Drug Targets in Chronic Pain: Focusing on Neuropathic Pain

Monoamines are involved in regulating the endogenous pain system and indeed, peripheral and central monoaminergic dysfunction has been demonstrated in certain types of pain, particularly in neuropathic pain. Accordingly, drugs that modulate the monaminergic system and that were originally designed to treat depression are now considered to be first line treatments for certain types of neuropathic pain (e.g., serotonin and noradrenaline (and also dopamine) reuptake inhibitors). The analgesia induced by these drugs seems to be mediated by inhibiting the reuptake of these monoamines, thereby reinforcing the descending inhibitory pain pathways. Hence, it is of particular interest to study the monoaminergic mechanisms involved in the development and maintenance of chronic pain. Other analgesic drugs may also be used in combination with monoamines to facilitate descending pain inhibition (e.g., gabapentinoids and opioids) and such combinations are often also used to alleviate certain types of chronic pain. By contrast, while NSAIDs are thought to influence the monoaminergic system, they just produce consistent analgesia in inflammatory pain. Thus, in this review we will provide preclinical and clinical evidence of the role of monoamines in the modulation of chronic pain, reviewing how this system is implicated in the analgesic mechanism of action of antidepressants, gabapentinoids, atypical opioids, NSAIDs and histaminergic drugs.

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

The upcoming 11th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD) of the World Health Organization (WHO) offers a unique opportunity to improve the representation of painful disorders. For this purpose, the International Association for the Study of Pain (IASP) has convened an interdisciplinary task force of pain specialists. Here, we present the case for a reclassification of nervous system lesions or diseases associated with persistent or recurrent pain for ≥3 months. The new classification lists the most common conditions of peripheral neuropathic pain: trigeminal neuralgia, peripheral nerve injury, painful polyneuropathy, postherpetic neuralgia, and painful radiculopathy. Conditions of central neuropathic pain include pain caused by spinal cord or brain injury, poststroke pain, and pain associated with multiple sclerosis. Diseases not explicitly mentioned in the classification are captured in residual categories of ICD-11. Conditions of chronic neuropathic pain are either insufficiently defined or missing in the current version of the ICD, despite their prevalence and clinical importance. We provide the short definitions of diagnostic entities for which we submitted more detailed content models to the WHO. Definitions and content models were established in collaboration with the Classification Committee of the IASP's Neuropathic Pain Special Interest Group (NeuPSIG). Up to 10% of the general population experience neuropathic pain. The majority of these patients do not receive satisfactory relief with existing treatments. A precise classification of chronic neuropathic pain in ICD-11 is necessary to document this public health need and the therapeutic challenges related to chronic neuropathic pain.

Consensus Guidelines on the Use of Intravenous Ketamine Infusions for Chronic Pain From the American Society of Regional Anesthesia and Pain Medicine, the American Academy of Pain Medicine, and the American Society of Anesthesiologists

BACKGROUND

Over the past 2 decades, the use of intravenous ketamine infusions as a treatment for chronic pain has increased dramatically, with wide variation in patient selection, dosing, and monitoring. This has led to a chorus of calls from various sources for the development of consensus guidelines.

METHODS

In November 2016, the charge for developing consensus guidelines was approved by the boards of directors of the American Society of Regional Anesthesia and Pain Medicine and, shortly thereafter, the American Academy of Pain Medicine. In late 2017, the completed document was sent to the American Society of Anesthesiologists' Committees on Pain Medicine and Standards and Practice Parameters, after which additional modifications were made. Panel members were selected by the committee chair and both boards of directors based on their expertise in evaluating clinical trials, past research experience, and clinical experience in developing protocols and treating patients with ketamine. Questions were developed and refined by the committee, and the groups responsible for addressing each question consisted of modules composed of 3 to 5 panel members in addition to the committee chair. Once a preliminary consensus was achieved, sections were sent to the entire panel, and further revisions were made. In addition to consensus guidelines, a comprehensive narrative review was performed, which formed part of the basis for guidelines.

RESULTS

Guidelines were prepared for the following areas: indications; contraindications; whether there was evidence for a dose-response relationship, or a minimum or therapeutic dose range; whether oral ketamine or another N-methyl-D-aspartate receptor antagonist was a reasonable treatment option as a follow-up to infusions; preinfusion testing requirements; settings and personnel necessary to administer and monitor treatment; the use of preemptive and rescue medications to address adverse effects; and what constitutes a positive treatment response. The group was able to reach consensus on all questions.

CONCLUSIONS

Evidence supports the use of ketamine for chronic pain, but the level of evidence varies by condition and dose range. Most studies evaluating the efficacy of ketamine were small and uncontrolled and were either unblinded or ineffectively blinded. Adverse effects were few and the rate of serious adverse effects was similar to placebo in most studies, with higher dosages and more frequent infusions associated with greater risks. Larger studies, evaluating a wider variety of conditions, are needed to better quantify efficacy, improve patient selection, refine the therapeutic dose range, determine the effectiveness of nonintravenous ketamine alternatives, and develop a greater understanding of the long-term risks of repeated treatments.

Curcumin alleviates pain and improves cognitive impairment in a rat model of cobra venom-induced trigeminal neuralgia

Background

Cognitive impairment is a common complication in patients with chronic neuropathic pain, without effective therapy. Recent works have indicated that curcumin (Cur) possesses antinociceptive and neuroprotective potentials, suggesting its possible effectiveness for the treatment of this complication.

Objective

The aim of this study was to explore the effects of Cur on pain behaviors and cognitive impairment in rats with cobra venom-induced trigeminal neuralgia (TN).

Design

This is a randomized, controlled experiment.

Setting

This study was conducted at the Experimental Animal Center, Beijing Friendship Hospital, Capital Medical University.

Subjects

A total of 40 adult male Sprague Dawley rats were used in this study.

Methods

A cobra venom solution was injected into the sheath of infraorbital nerve. Cur was administered intragastrically at 45 mg/kg twice daily for 28 successive days from postoperative day 15. Mechanical allodynia was evaluated using von Frey filaments. Free behaviors were observed using video recording. Cognitive capacity was tested using the Morris water maze. Both morphology and ultrastructure of the CA1 hippocampal region were visualized using hematoxylin and eosin (HE) staining and transmission electron microscopy, respectively.

Results

Cur treatment reduced mechanical allodynia and face-grooming activities but increased exploratory activities and improved spatial learning and memory deficits. Microscopic examination revealed nucleus pyknosis, swollen organelles, and decreased synapse density in the CA1 hippocampal region after cobra venom injection. However, chronic Cur treatment reversed damage to hippocampal neurons and synapses.

Conclusion

Cur can alleviate pain, improve spatial learning and memory deficits, and restore the damage to hippocampal neurons and synapses in cobra venom-induced TN rats. Cur may be useful as an adjuvant to treat chronic neuropathic pain-induced cognitive deficits.

Neuropathic pain is not adequately treated in the older general population: Results from the KORA F4 survey

PURPOSE

We evaluated the pharmacological treatment of distal sensorimotor polyneuropathy (DSPN) among older subjects from the general population.

METHODS

The study included subjects aged 61 to 82 years from the KORA F4 survey (2006-2008). DSPN was defined as the presence of bilaterally impaired foot-vibration perception and/or bilaterally impaired foot-pressure sensation. Pain intensity was assessed with the painDETECT questionnaire.

RESULTS

From the included 1076 older persons, 172 (16%) persons reported pain in the lower extremities and DSPN was present in 150 (14%) subjects. Forty-eight people with pain in the lower extremities reported DSPN. Only 38% of the subjects with DSPN reporting an average pain level of ≥4 during the past 4 weeks received medical treatment, predominantly nonsteroidal anti-inflammatory drugs (NSAIDs 20% and opioids 12%). The medication of choice for neuropathic pain, antidepressants, anticonvulsants, and opioids was relatively being underused. However, opioids and neuropathy preparations were prescribed preferably for subjects with painful DSPN.

CONCLUSIONS

In the older general population, only a small proportion of subjects with painful DSPN receive analgesic pharmacotherapy. Although not recommended by guidelines for the treatment of neuropathic pain, NSAIDs were the most frequently used class of analgesic drugs.

The antinociceptive effects of ferulic acid on neuropathic pain: involvement of descending monoaminergic system and opioid receptors

Neuropathic pain can be considered as a form of chronic stress that may share common neuropathological mechanism between pain and stress-related depression and respond to similar treatment. Ferulic acid (FA) is a major active component of angelica sinensis and has been reported to exert antidepressant-like effects; however, it remains unknown whether FA ameliorate chronic constriction injury (CCI)-induced neuropathic pain and the involvement of descending monoaminergic system and opioid receptors. Chronic treatment with FA (20, 40 and 80 mg/kg) ameliorated mechanical allodynia and thermal hyperalgesia in von Frey hair and hot plate tasks, accompanied by increasing spinal noradrenaline (NA) and serotonin (5-HT) levels. Subsequent study suggested that treatment of CCI animals with 40 and 80 mg/kg FA also inhibited spinal MAO-A levels. FA's effects on mechanical allodynia or thermal hyperalgesiawas blocked by 6-hydroxydopamine (6-OHDA) or p-chlorophenylalanine (PCPA) via pharmacological depletion of spinal noradrenaline or serotonin. Moreover, the anti-allodynic action of FA on mechanical stimuli was prevented by pre-treatment with beta2-adrenoceptor antagonist ICI 118,551, or by the delta-opioid receptor antagonist naltrindole. While the anti-hyperalgesia on thermal stimuli induced by FA was blocked by pre-treatment with 5-HT1A receptor antagonist WAY-100635, or with the irreversible mu-opioid receptor antagonist beta-funaltrexamine. These results suggest that the effect of FA on neuropathic pain is potentially mediated via amelioration of the descending monoaminergic system that coupled with spinal beta2- and 5-HT1A receptors and the downstream delta- and mu-opioid receptors differentially.

Acupuncture for neuropathic pain in adults

BACKGROUND

Neuropathic pain may be caused by nerve damage, and is often followed by changes to the central nervous system. Uncertainty remains regarding the effectiveness and safety of acupuncture treatments for neuropathic pain, despite a number of clinical trials being undertaken.

OBJECTIVES

To assess the analgesic efficacy and adverse events of acupuncture treatments for chronic neuropathic pain in adults.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, four Chinese databases, ClinicalTrials.gov and World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) on 14 February 2017. We also cross checked the reference lists of included studies.

SELECTION CRITERIA

Randomised controlled trials (RCTs) with treatment duration of eight weeks or longer comparing acupuncture (either given alone or in combination with other therapies) with sham acupuncture, other active therapies, or treatment as usual, for neuropathic pain in adults. We searched for studies of acupuncture based on needle insertion and stimulation of somatic tissues for therapeutic purposes, and we excluded other methods of stimulating acupuncture points without needle insertion. We searched for studies of manual acupuncture, electroacupuncture or other acupuncture techniques used in clinical practice (such as warm needling, fire needling, etc).

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by Cochrane. The primary outcomes were pain intensity and pain relief. The secondary outcomes were any pain-related outcome indicating some improvement, withdrawals, participants experiencing any adverse event, serious adverse events and quality of life. For dichotomous outcomes, we calculated risk ratio (RR) with 95% confidence intervals (CI), and for continuous outcomes we calculated the mean difference (MD) with 95% CI. We also calculated number needed to treat for an additional beneficial outcome (NNTB) where possible. We combined all data using a random-effects model and assessed the quality of evidence using GRADE to generate 'Summary of findings' tables.

MAIN RESULTS

We included six studies involving 462 participants with chronic peripheral neuropathic pain (442 completers (251 male), mean ages 52 to 63 years). The included studies recruited 403 participants from China and 59 from the UK. Most studies included a small sample size (fewer than 50 participants per treatment arm) and all studies were at high risk of bias for blinding of participants and personnel. Most studies had unclear risk of bias for sequence generation (four out of six studies), allocation concealment (five out of six) and selective reporting (all included studies). All studies investigated manual acupuncture, and we did not identify any study comparing acupuncture with treatment as usual, nor any study investigating other acupuncture techniques (such as electroacupuncture, warm needling, fire needling).One study compared acupuncture with sham acupuncture. We are uncertain if there is any difference between the two interventions on reducing pain intensity (n = 45; MD -0.4, 95% CI -1.83 to 1.03, very low-quality evidence), and neither group achieved 'no worse than mild pain' (visual analogue scale (VAS, 0-10) average score was 5.8 and 6.2 respectively in the acupuncture and sham acupuncture groups, where 0 = no pain). There was limited data on quality of life, which showed no clear difference between groups. Evidence was not available on pain relief, adverse events or other pre-defined secondary outcomes for this comparison.Three studies compared acupuncture alone versus other therapies (mecobalamin combined with nimodipine, and inositol). Acupuncture may reduce the risk of 'no clinical response' to pain than other therapies (n = 209; RR 0.25, 95% CI 0.12 to 0.51), however, evidence was not available for pain intensity, pain relief, adverse events or any of the other secondary outcomes.Two studies compared acupuncture combined with other active therapies (mecobalamin, and Xiaoke bitong capsule) versus other active therapies used alone. We found that the acupuncture combination group had a lower VAS score for pain intensity (n = 104; MD -1.02, 95% CI -1.09 to -0.95) and improved quality of life (n = 104; MD -2.19, 95% CI -2.39 to -1.99), than those receiving other therapy alone. However, the average VAS score of the acupuncture and control groups was 3.23 and 4.25 respectively, indicating neither group achieved 'no worse than mild pain'. Furthermore, this evidence was from a single study with high risk of bias and a very small sample size. There was no evidence on pain relief and we identified no clear differences between groups on other parameters, including 'no clinical response' to pain and withdrawals. There was no evidence on adverse events.The overall quality of evidence is very low due to study limitations (high risk of performance, detection, and attrition bias, and high risk of bias confounded by small study size) or imprecision. We have limited confidence in the effect estimate and the true effect is likely to be substantially different from the estimated effect.

AUTHORS' CONCLUSIONS

Due to the limited data available, there is insufficient evidence to support or refute the use of acupuncture for neuropathic pain in general, or for any specific neuropathic pain condition when compared with sham acupuncture or other active therapies. Five studies are still ongoing and seven studies are awaiting classification due to the unclear treatment duration, and the results of these studies may influence the current findings.

Pharmacological modulation of neuropathic pain-related depression of behavior: effects of morphine, ketoprofen, bupropion and [INCREMENT]9-tetrahydrocannabinol on formalin-induced depression of intracranial self-stimulation in rats

Neuropathic pain is often associated with behavioral depression. Intraplantar formalin produces sustained, neuropathy-associated depression of intracranial self-stimulation (ICSS) in rats. This study evaluated pharmacological modulation of formalin-induced ICSS depression. Rats with intracranial electrodes targeting the medial forebrain bundle responded for electrical brain stimulation in an ICSS procedure. Bilateral intraplantar formalin administration depressed ICSS for 14 days. Morphine (0.32-3.2 mg/kg), ketoprofen (0.1-10 mg/kg), bupropion (3.2-32 mg/kg), and [INCREMENT]9-tetrahydrocannabinol (THC; 0.32-3.2 mg/kg) were evaluated for their effectiveness to reverse formalin-induced depression of ICSS. Drug effects on formalin-induced mechanical allodynia were evaluated for comparison. Morphine and bupropion reversed both formalin-induced ICSS depression and mechanical allodynia, and effects on ICSS were sustained during repeated treatment. Ketoprofen failed to reverse either formalin effect. THC blocked mechanical allodynia, but decreased ICSS in control rats and exacerbated formalin-induced depression of ICSS. The failure of ketoprofen to alter formalin effects suggests that formalin effects result from neuropathy rather than inflammation. The effectiveness of morphine and bupropion to reverse formalin effects agrees with other evidence that these drugs block pain-depressed behavior in rats and relieve neuropathic pain in humans. The effects of THC suggest general behavioral suppression and do not support the use of THC to treat neuropathic pain.

Effect of Pregabalin and Diclofenac on tactile allodynia, mechanical hyperalgesia and pro inflammatory cytokine levels (IL-6, IL-1β) induced by chronic constriction injury of the infraorbital nerve in rats

The present study evaluated the effects of systemic pregabalin (PG) and diclofenac (Dic) on neuropathic orofacial pain induced by chronic constriction injury (CCI) of the infraorbital nerve (ION) and on the pro-inflammatory cytokines levels in the affected nerve. Fifty-four rats underwent left infra orbital nerve CCI, and 7 days after the procedure as the pain developed, the rats were randomly assigned to one of the treatment groups: PG 300, 30 or 10 mg/kg, Dic 10, 5 or 1 mg/kg or saline group (Sal) (n/group = 8). Addiitonal 8 rats served as naïve control group. Tactile-allodynia and Mechano-hyperalgesia were tested before the surgical procedure and at days 7, 8, and 9 postoperatively. On the 9th day, the rats were euthanized and the affected and contralateral sciatic nerves were harvested to assess IL-6 and IL-1β nerve levels employing enzyme linked immunosorbent assay (ELISA). Daily injection of PG (all doses) significantly reduced tactile-allodynia and mechano-hyperalgesia (p < .05) while Dic did not. On the 9th day, the ipsilateral nerve IL-6 levels were significantly decreased (p < .05) in the PG and DIC groups compared to the Sal group. IL-1β levels demonstrated a significant reduction (p < .05) in the PG group when compared to saline. These results suggest that PG but not Dic may be effective in reducing neuropathic orofacial pain. The mechanisms of action may be associated to some extent with reduction in IL-1β levels in the affected nerve.

Classification and Treatment of Chronic Neck Pain: A Longitudinal Cohort Study

BACKGROUND AND OBJECTIVES

Neck pain exerts a steep personal and socioeconomic toll, ranking as the fourth leading cause of disability. The principal determinant in treatment decisions is whether pain is neuropathic or nonneuropathic, as this affects treatment at all levels. Yet, no study has sought to classify neck pain in this manner.

METHODS

One hundred participants referred to an urban, academic military treatment facility with a primary diagnosis of neck pain were enrolled and followed up for 6 months. Pain was classified as neuropathic, possible neuropathic, or nonneuropathic using painDETECT and as neuropathic, mixed, or nociceptive by s-LANSS (self-completed Leeds Assessment of Neuropathic Symptoms and Signs pain scale) and physician designation. Based on previous studies, the intermediate possible neuropathic pain category was considered to be a mixed condition. The final classification was based on a metric combining all 3 systems, slightly weighted toward physician's judgment, which is considered the reference standard.

RESULTS

Fifty percent of participants were classified as having possible neuropathic pain, 43% as having nonneuropathic pain, and 7% with primarily neuropathic pain. Concordance was high between the various classification schemes, ranging from a low of 62% between painDETECT and physician designation for possible neuropathic pain, to 83% concordance between s-LANSS and the 2 other systems for neuropathic pain. Individuals with neuropathic pain reported higher levels of baseline disability, were more likely to have a coexisting psychiatric illness, and underwent surgery more frequently than other pain categories, but were also more likely to report greater reductions in disability after 6 months.

CONCLUSIONS

Although pure neuropathic pain comprised a small percentage of our cohort, 50% of our population consisted of mixed pain conditions containing a possible neuropathic component. There was significant overlap between the various classification schemes.

Non-steroidal anti-inflammatory drugs (NSAIDs) for chronic non-cancer pain in children and adolescents

BACKGROUND

Pain is a common feature of childhood and adolescence around the world, and for many young people, that pain is chronic. The World Health Organization guidelines for pharmacological treatments for children's persisting pain acknowledge that pain in children is a major public health concern of high significance in most parts of the world. While in the past pain was largely dismissed and was frequently left untreated, views on children's pain have changed over time, and relief of pain is now seen as important.We designed a suite of seven reviews on chronic non-cancer pain and cancer pain (looking at antidepressants, antiepileptic drugs, non-steroidal anti-inflammatory drugs, opioids, and paracetamol) in order to review the evidence for children's pain utilising pharmacological interventions.As the leading cause of morbidity in the world today, chronic disease (and its associated pain) is a major health concern. Chronic pain (that is pain lasting three months or longer) can arise in the paediatric population in a variety of pathophysiological classifications (nociceptive, neuropathic, or idiopathic) from genetic conditions, nerve damage pain, chronic musculoskeletal pain, and chronic abdominal pain, as well as for other unknown reasons.Non-steroidal anti-inflammatory drugs (NSAIDs) are used to treat pain, reduce fever, and for their anti-inflammation properties. They are commonly used within paediatric pain management. Non-steroidal anti-inflammatory drugs are currently licensed for use in Western countries, however they are not approved for infants under three months old. The main adverse effects include renal impairment and gastrointestinal issues. Common side effects in children include diarrhoea, headache, nausea, constipation, rash, dizziness, and abdominal pain.

OBJECTIVES

To assess the analgesic efficacy and adverse events of NSAIDs used to treat chronic non-cancer pain in children and adolescents aged between birth and 17 years, in any setting.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online, MEDLINE via Ovid, and Embase via Ovid from inception to 6 September 2016. We also searched the reference lists of retrieved studies and reviews, as well as online clinical trial registries.

SELECTION CRITERIA

Randomised controlled trials, with or without blinding, of any dose and any route, treating chronic non-cancer pain in children and adolescents, comparing any NSAID with placebo or an active comparator.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility. We planned to use dichotomous data to calculate risk ratio and number needed to treat for one additional event, using standard methods. We assessed GRADE and created three 'Summary of findings' tables.

MAIN RESULTS

We included seven studies with a total of 1074 participants (aged 2 to 18 years) with chronic juvenile polyarthritis or chronic juvenile rheumatoid arthritis. All seven studies compared an NSAID with an active comparator. None of the studies were placebo controlled. No two studies investigated the same type of NSAID compared with another. We were unable to perform a meta-analysis.Risk of bias varied. For randomisation and allocation concealment, one study was low risk and six studies were unclear risk. For blinding of participants and personnel, three studies were low risk and four studies were unclear to high risk. For blinding of outcome assessors, all studies were unclear risk. For attrition, four studies were low risk and three studies were unclear risk. For selective reporting, four studies were low risk, two studies were unclear risk, and one study was high risk. For size, three studies were unclear risk and four studies were high risk. For other potential sources of bias, seven studies were low risk. Primary outcomesThree studies reported participant-reported pain relief of 30% or greater, showing no statistically significant difference in pain scores between meloxicam and naproxen, celecoxib and naproxen, or rofecoxib and naproxen (P > 0.05) (low-quality evidence).One study reported participant-reported pain relief of 50% or greater, showing no statistically significant difference in pain scores between low-dose meloxicam (0.125 mg/kg) and high-dose meloxicam (0.25 mg/kg) when compared to naproxen 10 mg/kg (P > 0.05) (low-quality evidence).One study reported Patient Global Impression of Change, showing 'very much improved' in 85% of ibuprofen and 90% of aspirin participants (low-quality evidence). Secondary outcomesAll seven studies reported adverse events. Participants reporting an adverse event (one or more per person) by drug were: aspirin 85/202; fenoprofen 28/49; ibuprofen 40/45; indomethacin 9/30; ketoprofen 9/30; meloxicam 18/47; naproxen 44/202; and rofecoxib 47/209 (very low-quality evidence).All seven studies reported withdrawals due to adverse events. Participants withdrawn due to an adverse event by drug were: aspirin 16/120; celecoxib 10/159; fenoprofen 0/49; ibuprofen 0/45; indomethacin 0/30; ketoprofen 0/30; meloxicam 10/147; naproxen 17/285; and rofecoxib 3/209 (very low-quality evidence).All seven studies reported serious adverse events. Participants experiencing a serious adverse event by drug were: aspirin 13/120; celecoxib 5/159; fenoprofen 0/79; ketoprofen 0/30; ibuprofen 4/45; indomethacin 0/30; meloxicam 11/147; naproxen 10/285; and rofecoxib 0/209 (very low-quality evidence).There were few or no data for our remaining secondary outcomes: Carer Global Impression of Change; requirement for rescue analgesia; sleep duration and quality; acceptability of treatment; physical functioning as defined by validated scales; and quality of life as defined by validated scales (very low-quality evidence).We rated the overall quality of the evidence (GRADE rating) for our primary and secondary outcomes as very low because there were limited data from studies and no opportunity for a meta-analysis.

AUTHORS' CONCLUSIONS

We identified only a small number of studies, with insufficient data for analysis.As we could undertake no meta-analysis, we are unable to comment about efficacy or harm from the use of NSAIDs to treat chronic non-cancer pain in children and adolescents. Similarly, we cannot comment on our remaining secondary outcomes: Carer Global Impression of Change; requirement for rescue analgesia; sleep duration and quality; acceptability of treatment; physical functioning; and quality of life.We know from adult randomised controlled trials that some NSAIDs, such as ibuprofen, naproxen, and aspirin, can be effective in certain chronic pain conditions.

Non-steroidal anti-inflammatory drugs (NSAIDs) for cancer-related pain in children and adolescents

BACKGROUND

Pain is a common feature of childhood and adolescence around the world, and for many young people, that pain is chronic. The World Health Organization (WHO) guidelines for pharmacological treatments for persisting pain in children acknowledge that pain in children is a major public health concern of high significance in most parts of the world. Views on children's pain have changed over time and relief of pain is now seen as important. In the past, pain was largely dismissed and was frequently left untreated, and it was assumed that children quickly forgot about painful experiences.We designed a suite of seven reviews in chronic non-cancer pain and cancer pain (looking at antidepressants, antiepileptic drugs, non-steroidal anti-inflammatory drugs, opioids, and paracetamol as priority areas) to review the evidence for children's pain using pharmacological interventions.As one of the leading causes of mortality and morbidity for children and adolescents in the world today, childhood cancer (and its associated pain) is a major health concern. Specific mortality and morbidity data relating to children are not currently identified. All childhood cancer rates are on the rise; for example, in the USA approximately 10,380 children aged under 15 years were expected to be diagnosed with cancer by the end of 2016. However, with survival rates also increasing, over 80% of paediatric cancer patients are expected to survive for five years or more, thus identifying the need to address pain management in this population.Cancer pain in infants, children, and adolescents is primarily nociceptive pain with negative long term effects. Cancer-related pain is generally caused directly by the tumour itself such as compressing on the nerve or inflammation of the organs. Cancer-related pain generally occurs as a result of perioperative procedures, nerve damage caused by radiation or chemotherapy treatments, or mucositis. However, this review focused on pain caused directly by the tumour itself such as nerve infiltration, external nerve compression, and other inflammatory events.Non-steroidal anti-inflammatory drugs (NSAIDs) are used to treat pain, reduce fever, and for their anti-inflammatory properties. They are commonly used within paediatric pain management. NSAIDs are currently licensed for use in western countries, however not approved for infants aged under three months. Primary adverse effects include gastrointestinal issues and possible renal impairment with long term use. Other adverse effects in children include diarrhoea, headache, nausea, constipation, rash, dizziness, and abdominal pain.

OBJECTIVES

To assess the analgesic efficacy, and adverse events, of non-steroidal anti-inflammatory drugs (NSAIDs) used to treat cancer-related pain in children and adolescents aged from birth and 17 years, in any setting.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online, MEDLINE via Ovid, and Embase via Ovid from inception to 21 February 2017. We also searched the reference lists of retrieved studies and reviews, and searched online clinical trial registries.

SELECTION CRITERIA

Randomised, double-blind trials of any dose, and any route, treating cancer-related pain in children and adolescents, comparing NSAIDs with placebo or an active comparator.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility. We planned to use dichotomous data to calculate risk ratio and number needed to treat for one additional event, using standard methods. We assessed GRADE (Grading of Recommendations Assessment, Development and Evaluation) and planned to create a 'Summary of findings' table.

MAIN RESULTS

No studies were eligible for inclusion in this review (very low quality evidence). We downgraded the quality of evidence by three levels due to the lack of data reported for any outcome.

AUTHORS' CONCLUSIONS

There is no evidence from randomised controlled trials that non-steroidal anti-inflammatory drugs (NSAIDs) reduce cancer-related pain in children and adolescents. This means that no reliance or conclusions can be made about efficacy or harm in the use of NSAIDs to treat chronic cancer-related pain in children and adolescents.

Microglial TNFα Induces COX2 and PGI2 Synthase Expression in Spinal Endothelial Cells during Neuropathic Pain

Prostaglandins (PGs) are typical lipid mediators that play a role in homeostasis and disease. They are synthesized from arachidonic acid by cyclooxygenase 1 (COX1) and COX2. Although COX2 has been reported to be upregulated in the spinal cord after nerve injury, its expression and functional roles in neuropathic pain remain unclear. In this study, we investigated the expression of Cox2, PGI2 synthase (Pgis), and prostaglandin I2 receptor (IP receptor) mRNA in the rat spinal cord after spared nerve injury (SNI). Levels of Cox2 and Pgis mRNA increased in endothelial cells from 24 to 48 h after nerve injury. IP receptor mRNA was constitutively expressed in dorsal horn neurons. A COX2 inhibitor and IP receptor antagonists attenuated pain behavior in the early phase of neuropathic pain. Furthermore, we examined the relationship between COX2 and tumor necrosis factor-α (TNFα) in the spinal cord of a rat SNI model. Levels of TNFα mRNA transiently increased in the spinal microglia 24 h after SNI. The TNF receptors Tnfr1 and Tnfr2 mRNA were colocalized with COX2. Intrathecal injection of TNFα induced Cox2 and Pgis mRNA expression in endothelial cells. These results revealed that microglia-derived TNFα induced COX2 and PGIS expression in spinal endothelial cells and that endothelial PGI2 played a critical role in neuropathic pain via neuronal IP receptor. These findings further suggest that the glia–endothelial cell interaction of the neurovascular unit via transient TNFα is involved in the generation of neuropathic pain.

Oral nonsteroidal anti-inflammatory drugs for fibromyalgia in adults

BACKGROUND

Oral nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used in the treatment of pain in fibromyalgia, despite being considered not to be effective.

OBJECTIVES

To assess the analgesic efficacy, tolerability (drop-out due to adverse events), and safety (serious adverse events) of oral nonsteroidal anti-inflammatory drugs for fibromyalgia in adults.

SEARCH METHODS

We searched CENTRAL, MEDLINE, and Embase for randomised controlled trials from inception to January 2017. We also searched the reference lists of retrieved studies and reviews, and online clinical trial registries.

SELECTION CRITERIA

We included randomised, double-blind trials of two weeks' duration or longer, comparing any oral NSAID with placebo or another active treatment for relief of pain in fibromyalgia, with subjective pain assessment by the participant.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality and potential bias. Primary outcomes were participants with substantial pain relief (at least 50% pain relief over baseline or very much improved on Patient Global Impression of Change scale (PGIC)) or moderate pain relief (at least 30% pain relief over baseline or much or very much improved on PGIC), serious adverse events, and withdrawals due to adverse events; secondary outcomes were adverse events, withdrawals due to lack of efficacy, and outcomes relating to sleep, fatigue, and quality of life. Where pooled analysis was possible, we used dichotomous data to calculate risk difference (RD) and number needed to treat for an additional beneficial outcome (NNT), using standard methods. We assessed the quality of the evidence using GRADE and created a 'Summary of findings' table.

MAIN RESULTS

Our searches identified six randomised, double-blind studies involving 292 participants in suitably characterised fibromyalgia. The mean age of participants was between 39 and 50 years, and 89% to 100% were women. The initial pain intensity was around 7/10 on a 0 to 10 pain scale, indicating severe pain. NSAIDs tested were etoricoxib 90 mg daily, ibuprofen 2400 mg daily, naproxen 1000 mg daily, and tenoxicam 20 mg daily; 146 participants received NSAID and 146 placebo. The duration of treatment in the double-blind phase varied between three and eight weeks.Not all studies reported all the outcomes of interest. Analyses consistently showed no significant difference between NSAID and placebo: substantial benefit (at least 50% pain intensity reduction) (risk difference (RD) -0.07 (95% confidence interval (CI) -0.18 to 0.04) 2 studies, 146 participants; moderate benefit (at least 30% pain intensity reduction) (RD -0.04 (95% CI -0.16 to 0.08) 3 studies, 192 participants; withdrawals due to adverse events (RD 0.04 (95% CI -0.02 to 0.09) 4 studies, 230 participants; participants experiencing any adverse event (RD 0.08 (95% CI -0.03 to 0.19) 4 studies, 230 participants; all-cause withdrawals (RD 0.03 (95% CI -0.07 to 0.14) 3 studies, 192 participants. There were no serious adverse events or deaths. Although most studies had some measures of health-related quality of life, fibromyalgia impact, or other outcomes, none reported the outcomes beyond saying that there was no or little difference between the treatment groups.We downgraded evidence on all outcomes to very low quality, meaning that this research does not provide a reliable indication of the likely effect. The likelihood that the effect could be substantially different is very high. This is based on the small numbers of studies, participants, and events, as well as other deficiencies of reporting study quality allowing possible risks of bias.

AUTHORS' CONCLUSIONS

There is only a modest amount of very low-quality evidence about the use of NSAIDs in fibromyalgia, and that comes from small, largely inadequate studies with potential risk of bias. That bias would normally be to increase the apparent benefits of NSAIDs, but no such benefits were seen. Consequently, NSAIDs cannot be regarded as useful for treating fibromyalgia.

Non‐steroidal anti‐inflammatory drugs (NSAIDs) for chronic non‐cancer pain in children and adolescents

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To assess the analgesic efficacy, and adverse events, of NSAIDs used to treat chronic non‐cancer pain in children and adolescents aged between birth and 17 years, in any setting.

Prophylactic L-arginine and ibuprofen delay the development of tactile allodynia and suppress spinal miR-155 in a rat model of diabetic neuropathy

Diabetic neuropathy (DN) is a common complication of diabetes mellitus that is hardly reversible at the late stages. Since treatment of neuropathic pain is predominantly symptomatic, a prophylactic measure would be useful. Both ibuprofen and L-arginine exert antiallodynic effects on chronic constriction injury (CCI)-induced cold allodynia. Furthermore, ibuprofen is effective in CCI-induced mechanical allodynia. The aim of the study was to assess the antiallodynic effect of prophylactic ibuprofen and L-arginine in streptozotocin-induced DN in rats and to further investigate the role of spinal miR-155 and nitric oxide (NO) in this effect. Tactile allodynia was assessed weekly by von Frey filaments. Oral daily administration of ibuprofen, L-arginine and their combination, for 4 weeks starting 1 week after streptozotocin injection (ie, before the development of tactile allodynia), resulted in a significant decrease of tactile allodynia compared with the control diabetic group. This was evident in the fifth week of the experiment. The 3 treatments prevented the decrease in muscle fiber diameter and epidermal thickness, seen in the control diabetic group. Furthermore, ibuprofen, L-arginine and their combination prevented the increase in the spinal NO level and miRNA-155, seen in the control diabetic group. In conclusion, both ibuprofen and L-arginine delayed the development of behavioral and histologic changes of DN, with concomitant suppression of spinal miR-155 and NO level. L-arginine being tolerable may be useful prophylactically in diabetic patients.

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.

HCN2 ion channels: basic science opens up possibilities for therapeutic intervention in neuropathic pain

Nociception — the ability to detect painful stimuli — is an invaluable sense that warns against present or imminent damage. In patients with chronic pain, however, this warning signal persists in the absence of any genuine threat and affects all aspects of everyday life. Neuropathic pain, a form of chronic pain caused by damage to sensory nerves themselves, is dishearteningly refractory to drugs that may work in other types of pain and is a major unmet medical need begging for novel analgesics. Hyperpolarisation-activated cyclic nucleotide (HCN)-modulated ion channels are best known for their fundamental pacemaker role in the heart; here, we review data demonstrating that the HCN2 isoform acts in an analogous way as a ‘pacemaker for pain’, in that its activity in nociceptive neurons is critical for the maintenance of electrical activity and for the sensation of chronic pain in pathological pain states. Pharmacological block or genetic deletion of HCN2 in sensory neurons provides robust pain relief in a variety of animal models of inflammatory and neuropathic pain, without any effect on normal sensation of acute pain. We discuss the implications of these findings for our understanding of neuropathic pain pathogenesis, and we outline possible future opportunities for the development of efficacious and safe pharmacotherapies in a range of chronic pain syndromes.

Painful neuropathy: Mechanisms

Painful neuropathy, like the other complications of diabetes, is a growing healthcare concern. Unfortunately, current treatments are of variable efficacy and do not target underlying pathogenic mechanisms, in part because these mechanisms are not well defined. Rat and mouse models of type 1 diabetes are frequently used to study diabetic neuropathy, with rats in particular being consistently reported to show allodynia and hyperalgesia. Models of type 2 diabetes are being used with increasing frequency, but the current literature on the progression of indices of neuropathic pain is variable and relatively few therapeutics have yet been developed in these models. While evidence for spontaneous pain in rodent models is sparse, measures of evoked mechanical, thermal and chemical pain can provide insight into the pathogenesis of the condition. The stocking and glove distribution of pain tantalizingly suggests that the generator site of neuropathic pain is found within the peripheral nervous system. However, emerging evidence demonstrates that amplification in the spinal cord, via spinal disinhibition and neuroinflammation, and also in the brain, via enhanced thalamic activity or decreased cortical inhibition, likely contribute to the pathogenesis of painful diabetic neuropathy. Several potential therapeutic strategies have emerged from preclinical studies, including prophylactic treatments that intervene against underlying mechanisms of disease, treatments that prevent gains of nociceptive function, treatments that suppress enhancements of nociceptive function, and treatments that impede normal nociceptive mechanisms. Ongoing challenges include unraveling the complexity of underlying pathogenic mechanisms, addressing the potential disconnect between the perceived location of pain and the actual pain generator and amplifier sites, and finding ways to identify which mechanisms operate in specific patients to allow rational and individualized choice of targeted therapies.

SCISSOR-Spinal Cord Injury Study on Small molecule-derived Rho inhibition: a clinical study protocol

INTRODUCTION

The approved analgesic and anti-inflammatory drugs ibuprofen and indometacin block the small GTPase RhoA, a key enzyme that impedes axonal sprouting after axonal damage. Inhibition of the Rho pathway in a central nervous system-effective manner requires higher dosages compared with orthodox cyclooxygenase-blocking effects. Preclinical studies on spinal cord injury (SCI) imply improved motor recovery after ibuprofen/indometacin-mediated Rho inhibition. This has been reassessed by a meta-analysis of the underlying experimental evidence, which indicates an overall effect size of 20.2% regarding motor outcome achieved after ibuprofen/indometacin treatment compared with vehicle controls. In addition, ibuprofen/indometacin may also limit sickness behaviour, non-neurogenic systemic inflammatory response syndrome (SIRS), neuropathic pain and heterotopic ossifications after SCI. Consequently, 'small molecule'-mediated Rho inhibition after acute SCI warrants clinical investigation.

METHODS AND ANALYSIS

Protocol of an investigator-initiated clinical open-label pilot trial on high-dose ibuprofen treatment after acute traumatic, motor-complete SCI. A sample of n=12 patients will be enrolled in two cohorts treated with 2400 mg/day ibuprofen for 4 or 12 weeks, respectively. The primary safety end point is an occurrence of serious adverse events, primarily gastroduodenal bleedings. Secondary end points are pharmacokinetics, feasibility and preliminary effects on neurological recovery, neuropathic pain and heterotopic ossifications. The primary safety analysis is based on the incidence of severe gastrointestinal bleedings. Additional analyses will be mainly descriptive and casuistic.

ETHICS AND DISSEMINATION

The clinical trial protocol was approved by the responsible German state Ethics Board, and the Federal Institute for Drugs and Medical Devices. The study complies with the Declaration of Helsinki, the principles of Good Clinical Practice and all further applicable regulations. This safety and pharmacokinetics trial informs the planning of a subsequent randomised controlled trial. Regardless of the result of the primary and secondary outcome assessments, the clinical trial will be reported as a publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT02096913; Pre-results.

Does menopausal hormone therapy (MHT), exercise or a combination of both, improve pain and function in post-menopausal women with greater trochanteric pain syndrome (GTPS)? A randomised controlled trial

BACKGROUND

Greater trochanteric pain syndrome (GTPS) is pathology in the gluteus medius and minimus tendons and trochanteric bursa that causes debilitating tendon pain and dysfunction, particularly in post-menopausal women. Limited evidence in clinical studies suggests hormone changes after menopause may have a negative effect on tendon. This protocol describes a randomised controlled trial comparing the effectiveness of menopausal hormone therapy (MHT) and exercise therapy in reducing pain and dysfunction associated with GTPS in post-menopausal women.

METHOD

One hundred and sixteen post-menopausal women will be recruited and randomised to receive one of two exercise programs (sham or targeted intervention exercise) and transdermal creams (MHT cream containing oestradiol 50mcg and norethisterone acetate 140mcg or placebo cream). Interventions will be 12-weeks in duration and outcomes will be examined at baseline, 12-weeks and 52-weeks. The primary outcome measure will be the VISA-G questionnaire and secondary outcomes measures will include three hip pain and function questionnaires (Hip dysfunction and Osteoarthritis Outcome Score, Oxford Hip Score, Lateral Hip Pain questionnaire), a global change in symptom questionnaire (using a 15-point Likert scale) and a quality of life measure (AQoL-8D questionnaire). Data will be analysed using the intention to treat principle.

DISCUSSION

This study is the first randomised controlled trial to compare the effectiveness of menopausal hormone therapy therapy alone, and with the combination of exercise therapy, to treat pain and dysfunction associated with GTPS. This study has been pragmatically designed to ensure that the interventions in this study can be integrated into policy and clinical practice if found to be effective in the treatment of GTPS in post-menopausal women. If successful, there is potential for this treatment regimen to be explored in future studies of other persistent tendon conditions in the post-menopausal population.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12614001157662 Registered 31 October 2014.

Postherpetic neuralgia

Questions from patients about pain conditions and analgesic pharmacotherapy and responses from authors are presented to help educate patients and make them more effective self-advocates. This article is about postherpetic neuralgia (PHN), a devastating complication following reactivation of the varicella-zoster virus. The answer offers an explanation for why this pain occurs, and cites literature regarding its incidence and treatment.

Antinociceptive activity of astragaloside IV in the animal model of chronic constriction injury

To investigate the applicability of astragaloside IV (AG) for the treatment of refractory neuropathic pain, we systemically evaluated the antinociceptive activity of AG in the animal model of chronic constriction injury. We studied behaviors, electrophysiology, and biochemistry from day 2 to day 23 after the surgery. We found that when administered intraperitoneally at the dose of 60 mg/kg, AG caused significant inhibition of allodynia and hyperalgesia induced by mechanic and thermal stimuli as well as downregulation of the expressions of a series of proteins involved in mediating neuropathic pain in the dorsal root ganglia, such as P2X purinoceptor 3, glial cell-derived neurotrophic factor, glial cell-derived neurotrophic factor family receptor α1, and transient receptor potential cation channel subtypes A1 and V1. Further investigation showed that AG restored the nerve conduction velocity and the histological structure of the damaged sciatic nerve on day 23 after the surgery. Moreover, results from immunoelectron microscope showed that glial cell-derived neurotrophic factor family receptor α1 induced by AG could form a circular band in the myelin debris between the injured axons and Schwann cells, contributing toward restoration of the damaged nerve. In conclusion, in our animal model, AG effectively inhibited the neuropathic pain induced by chronic constriction injury.