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

The Role of Fat Grafting in Alleviating Neuropathic Pain: A Critical Review of the Literature

Background

Neuropathic pain is one of the more severe types of chronic pain and presents a great challenge as response to medical therapy remains often unpredictable. With the opioid epidemic and the search for ways to avoid narcotics, physicians are seeking other modalities to treat neuropathic pain. In recent years, surgeons have explored various surgical avenues to improve outcomes. The aim of this review was to evaluate the current clinical evidence regarding the efficacy of fat grafting for the treatment of neuropathic pain.

Methods

A critical review was conducted to examine the current clinical evidence of fat grafting as a therapy for neuropathic pain caused by neuromas, peripheral neuralgia, migraine and headaches, neuropathic scar pain, and postmastectomy pain syndrome.

Results

The precise mechanism role of fat grafting in modulating neuropathic pain remains unclear, but it appears to reduce pain levels through the anti-inflammatory effects of adipose-derived stem cells and mechanical cushioning by fat.

Conclusions

Fat grafting is an emerging therapy for chronic neuropathic pain of various etiologies. Although promising results have been reported, sample size and level of evidence of current studies are low. The encouraging results, however, are worthy of further clinical and scientific study. The minimally invasive nature of fat grafting and favorable risk profile make this an attractive therapy for neuropathic pain.

Effectiveness and tolerability of THC:CBD oromucosal spray as add-on measure in patients with severe chronic pain: analysis of 12-week open-label real-world data provided by the German Pain e-Registry

Objective: To evaluate effectiveness, tolerability and safety of an oromucosal spray containing Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), as add-on treatment in patients with severe chronic pain (SCP).

Methods: Exploratory analysis of anonymized 12-week routine/open-label data provided by the German Pain e-Registry (GPR) on adult SCP patients treated with THC:CBD oromucosal spray in 2017.

Results: Among those 30.228 cases documented in the GPR in 2017, 800 (2.6%; 57% female, mean ± SD age: 46.3±9.7 years) received a treatment with THC:CBD. All patients fulfilled the legislative preconditions for a treatment with cannabis as medicine as defined by the German Act Amending Narcotics and Other Regulations. THC:CBD-treatment was followed by an aggregated nine-factor symptom relief (ASR-9) improvement at end of week 12 vs baseline of 39.0±26.5% (95%-CI: 36.9–41.1, median: 42, range −41 to 85). A full ASR-9 response (ie, a 50%-improvement in all 9 factors) was found for 123 patients (15.4%), while 488 patients (56.0%) presented with an ≥50% improvement in at least 5 of 9 ASR factors. With a 54.9±17.2% (median: 56%, range: −6 to 85) improvement was significantly superior in the neuropathic pain subgroup (n=497, 62.1%) vs those with mixed (n=249, 31.1%; ASR-9: 18.2±12.0, median: 19, range: −12 to 42%) or nociceptive pain (n=54, 6.8%; ASR-9: −11.9±10.5, median: −11, range: −41% to 12%; p<0.001 for each). 159 patients (19.9%) reported at least one of 206 TEAEs, most of them of mild intensity (n=81.6%). Most frequently reported TEAEs were increased appetite (n=50, 6.3%) and dysgeusia (n=23, 2.9%). TEAE-related discontinuations were reported for 32 patients (4.0%). 113 (14.1%) patients discontinued due to inadequate pain relief, most of them with nociceptive pain (n=40, 74.1%), least with neuropathic pain (n=1, 0.2%; p<0.001).

Conclusion: THC:CBD oromucosal spray proved to be an effective and well-tolerated add-on treatment for patients with elsewhere refractory chronic pain – especially of neuropathic origin.

Intravenous lidocaine in the management of chronic peripheral neuropathic pain: a randomized-controlled trial

PURPOSE

Neuropathic pain, resulting from injury to the peripheral or central nervous system, is due to upregulation of aberrant sodium channels with neuronal hyperexcitability. Lidocaine blocks these channels and several studies show that intravenous (IV) lidocaine infusion provides significant relief in patients with chronic peripheral neuropathic pain in the short term (for up to six hours). Our objective was to determine if IV lidocaine provides significant pain relief and overall improvement in quality of life in the longer term (for up to four weeks).

METHODS

This single site randomized double-blind, crossover trial compared IV lidocaine infusion (5 mg·kg^-1) with active placebo infusion containing diphenhydramine (50 mg) in patients with chronic neuropathic pain of peripheral nerve origin of at least six months duration. The primary outcome was average pain intensity reduction from IV lidocaine relative to placebo at four weeks post-infusion. Secondary outcome measures included parameters of physical function, mood, and overall quality of life.

RESULTS

We enrolled 34 subjects in this trial-mostly with painful diabetic neuropathy and post-herpetic neuralgia. There were no significant differences between IV lidocaine and placebo infusions at any time point involving any of the outcome measures. Mean (standard deviation) pain intensity at week 4 for the placebo and lidocaine groups were not different [6.58 (1.97) vs 6.78 (1.56), respectively; between-group difference, 0.17; 95% confidence interval, - 0.50 to 0.84].

CONCLUSION

We found no significant long-term analgesic or quality of life benefit from IV lidocaine relative to control infusion for chronic peripheral neuropathic pain.

TRIAL REGISTRATION

clinicaltrials.gov (NCT01669967); registered 22 June, 2012.

Structural hybridization of pyrrolidine-based T-type calcium channel inhibitors and exploration of their analgesic effects in a neuropathic pain model

Highly effective and safe drugs for the treatment of neuropathic pain are urgently required and it was shown that blocking T-type calcium channels can be a promising strategy for drug development for neuropathic pain. We have developed pyrrolidine-based T-type calcium channel inhibitors by structural hybridization and subsequent assessment of in vitro activities against Ca_v3.1 and Ca_v3.2 channels. Profiling of in vitro ADME properties of compounds was also carried out. The representative compound 17h showed comparable in vivo efficacy to gabapentin in the SNL model, which indicates T-type calcium channel inhibitors can be developed as effective therapeutics for neuropathic pain.

TsNTxP, a non-toxic protein from Tityus serrulatus scorpion venom, induces antinociceptive effects by suppressing glutamate release in mice

Neuropathic pain is a common type of chronic pain caused by trauma or chemotherapy. However, this type of pain is undertreated. TsNTxP is a non-toxic protein isolated from the venom of the scorpion Tityus serrulatus, and it is structurally similar to neurotoxins that interact with voltage-gated sodium channels. However, the antinociceptive properties of this protein have not been characterized. The purpose of this study was to investigate the antinociceptive effects of TsNTxP in acute and neuropathic pain models. Male and female Swiss mice (25-30 g) were exposed to different models of acute pain (tail-flick test and nociception caused by capsaicin intraplantar injection) or neuropathic pain (chronic pain syndrome induced by paclitaxel or chronic constriction injury of the sciatic nerve). Hypersensitivity to mechanical or cold stimuli were evaluated in the models of neuropathic pain. The ability of TsNTxP to alter the release of glutamate in mouse spinal cord synaptosomes was also evaluated. The results showed that TsNTxP exerted antinociceptive effects in the tail-flick test to a thermal stimulus and in the intraplantar capsaicin administration model. Furthermore, TsNTxP was non-toxic and exerted antiallodynic effects in neuropathic pain models induced by chronic constriction injury of the sciatic nerve and administration of paclitaxel. TsNTxP reduced glutamate release from mouse spinal cord synaptosomes following stimulation with potassium chloride (KCl) or capsaicin. Thus, this T. serrulatus protein may be a promising non-toxic drug for the treatment of neuropathic pain.

Pain assessment in hospitalized spinal cord injured patients - a controlled cross-sectional study

Background and aims Following spinal cord injury (SCI), a majority of individuals may develop neuropathic pain, which further reduces quality of life. Pain is difficult to treat by medication; in fact, medication overuse may aggravate neuropathic pain in SCI by causing central sensitization (CS): a mechanism of hyper-reactivity of the dorsal horn neurons in the spinal cord with amplified cerebral pain response. The purpose of this study was to examine the presence of neuropathic pain and CS above the spinal lesion in SCI, and to investigate whether injury characteristics or medication influenced pain response. Methods Twenty-four SCI patients with various injury characteristics (eight subacute, traumatic injuries, eight chronic, traumatic injuries, eight non-traumatic injuries) and 12 able-bodied controls underwent sensory testing:pressure algometry, Von Frey filaments (sensitivity), and repetitive pinprick stimulation (pain windup). SCI participants also fulfilled a modified version of the McGill Pain Questionnaire. Data were analyzed regarding (i) SCI patients compared with controlgroup and (ii) SCI subgroup comparison (grouped by a) injury characteristics and (b) intake of analgesics, where low-medicated subgroup were prescribed only non-opioids and high-medicated potent opioids). Results Neuropathic pain was present in 21 of 24 SCI patients. Chronic and non-traumatic SCI patients reported considerably higher present pain intensity than sub-acute traumatic SCI patients on a five-point scale (3.13±0.99, 1.75±1.75 and 0.13±0.35, respectively, p<0.005). Reduced pressure pain detection thresholds (PPDT) were found in SCI patients at several supra-lesional anatomical points compared to controls. Contrarily, tactile detection thresholds were higher in SCI. SCI subgroup analyses showed that i) the low-medicated SCI subgroup displayed significantly lower PPDT compared to the high-medicated subgroup, ii) pain-windup was present in all subgroups although the sub-acute and non-traumatic subgroups displayed lesser pain windup than controls, and the chronic SCI subgroup mainly displayed higher pain windup. Conclusions The reduced PPDT found above lesion suggests the presence of CS in SCI. However, findings regarding SCI subgroup comparison did not support our hypothesis that more medication leads to increased CS. Implications The development of CS may complicate diagnosis and pain treatment following SCI. Prospective studies of SCI with a healthy control group are needed.

Decreased expression of lncRNA Malat1 in rat spinal cord contributes to neuropathic pain by increasing neuron excitability after brachial plexus avulsion

Purpose: Neuropathic pain (NP) is a challenging clinical problem due to its complex pathogenesis. In our previous study using microarray, we found that the levels of lncRNA Malat1 were decreased in the spinal cord of NP rat after brachial plexus avulsion, but its contribution to NP remain unclear. The purpose of this study was to investigate its role in the pathogenesis of NP.

Methods: In the NP model of complete brachial plexus avulsion rat, spinal cords were harvested, and fluorescence in situ hybridization (FISH) was used to test the spatial expression of Malat1 and qRT-PCR was used to confirm the quantitative expression of Malat1. In primary cultured neurons, Malat1 expression interfered with adenovirus. Spontaneous electric activities of neurons were tested using multi-electrode arrays and apoptosis of neurons was tested using TUNEL method. The change of intracellular calcium concentration was analyzed using calcium imaging method.

Results: Decreased Malat1 expression was confirmed using qRT-PCR, and Malat1 was identified in the cytoplasm of neurons in spinal cord, but not in glia. In vitro, the decrease of Malat1 resulted in an increase in the frequency of spontaneous electric activity in neurons but had no effect on neuronal apoptosis. Further analysis indicated during glutamate stimulation, the change of intracellular calcium concentration in neurons with downregulated Malat1 expression was significantly greater than that in normal neurons.

Conclusion: Reduced Malat1 expression may induce NP by increasing neuronal excitability in the spinal cord via regulation of calcium flux.

Inhibition of apoptosis signal-regulating kinase by paeoniflorin attenuates neuroinflammation and ameliorates neuropathic pain

BACKGROUND

Neuropathic pain is a serious clinical problem that needs to be solved urgently. ASK1 is an upstream protein of p38 and JNK which plays important roles in neuroinflammation during the induction and maintenance of chronic pain. Therefore, inhibition of ASK1 may be a novel therapeutic approach for neuropathic pain. Here, we aim to investigate the effects of paeoniflorin on ASK1 and neuropathic pain.

METHODS

The mechanical and thermal thresholds of rats were measured using the Von Frey test. Cell signaling was assayed using western blotting and immunohistochemistry.

RESULTS

Chronic constrictive injury (CCI) surgery successfully decreased the mechanical and thermal thresholds of rats and decreased the phosphorylation of ASK1 in the rat spinal cord. ASK1 inhibitor NQDI1 attenuated neuropathic pain and decreased the expression of p-p38 and p-JNK. Paeoniflorin mimicked ASK1 inhibitor NQDI1 and inhibited ASK1 phosphorylation. Paeoniflorin decreased the expression of p-p38 and p-JNK, delayed the progress of neuropathic pain, and attenuated neuropathic pain. Paeoniflorin reduced the response of astrocytes and microglia to injury, decreased the expression of IL-1β and TNF-α, and downregulated the expression of CGRP induced by CCI.

CONCLUSIONS

Paeoniflorin is an effective drug for the treatment of neuropathic pain in rats via inhibiting the phosphorylation of ASK1, suggesting it may be effective in patients with neuropathic pain.

Oral Lactobacillus reuteri LR06 or Bifidobacterium BL5b supplement do not produce analgesic effects on neuropathic and inflammatory pain in rats

BACKGROUND

Previous studies have reported that certain bacteria exert visceral antinociceptive activity in visceral pain and may also help to relieve neuropathic and inflammatory pain.

OBJECTIVE

The aim of this study was to explore the analgesic effect of Lactobacillus reuteri LR06 (LR06) or Bifidobacterium BL5b (BL5b) in chronic pain in vivo.

DESIGN

Rats were randomly assigned into four groups: sham, Chronic Constriction Injury (CCI)/Complete Freund's Adjuvant (CFA) + control, CCI/CFA + LR06, and CCI/CFA + BL5b. Rats from the probiotic groups were treated with 1 x 10⁹ cfu (LR06 or BL5b) daily through gavage for 14 days after a pain model was successfully established. Mechanical and thermal hyperalgesia were used to assess the analgesic effect of the probiotics. Iba1 was used to verify the microglial inflammatory reaction in the different groups.

RESULTS

The results showed that probiotics L. reuteri LR06 or Bifidobacterium BL5b had no significant antinociception effects in chronic pain rats. The chronic pain-induced activation of microglia (Iba1) was not relieved by probiotics in CCI/CFA-induced neuropathic or inflammatory pain rats.

CONCLUSION

Our results suggested that L. reuteri LR06 or Bifidobacterium BL5b had no antinociceptive effects on CCI-induced neuropathic pain and CFA-induced inflammatory pain in rats.

Diagnostic accuracy of upper limb neurodynamic tests for the assessment of peripheral neuropathic pain: A systematic review

BACKGROUND

Upper limb neurodynamic tests (ULNTs) are used to identify a neuropathic pain component in patients' presenting with arm and/or neck pain. Clinical tests with established diagnostic accuracy are required to not only to inform clinical management but also minimise costs associated with expensive medical investigations.

OBJECTIVE

To evaluate the role of ULNTs in assessment of peripheral neuropathic pain and to inform their value in clinical practice when assessing patients with arm and/or neck symptoms.

DESIGN

Systematic review was undertaken according to published guidelines, and reported in line with PRISMA-DTA.

METHOD

Key databases were searched up to 21/11/2017.

INCLUSION CRITERIA

Patient population experiencing arm and/or neck symptoms with suspected peripheral neuropathic involvement, studies that compared ULNT to a reference standard, any study design using primary diagnostic accuracy data. Two reviewers independently assessed risk of bias (ROB) using QUADAS-2. The overall quality of evidence was evaluated using GRADE.

RESULTS

Of eight included studies (n = 579), four were assessed as low ROB, although all had concerns regarding applicability. For carpal tunnel syndrome, ULNT1 sensitivity values ranged 0.4-0.93, specificity 0.13-0.93, positive likelihood ratio 0.86-3.67 and negative likelihood ratio 0.5-1.9. For cervical radiculopathy ULNT1 and the combined use of four ULNTs had sensitivity of 0.97 (95%CI 0.85-1.00) whereas the ULNT3 was the most specific (0.87, 95%CI 0.62-0.98). Positive likelihood ratio ranged 0.58-5.68 and negative likelihood ratio 0.12-1.62.

CONCLUSION

Based on the available evidence ULNTs cannot be utilised as a stand-alone test for the diagnosis of CTS. Limited evidence suggests that ULNTs may be clinically relevant for the diagnosis of CR, but only as a "ruling out" strategy. However, the overall quality of the body of evidence after applying the GRADE approach was low to very low across studies. Further higher quality research is needed to establish firm conclusions.

Hyperglycemia induces mechanical hyperalgesia and depolarization of the resting membrane potential of primary nociceptive neurons: Role of ATP-sensitive potassium channels

Cumulating data suggests that ion channel alterations in nociceptive neurons might be involved in the development of diabetic painful neuropathy. In the present study we investigated the involvement of ATP-sensitive potassium (K⁺_ATP) channels in the acute effect of high glucose solution in vitro and in vivo. High glucose concentrations depolarized cultured nociceptive neurons and depolarization was blocked by the K⁺_ATP opener, diazoxide or by insulin. Glucose injection at the rat dorsal root ganglia (L5) resulted in acute mechanical hyperalgesia that was blocked by diazoxide. Mannitol injection indicates that osmolarity changes are not responsible for glucose effect. Therefore, this study suggests that K⁺_ATP channels expressed in peripheral sensory neurons might be involved in the development of diabetic painful neuropathy. Since sulfonylureas, that act by blocking K⁺_ATP are used for diabetes treatment, it is important to evaluate the possible side effects of such drugs at primary sensory neurons.

Neuroinflammation and adult hippocampal neurogenesis in neuropathic pain and alkyl glycerol ethers treatment in aged mice

Neuropathic pain is a condition characterized by unpleasant sensory and emotional experiences associated with a number of diseases or injuries affecting the sensory system through various mechanisms. In this study, we focused on the impact of chronic neuropathic pain on the microglial state and hippocampal neurogenesis in aged mice. In addition, we examined the effects of alkyl glycerol ethers (AGE) treatment on behavioral parameters, hippocampal neuronal and microglial plasticity in aged C57BL/6 mice with neuropathic pain. For the induction of neuropathic pain, we used the model of chronic constriction injury (CCI) of the sciatic nerve. We observed painful behavior in animals subjected to CCI, expressed as a decrease in locomotor activity and the development of cold allodynia. A violation of working and long‑term memory was also observed. AGE administration reduced the severity of cold allodynia and prevented memory impairment. In addition to behavioral changes, neuropathic pain was accompanied by microglial activation, changes in the hippocampal production of pro‑ and anti‑inflammatory cytokines, as well as a decrease in neurogenesis. The administration of AGE prevented the neuropathic pain‑derived effects, including M1 microglial activation and neurogenesis disruption. However, in vitro experiments demonstrated the pro‑inflammatory activation of microglial cells, emphasizing the complexity of the mechanisms underlying the pharmacological effects of AGE. On the whole, the findings of this study demonstrate that AGE treatment prevented behavioral effects of neuropathic pain in mice, and AGE may thus have potential for use in the prevention or treatment of neuropathic pain cognitive and emotional effects. However, as the mechanisms underlying this type of pain are complex, further studies are required to determine the detailed pharmacological effects of AGE.

D2-like receptor agonist synergizes the μ-opioid agonist spinal antinociception in nociceptive, inflammatory and neuropathic models of pain in the rat

Opioids are potent analgesic drugs, but their use has been limited due to their side effects. Antinociceptive effects of D2-like receptor agonists such as quinpirole have been shown at the spinal cord level; however, their efficacy is not as high as that of opioids. Dopaminergic agonists are long-prescribed and well-tolerated drugs that have been useful to treat clinically and experimentally painful conditions. Because current pain treatments are not completely effective, the aim of this work was to determine if a D2-like receptor agonist improves the antinociceptive effects of a μ-opioid receptor agonist. Drugs were intrathecally administered in adult rats; mechanonociceptive and thermonociceptive tests were carried out. Intraplantar injection of complete Freund's adjuvant (CFA) and sciatic loose ligation (SLL) were used for inflammatory and neuropathic models of pain, respectively. In intact animals, D-Ala2, N-MePhe4, Gly-ol-enkephalin (DAMGO; a µ-opioid receptor agonist) increased the paw withdrawal latencies (PWL) in thermal and mechanical nociceptive tests in a dose-dependent manner. Quinpirole (D2-like receptor agonist) increased PWL only in mechanonociception. In the presence of quinpirole (1 nmol), the ED₅₀ of the mechanical antinociceptive effect of DAMGO was significantly decreased (8-fold). Coadministration of 1 nmol quinpirole and 30 pmol DAMGO completely reversed hyperalgesia in the CFA model, whereas 100 pmol DAMGO plus 1 nmol quinpirole reversed the allodynia in the SLL model. This work offers evidence about a synergistic antinociceptive effect between opioidergic and dopaminergic drugs. This combination may relieve painful conditions resistant to conventional treatments, and it may reduce the adverse effects of chronic opioid administration.

Spinal α2 -adrenoceptors and neuropathic pain modulation; therapeutic target

Neuropathic pain can arise from disease or damage to the nervous system. The most common symptoms of neuropathic pain include spontaneous pain, allodynia, and hyperalgesia. There is still limited knowledge about the factors that initiate and maintain neuropathic pain. However, ample evidence has proved the antinociceptive role of spinal α-adrenoceptors following nerve injury. It is well-documented that noradrenergic descending pathways from supraspinal loci exert an inhibitory influence on the spinal cord nociceptive neurons, mostly through the activation of spinal α₂ -adrenoceptors. This, in turn, suppresses transmission of pain input and the hyperexcitability of spinal dorsal horn neurons. There is considerable evidence demonstrating that spinal application of α₂ -adrenoceptor agonists leads to analgesic effects in animal models of neuropathic pain. Today, despite the recent rapid development of neuroscience and drug discovery, effective drugs with clear basic mechanisms have remained a mystery. Here, we give an overview of the cellular mechanisms through which brainstem adrenergic descending inhibitory processing can alter spinal pain transmission to the higher centres, and how these pathways change in neuropathic pain conditions focusing on the role of spinal α₂ -adrenoceptors in the spinal dorsal horn. We then suggest that α₂ -adrenoceptor agonist may be useful to treat neuropathic pain. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Nonmigraine Headache and Facial Pain

The vast majority of headache patients encountered in the outpatient general medicine setting will be diagnosed with a primary headache disorder, mostly migraine or tension-type headache. Other less common primary headaches and secondary headaches, related to or caused by another condition, are the topic of this article. Nonmigraine primary headaches include trigeminal autonomic cephalalgias, primarily cluster headache; facial pain, primarily trigeminal neuralgia; and miscellaneous headache syndromes, such as hemicrania continua and new daily persistent headache. Selected secondary headaches related to vascular disease, cerebrospinal fluid dynamics, and inflammatory conditions are also reviewed.

[Cannabis and cannabinoids-easier access, hype and disappointment : What has been confirmed in therapy?]

BACKGROUND

Cannabis products are being increasingly liberalized all over the world and there is a huge interest in cannabis-based medicine.

OBJECTIVES

Presentation of current studies on the efficacy of different cannabis-based medicine for the treatment of various diseases CURRENT DATA: In German pharmaceutical legislation, nabiximols is approved for the treatment of moderate to severe therapy-resistant spasticity in multiple sclerosis and nabilone is approved for the treatment of therapy-resistant chemotherapy-associated nausea and vomiting. In case of therapy failure cannabinoids, as part of an individual therapeutic attempt, may be considered for the treatment of chronic pain (neuropathic pain, cancer pain, non-neuropathic noncancer pain), cachexia in human immunodeficiency virus as well as for Dravet and Lennox-Gastaut syndrome. From the authors' perspective there is not enough evidence for the use in chemotherapy-associated nausea and vomiting and chronic non-neuropathic pain.

CONCLUSIONS

Currently, a wide use of cannabinoids does not seem probable in the near future. Further studies involving more patients and evaluating long-term effects are necessary.

Psychotherapeutic interventions for chronic pain: Evidence, rationale, and advantages

BACKGROUND

Long-term use of opioids to treat chronic pain incurs serious risks for the individual-including misuse, abuse, addiction, overdose and death-as well as creating economic, social, and cultural impacts on society as a whole. Chronic pain and substance use disorders are often co-morbid with other medical problems and at the present time, primary care clinicians serve most of this population. Primary care clinicians would benefit from having alternatives to opioids to employ in treating such patients.

METHOD

We electronically searched different medical databases for studies evaluating the effect of nonpharmacological treatments for chronic pain. We describe alternative approaches for the treatment of chronic pain and cite studies that provide substantial evidence in favor of the use of these treatments.

RESULTS

Cognitive behavioral therapy, acceptance and commitment therapy, and mindfulness-based programs have well-documented effectiveness for the treatment of chronic nonmalignant pain. Integration of such behavioral health therapies into primary care settings may optimize health resources and improve treatment outcomes.

CONCLUSION

Evidence-based psychotherapy for chronic pain has established efficacy and safety and improves quality of life and physical and emotional functioning. Such interventions may be used as an alternative or adjunct to pharmacological management. Chronic opioid use should be reserved for individuals undergoing active cancer treatment, palliative care, or end-of-life care.

The Role of Toxins in the Pursuit for Novel Analgesics

Chronic pain is a major medical issue which reduces the quality of life of millions and inflicts a significant burden on health authorities worldwide. Currently, management of chronic pain includes first-line pharmacological therapies that are inadequately effective, as in just a portion of patients pain relief is obtained. Furthermore, most analgesics in use produce severe or intolerable adverse effects that impose dose restrictions and reduce compliance. As the majority of analgesic agents act on the central nervous system (CNS), it is possible that blocking pain at its source by targeting nociceptors would prove more efficient with minimal CNS-related side effects. The development of such analgesics requires the identification of appropriate molecular targets and thorough understanding of their structural and functional features. To this end, plant and animal toxins can be employed as they affect ion channels with high potency and selectivity. Moreover, elucidation of the toxin-bound ion channel structure could generate pharmacophores for rational drug design while favorable safety and analgesic profiles could highlight toxins as leads or even as valuable therapeutic compounds themselves. Here, we discuss the use of plant and animal toxins in the characterization of peripherally expressed ion channels which are implicated in pain.

LPM580098, a Novel Triple Reuptake Inhibitor of Serotonin, Noradrenaline, and Dopamine, Attenuates Neuropathic Pain

Background and Purpose: Sedation and somnolence remain serious adverse effects of the existing analgesics (e.g., pregabalin, duloxetine) for neuropathic pain. The available evidence indicates that serotonin (5-HT), noradrenaline (NE), and dopamine (DA) play important roles in modulating the descending inhibitory pain pathway and sleep-wake cycle. The aim of this work was to test the hypothesis that LPM580098, a novel triple reuptake inhibitor (TRI) of 5-HT, NE, and DA, has analgesic effect, and does not induce significant adverse effects associated with central inhibition, such as sedation and somnolence. Methods: The analgesic activity of LPM580098 was assessed on formalin test and spinal nerve ligation (SNL)-induced neuropathic pain model. Locomotor activity, pentobarbital sodium-induced sleeping and rota-rod tests were also conducted. In vitro binding and uptake assays, and Western blotting were performed to examine the potential mechanisms. Results: LPM580098 suppressed the nocifensive behaviors during phase II of the formalin test in mice. In SNL rats, LPM580098 (16 mg kg^-1) inhibited mechanical allodynia, thermal hyperalgesia and hyperexcitation of wide-dynamic range (WDR) neurons, in which the effect of LPM580098 was similar to pregabalin (30 mg kg^-1). However, pregabalin altered the spontaneous locomotion, affected pentobarbital sodium-induced sleep, and showed a trend to perform motor dysfunction, which were not induced by LPM580098. Mechanistically, LPM580098 inhibited the uptake of 5-HT, NE, and DA, improved pain-induced changes of the synaptic functional plasticity and structural plasticity possibly via downregulating the NR2B/CaMKIIα/GluR1 and Rac1/RhoA signaling pathways. Conclusion: Our results suggest that LPM580098, a novel TRI, is effective in attenuating neuropathic pain without producing unwanted sedation and somnolence associated with central nervous system (CNS) depressants.

Altered gray matter volume in patients with herpes zoster and postherpetic neuralgia

Purpose

The aim of this study was to measure brain alterations in patients with herpes zoster (HZ) and postherpetic neuralgia (PHN) and compare their differences using a voxel-based morphometry (VBM) technique.

Materials and methods

Thirty-three patients with HZ, 22 patients with PHN, and 28 well-matched healthy controls (HCs) were recruited. Magnetic resonance imaging data were acquired for all subjects and analyzed using the VBM method. The changes in gray matter volume (GMV) in HZ and PHN groups were compared with those in HC group, and the GMV differences were also compared between the PHN and HZ groups. Further correlation analysis and receiver operating characteristic curves were used to confirm the significance of GMV changes in various brain regions.

Results

Compared with HCs, decreased GMV was found in the bilateral insular lobes and increased GMV was found in the bilateral thalamus in the HZ group. In the PHN group, GMV decreased in the bilateral insula lobes, right middle frontal gyrus, bilateral precentral gyrus, and left postcentral gyrus and increased in the left cerebellar posterior lobe, right parahippocampal gyrus, and right lentiform nucleus. In addition, the PHN group exhibited increased GMV in the left cerebellar tonsil, culmen, and left lentiform nucleus and decreased GMV in the right precentral gyrus compared with the HZ group. Further correlation analysis and receiver operating characteristic curves revalidate the significance of most of these abnormal brain regions.

Conclusion

The VBM method revealed widespread GMV abnormalities in HZ and PHN patients. The brains of PHN patients have broader abnormalities in nonpain-related regions, suggesting the complexity of a central mechanism. When PHN patients were compared with HZ patients, the left cerebellar tonsil, culmen, and left lentiform nucleus corresponded to greater area under the curve, suggesting that abnormalities in these regions are risk factors for HZ patients’ transformation to PHN.

Cerebral 18F-FDG metabolism alteration in a neuropathic pain model following brachial plexus avulsion: A PET/CT study in rats

The present study aimed to investigate cerebral metabolic changes in a neuropathic pain model following deafferentation. A total of 24 Sprague-Dawley rats were included for modeling of right brachial plexus avulsion (BPA) through the posterior approach. As nerve injury would cause central sensitization and facilitate pain sensitivity in other parts of the body, thermal withdrawal latency (TWL) of the intact forepaw was assessed to investigate the level of pain perception following BPA-induced neuropathic pain. [Fluorine-18]-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) positron emission tomography (PET) was applied to the brain before and after brachial plexus avulsion to explore metabolic changes in neuropathic pain following deafferentation. The TWL of the left (intact) forepaw was significantly lower after BPA than that of baseline (p < 0.001). Using TWL as a covariate, standardized uptake values (SUVs) of ¹⁸F-FDG significantly increased in the ipsilateral dorsolateral thalamus and contralateral anterodorsal hippocampus after BPA. Conversely, SUVs in multiple brain regions decreased, including the contralateral somatosensory cortex, ipsilateral cingulate cortex, and ipsilateral temporal association cortex. The Pearson correlation analysis showed that the SUVs of the contralateral anterodorsal hippocampus and ipsilateral dorsolateral thalamus were negatively related to the TWL of the intact forepaw, whereas the SUVs in the contralateral somatosensory cortex and ipsilateral cingulate cortex were positively related to it (p < 0.05). These findings indicate that upregulation of metabolism in the anterodorsal hippocampus and dorsolateral thalamus and downregulation metabolism in the contralateral somatosensory cortex and ipsilateral cingulate cortex could be a unique pattern of metabolic changes for neuropathic pain following brachial plexus avulsion.

LncRNA X inactive specific transcript contributes to neuropathic pain development by sponging miR-154-5p via inducing toll-like receptor 5 in CCI rat models

Noncoding RNAs, including long non-coding RNAs (lncRNAs) and microRNAs, are involved in the development of neuropathic pain. Currently, we investigated that lncRNA X inactive-specific transcript (XIST) and toll-like receptor 5 (TLR5) were greatly upregulated in chronic constriction injury rat models, whereas miR-154-5p (microRNA-154-5p) was significantly downregulated. Bioinformatics analysis was used to predict miR-154-5p as a target gene of XIST, and dual-luciferase reporter tests proved the correlation between them. We observed that miR-154-5p was negatively modulated by XIST in vitro. XIST overexpression markedly induced neuropathic pain development in rats with chronic constriction injury, whereas the upregulation of miR-154-5p could reverse this phenomenon. Furthermore, TLR5 was demonstrated to be a target gene of miR-154-5p by using bioinformatics predictions. miR-154-5p negatively regulated TLR5 expression in vitro, and TLR5 was able to promote neuropathic pain development. In addition, overexpressing miR-154-5p can reverse the role of TLR5 neuropathic pain in vivo. Taken these together, we indicated that XIST could increase TLR5 expression by acting as a sponge of miR-154-5p in neuropathic pain development. This study revealed that XIST can contribute to neuropathic pain progression in rats through decreasing miR-154-5p and increasing TLR5. The XIST/miR-154-5p/ TLR5 axis can be provided as a novel therapeutic target in treating neuropathic pain.

Cupping with neural glides for the management of peripheral neuropathic plantar foot pain: a case study

Background/purpose: Plantar foot pain of neural origin is a challenging diagnosis to identify and treat. The purpose of this paper is to illustrate the novel way in which cupping was utilized in conjunction with neural glides to better diagnose and manage a patient who presented with symptoms of peripheral neuropathic plantar foot pain. Case description: A 65-year-old male presented to physical therapy with the diagnosis of plantar fasciitis by an orthopedic surgeon. The presentation included a diffuse area of pain toward the medial border of the foot with a peripheral neuropathic pain description. Cupping was used to identify pain in the saphenous nerve distribution and aided in resolving symptoms with the concomitant use of lower quarter neural glides. Outcome: At discharge and 1-year follow-up, the patient had a full resolution of symptoms and a return to prior level of function. Self-report outcomes included the numeric pain rating scale and the lower extremity functional scale. Discussion: This case is the first to describe the use of cupping combined with neural glides in the diagnosis and management of peripheral neuropathic pain from the saphenous nerve that was previously diagnosed as plantar fasciitis. The proposed mechanisms behind this treatment are also reviewed. Conclusion: In patients that present with symptoms of plantar fasciitis, testing neural glides combined with cupping may be warranted to confirm or refute the presence of a peripheral neuropathic pain source. Further studies are necessary to determine the mechanisms and further utility of the combined interventions in well controlled trials. Level of Evidence: Level IV.

Analysis of Neuropathic Pain Using Magnetic Resonance Imaging T2 Mapping of Intervertebral Disc in Chronic Low Back Pain

Study Design

Cross sectional study.

Purpose

The study aimed to analyze mechanisms underlying chronic low back pain (CLBP) using magnetic resonance imaging (MRI) T2 mapping of the intervertebral disc (IVD).

Overview of Literature

MRI T2 mapping utilizes the T2 values for quantifying moisture content and collagen sequence breakdown. We previously used MRI T2 mapping for quantifying the extent of IVD degeneration (IVDD) and showed a correlation between the degeneration of the posterior annulus fibrosus (AF) and CLBP.

Methods

We enrolled 40 patients with CLBP (17 males, 23 females; mean age, 50.8±1.6 years; range, 22–60 years). IVDs were categorized as the anterior AF, nucleus pulposus (NP), and posterior AF, and T2 value for each disc was measured. T2 values, assessed using the Japanese neuropathic pain (NeP) screening questionnaire, of the NeP and nociceptive pain (NocP) groups were compared.

Results

T2 values of the NocP and NeP groups were 64.7±5.6 ms and 58.1±2.3 ms for the anterior AF; 67.0±4.6 ms and 59.6±2.1 ms for NP; and 70.7±4.6 ms and 51.0±1.2 ms for the posterior AF, respectively. T2 values for IVDD were significantly lower in the NeP group than those in the NocP group (p<0.01).

Conclusions

The results indicate a correlation between the degeneration of posterior AF and NeP. MRI T2 mapping may be beneficial for detecting NeP caused by IVDD and can help formulate targeted analgesic therapies.

Sensitized vasoactive C-nociceptors: key fibers in peripheral neuropathic pain

Introduction

Multiple mechanisms are involved in the development and persistence of neuropathic pain. Some patients with nerve damage will remain painless and develop a "loss of function" phenotype, whereas others develop painful neuropathies.

Objectives

The aim of this study is to investigate the role of a peripheral nervous system sensitization by analyzing patients with and without pain.

Methods

The topical application of capsaicin was investigated in peripheral nociceptors. Two groups of patients (painful vs painless) with length-dependent neuropathies and small-fiber impairment were tested. Quantitative sensory testing was assessed before and after topical application of 0.6% capsaicin in the affected skin. In addition, blood perfusion measurements and an axon reflex flare assessment were performed.

Results

Quantitative testing revealed that heat hyperalgesia was induced in all patients and volunteers (P < 0.01) without observing any significant differences between patient groups. By contrast, the extent of the axon reflex flare reaction (P < 0.01) as well as the blood perfusion (P < 0.05) was significantly greater in patients with pain than in neuropathy patients not experiencing pain.

Conclusion

Hyperexcitable vasoactive nociceptive C fibers might contribute to pain in peripheral neuropathies and therefore may serve as a key player in separating into a painless or painful condition.

Mechanisms for therapeutic effect of bulleyaconitine A on chronic pain

Bulleyaconitine A, a diterpenoid alkaloid isolated from Aconitum bulleyanum plants, has been used for the treatment of chronic pain in China since 1985. Clinical studies show that the oral administration of bulleyaconitine A is effective for treating different kinds of chronic pain, including back pain, joint pain, and neuropathic pain with minimal side effect in human patients. The experimental studies have revealed that bulleyaconitine A at therapeutic doses potently inhibits the peripheral sensitization and central sensitization that underlie chronic pain and has no effect on acute pain. Bulleyaconitine A preferably blocks tetrodotoxin-sensitive voltage-gated sodium channels in dorsal root ganglion neurons by inhibition of protein kinase C, and the effect is around 600 times more potent in neuropathic animals than in naïve ones. Bulleyaconitine A at 5 nM inhibits the hypersensitivity of dorsal root ganglion neurons in neuropathic rats but has no effect on excitability of dorsal root ganglion neurons in sham group. Bulleyaconitine A inhibits long-term potentiation at C-fiber synapses in spinal dorsal horn, a synaptic model of pathological pain, preferably in neuropathic pain rats over naïve rats. The following mechanisms may underlie the selective effect of bulleyaconitine A on chronic pain. (1) In neuropathic conditions, protein kinase C and voltage-gated sodium channels in dorsal root ganglion neurons are upregulated, which enhances bulleyaconitine A's effect. (2) Bulleyaconitine A use-dependently blocks voltage-gated sodium channels and therefore inhibits the ectopic discharges that are important for neuropathic pain. (3) Bulleyaconitine A is shown to inhibit neuropathic pain by the modulation of spinal microglia, which are involved in the chronic pain but not in acute (nociceptive) pain. Moreover, bulleyaconitine A facilitates the anesthetic effect of morphine and inhibits morphine tolerance in rats. Together, bulleyaconitine A is able to inhibit chronic pain by targeting at multiple molecules. Further clinical and experimental studies are needed for evaluating the efficacy of bulleyaconitine A in different forms of chronic pain in patients and for exploring the underlying mechanisms.

Latin American and Caribbean consensus on noninvasive central nervous system neuromodulation for chronic pain management (LAC2-NIN-CP)

Supplemental Digital Content is Available in the Text.

Introduction:

Chronic pain (CP) is highly prevalent and generally undertreated health condition. Noninvasive brain stimulation may contribute to decrease pain intensity and influence other aspects related to CP.

Objective:

To provide consensus-based recommendations for the use of noninvasive brain stimulation in clinical practice.

Methods:

Systematic review of the literature searching for randomized clinical trials followed by consensus panel. Recommendations also involved a cost-estimation study.

Results:

The systematic review wielded 24 transcranial direct current stimulation (tDCS) and 22 repetitive transcranial magnetic stimulation (rTMS) studies. The following recommendations were provided: (1) Level A for anodal tDCS over the primary motor cortex (M1) in fibromyalgia, and level B for peripheral neuropathic pain, abdominal pain, and migraine; bifrontal (F3/F4) tDCS and M1 high-definition (HD)-tDCS for fibromyalgia; Oz/Cz tDCS for migraine and for secondary benefits such as improvement in quality of life, decrease in anxiety, and increase in pressure pain threshold; (2) level A recommendation for high-frequency (HF) rTMS over M1 for fibromyalgia and neuropathic pain, and level B for myofascial or musculoskeletal pain, complex regional pain syndrome, and migraine; (3) level A recommendation against the use of anodal M1 tDCS for low back pain; and (4) level B recommendation against the use of HF rTMS over the left dorsolateral prefrontal cortex in the control of pain.

Conclusion:

Transcranial DCS and rTMS are recommended techniques to be used in the control of CP conditions, with low to moderate analgesic effects, and no severe adverse events. These recommendations are based on a systematic review of the literature and a consensus made by experts in the field. Readers should use it as part of the resources available to decision-making.

Possibilities of Application of Modern Neurophysiological Methods in Diagnosis of Vibration Disease

Vibration disease is one of the leading in the structure of occupational diseases. A more detailed study of the pathogenesis, expanding the possibilities of diagnosis of vibration disease, is necessary. The aim of the study is to determine the diagnostic value of stabilometry, quantitative sensory testing and neuroenergocarting in vibration disease associated with the combined effects of local and general vibration. Materials and methods. Two groups of patients were examined: with the diagnosis of vibration disease associated with the combined effect of local and general vibration – 50 people (age 48.7 ± 3.1 years), not in contact with vibration – 30 people (age 49.1 ± 2.8 years). The study of the equilibrium function, the determination of the level of the constant potential of the brain by 12 standard leads and the determination of temperature and pain sensitivity. Statistical processing of the results was carried out using the software package “Statistica 6.0” (StatSoft Inc., USA). Differences were considered statistically significant at p < 0.05. Results. In vibration disease, the vertical stance of patients is more unstable than in patients with no contact with vibration. In patients with vibration disease, there is a decrease in the threshold of cold sensitivity and an increase in the threshold of thermal sensitivity and thermal pain compared to the control group. According to our data, the increased level of permanent potential in patients with vibration disease is observed in the central (22.7 (12.6; 30.7) mV) and right central (20.4 (11.5; 27.1) mV), also the average level of permanent capacity in this group is increased – 17.1 (8.4; 25.8) mV.

Conclusion. The results obtained indicate the involvement of the neurosensory complex united by single thalamic and cortical centers in the pathological process and confirm the diagnostic value of the methods used.

Emerging relevance of circadian rhythms in headaches and neuropathic pain

Circadian rhythms of physiology are the keys to health and fitness, as dysregulation, by genetic mutations or environmental factors, increases disease risk and aggravates progression. Molecular and physiological studies have shed important light on an intrinsic clock that drives circadian rhythms and serves essential roles in metabolic homoeostasis, organ physiology and brain functions. One exciting new area in circadian research is pain, including headache and neuropathic pain for which new mechanistic insights have recently emerged. For example, cluster headache is an intermittent pain disorder with an exceedingly precise circadian timing, and preliminary evidence is emerging linking several circadian components (eg, Clock and Nr1d1) with the disease. In this review, we first discuss the broad metabolic and physiological relevance of the circadian timing system. We then provide a detailed review of the circadian relevance in pain disease and physiology, including cluster headache, migraine, hypnic headache and neuropathic pain. Finally, we describe potential therapeutic implications, including existing pain medicines and novel clock-modulating compounds. The physiological basis for the circadian rhythms in pain is an exciting new area of research with profound basic and translational impact.

A Systematic Review: Mindfulness Intervention for Cancer-Related Pain

Moderate-to-severe pain is a common problem experienced by patients with cancer. Although analgesic drugs are effective, adverse side effects are common and some analgesic drugs are addictive. Nonpharmacological treatment may be a way to treat cancer pain without causing negative side effects. Mindfulness is used as an effective nonpharmacological treatment to improve quality of life (QoL) and to address psychological problems including distress, anxiety, stress, and depression. However, the effect of mindfulness on pain severity has not been sufficiently investigated. Therefore, a systematic review was undertaken to describe the effectiveness of mindfulness interventions for pain and its underlying pathophysiologic mechanisms. The search was conducted in PubMed, Ovid MEDLINE, and CINAHL and included only empirical studies published from 2008 to 2017. Search terms included mindfulness, mindfulness-based intervention, meditation, cancer, pain, and cancer-related pain. Six studies met the search criteria. These studies tested several types of intervention including mindfulness-based stress reduction, mindfulness-based cognitive therapy, meditation with massage, and mindful awareness practices. Study outcomes include improved pain severity, anxiety, stress, depression, and QoL. However, most studies reviewed were conducted in the United States and Denmark. Further research is needed to test culturally appropriate mindfulness interventions to reduce pain.

Mindfulness-Based Meditation Versus Progressive Relaxation Meditation: Impact on Chronic Pain in Older Female Patients With Diabetic Neuropathy

Chronic pain, the most common complication of diabetes, is treated with medication often to no avail. Our study aimed to compare the use of mindfulness meditation and progressive relaxation to reduce chronic pain in older females with diabetes. Methods The 105 study participants were divided randomly into 3 groups: Group MM (mindfulness meditation), Group CM (control meditation), and Group PM (progressive relaxation meditation). Assessment of analgesic effectiveness required changes in average daily pain Brief Pain Inventory (BPI) modified for painful diabetic peripheral neuropathy and Patient Global Impression of Change using descriptive statistics, Student's t test, and analysis of variance where applicable. Results Both Groups MM and PM experienced significant (P < .05) reduction in average daily pain in last 24 hours at study end compared to baseline (28.7% and 39.7%, respectively). Group MM had more significant (P < .01) reduction of pain compared to control, a score of 5.2 ± 1.2 dropped to 3.0 ± 1.1 by week 12 of treatment. Groups MM and PM showed significant improvement in patients' impression at study end, 75 ± 5.1% (n = 36) and 61 ± 6.5% (n = 32), respectively. In Group MM, patient satisfaction scores increased significantly (P < .05) to 3.8 ± 1.9 by week 12. Conclusion Integrative therapies such as mindfulness meditation can be part of a comprehensive pain management plan. Benefits include reduction of pain-related medication consumption, better treatment outcomes, improvement in comorbid conditions such as anxiety and depression as well as no risk of addiction or abuse.

The antihyperalgesic effect of docosahexaenoic acid in streptozotocin-induced neuropathic pain in the rat involves the opioidergic system

Docosahexaenoic acid (DHA) is a polyunsaturated fatty acid that has shown an antinociceptive effect in multiple pain models, such as inflammatory and neuropathic pain by chronic constriction injury in rats; however, its mechanism of action is still not well-understood. Reports suggest that DHA activates opioid signaling, but there is no information on this from a model of neuropathic pain. As a result, the aims of this study were (1) to determine the antihyperalgesic and antiallodynic effect of peripheral DHA administration, and (2) to evaluate the participation of the opioid receptors in the antihyperalgesic effect of DHA on streptozotocin-induced neuropathic pain in the rat. Female Wistar rats were injected with streptozotocin (50 mg/kg, i.p.) to induce hyperglycemia. The formalin, Hargreaves, and von Frey filaments tests were used to assess the nociceptive activity. Intraplantar administration of DHA (100-1000 μg/paw) or gabapentin (562-1778 μg/paw) decreased formalin-evoked hyperalgesia in diabetic rats, in a dose-dependent manner. Furthermore, DHA (562 μg/paw) and gabapentin (1000 μg/paw) reduced thermal hyperalgesia and allodynia. Local peripheral administration of naloxone (non-selective opioid receptor antagonist; 100 μg/paw), naltrindole (selective δ receptor antagonist; 1 μg/paw), and CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2, μ receptor antagonist; 20 μg/paw) prevented formalin-evoked hyperalgesia in diabetic rats but not by GNTI (guanidinonaltrindole, κ receptor antagonist;1 µg/paw). It is suggested that peripheral DHA shows an antihyperalgesic effect in neuropathic pain in the rat. Furthermore, δ and μ receptors are involved in the antihyperalgesic peripheral effect of DHA in diabetic rats.

The clinical utility of repetitive transcranial magnetic stimulation in reducing the risks of transitioning from acute to chronic pain in traumatically injured patients

Pain is a multifaceted condition and a major ongoing challenge for healthcare professionals having to treat patients in whom pain put them at risk of developing other conditions. Significant efforts have been invested in both clinical and research settings in an attempt to demystify the mechanisms at stake and develop optimal treatments as well as to reduce individual and societal costs. It is now universally accepted that neuroinflammation and central sensitization are two key underlying factors causing pain chronification as they result from maladaptive central nervous system plasticity. Recent research has shown that the mechanisms of action of repetitive transcranial magnetic stimulation (rTMS) make it a particularly promising avenue in treating various pain conditions. This review will first discuss the contribution of neuroinflammation and central sensitization in the transition from acute to chronic pain in traumatically injured patients. A detailed discussion on how rTMS may allow the restoration from maladaptive plasticity in addition to breaking down the chain of events leading to pain chronification will follow. Lastly, this review will provide a theoretical framework of what might constitute optimal rTMS modalities in dealing with pain symptoms in traumatically injured patients based on an integrated perspective of the physiopathological mechanisms underlying pain.

Mu-Opioid Receptor Agonist Induces Kir3 Currents in Mouse Peripheral Sensory Neurons - Effects of Nerve Injury

Neuropathic pain often arises from damage to peripheral nerves and is difficult to treat. Activation of opioid receptors in peripheral sensory neurons is devoid of respiratory depression, sedation, nausea, and addiction mediated in the brain, and ameliorates neuropathic pain in animal models. Mechanisms of peripheral opioid analgesia have therefore gained interest, but the role of G protein-coupled inwardly rectifying potassium (Kir3) channels, important regulators of neuronal excitability, remains unclear. Whereas functional Kir3 channels have been detected in dorsal root ganglion (DRG) neurons in rats, some studies question their contribution to opioid analgesia in inflammatory pain models in mice. However, neuropathic pain can be diminished by activation of peripheral opioid receptors in mouse models. Therefore, here we investigated effects of the selective μ-opioid receptor (MOR) agonist [D-Ala², N-Me-Phe⁴, Gly⁵-ol]-enkephalin (DAMGO) on potassium conductance in DRG neurons upon a chronic constriction injury (CCI) of the sciatic nerve in mice. For verification, we also tested human embryonic kidney (HEK) 293 cells transfected with MOR and Kir3.2. Using patch clamp, we recorded currents at -80 mV and applied voltage ramps in high extracellular potassium concentrations, which are a highly sensitive measures of Kir3 channel activity. We found a significantly higher rate of HEK cells responding with potassium channel blocker barium-sensitive inward current (233 ± 51 pA) to DAMGO application in transfected than in untransfected group, which confirms successful recordings of inward currents through Kir3.2 channels. Interestingly, DAMGO induced similar inward currents (178 ± 36-207 ± 56 pA) in 15-20% of recorded DRG neurons from naïve mice and in 4-27% of DRG neurons from mice exposed to CCI, measured in voltage clamp or voltage ramp modes. DAMGO-induced currents in naïve and CCI groups were reversed by barium and a more selective Kir3 channel blocker tertiapin-Q. These data indicate the coupling of Kir3 channels with MOR in mouse peripheral sensory neuron cell bodies, which was unchanged after CCI. A comparative analysis of opioid-induced potassium conductance at the axonal injury site and peripheral terminals of DRG neurons could clarify the role of Kir3 channel-MOR interactions in peripheral nerve injury and opioid analgesia.

Spinal Cord Stimulation for Pain Treatment After Spinal Cord Injury

In addition to restoration of bladder, bowel, and motor functions, alleviating the accompanying debilitating pain is equally important for improving the quality of life of patients with spinal cord injury (SCI). Currently, however, the treatment of chronic pain after SCI remains a largely unmet need. Electrical spinal cord stimulation (SCS) has been used to manage a variety of chronic pain conditions that are refractory to pharmacotherapy. Yet, its efficacy, benefit profiles, and mechanisms of action in SCI pain remain elusive, due to limited research, methodological weaknesses in previous clinical studies, and a lack of mechanistic exploration of SCS for SCI pain control. We aim to review recent studies and outline the therapeutic potential of different SCS paradigms for traumatic SCI pain. We begin with an overview of its manifestations, classification, potential underlying etiology, and current challenges for its treatment. The clinical evidence for using SCS in SCI pain is then reviewed. Finally, future perspectives of pre-clinical research and clinical study of SCS for SCI pain treatment are discussed.

Effect of Pregabalin on Radiotherapy-Related Neuropathic Pain in Patients With Head and Neck Cancer: A Randomized Controlled Trial

PURPOSE

Neuropathic pain is an unavoidable treatment-related adverse event among patients with head and neck cancer who are undergoing radiotherapy. We aimed to test the efficacy and safety of pregabalin versus placebo in the treatment of radiotherapy-related neuropathic pain.

PATIENTS AND METHODS

This randomized, double-blind, placebo-controlled trial was conducted in four centers in China. Eligible patients with a mean pain intensity score of 4 or more on an 11-point numeric rating scale were randomly assigned to receive either active treatment with a flexible dose of pregabalin or placebo for 16 weeks. The primary efficacy outcome was pain reduction measured on the numeric rating scale.

RESULT

There were 128 patients who received treatment as randomly assigned. Pain intensity reduction was 2.44 in the pregabalin arm and 1.58 in the placebo arm at week 16, yielding an adjusted mean difference of 0.87 (95% CI, 0.30 to 1.44; P = .003). In the pregabalin arm, 38 patients (59.4%) achieved at least 30% pain relief versus 21 (32.8%) in the placebo arm ( P = .006). Nineteen patients (29.7%) in the pregabalin group and five (7.8%) in the placebo group achieved 50% or greater pain relief ( P = .003). Total scores on the Profile of Mood States-Short Form, pain severity and functional interference of Brief Pain Inventory-Short Form, as well as the physiology and psychology domain of the WHO Quality of Life-BREF all were reduced significantly at week 16 in patients who received pregabalin compared with those who received placebo. There was no significant difference ( P = .29) in the incidence of experiencing at least one adverse event in the pregabalin arm (n = 35; 54.7%) versus the placebo arm (n = 29; 45.3%).

CONCLUSION

Patients treated with pregabalin with radiotherapy-related neuropathic pain had greater pain alleviation, better mood states, and higher quality of life compared with patients in the placebo group, with a good tolerability.

Bulleyaconitine A attenuates hyperexcitability of dorsal root ganglion neurons induced by spared nerve injury: The role of preferably blocking Nav1.7 and Nav1.3 channels

Background

Oral administration of Bulleyaconitine A, an extracted diterpenoid alkaloid from Aconitum bulleyanum plants, is effective for treating chronic pain in rats and in human patients, but the underlying mechanisms are poorly understood.

Results

As the hyperexcitability of dorsal root ganglion neurons resulting from the upregulation of voltage-gated sodium (Nav) channels has been proved critical for development of chronic pain, we tested the effects of Bulleyaconitine A on Nav channels in rat spared nerve injury model of neuropathic pain. We found that Bulleyaconitine A at 5 nM increased the threshold of action potentials and reduced the firing rate of dorsal root ganglion neurons in spared nerve injury rats but not in sham rats. Bulleyaconitine A preferably blocked tetrodotoxin-sensitive Nav channels over tetrodotoxin-resistant ones in dorsal root ganglion neurons of spared nerve injury rats. Bulleyaconitine A was more potent for blocking Nav1.3 and Nav1.7 than Nav1.8 in cell lines. The half maximal inhibitory concentration (IC₅₀) values for resting Nav1.3, Nav1.7, and Nav1.8 were 995.6 ± 139.1 nM, 125.7 ± 18.6 nM, and 151.2 ± 15.4 μM, respectively, which were much higher than those for inactivated Nav1.3 (20.3 ± 3.4 pM), Nav1.7 (132.9 ± 25.5 pM), and Nav1.8 (18.0 ± 2.5 μM). The most profound use-dependent blocking effect of Bulleyaconitine A was observed on Nav1.7, less on Nav1.3, and least on Nav1.8 at IC₅₀ concentrations. Bulleyaconitine A facilitated the inactivation of Nav channels in each subtype.

Conclusions

Preferably blocking tetrodotoxin-sensitive Nav1.7 and Nav1.3 in dorsal root ganglion neurons may contribute to Bulleyaconitine A’s antineuropathic pain effect.

Down-regulation of Kv4.3 channels and a-type K+ currents in V2 trigeminal ganglion neurons of rats following oxaliplatin treatment

Chemotherapy drugs such as oxaliplatin can increase nociceptive neuron excitability to result in neuropathic pain in orofacial and other regions in patients following chemotherapy. However, mechanisms underlying chemotherapy-induced increases of nociceptive neuron excitability are not fully understood. Kv4.3 channels are voltage-gated K⁺ channels mediating A-type K⁺ (I_A) currents to control neuronal excitability. In the present study, we examined Kv4.3 channel expression on trigeminal neurons that innervate orofacial regions (V2 TG neurons) of rats using immunostaining method. We showed that strong Kv4.3 immunoreactivity (Kv4.3-ir) was present mainly in small-sized V2 TG neurons. The numbers of Kv4.3-ir positive V2 TG neurons were significantly reduced in oxaliplatin-treated rats, suggesting down-regulation of Kv4.3 channel expression on V2 TG neurons by the chemotherapy drug. Patch-clamp recordings from acutely dissociated rat V2 TG neurons showed that almost all nociceptive-like V2 TG neurons displayed I_A currents with slow inactivation kinetics. The amplitudes of I_A currents were significantly reduced in these nociceptive-like V2 TG neurons of oxaliplatin-treated group. Furthermore, we found that the excitability of nociceptive-like V2 TG neurons was significantly higher in the oxaliplatin-treated group than in the control group. These findings raise a possibility that down-regulation of Kv4.3 channels and I_A currents in nociceptive V2 TG neurons is an underlying mechanism of oxaliplatin-induced orofacial neuropathic pain.

Predicting factors of outcome in multidisciplinary treatment of chronic neuropathic pain

Purpose

Evidence of the effectiveness of multidisciplinary treatment with a focus on neuropathic pain is still rare. The present study investigated whether multidisciplinary treatment leads to improvement of neuropathic pain in outcome (pain intensity and disability) and psychological (depression, pain acceptance, and catastrophizing) variables at posttreatment and 3-month follow-up. We examined whether and to what extent psychological changes can predict long-term outcome at 3-month follow-up, when other variables are controlled for (baseline characteristics and changes in pain parameters).

Patients and methods

Patients suffering from a chronic neuropathic pain condition (n=141) attended an inpatient multidisciplinary program lasting about 15 continuous days with self-report data collected at pretreatment, posttreatment, and 3-month follow-up.

Results

Repeated-measures ANOVAs showed a significant improvement of pain intensity, disability, pain acceptance, catastrophizing, and depression at posttreatment. These improvements remained stable over the 3-month follow-up for all variables except for depression. The inclusion of psychological changes in multiple regression analyses greatly increased the variance in outcome, explained by baseline characteristics and changes in pain parameters.

Conclusion

The results could help clinicians to determine which variables should be emphasized during inpatient treatment and during the follow-up period, in order to maintain the gains after an inpatient multidisciplinary treatment for neuropathic pain.

Perspective

The present study demonstrates the beneficial effects of an inpatient multidisciplinary program for neuropathic pain and further question the resistant nature of neuropathic pain to treatment. The results add evidence to the relevance of cognitive-behavioral models of pain positing an important role for pain-related thoughts and emotions in long-term outcome following multidisciplinary pain treatment.

Botulinum toxin-A for the treatment of neuralgia: a systematic review and meta-analysis

AIM

This meta-analysis was performed to evaluate the efficacy and safety of botulinum toxin-A (BTX-A) for the treatment of neuralgia.

METHODS

We searched PubMed, EMBASE, and Cochrane databases to identify randomized controlled trials (RCTs) comparing BTX-A treatment with saline for alleviating neuropathic pain. Primary outcome measures were pain scores up to 24 weeks after treatment. Secondary outcomes were hours of sleep, Short Form-36 (SF-36) life quality questionnaire, and adverse events. We used Review Manager 5.3 for the data analyses.

RESULTS

Twelve RCTs were included (n=495). Pain scores in the BTX-A group were significantly lower compared to the saline group at 4 weeks (mean difference [MD] =-1.64, 95% CI [-3.21, -0.07], P=0.04), 12 weeks (MD =-1.49, 95% CI [-2.05, -0.93], P<0.00001), and 24 weeks (MD =-1.61, 95% CI [-2.81, -0.40], P=0.009). There were no significant differences in hours of sleep, SF-36 questionnaire, or the incidence of injection pain or hematoma between the two groups. No serious adverse events associated with BTX-A were noted. Fourteen out of 108 patients (12.9%) with trigeminal neuralgia experienced mild facial asymmetry after the BTX-A treatment.

CONCLUSION

Based on the current evidence, BTX-A may be an effective and safe option for the treatment of neuralgia. Due to the limited number of patients included in this meta-analysis, more trials are still needed to confirm these results.