Recent advances in pharmacological treatment of neuropathic pain

Pain Modulation in Chronic Musculoskeletal Disorders: Botulinum Toxin, a Descriptive Analysis

Botulinum neurotoxin (BoNT), a product of Clostridium botulinum, reversibly inhibits the presynaptic release of the neurotransmitter acetylcholine at the neuromuscular junction. In addition, BoNT blocks the transmission of other substances involved in pain perception and, together with a soft-tissue anti-inflammatory effect, may play a role in analgesia. When first-line treatment fails, second-line therapies might include BoNT. Studies on chronic and recurrent pain using different mechanisms offer heterogenous results that must be validated and standardized. Plantar fasciitis, severe knee osteoarthritis, painful knee and hip arthroplasty, antalgic muscular contractures, and neuropathic and myofascial pain syndromes may benefit from the administration of BoNT. Research on this topic has revealed the main musculoskeletal conditions that can benefit from BoNT, stressing the effects, modalities of administration, doses, and schedule.

Topical Capsaicin for the Treatment of Neuropathic Pain

BACKGROUND

Neuropathic pain (NP) is an egregious problem worldwide. Due to the side-effects of oral drugs, drugs delivered directly to the affected area of pain are preferred.

OBJECTIVE

Capsaicin, a chemical compound isolated from chili peppers, is used as an analgesic in topical ointments and dermal patches to alleviate pain. Objective of the study is to review the application and functionality of topical capsaicin in treatment of neuropathic pain.

DATA SOURCES

To systematically review capsaicin's functions on NP, we retrieved articles from the PubMed database published in the last ten years.

STUDY ELIGIBILITY CRITERIA

The inclusion criteria were capsaicin and the use of capsaicin for the treatment of NP; on the other hand, articles were excluded according to the mentioned criteria such as abstracts, articles written in any language other than English, incomplete articles, and conference papers.

PARTICIPANTS AND INTERVENTIONS

Out of 265 articles, 108 articles were selected after filtering through the inclusion and exclusion criteria. The data and knowledge currently existing for capsaicin treatment in NP are summarized.

RESULTS

This review indicates that capsaicin effectively improves NP treatment without affecting the motor and large nerve fibres involved in sensory function. Transient receptor potential channel vanilloid type 1 (TRPV1) is the capsaicin receptor expressed in central and peripheral terminals of a sensitive primary nerve cell. Conclusions and implications of key findings: Topical capsaicin has a sensible safety profile and is effective in reducing NP. Therefore, studies over the last decade suggest that capsaicin might be a potential drug for NP treatment.

Metformin: A Prospective Alternative for the Treatment of Chronic Pain

Metformin (biguanide) is a drug widely used for the treatment of type 2 diabetes. This drug has been used for 60 years as a highly effective antihyperglycemic agent. The search for the mechanism of action of metformin has produced an enormous amount of research to explain its effects on gluconeogenesis, protein metabolism, fatty acid oxidation, oxidative stress, glucose uptake, autophagy and pain, among others. It was only up the end of the 1990s and beginning of this century that some of its mechanisms were revealed. Metformin induces its beneficial effects in diabetes through the activation of a master switch kinase named AMP-activated protein kinase (AMPK). Two upstream kinases account for the physiological activation of AMPK: liver kinase B1 and calcium/calmodulin-dependent protein kinase kinase 2. Once activated, AMPK inhibits the mechanistic target of rapamycin complex 1 (mTORC1), which in turn avoids the phosphorylation of p70 ribosomal protein S6 kinase 1 and phosphatidylinositol 3-kinase/protein kinase B signaling pathways and reduces cap-dependent translation initiation. Since metformin is a disease-modifying drug in type 2 diabetes, which reduces the mTORC1 signaling to induce its effects on neuronal plasticity, it was proposed that these mechanisms could also explain the antinociceptive effect of this drug in several models of chronic pain. These studies have highlighted the efficacy of this drug in chronic pain, such as that from neuropathy, insulin resistance, diabetic neuropathy, and fibromyalgia-type pain. Mounting evidence indicates that chronic pain may induce anxiety, depression and cognitive impairment in rodents and humans. Interestingly, metformin is able to reverse some of these consequences of pathological pain in rodents. The purpose of this review was to analyze the current evidence about the effects of metformin in chronic pain and three of its comorbidities (anxiety, depression and cognitive impairment).

The Effect of Intradermal Botulinum Toxin a injections on painful diabetic polyneuropathy

BACKGROUND AND AIMS

Botulinum toxin type A (BTX-A) have been recently administered to improve Diabetic neuropathies; however, the efficacy of this treatment for relieving pain in painful diabetic polyneuropathy (DPN) has not been studied yet. Herein, we investigated the efficacy of botulinum toxin A (BTX-A) on DPN.

METHODS

This prospective, randomized, double-blind, controlled trial was performed in Imam Hossein Medical Center, pain clinic (Tehran, Iran). Diabetic patients (141 cases), between 40 and 70 years old with polyneuropathy in lower limbs were randomly assigned to one of these three groups: 1. Group D1 received 150 units of BTX-A in one foot and normal saline 0.9% in the other foot, 2. Group D2 received BTX-A 150 units in both feet, 3. Group N received normal saline 0.9% in both feet. All injections were performed intradermally using insulin syringes in 20 different points of foot. Visual analogue scale (VAS) and neuropathy pain scale (NPS) were used to compare the groups.

RESULTS

The improvement of VAS, pain intensity, sharp and hot sensation, sensitive and unpleasant sensation, deep and surface sensation was significant when comparing BTX-A and placebo groups. However, dull and cold sensations improvement (p = 0.114, and p = 0.653; respectively) did not show a significant difference between BTX-A injection and placebo groups. Furthermore, the percentage of changes after treatment indicated that sharp pain was improved more than other complaints (80%, 81%, and 37% for D1, D2, and N groups; respectively).

CONCLUSION

Intradermal administration of BTX-A was effective in improving VAS and all of the items of NPS in patients with diabetic polyneuropathy, except for dull and cold sensation.

Lumbar sympathetic pulsed radiofrequency combined with continuous epidural infusion for treatment of painful diabetic neuropathy: A report of two cases and a literature review

Diabetic neuropathy (DN), one of the most common late complications of diabetes mellitus, significantly affects distinct regions of the nervous system. Pain management is challenging in DN as no effective therapies exist that reverse the pathological course of DN. Several drugs are recommended as the first-line treatment for painful DN, but these are associated with various side-effects in the long term. This report presents two cases with painful DN who underwent lumbar sympathetic pulsed radiofrequency combined with continuous epidural infusion. The two cases were followed for 30 days. Lumbar sympathetic pulsed radiofrequency combined with continuous epidural infusion offered effective pain relief and improved the health-related quality of life in two patients with DN over this time period.

The effects of botulinum toxin type A injection on pain symptoms, quality of life, and sleep quality of patients with diabetic neuropathy: A randomized double-blind clinical trial

Background: Neuropathic pain is one of the most common problems in patients with diabetes mellitus (DM). In this study, the effect of botulinum toxin type A (BTX-A) on neuropathic pain, quality of sleep, and quality of life of diabetic patients with sensorimotor polyneuropathy was studied. Methods: This randomized placebo-controlled trial study was carried out in a double-blind (patient-researcher) method. The study was performed on 32 patients with type 2 DM. Neuropathy was confirmed by Douleur Neuropathique 4 (DN4) Questionnaire and nerve conduction study (NCS). The patients were randomly assigned to two intervention and control groups based on the random numbers table. After selecting the subjects, we used 36-Item Short Form Health Survey (SF-36), Neuropathic Pain Scale (NPS), Visual Analogue Scale (VAS), and Pittsburgh Sleep Quality Index (PSQI) questionnaires before and after 3 months of 100 units BTX-A injection (as intervention group) or same amount of chloride sodium (as control group) to the subjects' feet. The data were analyzed by SPSS software using independent two-sample t-test, chi-square test, and one-way repeated measures analysis of variance (ANOVA). Results: 12 male and 20 female patients participated in this study. There was a significant difference in the mean VAS, PSQI, physical dimension of the SF-36, and some NPS indices over time (12 weeks) (P < 0.001). Conclusion: The results of this study showed that BTX-A reduced neuropathic pain and improved the quality of life and sleep in people with diabetic neuropathy.

Efficacy of a Combination of N-Palmitoylethanolamide, Beta-Caryophyllene, Carnosic Acid, and Myrrh Extract on Chronic Neuropathic Pain: A Preclinical Study

Neuropathic pain (NP) is a common public health problem that poses a major challenge to basic scientists and health-care providers. NP is a complex problem with an unclear etiology and an often-inadequate response to current medications. Despite the high number of drugs available, their limited pharmacological efficacy and side effects hamper their chronic use. Thus, the search for novel treatments is a priority. In addition to pharmaceuticals, natural extracts and food supplements are often used to help treating patients with NP. One such supplement is Noxiall^®, a commercially available combination of N-Palmitoylethanolamide (PEA), beta-caryophyllene; carnosic acid and myrrh. Here, we compare the efficacy of Noxiall^® to that of the medications gabapentin and pregabalin in the NP model of chronic constriction injury (CCI) using sciatic nerve ligation in mouse. Following CCI, mice developed a significant increase in mechanical allodynia and thermal hyperalgesia. Results showed that administration of either Noxiall^®, pregabalin, or gabapentin significantly attenuated mechanical allodynia. The magnitude of the Noxiall^® effect was comparable to that of gabapentin or pregabalin. In addition, co-administration of non-effective doses of pregabalin and Noxiall^® resulted in a significant decrease in NP, suggesting an additive efficacy. Noxiall^® was efficacious also in reducing CCI-induced thermal hyperalgesia. These findings support the rationale of using natural remedies in conjunction with classical pharmacological agents to treat chronic NP.

Gabapentin as add-on to morphine for severe neuropathic or mixed pain in children from age 3 months to 18 years - evaluation of the safety, pharmacokinetics, and efficacy of a new gabapentin liquid formulation: study protocol for a randomized controlled trial

Background

Gabapentin has shown efficacy in the treatment of chronic neuropathic or mixed pain in adults. Although pediatric pain specialists have extensive experience with gabapentin for the treatment of neuropathic pain, its use is off-label. Its efficacy and safety in this context have never been shown. The aim of this trial is to compare gabapentin with placebo as add-on to morphine for the treatment of severe chronic mixed or neuropathic pain in children. This trial is part of the European Union Seventh Framework Programme project Gabapentin in Paediatric Pain (GAPP) to develop a pediatric use marketing authorization for a new gabapentin suspension.

Methods/design

The GAPP-2 study is a randomized, double-blind, placebo-controlled, multicenter superiority phase II study in children with severe chronic neuropathic or mixed pain. Its primary objective is to evaluate the efficacy of a gabapentin liquid formulation as adjunctive therapy to morphine. Sixty-six eligible children 3 months to 18 years of age with severe pain (pain scores ≥ 7), stratified in three age groups, will be randomized to receive gabapentin (to an accumulating dose of 45 to 63 mg/kg/day, dependent on age) or placebo, both in addition to morphine, for 12 weeks. Randomization will be preceded by a short washout period, and treatment will be initiated by a titration period of 3 weeks. After the treatment period, medication will be tapered during 4 weeks. The primary endpoint is the average pain scores in the two treatment groups (average of two measures each day for 3 days before the end-of-study visit [V10] assessed by age-appropriate pain scales (Face, Legs, Activity, Cry, Consolability scale; Faces Pain Scale–Revised; Numeric Rating Scale). Secondary outcomes include percentage responders to treatment (subjects with 30% reduction in pain scale), number of episodes of breakthrough pain, number of rescue interventions, number of pain-free days, participant dropouts, quality of life (Pediatric Quality of Life Inventory), and acceptability of treatment. Outcomes will be measured at the end-of-study visit after 12 weeks of treatment at the optimal gabapentin dose. Groups will be compared on an intention-to-treat basis.

Discussion

We hope to provide evidence that the combination of morphine and gabapentin will provide better analgesia than morphine alone and will be safe. We also aim to obtain confirmation of the recommended pediatric dose.

Trial registration

EudractCT, 2014-004897-40. Registered on 7 September 2017.

ClinicalTrials.gov, NCT03275012. Registered on 7 September 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-3169-3) contains supplementary material, which is available to authorized users.

Identification of the key genes associated with neuropathic pain

Neuropathic pain is a chronic pain state associated with multiple etiologies that results in considerable social and economic burden. The identification of key genes associated with neuropathic pain is important for the development of novel therapies. Therefore, the present study downloaded the gene expression profile GSE15041 from the Gene Expression Omnibus database. The unverified gene chip was removed and the microarray data was normalized following quality control. The limma package in R was used to screen the differentially expressed genes (DEGs), followed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Furthermore, a protein‑protein interaction (PPI) network based on the identified DEGs was constructed to select hub proteins, and reverse transcription‑quantitative polymerase chain reaction was performed to detect the expression of these proteins in a mouse model of neuropathic pain. In total, 86 common DEGs were identified. DEGs were significantly enriched in ̔extracellular space̓ and KEGG pathway enrichment analysis demonstrated that the DEGs were significantly enriched in inflammatory diseases and the mitogen‑activated protein kinase signaling pathway. The PPI network consisted of 27 nodes (proteins) and 47 PPI edges (interactions). Interleukin (IL)‑6, transcription factor AP‑1 (c‑Jun) and urikinase‑type plasminogen activator (Plau) were identified as hub proteins and key genes in neuropathic pain. The mRNA expression of these hub proteins was significantly increased in the neuropathic pain model, compared with the sham group. IL‑6, c‑Jun, and Plau may be involved in development of neuropathic pain and further research investigating the exact role of these key genes is required.

The Pharmacological Therapy of Chronic Neuropathic Pain

BACKGROUND

Chronic neuropathic pain, including painful peripheral polyneuropathy and post-herpetic neuralgia, affects 6.9-10% of the general population.

METHODS

In this article, we present current treatment recommendations on the basis of a selective review of the literature.

RESULTS

Neuropathic pain does not respond consistently to classic non-opioid analgesic drugs and is better treated with co-analgesic, antidepressant, and anticonvulsant drugs and topical agents. Under certain conditions, however, neuropathic pain can be treated with opioids, even chronically. It was concluded in a large-scale m eta- analysis that tricyclic antidepressants, selective serotonin- norepinephrine reuptake inhibitors, and calcium-channel anticonvulsants are the drugs of first choice, with a number needed to treat (NNT) of 3.5-7.7 for a 50% reduction of pain. An analysis of all studies yielded an estimated publication bias of 10%. Treatment planning must include adequate consideration of the patient's age and comorbidities, concomitant medication, and potential side effects.

CONCLUSION

Drugs are now chosen to treat neuropathic pain independently of the cause and symptoms of the pain. Topical agents are used only to treat peripheral neuropathy. The utility of a treatment approach based on the patient's symptoms and pathological mechanisms was recently demonstrated for the first time in a randomized trial. The goal of current research is to facilitate treatment planning on the basis of the clinical phenotype.

Membrane potential synchrony of neurons in anterior cingulate cortex plays a pivotal role in generation of neuropathic pain

The pathophysiology of neuropathic pain generation has not been fully investigated. Previous studies have primarily focused on changes in the properties of single neurons in the brain after nerve injury; however, little is known concerning the role of neuron-to-neuron connections in neuropathic pain pathogenesis. Synaptic transmission potentiation in anterior cingulate cortex (ACC) has been confirmed to be responsible for the formation of neuropathic pain. Thus, analysis of interneuronal connections in the ACC is an important approach for understanding the mechanism of neuropathic pain since it provides information on the potency of synaptic transmission. Here, we recorded membrane potentials from pairs of ACC neurons in anaesthetised rats and found that cross-correlations between pairs of ACC neurons significantly increased after surgery for chronic constriction injury (CCI). Moreover, CCI surgery could also enhance the power spectrum density of lower and higher-frequency membrane oscillations while having no effect on middle-frequency oscillations. The activation of membrane potential synchrony and power spectrum was reversed by the electrical synapse blocker mefloquine and pain behaviour was simultaneously alleviated. Our results may indicate that activation of membrane potential synchrony contributes to generation of neuropathic pain.

Activation of cannabinoid CB1 receptor contributes to suppression of spinal nociceptive transmission and inhibition of mechanical hypersensitivity by Aβ-fiber stimulation

Activation of Aβ-fibers is an intrinsic feature of spinal cord stimulation (SCS) pain therapy. Cannabinoid receptor type 1 (CB1) is important to neuronal plasticity and pain modulation, but its role in SCS-induced pain inhibition remains unclear. In this study, we showed that CB1 receptors are expressed in both excitatory and inhibitory interneurons in substantia gelatinosa (SG). Patch-clamp recording of the evoked excitatory postsynaptic currents (eEPSCs) in mice after spinal nerve ligation (SNL) showed that electrical stimulation of Aβ-fibers (Aβ-ES) using clinical SCS-like parameters (50 Hz, 0.2 millisecond, 10 μA) induced prolonged depression of eEPSCs to C-fiber inputs in SG neurons. Pretreatment with CB1 receptor antagonist AM251 (2 μM) reduced the inhibition of C-eEPSCs by Aβ-ES in both excitatory and inhibitory SG neurons. We further determined the net effect of Aβ-ES on spinal nociceptive transmission in vivo by recording spinal local field potential in SNL rats. Epidural SCS (50 Hz, Aβ-plateau, 5 minutes) attenuated C-fiber-evoked local field potential. This effect of SCS was partially reduced by spinal topical application of AM251 (25 μg, 50 μL), but not CB2 receptor antagonist AM630 (100 μg). Finally, intrathecal pretreatment with AM251 (50 μg, 15 μL) in SNL rats blocked the inhibition of behavioral mechanical hypersensitivity by SCS (50 Hz, 0.2 millisecond; 80% of motor threshold, 60 minutes). Our findings suggest that activation of spinal CB1 receptors may contribute to synaptic depression to high-threshold afferent inputs in SG neurons after Aβ-ES and may be involved in SCS-induced inhibition of spinal nociceptive transmission after nerve injury.

Recent advances in understanding neuropathic pain: glia, sex differences, and epigenetics

Neuropathic pain results from diseases or trauma affecting the nervous system. This pain can be devastating and is poorly controlled. The pathophysiology is complex, and it is essential to understand the underlying mechanisms in order to identify the relevant targets for therapeutic intervention. In this article, we focus on the recent research investigating neuro-immune communication and epigenetic processes, which gain particular attention in the context of neuropathic pain. Specifically, we analyze the role of glial cells, including microglia, astrocytes, and oligodendrocytes, in the modulation of the central nervous system inflammation triggered by neuropathy. Considering epigenetics, we address DNA methylation, histone modifications, and the non-coding RNAs in the regulation of ion channels, G-protein-coupled receptors, and transmitters following neuronal damage. The goal was not only to highlight the emerging concepts but also to discuss controversies, methodological complications, and intriguing opinions.

ERK1/2: Function, signaling and implication in pain and pain-related anxio-depressive disorders

Despite the increasing knowledge regarding pain modulation, the understanding of the mechanisms behind a complex and pathologic chronic pain condition is still insufficient. These knowledge gaps might result in ineffective therapeutic approaches to relieve painful sensations. As a result, severe untreated chronic pain frequently triggers the onset of new disorders such as depression and/or anxiety, and therefore, both the diagnosis and treatment of patients suffering from chronic pain become seriously compromised, prompting a self-perpetuating cycle of symptomatology. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) are molecules strongly implicated in the somatic component of pain at the spinal cord level and have been emerging as mediators of the emotional-affective component as well. Although these molecules might represent good biomarkers, their use as pharmacological targets is still open to discussion as paradoxical information has been obtained. Here we review the current scientific literature regarding ERK1/2 signaling in the modulation of pain, depression and anxiety, including the emotional-affective spheres of the pain experience.

Management of Neuropathic Pain Associated with Spinal Cord Injury

Spinal cord injury (SCI) is an injury to the spinal cord that leads to varying degrees of motor and/or sensory deficits and paralysis. Chronic pain of both neuropathic and nociceptive type is common and contributes to reduced quality of life. The aim of the review is to provide current clinical understanding as well as discuss and evaluate efficacy of pharmacological interventions demonstrated in the clinical studies. The review was based on literature search in PubMed and Medline with words "neuropathic pain" and "spinal cord injury". The review included clinical studies and not experimental data nor case reports. A limited number of randomized and placebo-controlled studies concerning treatment options of neuropathic pain after SCI were identified. Amitriptyline, a tricyclic antidepressant and the antiepileptic drugs, gabapentin and pregabalin, are most studied with demonstrated efficacy, and considered to be the primary choice. Opioids have demonstrated conflicting results in the clinical studies. In addition, administration route used in the studies as well as reported side effects restrict everyday use of opioids as well as ketamine and lidocaine. Topical applications of capsaicin or lidocaine as well as intradermal injections of Botulinum toxin are new treatment modalities that are so far not studied on SCI population and need further studies. Non-pharmacological approaches may have additional effect on neuropathic pain. Management of pain should always be preceded by thorough clinical assessment of the type of pain. Patients need a follow-up to evaluate individual effect of applied measures. However, the applied management does not necessarily achieve satisfactory pain reduction. Further clinical studies are needed to evaluate the effect of both established and novel management options.

Promising treatments for neuropathic pain

In the last few years the understanding of mechanisms and, consequently, the diagnosis of neuropathic pain (NP) has becoming progressively clearer in clinical practice. However, the treatment of such condition remains challenging so far. One of the reasons for such difficulty is the diversity of mechanisms involved in NP generation and its persistency. In the present review we discuss several treatment modalities for NP that are scantily applied in daily clinical practice. For that, we collected positive clinical evidence of unusual and SECS (Safe, Easy, Cheap, and Sensible) approaches for NP. The aim of this review is not to establish the “state of the art” or rigid guidelines for NP treatment. In a different way, we only want bring new possibilities of treatment to the readers and also to motivate investigators to confirm those positive preliminary but promising results for NP reliev.

Clinical value of tapentadol extended-release in painful diabetic peripheral neuropathy

Painful diabetic peripheral neuropathy is difficult to treat, partially because the underlying mechanism of pain is not fully understood. Various treatment guidelines recommend first-line agents, such as α2-δ ligands, serotonin-norepinephrine reuptake inhibitors, and tricyclic antidepressants but combination therapy of alternative agents including opiates is often warranted. Tapentadol extended-release has a novel dual mechanism of action; it is both a mu-opioid receptor agonist and a norephinephrine reuptake inhibitor. It has been in the spotlight since it was FDA-approved specifically for the treatment of painful diabetic peripheral neuropathy in 2012. Previous reviews of tapentadol have focused on chronic pain. The purpose of this review article is to assess the efficacy and safety of tapentadol extended-release in adult populations with painful diabetic peripheral neuropathy and provide guidance for formulary decisions.

Emotional consequences of neuropathic pain: insight from preclinical studies

Mood disorders such as depression and anxiety are frequently observed in patients suffering from chronic pain, including neuropathic pain. While this comorbidity is clinically well established, the underlying mechanism(s) remained unclear. The recent development of animal models now allows addressing the consequences of neuropathic pain. In this review, we report the preclinical evidences from anatomical, neuroimaging, behavioral, pharmacological and biochemical studies that address the anxiodepressive consequences of neuropathic pain. We present an overview of rodent models of these consequences and we discuss the challenges and parameters to consider for generating these models. We then discuss the possible mechanism(s) underlying anxiodepressive consequences by describing morphological and functional changes. Information is provided concerning neuroanatomical changes and plasticity, including LTP and LTD, in the anterior cingulate cortex, the insula, the hippocampus, the amygdala and the mesolimbic system, neuroendocrine parameters concerning the hypothalamo-pituitary-adrenal axis, neuroimmune response including the role of glial cells and cytokines, monoamine systems and changes in locus coeruleus noradrenergic system, and neurotrophic factors such as BDNF.

Heterogeneous responses of dorsal root ganglion neurons in neuropathies induced by peripheral nerve trauma and the antiretroviral drug stavudine

Background

Heterogeneity is increasingly recognized in clinical presentation of neuropathic pain (NP), but less often recognized in animal models. Neurochemical dysregulation in rodent dorsal root ganglia (DRG) is associated with peripheral nerve trauma, but poorly studied in non-traumatic NP conditions.

Methods

This study aimed to investigate the temporal expressions of activating transcription factor-3 (ATF-3), growth-associated protein-43 (GAP-43), neuropeptide Y (NPY) and galanin in traumatic and non-traumatic rat models of neuropathies associated with NP. Expressions of these markers were examined in the DRG at different time points following tibial nerve transection (TNT) injury and antiretroviral drug stavudine (d4T) administration using immunohistochemistry. The development of sensory gain following these insults was assessed by measuring limb withdrawal to a punctate mechanical stimulus.

Results

Both TNT-injured and d4T-treated rats developed hindpaw mechanical hypersensitivity. Robust expressions of ATF-3, GAP-43, NPY and galanin in both small- and large-sized L5 DRG neurons were observed in the DRG from TNT-injured rats. In contrast, d4T-treated rats did not exhibit any significant neurochemical changes in the DRG.

Conclusions

Taken together, the results suggest that ATF-3, GAP-43, NPY and galanin are likely indicators of nerve trauma-associated processes and not generic markers for NP. These experiments also demonstrate distinct expression patterns of neurochemical markers in the DRG and emphasize the mechanistic difference between nerve trauma and antiretroviral drug-associated NP.

The effects of intradermal botulinum toxin type a injections on pain symptoms of patients with diabetic neuropathy

BACKGROUND

Considering the dramatic increasing rate of diabetes and consequently its related complications, most importantly diabetic peripheral neuropathy (DPN), challenges regarding proper treatment of DPN and its effect on the quality-of-life and care of diabetic patients, the aim of this current study is to evaluate the effect of intradermal botulinum toxin type A (BTX-A) injections on pain symptoms of patients with diabetic neuropathic pain.

MATERIALS AND METHODS

In this randomized double-blind placebo-controlled clinical trial study, diabetic patients aged <70 years with neuropathic pain in both feet were enrolled. Diabetic neuropathy (DN) in selected patients was diagnosed using DN4 questionnaire and nerve conduction velocity examinations. They randomized in two intervention (BTX-A injection/100 unit, N = 20) and placebo groups (normal saline injection, N = 20). The outcome of injection on diabetic neuropathic pain was assessed using neuropathy pain scale (NPS) and visual analog scale (VAS) score and compared in two studied groups.

RESULTS

There was no significant difference in DN4, NPS and VAS scales of studied population after intervention in the placebo group. Intradermal injection of BTX-A reduced NPS scores for all items except cold sensation (P = 0.05). It reduced DN4 scores for electric shocks, burning, pins and needles and brushing (P < 0.05). According to VAS scale 30% and 0% of patients in intervention and placebo groups have no pain after intervention (P = 0.01).

CONCLUSION

Intradermal injection of BTX-A is a well-tolerated agent that has a significant effect on DPN pain.

Disruption of 5-HT2A receptor-PDZ protein interactions alleviates mechanical hypersensitivity in carrageenan-induced inflammation in rats

Despite common pathophysiological mechanisms, inflammatory and neuropathic pain do not respond equally to the analgesic effect of antidepressants, except for selective serotonin reuptake inhibitors (SSRIs), which show a limited efficacy in both conditions. We previously demonstrated that an interfering peptide (TAT-2ASCV) disrupting the interaction between 5-HT2A receptors and its associated PDZ proteins (e.g. PSD-95) reveals a 5-HT2A receptor-mediated anti-hyperalgesic effect and enhances the efficacy of fluoxetine (a SSRI) in diabetic neuropathic pain conditions in rats. Here, we have examined whether the same strategy would be useful to treat inflammatory pain. Sub-chronic inflammatory pain was induced by injecting λ-carrageenan (100 µl, 2%) into the left hind paw of the rat. Mechanical hyperalgesia was assessed after acute treatment with TAT-2ASCV or/and fluoxetine (SSRI) 2.5 h after λ-carrageenan injection. Possible changes in the level of 5-HT2A receptors and its associated PDZ protein PSD-95 upon inflammation induction were quantified by Western blotting in dorsal horn spinal cord. Administration of TAT-2ASCV peptide (100 ng/rat, intrathecally) but not fluoxetine (10 mg/kg, intraperitoneally) relieves mechanical hyperalgesia (paw pressure test) in inflamed rats. This anti-hyperalgesic effect involves spinal 5-HT2A receptors and GABAergic interneurons as it is abolished by a 5-HT2A antagonist (M100907, 150 ng/rat, intrathecally) and a GABAA antagonist, (bicuculline, 3 µg/rat, intrathecally). We also found a decreased expression of 5-HT2A receptors in the dorsal spinal cord of inflamed animals which could not be rescued by TAT-2ASCV injection, while the amount of PSD-95 was not affected by inflammatory pain. Finally, the coadministration of fluoxetine does not further enhance the anti-hyperalgesic effect of TAT-2ASCV peptide. This study reveals a role of the interactions between 5-HT2A receptors and PDZ proteins in the pathophysiological pathways of inflammatory pain and opens new perspectives in its control thanks to molecules disrupting 5-HT2A receptor/PDZ protein interactions.

Safety and efficacy outcomes of long-term treatment up to 4 years with 5% lidocaine medicated plaster in patients with post-herpetic neuralgia

OBJECTIVE

Prospective evaluation of the long-term efficacy and safety of the 5% lidocaine medicated plaster in patients with post-herpetic neuralgia (PHN).

RESEARCH DESIGN AND METHODS

Patients with persisting pain for ≥3 months after acute herpes zoster and a baseline pain intensity of at least 4 on an 11-point numerical rating scale (NRS 0-10) were treated with 5% lidocaine medicated plasters for up to 5 years and monitored in regular intervals. Efficacy parameters are presented for the first 4 years and include patients' recall of pain relief (6-point verbal rating scale (VRS), clinical global impression of change (CGIC), patients' global impression of change PGIC), and the global evaluations of study medication. Safety parameters (clinical examination, skin evaluation, laboratory) and adverse events (AEs) were assessed at regular visits.

CLINICAL TRIAL REGISTRATION

KF10004/02.

RESULTS

A total of 102 patients continuing from a 1 year main study period were included in an extension phase of up to 3 years. Ten patients (9.8%) dropped out due to lack of efficacy and 9 patients (8.8%) due to treatment-related AEs; 56 patients (54.9%) left the study for non-treatment-related reasons. Twenty-seven patients (26.4%) were still under treatment after a total treatment period of 4 years. On average, a pain relief of at least 4.3 (between moderate and a lot) was achieved throughout the study. At all visits the CGIC and the PGIC were much or very much improved in about 80% of patients. At the final visit, study medication was rated at least to be good by 91% of physicians and 89% of patients. Drug-related adverse events (DRAEs) were reported in 19 of 102 patients, mainly mild to moderate localized skin reactions. There were no hints for a reduced analgesic effect or an increase of DRAEs with long-term treatment.

CONCLUSIONS

This study demonstrates that long-term treatment of ≥12 months with the 5% lidocaine medicated plaster is effective and well tolerated in PHN patients. These findings support the recommendations to use the 5% lidocaine medicated plaster as baseline therapy for localized neuropathic pain after herpes zoster infection (PHN).

Use of 5% lidocaine medicated plaster to treat localized neuropathic pain secondary to traumatic injury of peripheral nerves

OBJECTIVE

The efficacy of 5% lidocaine medicated plaster (LMP) has previously been demonstrated in post-traumatic localized neuropathic pain. This study evaluated the use of LMP in localized neuropathic pain secondary to traumatic peripheral nerve injury.

PATIENTS AND METHODS

This prospective observational study enrolled patients with traumatic injuries to peripheral nerves that were accompanied by localized neuropathic pain of more than 3 months duration. Demographic variables, pain intensity (measured using the numeric rating scale; NRS), answers to the Douleur Neuropathique 4 (DN4) questionnaire, and the size of the painful area were recorded.

RESULTS

Nineteen patients were included, aged (mean ± standard deviation) 41.4 ± 15.7 years. Nerve injuries affected the upper (eight patients) or lower (11 patients) limbs. The mean duration of pain before starting treatment with LMP was 22.6 ± 43.5 months (median 8 months). Mean baseline values included: NRS 6.7 ± 1.6, painful area 17.8 ± 10.4 cm(2) (median 18 cm(2)), and DN4 score 6.7 ± 1.4. The mean duration of treatment with LMP was 19.5 ± 10.0 weeks (median 17.4 weeks). Mean values after treatment were: NRS 2.8 ± 1.5 (≥3 point reduction in 79% of patients, ≥50% reduction in 57.9% of patients) and painful area 2.1 ± 2.3 cm(2) (median 1 cm(2), ≥50% reduction in 94.7% of patients). Functional improvement after treatment was observed in 14/19 patients (73.7%).

CONCLUSION

LMP effectively treated traumatic injuries of peripheral nerves which presented with chronic localized neuropathic pain, reducing both pain intensity and the size of the painful area.

Prescribing cannabis for harm reduction

Neuropathic pain affects between 5% and 10% of the US population and can be refractory to treatment. Opioids may be recommended as a second-line pharmacotherapy but have risks including overdose and death. Cannabis has been shown to be effective for treating nerve pain without the risk of fatal poisoning. The author suggests that physicians who treat neuropathic pain with opioids should evaluate their patients for a trial of cannabis and prescribe it when appropriate prior to using opioids. This harm reduction strategy may reduce the morbidity and mortality rates associated with prescription pain medications.