Inflammation with no axonal damage of the rat saphenous nerve trunk induces ectopic discharge and mechanosensitivity in myelinated axons

Peripheral direct current reduces naturally evoked nociceptive activity at the spinal cord in rodent models of pain

Objective.Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation typically inhibit pain pathways indirectly and are not suitable for all types of chronic pain. Direct current (DC) stimulation is a recently developed technology which affects small-diameter fibres more strongly than pulsatile stimulation. Since nociceptors are predominantly small-diameter Aδand C fibres, we investigated if this property could be applied to preferentially reduce nociceptive signalling.Approach.We applied a DC waveform to the sciatic nerve in rats of both sexes and recorded multi-unit spinal activity evoked at the hindpaw using various natural stimuli corresponding to different sensory modalities rather than broad-spectrum electrical stimulus. To determine if DC neuromodulation is effective across different types of chronic pain, tests were performed in models of neuropathic and inflammatory pain.Main results.We found that in both pain models tested, DC application reduced responses evoked by noxious stimuli, as well as tactile-evoked responses which we suggest may be involved in allodynia. Different spinal activity of different modalities were reduced in naïve animals compared to the pain models, indicating that physiological changes such as those mediated by disease states could play a larger role than previously thought in determining neuromodulation outcomes.Significance.Our findings support the continued development of DC neuromodulation as a method for reduction of nociceptive signalling, and suggests that it may be effective at treating a broader range of aberrant pain conditions than existing devices.

Post-Traumatic Trigeminal Neuropathy: Neurobiology and Pathophysiology

Painful traumatic trigeminal neuropathy (PTTN) is a chronic neuropathic pain that may develop following injury to the trigeminal nerve. Etiologies include cranio-orofacial trauma that may result from dental, surgical, or anesthetic procedures or physical trauma, such as a motor vehicle accident. Following nerve injury, there are various mechanisms, including peripheral and central, as well as phenotypic changes and genetic predispositions that may contribute to the development of neuropathic pain. In this article, we review current literature pertaining to the cellular processes that occur following traumatic damage to the trigeminal nerve, also called cranial nerve V, that results in chronic neuropathic pain. We examine the neurobiology and pathophysiology based mostly on pre-clinical animal models of neuropathic/trigeminal pain.

Chronic pain and local pain in usually painless conditions including neuroma may be due to compressive proximal neural lesion

It has been unexplained why chronic pain does not invariably accompany chronic pain-prone disorders. This question-driven, hypothesis-based article suggests that the reason may be varying occurrence of concomitant peripheral compressive proximal neural lesion (cPNL), e.g., radiculopathy and entrapment plexopathies. Transition of acute to chronic pain may involve development or aggravation of cPNL. Nociceptive hypersensitivity induced and/or maintained by cPNL may be responsible for all types of general chronic pain as well as for pain in isolated tissue conditions that are usually painless, e.g., neuroma, scar, and Dupuytren's fibromatosis. Compressive PNL induces focal neuroinflammation, which can maintain dorsal root ganglion neuron (DRGn) hyperexcitability (i.e., peripheral sensitization) and thus fuel central sensitization (i.e., hyperexcitability of central nociceptive pathways) and a vicious cycle of chronic pain. DRGn hyperexcitability and cPNL may reciprocally maintain each other, because cPNL can result from reflexive myospasm-induced myofascial tension, muscle weakness, and consequent muscle imbalance- and/or pain-provoked compensatory overuse. Because of pain and motor fiber damage, cPNL can worsen the causative musculoskeletal dysfunction, which further accounts for the reciprocity between the latter two factors. Sensitization increases nerve vulnerability and thus catalyzes this cycle. Because of these mechanisms and relatively greater number of neurons involved, cPNL is more likely to maintain DRGn hyperexcitability in comparison to distal neural and non-neural lesions. Compressive PNL is associated with restricted neural mobility. Intermittent (dynamic) nature of cPNL may be essential in chronic pain, because healed (i.e., fibrotic) lesions are physiologically silent and, consequently, cannot provide nociceptive input. Not all patients may be equally susceptible to develop cPNL, because occurrence of cPNL may vary as vary patients' predisposition to musculoskeletal impairment. Sensitization is accompanied by pressure pain threshold decrease and consequent mechanical allodynia and hyperalgesia, which can cause unusual local pain via natural pressure exerted by space occupying lesions or by their examination. Worsening of local pain is similarly explainable. Neuroma pain may be due to cPNL-induced axonal mechanical sensitivity and hypersensitivity of the nociceptive nervi nervorum of the nerve trunk and its stump. Intermittence and symptomatic complexity of cPNL may be the cause of frequent misdiagnosis of chronic pain.

Pathophysiology of Post-Traumatic Trigeminal Neuropathic Pain

Trigeminal nerve injury is one of the causes of chronic orofacial pain. Patients suffering from this condition have a significantly reduced quality of life. The currently available management modalities are associated with limited success. This article reviews some of the common causes and clinical features associated with post-traumatic trigeminal neuropathic pain (PTNP). A cascade of events in the peripheral and central nervous system function is involved in the pathophysiology of pain following nerve injuries. Central and peripheral processes occur in tandem and may often be co-dependent. Due to the complexity of central mechanisms, only peripheral events contributing to the pathophysiology have been reviewed in this article. Future investigations will hopefully help gain insight into trigeminal-specific events in the pathophysiology of the development and maintenance of neuropathic pain secondary to nerve injury and enable the development of new therapeutic modalities.

Effects of neural mobilizations through movement representation techniques for the improvement of neural mechanosensitivity of the median nerve region: a randomized controlled trial

PURPOSE

The main objective was to compare the effects of neural mobilization (NM), NM performed through mirror therapy (MT), NM performed through action observation (AO) training and finally classic rehabilitation program (mobility and strength) exercises on neural mechanosensitivity, widespread of proximal and distal pain and pressure pain thresholds (PPT). The second objective was to assess the effects of these interventions on handgrip strength, conditioned pain modulation, motor imagery ability and temporal summation.

MATERIALS AND METHODS

Single-blinded randomized controlled trial. Fifty-four healthy subjects were randomly assigned to each group. Neural mechanosensitivity, widespread pain and PPT were the main variables. The secondary variables included handgrip strength, conditioned pain modulation, motor imagery ability and temporal summation.

RESULTS

All groups showed significant differences in time*factor for neural mechanosensitivity (p = 0.001), PPT in the dermatome of the median nerve (p = 0.007), PPT at carpal tunnel (p < 0.05) and proximal widespread (p = 0.01). No differences were found for distal widespread, conditioned pain modulation, handgrip strength motor imagery ability or temporal summation (p > 0.05). There is an absence of statistically significant differences between groups.

CONCLUSIONS

NM through movement representation techniques can reduce mechanosensitivity and mechanical hyperalgesia in the median nerve dermatome and forearm, although no differences were found between groups.

Extending the straight leg raise test for improved clinical evaluation of sciatica: reliability of hip internal rotation or ankle dorsiflexion

Background

The straight leg raise (SLR) is the most commonly applied physical tests on patients with sciatica, but the sensitivity and specificity ratings for disc hernia and neural compression leave areas for improvement. Hip internal rotation tensions the lumbosacral nerve roots and ankle dorsiflexion tensions the sciatic nerve along its course. We added these movements to the SLR (extended SLR = ESLR) as structural differentiators and tested inter-rater reliability in patients with LBP, with and without sciatica.

Methods

Forty subjects were recruited to the study by the study controller (SC), 20 in the sciatic group and in the control group. Two independent examiners (E1&E2) performed the ESLR and did not communicate to the subjects other than needed to determine the outcome of the ESLR. First, SLR was performed traditionally until first responses were evoked. At this hip flexion angle, a location-specific structural differentiation was performed to confirm whether the emerged responses were of neural origin. Cohen’s Kappa score (CK) for interrater reliability was calculated for ESLR result in detection of sciatic patients. Also, the examiners’ ESLR results were compared to the traditional SLR results.

Results

The interrater agreement between Examiner 1 and Examiner 2 for the ESLR was 0.85 (p < 0.001, 95%CI: 0.71–0.99) translating to almost perfect agreement as measured by Cohen’s Kappa When the ESLR was compared to the traditional SLR, the overall agreement rate was 75% (30/40). Kappa values between the traditional SLR and the E1’s or E2’s ESLR results were 0.50 (p < 0.0001; 95%CI 0.27–0.73) and 0.54 (p < 0.0001; 95%CI 0.30–0.77), respectively.

Conclusions

ESLR with the addition of location-specific structural differentiation is a reliable and repeatable tool in discerning neural symptoms from musculoskeletal in patients with radiating low back pain. We recommend adding these movements to the standard SLR with aim of improving diagnostic ability.

Molecular mechanisms of painful traumatic trigeminal neuropathy-Evidence from animal research and clinical correlates

Painful traumatic trigeminal neuropathy (PTTN) may occur following major craniofacial or oral trauma, or may be subsequent to relatively minor dental interventions. Following injury, pain may originate from a peripheral nerve, a ganglion, or from the central nervous system. In this review, we focus on molecular mechanisms of pain resulting from injury to the peripheral branch of the trigeminal nerve. This syndrome has been termed painful traumatic trigeminal neuropathy (PTTN) by the International Headache Society and replaces previous terms including atypical odontalgia, deafferentation pain, traumatic neuropathy and phantom toothache. We emphasize the scientific evidence supporting the events purported to lead to PTTN by reviewing the pathophysiology of PTTN based on relevant animal models. Additionally, we briefly overview clinical correlates and pathophysiological manifestations of PTTN.

Inadequacies of the Lasègue test, and how the Slump and Bowstring tests are useful for the diagnosis of sciatica

Diagnosis of sciatica mainly relies on pain reproduction by stretching of the lumbar roots since neurological examination and medical history are usually not sufficient to guarantee diagnosis. The Lasègue test is the most popular method, which starts with the straight leg-raising test (SLR). However it is not perfect, and is not always well performed or interpreted. Passive ankle dorsiflexion at the end of the SLR (Bragard test) is more sensitive, but can also remain normal in some cases of sciatica. Other stretching tests can help to recognise lumbar root damage in patients with poorly defined pain in a lower extremity: firstly, the Christodoulides test, i.e. reproduction of L5 sciatic pain by a femoral stretch test; secondly, the Slump test, performed on a patient in a sitting position, by slowly extending their painful leg then passively bending their neck (or the opposite); and thirdly, the Bowstring test, which requires, at the end of the Lasègue test, once the knee has been slightly flexed, pressing on the course of the peroneal and/or tibial nerves in the popliteal fossea to try and reproduce the exact pain felt by the patient. The combination of all these tests takes less than 2minutes, and could improve both the sensitivity and specificity of the physical examination for the diagnosis of sciatica. This article is a review of the limitations of the Lasègue/SLR tests and of the efficacy of these other tests for stretching the lumbar roots.

Recovery from nerve injury induced behavioral hypersensitivity in rats parallels resolution of abnormal primary sensory afferent signaling

Pain and hypersensitivity months after peripheral injury reflect abnormal input from peripheral afferents likely in conjunction with central sensitization. We hypothesize that peripheral changes occur in defined sensory afferents and resolve as behavioral response to injury resolves. Male Sprague-Dawley rats underwent sham or partial L5 spinal nerve ligation, and paw withdrawal threshold (PWT) was sequentially measured during recovery. At 2, 4, 8, and 12 weeks after injury, randomized animals underwent electrophysiologic assessment of L4 fast-conducting high- and low-threshold mechanoreceptors, and individual neuronal mechanical thresholds (MTs) were contrasted with PWTs in the same animals. Paw withdrawal thresholds decreased after injury and resolved over time (P < 0.001). Similarly, MTs of fast-conducting high-threshold mechanoreceptors decreased after injury and resolved over time (P < 0.001). By contrast, MTs of low-threshold mechanoreceptors increased after injury and resolved over time (P < 0.001). Distributions of recordings from each afferent subtype were perturbed after injury, and this too resolved over time. After resolution of behavioral changes, several electrical abnormalities persisted in both neuronal subtypes. These data extend previous findings that mechanically sensitive nociceptors are sensitized, whereas tactile, largely Aβ afferents are desensitized after nerve injury by showing that the time course of resolution of these changes mirrors that of behavioral hypersensitivity in a surgical injury including neural damage. These data support a role of abnormal peripheral input, from both nociceptor and tactile afferents, during recovery from peripheral injury and underscore the potential importance of both classes of afferents as potential targets for pain treatment.

Characterizing the Mechanical Properties of Ectopic Axonal Receptive Fields in Inflamed Nerves and Following Axonal Transport Disruption

Radiating pain is a significant feature of chronic musculoskeletal pain conditions such as radiculopathies, repetitive motion disorders and whiplash associated disorders. It is reported to be caused by the development of mechanically-sensitive ectopic receptive fields along intact nociceptor axons at sites of peripheral neuroinflammation (neuritis). Since inflammation disrupts axonal transport, we have hypothesised that anterogradely-transported mechanically sensitive ion channels accumulate at the site of disruption, which leads to axonal mechanical sensitivity (AMS). In this study, we have characterised the mechanical properties of the ectopic axonal receptive fields in the rat and have examined the contribution of mechanically sensitive ion channels to the development of AMS following neuritis and vinblastine-induced axonal transport disruption. In both models, there was a positive force-discharge relationship and mechanical thresholds were low (∼9 mN/mm²). All responses were attenuated by Ruthenium Red and FM1-43, which block mechanically sensitive ion channels. In both models, the transport of TRPV1 and TRPA1 was disrupted, and intraneural injection of agonists of these channels caused responses in neurons with AMS following neuritis but not vinblastine treatment. In summary, these data support a role for mechanically sensitive ion channels in the development of AMS.

Rethinking the causes of pain in herpes zoster and postherpetic neuralgia: the ectopic pacemaker hypothesis

INTRODUCTION

Pain in herpes zoster (HZ) and postherpetic neuralgia (PHN) is traditionally explained in terms of 2 processes: irritable nociceptors in the rash-inflamed skin and, later, deafferentation due to destruction of sensory neurons in one virally infected dorsal root ganglion.

OBJECTIVES AND METHODS

Consideration of the evidence supporting this explanation in light of contemporary understanding of the pain system finds it wanting. An alternative hypothesis is proposed as a replacement.

RESULTS

This model, the ectopic pacemaker hypothesis of HZ and PHN, proposes that pain in both conditions is driven by hyperexcitable ectopic pacemaker sites at various locations in primary sensory neurons affected by the causative varicella zoster virus infection. This peripheral input is exacerbated by central sensitization induced and maintained by the ectopic activity.

CONCLUSIONS

The shift in perspective regarding the pain mechanism in HZ/PHN has specific implications for clinical management.

Chronic orofacial pain animal models - progress and challenges

INTRODUCTION

Chronic orofacial pain is one of the most common pain conditions experienced by adults. Animal models are often selected as the most useful scientific methodology to explore the pathophysiology of the disorders that cause this disabling pain to facilitate the development of new treatments. The creation of new models or the improvement of existing ones is essential for finding new ways to approach the complex neurobiology of this type of pain. Areas covered: The authors describe and discuss a variety of animal models used in chronic orofacial pain (COFP). Furthermore, they examine in detail the mechanisms of action involved in orofacial neuropathic pain and orofacial inflammatory pain. Expert opinion: The use of animal models has several advantages in chronic orofacial pain drug discovery. Choosing an animal model that most closely represents the human disease helps to increase the chances of finding effective new therapies and is key to the successful translation of preclinical research to clinical practice. Models using genetically modified animals seem promising but have not yet been fully developed for use in chronic orofacial pain research. Although animal models have provided significant advances in the pharmacological treatment of orofacial pain, several barriers still need to be overcome for better treatment options.

Evidence for Increased Magnetic Resonance Imaging Signal Intensity and Morphological Changes in the Brachial Plexus and Median Nerves of Patients With Chronic Arm and Neck Pain Following Whiplash Injury

Background Whiplash following a motor vehicle accident can result in chronic neck and arm pain. Patients frequently present with cutaneous hypersensitivities and hypoesthesia, but without obvious clinical signs of nerve injury. T2-weighted magnetic resonance imaging (MRI) has previously been used to identify nerve pathology. Objectives To determine whether there are signs of peripheral nerve pathology on MRI in patients with chronic arm and neck pain following whiplash injury. Methods This cross-sectional study used T2-weighted MRI to examine the brachial plexus and median nerve in patients and age-matched, healthy control subjects. Clinical examination included tests of plexus and nerve trunk mechanical sensitivity. Results The T2 signal intensity was greater in the brachial plexus and median nerve at the wrist in the patient group (mean intensity ratio = 0.52 ± 0.13 and 2.09 ± 0.33, respectively) compared to the control group (mean intensity ratio = 0.45 ± 0.07 and 1.38 ± 0.31, respectively; P<.05). Changes in median nerve morphology were also observed, which included an enlargement (mean area: patient group, 8.05 ± 1.29 mm²; control group, 6.52 ± 1.08 mm²; P<.05) and flattening (mean aspect ratio: patient group, 2.46 ± 0.53; control group, 1.62 ± 0.30; P<.05) at the proximal carpal row. All patients demonstrated signs of nerve trunk mechanical sensitivity. Conclusion These findings suggest that patients with chronic whiplash may have inflammatory changes and/or mild neuropathy, which may contribute to symptoms. J Orthop Sports Phys Ther 2018;48(7):523-532. Epub 24 Apr 2018. doi:10.2519/jospt.2018.7875.

Intraneural injection of a test dose of local anesthetic in peripheral nerves - does it induce histological changes in nerve tissue?

BACKGROUND & OBJECTIVES

Most anesthesiologists use the injection of a test dose of local anesthetic in order to evaluate the final needle tip position. Thus, the intraneural injection of a full dose can be avoided. The aim of this study was to analyze whether an intraneural injection of a test dose of bupivacaine could trigger histological changes.

METHODS

Intraneural injections under direct vision were performed in 40 brachial plexus nerves in seven anesthetized pigs. Tibial nerves served as positive and negative controls. Two milliliter of bupivacaine 0.5% was injected in three nerves on the left brachial plexus. For control of local anesthetic's toxicity Ringer's solution was applied intraneurally on the right side. After maintaining 48 h of general anesthesia, the nerves were resected. The specimens were processed for histological examination and assessed for inflammation (hematoxylin and eosin stain, CD68-immunohistochemistry) and myelin damage (Kluver-Barrera stain). The degree of nerve injury was rated on a scale from 0 (no injury) to 4 (severe injury).

RESULTS

Statistical analysis showed no significant differences between the bupivacaine group [median (interquartile range) 1 (1-1.5)] and the Ringer's solution group [1 (0.5-2) P = 0.772]. Mild myelin alteration was found in 12.5% of all specimens following intraneural injection, irrespective of the applied substance.

CONCLUSIONS

"In our experimental study, intraneural injection of 2 ml of bupivacaine or Ringer's solution showed comparable mild inflammation. Nevertheless, inflammation can only be prevented by strictly avoiding nerve perforation followed by intraneural injection, as mechanical nerve perforation is a key factor for evolving inflammation.

Vagus nerve stimulator-related speech/exercise induced cough

Vagal nerve stimulation (VNS) therapy is an effective adjunctive treatment for chronic or recurrent treatment resistant depression. Although considered a safe procedure, increasing output current can be associated with stimulation induced side effects. We report the first case of dry cough induced by speech and mild exercise, occurring in the off mode following implantation of a vagal nerve stimulator (VNSor). We discuss the possible pathophysiology and the potential treatment options of this rare complication.

Orofacial Pain in Cancer: Part I—Mechanisms

The mechanisms involved, and possible treatment targets, in orofacial pain due to cancer are poorly understood. The aim of the first of this two-part series is to review the involved pathophysiological mechanisms and explore their possible roles in the orofacial region. However, there is a lack of relevant research in the trigeminal region, and we have therefore applied data accumulated from experiments on cancer pain mechanisms in rodent spinal models. In the second part, we review the clinical presentation of cancer-associated orofacial pain at various stages: initial diagnosis, during therapy (chemo-, radiotherapy, surgery), and in the post-therapy period. In the present article, we provide a brief outline of trigeminal functional neuro-anatomy and pain-modulatory pathways. Tissue destruction by invasive tumors (or metastases) induces inflammation and nerve damage, with attendant acute pain. In some cases, chronic pain, involving inflammatory and neuropathic mechanisms, may ensue. Distant, painful effects of tumors include paraneoplastic neuropathic syndromes and effects secondary to the release of factors by the tumor (growth factors, cytokines, and enzymes). Additionally, pain is frequent in cancer management protocols (surgery, chemotherapy, and radiotherapy). Understanding the mechanisms involved in cancer-related orofacial pain will enhance patient management.

Progress of clinical practice on the management of burn-associated pain: Lessons from animal models

Opioid-based analgesics provide the mainstay for attenuating burn pain, but they have a myriad of side effects including respiratory depression, nausea, impaired gastrointestinal motility, sedation, dependence, physiologic tolerance, and opioid-induced hyperalgesia. To test and develop novel analgesics, validated burn-relevant animal models of pain are indispensable. Herein we review such animal models, which are mostly limited to rodent models of burn-induced, inflammatory, and neuropathic pain. The latter two are pain syndromes that provide insight into the pain caused by systemic pro-inflammatory cytokines and direct injury to nerves (e.g., after severe burn), respectively. To date, no single animal model optimally mimics the complex pathophysiology and pain that a human burn patient experiences. No currently available burn-pain model examines effects of pharmacological intervention on wound healing. As cornerstones of pain and wound healing, pro-inflammatory mediators may be utilized for insight into both processes. Moreover, common clinical concerns such as systemic inflammatory response syndrome and multiple organ dysfunction remain unaddressed. For development of analgesics, these aberrations can significantly alter the potential efficacy and/or adverse effects of a prescribed analgesic following burn trauma. We therefore suggest that a multi-model strategy would be the most clinically relevant when evaluating novel analgesics for use in burn patients.

Perspectives on next steps in classification of oro-facial pain - Part 3: biomarkers of chronic oro-facial pain - from research to clinic

The purpose of this study was to review the current status of biomarkers used in oro-facial pain conditions. Specifically, we critically appraise their relative strengths and weaknesses for assessing mechanisms associated with the oro-facial pain conditions and interpret that information in the light of their current value for use in diagnosis. In the third section, we explore biomarkers through the perspective of ontological realism. We discuss ontological problems of biomarkers as currently widely conceptualised and implemented. This leads to recommendations for research practice aimed to a better understanding of the potential contribution that biomarkers might make to oro-facial pain diagnosis and thereby fulfil our goal for an expanded multidimensional framework for oro-facial pain conditions that would include a third axis.

Sensory axons excitability changes in carpal tunnel syndrome after neural mobilization

Increased mechanosensitivity of the median nerve in carpal tunnel syndrome (CTS) has been demonstrated during upper limb tension test 1 (ULTT1) when the nerve is passively elongated. However, the neurophysiological changes of the sensory axons during stressing activities are unknown. The aim of present study was to verify possible changes in the excitability of median nerve afferent axons following nerve stress in elongation, in subjects with and without CTS. Eight CTS hands and eight controls were selected. Recruitment properties of the median nerve were studied by analyzing the relationship between the intensity of electrical stimulation and the size of motor response, before and after intermittent-repetitive neural mobilization. Only in CTS hands, after the intervention, the stimulus-response curve was strikingly abnormal: both plateau and slope values were significantly lower. During anatomical stress across the median nerve in elongation, compressive forces may exert mechanical traction on the median nerve, since it is 'tethered' at the carpal tunnel, resulting inactivation of Na(+) channels at the wrist, or impairment of energy-dependent processes which affect axonal conduction block. We conclude that in entrapment neuropathies, neural mobilization during nerve elongation may generate conduction failure in peripheral nerve. Our study supports specific considerations for patient education and therapeutic approaches.

Predictors for identifying patients with patellofemoral pain syndrome responding to femoral nerve mobilization

OBJECTIVE

To identify the predictors for successful neurodynamic management in patients with patellofemoral pain syndrome.

DESIGN

Prospective cohort, prediction rule study.

SETTING

Hospital.

PARTICIPANTS

Patients with patellofemoral pain syndrome (N=51) underwent clinical examination and measurement of physical parameters, including femoral slump test, lower-extremity alignment, flexibility and muscle strength, and functional level.

INTERVENTION

Patients received 6 treatment sessions of femoral nerve mobilization within 2 weeks.

MAIN OUTCOME MEASURES

Pain level during functional testing was assessed before and after the first and sixth session of treatment. Patients were then grouped into responder and nonresponder groups. Criteria for the responder group was a pain score decrease ≥50% or Global Rating Scale score ≥4. Chi-square and independent t tests were used to identify potential variables with a significance level of .10, and stepwise logistic regression was used to find predictors with a significance level of .05.

RESULTS

Twenty-five patients responded to the initial treatment (immediate effect), and 28 patients responded after 6 sessions (longer-term effect). A positive femoral slump test was identified as the predictor for the immediate treatment effect. The prediction factors for the longer-term effect included responding to femoral nerve mobilization the first time and a bilateral difference in hip extension angles. Application of the clinical predictors improved the success rate to 90% for 1 treatment session and 93% for 6 treatment sessions.

CONCLUSIONS

Clinicians could use the positive femoral slump test and a bilateral difference in hip extension angles during the femoral slump test to determine whether or not patients with patellofemoral pain syndrome might benefit from femoral nerve mobilization.

Contribution of hyperpolarization-activated channels to heat hypersensitivity and ongoing activity in the neuritis model

Neuritis can cause pain hypersensitivities in the absence of axonal degeneration. Such hypersensitivities are reputed to be maintained by ongoing activity into the spinal cord, which, in the neuritis model, is mainly generated from intact C-fiber neurons. The hyperpolarization-activated cyclic nucleotide-gated (HCN) family of ion channels has been implicated in nerve injury-induced pain hypersensitivities. The present study has examined the role of these channels in the development of heat and mechanical hypersensitivities in the neuritis model. The systemic administration of the HCN-specific blocker ZD7288 produced a reversal of heat but not mechanical hypersensitivity within one hour post-administration. Recordings from C-fiber neurons were performed to determine whether ZD7288 acts by inhibiting ongoing activity. ZD7288 (0.5mM) caused a 44.1% decrease in the ongoing activity rate following its application to the neuritis site. Immunohistochemical examination of the HCN2 channel subtype within the L5 dorsal root ganglia revealed an increase in expression in neuronal cell bodies of all sizes post-neuritis. In conclusion, HCN channels contribute to the development of neuritis-induced heat hypersensitivity and ongoing activity. Drugs that target HCN channels may be beneficial in the treatment of neuropathic pain in patients with nerve inflammation.

Topical medications as treatment of neuropathic orofacial pain

Understanding mechanisms of neuropathic orofacial pain, targets of treatment, and basic pharmacology and working with informed compounding pharmacists may result in significant benefit for patients. The clinical significance of topical medications is improvement of quality of life for patients by providing a unique medication delivery system for neuropathic orofacial pain and other dental and extraoral conditions. The use of this route of administration has decreased or minimized side effects compared with other methods and is especially useful in medically compromised and elderly patients. These innovations, supported and improved by ongoing research, will augment the armamentarium of the clinician treating orofacial pain disorders.

ARA290 in a rat model of inflammatory pain

Chronic pain affects as many as one in five people. A proportion of patients with symptoms of neuropathic -pain do not have clinical signs of any obvious tissue or nerve injury. Such patients include those with diffuse limb pain, back pain, and complex regional pain syndrome type 1. These patients remain a clinical enigma. However, through the development of the neuritis model, it has become apparent that local nerve inflammation in the absence of gross pathology (i.e., axonal degeneration and demyelination) may underlie part of the mechanisms of pain. In this chapter, we describe a method to induce the neuritis model. We also describe in detail a reliable method to test for mechanical allodynia and heat hyperalgesia. Data that demonstrates the potential benefits of the neuroprotective agent ARA290 in reducing pain behavior in the neuritis model are presented.

The erythropoietin-derived peptide ARA290 reverses mechanical allodynia in the neuritis model

Studies on the neuritis model suggest that in many patients with neuropathic pain, symptoms may be due to nerve inflammation rather than frank nerve injury. Treatments for these patients are often ineffective. The neuroprotective and hematopoietic agent erythropoietin (EPO) has been shown to reverse pain behaviors in nerve injury models and therefore may be of therapeutic benefit. However, EPO can cause thrombosis. ARA290 is an analog of EPO that has the neuroprotective activities of EPO without stimulating hematopoiesis. The present study has examined the effects of ARA290 on pain behavior in the neuritis model. Following neuritis induction, 30 or 120 μg/kg ARA290 or saline vehicle was injected intraperitoneally into rats daily from day 1 post surgery. Animals were assessed for mechanical allodynia and heat hyperalgesia. Levels of the cytokine tumor necrosis factor-α (TNF-α) and chemokine (CC motif) ligand 2 (CCL2) mRNA were also assessed using polymerase chain reaction. Vehicle-treated neuritis animals (n=20) developed signs of mechanical allodynia and heat hyperalgesia that reached a maximum on day 4 and 3 of testing, respectively. Treatment with either 30 (n=11) or 120 μg/kg ARA290 (n=9) prevented the development of mechanical allodynia. However, ARA290 did not significantly affect heat hyperalgesia. There was no significant difference between the effects of each drug dose (p<0.05, unpaired t test comparing area under the curve for mechanical allodynia). The levels of CCL2 and TNF-α mRNA in the nerve and Gelfoam were not significantly different following 120 μg/kg ARA290 treatment (n=3-7) compared to vehicle-treated animals (n=3-7; p=0.24; unpaired t tests). In summary, ARA290 may be beneficial in the treatment of neuropathic pain symptoms where signs of nerve injury are absent on clinical assessment. The mechanisms of action do not appear to involve the inhibition of TNF-α or CCL2 production.

Interventions in the disturbances in the motor and sensory environment

Treatment of peripheral nervous system (PNS) pathology presents intervention challenges to every therapist. Many of the current and future interventions will be directed at restoring the normal anatomy, function, and biomechanical properties of the PNS, restoring normal neural physiology and ultimately patient function and quality of life. Present interventions use mechanical (movement) or electrical procedures to affect various properties of the peripheral nerve. The purpose of this article was to apply basic science to clinical practice. The pathology and accompanying structural and biomechanical changes in the PNS will be presented in three specific areas commonly encountered in the clinic: nerve injury and laceration; compression neuropathies; and neuropathic pain and neural tension dysfunction. The intent is to address possible interventions exploring the clinical reasoning process that combines basic science and evidence-based best practice. The current lack of literature to support any one intervention requires a strong foundation and understanding of the PNSs' structure and function to refine current and develop new intervention strategies. Current evidence will be presented and linked with future considerations for intervention and research. During this interlude of development and refinement, best practice will rely on sound clinical reasoning skills that incorporate basic science to achieve a successful outcome when treating these challenging patients.

Mechanosensitivity of the median nerve in patients with chronic carpal tunnel syndrome

The aim was to investigate the relationship between the effects of median nerve strain during the elbow extension component of the upper limb neurodynamic test 1 (ULNT1) and the evoked musculoskeletal changes. 11 patients with chronic carpal tunnel syndrome (CTS) and 11 matched asymptomatic controls participated in the study. In all subjects, elbow extension was carried out in both ULNT1 and neutral positions of the shoulder and arm. From these two starting positions a KIN-COM(®) dynamometer carried out passive elbow extension while EMG activity of 10 arm and shoulder muscles, elbow-flexor resistive torque and elbow extension ROM were measured concurrently. The result showed that, in the ULNT1 position, increased EMG activity of the involved muscles, increased elbow extension resistive torque and pain responses occurred much earlier in the range of elbow extension in the CTS group compared to healthy controls. These findings demonstrated increased mechanosensitivity of the median nerve in CTS patients compared to healthy controls.

Quantitative sensory testing somatosensory profiles in patients with cervical radiculopathy are distinct from those in patients with nonspecific neck-arm pain

The aim of this study was to establish the somatosensory profiles of patients with cervical radiculopathy and patients with nonspecific neck-arm pain associated with heightened nerve mechanosensitivity (NSNAP). Sensory profiles were compared to healthy control (HC) subjects and a positive control group comprising patients with fibromyalgia (FM). Quantitative sensory testing (QST) of thermal and mechanical detection and pain thresholds, pain sensitivity and responsiveness to repetitive noxious mechanical stimulation was performed in the maximal pain area, the corresponding dermatome and foot of 23 patients with painful C6 or C7 cervical radiculopathy, 8 patients with NSNAP in a C6/7 dermatomal pain distribution, 31 HC and 22 patients with FM. For both neck-arm pain groups, all QST parameters were within the 95% confidence interval of HC data. Patients with cervical radiculopathy were characterised by localised loss of function (thermal, mechanical, vibration detection P<.009) in the maximal pain area and dermatome (thermal detection, vibration detection, pressure pain sensitivity P<.04), consistent with peripheral neuronal damage. Both neck-arm pain groups demonstrated increased cold sensitivity in their maximal pain area (P<.03) and the foot (P<.009), and this was also the dominant sensory characteristic in patients with NSNAP. Both neck-arm pain groups differed from patients with FM, the latter characterised by a widespread gain of function in most nociceptive parameters (thermal, pressure, mechanical pain sensitivity P<.027). Despite commonalities in pain characteristics between the 2 neck-arm pain groups, distinct sensory profiles were demonstrated for each group.

The validity of upper-limb neurodynamic tests for detecting peripheral neuropathic pain

The validity of upper-limb neurodynamic tests (ULNTs) for detecting peripheral neuropathic pain (PNP) was assessed by reviewing the evidence on plausibility, the definition of a positive test, reliability, and concurrent validity. Evidence was identified by a structured search for peer-reviewed articles published in English before May 2011. The quality of concurrent validity studies was assessed with the Quality Assessment of Diagnostic Accuracy Studies tool, where appropriate. Biomechanical and experimental pain data support the plausibility of ULNTs. Evidence suggests that a positive ULNT should at least partially reproduce the patient's symptoms and that structural differentiation should change these symptoms. Data indicate that this definition of a positive ULNT is reliable when used clinically. Limited evidence suggests that the median nerve test, but not the radial nerve test, helps determine whether a patient has cervical radiculopathy. The median nerve test does not help diagnose carpal tunnel syndrome. These findings should be interpreted cautiously, because diagnostic accuracy might have been distorted by the investigators' definitions of a positive ULNT. Furthermore, patients with PNP who presented with increased nerve mechanosensitivity rather than conduction loss might have been incorrectly classified by electrophysiological reference standards as not having PNP. The only evidence for concurrent validity of the ulnar nerve test was a case study on cubital tunnel syndrome. We recommend that researchers develop more comprehensive reference standards for PNP to accurately assess the concurrent validity of ULNTs and continue investigating the predictive validity of ULNTs for prognosis or treatment response.

Central sensitization phenomena after third molar surgery: A quantitative sensory testing study

BACKGROUND

Surgical removal of third molars may carry a risk of developing persistent orofacial pain, and central sensitization appears to play an important role in the transition from acute to chronic pain.

AIM

The aim of this study was to investigate sensitization (primarily central sensitization) after orofacial trauma using quantitative sensory testing (QST).

METHODS

A total of 32 healthy men (16 patients and 16 age-matched control subjects) underwent a battery of quantitative tests adapted to the trigeminal area at baseline and 2, 7, and 30 days following surgical removal of a lower impacted third molar.

RESULTS

Central sensitization for at least one week was indicated by significantly increased pain intensity evoked by intraoral repetitive pinprick and electrical stimulation (p<0.05) including facilitation of temporal summation mechanisms (p<0.05), extraoral repetitive electrical stimulation (p<0.001), significantly more frequent aftersensation in patients (p<0.001), extraoral hyperalgesia due to single pinprick stimulation (p<0.05) and larger pain areas due to intranasal stimulation (p<0.001). Peripheral sensitization was indicated by intraoral hyperalgesia due to single pinprick (p<0.05).

CONCLUSION

We found clear signs of sensitization of the trigeminal nociceptive system for at least one week after the surgery. Our results indicate that even a minor orofacial surgical procedure may be sufficient to evoke signs of both central and peripheral sensitization, which may play a role in the transition from acute to chronic pain in susceptible individuals.

CCL2 has similar excitatory effects to TNF-α in a subgroup of inflamed C-fiber axons

Peripheral nerve inflammation can cause neuronal excitability changes that have been implicated in the pathogenesis of chronic pain. Although the neuroimmune interactions that lead to such physiological changes are unclear, in vitro studies suggest that the chemokine CCL2 may be involved. This in vivo study examines the effects of CCL2 on untreated and inflamed neurons and compares its effects with those of TNF-α. Extracellular recordings were performed in the anesthetized rat on isolated neurons with C-fiber axons. On untreated neurons, CCL2, as well as TNF-α, had negligible effects. Following neuritis, both cytokines transiently caused the firing of action potentials in 27–30% of neurons, which were either silent or had background (ongoing) activity. The neurons with ongoing activity, which responded to either cytokine, had significantly slower baseline firing rates {median = 3.0 spikes/min [interquartile range (IQR) 3.0]} compared with the nonresponders [median = 24.4 spikes/min (IQR 24.6); P < 0.001]. In an additional group, 26–27% of neurons, which were sensitized due to repeated noxious mechanical stimulation of the periphery, also responded to the effects of both cytokines. Neither cytokine caused axons to become mechanically sensitive. Immunohistochemistry confirmed that the cognate CCL2 receptor, CCR2, is mainly expressed on glia and is therefore not likely to be an axonal target for CCL2 following inflammation. In contrast, the cognate TNF-α receptor (TNFR), TNFR1, was present on untreated and inflamed neurons. In summary, CCL2 can excite inflamed C-fiber neurons with similar effects to TNF-α, although the underlying mechanisms may be different. The modulatory effects of both cytokines are limited to a subgroup of neurons, which may be subtly inflamed.

A new animal model of trigeminal neuralgia produced by administration of cobra venom to the infraorbital nerve in the rat

BACKGROUND

Understanding the mechanism of trigeminal neuralgia may be elucidated by developing laboratory animal models that closely mimic the features of this specific type of neuropathic pain. We have developed an experimental animal model for trigeminal neuralgia using a technique of injecting cobra venom into the infraorbital nerve (ION) trunk.

METHODS

Male Sprague-Dawley rats were subjected to the administration of cobra venom or saline into the ION trunk. Mechanical stimuli were applied to the ION territory in consecutive days after surgery. Mechanical thresholds were measured over a 90-day period on the bilateral facial region. Vascular permeability in the ION territory was measured using Evans blue dye.

RESULTS

The cobra venom-treated rats developed mechanical allodynia 3 days after surgery that lasted for 60 days postoperatively at the ipsilateral side. The mechanical thresholds of the contralateral ION territory also showed a profound decrease but were sustained for only approximately 30 days. There was no change of mechanical thresholds in the control groups. The extravasation of Evans blue increased significantly in the skin after administration of cobra venom to the ION compared with control rats (P < 0.05).

CONCLUSION

The cobra venom model may provide a reasonable model for investigating the mechanism of trigeminal neuropathic pain.

Diagnosis and management of trigeminal neuropathic pains

SUMMARY Trigeminal neuropathic pains have presented diagnostic and therapeutic challenges to providers. In addition, knowledge of pathophysiology, current classification systems, taxonomy and phenotyping of these conditions are incomplete. While trigeminal neuralgia is the most identifiable and studied, other conditions are being recognized and require distinct management approaches. Furthermore, other facial pain conditions such as atypical odontalgia and burning mouth syndrome are now considered to have neuropathic elements in their etiology. This article reviews current knowledge on the pathophysiology, diagnosis and management of neuropathic pain conditions involving the trigeminal nerve, to include: trigeminal neuralgia, trigeminal neuropathic pain (with traumatically induced neuralgia and atypical odontalgia) and burning mouth syndrome. Treatment modalities are reviewed based on current and best available evidence. Trigeminal neuralgia is managed with anticonvulsant drugs as the first line, with surgical options providing variable results. Trigeminal neuropathic pain is managed medically based on the guidelines for other neuropathic pain conditions. Burning mouth syndrome is also treated with a number of neuropathic medications, both topical and systemic. In all these conditions, patients need to be thoroughly educated about their condition, involved in its management, and be provided with supportive and adjunctive treatment resources.

Histological Consequences of Needle-Nerve Contact following Nerve Stimulation in a Pig Model

Background. Nerve stimulation can facilitate correct needle placement in peripheral regional anesthesia. The aim of this study was to determine whether the high threshold current is associated with reduced nerve injury due to fewer needle-nerve contacts compared with low current. Methods. In anaesthetized pigs, thirty-two nerves of the brachial plexus underwent needle placement at low (0.2 mA) or high current (1.0 mA). The occurrence of needle-nerve contact was recorded. After 48 hours, the nerves were analyzed for occurrence of histological changes. Nerve injury was scored ranging from 0 (no injury) to 4 (severe injury). Results. The frequency of needle-nerve contact was 94% at low compared to 6% at high current. The score was significantly higher at low (median [interquartile range] 2.0 [1.0-2.0]) compared to high current (0.0 [0.0-1.0] P = .001). Conclusions. Inflammatory responses were directly related to needle-nerve contacts. Hence, posttraumatic inflammation may be diminished using higher current for nerve localization.

Nerve perforation with pencil point or short bevelled needles: histological outcome

BACKGROUND

In the case of needle nerve contact during peripheral blocks, pencil point needles are considered less traumatic compared with bevelled needles. However, there are not enough data to prove this notion. Therefore, the aim of this study was to challenge the hypothesis that nerve perforation with short bevelled needles is associated with major nerve damage compared with pencil point needles.

METHODS

In five anaesthetised pigs, the brachial plexus was exposed bilaterally. Up to eight nerves underwent needle nerve perforation using a pencil point needles cannula or an short bevelled needle. After 48 h, the nerves were resected. The specimens were processed for visual examination and the detection of inflammatory cells (haematoxylin-eosin, i.e. CD68-immunohistochemistry to detect macrophages), myelin damage (Kluver-Barrera staining) and intraneural haematoma. The grade of nerve injury was characterised by an objective score ranging from 0 (no injury) to 4 (severe injury).

RESULTS

Fifty nerves were examined. According to the injury score applied, there was no significant difference between the pencil point needles [median (inter-quartile range) 2.0 (2.0-2.0)] and the short bevelled-needle group [median 2.0 (2.0-2.0) P=0.23]. No myelin damage was observed. Signs of post-traumatic inflammation were equally distributed among both groups.

CONCLUSIONS

In the present study, the magnitude of nerve injury after needle nerve perforation was not related to one of the applied needle types. Post-traumatic inflammation rather than structural damage of nerve tissue is the only notable sign of nerve injury after needle nerve perforation with either needle type. However, neither the pencil point- nor the short bevelled needle can be designated a less traumatic device.

Upper limb neurodynamic test of the radial nerve: a study of responses in symptomatic and asymptomatic subjects

STUDY DESIGN

Clinical measurement.

INTRODUCTION

Nonspecific cervical pain is a common clinical presentation. The role of upper limb neurodynamic tests (ULNT), for evaluation and treatment intervention, is not well defined for this population.

PURPOSE OF THE STUDY

This study's purpose was to determine if the radial-biased (RB)-ULNT discriminates any response differences between symptomatic subjects with a positive (+) RB-ULNT (n=36), symptomatic subjects with a negative (-) RB-ULNT (n=24), and asymptomatic subjects (n=60).

METHODS

Sixty asymptomatic and 60 subjects presenting with nonspecific cervical and/or unilateral upper extremity pain were compared using the RB-ULNT. Symptomatic subjects were further divided in (+) and (-) RB-ULNT groups due to their response to the RB-ULNT. Within the symptomatic population, a positive response to the RB-ULNT was defined by the symptomatic subject reporting their sensations were increased with contralateral cervical lateral flexion and decreased with ipsilateral cervical lateral flexion. Sensation provocation and location were evaluated using the RB-ULNT in all the subjects during each stage of the testing.

RESULTS

Significant differences on stage of reproduction and type of sensations were identified between 1) the (+) RB-ULNT symptomatic subjects, 2) the (-) RB-ULNT symptomatic subjects, and 3) the asymptomatic subjects. The (+) RB-ULNT group showed significantly increased pain responses during the first stage of the RB-ULNT compared with the (-) RB-ULNT group and the asymptomatic subjects. The (+) RB-ULNT also showed significantly decreased glenohumeral abduction passive range of motion when compared with the asymptomatic group.

CONCLUSION

Clinically, the differences found between the groups in their response to the RB-ULNT suggest heightened mechanosensitivity in the (+) RB-ULNT group.

LEVEL OF EVIDENCE

3a.