Translation of symptoms and signs into mechanisms in neuropathic pain

Co-occurring Chronic Pain and PTSD Among US Military Veterans: Prevalence, Correlates, and Functioning

BACKGROUND

The prevalence of co-occurring chronic pain and posttraumatic stress disorder (PTSD) has yet to be established in a nationally representative sample of US veterans, and little is known about the individual contributing roles of these disorders to the psychiatric and functional burden of this comorbidity.

OBJECTIVE

To determine the prevalence of chronic pain, PTSD, and co-occurring chronic pain and PTSD, and psychiatric comorbidities and psychosocial functioning in these groups.

DESIGN

Data were analyzed from the National Health and Resilience in Veterans Study, which surveyed a nationally representative sample of US veterans.

PARTICIPANTS

Veterans (n=4069) were classified into four groups: control (i.e., no PTSD or chronic pain), chronic pain only, PTSD only, and co-occurring chronic pain and PTSD.

MAIN MEASURES

A probable PTSD diagnosis was established using the PTSD Checklist for DSM-5, and a chronic pain diagnosis using a self-report item that queried health care professional diagnoses. Psychiatric and functional status were assessed using the Patient Health Questionnaire-4, Alcohol Use Disorders Identification Test, Screen of Drug Use, Suicide Behaviors Questionnaire-Revised, Short Form Health Survey-8, Brief Inventory of Psychosocial Functioning, and Medical Outcomes Study Cognitive Functioning Scale.

KEY RESULTS

A total of 3.8% of veterans reported both probable PTSD and a diagnosis of chronic pain. Relative to veterans with chronic pain alone, those with co-occurring chronic pain and probable PTSD were more likely to screen positive for psychiatric disorders (odds ratios [ORs]=2.59-9.88) and scored lower on measures of psychosocial functioning (Cohen's ds=0.38-1.43). Relative to veterans with probable PTSD only, those with co-occurring chronic pain and probable PTSD were more likely to have attempted suicide (OR=4.79; 95%CI, 1.81-12.69).

CONCLUSIONS

Results underscore the importance of whole health care that considers a broad range of health and functional domains in the assessment and treatment of co-occurring chronic pain and PTSD in veterans.

A Comprehensive Narrative Review of Neuropathic Pain: From Pathophysiology to Surgical Treatment

Neuropathic pain is a challenging condition. Despite the immense progress made in the pathophysiology and treatment of such conditions, so much work still has to be done. New frontiers previously unexplored are now objects of study with exciting results, mainly regarding neuromodulation and optogenetics. This review explores the already known pathophysiology and the clinical and surgical treatment in the light of evidence-based medicine. Additionally, new concepts and insights are discussed, presenting the hope for the development of new paradigms in the treatment of neuropathic pain.

The pathogenesis of painful diabetic neuropathy and clinical presentation

Diabetic neuropathy is a common complication of diabetes that affects up to 50% of patients during the course of the disease; 20-30% of the patients also develop neuropathic pain. The mechanisms underlying neuropathy are not known in detail, but both metabolic and vascular factors may contribute to the development of neuropathy. The development of the most common type of neuropathy is insidious, often starting distally in the toes and feet and gradually ascending up the leg and later also involving fingers and hands. The symptoms are mainly sensory with either sensory loss or positive symptoms with different types of paresthesia or painful sensations. In more advanced cases motor dysfunction may occur, causing gait disturbances and falls. The diagnosis of neuropathy is based on history and a careful examination, which includes a sensory examination of both large and small sensory nerve fiber function, as well as an examination of motor function and deep tendon reflexes of the lower limbs. Attention needs to be paid to the feet including examination of the skin, joints, and vascular supply. Nerve conduction studies are rarely needed to make a diagnosis of neuropathy. In patients with clear motor deficit or with an asymmetrical presentation, additional electrophysiological examination may be necessary. Early detection of diabetic neuropathy is important to avoid further irreversible injury to the peripheral nerves.

Endoscopic visualization of the inferior alveolar nerve associated with somatosensory changes after impacted mandibular third molar extraction

The aim of this study is to assess the relationship between somatosensory functional changes and inferior alveolar nerve (IAN) exposure after impacted mandibular third molars (M3M) removal. We recruited 35 patients who underwent impacted M3M extraction near the IAN. The M3Ms were extracted by combined endoscopy, piezosurgery, and contra-angle high-speed turbine handpiece. All IAN canal perforations and exposed regions were recorded and measured by endoscopy after extraction and on cone-beam computed tomography (CBCT) images before extraction. The patients were followed up 1, 7, and 35 days after surgery. A standardized quantitative sensory testing (QST) battery was performed on the lower lip skin. All of 35 cases had exposed IAN on CBCT images, 5 of which had no exposed IAN under endoscopy. For the other 30 cases, the endoscopy-measured IAN length and width were shorter than the CBCT measurements (P < 0.001). The warm and mechanical detection thresholds (MDT) on the operation side were significantly higher than the contralateral side after surgery (P < 0.05). Thermal sensory limen, MDT, and cold pain threshold were strongly correlated with the exposed IAN length and MDT also with the exposed IAN width one day after surgery. In conclusion, it was found that not all exposed IAN in CBCT images were real exposure after surgery. The intraoperative exposed IAN endoscopic measurements were smaller than by CBCT and strongly correlated with some QST parameters.

Neuropathic Pain and Spinal Cord Injury: Management, Phenotypes, and Biomarkers

Chronic neuropathic pain after a spinal cord injury (SCI) continues to be a complex condition that is difficult to manage due to multiple underlying pathophysiological mechanisms and the association with psychosocial factors. Determining the individual contribution of each of these factors is currently not a realistic goal; however, focusing on the primary mechanisms may be more feasible. One approach used to uncover underlying mechanisms includes phenotyping using pain symptoms and somatosensory function. However, this approach does not consider cognitive and psychosocial mechanisms that may also significantly contribute to the pain experience and impact treatment outcomes. Indeed, clinical experience supports that a combination of self-management, non-pharmacological, and pharmacological approaches is needed to optimally manage pain in this population. This article will provide a broad updated summary integrating the clinical aspects of SCI-related neuropathic pain, potential pain mechanisms, evidence-based treatment recommendations, neuropathic pain phenotypes and brain biomarkers, psychosocial factors, and progress regarding how defining neuropathic pain phenotypes and other surrogate measures in the neuropathic pain field may lead to targeted treatments for neuropathic pain after SCI.

Mirror Therapy in Patients with Somatoform Pain Disorders-A Pilot Study

Patients with chronic pain report reduced quality of life and high symptom burden while often responding insufficiently to treatment options. Mirror therapy has been proven to be effective in treating phantom limb pain and other conditions such as CRPS. This study was designed to investigate the efficacy of mirror therapy in patients with somatoform pain disorders on symptom severity and associated physiological parameters. Fifteen patients with persistent somatoform pain disorder (F45.40) or chronic pain disorder with somatic and psychological factors (F45.41) participated and received four weeks of tablet-based mirror therapy. Symptom severity was measured with established questionnaires, and their thermal detection, pain thresholds, and heart rate variability (HRV) were also assessed. After mirror therapy, pain intensity was reduced (z = -2.878, p = 0.004), and pain thresholds for cold stimuli were also diminished, i.e., the subjects became more sensitive to cold stimuli (z = -2.040, p = 0.041). In addition, a reduction of absolute power in the low-frequency band of HRV (t(13) = 2.536, p = 0.025) was detected. These findings indicate that this intervention may reduce pain intensity and modulate associated physiological parameters. As these results are limited by several factors, e.g., a small sample size and no control group, they should be validated in further studies investigating this novel intervention in these patients.

Thoracic pain in patients with chronic interstitial lung disease-an underestimated symptom

Introduction

Prevalence and predisposing factors for the development of thoracic pain (TP) in patients with chronic interstitial lung disease (cILD) are largely unknown. Underestimation and insufficient therapy of pain can lead to worsened ventilatory function. Quantitative sensory testing is an established tool for characterization of chronic pain and its neuropathic components. We investigated frequency and intensity of TP in cILD patients and the potential association with lung function and quality of life.

Materials and methods

We prospectively investigated patients with chronic interstitial lung disease to analyze risk factors for the development of thoracic pain and quantify thoracic pain through quantitative sensory testing. In addition, we studied the relationship between pain sensitivity and lung function impairment.

Results

Seventy-eight patients with chronic interstitial lung disease and 36 healthy controls (HCs) were included. Thoracic pain occurred in 38 of 78 patients (49%), most frequently in 13 of 18 (72%, p = 0.02) patients with pulmonary sarcoidosis. The occurrence was mostly spontaneous and not related to thoracic surgical interventions (76%, p = 0.48). Patients with thoracic pain showed a significant impairment of mental well-being (p = 0.004). A higher sensitivity to pinprick stimulation during QST can be observed in patients with thoracic pain (p < 0.001). Steroid treatment was associated with lower sensitivity within thermal (p = 0.034 and p = 0.032) and pressure pain testing (p = 0.046). We observed a significant correlation between total lung capacity and thermal (p = 0.019 and p = 0.03) or pressure pain sensitivity (p = 0.006 and p = 0.024).

Conclusion

This study was performed to investigate prevalence, risk factors and thoracic pain in patients with chronic interstitial lung disease. Thoracic pain mostly occurs spontaneous as a frequent symptom, and seems to be an underestimated symptom in patients with chronic interstitial lung disease, especially those with pulmonary sarcoidosis. Timely identification of thoracic pain may allow starting symptomatic treatment at early stage, before impairment in quality of life occurs.

Clinical Trial Registration

https://www.drks.de/drks_web/, Deutsches Register Klinischer Studien (DRKS) DRKS00022978.

[Etiopathogenetic substantiation of surgical treatment of neurogenic pain syndromes]

The purpose of the study was to improve classification of neurogenic (neuropathic) pain syndromes. This will make it possible to define the indications for appropriate analgesic surgery for each type of drug-resistant neurogenic pain syndrome. Incorrect management of neurogenic pain syndromes is usually associated with underestimation of pathogenetic prerequisites for its occurrence. Differentiation of compression, deafferentation and mixed neurogenic pain syndromes makes it possible to determine appropriate surgery and avoid tactical errors. Moreover, this approach allows you to save patients from unreasonable long-standing suffering. Patients with chronic pain syndromes often become disabled, sometimes in the prime of life, and isolated from society and family. Therefore, treatment of chronic pain is currently an urgent problem.

Sphaeranthus indicus Linn ameliorates streptozotocin-induced experimental diabetic neuropathy by targeting oxidative stress-mediated alterations

Background

Diabetes-induced neuropathic pain is manifested as a lowering of nerve transmission rate, increased discomfort, sensual loss, and axonal degradation, and is the most prevalent secondary consequence of diabetes. Diabetes is a devitalizing disease affecting people from diverse groups in both developing and industrialized countries. The inflammation pathway and oxidative stress both contribute considerably to diabetic peripheral neuropathy via the activation of inflammatory cytokines. Hyperglycemia-mediated neural oxidative stress and damage activates a number of metabolic pathways, causing diabetic neuropathy. The current study investigated the neuroprotective potential of methanolic extract of Sphaeranthus indicus Linn (MESI) in ameliorating diabetic neuropathic pain induced by administration of streptozotocin in rats.

Results

Four weeks after intraperitoneal treatment of streptozotocin (STZ), there was a significant decrease in mechano-tactile allodynia and mechanical and thermal hyperalgesia. Furthermore, STZ-induced oxidative stress increases the extent of neural lipid peroxidation (LPO), as evidenced by increased MDA levels, decreases the activities of endogenous antioxidants such as superoxide dismutase (SOD) and glutathione (GSH), and alters sciatic neural histoarchitecture. Chronic administration of methanolic extract of Sphaeranthus indicus Linn (MESI) for 4 weeks significantly and dose-dependently attenuated the decrease in levels of nociceptive thresholds, endogenous antioxidants (SOD and GSH), and increase in LPO. Furthermore, MESI significantly restored sciatic neural histoarchitecture.

Conclusion

The amelioration of streptozotocin-induced diabetic neuropathy by methanolic extract of Sphaeranthus indicus Linn (MESI) could be attributed to its antinociceptive, antioxidant, and neuroprotective properties.

Cold allodynia is correlated to paroxysmal and evoked mechanical pain in complex regional pain syndrome (CRPS)

OBJECTIVES

Mechanisms of complex regional pain syndrome (CRPS) are still debated. Identifying subgroups of patients have been attempted in the hope of linking clinical findings to possible mechanisms. The aim of the present study was to investigate whether subgroups of CRPS (based on quantitative sensory testing (QST)-results) differed with respect to different characteristics of pain like spontaneous ongoing or paroxysmal pain and mechanical dynamic allodynia.

METHODS

61 CRPS-patients (type 1 and 2) were examined clinically and with QST, in affected and contralateral extremity, with assessment of thresholds for warmth, cold and heat-and cold pain.

RESULTS

43 patients (20 men, 23 men) were diagnosed with CRPS 1 (70.5%) and 18 patients (8 women and 10 men) with CRPS 2 (29.5%). Three subgroups were defined based on thermal thresholds; A (thermal allodynia 22.9%), B (thermal hyposensitivity 37.3%), C (thermal allodynia and hyposensitivity 39.3%). Paroxysmal pain was more prevalent in patients with thermal allodynia (merging group A + C, 25/38-65.8%) compared to patients without thermal allodynia (group B, 5/23-21.7%) (p-value=0.00085).

CONCLUSIONS

We suggest that cold allodynia is based on hyper-excitability of very superficial skin nociceptors. The correlation between paroxysmal pain, allodynia to light touch and cold allodynia suggests that activity in those peripheral nociceptors can drive both, paroxysmal pain and spinal sensitization leading to stroke evoked allodynia. Mechanistically, the physical cold stimulus can unmask disease-related hyperexcitability by closure of temperature-sensitive potassium channels or induction of resurgent currents. Small fiber degeneration alone may not be the crucial mechanism in CRPS, nor explain pain.

Peripheral Neuropathies Derived from COVID-19: New Perspectives for Treatment

Peripheral neuropathies constitute a group of disorders affecting the peripheral nervous system. Neuropathies have multiple causes such as infections (i.e., COVID-19), diabetes, and nutritional (low vitamin levels), among others. Many micronutrients, such as vitamins (A, C, D, E, B6, B12, and folate), certain minerals (Fe, Mg, Zn, Se, and Cu), and ω-3 fatty acids have immunomodulatory effects. Therefore, they may play an instrumental role in the treatment of COVID-19 infection. However, many COVID-19 patients can undergo neuropathy. In this context, there is a wealth of information on a variety of first-, second-, and third-line treatment options. This review focuses on the application of nutraceutical strategies in order to improve the symptomatology of neuropathy and neuropathic pain in patients that suffered from COVID-19. Our aim is to provide an alternative vision to traditional medical-pharmacological treatment through nutraceuticals.

The neurologic pain signature responds to nonsteroidal anti-inflammatory treatment vs placebo in knee osteoarthritis

Supplemental Digital Content is Available in the Text.

fMRI-based measures, validated for nociceptive pain, respond to acute osteoarthritis pain, are not sensitive to placebo, and are mild-to-moderately sensitive to naproxen.

Introduction:

Many drug trials for chronic pain fail because of high placebo response rates in primary endpoints. Neurophysiological measures can help identify pain-linked pathophysiology and treatment mechanisms. They can also help guide early stop/go decisions, particularly if they respond to verum treatment but not placebo. The neurologic pain signature (NPS), an fMRI-based measure that tracks evoked pain in 40 published samples and is insensitive to placebo in healthy adults, provides a potentially useful neurophysiological measure linked to nociceptive pain.

Objectives:

This study aims to validate the NPS in knee osteoarthritis (OA) patients and test the effects of naproxen on this signature.

Methods:

In 2 studies (50 patients, 64.6 years, 75% females), we (1) test the NPS and other control signatures related to negative emotion in knee OA pain patients; (2) test the effect of placebo treatments; and (3) test the effect of naproxen, a routinely prescribed nonsteroidal anti-inflammatory drug in OA.

Results:

The NPS was activated during knee pain in OA (d = 1.51, P < 0.001) and did not respond to placebo (d = 0.12, P = 0.23). A single dose of naproxen reduced NPS responses (vs placebo, NPS d = 0.34, P = 0.03 and pronociceptive NPS component d = 0.38, P = 0.02). Naproxen effects were specific for the NPS and did not appear in other control signatures.

Conclusion:

This study provides preliminary evidence that fMRI-based measures, validated for nociceptive pain, respond to acute OA pain, do not appear sensitive to placebo, and are mild-to-moderately sensitive to naproxen.

Reflections of the sensory findings in the central nervous system in patients with neuropathic pain

This study aimed to evaluate whether there was a difference in functional magnetic resonance imaging (fMRI) findings in patients who were found having hyperalgesia or hypoesthesia according to Quantitative Sensory Tests (QST). Forty participants were included in the study: 20 with neuropathic pain (NP) due to cervical disc pathology (NP group) and 20 healthy volunteers. After obtaining the socio-demographic and clinical data of the participants, the painDETECT questionnaire was administered, followed by QST analysis to show the presence of hypoesthesia and/or hyperalgesia, and fMRI examinations, which included sensory stimulation of both extremities. Sensory threshold tests were found to be higher in the NP group compared with the healthy volunteers, and the heat pain threshold was found to be lower in the tests showing pain thresholds in the intergroup analyses (p < 0.05). The changes described were found in both painful and non-painful limbs. In the hypoesthetic NP group, a lower somatosensory cortex activity was found in non-painful limbs compared with the healthy volunteers (p < 0.05). In the unilateral hyperalgesic NP group, a lower somatosensory cortex activity was found on the painful side, and if the hyperalgesia was widespread, lower blood oxygen-level-dependent activity was also found in the operculum and insular cortex (p < 0.05). The patients with different phenotypes of NP had different activities in the areas related to the processing of pain, and were more prominent in patients with widespread hyperalgesia. Studies with larger numbers of patients are required for a definite statement.

Bupivacaine Induces ROS-Dependent Autophagic Damage in DRG Neurons via TUG1/mTOR in a High-Glucose Environment

Bupivacaine (BP) is a commonly clinically used local anesthetic (LA). Current studies suggest that neurological complications are increased in diabetic patients after LA application, but the molecular mechanism is poorly understood. LA-induced autophagy and neuronal injury have been reported. We hypothesized that a high-glucose environment aggravates BP-induced autophagic damage. Mouse dorsal root ganglion (DRG) neurons were treated with BP in a high-glucose environment, and the results showed that reactive oxygen species (ROS) levels increased, autophagy was activated, autophagy flux was blocked, and cell viability decreased. Pretreatment with the ROS scavenger N-acetyl-cysteine (NAC) attenuated ROS-mediated autophagy regulation. Moreover, the expression of the long noncoding RNA (lncRNA) taurine upregulated gene 1 (TUG1) increased, and NAC and TUG1 siRNA inhibited the expression of TUG1/mammalian target of rapamycin (mTOR) in DRGs treated with BP in a high-glucose environment. Intriguingly, contrary to previous reports on a positive effect on neurons, we found that rapamycin, an autophagy activator, and chloroquine, an autophagy and lysosome inhibitor, both exacerbated autophagic damage. These data suggest that a high-glucose environment exacerbated BP induced ROS-dependent autophagic damage in DRG neurons through the TUG1/mTOR signaling pathway, which provides a theoretical basis and target for the clinical prevention and treatment of BP neurotoxicity in diabeties.

Probucol attenuates NF-κB/NLRP3 signalling and augments Nrf-2 mediated antioxidant defence in nerve injury induced neuropathic pain

Neuroinflammation is one of the most significant pathological drivers following nerve injury which along with immune cell activation, oxidative stress and other associated molecular mechanisms contribute to development of neuropathic pain characterized by hyperalgesia and allodynia. In the current study we have investigated the pharmacological effect of probucol (prb) using chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain (NP) model in rats. CCI of sciatic nerve resulted in marked decrease in pain threshold along with perturbations in anti-oxidant defence, enhanced inflammatory mediators and abnormal foot posture. Administration of prb at the doses of 8 and 16 mg/kg, p.o. for 14 days significantly attenuated the behavioural, biochemical and functional deficits following CCI of sciatic nerve. To further explore the molecular mechanisms of prb, we assessed the post treatment levels of inflammatory and oxidative stress markers like NLRP3 inflammasome, NF-κB and associated proinflammatory molecules such as IL-1 β, TNF-α & IL-6 along with Nrf-2 and HO-1. Our findings demonstrated that CCI induced changes in levels of these markers were dose dependently reversed by administration of prb. Of note, at molecular level the elevated expression of transcription factors such as NF-κB which is crucial for Nlrp3 activation and diminished levels of Nrf-2 were manifested following CCI induction, these changes were markedly reversed with 14 days treatment of prb at both the doses. Our findings highlighted the dual pharmacological effect of prb, anti-inflammatory and anti-oxidant via modulation of NF-κB/NLRP3 signalling and Nrf-2 pathway in attenuation of CCI of sciatic nerve induced NP.

Neuropathic pain modeling: Focus on synaptic and ion channel mechanisms

Animal models of pain consist of modeling a pain-like state and measuring the consequent behavior. The first animal models of neuropathic pain (NP) were developed in rodents with a total lesion of the sciatic nerve. Later, other models targeting central or peripheral branches of nerves were developed to identify novel mechanisms that contribute to persistent pain conditions in NP. Objective assessment of pain in these different animal models represents a significant challenge for pre-clinical research. Multiple behavioral approaches are used to investigate and to validate pain phenotypes including withdrawal reflex to evoked stimuli, vocalizations, spontaneous pain, but also emotional and affective behaviors. Furthermore, animal models were very useful in investigating the mechanisms of NP. This review will focus on a detailed description of rodent models of NP and provide an overview of the assessment of the sensory and emotional components of pain. A detailed inventory will be made to examine spinal mechanisms involved in NP-induced hyperexcitability and underlying the current pharmacological approaches used in clinics with the possibility to present new avenues for future treatment. The success of pre-clinical studies in this area of research depends on the choice of the relevant model and the appropriate test based on the objectives of the study.

The role of cyclin-dependent kinase 5 in neuropathic pain

The chronification of pain can be attributed to changes in membrane receptors and channels underlying neuronal plasticity and signal transduction largely within nociceptive neurons that initiate and maintain pathological pain states. These proteins are subject to dynamic modification by posttranslational modifications, creating a code that controls protein function in time and space. Phosphorylation is an important posttranslational modification that affects ∼30% of proteins in vivo. Increased phosphorylation of various nociceptive ion channels and of their modulators underlies sensitization of different pain states. Cyclin-dependent kinases are proline-directed serine/threonine kinases that impact various biological and cellular systems. Cyclin-dependent kinase 5 (Cdk5), one member of this kinase family, and its activators p35 and p39 are expressed in spinal nerves, dorsal root ganglia, and the dorsal horn of the spinal cord. In neuropathic pain conditions, expression and/or activity of Cdk5 is increased, implicating Cdk5 in nociception. Experimental evidence suggests that Cdk5 is regulated through its own phosphorylation, through increasing p35's interaction with Cdk5, and through cleavage of p35 into p25. This narrative review discusses the molecular mechanisms of Cdk5-mediated regulation of target proteins involved in neuropathic pain. We focus on Cdk5 substrates that have been linked to nociceptive pathways, including channels (eg, transient receptor potential cation channel and voltage-gated calcium channel), proteins involved in neurotransmitter release (eg, synaptophysin and collapsin response mediator protein 2), and receptors (eg, glutamate, purinergic, and opioid). By altering the phosphoregulatory "set point" of proteins involved in pain signaling, Cdk5 thus appears to be an attractive target for treating neuropathic pain conditions.

The multiple faces of ketamine in anaesthesia and analgesia

Objective

Ketamine is an anaesthetic agent with a unique dissociative profile and pharmacological effects ranging from the induction and maintenance of anaesthesia to analgesia and sedation, depending on the dose. This article provides information for the clinical use of ketamine in anaesthesia, in both conventional and special circumstances.

Methods

This is a non-systematic review of the literature, through a PubMed search up to February 2021.

Results

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations. It is suitable for patients with many heart conditions and, unlike other anaesthetics, its potential for cardiorespiratory depression is low. Furthermore, it may be used when venous access is difficult as it may be administered through various routes. Ketamine is the anaesthetic of choice for patients with bronchospasm thanks to its bronchodilatory and anti-inflammatory properties.

Conclusion

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations and is suitable for patients with many cardiac and respiratory conditions.

Methylmercury induces hyperalgesia/allodynia through spinal cord dorsal horn neuronal activation and subsequent somatosensory cortical circuit formation in rats

Methylmercury (MeHg) is known to cause serious neurological deficits in humans. In this study, we investigated the occurrence of MeHg-mediated neuropathic pain and identified the underlying pathophysiological mechanism in a rat model of MeHg exposure. Rats were exposed to MeHg (20 ppm in drinking water) for 3 weeks. Neurological damage was observed in the primary afferent neuronal system, including the dorsal root nerve and the dorsal column of the spinal cord. The MeHg-exposed rats showed hyperalgesia/allodynia, compared to controls, as evidenced by a significant decrease in the threshold of mechanical pain evaluated using an algometer with calibrated forceps. Immunohistochemistry revealed the accumulation of activated microglia in the dorsal root nerve, dorsal column, and dorsal horn of the spinal cord. Western blot analyses of the dorsal part of the spinal cord demonstrated an increase in inflammotoxic and inflammatory cytokines and a neuronal activation related protein, phospho-CRE bunding protein (CREB). The results suggest that dorsal horn neuronal activation was mediated by inflammatory factors excreted by accumulated microglia. Furthermore, analyses of the cerebral cortex demonstrated increased expression of phospho-CREB and thrombospondin-1, which is known to be an important factor for excitatory synapse formation, specifically in the somatosensory cortical area. In addition, the expression of pre- and post-synaptic markers was increased in this cortex area. These results suggested that the new cortical circuit was wired specifically in the somatosensory cortex. In conclusion, MeHg-mediated dorsal horn neuronal activation with inflammatory microglia might induce somatosensory cortical rewiring, leading to hyperalgesia/allodynia.

Painful and non-painful diabetic neuropathy, diagnostic challenges and implications for future management

Peripheral neuropathy is one of the most common complications of both type 1 and type 2 diabetes. Up to half of patients with diabetes develop neuropathy during the course of their disease, which is accompanied by neuropathic pain in 30-40% of cases. Peripheral nerve injury in diabetes can manifest as progressive distal symmetric polyneuropathy, autonomic neuropathy, radiculo-plexopathies, and mononeuropathies. The most common diabetic neuropathy is distal symmetric polyneuropathy, which we will refer to as DN, with its characteristic glove and stocking like presentation of distal sensory or motor function loss. DN or its painful counterpart, painful DN, are associated with increased mortality and morbidity; thus, early recognition and preventive measures are essential. Nevertheless, it is not easy to diagnose DN or painful DN, particularly in patients with early and mild neuropathy, and there is currently no single established diagnostic gold standard. The most common diagnostic approach in research is a hierarchical system, which combines symptoms, signs, and a series of confirmatory tests. The general lack of long-term prospective studies has limited the evaluation of the sensitivity and specificity of new morphometric and neurophysiological techniques. Thus, the best paradigm for screening DN and painful DN both in research and in clinical practice remains uncertain. Herein, we review the diagnostic challenges from both clinical and research perspectives and their implications for managing patients with DN. There is no established DN treatment, apart from improved glycaemic control, which is more effective in type 1 than in type 2 diabetes, and only symptomatic management is available for painful DN. Currently, less than one-third of patients with painful DN derive sufficient pain relief with existing pharmacotherapies. A more precise and distinct sensory profile from patients with DN and painful DN may help identify responsive patients to one treatment versus another. Detailed sensory profiles will lead to tailored treatment for patient subgroups with painful DN by matching to novel or established DN pathomechanisms and also for improved clinical trials stratification. Large randomized clinical trials are needed to identify the interventions, i.e. pharmacological, physical, cognitive, educational, etc., which lead to the best therapeutic outcomes.

Pharmacological Modulation of Rate-Dependent Depression of the Spinal H-Reflex Predicts Therapeutic Efficacy against Painful Diabetic Neuropathy

Impaired rate-dependent depression (RDD) of the spinal H-reflex occurs in diabetic rodents and a sub-set of patients with painful diabetic neuropathy. RDD is unaffected in animal models of painful neuropathy associated with peripheral pain mechanisms and diabetic patients with painless neuropathy, suggesting RDD could serve as a biomarker for individuals in whom spinal disinhibition contributes to painful neuropathy and help identify therapies that target impaired spinal inhibitory function. The spinal pharmacology of RDD was investigated in normal rats and rats after 4 and 8 weeks of streptozotocin-induced diabetes. In normal rats, dependence of RDD on spinal GABAergic inhibitory function encompassed both GABA_A and GABA_B receptor sub-types. The time-dependent emergence of impaired RDD in diabetic rats was preceded by depletion of potassium-chloride co-transporter 2 (KCC2) protein in the dorsal, but not ventral, spinal cord and by dysfunction of GABA_A receptor-mediated inhibition. GABA_B receptor-mediated spinal inhibition remained functional and initially compensated for loss of GABA_A receptor-mediated inhibition. Administration of the GABA_B receptor agonist baclofen restored RDD and alleviated indices of neuropathic pain in diabetic rats, as did spinal delivery of the carbonic anhydrase inhibitor acetazolamide. Pharmacological manipulation of RDD can be used to identify potential therapies that act against neuropathic pain arising from spinal disinhibition.

Opening eyes to therapeutic perspectives of bioactive polyphenols and their nanoformulations against diabetic neuropathy and related complications

Introduction: Diabetic neuropathy (DN) is one of the major complications arising from hyperglycaemia in diabetic patients. In recent years polyphenols present in plants have gained attention to treat DN. The main advantages associated with them are their action via different molecular pathways to manage DN and their safety. However, they failed to gain clinical attention due to challenges associated with their formulation development such as lipophilicity,poor bioavailability, rapid systemic elimination, and enzymatic degradation.Area covered: This article includes different polyphenols that have shown their potential against DN in preclinical studies and the research carried out towards development of their nanoformulations in order to overcome aforementioned issues.Expert opinion: In this review various polyphenol based nanoformulations such as nanospheres, self-nanoemulsifying drug delivery systems, niosomes, electrospun nanofibers, metallic nanoparticles explored exclusively to treat DN are discussed. However, the literature available related to polyphenol based nanoformulations to treat DN is limited. Moreover, these experiments are limited to preclinical studies. Hence, more focus is required towards  development of nanoformulations using simple and single step process as well as inexpensive and non-toxic excipients so that a stable, scalable, reproducible and non-toxic formulation could be achieved and clinical trials could be initiated.

Persian version of the LANSS and S-LANSS questionnaires: A study for cultural adaptation and validation

The aim of this study was to culturally adapt and validate Leeds assessment of neuropathic symptoms and signs (LANSS) and self-report LANSS (S-LANSS) tools. Patients with chronic pain (n = 206) were categorized into neuropathic pain (NeP) (n = 101) or non-NeP (n = 105). After the translation process, both questionnaires and the Persian Douleur Neuropathique 4 (P-DN4) were administered to patients to assess the clinometric properties. The mean overall score of both tools was significantly higher in the NeP group (p < 0.01). Test-retest reliability analysis of the overall score of the Persian (P)-LANSS and PS-LANSS were 0.99 and 0.98, respectively. α-Cronbach value for P-LANSS and PS-LANSS were 0.64 and 0.61, respectively. Factor analysis of both questionnaires yielded two components explaining most of the observable variance. The P-LANSS was significantly correlated with PS-LANSS and P-DN4 (ρ = 0.92, p = 0.01, for both). PS-LANSS was also significantly correlated with P-DN4 (ρ = 0.79, p = 0.01). Both tools successfully diagnosed NeP patients at the cutoff point of ≥12 with 88.12% sensitivity and 76.19% specificity for P-LANSS and 83.17% sensitivity and 95.24% specificity for PS-LANSS. P-LANSS and PS-LANSS are reliable and valid tools to identify NeP component in chronic pain patients. PS-LANSS was found to be an acceptable alternative for P-LANSS.

Clinical Reasoning for the Examination and Physical Therapy Treatment of Temporomandibular Disorders (TMD): A Narrative Literature Review

The current narrative literature review aims to discuss clinical reasoning based on nociceptive pain mechanisms for determining the most appropriate assessment and therapeutic strategy and to identify/map the most updated scientific evidence in relation to physical therapy interventions for patients with temporomandibular disorders (TMDs). We will also propose an algorithm for clinical examination and treatment decisions and a pain model integrating current knowledge of pain neuroscience. The clinical examination of patients with TMDs should be based on nociceptive mechanisms and include the potential identification of the dominant, central, or peripheral sensitization driver. Additionally, the musculoskeletal drivers of these sensitization processes should be assessed with the aim of reproducing symptoms. Therapeutic strategies applied for managing TMDs can be grouped into tissue-based impairment treatments (bottom-up interventions) and strategies targeting the central nervous system (top-down interventions). Bottom-up strategies include joint-, soft tissue-, and nerve-targeting interventions, as well as needling therapies, whereas top-down strategies include exercises, grade motor imagery, and also pain neuroscience education. Evidence shows that the effectiveness of these interventions depends on the clinical reasoning applied, since not all strategies are equally effective for the different TMD subgroups. In fact, the presence or absence of a central sensitization driver could lead to different treatment outcomes. It seems that multimodal approaches are more effective and should be applied in patients with TMDs. The current paper also proposes a clinical decision algorithm integrating clinical diagnosis with nociceptive mechanisms for the application of the most appropriate treatment approach.

Precollision Medical Diagnoses Predict Chronic Neck Pain Following Acute Whiplash Trauma

OBJECTIVES

The reason why some individuals develop chronic symptoms, whiplash-associated disorder, following whiplash trauma is poorly understood. We explored whether precollision pain-related diagnoses, medically unexplained symptoms, and psychiatric diagnoses are related to whiplash-associated disorder.

MATERIALS AND METHODS

A cohort of 719 individuals exposed to whiplash trauma and subsequently experiencing symptoms within 72 hours (whiplash-exposed cohort) and 3595 matched controls were included in this observational prospective study. At 12 months postcollision, the whiplash-exposed cohort rated their neck pain using the Visual Analog Scale. Data on health were obtained from the Danish National Patient Register for the whiplash-exposed cohort and for the controls for a 5-year period before collision.

RESULTS

The whiplash-exposed cohort had significantly increased incidences of precollision pain-related diagnoses: χ(1)=17.42, P<0.001 and medically unexplained symptoms: χ(1)=22.2, P<0.001 but not psychiatric diagnoses: χ(1)=3.60, P>0.05 compared with controls in the 5-year period. Participants from the whiplash-exposed cohort with precollision pain-related diagnoses (odds ratio=2.46; 95% confidence interval, 1.39; 4.35) and medically unexplained symptoms (odds ratio, 1.72; 95% confidence interval, 1.04; 2.84) had significantly increased odds for neck pain at follow-up.

DISCUSSION

Precollision pain and medically unexplained symptoms predict chronic neck pain following whiplash trauma. This may indicate that a sensitization process was initiated before the collision or that individuals with precollision low threshold for contacting health care services maintain this behavior postcollision. The collision may trigger existing individual vulnerabilities that constitute to be a risk factor for chronic whiplash.

Association of quantitative sensory testing parameters with clinical outcome in patients with lumbar radiculopathy undergoing microdiscectomy

Background/Aim

This study aimed to establish the somatosensory profile of patients with lumbar radiculopathy at pre‐and post‐microdiscectomy and to explore any association between pre‐surgical quantitative sensory test (QST) parameters and post‐surgical clinical outcomes.

Methods

A standardized QST protocol was performed in 53 patients (mean age 38 ± 11 years, 26 females) with unilateral L5/S1 radiculopathy in the main pain area (MPA), affected dermatome and contralateral mirror sites and in age‐ and gender‐,and body site‐matched healthy controls. Repeat measures at 3 months included QST, the Oswestry Disability Index (ODI) and numerous other clinical measures; at 12 months, only clinical measures were repeated. A change <30% on the ODI was defined as ‘no clinically meaningful improvement’.

Results

Patients showed a significant loss of function in their symptomatic leg both in the dermatome (thermal, mechanical, vibration detection p < .002), and MPA (thermal, mechanical, vibration detection, mechanical pain threshold, mechanical pain sensitivity p < .041) and increased cold sensitivity in the MPA (p < .001). Pre‐surgical altered QST parameters improved significantly post‐surgery in the dermatome (p < .018) in the symptomatic leg and in the MPA (p < .010), except for thermal detection thresholds and cold sensitivity. Clinical outcomes improved at 3 and 12 months (p < .001). Seven patients demonstrated <30% change on the ODI at 12 months. Baseline loss of function in mechanical detection in the MPA was associated with <30% change on the ODI at 12 months (OR 2.63, 95% CI 1.09–6.37, p = .032).

Conclusion

Microdiscectomy resulted in improvements in affected somatosensory parameters and clinical outcomes. Pre‐surgical mechanical detection thresholds may be predictive of clinical outcome.

Significance

This study documented quantitative sensory testing (QST) profiles in patients with lumbar radiculopathy in their main pain area (MPA) and dermatome pre‐ and post‐microdiscectomy and explored associations between QST parameters and clinical outcome. Lumbar radiculopathy was associated with loss of function in modalities mediated by large and small sensory fibres. Microdiscectomy resulted in significant improvements in loss of function and clinical outcomes in 85% of our cohort. Pre‐surgical mechanical detection thresholds in the MPA may be predictive of clinical outcome.

Identifying predictive factors for neuropathic pain after breast cancer surgery using machine learning

INTRODUCTION

Neuropathic pain (NP) remains a major debilitating condition affecting more than 26% of breast cancer survivors worldwide. NP is diagnosed using a validated 10-items Douleur Neuropathique - 4 screening questionnaire which is administered 3 months after surgery and requires patient-doctor interaction. To develop an effective prognosis model admissible soon after surgery, without the need for patient-doctor interaction, we sought to [1] identify specific pain characteristics that can help determine which patients may be susceptible to NP after BC surgery, and 2) assess the utility of machine learning models developed in objective [1] as a knowledge discovery tool for downstream analysis.

METHODS

The dataset is from a prospective cohort study of female patients scheduled to undergo breast cancer surgery for the first time at the Jewish General Hospital, Montreal, Canada between November 2014 and March 2019. NP was assessed at 3 months after surgery using Douleur Neuropathique - 4 interview scores (in short, DN4-interview; range: 0-7). For the primary analysis, we constructed six ML algorithms (least square, ridge, elastic net, random forest, gradient boosting, and neural net) to identify the most relevant predictors for DN4-interview score; and compared model performance based on root mean square error (RMSE). For the secondary analysis, we built a logistic classification model for neuropathic pain (DN4-interview score ≥ 3 versus DN4-interview score < 3) using the relevant-consensus-predictors from the primary analysis.

RESULTS

Anxiety, type of surgery, preoperative baseline pain and acute pain on movement were identified as the most relevant predictors for DN4 - interview score. The least square regression model (RMSE = 1.43) is comparable in performance with random forest (RMSE = 1.39) and neural network model (RMSE = 1.50). The Gradient boosting model (RMSE = 1.16) outperformed the models compared including the penalized regression models (ridge regressions, RMSE = 1.28; and elastic net, RMSE = 1.31). In the secondary analysis, the preferred logistic regression classier for NP had an area under the curve (AUC) of 0.68 (95% CI = 0.57 to 0.79). Anxiety was significantly associated with the likelihood of NP (odds ratio = 2.18; 95% CI = 1.05-4.49). In comparison to their counterparts, the odds of NP were higher in participants with acute pain on movement or with present preoperative baseline pain or participants who performed total mastectomy surgery, but the differences were not statistically significant.

CONCLUSIONS

Modern machine learning models show improvements over traditional least square regression in predicting of DN4-interview score. Penalized regression methods and the Gradient boosting model out-perform other models. As a predictor discovery tool, machine learning algorithms identify relevant predictors for DN4-interview score that remain statistically significant indicators of neuropathic pain in the classification model. Anxiety, type of surgery and acute pain on movement remain the most useful predictors for neuropathic pain.

Exploring the Promise of Flavonoids to Combat Neuropathic Pain: From Molecular Mechanisms to Therapeutic Implications

Neuropathic pain (NP) is the result of irregular processing in the central or peripheral nervous system, which is generally caused by neuronal injury. The management of NP represents a great challenge owing to its heterogeneous profile and the significant undesirable side effects of the frequently prescribed psychoactive agents, including benzodiazepines (BDZ). Currently, several established drugs including antidepressants, anticonvulsants, topical lidocaine, and opioids are used to treat NP, but they exert a wide range of adverse effects. To reduce the burden of adverse effects, we need to investigate alternative therapeutics for the management of NP. Flavonoids are the most common secondary metabolites of plants used in folkloric medicine as tranquilizers, and have been claimed to have a selective affinity to the BDZ binding site. Several studies in animal models have reported that flavonoids can reduce NP. In this paper, we emphasize the potentiality of flavonoids for the management of NP.

Formononetin Ameliorates Diabetic Neuropathy by Increasing Expression of SIRT1 and NGF

Diabetic neuropathy is commonly observed complication in more than 50 % of type 2 diabetic patients. Histone deacetylases including SIRT1 have significant role to protect neuron from hyperglycemia induced damage. Formononetin (FMNT) is known for its effect to control hyperglycemia and also activate SIRT1. In present study, we evaluated effect of FMNT as SIRT1 activator in type 2 diabetic neuropathy. Type 2 diabetic neuropathy was induced in rats by modification of diet for 15 days using high fat diet and administration of streptozotocin (35 mg/kg/day, i. p.). FMNT treatment was initiated after confirmation of type 2 diabetes. Treatment was given for 16 weeks at 10, 20 and 40 mg/kg/day dose orally. FMNT treatment-controlled hypoglycemia and reduced insulin resistance significantly in diabetic animals. FMNT treatment reduced oxidative stress in sciatic nerve tissue. FMNT treatment also reduced thermal hyperalgesia and mechanical allodynia significantly. It improved conduction velocity in nerve and unregulated SIRT1 and NGF expression in sciatic nerve tissue. Results of present study indicate that continuous administration of FMNT protected diabetic animals from hyperglycemia induced neuronal damage by controlling hyperglycemia and increasing SIRT1 and NGF expression in nerve tissue. Thus, FMNT can be an effective candidate for treatment of type 2 diabetic neuropathy.

All about pain pharmacology: what pain physicians should know

From the perspective of the definition of pain, pain can be divided into emotional and sensory components, which originate from potential and actual tissue damage, respectively. The pharmacologic treatment of the emotional pain component includes antianxiety drugs, antidepressants, and antipsychotics. The anti-anxiety drugs have anti-anxious, sedative, and somnolent effects. The antipsychotics are effective in patients with positive symptoms of psychosis. On the other hand, the sensory pain component can be divided into nociceptive and neuropathic pain. Non-steroidal anti-inflammatory drugs (NSAIDs) and opioids are usually applied for somatic and visceral nociceptive pain, respectively; anticonvulsants and antidepressants are administered for the treatment of neuropathic pain with positive and negative symptoms, respectively. The NSAIDs, which inhibit the cyclo-oxygenase pathway, exhibit anti-inflammatory, antipyretic, and analgesic effects; however, they have a therapeutic ceiling. The adverse reactions (ADRs) of the NSAIDs include gastrointestinal problems, generalized edema, and increased bleeding tendency. The opioids, which bind to the opioid receptors, present an analgesic effect only, without anti-inflammatory, antipyretic, or ceiling effects. The ADRs of the opioids start from itching and nausea/vomiting to cardiovascular and respiratory depression, as well as constipation. The anticonvulsants include carbamazepine, related to sodium channel blockade, and gabapentin and pregabalin, related to calcium blockade. The antidepressants show their analgesic actions mainly through inhibiting the reuptake of serotonin or norepinephrine. Most drugs, except NSAIDs, need an up-dose titration period. The principle of polypharmacy for analgesia in case of mixed components of pain is increasing therapeutic effects while reducing ADRs, based on the origin of the pain.

Psychological factors can cause false pain classification on painDETECT

Background and aims The painDETECT questionnaire (PD-Q) has been widely used as a screening tool for the identification of neuropathic pain (NeP) as well as a tool for the characterization of patients' pain profile. In contrast to other NeP screening tools, the PD-Q is the only screening tool with weighted sensory descriptors. It is possible that responses to the PD-Q sensory descriptors are influenced by psychological factors, such as catastrophizing or anxiety, which potentially might contribute to an overall higher score of PD-Q and a false positive identification of NeP. This study aimed to explore (i) the relationship between psychological factors (catastrophizing, anxiety, depression and stress) and the total PD-Q score and (ii) if psychological factors are associated with false positive identifications of NeP on the PD-Q compared to clinically diagnosed NeP. Methods The study was a retrospective review of 1,101 patients attending an outpatient pain centre. Patients were asked to complete the PD-Q, the Pain Catastrophizing Scale (PCS), the Depression, Anxiety and Stress Scale (DASS) and the Brief Pain Inventory (BPI). For patients who were identified by PD-Q as having NeP, their medical records were reviewed to establish if they had a clinical diagnosis of NeP. Results Accounting for missing data, complete datasets of 652 patients (mean age 51 (SD14) years, range 18-88; 57% females) were available for analysis. Based on PD-Q scoring, NeP was likely present in 285 (44%) patients. Depression, anxiety, stress, catastrophizing, BPI pain and BPI interference were all significantly related to each other (p < 0.0001) and patients displaying these traits were significantly more likely to have a positive PD-Q score (p < 0.0001). For patients classified by PD-Q as having NeP, only 50% of patients had a clinical diagnosis of NeP. Anxiety was significantly associated with a false positive classification of NeP on PD-Q (p = 0.0036). Conclusions Our retrospective study showed that psychological factors including catastrophizing, depression, anxiety, and stress were all influential in producing a higher score on the PD-Q. We observed a high rate of false positive NeP classification which was associated with the presence of anxiety. Implications Clinicians and researchers should be aware that a patient's psychological state may influence the responses to PD-Q and consequently the final PD-Q score and its NeP classification.

Quantitative Sensory Testing in Patients with Multisomatoform Disorder with Chronic Pain as the Leading Bodily Symptom-a Matched Case-Control Study

OBJECTIVE

Chronic pain is a debilitating condition of multifactorial origin, often without physical findings to explain the presenting symptoms. Of the possible etiologies of persisting painful symptoms, somatoform disorders and functional somatic syndromes (FSS) are among the most challenging, with a prevalence of 8-20%. Many different somatoform disorders and FSS have overlapping symptoms, with pain being the most prevalent one. The concept of multisomatoform disorder (MSD) has been developed to acknowledge that fact. We hypothesized that the concept of MSD will be reflected in a distinct sensory profile of patients compared with healthy controls and possibly provide insight into the type and pathophysiology of the pain commonly experienced by patients.

DESIGN

We performed comprehensive quantitative sensory testing (QST) in 151 patients and 149 matched controls.

RESULTS

There were significant differences in the sensory profiles of patients compared with controls. Patients with MSD showed a combination of tactile and thermal hypesthesia combined with mechanical and cold hyperalgesia. This was true for measurements at test and control sites, with the exception of vibration detection threshold and mechanical pain threshold. Among the observed changes, a marked sensory loss of function, as evidenced by an increase in cold detection threshold, and a marked gain of function, as evidenced by a decrease of pressure pain threshold, were most notable. There was no evidence of concurrent medication influencing QST results.

CONCLUSIONS

The observed somatosensory profile of patients with MSD resembles that of patients suffering from neuropathic pain with evidence of central sensitization.

Beneficial effects of fish oil enriched in omega-3 fatty acids on the development and maintenance of neuropathic pain

OBJECTIVE

The aim of this work was to assess the preventive effect of an eicosapentaenoic acid/docosahexaenoic acid-concentrate fish oil on neuropathic pain development and regenerative features of sciatic nerve in rats.

METHODS

In the present study, rats with chronic constriction injury (CCI) of the sciatic nerve and sham-operated ones received fish oil enriched in omega-3 fatty acids (0.36 or 0.72 g/kg per day, oral) or saline solution for 21 days, with thermal hyperalgesia and mechanical allodynia being assessed before and 3, 7, 14 and 21 days after injury.

KEY FINDINGS

Fish oil enriched in omega-3 fatty acids (0.72 g/kg) reversed thermal hyperalgesia and significantly reduced mechanical allodynia. In addition, ω-3 treatment (0.72 g/kg) promoted the recovery of the Sciatic Functional Index as well as restored axonal density and morphology, without the formation of neuroma in the injured sciatic nerves after 21 days.

CONCLUSION

We conclude that the fish oil enriched in omega-3 fatty acids administration relieves thermal hyperalgesia and mechanical allodynia effectively and also enhances the recovery process in rats with CCI of the sciatic nerve. These findings might contribute to new therapeutic approaches including omega-3 fatty acids in neuropathic pain treatment.

Painful and non-painful diabetic polyneuropathy: Clinical characteristics and diagnostic issues

Diabetic neuropathy (DN) is a common complication of diabetes and can be either painful or non-painful. It is challenging to diagnose this complication, as no biomarker or clear consensus on the clinical definition of either painful or non-painful DN exists. Hence, a hierarchical classification has been developed categorizing the probability of the diagnosis into: possible, probable or definite, based on the clinical presentation of symptoms and signs. Pain is a warning signal of tissue damage, and non-painful DN therefore represents a clinical and diagnostic challenge because it often goes unnoticed until irreversible nerve damage has occurred. Simple clinical tests seem to be the best for evaluation of DN in the general care for diabetes. Screening programs at regular intervals might be the most optimal strategy for early detection and interventions to possibly prevent further neuronal damage and to lower the economic burden of this complication.

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

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

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

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

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

Prognosis in case of nerve disturbance after mandibular implant surgery in relation to computed tomography findings and symptoms

Purpose

The aim of this study was to evaluate the computed tomography (CT) imaging findings and clinical symptoms of patients who complained of neurosensory disturbances after mandibular implant surgery, and to investigate the relationships of these parameters with the prognosis for recovery.

Methods

CT scans were reviewed in 56 patients with nerve disturbance after mandibular implant surgery. Two oral radiologists classified the imaging findings into intrusion, contact, close, and separate groups according to the distance from the inferior border of the implant to the roof of the mandibular canal (MC). The symptoms of 56 patients were classified into 8 groups and the frequency of each group was investigated. Patients were categorized according to symptom improvement into no recovery and recovery groups, and the relationships of recovery with the CT classification and specific symptom groups were analyzed.

Results

Thirty-eight of the 56 nerve disturbance cases showed improvement. The close and separate groups in the CT classification had a strong tendency for recovery (90.9% and 81.8%, respectively) (P<0.05). Although the lowest recovery rate was found in the intrusion group, it was non-negligible, at 50%. The 6 patients with a worm crawling feeling all improved, while the 8 cases with a tightening sensation showed the lowest recovery rate, at 12.5%, and the symptom of a tightening sensation occurred only in the intrusion and contact groups.

Conclusions

The closer the implant fixture was to the MC on CT images, the less likely the patient was to recover. Regarding paresthesia symptoms, while a worm crawling feeling is thought to be a predictor of recovery, a tightening sensation appeared to be associated with a lower recovery rate.

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

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

Biomarkers mapping of neuropathic pain in a nerve chronic constriction injury mice model

Neuropathic pain is caused by a lesion or disease of the somatosensory nervous system and has a considerable impact on the quality of life. Neuropathic pain has a dynamic and complex aetiology and gives heterogeneous symptoms across patients; therefore, it represents an important clinical challenge. Current pharmacological treatment includes tricyclic antidepressant serotonin-noradrenaline uptake inhibitors such as duloxetine, pregabalin, and gabapentin. However, these drugs do not show efficacy in all patients suffering from neuropathic pain. In this work we used a nerve chronic constriction injury mice model based on the ligation of sciatic nerve to analyse, by two-dimensional electrophoresis and mass spectrometry, blood proteins significantly altered by neuropathic pain one-week after surgery. A sham-ligated group of mice acting as control and a group of ligated mice treated with gabapentin were also analysed. The results indicated that four haptoglobin isoforms were significantly more expressed, while transthyretin and alpha-2-macroglobulin expression decreased in the serum of the murine neuropathic pain model with respect to the control mice. Interestingly, the treatment with the gabapentin reversed these conditions. The outcomes of this study can provide a further understanding of the pathophysiological meaning of the biomarkers involved in neuropathic pain.

A model of pain behaviors in freely moving rats generated by controllable electrical stimulation of the peripheral nerve

BACKGROUND

Neuropathic pain patients have described experiencing unprovoked, intermittent pain attacks with shooting, stabbing, and burning qualities. Rodent models used in previous literature usually only involve acute exposure, and/or are unable to manipulate the stimulation intensity in vivo by the experimenter during an experiment.

NEW METHOD

This paper describes a method to induce controllable pain behaviors in rodents using a wireless portable electronic device that can be manipulated within the course of an experiment. A stimulating electrode was implanted at the L5 spinal nerve location in Sprague-Dawley rats and our custom-built wireless stimulating device was attached to deliver variable stimulation in freely moving animals (50 Hz, 0.5 V; 100 Hz, 1 V).

RESULTS

Implantation itself did not induce hypersensitivity as measured by the mechanical paw withdrawal threshold test. Observation of pain behaviors (paw elevation and licking) indicated that high stimulation intensity yielded a significant increase in pain behaviors. Even further, high intensity stimulation resulted in a behavioral "wind-up" of pain behaviors that persisted into the resting period when no stimulation was applied.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

This method can be used to study pain behaviors in a controllable way in freely moving rodents in comparison to existing models that are acute and/or are unable to manipulate the stimulation intensity in vivo.

Comparison of unpleasant and pain thresholds of thermal stimuli in the orofacial regions: a psychophysical study using quantitative sensory testing in healthy young men

Purpose/Aim: To gain a better understanding of the psychophysics of thermal pain perception in a clinical setting, this study investigated whether thermal thresholds of unpleasantness are different from pain thresholds of cold and heat stimuli. Of particular interest was the relationship between unpleasantness and pain thresholds for cold vs heat stimuli.

MATERIAL AND METHODS

Thirty healthy male volunteers (mean age 26.1 years, range 23 to 32 years) participated. Thermal detection, cold pain (CPT) and heat pain (HPT) thresholds were measured at 5 trigeminal sites by the method of limits using quantitative sensory testing (QST), followed by cold unpleasant (CUT) and heat unpleasant (HUT) thresholds.

RESULTS

The temperatures at which individuals first reported thermal sensations as unpleasant or painful substantially differed among subjects. CUT exhibited a higher mean value with less variability than CPT, and HUT presented a lower mean than HPT (p < .001). As with CPT, CUT did not show any significant difference between the test sites. On the other hand, HUT, like HPT, exhibited site differences (p < .001). There was moderate correlation between CUT and CPT, whereas HUT and HPT were strongly correlated. The relationship between unpleasant and pain thresholds of cold vs heat stimuli was significantly different even when controlling for test site variability (p < .001).

CONCLUSION

These findings indicate that unpleasant and pain thresholds to thermal stimuli differ in healthy young men. Of particular note is the distinct relationship of unpleasant and pain thresholds of cold vs heat stimuli, revealing the thermal difference in temperature transition from unpleasantness to pain.

Assessment and manifestation of central sensitisation across different chronic pain conditions

Different neuroplastic processes can occur along the nociceptive pathways and may be important in the transition from acute to chronic pain and for diagnosis and development of optimal management strategies. The neuroplastic processes may result in gain (sensitisation) or loss (desensitisation) of function in relation to the incoming nociceptive signals. Such processes play important roles in chronic pain, and although the clinical manifestations differ across condition processes, they share some common mechanistic features. The fundamental understanding and quantitative assessment of particularly some of the central sensitisation mechanisms can be translated from preclinical studies into the clinic. The clinical perspectives are implementation of such novel information into diagnostics, mechanistic phenotyping, prevention, personalised treatment, and drug development. The aims of this paper are to introduce and discuss (1) some common fundamental central pain mechanisms, (2) how they may translate into the clinical signs and symptoms across different chronic pain conditions, (3) how to evaluate gain and loss of function using quantitative pain assessment tools, and (4) the implications for optimising prevention and management of pain. The chronic pain conditions selected for the paper are neuropathic pain in general, musculoskeletal pain (chronic low back pain and osteoarthritic pain in particular), and visceral pain (irritable bowel syndrome in particular). The translational mechanisms addressed are local and widespread sensitisation, central summation, and descending pain modulation.

Significance

Central sensitisation is an important manifestation involved in many different chronic pain conditions. Central sensitisation can be different to assess and evaluate as the manifestations vary from pain condition to pain condition. Understanding central sensitisation may promote better profiling and diagnosis of pain patients and development of new regimes for mechanism based therapy. Some of the mechanisms underlying central sensitisation can be translated from animals to humans providing new options in development of therapies and profiling drugs under development.

Somatosensory Test Responses and Physical and Psychological Functioning of Children and Adolescents with Chronic Non-neuropathic Pain: An Exploratory Study

OBJECTIVES

This study was designed to establish preliminary feasibility testing of a set of inherently benign somatosensory stimulus-response tests (to cutaneous and deep stimuli) for bedside or office evaluation of pain disorders in children and adolescents. Associations between, and the relative influence of, cutaneous somatosensory testing (SST) responses, deep SST responses, and psychological factors (depression, pain-related catastrophizing) on pain outcomes (worst pain intensity, pain-related disability) were considered.

METHODS

Sixty participants (6 to 18 y) were recruited from the pediatric chronic pain clinic. SST responses were assessed at the pain site (PS) and control sites to diverse stimuli (static/dynamic touch, punctate pressure, vibration, cool, deep pressure) using Colored Analogue Scales (CAS) with modified anchors. Validated measures of depression, pain-related catastrophizing, and pain-related functional interference were administered.

RESULTS

Responses at the PS were more frequently hypersensitive than hyposensitive for all SST measures except vibration. Deep pressure responses were the only statistically significant predictor of worst pain intensity. Depression and pain-related catastrophizing accounted for a statistically significant amount of variance of pain-related disability, over and above that which was accounted for by SST responses.

DISCUSSION

Preliminary feasibility of a set of somatosensory stimulus-response tests for bedside or office evaluation of pain disorders in children and adolescents was established. Deep pressure responses contributed unique information in predicting worst pain intensity but not functional interference. Although cutaneous SST responses at the PSs were frequently abnormal, cutaneous SST responses were not confirmed in this study to have clinical utility, but rather might be centrally mediated epiphenomena.

Antiallodynic Effects of Endomorphin-1 and Endomorphin-2 in the Spared Nerve Injury Model of Neuropathic Pain in Mice

BACKGROUND

The spared nerve injury (SNI) model is a new animal model that can mimic several characteristics of clinical neuropathic pain. Opioids are recommended as treatment of neuropathic pain. Therefore, the present study was conducted to investigate the antinociceptive effects of endomorphin-1 (EM-1) and endomorphin-2 (EM-2) given centrally and peripherally in the SNI model of neuropathic pain in mice.

METHODS

The SNI model was made in mice by sparing the sural nerve intact, when the other 2 of 3 terminal branches of the sciatic nerve (common peroneal and tibial nerves) were tightly ligated and cut. Von Frey monofilaments were used to measure the SNI-induced mechanical allodynia-like behavior. The antiallodynic effects of EM-1 and EM-2 were determined after central and peripheral administration in the SNI model of neuropathic pain. Also, the specific opioid receptor antagonists were used to determine the opioid mechanisms of EMs involved in neuropathic pain. Values were expressed as the mean ± standard deviation.

RESULTS

Our results showed that the SNI mice developed prolonged mechanical allodynia-like behavior in ipsilateral paw after surgery, with the withdrawal threshold value being 0.061 ± 0.02 g after 14 days. EM-1 and EM-2 produced significant antiallodynic effects in ipsilateral paw after intracerebroventricular (i.c.v.) administration, more effective than that of morphine. The peak withdrawal thresholds of 10 nmol EM-1 and EM-2 determined at 5 minutes after injection were 0.92 ± 0.36 and 0.87 ± 0.33 g, respectively, higher than that of morphine (0.46 ± 0.20 g). Moreover, both EMs (10 nmol, i.c.v.) exerted significant antiallodynic effects in the contralateral paw, whereas no significant antinociceptive activity was seen after i.c.v. administration of morphine with equimolar dose. It was noteworthy that EM-1 and EM-2 produced antinociception through distinct μ1- and μ2-opioid receptor subtypes, and the EM-2-induced antiallodynia contained an additional component that was mediated by the release of endogenous dynorphin A, acting on κ-opioid receptor. In addition, the antiallodynic activities of peripheral administration of EM-1, EM-2, and morphine were also investigated. Intraplantar, but not subcutaneous administration of EM-1 and EM-2 also exhibited potent antinociception, establishing the peripheral and local effects. Both μ1- and μ2-opioid receptor subtypes, but not the δ- or κ-opioid receptors were involved in the peripheral antiallodynia of EMs.

CONCLUSIONS

The present investigation demonstrated that both EM-1 and EM-2 given centrally and peripherally produced potent antiallodynic activities in SNI mice, and differential opioid mechanisms were involved.

Peripheral neuropathic pain: a mechanism-related organizing principle based on sensory profiles

More than 1100 patients with neuropathic pain were examined using quantitative sensory testing. Independent of the etiology, 3 subtypes with distinct sensory profiles were identified and replicated.

Patients with neuropathic pain are heterogeneous in etiology, pathophysiology, and clinical appearance. They exhibit a variety of pain-related sensory symptoms and signs (sensory profile). Different sensory profiles might indicate different classes of neurobiological mechanisms, and hence subgroups with different sensory profiles might respond differently to treatment. The aim of the investigation was to identify subgroups in a large sample of patients with neuropathic pain using hypothesis-free statistical methods on the database of 3 large multinational research networks (German Research Network on Neuropathic Pain (DFNS), IMI-Europain, and Neuropain). Standardized quantitative sensory testing was used in 902 (test cohort) and 233 (validation cohort) patients with peripheral neuropathic pain of different etiologies. For subgrouping, we performed a cluster analysis using 13 quantitative sensory testing parameters. Three distinct subgroups with characteristic sensory profiles were identified and replicated. Cluster 1 (sensory loss, 42%) showed a loss of small and large fiber function in combination with paradoxical heat sensations. Cluster 2 (thermal hyperalgesia, 33%) was characterized by preserved sensory functions in combination with heat and cold hyperalgesia and mild dynamic mechanical allodynia. Cluster 3 (mechanical hyperalgesia, 24%) was characterized by a loss of small fiber function in combination with pinprick hyperalgesia and dynamic mechanical allodynia. All clusters occurred across etiologies but frequencies differed. We present a new approach of subgrouping patients with peripheral neuropathic pain of different etiologies according to intrinsic sensory profiles. These 3 profiles may be related to pathophysiological mechanisms and may be useful in clinical trial design to enrich the study population for treatment responders.

Protective effects of methanolic extract of Juglans regia L. leaf on streptozotocin-induced diabetic peripheral neuropathy in rats

Background

Oxidative stress has a pivotal role in the pathogenesis and development of diabetic peripheral neuropathy (DPN), the most common and debilitating complications of diabetes mellitus. There is accumulating evidence that Juglans regia L. (GRL) leaf extract, a rich source of phenolic components, has hypoglycemic and antioxidative properties. This study aimed to determine the protective effects of Juglans regia L. leaf extract against streptozotocin-induced diabetic neuropathy in rat.

Methods

The DPN rat model was generated by intraperitoneal injection of a single 55 mg/kg dose of streptozotocin (STZ). A subset of the STZ-induced diabetic rats intragastically administered with GRL leaf extract (200 mg/kg/day) before or after the onset of neuropathy, whereas other diabetic rats received only isotonic saline as the same volume of GRL leaf extract. To evaluate the effects of GRL leaf extract on the diabetic neuropathy various parameters, including histopathology and immunohistochemistry of apoptotic and inflammatory factors were assessed along with nociceptive and biochemical assessments.

Results

Degeneration of the sciatic nerves which was detected in the STZ-diabetic rats attenuated after GRL leaf extract administration. Greater caspase-3, COX-2, and iNOS expression could be detected in the STZ-diabetic rats, which were significantly attenuated after GRL leaf extract administration. Also, attenuation of lipid peroxidation and nociceptive response along with improved antioxidant status in the sciatic nerve of diabetic rats were detected after GRL leaf extract administration. In other word, GRL leaf extract ameliorated the behavioral and structural indices of diabetic neuropathy even after the onset of neuropathy, in addition to blood sugar reduction.

Conclusion

Our results suggest that GRL leaf extract exert preventive and curative effects against STZ-induced diabetic neuropathy in rats which might be due to its antioxidant, anti-inflammatory, and antiapoptotic properties.

Graphical abstract

Protection against neuropathy

Chemotherapy-Induced Neuropathy in Cancer Survivors

CONTEXT

Evidence suggests that chemotherapy-induced neuropathy (CIN) is a significant problem for cancer survivors. However, a detailed phenotypic characterization of CIN in cancer survivors is not available.

OBJECTIVES

To evaluate between-group differences in demographic and clinical characteristics, as well as in measures of sensation, function, and postural control, in a sample of cancer survivors who received a platinum and/or a taxane-based CTX regimen and did (n = 426) and did not (n = 197) develop CIN.

METHODS

Survivors completed self-report questionnaires and underwent objective testing (i.e., light touch, pain sensation, cold sensation, vibration, muscle strength, grip strength, Purdue Pegboard test, Timed Get Up and Go test, Fullerton Advanced Balance test). Parametric and nonparametric statistics were used to compare between-group differences in study outcomes.

RESULTS

Of the 426 survivors with CIN, 4.9% had CIN only in their upper extremities, 27.0% only in their lower extremities, and 68.1% in both their upper and lower extremities. Demographic and clinical characteristics associated with CIN included the following: older age, lower annual income, higher body mass index, a higher level of comorbidity, being born prematurely, receipt of a higher cumulative dose of chemotherapy, and a poorer functional status. Survivors with CIN had worse outcomes for all of the following objective measures: light touch, pain, temperature, vibration, upper and lower extremity function, and balance.

CONCLUSIONS

This study is the first to provide a detailed phenotypic characterization of CIN in cancer survivors who received a platinum and/or a taxane compound. These data can serve as a benchmark for future studies of CIN in cancer survivors.

Neuropathic Pain and Spinal Cord Injury: Phenotypes and Pharmacological Management

Chronic neuropathic pain is a complicated condition after a spinal cord injury (SCI) that often has a lifelong and significant negative impact on life after the injury; therefore, improved pain management is considered a significant and unmet need. Neuropathic pain mechanisms are heterogeneous and the difficulty in determining their individual contribution to specific pain types may contribute to poor treatment outcomes in this population. Thus, identifying human neuropathic pain phenotypes based on pain symptoms, somatosensory changes, or cognitive and psychosocial factors that reflect specific spinal cord or brain mechanisms of neuropathic pain is an important goal. Once a pain phenotype can be reliably replicated, its relationship with biomarkers and clinical treatment outcomes can be analyzed, and thereby facilitate translational research and further the mechanistic understanding of individual differences in the pain experience and in clinical trial outcomes. The present article will discuss clinical aspects of SCI-related neuropathic pain, neuropathic pain phenotypes, pain mechanisms, potential biomarkers and pharmacological interventions, and progress regarding how defining neuropathic pain phenotypes may lead to more targeted treatments for these difficult pain conditions.