Neuroinflammation of the spinal cord and nerve roots in chronic radicular pain patients

Investigating the potential of minocycline in reducing brain inflammation in chronic low back pain: a randomized, placebo-controlled mechanistic clinical trial

ABSTRACT

Our group has shown that translocator protein (TSPO) levels, a putative marker of neuroinflammation, are increased in the brain and spinal cord of patients with chronic low back pain (cLBP). Whether neuroinflammation might be a therapeutic target for this condition is unknown. In this phase II double-blind, placebo-controlled, randomized clinical trial, we sought to evaluate whether the tetracycline antibiotic minocycline, which is commonly used as a glial inhibitor in preclinical models, has an effect on brain TSPO levels in adults with cLBP. Participants randomly received 100-mg minocycline or placebo, once a day for 2 weeks. The primary outcome was the change (pretreatment vs posttreatment) in thalamic TSPO levels, measured using [11C]PBR28 positron emission tomography signal (standardized uptake value ratio) and analyzed with a mixed effect model. Secondary outcome measures included the change in Brief Pain Inventory, severity subscore. Among 60 enrolled participants, 48 completed the trial. Of these, 25 received minocycline (age [years], mean ± SD: 44.6 ± 16.9; 9 female), and 23 received placebo (49 ± 17.1; 9 female). The mean thalamic positron emission tomography standard uptake value ratio was very stable across visits in both groups, with no significant group-by-time interaction (P = 0.956). Similarly, both groups demonstrated a comparable decrease over time in Brief Pain Inventory severity scores (P = 0.018) and no significant group-by-time interaction (P = 0.329). Our results suggest that minocycline, at the tested regimen, may neither reduce brain TSPO levels nor have clinically meaningful effects on clinical pain in patients with cLBP.

Neuroinflammation at the Neuroforamina and Spinal Cord in Patients with Painful Cervical Radiculopathy and Pain-Free Participants: An [11C]DPA713 PET/CT Proof-of-Concept Study

Background/Objectives: The complex pathophysiology of painful cervical radiculopathy is only partially understood. Neuroimmune activation in the dorsal root ganglion and spinal cord is assumed to underlie the genesis of radicular pain. Molecular positron emission tomography (PET) using the radiotracer [11C]DPA713, which targets the 18-kDa translocator protein (TSPO), offers the ability to quantify neuroinflammation in humans in vivo. The primary objectives of this study were to (1) assess whether uptake of [11C]DPA713, a metric of neuroinflammation, is higher in the neuroforamina and spinal cord of patients with painful cervical radiculopathy compared with that in pain-free participants and (2) assess whether [11C]DPA713 uptake is associated with clinical parameters, such as pain intensity. Methods: Dynamic 60 min [11C]DPA713 PET/CT scans were acquired, and regions of interest were defined for neuroforamina and spinal cord. Resulting time-activity curves were fitted to a single-tissue compartment model using an image-derived input function, corrected for plasma-to-whole blood ratios and parent fractions, to obtain the volume of distribution (VT) as the primary outcome measure. Secondary neuroinflammation metrics included 1T2k VT without metabolite correction (1T2k_WB) and Logan VT. Results: The results indicated elevated levels of 1T2k VT at the neuroforamina (p < 0.04) but not at the spinal cord (p = 0.16). Neuroforamina and spinal cord 1T2k VT lack associations with clinical parameters. Secondary neuroinflammatory metrics show associations with clinical parameters such as the likelihood of neuropathic pain. Conclusions: These findings enhance our understanding of painful cervical radiculopathy's pathophysiology, emphasizing the neuroforamina levels of neuroinflammation as a potential therapeutic target.

Added value of 18Fluorine-fluorodeoxyglucose (18F-FDG) PET/MRI for evaluation of failed back surgery syndrome: comparison with non-contrast MRI

OBJECTIVES

Given increasing research suggesting the utility of positron emission tomography/magnetic resonance imaging (PET/MRI) in identifying the pain generator of low back pain, our study aims to assess its effectiveness in evaluating the source of pain in patients with failed back surgery syndrome (FBSS) by comparing the performance of fluorine-18-labeled fluorodeoxyglucose (18F-FDG) PET/MRI with conventional MRI.

METHODS

We retrospectively analyzed data from patients with FBSS who underwent 18F-FDG PET and MRI of the lumbar vertebrae and lower extremities for undetermined sources of pain. We assessed 1) The diagnostic reliability and efficacy of MRI and 18F-FDG PET/MRI according to correct differential diagnosis, affected level, and affected side of the pain source compared to the findings of selective root or peripheral nerve block or revision lumbar spine surgery; and 2) The association between standardized uptake value (SUV) and standardized uptake value ratio (SUVR) threshold and accuracy of the suspected pathology on 18F-FDG PET/MRI.

RESULTS

Among 30 included patients, the diagnostic accuracy of pain source recognition was higher for 18F-FDG PET/MRI than for MRI alone (1.0 vs. 0.4 in spinal disease and 0.8 vs. 0 in lower extremity disease, both p < 0.05). SUVR values of 1.4-1.5 showed the highest accuracy (0.93), higher than the accuracy obtained using the SUV threshold (0.87).

CONCLUSION

18F-FDG PET/MRI added value to MRI alone in detecting of hypermetabolic activity associated with pain from spinal and non-spinal sources.

Pathophysiology-Directed Engineering of a Combination Nanoanalgesic for Neuropathic Pain

Neuropathic pain, one of the most refractory pain diseases, remains a formidable medical challenge. There is still an unmet demand for effective and safe therapies to address this condition. Herein, a rat model of nerve injury-induced neuropathic pain is first established to explore its pathophysiological characteristics. Recognizing the role of neuroinflammation, an inflammation-resolving amphiphilic conjugate PPT is designed and synthesized by simultaneously conjugating polyethylene glycol, phenylboronic acid pinacol ester, and Tempol onto a cyclic scaffold. PPT can self-assemble into nanomicelles (termed PPTN). Following intravenous injection, PPTN preferentially accumulates in the injured nerve, ameliorates the neuroinflammatory milieu, and promotes nerve regeneration, thereby shortening neuropathic pain duration in rats. Moreover, the Ca2+ channel α2δ1 subunit is identified as a therapeutic target by RNA-sequencing analysis of the injured nerve. Based on this target, a mimicking peptide (AD peptide) is screened as an analgesic. By packaging AD peptide into PPTN, a combination nano-analgesic APTN is developed. Besides potentiated anti-hyperalgesic effects due to site-specific delivery and on-demand release of AD peptide at target sites, APTN simultaneously inhibits neuroinflammation and promotes nerve regeneration by reprogramming macrophages via regulating MAPK/NF-kB signaling pathways and NLRP3 inflammasome activation, thus affording synergistic efficacies in treating nerve injury-induced neuropathic pain.

"Neuroinflammation": does it have a role in chronic pain? Evidence from human imaging

ABSTRACT

Despite hundreds of studies demonstrating the involvement of neuron-glia-immune interactions in the establishment and/or maintenance of persistent pain behaviors in animals, the role (or even occurrence) of so-called "neuroinflammation" in human pain has been an object of contention for decades. Here, I present the results of multiple positron emission tomography (PET) studies measuring the levels of the 18 kDa translocator protein (TSPO), a putative neuroimmune marker, in individuals with various pain conditions. Overall, these studies suggest that brain TSPO PET signal: (1) is elevated, compared to healthy volunteers, in individuals with chronic low back pain (with additional elevations in spinal cord and neuroforamina), fibromyalgia, migraine and other conditions characterized by persistent pain; (2) has a spatial distribution exhibiting a degree of disorder specificity; (3) is parametrically linked to pain characteristics or comorbid symptoms (eg, nociplastic pain, fatigue, depression), as well as measures of brain function (ie, functional connectivity), in a regionally-specific manner. In this narrative, I also discuss important caveats to consider in the interpretation of this work (eg, regarding the cellular source of the signal and the complexities inherent in its acquisition and analysis). While the biological and clinical significance of these findings awaits further work, this emerging preclinical literature supports a role of neuron-glia-immune interactions as possible pathophysiological underpinnings of human chronic pain. Gaining a deeper understanding of the role of neuroimmune function in human pain would likely have important practical implications, possibly paving the way for novel interventions.

Transforaminal Steroid Injection After Dorsal Root Ganglion Pulsed Radiofrequency (DRG-PRF): Impact on Pain Intensity and Disability

INTRODUCTION

Dorsal root ganglion pulsed radiofrequency (DRG-PRF) is frequently used for the treatment of chronic lumbar radicular pain with good outcomes in terms of pain management. Transforaminal epidural steroid injection (TFESI) is often administered immediately after DRG-PRF to increase the anti-inflammatory effects, but support for the synergic mechanism is lacking in the literature. The aim of this study was to investigate the potential role of TFESI immediately after DRG-PRF and its possible role on pain intensity and patient disability.

METHODS

A database of patients who underwent DRG-PRF with or without TFESI immediately after DRG-PRF was retrospectively analysed; propensity score matching was applied to the analysis to reduce possible bias. Pain intensity (numerical rating scale [NRS]) and Oswestry disability index (ODI) were recorded pre-operatively and at the 1- and 3-month follow-up in the two groups of patients.

RESULTS

A total of 252 patients were included in this retrospective analysis, 126 patients in the DRG-PRF + TFESI group and 126 patients in the DRG-PRF group after propensity score matching. Both groups displayed a significant reduction in pain intensity (NRS score reduction; p < 0.0001) and improvement in the ODI (p < 0.0001) from baseline at the 3-month follow-up. Interestingly, the use of TFESI after DRG-PRF was not associated with any clinical benefit as no difference in NRS and ODI was found between the two groups at the 1- and 3-month follow-ups.

CONCLUSIONS

Our study revealed a significant pain reduction and disability improvement after DRG-PRF in patients with lumbar radicular pain. Interestingly, no positive role of TFESI immediately after DRG-PRF was observed. These findings suggest that DRG-PRF provides substantial pain relief, and no added benefit is obtained with subsequent steroid injection. Future prospective studies with expanded follow-up periods are needed to confirm these findings.

Neuroinflammatory activation in sensory and motor regions of the cortex is related to sensorimotor function in individuals with low back pain maintained by nociplastic mechanisms: A preliminary proof-of-concept study

BACKGROUND

Chronic pain involves communication between neural and immune systems. Recent data suggest localization of glial (brain immune cells) activation to the sensorimotor regions of the brain cortex (S1/M1) in chronic low back pain (LBP). As glia perform diverse functions that impact neural function, activation might contribute to sensorimotor changes, particularly in LBP maintained by increased nervous system sensitivity (i.e., nociplastic pain). This preliminary proof-of-concept study aimed to: (i) compare evidence of neuroinflammatory activation in S1/M1 between individuals with and without LBP (and between nociceptive and nociplastic LBP phenotypes), and (ii) evaluate relationships between neuroinflammatory activation and sensorimotor function.

METHODS

Simultaneous PET-fMRI measured neuroinflammatory activation in functionally defined S1/M1 in pain-free individuals (n = 8) and individuals with chronic LBP (n = 9; nociceptive: n = 4, nociplastic: n = 5). Regions of S1/M1 related to the back were identified using fMRI during motor tasks and thermal stimuli. Sensorimotor measures included single and paired-pulse transcranial magnetic stimulation (TMS) and quantitative sensory testing (QST). Sleep, depression, disability and pain questionnaires were administered.

RESULTS

Neuroinflammatory activation was greater in the lower back cortical representation of S1/M1 of the nociplastic LBP group than both nociceptive LBP and pain-free groups. Neuroinflammatory activation in S1/M1 was positively correlated with sensitivity to hot (r = 0.52) and cold (r = 0.55) pain stimuli, poor sleep, depression, disability and BMI, and negatively correlated with intracortical facilitation (r = -0.41).

CONCLUSION

This preliminary proof-of-concept study suggests that neuroinflammation in back regions of S1/M1 in individuals with nociplastic LBP could plausibly explain some characteristic features of this LBP phenotype.

SIGNIFICANCE STATEMENT

Neuroinflammatory activation localized to sensorimotor areas of the brain in individuals with nociplastic pain might contribute to changes in sensory and motor function and aspects of central sensitization. If cause-effect relationships are established in longitudinal studies, this may direct development of therapies that target neuroinflammatory activation.

Recent developments and challenges in positron emission tomography imaging of gliosis in chronic neuropathic pain

ABSTRACT

Understanding the mechanisms that underpin the transition from acute to chronic pain is critical for the development of more effective and targeted treatments. There is growing interest in the contribution of glial cells to this process, with cross-sectional preclinical studies demonstrating specific changes in these cell types capturing targeted timepoints from the acute phase and the chronic phase. In vivo longitudinal assessment of the development and evolution of these changes in experimental animals and humans has presented a significant challenge. Recent technological advances in preclinical and clinical positron emission tomography, including the development of specific radiotracers for gliosis, offer great promise for the field. These advances now permit tracking of glial changes over time and provide the ability to relate these changes to pain-relevant symptomology, comorbid psychiatric conditions, and treatment outcomes at both a group and an individual level. In this article, we summarize evidence for gliosis in the transition from acute to chronic pain and provide an overview of the specific radiotracers available to measure this process, highlighting their potential, particularly when combined with ex vivo / in vitro techniques, to understand the pathophysiology of chronic neuropathic pain. These complementary investigations can be used to bridge the existing gap in the field concerning the contribution of gliosis to neuropathic pain and identify potential targets for interventions.

Photobiomodulation in the infrared spectrum reverses the expansion of circulating natural killer cells and brain microglial activation in Sanfilippo mice

Sanfilippo syndrome results from inherited mutations in genes encoding lysosomal enzymes that catabolise heparan sulfate (HS), leading to early childhood-onset neurodegeneration. This study explores the therapeutic potential of photobiomodulation (PBM), which is neuroprotective and anti-inflammatory in several neurodegenerative diseases; it is also safe and PBM devices are readily available. We investigated the effects of 10-14 days transcranial PBM at 670 nm (2 or 4 J/cm2/day) or 904 nm (4 J/cm2/day) in young (3 weeks) and older (15 weeks) Sanfilippo or mucopolysaccharidosis type IIIA (MPS IIIA) mice. Although we found no PBM-induced changes in HS accumulation, astrocyte activation, CD206 (an anti-inflammatory marker) and BDNF expression in the brains of Sanfilippo mice, there was a near-normalisation of microglial activation in older MPS IIIA mice by 904 nm PBM, with decreased IBA1 expression and a return of their morphology towards a resting state. Immune cell immunophenotyping of peripheral blood with mass cytometry revealed increased pro-inflammatory signalling through pSTAT1 and p-p38 in NK and T cells in young but not older MPS IIIA mice (5 weeks of age), and expansion of NK, B and CD8+ T cells in older affected mice (17 weeks of age), highlighting the importance of innate and adaptive lymphocytes in Sanfilippo syndrome. Notably, 670 and 904 nm PBM both reversed the Sanfilippo-induced increase in pSTAT1 and p-p38 expression in multiple leukocyte populations in young mice, while 904 nm reversed the increase in NK cells in older mice. In conclusion, this is the first study to demonstrate the beneficial effects of PBM in Sanfilippo mice. The distinct reduction in microglial activation and NK cell pro-inflammatory signalling and number suggests PBM may alleviate neuroinflammation and lymphocyte activation, encouraging further investigation of PBM as a standalone, or complementary therapy in Sanfilippo syndrome.

Toward Functional PET Imaging of the Spinal Cord

At present, spinal cord imaging primarily uses magnetic resonance imaging (MRI) or computed tomography (CT), but the greater sensitivity of positron emission tomography (PET) techniques and the development of new radiotracers are paving the way for a new approach. The substantial rise in publications on PET radiotracers for spinal cord exploration indicates a growing interest in the functional and molecular imaging of this organ. The present review aimed to provide an overview of the various radiotracers used in this indication, in preclinical and clinical settings. Firstly, we outline spinal cord anatomy and associated target pathologies. Secondly, we present the state-of-the-art of spinal cord imaging techniques used in clinical practice, with their respective strengths and limitations. Thirdly, we summarize the literature on radiotracers employed in functional PET imaging of the spinal cord. In conclusion, we propose criteria for an ideal radiotracer for molecular spinal cord imaging, emphasizing the relevance of multimodal hybrid cameras, and particularly the benefits of PET-MRI integration.

Systemic low-grade C-reactive protein is associated with proximal symptom spread in carpal tunnel syndrome

Introduction

Neuropathic pain is a highly prevalent condition associated with persistent disability. Some patients with neuropathic pain experience symptom spread outside neuroanatomical boundaries; these patients report more severe sensory symptoms and greater disability. However, the mechanisms behind such symptom spread are not fully understood.

Objective

We used pre-surgical carpal tunnel syndrome (CTS) as a human model system of neuropathic pain to identify differences in the concentration of serologic inflammatory mediators between patients with CTS with territorial symptoms and those with proximal symptom spread to either the elbow or shoulder/neck.

Methods

We performed a post-hoc analysis, comparing levels of serologic inflammatory mediators in a discovery cohort among 3 symptoms spread profiles (n = 55; n = 25 no spread, n = 21 spread to elbow, n = 9 spread to shoulder/neck). We then de-novo analysed the significantly dysregulated mediators in an independent validation cohort (n = 72; n = 34 no spread, n = 16 spread to elbow, n = 22 spread to shoulder/neck).

Results

The discovery cohort revealed higher serum concentrations of C-reactive protein (CRP) and interleukin-6 in patients with any symptom spread proximal to the wrist; interferon-γ was higher in patients with symptom spread to the elbow compared with those without proximal spread. The validation study replicated the association of higher CRP concentrations in patients with proximal spread to the elbow (no spread: median [interquartile range] 2.5 [5.4]; spread to elbow 6.2 [4.6]; spread to shoulder/neck 2.6 [3.7], P = 0.006). No other markers replicated in the validation cohort.

Conclusions

Our findings suggest that proximal symptom spread in the context of neuropathic symptoms is associated with low-grade inflammation.

[ 11 C]-PBR28 positron emission tomography signal as an imaging marker of joint inflammation in knee osteoarthritis

ABSTRACT

Although inflammation is known to play a role in knee osteoarthritis (KOA), inflammation-specific imaging is not routinely performed. In this article, we evaluate the role of joint inflammation, measured using [ 11 C]-PBR28, a radioligand for the inflammatory marker 18-kDa translocator protein (TSPO), in KOA. Twenty-one KOA patients and 11 healthy controls (HC) underwent positron emission tomography/magnetic resonance imaging (PET/MRI) knee imaging with the TSPO ligand [ 11 C]-PBR28. Standardized uptake values were extracted from regions-of-interest (ROIs) semiautomatically segmented from MRI data, and compared across groups (HC, KOA) and subgroups (unilateral/bilateral KOA symptoms), across knees (most vs least painful), and against clinical variables (eg, pain and Kellgren-Lawrence [KL] grades). Overall, KOA patients demonstrated elevated [ 11 C]-PBR28 binding across all knee ROIs, compared with HC (all P 's < 0.005). Specifically, PET signal was significantly elevated in both knees in patients with bilateral KOA symptoms (both P 's < 0.01), and in the symptomatic knee ( P < 0.05), but not the asymptomatic knee ( P = 0.95) of patients with unilateral KOA symptoms. Positron emission tomography signal was higher in the most vs least painful knee ( P < 0.001), and the difference in pain ratings across knees was proportional to the difference in PET signal ( r = 0.74, P < 0.001). Kellgren-Lawrence grades neither correlated with PET signal (left knee r = 0.32, P = 0.19; right knee r = 0.18, P = 0.45) nor pain ( r = 0.39, P = 0.07). The current results support further exploration of [ 11 C]-PBR28 PET signal as an imaging marker candidate for KOA and a link between joint inflammation and osteoarthritis-related pain severity.

Preliminary study on the dynamic positron emission tomography imaging with 11C-ER176 to delineate macrophage activation in diabetic gastroparesis

BACKGROUND

Animal models and human data have suggested macrophage-driven immune dysregulation in diabetic gastroparesis (DG). Translocator protein (TSPO) upregulation has been suggested to indicate activated state of macrophages and ER176 is a high affinity third generation TSPO-specific radioligand. The aim of this study was to determine feasibility of dynamic 11C-ER 176 PET to identify macrophage activation in DG.

METHODS

Twelve patients, all females, were recruited (4 DG, 4 diabetics, and 4 healthy volunteers) for 11C-ER 176 PET/CT scanning. The standardized uptake value (SUVmax) in the gastric fundus, body, pylorus, and descending part of the duodenum were compared between three groups using Kruskal-Wallis test to perform the comparisons, and a p-value of 0.05 was considered statistically significant.

KEY RESULTS

Age was comparable among the three groups with a median of 53 years. The uptake was higher in pylorus in diabetics compared to DG and healthy (SUVmax healthy 4.6 ± 0.2, diabetics 8.4 ± 4.1, DG 5.5 ± 1.0, p = 0.04). The uptake was similar in gastric fundus (9.0 ± 1.6, 13.1 ± 8.3, 7.8 ± 1.9 respectively, p = 0.3), body (7.7 ± 1.9, 13 ± 9.2, 7.8 ± 1.9 respectively, p = 0.8), and duodenum (6.2 ± 2.1, 9.5 ± 6.8, 7.0 ± 1.8 respectively, p = 0.6). No correlation was observed between SUVmax uptake and either HbA1C or fasting blood glucose.

CONCLUSIONS AND INFERENCES

Female diabetic gastroparesis patients did not demonstrate increased TSPO ligand 11C-ER 176 uptake in the stomach. Possible explanations include lack of specificity of ligand for specific macrophage phenotypes in DG, sex effect, or small sample size. Further studies investigating non-invasive ways of analyzing immune dysregulation in neurogastrointestinal disorders are warranted.

Impaired amygdala astrocytic signaling worsens neuropathic pain-associated neuronal functions and behaviors

Introduction: Pain is a clinically relevant health care issue with limited therapeutic options, creating the need for new and improved analgesic strategies. The amygdala is a limbic brain region critically involved in the regulation of emotional-affective components of pain and in pain modulation. The central nucleus of amygdala (CeA) serves major output functions and receives nociceptive information via the external lateral parabrachial nucleus (PB). While amygdala neuroplasticity has been linked causally to pain behaviors, non-neuronal pain mechanisms in this region remain to be explored. As an essential part of the neuroimmune system, astrocytes that represent about 40-50% of glia cells within the central nervous system, are required for physiological neuronal functions, but their role in the amygdala remains to be determined for pain conditions. In this study, we measured time-specific astrocyte activation in the CeA in a neuropathic pain model (spinal nerve ligation, SNL) and assessed the effects of astrocyte inhibition on amygdala neuroplasticity and pain-like behaviors in the pain condition. Methods and Results: Glial fibrillary acidic protein (GFAP, astrocytic marker) immunoreactivity and mRNA expression were increased at the chronic (4 weeks post-SNL), but not acute (1 week post-SNL), stage of neuropathic pain. In order to determine the contribution of astrocytes to amygdala pain-mechanisms, we used fluorocitric acid (FCA), a selective inhibitor of astrocyte metabolism. Whole-cell patch-clamp recordings were performed from neurons in the laterocapsular division of the CeA (CeLC) obtained from chronic neuropathic rats. Pre-incubation of brain slices with FCA (100 µM, 1 h), increased excitability through altered hyperpolarization-activated current (Ih) functions, without significantly affecting synaptic responses at the PB-CeLC synapse. Intra-CeA injection of FCA (100 µM) had facilitatory effects on mechanical withdrawal thresholds (von Frey and paw pressure tests) and emotional-affective behaviors (evoked vocalizations), but not on facial grimace score and anxiety-like behaviors (open field test), in chronic neuropathic rats. Selective inhibition of astrocytes by FCA was confirmed with immunohistochemical analyses showing decreased astrocytic GFAP, but not NeuN, signal in the CeA. Discussion: Overall, these results suggest a complex modulation of amygdala pain functions by astrocytes and provide evidence for beneficial functions of astrocytes in CeA in chronic neuropathic pain.

Electroacupuncture Reduces Fibromyalgia Pain via Neuronal/Microglial Inactivation and Toll-like Receptor 4 in the Mouse Brain: Precise Interpretation of Chemogenetics

Fibromyalgia (FM) is a complex, chronic, widespread pain syndrome that can cause significant health and economic burden. Emerging evidence has shown that neuroinflammation is an underlying pathological mechanism in FM. Toll-like receptors (TLRs) are key mediators of the immune system. TLR4 is expressed primarily in microglia and regulates downstream signaling pathways, such as MyD88/NF-κB and TRIF/IRF3. It remains unknown whether electroacupuncture (EA) has therapeutic benefit in attenuating FM pain and what role the TLR4 pathway may play in this effect. We compared EA with sham EA to eliminate the placebo effect due to acupuncture. We demonstrated that intermittent cold stress significantly induced an increase in mechanical and thermal FM pain in mice (mechanical: 2.48 ± 0.53 g; thermal: 5.64 ± 0.32 s). EA but not sham EA has an analgesic effect on FM mice. TLR4 and inflammatory mediator-related molecules were increased in the thalamus, medial prefrontal cortex, somatosensory cortex (SSC), and amygdala of FM mice, indicating neuroinflammation and microglial activation. These molecules were reduced by EA but not sham EA. Furthermore, a new chemogenetics method was used to precisely inhibit SSC activity that displayed an anti-nociceptive effect through the TLR4 pathway. Our results imply that the analgesic effect of EA is associated with TLR4 downregulation. We provide novel evidence that EA modulates the TLR4 signaling pathway, revealing potential therapeutic targets for FM pain.

Effectiveness of combined dorsal root ganglion and spinal cord stimulation: a retrospective, single-centre case series for chronic focal neuropathic pain

OBJECTIVE

This case series retrospectively reviewed the outcomes in patients implanted with combined, synchronous dorsal root ganglion stimulation (DRGS) and spinal cord stimulation (SCS) connected to a single implantable pulse generator (IPG) in a tertiary referral neuromodulation centre in the United Kingdom.

METHODS

Twenty-six patients underwent a trial of DRGS+SCS for treating focal neuropathic pain between January 2016 and December 2019, with a follow-up in February 2022. A Transgrade approach was employed for DRGS. Patients were provided with 3 possible stimulation programs: DRGS-only, SCS-only, or DRGS+SCS. Patients were assessed for pain intensity, patients' global impression of change (PGIC), preferred lead(s) and complications.

RESULTS

Twenty patients were successful and went on for full implantation. The most common diagnosis was Complex Regional Pain Syndrome. After an average of 3.1 years follow-up, 1 patient was lost to follow-up, and 2 were non-responders. Of the remaining 17 patients, 16 (94%) continued to report a PGIC of 7. The average pain intensity at Baseline was 8.5 on an NRS scale of 0-10. At the last follow-up, the average NRS reduction overall was 78.9% with no statistical difference between those preferring DRGS+SCS (n = 9), SCS-only (n = 3) and DRGS-only (n = 5). The combination of DRGS+SCS was preferred by 53% at the last follow-up. There were no serious neurological complications.

CONCLUSIONS

This retrospective case series demonstrates the potential effectiveness of combined DRGS+SCS with sustained analgesia observed at an average follow-up of over 3 years. Implanting combined DRGS+SCS may provide programming flexibility and therapeutic alternatives.

Central Sensitization and Pain: Pathophysiologic and Clinical Insights

Central sensitization is an increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input.

AIM

To explain how the notion of central sensitization has changed our understanding of pain conditions, discuss how this knowledge can be used to improve the management of pain, and highlight knowledge gaps that future research needs to address.

METHODS

Overview of definitions, assessment methods, and clinical implications.

RESULTS

Human pain models, and functional and molecular imaging have provided converging evidence that central sensitization occurs and is clinically relevant. Measures to assess central sensitization in patients are available; however, their ability to discriminate sensitization of central from peripheral neurons is unclear. Treatments that attenuate central sensitization are available, but the limited understanding of molecular and functional mechanisms hampers the development of target-specific treatments. The origin of central sensitization in human pain conditions that are not associated with tissue damage remains unclear.

CONCLUSION

The knowledge of central sensitization has revolutionized our neurobiological understanding of pain. Despite the limitations of clinical assessment in identifying central sensitization, it is appropriate to use the available tools to guide clinical decisions towards treatments that attenuate central sensitization. Future research that elucidates the causes, molecular and functional mechanisms of central sensitization would provide crucial progress towards the development of treatments that target specific mechanisms of central sensitization.

Up-and-coming Radiotracers for Imaging Pain Generators

Chronic musculoskeletal pain is among the most highly prevalent diseases worldwide. Managing patients with chronic pain remains very challenging because current imaging techniques focus on morphological causes of pain that can be inaccurate and misleading. Moving away from anatomical constructs of disease, molecular imaging has emerged as a method to identify diseases according to their molecular, physiologic, or cellular signatures that can be applied to the variety of biomolecular changes that occur in nociception and pain processing and therefore have tremendous potential for precisely pinpointing the source of a patient's pain. Several molecular imaging approaches to image the painful process are now available, including imaging of voltage-gated sodium channels, calcium channels, hypermetabolic processes, the substance P receptor, the sigma-1 receptor, and imaging of macrophage trafficking. This article provides an overview of promising molecular imaging approaches for the imaging of musculoskeletal pain with a focus on preclinical methods.

Low-carbohydrate and ketogenic diets: a scoping review of neurological and inflammatory outcomes in human studies and their relevance to chronic pain

Dietary restriction of carbohydrate has been demonstrated to be beneficial for nervous system dysfunction in animal models and may be beneficial for human chronic pain. The purpose of this review is to assess the impact of a low-carbohydrate/ketogenic diet on the adult nervous system function and inflammatory biomarkers to inform nutritional research for chronic pain. An electronic database search was carried out in May 2021. Publications were screened for prospective research with dietary carbohydrate intake <130 g per day and duration of ≥2 weeks. Studies were categorised into those reporting adult neurological outcomes to be extracted for analysis and those reporting other adult research outcomes. Both groups were screened again for reported inflammatory biomarkers. From 1548 studies, there were 847 studies included. Sixty-four reported neurological outcomes with 83% showing improvement. Five hundred and twenty-three studies had a different research focus (metabolic n = 394, sport/performance n = 51, cancer n = 33, general n = 30, neurological with non-neuro outcomes n = 12, or gastrointestinal n = 4). The second screen identified sixty-three studies reporting on inflammatory biomarkers, with 71% reporting a reduction in inflammation. The overall results suggest a favourable outcome on the nervous system and inflammatory biomarkers from a reduction in dietary carbohydrates. Both nervous system sensitisation and inflammation occur in chronic pain, and the results from this review indicate it may be improved by low-carbohydrate nutritional therapy. More clinical trials within this population are required to build on the few human trials that have been done.

The Value of 18F-FDG PET/MRI in Detecting Lumbar Radiculopathy for Selective Percutaneous Endoscopic Discectomy: a Case Report

Magnetic resonance imaging (MRI) is the most popular imaging modality for investigating intervertebral disc herniation. However, it has a high chance for identifying incidental findings that are morphologically or structurally abnormal but not responsible for patients' symptoms. Although a previous study suggested that 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) may help identify neuroinflammation in lumbar radiculopathy, there is currently no direct evidence obtained from surgery. Here, we describe the case of a 32-year-old man with low back pain and right leg paresthesia for 7 months. MRI demonstrated disc herniation at the L3-L4, L4-L5 and L5-S1 levels, causing bilateral L5 and left S1 root compression. 18F-FDG PET/MRI demonstrated increased 18F-FDG uptake at the right L5 root, which was compatible with the patient's symptoms. Transforaminal percutaneous endoscopic lumbar discectomy (PELD) was performed. Intraoperative images revealed a swollen nerve root at the right L5 after removal of the herniated disc. After surgery, the patient experienced immediate pain relief and had no recurrence at the 6-month follow-up. When performing PELD in patients with multilevel radiculopathy identified on MRI, the use of 18F-FDG PET/MRI can help in accurate localization of the symptomatic roots and minimize surgical incision and soft-tissue injury.

Integrating jigsaw puzzle thinking into practice: the assessment of cervical spine radiculopathy

PURPOSE OF REVIEW

Cervical spine radiculopathy (CSR) presents a complex socioeconomic problem for patients, clinicians, families, employers and healthcare systems. Due to the heterogeneity of clinical presentation and underlying mechanisms, clinical assessment can be challenging. This review will examine the literature on the underlying pathophysiology and studies investigating the holistic assessment strategies for this disabling condition. The authors will focus particular attention on the psychological factors associated with CSR and the physical and imaging strategies to establish a diagnosis.

RECENT FINDINGS

Contemporary CSR assessment should identify the underlying pathomechanisms and how this may impact the somatosensory nervous system integrity and function. No physical assessment test in isolation will establish CSR diagnosis; therefore, clinicians should utilise a cluster of tests and recognise the potential limitations as part of a clinical reasoning framework. The assessment of the somatosensory nervous system can provide insights into particular subgroups of CSR presentation, which may provide interesting opportunities to continue to enhance individualised assessment and management strategies for CSR. The interplay between psychological factors can influence the diagnosis and recovery times for a person with CSR, and clinicians should continue to explore how these factors may influence a person's prognosis. The authors will discuss the opportunities for future research and limitations of contemporary approaches to assessment, underpinned by evidence, and how this supports a clinical assessment to establish CSR diagnosis.

SUMMARY

Research should continue to investigate how clinicians assess the interplay between physical and psychological factors to inform the establishment of CSR. Specifically, there is a need to investigate the validity and reliability of combining somatosensory, motor and imaging assessment findings to reach a diagnosis and inform onward management plans.

Analysis of Conservative Treatment Trends for Lumbar Disc Herniation with Radiculopathy in Korea: A Population-Based Cross-Sectional Study

This study aimed to analyze the trends in conservative treatment and associated medical costs for lumbar intervertebral disc disorders with radiculopathy in Korea. This population-based cross-sectional study included patients aged ≥ 20 years with at least one "intervertebral disc disorder with radiculopathy" claim (Korean Standard Classification of Diseases (KCD)-7 code: M511) who sought treatment from tertiary, general, or Korean Medicine hospitals or clinics between 2010 and 2019 and whose data were extracted from the Korean Health Insurance Review and Assessment Service National Patients Sample database. Intervention frequency, ratio, and medical costs, including medication, were analyzed. The number of patients with lumbar intervertebral disc disorders and radiculopathy undergoing conservative treatment increased by >30%, and medical costs increased from USD 3,342,907 to USD 5,600,456 during the 10-year period. The non-surgical treatments mainly used were medication and physiotherapy, and the most commonly prescribed medication was non-opioid analgesics. Meanwhile, the number of patients who used nerve plexus and root and ganglion nerve blocks showed the most significant increase. In conclusion, the number of patients with radiculopathy who received nerve blocks, particularly nerve plexus and root and ganglion nerve blocks, and related expenditure increased, implying a gradual shift in medical decisions from systemic pain reduction to specific and targeted pain treatments. Future studies and clinical practice guidelines may require further inspection of real-world practice to advise optimal treatment choices for an effective treatment plan.

The therapeutic potential of natural killer cells in neuropathic pain

Novel disease-modifying treatments for neuropathic pain are urgently required. The cellular immune response to nerve injury represents a promising target for therapeutic development. Recently, the role of natural killer (NK) cells in both CNS and PNS disease has been the subject of growing interest. In this opinion article, we set out the case for NK cell-based intervention as a promising avenue for development in the management of neuropathic pain. We explore the potential cellular and molecular targets of NK cells in the PNS by contrasting with their reported functional roles in CNS diseases, and we suggest strategies for using the beneficial functions of NK cells and immune-based therapeutics in the context of neuropathic pain.

Alleviating effect of lycorine on CFA‑induced arthritic pain via inhibition of spinal inflammation and oxidative stress

Chronic pain is the primary symptom of osteoarthritis affecting a patient's quality of life. Neuroinflammation and oxidative stress in the spinal cord contribute to arthritic pain and represent ideal targets for pain management. In the present study, a model of arthritis was established by intra-articular injection of complete Freund's adjuvant (CFA) into the left knee joint in mice. After CFA inducement, knee width and pain hypersensitivity in the mice were increased, motor disability was impaired, spinal inflammatory reaction was induced, spinal astrocytes were activated, antioxidant responses were decreased, and glycogen synthase kinase 3β (GSK-3β) activity was inhibited. To explore the potential therapeutic options for arthritic pain, lycorine was intraperitoneally injected for 3 days in the CFA mice. Lycorine treatment significantly reduced mechanical pain sensitivity, suppressed spontaneous pain, and recovered motor coordination in the CFA-induced mice. Additionally, in the spinal cord, lycorine treatment decreased the inflammatory score, reduced NOD-like receptor protein 3 inflammasome (NLRP3) activity and IL-1β expression, suppressed astrocytic activation, downregulated NF-κB levels, increased nuclear factor erythroid 2-related factor 2 expression and superoxide dismutase activity. Furthermore, lycorine was shown to bind to GSK-3β through three electrovalent bonds, to inhibit GSK-3β activity. In summary, lycorine treatment inhibited GSK-3β activity, suppressed NLRP3 inflammasome activation, increased the antioxidant response, reduced spinal inflammation, and relieved arthritic pain.

Posttranscriptional Regulation of Gene Expression Participates in the Myelin Restoration in Mouse Models of Multiple Sclerosis: Antisense Modulation of HuR and HuD ELAV RNA Binding Protein

Neuropathic pain is the most difficult-to-treat pain syndrome in multiple sclerosis. Evidence relates neuropathic pain to demyelination, which often originates from unresolved neuroinflammation or altered immune response. Posttranscriptional regulation of gene expression might play a fundamental role in the regulation of these processes. The ELAV RNA-binding proteins HuR and HuD are involved in the promotion of inflammatory phenomena and in neuronal development and maintenance, respectively. Thus, the aim of this study was to investigate the role of HuR and HuD in demyelination-associated neuropathic pain in the mouse experimental autoimmune encephalomyelitis (EAE) model. HuR resulted overexpressed in the spinal cord of MOG_35-55-EAE and PLP_139-151-EAE mice and was detected in CD11b + cells. Conversely, HuD was largely downregulated in the MOG-EAE spinal cord, along with GAP43 and neurofilament H, while in PLP-EAE mice, HuD and neuronal markers remained unaltered. Intranasal antisense oligonucleotide (ASO) delivery to knockdown HuR, increased myelin basic protein expression, and Luxol Fast Blue staining in both EAE models, an indication of increased myelin content. These effects temporally coincided with attenuation of pain hypersensitivity. Anti-HuR ASO increased the expression of HuD in GAP43-expressing cells and promoted a HuD-mediated neuroprotective activity in MOG-EAE mice, while in PLP-EAE mice, HuR silencing dampened pro-inflammatory responses mediated by spinal microglia activation. In conclusion, anti-HuR ASO showed myelin protection at analgesic doses with multitarget mechanisms, and it deserves further consideration as an innovative agent to counteract demyelination in neuropathic pain states.

Assessing the potential anti-neuroinflammatory effect of minocycline in chronic low back pain: Protocol for a randomized, double-blind, placebo-controlled trial

INTRODUCTION

Both preclinical studies, and more recent clinical imaging studies, suggest that glia-mediated neuroinflammation may be implicated in chronic pain, and therefore might be a potential treatment target. However, it is currently unknown whether modulating neuroinflammation effectively alleviates pain in humans. This trial tests the hypothesis that minocycline, an FDA-approved tetracycline antibiotic and effective glial cell inhibitor in animals, reduces neuroinflammation and may reduce pain symptoms in humans with chronic low back pain.

METHODS AND ANALYSIS

This study is a randomized, double-blind, placebo-controlled clinical trial. Subjects, aged 18-75, with a confirmed diagnosis of chronic (≥ six months) low back pain (cLBP) and a self-reported pain rating of at least four out of ten (for at least half of the days during an average week) are enrolled via written, informed consent. Eligible subjects are randomized to receive a 14-day course of either active drug (minocycline) or placebo. Before and after treatment, subjects are scanned with integrated Positron Emission Tomography/Magnetic Resonance Imaging (PET/MRI) using [¹¹C]PBR28, a second-generation radiotracer for the 18 kDa translocator protein (TSPO), which is highly expressed in glial cells and thus a putative marker of neuroinflammation. Pain levels are evaluated via daily surveys, collected seven days prior to the start of medication, and throughout the 14 days of treatment. General linear models will be used to assess pain levels and determine the treatment effect on brain (and spinal cord) TSPO signal.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov (NCT03106740).

Downregulation of nuclear STAT2 protein in the spinal dorsal horn is involved in neuropathic pain following chronic constriction injury of the rat sciatic nerve

Regulation of gene transcription in the spinal dorsal horn (SDH) plays a critical role in the pathophysiology of neuropathic pain. In this study, we investigated whether the transcription factor STAT2 affects neuropathic pain and evaluated its possible mechanisms. A proteomic analysis showed that the nuclear fraction of STAT2 protein in the SDH was downregulated after chronic constriction injury of the rat sciatic nerve, which was associated with the development of neuropathic pain. Similarly, siRNA-induced downregulation of STAT2 in the SDH of naïve rats also resulted in pain hypersensitivity. Using RNA-sequencing analysis, we showed that reduction of nuclear STAT2 after chronic constriction injury was associated with increased expression of microglial activation markers, including the class II transactivator and major histocompatibility complex class II proteins. In addition, siRNA-induced downregulation of STAT2 promoted microglial activation and pro-inflammatory cytokine expression in the SDH. Taken together, these results showed that chronic constriction injury caused downregulation of nuclear STAT2 in the SDH, which may result in microglial activation and development of neuropathic pain. Our findings indicate that restoration of nuclear expression of STAT2 could be a potential pathway for the treatment of neuropathic pain.

[Quantitative sensory testing for neuropathic pain and its relevance for physiotherapy]

BACKGROUND

Neuropathic pain syndromes are typically characterized by high chronification rates as well as long and intensive pain episodes. Early and accurate diagnosis of neuropathic pain is a basic skill of physiotherapists and other medical professionals, may allow for appropriate medical treatment and help to prevent possible consequential damage. Quantitative sensory testing (QST) can be applied as a supplement to conventional neurological bedside testing in the evaluation of neuropathic pain. Over recent decades, QST has come to hold a significant position in the field of pain research. However, despite these developments, the application of QST in clinical practice has lagged behind.

OBJECTIVES

What is the value of QST in the study of neuropathic pain? Have the conditions for personal clinical use of the QST been established in physiotherapy practice? Have the pathways for specific implementation of the QST been defined?

METHOD

Literature research as part of a Bachelor thesis in Physiotherapy.

RESULTS

QST constitutes a valid examination tool that is able to evaluate the complete somatosensory profile. In this way, QST may provide substantial additional benefit in the examination of neuropathic pain patients compared to other conventional testing procedures, especially when it comes to small-fibre neuropathies. These small fibres seem to be particularly affected in asymptomatic patients as well as early phases of neuropathies and cannot be investigated via conventional testing procedures. This makes the use of partial aspects of the QST a proven instrument for physiotherapists and medical staff, which was particularly useful in the decision-making process for neuropathies.

DISCUSSION

Nonetheless, regarding the results, there are still several limiting factors that hamper the routine use of QST. Some of these can be resolved by precisely adhering to testing protocols and taking precautions. Other highly relevant issues for clinical practice, such as the immense cost of equipment and the excessive time required for testing, have not been satisfactorily overcome as yet. Less comprehensive testing protocols as well as the innovation of handy and cost-effective testing devices might offer initial approaches to enhance the widespread use of QST. Complementing conventional bedside testing by adding thermal discrimination tests and pain detection threshold tests might prove to be another possibility to integrate the benefit of QST into clinical practice.

CONCLUSION

QST makes a significant contribution to the investigation and diagnosis of neuropathies. Physiotherapists are encouraged to implement partial aspects of the QST in a standard examination in order to have a positive effect on both early detection and treatment.

Study protocol for a phase II, double-blind, randomised controlled trial of cannabidiol (CBD) compared with placebo for reduction of brain neuroinflammation in adults with chronic low back pain

INTRODUCTION

Chronic pain is a debilitating medical problem that is difficult to treat. Neuroinflammatory pathways have emerged as a potential therapeutic target, as preclinical studies have demonstrated that glial cells and neuroglial interactions play a role in the establishment and maintenance of pain. Recently, we used positron emission tomography (PET) to demonstrate increased levels of 18 kDa translocator protein (TSPO) binding, a marker of glial activation, in patients with chronic low back pain (cLBP). Cannabidiol (CBD) is a glial inhibitor in animal models, but studies have not assessed whether CBD reduces neuroinflammation in humans. The principal aim of this trial is to evaluate whether CBD, compared with placebo, affects neuroinflammation, as measured by TSPO levels.

METHODS AND ANALYSIS

This is a double-blind, randomised, placebo-controlled, phase II clinical trial. Eighty adults (aged 18-75) with cLBP for >6 months will be randomised to either an FDA-approved CBD medication (Epidiolex) or matching placebo for 4 weeks using a dose-escalation design. All participants will undergo integrated PET/MRI at baseline and after 4 weeks of treatment to evaluate neuroinflammation using [11C]PBR28, a second-generation radioligand for TSPO. Our primary hypothesis is that participants randomised to CBD will demonstrate larger reductions in thalamic [11C]PBR28 signal compared with those receiving placebo. We will also assess the effect of CBD on (1) [11C]PBR28 signal from limbic regions, which our prior work has linked to depressive symptoms and (2) striatal activation in response to a reward task. Additionally, we will evaluate self-report measures of cLBP intensity and bothersomeness, depression and quality of life at baseline and 4 weeks.

ETHICS AND DISSEMINATION

This protocol is approved by the Massachusetts General Brigham Human Research Committee (protocol number: 2021P002617) and FDA (IND number: 143861) and registered with ClinicalTrials.gov. Results will be published in peer-reviewed journals and presented at conferences.

TRIAL REGISTRATION NUMBER

NCT05066308; ClinicalTrials.gov.

Normalization of Neuroinflammation: A New Strategy for Treatment of Persistent Pain and Memory/Emotional Deficits in Chronic Pain

Chronic pain, which affects around 1/3 of the world population and is often comorbid with memory deficit and mood depression, is a leading source of suffering and disability. Studies in past decades have shown that hyperexcitability of primary sensory neurons resulting from abnormal expression of ion channels and central sensitization mediated pathological synaptic plasticity, such as long-term potentiation in spinal dorsal horn, underlie the persistent pain. The memory/emotional deficits are associated with impaired synaptic connectivity in hippocampus. Dysregulation of numerous endogenous proteins including receptors and intracellular signaling molecules is involved in the pathological processes. However, increasing knowledge contributes little to clinical treatment. Emerging evidence has demonstrated that the neuroinflammation, characterized by overproduction of pro-inflammatory cytokines and glial activation, is reliably detected in humans and animals with chronic pain, and is sufficient to induce persistent pain and memory/emotional deficits. The abnormal expression of ion channels and pathological synaptic plasticity in spinal dorsal horn and in hippocampus are resulting from neuroinflammation. The neuroinflammation is initiated and maintained by the interactions of circulating monocytes, glial cells and neurons. Obviously, unlike infectious diseases and cancer, which are caused by pathogens or malignant cells, chronic pain is resulting from alterations of cells and molecules which have numerous physiological functions. Therefore, normalization (counterbalance) but not simple inhibition of the neuroinflammation is the right strategy for treating neuronal disorders. Currently, no such agent is available in clinic. While experimental studies have demonstrated that intracellular Mg²⁺ deficiency is a common feature of chronic pain in animal models and supplement Mg²⁺ are capable of normalizing the neuroinflammation, activation of upregulated proteins that promote recovery, such as translocator protein (18k Da) or liver X receptors, has a similar effect. In this article, relevant experimental and clinical evidence is reviewed and discussed.

The Role of Neuro-Immune Interactions in Chronic Pain: Implications for Clinical Practice

Chronic pain remains a public health problem and contributes to the ongoing opioid epidemic. Current pain management therapies still leave many patients with poorly controlled pain, thus new or improved treatments are desperately needed. One major challenge in pain research is the translation of preclinical findings into effective clinical practice. The local neuroimmune interface plays an important role in the initiation and maintenance of chronic pain and is therefore a promising target for novel therapeutic development. Neurons interface with immune and immunocompetent cells in many distinct microenvironments along the nociceptive circuitry. The local neuroimmune interface can modulate the activity and property of the neurons to affect peripheral and central sensitization. In this review, we highlight a specific subset of many neuroimmune interfaces. In the central nervous system, we examine the interface between neurons and microglia, astrocytes, and T lymphocytes. In the periphery, we profile the interface between neurons in the dorsal root ganglion with T lymphocytes, satellite glial cells, and macrophages. To bridge the gap between preclinical research and clinical practice, we review the preclinical studies of each neuroimmune interface, discuss current clinical treatments in pain medicine that may exert its action at the neuroimmune interface, and highlight opportunities for future clinical research efforts.

IL-10 alleviates radicular pain by inhibiting TNF-α/p65 dependent Nav1.7 up-regulation in DRG neurons of rats

BACKGROUND

Lumbar disc herniation (LDH) may induce radicular pain, the upregulation of voltage-gated sodium channels (VGSCs) in dorsal root ganglion (DRG) contributes to radicular pain by generating ectopic discharge of neurons, but the mechanism is unclear. Previously, we reported pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) up-regulated VGSCs in diabetic neuropathy. In this study, we explored the effect of anti-inflammatory cytokine interleukin-10 (IL-10) on radicular pain and the possible mechanisms.

METHODS

Rat model of LDH was induced by implanting autologous nucleus pulposus (NP). Mechanical and thermal pain thresholds were assessed by von Frey filaments and hotplate test respectively. IL-10 and TNF-α level in DRG and cerebrospinal fluid (CSF) were assessed by Enzyme-linked immunosorbent assay (ELISA). IL-10 was intrathecally delivered for 12 days. The expression of IL-10R1 and sodium channel Nav1.7 was displayed by immunofluorescence staining. The protein level of TNF-α and p-p65 was measured by western blotting.

RESULTS

NP implantation increased Nav1.7 expression in DRG neurons, decreased IL-10 level and increased TNF-α level in DRG and CSF. IL-10 significantly alleviated pain behaviors of rats with NP. IL-10R1 was co-localized with neurons but not with satellite cells in DRG. IL-10 decreased Nav1.7 and TNF-α/p-p65 expression in DRG of rats with NP. Co-administration of TNF-α with IL-10 counteracted the effect of IL-10 on pain behaviors, Nav1.7 and TNF-α/p-p65 expression of rats with NP.

CONCLUSIONS

The study revealed that IL-10 alleviated radicular pain by inhibiting TNF-α/p-p65 dependent Nav1.7 up-regulation in DRG neurons.

T2 mapping and fat quantification of lumbar paraspinal muscle in ankylosing spondylitis: a case control study

BACKGROUND

To compare changes in the composition of paraspinal muscles of patients with ankylosing spondylitis (AS) and matched healthy controls using T2 mapping and T2 IDEAL and correlate the quantitative magnetic resonance imaging (qMRI) results with clinical assessments of AS patients.

METHOD

In total, 37 AS patients and 37 healthy controls were enrolled in the case control study. T2 mapping with and without fat saturation and IDEAL imaging were used to assess the multifidus (MF) and erector spinae (ES) at the levels of L3/L4 and L4/L5 for all subjects. Mean T2_non-fatsat, T2_fat, T2_fatsat, cross-sectional area (CSA), and fat fraction (FF) were compared between AS and healthy controls. Correlations of qMRI results with clinical assessments were analyzed in AS.

RESULTS

Significantly elevated mean T2_non-fatsat values and the FF of the MF and ES at both levels were observed in AS and compared to the controls (p < 0.05). The mean T2_fatsat values of ES and MF were significantly higher only at the level of L3/L4 in AS compared to healthy controls (p < 0.05). A loss of muscle CSA compatible with atrophy was present in MF and ES at both levels in AS compared to the controls (p < 0.05). Weak to moderate positive correlations were found between FF and age and disease duration in AS (r = 0.318-0.415, p < 0.05). However, such positive correlation was not observed between FF and disease duration after adjusting for age (p > 0.05).

CONCLUSIONS

Our findings indicate that using a combination of IDEAL and T2 mapping may provide deeper insights into the pathophysiological degeneration of paraspinal muscles in AS.

Transcriptional and cellular signatures of cortical morphometric remodelling in chronic pain

ABSTRACT

Chronic pain is a highly debilitating and difficult to treat condition, which affects the structure of the brain. Although the development of chronic pain is moderately heritable, how disease-related alterations at the microscopic genetic architecture drive macroscopic brain abnormalities is currently largely unknown. Here, we examined alterations in morphometric similarity (MS) and applied an integrative imaging transcriptomics approach to identify transcriptional and cellular correlates of these MS changes, in 3 independent small cohorts of patients with distinct chronic pain syndromes (knee osteoarthritis, low back pain, and fibromyalgia) and age-matched and sex-matched pain-free controls. We uncover a novel pattern of cortical MS remodelling involving mostly small-to-medium MS increases in the insula and limbic cortex (none of these changes survived stringent false discovery rate correction for the number of regions tested). This pattern of changes is different from that observed in patients with major depression and cuts across the boundaries of specific pain syndromes. By leveraging transcriptomic data from Allen Human Brain Atlas, we show that cortical MS remodelling in chronic pain spatially correlates with the brain-wide expression of genes related to pain and broadly involved in the glial immune response and neuronal plasticity. Our findings bridge levels to connect genes, cell classes, and biological pathways to in vivo imaging correlates of chronic pain. Although correlational, our data suggest that cortical remodelling in chronic pain might be shaped by multiple elements of the cellular architecture of the brain and identifies several pathways that could be prioritized in future genetic association or drug development studies.

Case Report: Nerve Root Entrapment Due to Epidural Fibrosis in a Patient With Failed Back Surgery Syndrome: Value of 2-18F-Fluorodeoxyglucose Simultaneous Positron Emission Tomography-Magnetic Resonance Imaging

Failed back surgery syndrome (FBSS) is a highly prevalent condition in patients after spine surgery. Although magnetic resonance imaging (MRI) is the gold standard for the diagnosis of epidural fibrosis, it is sometimes difficult to determine if epidural fibrosis contributes to radiculopathy. Herein, we share our experience in locating radiculopathy lesions using simultaneous positron emission tomography (PET)/MRI. 2-[¹⁸F]-FDG (¹⁸F-fluorodeoxyglucose) simultaneous PET/MRI maps of body glucose metabolism detected using PET can be used to correlate anatomical details provided by MRI to offer a very clear picture of neural inflammation due to extensive epidural fibrosis. More applications of 2-[¹⁸F]-FDG simultaneous PET/MRI in low back pain and other musculoskeletal diseases should be further investigated in the future.

Neuroimmune responses following joint mobilisation and manipulation in people with persistent neck pain: a protocol for a randomised placebo-controlled trial

INTRODUCTION

Joint mobilisation and manipulation often results in immediate pain relief in people with neck pain. However, the biological mechanisms behind pain relief are largely unknown. There is preliminary evidence that joint mobilisation and manipulation lessens the upregulated neuroimmune responses in people with persistent neck pain.

METHODS AND ANALYSIS

This study protocol describes a randomised placebo-controlled trial to investigate whether joint mobilisation and manipulation influence neuroimmune responses in people with persistent neck pain. People with persistent neck pain (N=100) will be allocated, in a randomised and concealed manner, to the experimental or control group (ratio 3:1). Short-term (ie, baseline, immediately after and 2 hours after the intervention) neuroimmune responses will be assessed, such as inflammatory marker concentration following in vitro stimulation of whole blood cells, systemic inflammatory marker concentrations directly from blood samples, phenotypic analysis of peripheral blood mononuclear cells and serum cortisol. Participants assigned to the experimental group (N=75) will receive cervical mobilisations targeting the painful and/or restricted cervical segments and a distraction manipulation of the cervicothoracic junction. Participants assigned to the control group (N=25) will receive a placebo mobilisation and placebo manipulation. Using linear mixed models, the short-term neuroimmune responses will be compared (1) between people in the experimental and control group and (2) within the experimental group, between people who experience a good outcome and those with a poor outcome. Furthermore, the association between the short-term neuroimmune responses and pain relief following joint mobilisation and manipulation will be tested in the experimental group.

ETHICS AND DISSEMINATION

This trial is approved by the Medical Ethics Committee of Amsterdam University Medical Centre, location VUmc (Approval number: 2018.181).

TRIAL REGISTRATION NUMBER

NL6575 (trialregister.nl.

Noninvasive intracranial pressure monitoring in women with migraine

This cross-sectional study aimed to compare the waveform morphology through noninvasive intracranial pressure (ICP-NI) measurement between patients with migraine and controls, and to analyze the association with clinical variables. Twenty-nine women with migraine, age 32.4 (11.2) years and headache frequency of 12.6 (7.5) days per month and twenty-nine women without headache, age 32.1 (9.0) years, were evaluated. Pain intensity, migraine disability, allodynia, pain catastrophizing, central sensitization and depression were evaluated. The ICP-NI monitoring was performed by a valid method consisting of an extracranial deformation sensor positioned in the patients’ scalp, which allowed registration of intracranial pressure waveforms. Heart rate and blood pressure measurements were simultaneously recorded during 20 min in the supine position. The analyzed parameter was the P2/P1 ratio based on mean pulse per minute which P1 represents the percussion wave related to the arterial blood pression maximum and P2 the tidal wave, middle point between the P1 maximum and the dicrotic notch. There was no between-groups difference in the P2/P1 ratio (mean difference: 0.04, IC95%: -0.07 to 0.16, p = 0.352, F (1,1) = 0.881) adjusted by body mass index covariable. The Multiple Linear Regression showed non-statistical significance [F (5,44) = 1.104; p = 0.372; R² = 0.11)] between the P2/P1 ratio and body mass index, presence of migraine, central sensitization, pain catastrophizing and depression. We found no correlation (p > 0.05) between P2/P1 ratio and migraine frequency, migraine onset, pain intensity, pain intensity at day of examination, disability, allodynia. Migraine patients did not present alterations in the waveform morphology through ICP-NI compared to women without headache and no association with clinical variables was found.

Have (R)-[11C]PK11195 challengers fulfilled the promise? A scoping review of clinical TSPO PET studies

PURPOSE

The prototypical TSPO radiotracer (R)-[11C]PK11195 has been used in humans for more than thirty years to visualize neuroinflammation in several pathologies. Alternative radiotracers have been developed to improve signal-to-noise ratio and started to be tested clinically in 2008. Here we examined the scientific value of these "(R)-[11C]PK11195 challengers" in clinical research to determine if they could supersede (R)-[11C]PK11195.

METHODS

A systematic MEDLINE (PubMed) search was performed (up to end of year 2020) to extract publications reporting TSPO PET in patients with identified pathologies, excluding studies in healthy subjects and methodological studies.

RESULTS

Of the 288 publications selected, 152 used 13 challengers, and 142 used (R)-[11C]PK11195. Over the last 20 years, the number of (R)-[11C]PK11195 studies remained stable (6 ± 3 per year), but was surpassed by the total number of challenger studies for the last 6 years. In total, 3914 patients underwent a TSPO PET scan, and 47% (1851 patients) received (R)-[11C]PK11195. The 2 main challengers were [11C]PBR28 (24%-938 patients) and [18F]FEPPA (11%-429 patients). Only one-in-ten patients (11%-447) underwent 2 TSPO scans, among whom 40 (1%) were scanned with 2 different TSPO radiotracers.

CONCLUSIONS

Generally, challengers confirmed disease-specific initial (R)-[11C]PK11195 findings. However, while their better signal-to-noise ratio seems particularly useful in diseases with moderate and widespread neuroinflammation, most challengers present an allelic-dependent (Ala147Thr polymorphism) TSPO binding and genetic stratification is hindering their clinical implementation. As new challengers, insensitive to TSPO human polymorphism, are about to enter clinical evaluation, we propose this systematic review to be regularly updated (living review).

Neurodynamics: is tension contentious?

Tensioning techniqueswere the first neurodynamic techniques used therapeutically in the management of people with neuropathies. This article aims to provide a balanced evidence-informed view on the effects of optimal tensile loading on peripheral nerves and the use of tensioning techniques. Whilst the early use of neurodynamics was centered within a mechanical paradigm, research into the working mechanisms of tensioning techniques revealed neuroimmune, neurophysiological, and neurochemical effects. In-vitro and ex-vivo research confirms that tensile loading is required for mechanical adaptation of healthy and healing neurons and nerves. Moreover, elimination of tensile load can have detrimental effects on the nervous system. Beneficial effects of tensile loading and tensioning techniques, contributing to restored homeostasis at the entrapment site, dorsal root ganglia and spinal cord, include neuronal cell differentiation, neurite outgrowth and orientation, increased endogenous opioid receptors, reduced fibrosis and intraneural scar formation, improved nerve regeneration and remyelination, increased muscle power and locomotion, less mechanical and thermal hyperalgesia and allodynia, and improved conditioned pain modulation. However, animal and cellular models also show that ‘excessive’ tensile forces have negative effects on the nervous system. Although robust and designed to withstand mechanical load, the nervous system is equally a delicate system. Mechanical loads that can be easily handled by a healthy nervous system, may be sufficient to aggravate clinical symptoms in patients. This paper aims to contribute to a more balanced view regarding the use of neurodynamics and more specifically tensioning techniques.

[11C]PBR28 radiotracer kinetics are not driven by alterations in cerebral blood flow

The positron emission tomography (PET) radiotracer [¹¹C]PBR28 has been increasingly used to image the translocator protein (TSPO) as a marker of neuroinflammation in a variety of brain disorders. Interrelatedly, similar clinical populations can also exhibit altered brain perfusion, as has been shown using arterial spin labelling in magnetic resonance imaging (MRI) studies. Hence, an unsolved debate has revolved around whether changes in perfusion could alter delivery, uptake, or washout of the radiotracer [¹¹C]PBR28, and thereby influence outcome measures that affect interpretation of TSPO upregulation. In this simultaneous PET/MRI study, we demonstrate that [¹¹C]PBR28 signal elevations in chronic low back pain patients are not accompanied, in the same regions, by increases in cerebral blood flow (CBF) compared to healthy controls, and that areas of marginal hypoperfusion are not accompanied by decreases in [¹¹C]PBR28 signal. In non-human primates, we show that hypercapnia-induced increases in CBF during radiotracer delivery or washout do not alter [¹¹C]PBR28 outcome measures. The combined results from two methodologically distinct experiments provide support from human data and direct experimental evidence from non-human primates that changes in CBF do not influence outcome measures reported by [¹¹C]PBR28 PET imaging studies and corresponding interpretations of the biological meaning of TSPO upregulation.

Heme oxygenase-1 in the spinal cord plays crucial roles in the analgesic effects of pregabalin and gabapentin in a spared nerve-injury mouse model

INTRODUCTION

Neuropathic pain remains one of the most intractable types of pain; although calcium channel α₂δ ligands, such as pregabalin and gabapentin, are classified as first-line drugs, they have only modest efficacy. Heme oxygenase-1 (HO-1) signaling attenuates glial activation during neuropathic pain. Thus, this study aimed to investigate the effects of the blood-brain barrier (BBB)-permeable HO-1 inhibitor, tin protoporphyrin IX (SnPP), or the BBB-impermeable HO-1 inhibitor, zinc (II) protoporphyrin IX (ZnPP), on the analgesic efficacy of pregabalin and gabapentin. Additionally, we examined the effects of co-administration of SnPP with pregabalin or gabapentin on the expression of glial markers or other genes.

METHODS

Neuropathic pain was induced by spared nerve injury (SNI) of the sciatic nerve. The mechanical threshold was tested using the von Frey filaments. The expression of spinal glial markers or other genes was examined using reverse transcription polymerase chain reaction.

RESULTS

Systemic HO-1 inhibition reversed the mechanical antiallodynic effects of pregabalin and gabapentin, although peripheral HO-1 inhibition did not alter the mechanical antiallodynic effects of either pregabalin or gabapentin. Intrathecal injection of SnPP or ZnPP abolished the mechanical antiallodynic effects of pregabalin and gabapentin. Pregabalin and gabapentin increased HO-1, arginase-1, and endogenous opioid precursor preproenkephalin gene expression and decreased the expression of glial markers, interleukin-1β, and inducible nitric oxide synthase.

CONCLUSIONS

This study suggests that spinal HO-1 plays a crucial role in the analgesic effects of calcium channel α₂δ ligands through the attenuation of glial activation and endogenous opioid release.

Effect of epidural polydeoxyribonucleotide in a rat model of lumbar foraminal stenosis

Background

We aimed to investigate the effect of epidural polydeoxyribonucleotide (PDRN) on mechanical allodynia and motor dysfunction in a rat model of lumbar foraminal stenosis (LFS).

Methods

This study was conducted in two stages, using male Sprague-Dawley rats. The rats were randomly divided into eight groups. In the first stage, the groups were as follows vehicle (V), sham (S), and epidural PDRN at 5 (P5), 8 (P8), and 10 (P10) mg/kg; and in the second stage, they were as follows intraperitoneal PDRN 8 mg/kg, epidural 3,7-dimethyl-1-propargilxanthine (DMPX) (0.1 mg/kg), and DMPX (0.1 mg/kg). The LFS model was established, except for the S group. After an epidural injection of the test solutions, von Frey and treadmill tests were conducted for 3 weeks. Subsequently, histopathologic examinations were conducted in the V, S, P5, and P10 groups.

Results

A total of 65 rats were included. The P8 and P10 groups showed significant recovery from mechanical allodynia and motor dysfunction at all time points after drug administration compared to the V group. These effects were abolished by concomitant administration of DMPX. On histopathological examination, no epineurial inflammation or fibrosis was observed in the epidural PDRN groups.

Conclusions

Epidural injection of PDRN significantly improves mechanical allodynia and motor dysfunction in a rat model of LFS, which is mediated by the spinal adenosine A_2A receptor. The present data support the need for further research to determine the role of epidural PDRN in spinal stenosis treatment.

Effects of a low-carbohydrate ketogenic diet on reported pain, blood biomarkers and quality of life in patients with chronic pain: A pilot randomised clinical trial

BACKGROUND

A low-carbohydrate ketogenic diet has been reported to improve chronic pain by reducing inflammation, oxidative stress, and sensitivity within the nervous system. The main aim of this trial is to evaluate the effects of a ketogenic diet on reported pain, blood biomarkers and quality of life in patients with chronic pain.

METHODS

Participants with chronic musculoskeletal pain were recruited for a 12-week diet intervention that commenced with a 3-week run-in diet removing ultra-processed foods, followed by randomisation to either a whole-food/well-formulated ketogenic diet (WFKD) or to continue with the minimally processed whole-food diet (WFD). Outcome measures included: average pain (visual analogue scale VAS), blood biomarkers, anthropometrics, adherence, depression, anxiety, sleep, ketones, quality of life, diet satisfaction and macronutrient intake.

RESULTS

Average weekly pain improved for both groups. WFKD group VAS reduced by 17.9 ± 5.2 mm (p = 0.004) and the WFD group VAS reduced 11.0 ± 9.0 mm (p = 0.006). Both groups also reported improved quality of life (WFKD = 11.5 ± 2.8%, p = 0.001 and WFD = 11.0 ± 3.5%, p = 0.014). The WFKD group also demonstrated significant improvements in pain interference (p = 0.013), weight (p < 0.005), depression (p = 0.015), anxiety (p = 0.013), and inflammation (hsCRP) (p = 0.009). Significant average pain reduction remained at three-month follow-up for both groups (WFKD p = 0.031, WFD p = 0.011).

CONCLUSION

The implementation of a whole-food diet that restricts ultra-processed foods is a valid pain management tool, however a low-carbohydrate ketogenic diets may have potentially greater pain reduction, weight loss and mood improvements.

Neuro-immune signatures in chronic low back pain subtypes

We recently showed that patients with different chronic pain conditions (such as chronic low back pain, fibromyalgia, migraine, and Gulf War Illness) demonstrated elevated brain and/or spinal cord levels of the glial marker 18 kDa translocator protein, which suggests that neuroinflammation might be a pervasive phenomenon observable across multiple etiologically heterogeneous pain disorders. Interestingly, the spatial distribution of this neuroinflammatory signal appears to exhibit a degree of disease specificity (e.g. with respect to the involvement of the primary somatosensory cortex), suggesting that different pain conditions may exhibit distinct "neuroinflammatory signatures". To further explore this hypothesis, we tested whether neuroinflammatory signal can characterize putative etiological subtypes of chronic low back pain patients based on clinical presentation. Specifically, we explored neuroinflammation in patients whose chronic low back pain either did or did not radiate to the leg (i.e. "radicular" vs. "axial" back pain). Fifty-four chronic low back pain patients, twenty-six with axial back pain (43.7 ± 16.6 y.o. [mean±SD]) and twenty-eight with radicular back pain (48.3 ± 13.2 y.o.), underwent PET/MRI with [11C]PBR28, a second-generation radioligand for the 18 kDa translocator protein. [11C]PBR28 signal was quantified using standardized uptake values ratio (validated against volume of distribution ratio; n = 23). Functional MRI data were collected simultaneously to the [11C]PBR28 data 1) to functionally localize the primary somatosensory cortex back and leg subregions and 2) to perform functional connectivity analyses (in order to investigate possible neurophysiological correlations of the neuroinflammatory signal). PET and functional MRI measures were compared across groups, cross-correlated with one another and with the severity of "fibromyalgianess" (i.e. the degree of pain centralization, or "nociplastic pain"). Furthermore, statistical mediation models were employed to explore possible causal relationships between these three variables. For the primary somatosensory cortex representation of back/leg, [11C]PBR28 PET signal and functional connectivity to the thalamus were: 1) higher in radicular compared to axial back pain patients, 2) positively correlated with each other and 3) positively correlated with fibromyalgianess scores, across groups. Finally, 4) fibromyalgianess mediated the association between [11C]PBR28 PET signal and primary somatosensory cortex-thalamus connectivity across groups. Our findings support the existence of "neuroinflammatory signatures" that are accompanied by neurophysiological changes, and correlate with clinical presentation (in particular, with the degree of nociplastic pain) in chronic pain patients. These signatures may contribute to the subtyping of distinct pain syndromes and also provide information about inter-individual variability in neuro-immune brain signals, within diagnostic groups, that could eventually serve as targets for mechanism-based precision medicine approaches.

Cross-Disorder Genomics Data Analysis Elucidates a Shared Genetic Basis Between Major Depression and Osteoarthritis Pain

Osteoarthritis (OA) and major depression (MD) are two debilitating disorders that frequently co-occur and affect millions of the elderly each year. Despite the greater symptom severity, poorer clinical outcomes, and increased mortality of the comorbid conditions, we have a limited understanding of their etiologic relationships. In this study, we conducted the first cross-disorder investigations of OA and MD, using genome-wide association data representing over 247K cases and 475K controls. Along with significant positive genome-wide genetic correlations (r g = 0.299 ± 0.026, p = 9.10 × 10-31), Mendelian randomization (MR) analysis identified a bidirectional causal effect between OA and MD (βOA → MD = 0.09, SE = 0.02, z-score p-value < 1.02 × 10-5; βMD → OA = 0.19, SE = 0.026, p < 2.67 × 10-13), indicating genetic variants affecting OA risk are, in part, shared with those influencing MD risk. Cross-disorder meta-analysis of OA and MD identified 56 genomic risk loci (P meta ≤ 5 × 10-8), which show heightened expression of the associated genes in the brain and pituitary. Gene-set enrichment analysis highlighted "mechanosensory behavior" genes (GO:0007638; P gene_set = 2.45 × 10-8) as potential biological mechanisms that simultaneously increase susceptibility to these mental and physical health conditions. Taken together, these findings show that OA and MD share common genetic risk mechanisms, one of which centers on the neural response to the sensation of mechanical stimulus. Further investigation is warranted to elaborate the etiologic mechanisms of the pleiotropic risk genes, as well as to develop early intervention and integrative clinical care of these serious conditions that disproportionally affect the aging population.

[Entrapment neuropathies: a contemporary approach to pathophysiology, clinical assessment, and management : German version]

Entrapment neuropathies such as carpal tunnel syndrome, radiculopathies, or radicular pain are the most common peripheral neuropathies and also the most common cause for neuropathic pain. Despite their high prevalence, they often remain challenging to diagnose and manage in a clinical setting. Summarising the evidence from both preclinical and clinical studies, this review provides an update on the aetiology and pathophysiology of entrapment neuropathies. Potenzial mechanisms are put in perspective with clinical findings. The contemporary assessment is discussed and diagnostic pitfalls highlighted. The evidence for the noninvasive and surgical management of common entrapment neuropathies is summarised and future areas of research are identified.

Effects of Dorsal Column Spinal Cord Stimulation on Neuroinflammation: Revisiting Molecular Mechanisms and Clinical Outcomes on Chronic Lumbar/Leg Pain and Failed Back Surgery Syndrome

OBJECTIVE

In this narrative review, we reviewed and discussed current literature describing the molecular mechanisms leading to neuroinflammation and its role in the onset and progression of chronic neuropathic lumbar and leg pain in patients with persistent spinal pain syndrome. In addition, we reviewed the proposed mechanisms and impact of spinal cord stimulation (SCS) on neuroinflammation.

METHODS

A broad search of current literature in PubMed, Embase, Scopus, Cochrane library, Medline/Ovid, and Web of Science was performed using the following terms and their combinations: "biomarkers", "chronic back and leg pain", "cytokines", "neuroinflammation", "spinal cord stimulation (scs)," and "spinal cord modulation". We selected: 1) articles published in the English language between January 2000 and July 2020 2) preclinical and clinical data 3) case reports 4) meta-analysis and systematic reviews and 5) conference abstracts. Manuscripts not disclosing methodology or without full-text availability were excluded.

DISCUSSION

SCS techniques have gradually evolved since inception to include novel methods such as burst-SCS, high frequency SCS, and differential targeted multiplexed SCS. The incidence of chronic pain after spine surgery is highly variable, with at least one third of patients developing persistent spinal pain syndrome. Novel SCS techniques have been associated with improved clinical and functional outcomes thus increasing patient quality of life.

CONCLUSION

Currently, health care providers rely on different options and methods for SCS when treating patients with refractory chronic lumbar pain and persistent spinal pain syndrome. Nevertheless, compelling clinical trials remain necessary to elucidate the long-term benefits and mechanisms of neuromodulation of all different types of SCS.

Thalamic neurometabolite alterations in patients with knee osteoarthritis before and after total knee replacement

ABSTRACT

The weak association between disability levels and "peripheral" (ie, knee) findings suggests that central nervous system alterations may contribute to the pathophysiology of knee osteoarthritis (KOA). Here, we evaluated brain metabolite alterations in patients with KOA, before and after total knee arthroplasty (TKA), using 1H-magnetic resonance spectroscopy (MRS). Thirty-four presurgical patients with KOA and 13 healthy controls were scanned using a PRESS sequence (TE = 30 ms, TR = 1.7 seconds, voxel size = 15 × 15 × 15 mm). In addition, 13 patients were rescanned 4.1 ± 1.6 (mean ± SD) weeks post-TKA. When using creatine (Cr)-normalized levels, presurgical KOA patients demonstrated lower N-acetylaspartate (NAA) (P < 0.001), higher myoinositol (mIns) (P < 0.001), and lower Choline (Cho) (P < 0.05) than healthy controls. The mIns levels were positively correlated with pain severity scores (r = 0.37, P < 0.05). These effects reached statistical significance also using water-referenced concentrations, except for the Cho group differences (P ≥ 0.067). Post-TKA patients demonstrated an increase in NAA (P < 0.01), which returned to the levels of healthy controls (P > 0.05), irrespective of metric. In addition, patients demonstrated postsurgical increases in Cr-normalized (P < 0.001), but not water-referenced mIns, which were proportional to the NAA/Cr increases (r = 0.61, P < 0.05). Because mIns is commonly regarded as a glial marker, our results are suggestive of a possible dual role for neuroinflammation in KOA pain and post-TKA recovery. Moreover, the apparent postsurgical normalization of NAA, a putative marker of neuronal integrity, might implicate mitochondrial dysfunction, rather than neurodegenerative processes, as a plausible pathophysiological mechanism in KOA. More broadly, our results add to a growing body of literature suggesting that some pain-related brain alterations can be reversed after peripheral surgical treatment.

Spinal nerve signal intensity on Dixon T2-weighted water-only sequence: an important outcome predictor after lumbar transforaminal epidural injection

OBJECTIVES

To evaluate the role of Dixon T2-weighted water-fat separation technique in predicting the outcome of lumbar transforaminal epidural injections (TFESIs).

METHODS

Patients who underwent TFESI of a single spinal nerve within 3 months after magnetic resonance imaging (MRI) exam between August 2018 and April 2020 were identified. The patients were classified into positive or negative outcome groups based on the response to the TFESI procedure. Two musculoskeletal radiologists measured the signal intensity of the injected side spinal nerves, contralateral side spinal nerves, and subcutaneous fat on axial Dixon T2-weighted water-only images, and the diameter of spinal nerve on axial Dixon T2-weighted in-phase images of the pre-procedural MRI. The measured values of the injected side spinal nerves were compared between the two groups and with the contralateral side spinal nerve.

RESULTS

A total of 94 patients were included, 76 in the positive outcome group and 18 in the negative outcome group. The mean signal intensity and the nerve-to-fat signal ratio of the injected side spinal nerve were significantly higher in the positive outcome group than in the negative outcome group (793.78 vs. 679.19, p = 0.016; 4.21 vs. 3.28, p = 0.003). In the positive outcome group, the diameter of the spinal nerve was significantly higher on the injected side than on the contralateral side (6.91 mm vs. 6.37 mm, p = 0.016).

CONCLUSIONS

The mean signal intensity and the nerve-to-fat signal ratio of the spinal nerve on axial Dixon T2-weighted water-only images can help predict patient response to the TFESI.

KEY POINTS

• Applying the Dixon technique to lumbar spine MRI can help predict patient response to the TFESI procedure. • An increased nerve-to-fat signal ratio and mean spinal nerve signal intensity on axial Dixon T2-weighted water-only images predicted favorable TFESI outcomes.

Effects of joint and nerve mobilisation on neuroimmune responses in animals and humans with neuromusculoskeletal conditions: a systematic review and meta-analysis

Supplemental Digital Content is Available in the Text.

There is evidence that joint and nerve mobilisations compared with sham or no intervention positively influence various neuroimmune responses in animal and human neuromusculoskeletal conditions.

Several animal and human studies revealed that joint and nerve mobilisations positively influence neuroimmune responses in neuromusculoskeletal conditions. However, no systematic review and meta-analysis has been performed. Therefore, this study aimed to synthesize the effects of joint and nerve mobilisation compared with sham or no intervention on neuroimmune responses in animals and humans with neuromusculoskeletal conditions. Four electronic databases were searched for controlled trials. Two reviewers independently selected studies, extracted data, assessed the risk of bias, and graded the certainty of the evidence. Where possible, meta-analyses using random effects models were used to pool the results. Preliminary evidence from 13 animal studies report neuroimmune responses after joint and nerve mobilisations. In neuropathic pain models, meta-analysis revealed decreased spinal cord levels of glial fibrillary acidic protein, dorsal root ganglion levels of interleukin-1β, number of dorsal root ganglion nonneuronal cells, and increased spinal cord interleukin-10 levels. The 5 included human studies showed mixed effects of spinal manipulation on salivary/serum cortisol levels in people with spinal pain, and no significant effects on serum β-endorphin or interleukin-1β levels in people with spinal pain. There is evidence that joint and nerve mobilisations positively influence various neuroimmune responses. However, as most findings are based on single studies, the certainty of the evidence is low to very low. Further studies are needed.