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

Low doses of dextromethorphan have a beneficial effect in the treatment of neuropathic pain

N-methyl-D-aspartate receptor (NMDAR) antagonists may be given in persistent neuropathic pain, but adverse events especially with ketamine may limit their clinical use. Less central and cognitive adverse events are described with dextromethorphan and memantine. These molecules have been explored in many preclinical and clinical studies, but data are conflicting as regards neuropathic pain alleviation. Dextromethorphan and memantine have been administered to animals after spinal nerve ligation (SNL) to evaluate their antinociceptive/cognitive effects and associated molecular events, including the phosphorylation of several tyrosine (pTyr(1336), pTyr(1472)) residues in the NR2B NMDAR subunit. Spinal nerve ligation and sham animals received dextromethorphan (10 mg/kg, i.p.), memantine (20 mg/kg, i.p.) or saline (1 mL/kg, i.p.). These drugs were administered once symptoms of allodynia and hyperalgesia had developed. Tests were carried out before and after surgery. Tactile allodynia, mechanical hyperalgesia and spatial memory were, respectively, evaluated by von Frey, Randall & Selitto and Y-maze tests and molecular events by Western blot analysis. Spinal nerve-ligated animals displayed nociception and impaired spatial memory. Dextromethorphan, but not memantine, reversed neuropathic pain (NP) symptoms, restored spatial memory integrity and decreased the expression of pTyr(1336)NR2B. Following postoperative administration of dextromethorphan, this study has demonstrated for the first time a concordance between behaviour, cognitive function and molecular events via pTyr(1336)NR2B for neuropathic pain alleviation. Confirmation of these findings in patients would constitute a major step forward in the treatment of neuropathic pain and in the improvement of cognitive function and quality of life.

Capsaicin 8% patch for peripheral neuropathic pain: review of treatment best practice from 'real-world' clinical experience

SUMMARY The capsaicin 8% patch is licensed in Europe for the treatment of peripheral neuropathic pain in nondiabetic adults. In controlled trials it provided pain relief for up to 3 months with a single 30- or 60-min application. In this article, a group of pain specialists from Germany and the UK share their considerable experience of real-world use of the capsaicin 8% patch. This experience comes from treating >200 patients with a variety of neuropathic pain etiologies including postherpetic neuralgia, peripheral neuropathy and cancer-related neuropathy. These patients, a slight majority of whom were female, had experienced neuropathic pain for varied lengths of time (3 months to >15 years) and the majority were receiving concomitant medications for their pain at the time of capsaicin 8% patch treatment. Observations by the group suggest that patients with positive symptoms might respond best to therapy. To optimize response to treatment, the group reports that it is important to achieve good adhesion of the patch to the skin. The experience of the group is that the capsaicin 8% patch is a tolerable treatment and local anesthetic pretreatment may not always be required. Cooling measures used after treatments were found to be the most practical and beneficial means of relieving any treatment-related discomfort. The group observed that transient, clinically important increases in blood pressure owing to treatment-related discomfort are very rare and they have seen no correlation between treatment-related discomfort or erythema and response to treatment. In the real-life clinical setting, response to capsaicin 8% patch treatment may be higher than observed in the clinical trial program. Response to retreatment also appears to be equal to that of the first treatment, even in patients treated for the fifth time. It was also observed that patients receiving capsaicin 8% patch treatment are often able to reduce their intake of concomitant pain medications. Observations from real-life use of the capsaicin 8% patch will help to maximize its therapeutic potential.

Topical high-concentration menthol: reproducibility of a human surrogate pain model

BACKGROUND

Human experimental pain models play an important role in studying neuropathic pain mechanisms. The objective of the present study was to test the reproducibility of the topical menthol model over a 1-week period.

METHOD

We performed an open, two-period study in 10 healthy volunteers with 40 menthol applications. The side of menthol application was randomly assigned. Two trial periods were separated by 1 week. Before and after applying menthol, selected quantitative sensory testing (QST) was performed. The area of mechanical pin-prick hyperalgesia was quantified. Spontaneous pain was recorded.

RESULTS

Application of menthol induced a statistically significant decrease in the cold pain threshold (CPT) (p < 0.001) and mechanical pain threshold and an increase in the mechanical pain sensitivity (MPS) (p < 0.001), indicating cold and mechanical (pin-prick) hyperalgesia. Test-retest reliability was best for CPT (r = 0.959) and MPS (r = 0.930). Intraclass correlation values showed excellent reliability for cold pain and MPS (ICC = 0.96, 0.89). The QST values post-menthol showed high inter-period correlation factors and no significant inter-period differences (paired t-test, t = 1.767-1.361; p = 0.111-0.988). The area size of mechanical hyperalgesia was not reliably reproducible.

CONCLUSION

For an observation period of 1 week, the signs of cold and mechanical hyperalgesia were reproducible with a highly significant correlation of about r = 0.8 and good agreement except for the area size of mechanical pin-prick hyperalgesia. These results demonstrate that the topical menthol pain model is suitable for pharmacological interventions repeated within an observation period of 1 week.

Consequences of a human TRPA1 genetic variant on the perception of nociceptive and olfactory stimuli

Background

TRPA1 ion channels are involved in nociception and are also excited by pungent odorous substances. Based on reported associations of TRPA1 genetics with increased sensitivity to thermal pain stimuli, we therefore hypothesized that this association also exists for increased olfactory sensitivity.

Methods

Olfactory function and nociception was compared between carriers (n = 38) and non-carriers (n = 43) of TRPA1 variant rs11988795 G>A, a variant known to enhance cold pain perception. Olfactory function was quantified by assessing the odor threshold, odor discrimination and odor identification, and by applying 200-ms pulses of H₂S intranasal. Nociception was assessed by measuring pain thresholds to experimental nociceptive stimuli (blunt pressure, electrical stimuli, cold and heat stimuli, and 200-ms intranasal pulses of CO₂).

Results

Among the 11 subjects with moderate hyposmia, carriers of the minor A allele (n = 2) were underrepresented (34 carriers among the 70 normosmic subjects; p = 0.049). Moreover, carriers of the A allele discriminated odors significantly better than non-carriers (13.1±1.5 versus 12.3±1.6 correct discriminations) and indicated a higher intensity of the H₂S stimuli (29.2±13.2 versus 21±12.8 mm VAS, p = 0.006), which, however, could not be excluded to have involved a trigeminal component during stimulation. Finally, the increased sensitivity to thermal pain could be reproduced.

Conclusions

The findings are in line with a previous association of a human TRPA1 variant with nociceptive parameters and extend the association to the perception of odorants. However, this addresses mainly those stimulants that involve a trigeminal component whereas a pure olfactory effect may remain disputable. Nevertheless, findings suggest that future TRPA1 modulating drugs may modify the perception of odorants.

Neuropathic cancer pain: What we are dealing with? How to manage it?

Cancer pain is a serious health problem, and imposes a great burden on the lives of patients and their families. Pain can be associated with delay in treatment, denial of treatment, or failure of treatment. If the pain is not treated properly it may impair the quality of life. Neuropathic cancer pain (NCP) is one of the most complex phenomena among cancer pain syndromes. NCP may result from direct damage to nerves due to acute diagnostic/therapeutic interventions. Chronic NCP is the result of treatment complications or malignancy itself. Although the reason for pain is different in NCP and noncancer neuropathic pain, the pathophysiologic mechanisms are similar. Data regarding neuropathic pain are primarily obtained from neuropathic pain studies. Evidence pertaining to NCP is limited. NCP due to chemotherapeutic toxicity is a major problem for physicians. In the past two decades, there have been efforts to standardize NCP treatment in order to provide better medical service. Opioids are the mainstay of cancer pain treatment; however, a new group of therapeutics called coanalgesic drugs has been introduced to pain treatment. These coanalgesics include gabapentinoids (gabapentin, pregabalin), antidepressants (tricyclic antidepressants, duloxetine, and venlafaxine), corticosteroids, bisphosphonates, N-methyl-D-aspartate antagonists, and cannabinoids. Pain can be encountered throughout every step of cancer treatment, and thus all practicing oncologists must be capable of assessing pain, know the possible underlying pathophysiology, and manage it appropriately. The purpose of this review is to discuss neuropathic pain and NCP in detail, the relevance of this topic, clinical features, possible pathology, and treatments of NCP.

Spinal and supraspinal processing of thermal stimuli: an fMRI study

PURPOSE

To assess and characterize responses to innocuous/noxious thermal stimuli and heat allodynia using functional spinal magnetic resonance imaging (spinal fMRI).

MATERIALS AND METHODS

Spinal/supraspinal activation patterns of 16 healthy subjects were investigated by applying painful and nonpainful heat stimuli to dermatome C6 baseline and after sensitization with the heat/capsaicin model using fMRI (3T, single-shot TSE, TR 9000 msec, TE 38 msec, FOV 288 × 144 × 20 mm, matrix 192 × 96, voxel size 1 × 1 × 2 mm).

RESULTS

Increased activity was observed in ipsi- and contralateral ventral and dorsal spinal horn during noxious heat and heat allodynia. During noxious heat, but not during heat allodynia, activations were visible in the periaqueductal gray, ipsilateral cuneiform nucleus, and ipsilateral dorsolateral pontine tegmentum (DLPT). However, during heat allodynia activations were observed in bilateral ruber nuclei, contralateral DLPT, and rostral ventromedial medulla oblongata (RVM). Activations in contralateral subnucleus reticularis dorsalis (SRD) were visible during both noxious heat and heat allodynia (T >2.5, P < 0.01 for all of the above). After sensitization, activations in RVM and SRD correlated with activations in the ipsilateral dorsal horn of the spinal cord (R = 0.52-0.98, P < 0.05).

CONCLUSION

Spinal fMRI successfully demonstrates increased spinal activity and secondary changes in activation of supraspinal centers involved in pain modulation caused by peripheral nociceptor sensitization. J. Magn. Reson. Imaging 2015;41:1046-1055. © 2014 Wiley Periodicals, Inc.

Vaccination against and treatment of acute herpes zoster for prevention of post-herpetic neuralgia

Zostavax (zoster vaccine) is a 1-dose, high-potency, live, attenuated varicella zoster virus (VZV) vaccine that boosts VZV-specific cell-mediated immunity (CMI), and this is its presumed mechanism of action. Other strategies focus on preventing the major complication of HZ, post-herpetic neuralgia (PHN). Evidence that the vaccine is effective in older patients comes from the pivotal Shingles Prevention Study. That study demonstrated that HZ vaccine significantly reduced morbidity due to HZ and PHN in older patients. However, the duration of efficacy beyond 5 years after vaccination remains unclear. The Long-Term Persistence Substudy, currently under analysis, may provide additional data on the duration of efficacy for zoster vaccine. This review discusses vaccination against HZ, and further reviews recent pharmacotherapy for prevention of PHN.

Fabry disease: a rare cause of neuropathic pain

Fabry disease is characterized by burning or shooting pains in hands and feet, which have a severe impact on the quality of life of patients. It is therefore of importance that Fabry patients receive adequate diagnosis, counseling, treatment and follow up. This review describes neuropathic pain in classical Fabry disease with the aim to help clinicians to recognize Fabry patients among patients presenting with chronic extremity pain. The diagnostic dilemmas in patients with neuropathic pain and a non-classical disease course are discussed, together with the available diagnostic modalities, pain medication options and the effect of enzyme replacement therapy on small fiber neuropathy.

Conditioned pain modulation: a predictor for development and treatment of neuropathic pain

Psychophysical evaluation of endogenous pain inhibition via conditioned pain modulation (CPM) represents a new generation of laboratory tests for pain assessment. In this review we discuss recent findings on CPM in neuropathic pain and refer to psychophysical, neurophysiological, and methodological aspects of its clinical implications. Typically, chronic neuropathic pain patients express less efficient CPM, to the extent that incidence of acquiring neuropathic pain (e.g. post-surgery) and its intensity can be predicted by a pre-surgery CPM assessment. Moreover, pre-treatment CPM evaluation may assist in the correct choice of serotonin-noradrenalin reuptake inhibitor analgesic agents for individual patients. Evaluation of pain modulation capabilities can serve as a step forward in individualizing pain medicine.

Neuromodulatory treatments for chronic pain: efficacy and mechanisms

Chronic pain is common, and the available treatments do not provide adequate relief for most patients. Neuromodulatory interventions that modify brain processes underlying the experience of pain have the potential to provide substantial relief for some of these patients. The purpose of this Review is to summarize the state of knowledge regarding the efficacy and mechanisms of noninvasive neuromodulatory treatments for chronic pain. The findings provide support for the efficacy and positive side-effect profile of hypnosis, and limited evidence for the potential efficacy of meditation training, noninvasive electrical stimulation procedures, and neurofeedback procedures. Mechanisms research indicates that hypnosis influences multiple neurophysiological processes involved in the experience of pain. Evidence also indicates that mindfulness meditation has both immediate and long-term effects on cortical structures and activity involved in attention, emotional responding and pain. Less is known about the mechanisms of other neuromodulatory treatments. On the basis of the data discussed in this Review, training in the use of self-hypnosis might be considered a viable 'first-line' approach to treat chronic pain. More-definitive research regarding the benefits and costs of meditation training, noninvasive brain stimulation and neurofeedback is needed before these treatments can be recommended for the treatment of chronic pain.

ARA 290, a peptide derived from the tertiary structure of erythropoietin, produces long-term relief of neuropathic pain coupled with suppression of the spinal microglia response

Background

Neuropathic pain is a difficult to treat disorder arising from central or peripheral nervous system lesions. The etiology of neuropathic pain consists of several overlapping pathways converging into an exaggerated pain state with symptoms such as allodynia and hyperalgesia. One of these pathways involves activation of spinal cord microglia and astrocytes, which drive and maintain the inflammatory response following the lesion. These cells are a potential target for drugs for neuropathic pain relief. In this current study, we investigated the dose-effect relationship of the tissue protective peptide ARA 290, derived from the tertiary structure of erythropoietin, on allodynia and concurrent spinal cord microglia and astrocytes.

Results

Following a spared nerve injury in rats, vehicle or ARA290 (administered in either one of 4 doses: 3, 10, 30 and 60 μg/kg) was administered on days 1, 3, 6, 8 and 10. ARA290 exerted a dose–response effect by significantly reducing mechanical allodynia up to 20 weeks when compared to vehicle. The reduction of cold allodynia was significant up to 20 weeks for the doses 3, 10, 30 and 60 μg/kg when compared to vehicle. The effect 10 and 30 μg/kg ARA290 and vehicle on the microglia response (iba-1-immunoreactivity, iba-1-IR) and astrocyte reaction (GFAP-immunoreactivity, GFAP-IR) was investigated in animals surviving 2 (group 1) or 20 (group 2) weeks following lesion or sham surgery. In group 1, significant microglia reactivity was observed in the L5 segment of the spinal cord of animals treated with vehicle when compared to sham operated, while animals treated with 10 or 30 μg/kg did not show a increase. In group 2, a more widespread and increased microglia reactivity was observed for animals treated with 0 and 10 μg/kg when compared to sham operated animals, indicated by involvement of more spinal cord segments and higher iba-1-IR. Animals treated with 30 μg/kg did not show increased microglia reactivity. No difference in astrocyte reaction was observed.

Conclusions

The erythropoietin-analogue ARA290 dose-dependently reduced allodynia coupled to suppression of the spinal microglia response, suggestive of a mechanistic link between ARA290-induced suppression of central inflammation and relief of neuropathic pain symptoms.

Impaired neuropathic pain and preserved acute pain in rats overexpressing voltage-gated potassium channel subunit Kv1.2 in primary afferent neurons

Voltage-gated potassium (Kv) channels are critical in controlling neuronal excitability and are involved in the induction of neuropathic pain. Therefore, Kv channels might be potential targets for prevention and/or treatment of this disorder. We reported here that a majority of dorsal root ganglion (DRG) neurons were positive for Kv channel alpha subunit Kv1.2. Most of them were large and medium, although there was a variety of sizes. Peripheral nerve injury caused by lumbar (L)₅ spinal nerve ligation (SNL) produced a time-dependent reduction in the number of Kv1.2-positive neurons in the ipsilateral L₅ DRG, but not in the contralateral L₅ DRG. Such reduction was also observed in the ipsilateral L₅ DRG on day 7 after sciatic nerve axotomy. Rescuing nerve injury-induced reduction of Kv1.2 in the injured L₅ DRG attenuated the development and maintenance of SNL-induced pain hypersensitivity without affecting acute pain and locomotor function. This effect might be attributed to the prevention of SNL-induced upregulation of endogenous Kv1.2 antisense RNA, in addition to the increase in Kv1.2 protein expression, in the injured DRG. Our findings suggest that Kv1.2 may be a novel potential target for preventing and/or treating neuropathic pain.

Review of the complications associated with treatment of oropharyngeal cancer: a guide for the dental practitioner

OBJECTIVES

Oropharyngeal cancer (OPC) is the sixth most common cancer worldwide. Focus on risk factors, improved diagnostic methods and effective management strategies have made it possible to successfully treat OPC. However, the 5-year survival rate has not improved for several years due to multiple treatment complications, tissue morbidity, loss of function, and diminished quality of life. Survivors are faced with complications like oral mucositis, hyposalivation, osteoradionecrosis, tissue fibrosis, morbidity from jaw resection, disfigurement, and loss of function that further diminish quality of life. The aim of this review is to highlight major complications associated with treatment of OPC via a literature search and review of available options for identification and management of these complications.

DATA SOURCES

Relevant publications on oral complications of OPC therapy were thoroughly reviewed from the literature published between the years 1988 and 2012. We evaluated reported incidence, prevalence, and risk factors for oral complications of chemotherapy and radiotherapy for OPC. The authors conducted an electronic search using English language databases, namely PubMed Plus, Medline (Pre-Medline and Medline), Cochrane Database of Systematic Reviews (evidence-based medicine), Dentistry & Oral Sciences Source, A ccessScience, Embase, Evidence-Based Medicine Reviews Multifile, Google Scholar, ISI Journal Citation Reports, and Ovid Multi-Database.

CONCLUSION

We identified the most common complications associated with the treatment of oral cancers. Based on the information gathered, there is evidence that survival of OPC extends beyond eradication of the diseased tissue. Understanding the potential treatment complications and utilizing available resources to prevent and minimize them are important. Caring for OPC survivors should be a multidisciplinary team approach involving the dentist, oncologist, internist, and social worker to improve the currently stagnant 5-year survival rate of OPC. More emphasis on improved quality of life after elimination of the cancer will ultimately improve OPC survivorship.

Ketamine reduces the induced spinal p38 MAPK and pro-inflammatory cytokines in a neuropathic rats

BACKGROUND

Neuropathic rats created by spinal nerve ligation are known to show higher levels of p38, c-Jun NH2-terminal kinase, and extracellular signal-regulated kinase p44/42 (ERK 1/2) of the mitogen-activated protein kinases (MAPKs). The authors of this study aimed to understand the effect of ketamine on p38 MAPK and inflammatory responses, as well as its effect on the development of neuropathic pain.

METHODS

The neuropathic rats were prepared by Chung's method with Sprague-Dawley rats. The research was carried out on three groups, a sham-operated group, a neuropathic pain and normal saline (NP + NS) group, and a neuropathic pain and ketamine (NP + Keta) group. The normal saline or ketamine was infused into the neuropathic rats through a mini-osmotic pump implanted in the subcutaneous space. After a week, the quantities of phospho-p38, p38 MAPK and pro-inflammatory cytokines were measured and compared through western blots and reverse transcriptase-polymerase chain reaction.

RESULTS

In comparison to the control group, the NP + NS group showed a significant increase of phospho-p38 and p38 MAPK, as well as of the proinflammatory cytokines, tumor necrosis factor α (TNFα), and intercellular adhesion molecule 1 (ICAM1). However, in the NP + Keta group, phospho-p38, p38 MAPK and TNFα and, ICAM1 were reduced in comparison to the NP + NS group. The paw withdrawal threshold test also showed the trend of recovery from the mechanical allodynia in the NP + Keta group.

CONCLUSIONS

In the development of neuropathic pain, p38 MAPK and inflammatory responses are significantly related, and the use of ketamine reduces p38 MAPK and proinflammatory cytokines. Thus, the adequate use of ketamine could be effective for the prevention and treatment of neuropathic pain following peripheral injury.

Opportunities for rehabilitation of patients with radiation fibrosis syndrome

This review discusses the pathophysiology, evaluation, and treatment of neuromuscular, musculoskeletal, and functional disorders that can result as late effects of radiation treatment. Although radiation therapy is often an effective method of killing cancer cells, it can also damage nearby blood vessels that nourish the skin, ligaments, tendons, muscles, nerves, bones and lungs. This can result in a progressive condition called radiation fibrosis syndrome (RFS). It is generally a late complication of radiotherapy which may manifest clinically years after treatment. Radiation-induced damage can include "myelo-radiculo-plexo-neuro-myopathy," causing muscle weakness and dysfunction and contributing to neuromuscular injury. RFS is a serious and lifelong disorder which, nevertheless, may often be decremented when identified and rehabilitated early enough. This medical treatment should be a complex procedure consisting of education, physical therapy, occupational therapy, orthotics as well as medications.

Changes in epidermal thickness and cutaneous innervation during maturation in long-term diabetes

AIM

Peripheral nerve fiber depletion in patients with chronic diabetes mellitus (DM) was linked to neuropathic symptoms, development of pain, foot ulcerations and lower extremity amputation. The aim of this study was to analyze cutaneous changes, including paw epidermal thickness and intraepidermal nerve fiber (IENF) density in long-term diabetes, in rats 6 months and 12 months after induction of diabetes.

MATERIALS AND METHODS

Epidermal thickness and IENF density were studied in Sprague-Dawley diabetic rats 6 months and 12 months after diabetes induction with streptozotocin. Epidermal thickness was evaluated using hematoxylin and eosin staining. Peripheral nerve fibers were stained with polyclonal antiserum against protein gene product 9.5 (PGP 9.5). Successful diabetes induction was validated by measuring plasma glucose and body mass regularly throughout the experiment.

RESULTS

This study showed that long-term diabetes, induced in Sprague-Dawley rats with streptozotocin, is characterized with significant epidermal thinning and reduction of intraepidermal nerve fibers, 6 months and 12 months after induction of diabetes.

CONCLUSION

Long-term studies of streptozotocin models of diabetes could be used for making normative IENF densities that can be later used as age-dependent normative values for studying new treatment modalities.

Lidocaine Patch (5%) in Treatment of Persistent Inguinal Postherniorrhaphy Pain

Background:

Evidence-based pharmacological treatment options for patients with persistent inguinal postherniorrhaphy pain are lacking.

Methods:

Twenty-one male patients, with severe, unilateral, persistent inguinal postherniorrhaphy pain, participated in a randomized, double-blind, placebo-controlled crossover trial, receiving lidocaine patch (5%) and placebo patch treatments in periods of 14 days separated by a 14-day wash-out period. Pain intensities (at rest, during movement, and pressure evoked [Numerical Rating Scale]) were assessed before treatment and on the last 3 days of each treatment period. Patients were a priori divided into two subgroups based on quantitative sensory testing (+/− thermal “hyposensitivity”). Skin biopsies for intraepidermal nerve fiber density assessment were taken at baseline, and quantitative sensory testing was performed before and after each treatment period. The primary outcome was change in pain intensity assessed as the difference in summed pain intensity differences between lidocaine and placebo patch treatments.

Results:

There was no difference in summed pain intensity differences between lidocaine and placebo patch treatments in all patients (mean difference 6.2% [95% CI = −6.6 to 18.9%]; P = 0.33) or in the two subgroups (+/− thermal “hyposensitivity”). The quantitative sensory testing (n = 21) demonstrated an increased pressure pain thresholds after lidocaine compared with placebo patch treatment. Baseline intraepidermal nerve fiber density (n = 21) was lower on the pain side compared with the nonpain side (−3.8 fibers per millimeter [95% CI = −6.1 to −1.4]; P = 0.003). One patient developed mild erythema in the groin during both treatments.

Conclusions:

Lidocaine patch treatment did not reduce combined resting and dynamic pain ratings compared with placebo in patients with severe, persistent inguinal postherniorrhaphy pain.

Sensory profile and its impact on quality of life in patients with painful diabetic polyneuropathy

Context:

Painful diabetic polyneuropathy (PDN) is common and causes significant disability. The sensory profile in each patient is different and affects quality of life.

Aim:

To describe the demographic, details of sensory profile and its impact on quality of life in patients with PDN.

Settings and Design:

A cross-sectional survey in patients with PDN who were treated in a University Hospital.

Materials and Methods:

They were interviewed with standard questionnaires, which included neuropathic pain scale (NPS), a short-form McGill Pain Questionnaire (SF-MPQ) and a short form-36 quality of life survey (SF-36).

Statistical Analysis Used:

Descriptive statistics were used in demographic data. Student's t test was used to analyze continuous data. Multiple comparisons for proportions and correlations were made using Fisher Exact test and Pearson's coefficient of correlation, respectively.

Results:

Thirty three patients were included in this study. In NPS, sharp pain was the most common symptom and itching was the least common. Almost all patients had more than one type of pain. The mean VAS was 53 mm. In SFMPQ, the sensory score, affective score and the present pain score fell in the moderate range. In SF-36, physical functioning was the most affected and social function was the least affected.

Conclusions:

PDN significantly affects patients’ quality of life, especially physical function and role limitation due to a physical problem. Almost all patients have many types of pain and sharp pain is the most common.

Foot compartment syndrome: diagnosis and management

Although uncommon, foot compartment syndrome (FCS) is a distinct clinical entity that typically results from high-energy fractures and crush injuries. In the literature, the reported number of anatomic compartments in the foot has ranged from 3 to 10, and the clinical relevance of these compartments has recently been investigated. Diagnosis of FCS can be challenging because the signs and symptoms are less reliable indicators than those of compartment syndrome in other areas of the body. This may lead to a delay in diagnosis. The role of fasciotomy in management of FCS has been debated, but no high-level evidence exists to guide decision making. Nevertheless, emergent fasciotomy is commonly recommended with the goal of preventing chronic pain and deformity. Surgical intervention may also be necessary for the correction of secondary deformity.

Analgesic treatment with pregabalin does not prevent persistent pain after peripheral nerve injury in the rat

Reducing the risk of chronic postoperative pain through preventive analgesia is an attractive therapeutic concept. Because peripheral nerve lesions are a major cause of chronic pain after surgery, we tested in rats whether analgesic treatment with pregabalin (PGB) has the capacity to mitigate the development of persistent neuropathic pain-like behavior. Starting on the day of spared nerve injury or 1week later, we treated rats with a continuous intrathecal infusion of PGB (300 or 900μg/24hours) or vehicle for up to 28days. Rats receiving early PGB treatment had almost normal withdrawal thresholds for punctate mechanical stimuli and were clearly less sensitive to pinprick or cold stimulation. The responses to punctate mechanical and cold stimulation were still reduced for a brief period after the infusion was terminated, but the difference from vehicle-treated rats was minor. Essentially, the analgesic effect of PGB was limited to the duration of the infusion, whether analgesia started at the time of surgery or with a delay of 1week, independently of the length of the treatment. PGB did not suppress the activation of spinal microglia, indicating that analgesia alone does not eliminate certain pain mechanisms even if they depend, at least partially, on nociceptive input. Unexpectedly, intrathecal infusion of PGB did not inhibit the nerve injury-induced accumulation of its binding target, the voltage-gated calcium channel subunit α2δ1, at primary afferent terminals in the spinal cord. Interference with the synaptic trafficking of α2δ1 is not required to achieve analgesia with PGB.

Electrophysiological characterization of spinal neuron sensitization by elevated calcium channel alpha-2-delta-1 subunit protein

BACKGROUND

Voltage-gated calcium channel α2 δ1 subunit is the binding site for gabapentin, an effective drug in controlling neuropathic pain states including thermal hyperalgesia. Hyperalgesia to noxious thermal stimuli in both spinal nerve-ligated (SNL) and voltage-gated calcium channel α2 δ1 overexpressing transgenic (Tg) mice correlates with higher α2 δ1 levels in dorsal root ganglia and dorsal spinal cord. In this study, we investigated whether abnormal synaptic transmission is responsible for thermal hyperalgesia induced by elevated α2 δ1 expression in these models.

METHODS

Behavioural sensitivities to thermal stimuli were test in L4 SNL and sham mice, as well as in α2 δ1 Tg and wild-type mice. Miniature excitatory (mEPSC) and inhibitory (mIPSC) post-synaptic currents were recorded in superficial dorsal spinal cord neurons from these models using whole-cell patch clamp slice recording techniques.

RESULTS

The frequency, but not amplitude, of mEPSC in superficial dorsal horn neurons was increased in SNL and α2 δ1 Tg mice, which could be attenuated by gabapentin dose dependently. Intrathecal α2 δ1 antisense oligodeoxynucleotide treatment diminished increased mEPSC frequency and gabapentin's inhibitory effects in elevated mEPSC frequency in the SNL mice. In contrast, neither the frequency nor the amplitude of mIPSC was altered in superficial dorsal horn neurons from the SNL and α2 δ1 Tg mice.

CONCLUSIONS

Our findings support a role of peripheral nerve injury-induced α2 δ1 in enhancing pre-synaptic excitatory input onto superficial dorsal spinal cord neurons that contributes to nociception development.

Evidence-based guidance for the management of postherpetic neuralgia in primary care

This article aims to help primary care physicians negotiate gaps in current guidelines for postherpetic neuralgia (PHN). The objectives of this article are to: 1) briefly review the available guidelines and identify their strengths and weaknesses; 2) review the gaps in the guidelines; 3) review new data that were not included in the most recent guidelines; 4) provide expert opinion on how the new data and current guidelines can be used to make treatment decisions; and 5) review several important dimensions of care (eg, tolerability, dosing) and provide guidance. In general, all guidelines recognize the α2δ ligands, tricyclic antidepressants (TCAs), opioids, and tramadol as efficacious systemic options, with topical lidocaine serving as an efficacious nonsystemic approach for localized PHN treatment. The first-line treatment options typically recommended in the guidelines are α2δ ligands and TCAs, while opioids and tramadol are often recommended as second- or third-line options. Since the latest guidelines were published, newer agents (eg, topical capsaicin [8%] patch and gastroretentive gabapentin) have met the standard as first-line therapy with the publication of ≥ 1 randomized controlled trial. However, gabapentin enacarbil has not met this standard due to a lack of a published randomized controlled trial in PHN.

Epigenetic upregulation of CCL2 and CCL3 via histone modifications in infiltrating macrophages after peripheral nerve injury

To gain insight into the epigenetic regulation of CC-chemokine ligand (CCL) 2 and CCL3, key players in the peripheral sensitization leading to neuropathic pain, we examined the relationship between histone H3 modification and the upregulation of these molecules using a mouse model of neuropathic pain after partial sciatic nerve ligation (PSL). We found that circuiting bone marrow (BM)-derived macrophages infiltrated into the injured sciatic nerve (SCN) using enhanced green fluorescent protein chimeric mice. The mRNA levels of CCL2, CCL3 and their receptors (CCR2 and CCR1/CCR5, respectively) were increased in the injured SCN. Chromatin immunoprecipitation assay revealed that levels of lysine 9-acetylated histone H3 (H3K9Ac) and lysine 4-trimethylated H3 (H3K4me(3)) in the promoter regions of the CCL2 and CCL3 genes were increased in the injured SCN after PSL, indicating the enhancement of gene expression. Immunoreactivity for H3K9Ac and H3K4me(3) was localized in the nuclei of infiltrating BM-derived cells and CCL-expressing cells in the injured SCN. We observed H3K9Ac and H3K4me(3) mainly in the nuclei of recruited macrophages on day 7 after PSL. Furthermore, upregulation of CCLs and CCRs were suppressed by histone acetyltransferase inhibitor, anacardic acid. Taken together, our findings demonstrate that CCL2 and CCL3 are upregulated in the injured peripheral nerve through epigenetic histone modification in infiltrating immune cells such as macrophages. These chemokine cascades may subsequently elicit chronic neuroinflammation following nerve injury.

Assessment of allodynia relief by tissue-protective molecules in a rat model of nerve injury-induced neuropathic pain

Neuropathic pain following nerve injury is a chronic disease characterized by allodynia and hyperalgesia of either mechanical or thermal origin. The mechanism underlying this disease is poorly understood leading to pharmacologic and physiotherapeutic control that is often insufficient. In this chapter, we describe a method to induce nerve injury in rats to create a robust animal model for studying neuropathic pain. Additionally we describe a method to follow up on animals in the process of testing treatments for efficacy in alleviating allodynia by testing for both mechanical and thermal allodynia with reproducible results.

Stronger antinociceptive efficacy of opioids at the injured nerve trunk than at its peripheral terminals in neuropathic pain

Activation of opioid receptors on peripheral sensory neurons has the potential for safe pain control, as it lacks centrally mediated side effects. While this approach often only partially suppressed neuropathic pain in animal models, opioids were mostly applied to animal paws although neuropathy was induced at the nerve trunk. Here we aimed to identify the most relevant peripheral site of opioid action for efficient antinociception in neuropathy. On days 2 and 14 following a chronic constriction injury (CCI) of the sciatic nerve in mice, we evaluated dose and time relationships of the effects of μ-, δ-, and κ-opioid receptor agonists injected either at the CCI site or intraplantarly (i.pl.) into the lesioned nerve-innervated paw, on spontaneous paw lifting and heat and mechanical hypersensitivity (using Hargreaves and von Frey tests, respectively). We found that neither agonist diminished spontaneous paw lifting, despite the application site. Heat hypersensitivity was partially attenuated by i.pl. μ-receptor agonist only, while it was improved by all three agonists applied at the CCI site. Mechanical hypersensitivity was slightly diminished by all agonists administered i.pl., whereas it was completely blocked by all opioids injected at the CCI site. These antinociceptive effects were opioid receptor type-selective and site-specific. Thus, opioids might not be effective against spontaneous pain, but they improve heat and mechanical hypersensitivity in neuropathy. Importantly, efficient alleviation of hypersensitivity is governed by peripheral opioid receptors at the injured nerve trunk rather than at its peripheral terminals. Identifying the primary action site of analgesics is important for the development of adequate pain therapies.

Neuropathic pain symptoms on the modified painDETECT correlate with signs of central sensitization in knee osteoarthritis

OBJECTIVE

Clinical tools are needed to identify and target a neuropathic-like phenotype, which may be associated with central sensitization (CS), in osteoarthritis (OA). The modified painDETECT questionnaire (mPD-Q) has face and content validity for identifying neuropathic-like symptoms in knee OA. To further validate the mPD-Q, this study assessed the unknown relationship between mPD-Q scores and signs of CS on quantitative sensory testing (QST) in knee OA.

DESIGN

36 Individuals were recruited with chronic, symptomatic, knee OA without other pain/neurological conditions. Reference QST data were obtained from 18 controls/32 eligible knees, enabling identification of sensory abnormalities/CS among case knees. A standardized questionnaire assessed psychological factors (depressive symptoms and pain catastrophizing), and for individual knees, mPD-Q and pain intensity scores. A standardized/comprehensive QST protocol was conducted for each knee. QST signs of CS were defined as: mechanical hyperalgesia and/or enhanced temporal summation and/or allodynia. The relationship between the presence of CS (yes/no) and a pre-selected mPD-Q score (≤12 or >12), by knees, was assessed using generalized estimating equations.

RESULTS

Among 57 eligible case knees, 45.6% had ≥1 sign of CS. Controlling for age, knees with higher mPD-Q scores (>12.0) had higher odds of having QST signs of CS (adjusted odds ratio (OR) = 5.6; 95% confidence interval (CI), 1.3-22.9). This relationship was unaffected by controlling for depression and pain intensity, but was attenuated by pain catastrophizing.

CONCLUSIONS

Among painful OA knees, higher mPD-Q scores were associated with greater odds of having signs of CS. Thus, the mPD-Q may aid the identification of CS in people with chronic knee OA.

Pain in chemotherapy-induced neuropathy--more than neuropathic?

Chemotherapy-induced neuropathy (CIN) is an adverse effect of chemotherapy. Pain in CIN might comprise neuropathic and nonneuropathic (ie, musculoskeletal) pain components, which might be characterized by pain patterns, electrophysiology, and somatosensory profiling. Included were 146 patients (100 female, 46 male; aged 56 ± 0.8 years) with CIN arising from different chemotherapy regimens. Patients were characterized clinically through nerve conduction studies (NCS) and quantitative sensory testing (QST). Questionnaires for pain (McGill) and anxiety/depression (Hospital Anxiety and Depression Scale) were supplied. Patients were followed-up after 17 days. Large- (61%) and mixed- (35%) fibre neuropathies were more frequent than small-fibre neuropathy (1.4%). The 5 major chemotherapeutic regimens impacted differently on large- but not on small-fibre function and did not predict painfulness. Chronic pain associated with CIN was reported in 41.7%. Painless and painful CIN did not differ in QST profiles or electrophysiological findings, but different somatosensory patterns were found in CIN subgroups (pain at rest [RestP], n = 25; movement-associated pain [MovP], n = 15; both pain characteristics [MovP+RestP], n = 21; or no pain [NonP], n = 85): small-fibre function (cold-detection threshold, CDT: z score: -1.46 ± 0.21, P < 0.01) was most impaired in RestP; mechanical hyperalgesia was exclusively found in MovP (z score: +0.81 ± 0.30, P < 0.05). "Anxiety" discriminated between painful and painless CIN; "CDT" and "anxiety" discriminated between patients with ongoing (RestP) and movement-associated pain (MovP) or pain components (MovP+RestP). The detrimental effect of chemotherapy on large fibres failed to differentiate painful from painless CIN. Patients stratified for musculoskeletal or neuropathic pain, however, differed in psychological and somatosensory parameters. This stratification might allow for the application of a more specific therapy.

Opioids for neuropathic pain

BACKGROUND

This is an updated version of the original Cochrane review published in Issue 3, 2006, which included 23 trials. The use of opioids for neuropathic pain remains controversial. Studies have been small, have yielded equivocal results, and have not established the long-term profile of benefits and risks for people with neuropathic pain.

OBJECTIVES

To reassess the efficacy and safety of opioid agonists for the treatment of neuropathic pain.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (to 24th October 2012), MEDLINE (1966 to 24th October 2012 ), and EMBASE (1980 to 24th October 2012) for articles in any language, and reference lists of reviews and retrieved articles.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in which opioid agonists were given to treat central or peripheral neuropathic pain of any etiology. Pain was assessed using validated instruments, and adverse events were reported. We excluded studies in which drugs other than opioid agonists were combined with opioids or opioids were administered epidurally or intrathecally.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and included demographic variables, diagnoses, interventions, efficacy, and adverse effects.

MAIN RESULTS

Thirty-one trials met our inclusion criteria, studying 10 different opioids: 23 studies from the original 2006 review and eight additional studies from this updated review.Seventeen studies (392 participants with neuropathic pain, average 22 participants per study) provided efficacy data for acute exposure to opioids over less than 24 hours. Sixteen reported pain outcomes, with contradictory results; 8/16 reported less pain with opioids than placebo, 2/16 reported that some but not all participants benefited, 5/16 reported no difference, and 1/16 reported equivocal results. Six studies with about 170 participants indicated that mean pain scores with opioid were about 15/100 points less than placebo.Fourteen studies (845 participants, average 60 participants per study) were of intermediate duration lasting 12 weeks or less; most studies lasted less than six weeks. Most studies used imputation methods for participant withdrawal known to be associated with considerable bias; none used a method known not to be associated with bias. The evidence, therefore, derives from studies predominantly with features likely to overestimate treatment effects, i.e. small size, short duration, and potentially inadequate handling of dropouts. All demonstrated opioid efficacy for spontaneous neuropathic pain. Meta-analysis demonstrated at least 33% pain relief in 57% of participants receiving an opioid versus 34% of those receiving placebo. The overall point estimate of risk difference was 0.25 (95% confidence interval (CI) 0.13 to 0.37, P < 0.0001), translating to a number needed to treat for an additional beneficial outcome (NNTB) of 4.0 (95% CI 2.7 to 7.7). When the number of participants achieving at least 50% pain relief was analyzed, the overall point estimate of risk difference between opioids (47%) and placebo (30%) was 0.17 (95% CI 0.02 to 0.33, P = 0.03), translating to an NNTB of 5.9 (3.0 to 50.0). In the updated review, opioids did not demonstrate improvement in many aspects of emotional or physical functioning, as measured by various validated questionnaires. Constipation was the most common adverse event (34% opioid versus 9% placebo: number needed to treat for an additional harmful outcome (NNTH) 4.0; 95% CI 3.0 to 5.6), followed by drowsiness (29% opioid versus 14% placebo: NNTH 7.1; 95% CI 4.0 to 33.3), nausea (27% opioid versus 9% placebo: NNTH 6.3; 95% CI 4.0 to 12.5), dizziness (22% opioid versus 8% placebo: NNTH 7.1; 95% CI 5.6 to 10.0), and vomiting (12% opioid versus 4% placebo: NNTH 12.5; 95% CI 6.7 to 100.0). More participants withdrew from opioid treatment due to adverse events (13%) than from placebo (4%) (NNTH 12.5; 95% CI 8.3 to 25.0). Conversely, more participants receiving placebo withdrew due to lack of efficacy (12%) versus (2%) receiving opioids (NNTH -11.1; 95% CI -20.0 to -8.3).

AUTHORS' CONCLUSIONS

Since the last version of this review, new studies were found providing additional information. Data were reanalyzed but the results did not alter any of our previously published conclusions. Short-term studies provide only equivocal evidence regarding the efficacy of opioids in reducing the intensity of neuropathic pain. Intermediate-term studies demonstrated significant efficacy of opioids over placebo, but these results are likely to be subject to significant bias because of small size, short duration, and potentially inadequate handling of dropouts. Analgesic efficacy of opioids in chronic neuropathic pain is subject to considerable uncertainty.  Reported adverse events of opioids were common but not life-threatening. Further randomized controlled trials are needed to establish unbiased estimates of long-term efficacy, safety (including addiction potential), and effects on quality of life.

Chinese Medicinal Formula (MHGWT) for Relieving Diabetic Neuropathic Pain: A Randomized, Double-Blind, Placebo-Controlled Trial

Objective. To investigate the effects of modified Hungqi Guizhi Wuwu Tang (MHGWT), a formula that comprises Chinese medicinal herbs, in relieving neuropathic pain in diabetics. Method. Between March 2008 and April 2009, 112 participants were randomly assigned to either the MHGWT group, whose members received MHGWT (n = 56), or the control group, whose members received a placebo (n = 56). Diabetic neuropathic pain (DNP) was rated using the 15-item Short-Form Brief Pain Inventory (SF-BPI), the 17-item Short-Form McGill Pain Questionnaire (SF-MPQ), the 13-item Modified Michigan Neuropathy Screening Instrument (MMNSI), and the 36-item “SF-36.” Nerve conduction studies (NCSs) were performed before and after treatment. Results. After 12 weeks of treatment, the SF-MPQ and SF-BPI scores of the MHGWT group were significantly (P < 0.05) reduced and a significant difference between the groups was observed (P < 0.05). The levels of NCS in the MHGWT group were nonsignificantly (P > 0.05) reduced, and no significant difference in NCS level was observed between the groups (P > 0.05). Conclusions. MHGWT shows promise in relieving DNP and deserves further investigation.

Image-guided nerve cryoablation for post-thoracotomy pain syndrome

Chronic post-thoracotomy pain syndrome (PTPS) can cause significant patient distress and is frequently difficult to manage. Percutaneous intercostal nerve (ICN) cryoablation by palpation of surface landmarks can be risky, as inaccurate probe placement can lead to hemo- or pneumothorax. Experience with image-guided ICN cryoablation with treatment planning and device navigation is limited. A patient with intractable PTPS was treated with ICN cryoablation under cone-beam computed tomography guidance with software-assisted needle trajectory planning and ablation zone simulation. This procedure provided the patient ~8 weeks of relief. This case demonstrated that ICN cryoablation is feasible under image guidance with device navigation and ablation simulation and may result in a few months of pain relief in cases of intractable PTPS.

Evaluation of the analgesic efficacy and psychoactive effects of AZD1940, a novel peripherally acting cannabinoid agonist, in human capsaicin-induced pain and hyperalgesia

The aim of the present study was to investigate the effects of AZD1940, a novel peripherally acting cannabinoid CB(1) /CB(2) receptor agonist, on capsaicin-induced pain and hyperalgesia, as well as on biomarkers of cannabinoid central nervous system (CNS) effects. The present study was a randomized, double-blind, placebo-controlled, four-sequence, two-period, cross-over study in 44 male healthy volunteers aged 20-45 years. The effects of two single oral doses of AZD1940 (400 and 800 μg) were compared with placebo. Pain intensity after intradermal capsaicin injections in the forearm was assessed on a continuous visual analogue scale (VAS; 0-100 mm). Primary and secondary hyperalgesia induced by application of capsaicin cream on the calf were assessed by measuring heat pain thresholds and the area of mechanical allodynia, respectively. The CNS effects were assessed at baseline and up to 24 h after dosing using a visual analogue mood scales (VAMS) for feeling 'stimulated', 'high', 'anxious', 'sedated' or 'down'. AZD1940 did not significantly attenuate ongoing pain or primary or secondary hyperalgesia compared with placebo. Mild CNS effects for AZD1940were observed on the VAMS for 'high' and 'sedated'. Dose-dependent mild-to-moderate CNS-related and gastrointestinal adverse events were reported following treatment with AZD1940. No evidence of analgesic efficacy was found for a peripherally acting CB(1)/CB(2) receptor agonist in the human capsaicin pain model. The emergence of mild dose-dependent CNS effects suggests that the dose range predicted from preclinical data had been attained.