A longitudinal study of pain, personality, and brain plasticity following peripheral nerve injury

Regional and interregional functional and structural brain abnormalities in neuropathic pain

Neuropathic pain is a severe form of chronic pain due to a lesion or disease of the somatosensory nervous system. Here we provide an overview of the neuroimaging approaches that can be used to assess brain abnormalities in a chronic pain condition, with particular focus on people with neuropathic pain and then summarize the findings of studies that applied these methodologies to study neuropathic pain. First, we review the most commonly used approaches to examine grey and white matter abnormalities using magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) and then review functional neuroimaging techniques to measure regional activity and inter-regional communication using functional MRI, electroencephalography (EEG) and magnetoencephalography (MEG). In neuropathic pain the most prominent structural abnormalities have been found to be in the primary somatosensory cortex, insula, anterior cingulate cortex and thalamus, with differences in volume directionality linked to neuropathic pain symptomology. Functional connectivity findings related to treatment outcome point to a potential clinical utility. Some prominent abnormalities in neuropathic pain identified with EEG and MEG throughout the dynamic pain connectome are slowing of alpha activity and higher regional oscillatory activity in the theta and alpha band, lower low beta and higher high beta band power. Finally, connectivity and coupling findings placed into context how regional abnormalities impact the networks and pathways of the dynamic pain connectome. Overall, functional and structural neuroimaging have the potential to identify predictive biomarkers that can be used to guide development of personalized pain management of neuropathic pain.

Effects of Ultrasound-Guided Thoracic Paravertebral Nerve Block Combined with Perineural or IV Dexmedetomidine on Acute and Chronic Pain After Thoracoscopic Resection of Lung Lesions: A Double-Blind Randomized Trial

Background

Thoracic paravertebral block (TPVB) analgesia can be prolonged by local anesthetic adjuvants such as dexmedetomidine. This study aimed to evaluate the two administration routes of dexmedetomidine on acute pain and chronic neuropathic pain (NeuP) prevention compared with no dexmedetomidine.

Methods

A total of 216 patients were randomized to receive TPVB using 0.4% ropivacaine alone (R Group), with perineural dexmedetomidine 0.5 μg·kg-1 (RD0.5 Group) or 1.0 μg·kg-1 (RD1.0 Group), or intravenous (IV) dexmedetomidine 0.5 μg·kg-1·h-1 (RDiv Group). The primary outcome was the incidence of chronic NeuP, defined as a Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) pain score > 12 points at 3-month after surgery.

Results

(1) For the primary outcome, RD0.5 Group and RD1.0 Group demonstrated a decreased incidence of chronic NeuP at 3-month after surgery; (2) Compared with R Group, RDiv Group, RD0.5 Group, and RD1.0 Group can reduce VAS scores at rest and movement and Prince-Henry Pain scores at 12 and 24-h after surgery, the consumption of oral morphine equivalent (OME) and improve QOD-15 at POD1; (3) Compared with RDiv Group, RD0.5 Group and RD1.0 Group can reduce VAS scores at rest and movement and Prince-Henry Pain scores at 12 and 24-h after surgery, the consumption of postoperative OME and improve QOD-15 at POD1; (4) Compared with RD0.5 Group, RD1.0 Group effectively reduced VAS scores at rest at 12 and 24-h after surgery, VAS scores in movement and Prince-Henry Pain scores at 12-h after surgery. However, RD1.0 Group showed an increased incidence of drowsiness.

Conclusion

Perineural or IV dexmedetomidine are similarly effective in reducing acute pain, but only perineural dexmedetomidine reduced chronic NeuP. Moreover, considering postoperative complications such as drowsiness, perineural dexmedetomidine (0.5 μg·kg-1) may be a more appropriate choice.

Clinical Trial Registration

Chinese Clinical Trial Registry (ChiCTR2200058982).

Case-based report of graded motor imagery experience in traumatic brachial plexus injury: The art of moving without moving

BACKGROUND

We reported a 24-year-old woman who sustained multiple upper limb injuries after a traffic accident in March 2017. She sustained a C7-T1 brachial plexus injury and radial nerve injury on the left side diagnosed in November 2017. The patient underwent radial nerve reconstruction. The patient began her comprehensive therapy program in January 2018.

PURPOSE

To describe the use of graded motor imagery (GMI) and outcomes after traumatic brachial plexus palsy. We presented changes in electromyographic (EMG) activity of target muscles during task execution and functional status following 10-session GMI therapy.

STUDY DESIGN

Case report.

METHODS

The program included 4 sessions of motor imagery and 6 sessions of a combination of motor imagery and mirror therapy.

RESULTS

The patient successfully participated in the program with reported improvements in EMG activity, functional status, emotional well-being, and body awareness.

CONCLUSIONS

GMI therapy appears to have peripheral motor effects, including altered surface EMG activity and contributes to a favorable outcome in the functional level of the affected arm. An improved emotional state and awareness of the affected hand could have a positive effect on function. Future long-term randomized controlled trials are needed to investigate the cumulative peripheral effects of treatment of graded motor imagery and the effects of variables mediating its effects on functional performance in patients with nerve injury.

Neural regeneration therapy after spinal cord injury induces unique brain functional reorganizations in rhesus monkeys

PURPOSE

Spinal cord injury (SCI) destroys the sensorimotor pathway and induces brain plasticity. However, the effect of treatment-induced spinal cord tissue regeneration on brain functional reorganization remains unclear. This study was designed to investigate the large-scale functional interactions in the brains of adult female Rhesus monkeys with injured and regenerated thoracic spinal cord.

MATERIALS AND METHODS

Resting-state functional magnetic resonance imaging (fMRI) combined with Granger Causality analysis (GCA) and motor behaviour analysis were used to assess the causal interaction between sensorimotor cortices, and calculate the relationship between causal interaction and hindlimb stepping in nine Rhesus monkeys undergoing lesion-induced spontaneous recovery (injured, n = 4) and neurotrophin-3/chitosan transplantation-induced regeneration (NT3-chitosan, n = 5) after SCI.

RESULTS

The results showed that the injured and NT3-chitosan-treated animals had distinct spatiotemporal features of brain functional reorganization. The spontaneous recovery followed the model of "early intra-hemispheric reorganization dominant, late inter-hemispheric reorganization dominant", whereas regenerative therapy animals showed the opposite trend. Although the variation degree of information flow intensity was consistent, the tendency and the relationship between local neuronal activity properties and coupling strength were different between the two groups. In addition, the injured and NT3-chitosan-treated animals had similar motor adjustments but various relationship modes between motor performance and information flow intensity.

CONCLUSIONS

Our findings show that brain functional reorganization induced by regeneration therapy differed from spontaneous recovery after SCI. The influence of unique changes in brain plasticity on the therapeutic effects of future regeneration therapy strategies should be considered. Key messagesNeural regeneration elicited a unique spatiotemporal mode of brain functional reorganization in the spinal cord injured monkeys, and that regeneration does not simply reverse the process of brain plasticity induced by spinal cord injury (SCI).Independent "properties of local activity - intensity of information flow" relationships between the injured and treated animals indicating that spontaneous recovery and regenerative therapy exerted different effects on the reorganization of the motor network after SCI.A specific information flow from the left thalamus to the right insular can serve as an indicator to reflect a heterogeneous "information flow - motor performance" relationship between injured and treated animals at similar motor adjustments.

Evaluation of Cold Sensitivity in Patients With Upper Extremity Nerve Compression Syndromes: A Scoping Review

PURPOSE

The aim of this study was to review the literature to determine the prevalence of cold sensitivity in upper extremity nerve compression syndromes and the impact of treating nerve compression syndromes on cold sensitivity.

METHODS

Following a standardized scoping review protocol, this study included interventional and observational study designs assessing patients with cold sensitivity and upper extremity nerve compression syndromes. Review articles, case reports, and small case series (n < 5) were excluded. The abstracts and eligible full texts were screened by 2 independent reviewers. Data were extracted and reported according to PRISMA extension for scoping reviews statement.

RESULTS

Three databases were searched (Ovid MEDLINE, Ovid EMBASE, and CINAHL on EBSCO); 274 references were reviewed. Fifteen studies from the database search and 8 studies from the reference search were eligible for this review (n = 23). Two interventional and 21 observational studies were identified. The most common method for assessing cold sensitivity was cold pain threshold testing (n = 12), followed by subjective patient reporting (n = 4). The Cold Intolerance Symptom Severity questionnaire was the most common validated patient-reported outcome questionnaire used in the studies (n = 3). Cold sensitivity was most commonly reported in carpal tunnel syndrome (96% of the studies). The prevalence of cold sensitivity in nerve compression syndromes ranged from 20% to 69%. Nerve decompression improved the severity of cold sensitivity in 5 of 6 studies where cold sensitivity was studied.

CONCLUSIONS

There is heterogenicity in the studies assessing cold sensitivity in nerve compression syndromes. Despite moderate prevalence in patients with carpal tunnel syndrome, cold sensitivity is understudied. Within the limitations of eligible studies reviewed, surgical decompression improved the severity of cold sensitivity in some studies.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Amygdalar Functional Connectivity Differences Associated With Reduced Pain Intensity in Pediatric Peripheral Neuropathic Pain

Background

There is evidence of altered corticolimbic circuitry in adults with chronic pain, but relatively little is known of functional brain mechanisms in adolescents with neuropathic pain (NeuP). Pediatric NeuP is etiologically and phenotypically different from NeuP in adults, highlighting the need for pediatric-focused research. The amygdala is a key limbic region with important roles in the emotional-affective dimension of pain and in pain modulation.

Objective

To investigate amygdalar resting state functional connectivity (rsFC) in adolescents with NeuP.

Methods

This cross-sectional observational cohort study compared resting state functional MRI scans in adolescents aged 11–18 years with clinical features of chronic peripheral NeuP (n = 17), recruited from a tertiary clinic, relative to healthy adolescents (n = 17). We performed seed-to-voxel whole-brain rsFC analysis of the bilateral amygdalae. Next, we performed post hoc exploratory correlations with clinical variables to further explain rsFC differences.

Results

Adolescents with NeuP had stronger negative rsFC between right amygdala and right dorsolateral prefrontal cortex (dlPFC) and stronger positive rsFC between right amygdala and left angular gyrus (AG), compared to controls (P_FDR<0.025). Furthermore, lower pain intensity correlated with stronger negative amygdala-dlPFC rsFC in males (r = 0.67, P = 0.034, n = 10), and with stronger positive amygdala-AG rsFC in females (r = −0.90, P = 0.006, n = 7). These amygdalar rsFC differences may thus be pain inhibitory.

Conclusions

Consistent with the considerable affective and cognitive factors reported in a larger cohort, there are rsFC differences in limbic pain modulatory circuits in adolescents with NeuP. Findings also highlight the need for assessing sex-dependent brain mechanisms in future studies, where possible.

Postoperative Pain Is Associated With Psychological and Physical Readiness to Return to Sports One-Year After Anterior Cruciate Ligament Reconstruction

Purpose

To identify whether any patient factors, injury factors, or symptom severity scores are associated with either psychological or physical readiness to return to sport after anterior cruciate ligament reconstruction (ACLR).

Methods

Consecutive patients with an ACL injury that required surgical treatment were included in this study. All patients completed the single-legged hop testing and the Anterior Cruciate Ligament Return to Sport Index (ACL-RSI) at 1 year postoperatively. Multivariable regression analysis models were used to determine whether an independent relationship existed between baseline patient factors (age, sex, BMI, preinjury Marx Activity Score), injury factors (meniscal tear and chondral injury), physical symptoms (Knee Injury and Osteoarthritis Outcome Score [KOOS] for pain and symptoms), and the dependent variables of physical and psychological readiness to return to sport (single-legged hop and ACL-RSI).

Results

Of the 113 patients who were included, 37% were female, and the mean age of our population was 28.2 years (SD = 8.1). Multivariable regression models demonstrated that patient-reported pain symptoms at 1 year postoperatively, as measured by the KOOS pain subscale, was significantly associated with both ACL-RSI score (Beta estimate: 1.11 [95% CI: .62-1.60] P < .001) and the ability to pass the single-legged hop test (OR: 1.07 [95% CI: 1.004-1.142] P = .037).

Conclusions

Patients with higher reported pain levels at 1 year following ACLR have lower psychological and physical readiness to return to sport.

Level of Evidence

Level 3, retrospective cohort study.

Beyond the Knife-Reviewing the Interplay of Psychosocial Factors and Peripheral Nerve Lesions

Peripheral nerve injuries are a common clinical problem. They not only affect the physical capabilities of the injured person due to loss of motor or sensory function but also have a significant impact on psychosocial aspects of life. The aim of this work is to review the interplay of psychosocial factors and peripheral nerve lesions. By reviewing the published literature, we identified several factors to be heavily influenced by peripheral nerve lesions. In addition to psychological factors like pain, depression, catastrophizing and stress, social factors like employment status and worker's compensation status could be identified to be influenced by peripheral nerve lesions as well as serving as predictors of functional outcome themselves, respectively. This work sheds a light not only on the impact of peripheral nerve lesions on psychosocial aspects of life, but also on the prognostic values of these factors of functional outcome. Interdisciplinary, individualized treatment of patients is required to identify patient at risk for adverse outcomes and provide them with emotional support when adapting to their new life situation.

Evidence-Based Approach to Timing of Nerve Surgery: A Review

ABSTRACT

Events causing acute stress to the health care system, such as the COVID-19 pandemic, place clinical decisions under increased scrutiny. The priority and timing of surgical procedures are critically evaluated under these conditions, yet the optimal timing of procedures is a key consideration in any clinical setting. There is currently no single article consolidating a large body of current evidence on timing of nerve surgery. MEDLINE and EMBASE databases were systematically reviewed for clinical data on nerve repair and reconstruction to define the current understanding of timing and other factors affecting outcomes. Special attention was given to sensory, mixed/motor, nerve compression syndromes, and nerve pain. The data presented in this review may assist surgeons in making sound, evidence-based clinical decisions regarding timing of nerve surgery.

Brain plasticity after peripheral nerve injury treatment with massage therapy based on resting-state functional magnetic resonance imaging

Massage therapy is an alternative treatment for chronic pain that is potentially related to brain plasticity. However, the underlying mechanism remains unclear. We established a peripheral nerve injury model in rats by unilateral sciatic nerve transection and direct anastomosis. The experimental rats were treated over the gastrocnemius muscle of the affected hindlimb with a customized massage instrument (0.45 N, 120 times/min, 10 minutes daily, for 4 successive weeks). Resting-state functional magnetic resonance imaging revealed that compared with control rats, the amplitude of low-frequency fluctuations in the sensorimotor cortex contralateral to the affected limb was significantly lower after sciatic nerve transection. However, amplitudes were significantly higher in the massage group than in a sham-massage group. These findings suggest that massage therapy facilitated adaptive change in the somatosensory cortex that led to the recovery of peripheral nerve injury and repair. This study was approved by the Animal Ethics Committee of Shanghai University of Traditional Chinese Medicine of China (approval No. 201701001) on January 12, 2017.

Structural remodeling in related brain regions in patients with facial synkinesis

Facial synkinesis is a troublesome sequelae of facial nerve malfunction. It is difficult to recover from synkinesis, despite improved surgical techniques for isolating the peripheral facial nerve branches. Furthermore, it remains unclear whether long-term dysfunction of motor control can lead to irreversible plasticity-induced structural brain changes. This case-control study thus investigated the structural brain alterations associated with facial synkinesis. The study was conducted at Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, China. Twenty patients with facial synkinesis (2 male and 18 female, aged 33.35 ± 6.97 years) and 19 healthy volunteers (2 male and 17 female, aged 33.21 ± 6.75 years) underwent magnetic resonance imaging, and voxel-based and surface-based morphometry techniques were used to analyze data. There was no significant difference in brain volume between patients with facial synkinesis and healthy volunteers. Patients with facial synkinesis exhibited a significantly reduced cortical thickness in the contralateral superior and inferior temporal gyri and a reduced sulcal depth of the ipsilateral precuneus compared with healthy volunteers. In addition, sulcal depth of the ipsilateral precuneus was negatively correlated with the severity of depression. These findings suggest that there is a structural remodeling of gray matter in patients with facial synkinesis after facial nerve malfunction. This study was approved by the Ethics Review Committee of the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, China (approval No. 2017-365-T267) on September 13, 2017, and was registered with the Chinese Clinical Trial Registry (registration number: ChiCTR1800014630) on January 25, 2018.

Effects of Resistance Training and Bowdichia virgilioides Hydroethanolic Extract on Oxidative Stress Markers in Rats Submitted to Peripheral Nerve Injury

The objective of this study was to analyze the effects of the combination of resistance training (RT) and the hydroethanolic extract (EHE) of Bowdichia virgilioides as markers of oxidative stress (OS) in rats with peripheral nerve injury (PNI). Rats were allocated into six groups (n = 10): animals without interventions (C), animals with an exposed nerve but without injury, injured animals, trained and injured animals, injured animals that received EHE, and animals that received a combination of RT and EHE. RT comprised the climbing of stairs. EHE was orally administered (200 mg/kg) for 21 days after PNI induction. RT reduced the amount of lipoperoxidation in plasma (14.11%). EHE reduced lipoperoxidation in the plasma (20.72%) and the brain (41.36). RT associated with the extract simultaneously reduced lipoperoxidation in the plasma (34.23%), muscle (25.13%), and brain (43.98%). There was an increase in total sulhydrilyl levels (a) in the brain (33.33%) via RT; (b) in the brain (44.44%) and muscle (44.51%) using EHE; and (c) in the plasma (54.02%), brain (54.25%), and muscle using the combination of RT + EHE. These results suggest that RT associated with oral EHE results in a decrease in OS.

Neuropathic Pain: From Mechanisms to Treatment

Neuropathic pain caused by a lesion or disease of the somatosensory nervous system is a common chronic pain condition with major impact on quality of life. Examples include trigeminal neuralgia, painful polyneuropathy, postherpetic neuralgia, and central poststroke pain. Most patients complain of an ongoing or intermittent spontaneous pain of, for example, burning, pricking, squeezing quality, which may be accompanied by evoked pain, particular to light touch and cold. Ectopic activity in, for example, nerve-end neuroma, compressed nerves or nerve roots, dorsal root ganglia, and the thalamus may in different conditions underlie the spontaneous pain. Evoked pain may spread to neighboring areas, and the underlying pathophysiology involves peripheral and central sensitization. Maladaptive structural changes and a number of cell-cell interactions and molecular signaling underlie the sensitization of nociceptive pathways. These include alteration in ion channels, activation of immune cells, glial-derived mediators, and epigenetic regulation. The major classes of therapeutics include drugs acting on α₂δ subunits of calcium channels, sodium channels, and descending modulatory inhibitory pathways.

Cold intolerance and neuropathic pain after peripheral nerve injury in upper extremity

Cold intolerance and pain can be a substantial problem in patients with peripheral nerve injury. We aimed at investigating the relationships among sensory recovery, cold intolerance, and neuropathic pain in patients affected by upper limb peripheral nerve injury (Sunderland type V) treated with microsurgical repair, followed by early sensory re-education. In a cross-sectional clinical study, 100 patients (male/female 81/19; age 40.5 ± 14.8 years and follow-up 17 ± 5 months, mean ± SD), with microsurgical nerve repair and reconstruction in the upper extremity and subsequent early sensory re-education, were evaluated, using Cold Intolerance Symptoms Severity questionnaire-Italian version (CISS-it, cut-off pathology >30/100 points), CISS questionnaire-12 item version (CISS-12, 0-46 points-grouping: healthy that means no cold intolerance [0-14], mild [15-24], moderate [25-34], severe [35-42], very severe [43-46] cold intolerance), probability of neuropathic pain (DouleurNeuropathique-4; [DN4] 4/10), deep and superficial sensibility, tactile threshold (monofilaments), and two-point discrimination (cutoff S2; Medical Research Council scale for sensory function; [MRC-scale]). A high CISS score is associated with possible neuropathic pain (DN4 ≥ 4). Both a low CISS-it score (ie, < 30) and DN4 < 4 is associated with good sensory recovery (MRC ≥ 2). In conclusion patients affected by upper limb peripheral nerve injuries with higher CISS scores more often suffer from cold intolerance and neuropathic pain, and the better their sensory recovery is, the less likely they are to suffer from cold intolerance and neuropathic pain.

Enhanced performance of chitosan/keratin membranes with potential application in peripheral nerve repair

Although surgical management of peripheral nerve injuries (PNIs) has improved over time, autografts are still the current "gold standard" treatment for PNIs, which presents numerous limitations. In an attempt to improve natural biomaterial-based nerve guidance conduits (NGCs), chitosan (CHT), a derivative of the naturally occurring biopolymer chitin, has been explored for peripheral nerve regeneration (PNR). In addition to CHT, keratin has gained enormous attention as a biomaterial and tissue engineering scaffolding. In this study, biomimetic CHT/keratin membranes were produced using a solvent casting technique. These membranes were broadly characterized in terms of their surface topography and physicochemical properties, with techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), contact angle, weight loss and water uptake measurements, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Biological in vitro assays were also performed, where a preliminary cytotoxicity screening with the L929 fibroblast cell line revealed that the membranes and respective materials are suitable for cell culture. In addition, Schwann cells, fibroblasts and endothelial cells were directly seeded in the membranes. Quantitative and qualitative assays revealed that the addition of keratin enhanced cell viablity and adhesion. Based on the encouraging in vitro results, the in vivo angiogenic/antiangiogenic potential of CHT and CHT/keratin membranes was assessed, using an optimized chick embryo chorioallantoic membrane assay, where higher angiogenic responses were seen in keratin-enriched materials. Overall, the obtained results indicate the higher potential of CHT/keratin membranes for guided tissue regeneration applications in the field of PNR.

Pain thresholds and intensities of CRPS type I and neuropathic pain in respect to sex

BACKGROUND AND AIMS

Healthy women have generally been found to have increased experimental pain perception and chronic pain has a higher prevalence in female as compared to male patients. However, no study has investigated whether pain intensity and pain perception thresholds are distinct or similar between sexes within various chronic pain entities. We investigated whether average pain intensities and pain thresholds assessed using quantitative sensory testing (QST) differed between women and men suffering from three distinct chronic pain conditions: Complex Regional Pain Syndrome (CRPS type I), peripheral nerve injury (PNI) or polyneuropathy (PNP), as compared to paired healthy volunteers.

METHODS

QST data of 1,252 patients (669 female, 583 male) with PNI (n = 342), PNP (n = 571) or CRPS (n = 339), and average pain intensity reports from previously published studies were included. Absolute and z-values (adjusted for age and body region) of cold, heat, pressure (PPT) and pinprick pain thresholds were compared in generalized linear models with aetiology, duration of underlying pain disease and average pain intensity as fixed effects.

RESULTS

Average pain intensity during the past four weeks did not differ between women and men, in both mean and range. In women absolute pain thresholds for cold, heat and pinprick were lower than in males across all diagnoses (p < .05). However, after z-transformation these differences disappeared except for PPT in CRPS (p = .001).

DISCUSSION

Pain thresholds in patients show only minor sex differences. However, these differences mimic those observed in healthy subjects and do not seem to be linked to specific pathophysiological processes.

SIGNIFICANCE

Female healthy participants and female patients with neuropathic pain conditions or CRPS I report lower pain thresholds compared to males, but pain intensity is similar and there is no sex difference in the extent to which the thresholds are altered in neuropathic pain or CRPS. Thus, the sex differences observed in various chronic pain conditions mimic those obtained in healthy participants, indicating that these differences are not linked to specific pathophysiological processes and are of minor clinical relevance.

Imaging vs quantitative sensory testing to predict chronic pain treatment outcomes

In this article, I review the concept of personalized pain management and consider how brain imaging and quantitative sensory testing can be used to derive biomarkers of chronic pain treatment outcome. I review how different modalities of brain imaging can be used to acquire information about brain structure and function and how this information can be linked to individual measures of pain.

Modern Trends for Peripheral Nerve Repair and Regeneration: Beyond the Hollow Nerve Guidance Conduit

Peripheral nerve repair and regeneration remains among the greatest challenges in tissue engineering and regenerative medicine. Even though peripheral nerve injuries (PNIs) are capable of some degree of regeneration, frail recovery is seen even when the best microsurgical technique is applied. PNIs are known to be very incapacitating for the patient, due to the deprivation of motor and sensory abilities. Since there is no optimal solution for tackling this problem up to this day, the evolution in the field is constant, with innovative designs of advanced nerve guidance conduits (NGCs) being reported every day. As a basic concept, a NGC should act as a physical barrier from the external environment, concomitantly acting as physical guidance for the regenerative axons across the gap lesion. NGCs should also be able to retain the naturally released nerve growth factors secreted by the damaged nerve stumps, as well as reducing the invasion of scar tissue-forming fibroblasts to the injury site. Based on the neurobiological knowledge related to the events that succeed after a nerve injury, neuronal subsistence is subjected to the existence of an ideal environment of growth factors, hormones, cytokines, and extracellular matrix (ECM) factors. Therefore, it is known that multifunctional NGCs fabricated through combinatorial approaches are needed to improve the functional and clinical outcomes after PNIs. The present work overviews the current reports dealing with the several features that can be used to improve peripheral nerve regeneration (PNR), ranging from the simple use of hollow NGCs to tissue engineered intraluminal fillers, or to even more advanced strategies, comprising the molecular and gene therapies as well as cell-based therapies.

Peripheral nerve injuries, pain, and neuroplasticity

INTRODUCTION

Peripheral nerve injuries (PNIs) cause both structural and functional brain changes that may be associated with significant sensorimotor abnormalities and pain.

PURPOSE OF THE STUDY

The aim of this narrative review is to provide hand therapists an overview of PNI-induced neuroplasticity and to explain how the brain changes following PNI, repair, and during rehabilitation.

METHODS

Toward this goal, we review key aspects of neuroplasticity and neuroimaging and discuss sensory testing techniques used to study neuroplasticity in PNI patients.

RESULTS

We describe the specific brain changes that occur during the repair and recovery process of both traumatic (eg, transection) and nontraumatic (eg, compression) nerve injuries. We also explain how these changes contribute to common symptoms including hypoesthesia, hyperalgesia, cold sensitivity, and chronic neurogenic pain. In addition, we describe how maladaptive neuroplasticity as well as psychological and personality characteristics impacts treatment outcome.

DISCUSSION AND CONCLUSION

Greater understanding of the brain's contribution to symptoms in recovering PNI patients could help guide rehabilitation strategies and inform the development of novel techniques to counteract these maladaptive brain changes and ultimately improve outcomes.

Diffusional plasticity induced by electroacupuncture intervention in rat model of peripheral nerve injury

Electroacupuncture (EA) is an adjuvant therapy for peripheral nerve injury (PNI). Both peripheral and central alterations contribute to the rehabilitation process. We employed diffusion tensor imaging (DTI) to investigate the diffusion plasticity of afferent and efferent pathways caused by EA in model of peripheral nerve injury and reparation. Twenty-four rats were divided into three groups: normal group, model group and intervention group. Rats of the model group and the intervention group underwent sciatic nerve transection and anastomosis. EA intervention was performed on the intervention group at ST-36 and GB-30 for three months. Gait assessment and DTI were conducted at days post-operative (DPO) 30, 60 and 90. We selected corticospinal tract, spinothalamic tract and internal capsule as regions of interest and analyzed diffusion metrics including fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD). FA values and RD values displayed significant differences or obvious tendency while AD values maintained a stable level. RD values displayed better indicative performance than FA in internal capsule. The intervention group presented significant correlation between RD values and Regularity Index (RI) during the intervention period. The effect of EA on peripheral nerve injury repairing rats appeared to be accelerated recovery process of sensory and motor neural pathway. We proposed that RD was a potential in vivo indicator for structural plasticity caused by EA and PNI.

A systematic review of structural and functional MRI studies on pain catastrophizing

Objectives: Pain catastrophizing is reliably associated with pain reports during experimental pain in healthy, pain-free subjects and in people with chronic pain. It also correlates with self-reports of clinical pain intensity/severity in a variety of disorders characterized by chronic pain in adults, adolescents and children. However, processes, through which it exerts its effects are yet unclear. In this paper, our primary aim was to synthesize neuroimaging research to open a window to possible mechanisms underlying pain catastrophizing in both chronic pain patients and healthy controls. We also aimed to compare whether the neural correlates of pain catastrophizing are similar in these two groups.

Methods: PubMed and the Web of Science were searched for magnetic resonance imaging (MRI) studies that explored neural correlates of pain catastrophizing.

Results: Twenty articles met the inclusion criteria. The results of our review show a connection between pain catastrophizing and brain areas tightly connected to pain perception (including the somatosensory cortices, anterior insula, anterior cingulate cortex and thalamus) and/or modulation (eg, the dorsolateral prefrontal cortex). Our results also highlight that these processes - in relation to pain catastrophizing - are more pronounced in chronic pain patients, suggesting that structural and functional brain alterations (and perhaps mechanisms) related to pain catastrophizing may depend on prior and/or relatively stable/constant pain experience. However, we also found methodological issues and differences that could lead to divergent results.

Discussion: Based on our results, pain catastrophizing might be related to salience detection, pain processing, and top-down attentional processes. More research is recommended to explore neural changes to specific types of catastrophizing thoughts (eg, experimentally induced and/or state). Furthermore, we provide ideas regarding pain catastrophizing studies in the future for a more standardized approach.

AAPT Diagnostic Criteria for Peripheral Neuropathic Pain: Focal and Segmental Disorders

Peripheral neuropathic pain is among the most prevalent types of neuropathic pain. No comprehensive peripheral neuropathic pain classification system that incorporates contemporary clinical, diagnostic, biological, and psychological information exists. To address this need, this article covers the taxonomy for 4 focal or segmental peripheral neuropathic pain disorders, as part of the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership and the American Pain Society (APS) collaborative to develop a standardized, evidence-based taxonomy initiative: the ACTTION-APS Pain Taxonomy (AAPT). The disorders-postherpetic neuralgia, persistent posttraumatic neuropathic pain, complex regional pain disorder, and trigeminal neuralgia-were selected because of their clinical and clinical research relevance. The multidimensional features of the taxonomy are suitable for clinical trials and can also facilitate hypothesis-driven case-control and cohort epidemiologic studies. PERSPECTIVE: The AAPT peripheral neuropathic pain taxonomy subdivides the peripheral neuropathic pain disorders into those that are generalized and symmetric and those that are focal or segmental and asymmetric. In this article, we cover the focal and segmental disorders: postherpetic neuralgia, persistent posttraumatic neuropathic pain, complex regional pain disorder, and trigeminal neuralgia. The taxonomy is evidence-based and multidimensional, with the following dimensions: 1) core diagnostic criteria; 2) common features; 3) common medical and psychiatric comorbidities; 4) neurobiological, psychosocial, and functional consequences; and 5) putative neurobiological and psychosocial mechanisms, risk factors, and protective factors.

Inferring distinct mechanisms in the absence of subjective differences: Placebo and centrally acting analgesic underlie unique brain adaptations

Development and maintenance of chronic pain is associated with structural and functional brain reorganization. However, few studies have explored the impact of drug treatments on such changes. The extent to which long-term analgesia is related to brain adaptations and its effects on the reversibility of brain reorganization remain unclear. In a randomized placebo-controlled clinical trial, we contrasted pain relief (3-month treatment period), and anatomical (gray matter density [GMD], assessed by voxel-based morphometry) and functional connectivity (resting state fMRI nodal degree count [DC]) adaptations, in 39 knee osteoarthritis (OA) patients (22 females), randomized to duloxetine (DLX, 60 mg once daily) or placebo. Pain relief was equivalent between treatment types. However, distinct circuitry (GMD and DC) could explain pain relief in each group: up to 85% of variance for placebo analgesia and 49% of variance for DLX analgesia. No behavioral measures (collected at entry into the study) could independently explain observed analgesia. Identified circuitry were outside of nociceptive circuitry and minimally overlapped with OA-abnormal or placebo response predictive brain regions. Mediation analysis revealed that changes in GMD and DC can influence each other across remote brain regions to explain observed analgesia. Therefore, we can conclude that distinct brain mechanisms underlie DLX and placebo analgesia in OA. The results demonstrate that even in the absence of differences in subjective pain relief, pharmacological treatments can be differentiated from placebo based on objective brain biomarkers. This is a crucial step to untangling mechanisms and advancing personalized therapy approaches for chronic pain.

Pain in ankylosing spondylitis: a neuro-immune collaboration

Clinicians have commonly differentiated chronic back pain into two broad subsets: namely, non-inflammatory (or mechanical) back pain and inflammatory back pain. As the terminology suggests, the latter category, in which ankylosing spondylitis (AS) is prominent, presupposes a close link between pain and inflammation. Advances in research into the genetics and immunology of AS have improved our understanding of the inflammatory processes involved in this disease, and have led to the development of potent anti-inflammatory biologic therapeutic agents. However, evidence from clinical trials and from biomarker and imaging studies in patients with AS indicate that pain and inflammation are not always correlated. Thus, the assumption that pain in AS is a reliable surrogate marker for inflammation might be an over-simplification. This Review provides an overview of current concepts relating to neuro-immune interactions in AS and summarizes research that reveals an increasingly complex interplay between the activation of the immune system and pain pathways in the nervous system. The different types of pain experienced by patients with AS, insights from brain imaging studies, neurological mechanisms of pain, sex bias in pain and how the immune system can modify pain in patients with AS are also discussed.

"Three Methods and Three Points" regulates p38 mitogen-activated protein kinase in the dorsal horn of the spinal cord in a rat model of sciatic nerve injury

Tuina is a traditional Chinese treatment for sensory disturbances caused by peripheral nerve injury and related diseases. Our previous studies showed that tuina regulates relevant regions and indices of the spinal dorsal horn using the Dian, Bo, and Rou method in Yinmen (BL37), Yanglingquan (GB34), and Weizhong (BL40). Treatment prevents muscle atrophy, protects spinal cord neurons, and promotes sciatic nerve repair. The mechanisms of action of tuina for treating peripheral nerve injury remain poorly understood. This study established rat models of sciatic nerve injury using the crushing method. Rats received Chinese tuina in accordance with the principle of "Three Methods and Three Points," once daily for 20 days. Tuina intervention reduced paw withdrawal latency and improved wet weight of the gastrocnemius muscle, as well as promoting morphological recovery of sciatic nerve fibers, Schwann cells, and axons. The protein expression levels of phospho-p38 mitogen-activated protein kinase, tumor necrosis factor-α, and interleukin-1β also decreased. These findings indicate that "Three Methods and Three Points" promoted morphological recovery and improved behavior of rats with peripheral nerve injury.