Predicting transition to chronic pain

Bringing Endometriosis to the Road of Contemporary Pain Science

BACKGROUND

Endometriosis pain is mainly understood based on peripheral lesion characteristics and an outdated perspective equating nociception with pain. This limited view may divert understanding of interventions beyond peripheral logic, leading clinicians to see approaches targeting other processes as supplementary, limiting the effective addressing of treatment failure. Integrating critical advancements in pain and endometriosis can promote more comprehensive knowledge.

OBJECTIVES

This article provides a conceptual framework focusing on overlooked or less clearly linked areas concerning the interplay between nociception and factors influencing endometriosis pain. It explores the complexity of nociceptive processing, the association between neuromerically connected structures, and the role of the brain in pain perception. Further, it emphasizes adopting mechanism-based understanding of pain that integrates neurobiological aspects of the nociceptive apparatus and related systems, shaped by psychosocial factors contributing to a possible negative spiral in those living with endometriosis.

CONCLUSION

Aware of such a broader perspective can incentivize a balanced effort to inquire into peripheral lesion-related mechanisms and other domains potentially impacting endometriosis pain.

The phenotype of recovery XII: A reinforcer pathology perspective on associations between delay discounting and pain catastrophizing in substance use disorder recovery

BACKGROUND

Substance use disorder (SUD) and pain are highly comorbid conditions and several pain indices (e.g., pain intensity) are associated with an increased risk of relapse. However, the cognitive-emotional experience of pain (i.e., pain catastrophizing) is understudied in SUD recovery. Further, how the association between pain catastrophizing and delay discounting - a posited biomarker of addiction, impacts multidimensional aspects of SUD recovery, including remission and quality of life (QOL), has yet to be examined.

METHODS

Individuals (n = 170) in SUD recovery reporting pain were asked about their chronic pain status, completed the Brief Pain Inventory, the Pain Catastrophizing Scale, an Adjusting Amount Delay Discounting Task, and the World Health Organization QOL-BREF scale. Univariate logistic and linear regressions examined associations between delay discounting and several pain indices with remission and QOL. Mediation analyses were investigated whether pain catastrophizing mediates the relationship between delay discounting and 1) sustained remission and 2) QOL.

RESULTS

Significant negative associations were found between delay discounting (p < .001) and pain catastrophizing (p = .001) with sustained remission. Pain catastrophizing significantly mediated the relationship between delay discounting and physical QOL (p = .044), psychological QOL (p = .009), social (p = .018), and environmental QOL (p = .014). Pain catastrophizing did not mediate the relationship between DD and sustained remission.

CONCLUSION

Individuals with greater DD exhibited greater pain catastrophizing, contributing to poorer QOL in SUD recovery. Our findings support that a Reinforcer Pathology framework is useful to understanding the cognitive-emotional experience of pain within the context of SUD recovery. Interventions that target both delay discounting and maladaptive cognitive and emotional responses to pain may lessen the negative impact of pain on SUD recovery and improve SUD outcomes.

Pain severity contributes to worse outcomes in opioid use disorder recovery than pain status

BACKGROUND

Opioid use disorder (OUD) continues to pose a significant challenge to public health in the United States. Chronic pain and OUD are highly comorbid conditions, yet few studies have examined the relative associations of pain status and severity toward multidimensional OUD recovery outcomes (e.g., psychopathology and withdrawal).

METHODS

Participants (N = 214) were from the RECOVER-LT study, conducted 4.2-years after completion of a clinical trial program assessing extended-release buprenorphine. Group differences by pain status (i.e., chronic, acute, or no pain) were evaluated in this cross-sectional data set using analysis of variance and Fisher's exact test. Linear regression was utilized to understand the associations between average pain severity and recovery outcomes. Model selection was performed to examine the relative importance of pain status and average pain severity to recovery outcomes.

RESULTS

A majority of the sample endorsed chronic pain (73.8 %). The multivariate regression analysis with model selection found that higher average pain severity (p < .001), but not pain status, was significantly associated with the multidimensional recovery outcomes greater total number of DSM-5 OUD symptoms, higher opioid withdrawal score, reduced physical quality of life, higher depressive symptoms, negative affect, and greater psychological distress. Pain status and average pain severity were not associated with past 7- or 30-day opioid use (p > 0.001).

CONCLUSIONS

These findings highlight pain severity, but not pain status, as a key dimension of OUD recovery. This suggests a need for integration of OUD treatment and pain management, particularly for individuals experiencing elevated pain severity regardless of pain status.

Impact of different treatments for chronic pain on cognitive function: A systematic review

Introduction

Experimental evidence supports the hypothesis of reciprocal influence between neural systems involved in cognition and central pain processing circuits. Furthermore, studies have demonstrated bidirectional communication between central pain processing areas and the immune system, leading to changes in behaviour, sensory perception, mood, and cognition. However, the academic community has not yet reached a consensus on whether effective analgesic interventions can mitigate or reverse cognitive deterioration.

Methods

This systematic review evaluated the effectiveness of various therapeutic interventions in improving cognitive functions (primary outcome) and altering the profile of immunological markers (secondary outcome) in chronic pain patients. The review was limited to randomised controlled trials addressing chronic pain of any aetiology, with searches conducted in PubMed, EMBASE, and Scopus databases.

Results

The qualitative synthesis of twelve studies conducted between 2003 and 2021, involving 1432 participants in experimental (n = 950) and control (n = 482) groups, revealed some interesting patterns. Only half of the studies (6/12) reported cognitive improvement, with attention being the most analysed cognitive domain, followed by memory and executive function. Fibromyalgia was the most studied aetiology of chronic pain. The strategies of intervention/treatment and durations varied widely; however, milnacipran versus placebo emerged as the most frequently employed intervention. Only one study reported immunological markers, limiting the evaluation of this outcome.

Conclusion

Based on this analysis, it is not possible to affirm that interventions targeting chronic pain improve cognition. This review suggests new research directions and calls for more robust methodological approaches.

Nucleus accumbens myocyte enhancer factor 2C mediates the maintenance of peripheral nerve injury-induced physiological and behavioral maladaptations

ABSTRACT

Preclinical and clinical work has demonstrated altered plasticity and activity in the nucleus accumbens (NAc) under chronic pain states, highlighting critical therapeutic avenues for the management of chronic pain conditions. In this study, we demonstrate that myocyte enhancer factor 2C (MEF2C), a master regulator of neuronal activity and plasticity, is repressed in NAc neurons after prolonged spared nerve injury (SNI). Viral-mediated overexpression of Mef2c in NAc neurons partially ameliorated sensory hypersensitivity and emotional behaviors in mice with SNI, while also altering transcriptional pathways associated with synaptic signaling. Mef2c overexpression also reversed SNI-induced potentiation of phasic dopamine release and neuronal hyperexcitability in the NAc. Transcriptional changes induced by Mef2c overexpression were different than those observed after desipramine treatment, suggesting a mechanism of action different from antidepressants. Overall, we show that interventions in MEF2C-regulated mechanisms in the NAc are sufficient to disrupt the maintenance of chronic pain states, providing potential new treatment avenues for neuropathic pain.

Altered structure and functional connection of subcortical gray matter in female patients with classical trigeminal neuralgia

The etiology of classical trigeminal neuralgia (CTN) is still unclear. A better understanding of the cerebral structural and functional changes in female patients with CTN may provide important novel insights into the pathophysiologic mechanisms of female CTN. A total 37 female CTN patients were included and referred to MRI scans, comprising with 19 left CTN and 18 right CTN patients. We analyzed the volume and shape of subcortical gray matter (GM), and the functional connectivity (FC) between the accumbens nucleus (NAc) and whole brain in right and left CTN patients respectively. We found left CTN patients had a reduced right NAc volume compared to controls, similarly, the right CTN had the decreased volume in the left NAc. Vertex-wise shapes of right NAc in left CTN patients showed significant regional shape deformation on the anterior, medial and ventroposterior aspects, in contrast, left NAc of right CTN patients showed significant regional shape deformation on the anterior and posterior aspect. Furthermore, patients with left CTN showed significantly lower FC between the right NAc and right orbitofrontal cortex than control subjects. The volume of NAc in all CTN was significantly related to the perception of present pain intensity. The CTN might be majorly caused by volume reduction in NAc. A greater understanding of the neurobiological basis of pain-related changes in NAc will provide the knowledge for the development of novel NAc based therapeutic targets for pain management or even prevention in CTN patients.

Neuroanatomy of the nociceptive system: From nociceptors to brain networks

This chapter reviews the neuroanatomy of the nociceptive system and its functional organization. We describe three main compartments of the nervous system that underlie normal nociception and the resulting pain percept: Peripheral, Spinal Cord, and Brain. We focus on how ascending nociceptive processing streams traverse these anatomical compartments, culminating in the multidimensional experience of pain. We also describe neuropathic pain conditions, in which nociceptive processing is abnormal, not only because of the primary effects of a lesion or disease affecting peripheral nerves or the central nervous system (CNS), but also due to secondary effects on ascending pathways and brain networks. We discuss how the anatomical components (circuits/networks) reorganize under various etiologies of neuropathic pain and how these changes can give rise to pathological pain states.

Altered Endogenous Pain-Inhibitory Function in Older Adults With Chronic Pain Is Associated With Disruptions in Functional Connectivity During Resting State

Increasing research points to a decline in the ability to internally regulate pain as a contributing factor to the increased pain susceptibility in aging. This study investigated the connection between pain regulation and resting-state functional connectivity (rsFC) in older adults with chronic pain. We compared functional magnetic resonance imaging rsFC of 30 older adults with chronic pain (69.5 ± 6.58 years, 14 males), 29 pain-free older (70.48 ± 4.60, 15 males), and 30 younger adults (20.0 ± 1.58, 15 males). Pain inhibition and facilitatory capabilities were assessed using conditioned pain modulation (CPM) and temporal summation. Older adults with chronic pain displayed lower pain inhibition during the CPM than pain-free older and younger adults. rsFC analysis showed that older adults with chronic pain, in comparison with younger participants, displayed an abnormal hyperconnectivity between right dorsolateral prefrontal cortex and left amygdala, which was significantly correlated with lower pain inhibition during the CPM. Older adults with chronic pain displayed higher connectivity between the primary somatosensory cortex and nucleus accumbens than pain-free older adults. Finally, both older adult groups displayed reduced connectivity between brain structures involved in pain inhibition and processing in comparison with younger adults. Altogether, our results suggest that suffering from pain during aging leads to a dysfunction of pain-inhibitory processes, which significantly surpass those caused by normal aging. Furthermore, our results point to a key role of emotional and motivational brain areas, and their interaction with executive and somatosensory areas, in the reduced inhibitory capacity and likely the maintenance of chronic pain in aging. PERSPECTIVE: This study examines the link between reduced pain-inhibition capacity and increased resting-state connectivity between affective, sensory, and executive brain structures in older adults with chronic pain. These findings could inform new pain assessment and treatment programs for this population.

Biobehavioral Predictors of Pain Intensity, Pain Interference, and Chronic Pain Episodes: A Prospective Cohort Study of African-American Adults

Racial disparities in pain experiences are well-established, with African-American (AA) adults reporting higher rates of daily pain, increased pain severity, and greater pain-related interference compared to non-Hispanic Whites. However, the biobehavioral factors that predict the transition to chronic pain among AA adults are not well understood. This prospective cohort study provided a unique opportunity to evaluate predictors of chronic pain onset among 130 AA adults (81 women), ages 18 to 44, who did not report chronic pain at their baseline assessment and subsequently completed follow-up assessments at 6- and 12-months. Outcome measures included pain intensity, pain-related interference, and chronic pain status. Comprehensive assessments of sociodemographic and biobehavioral factors were used to evaluate demographics, socioeconomic status, stress exposure, psychosocial factors, prolonged hypothalamic-pituitary-adrenal secretion, and quantitative sensory testing responses. At baseline, 30 adults (23.1%) reported a history of prior chronic pain. Over the 12-month follow-up period, 13 adults (10.0%) developed a new chronic pain episode, and 18 adults (13.8%) developed a recurrent chronic pain episode. Whereas socioeconomic status measures (ie, annual income, education) predicted changes in pain intensity over the follow-up period, quantitative sensory testing measures (ie, pain threshold, temporal summation of pain) predicted changes in pain interference. A history of chronic pain and higher depressive symptoms at baseline independently predicted the onset of a new chronic pain episode. The present findings highlight distinct subsets of biobehavioral factors that are differentially associated with trajectories of pain intensity, pain-related interference, and onset of chronic pain episodes in AA adults. PERSPECTIVE: This prospective study sought to advance understanding of biobehavioral factors that predicted pain outcomes over a 12-month follow-up period among AA adults without chronic pain at their initial assessment. Findings revealed distinct subsets of factors that were differentially associated with pain intensity, pain-related interference, and onset of chronic pain episodes.

Chronic Postsurgical Pain in Children and Adolescents: A Call for Action

Chronic postsurgical pain (CPSP) affects a significant proportion of children and adolescents after major surgery and is a detriment to both short- and long-term recovery outcomes. While clinical characteristics and psychosocial risk factors for developing CPSP in children and adults are well established in the literature, there has been little progress on the prevention and management of CPSP after pediatric surgery. Limited evidence to support current pharmacologic approaches suggests a fundamentally new paradigm must be considered by clinicians to both conceptualize and address this adverse complication. This narrative review provides a comprehensive evaluation of both the known and emerging mechanisms that support our current understanding of CPSP. Additionally, we discuss the importance of optimizing perioperative analgesic strategies to mitigate CPSP based on individual patient risks. We highlight the importance of postoperative pain trajectories to identify those most at risk for developing CPSP, the early referral to multi-disciplinary pain clinics for comprehensive evaluation and treatment of CPSP, and additional work needed to differentiate CPSP characteristics from other chronic pain syndromes in children. Finally, we recognize ongoing challenges associated with the universal implementation of available knowledge about pediatric CPSP into practically useful care plans for clinicians.

Pain mechanisms in the transgender individual: a review

Specific Aim

Provide an overview of the literature addressing major areas pertinent to pain in transgender persons and to identify areas of primary relevance for future research.

Methods

A team of scholars that have previously published on different areas of related research met periodically though zoom conferencing between April 2021 and February 2023 to discuss relevant literature with the goal of providing an overview on the incidence, phenotype, and mechanisms of pain in transgender patients. Review sections were written after gathering information from systematic literature searches of published or publicly available electronic literature to be compiled for publication as part of a topical series on gender and pain in the Frontiers in Pain Research.

Results

While transgender individuals represent a significant and increasingly visible component of the population, many researchers and clinicians are not well informed about the diversity in gender identity, physiology, hormonal status, and gender-affirming medical procedures utilized by transgender and other gender diverse patients. Transgender and cisgender people present with many of the same medical concerns, but research and treatment of these medical needs must reflect an appreciation of how differences in sex, gender, gender-affirming medical procedures, and minoritized status impact pain.

Conclusions

While significant advances have occurred in our appreciation of pain, the review indicates the need to support more targeted research on treatment and prevention of pain in transgender individuals. This is particularly relevant both for gender-affirming medical interventions and related medical care. Of particular importance is the need for large long-term follow-up studies to ascertain best practices for such procedures. A multi-disciplinary approach with personalized interventions is of particular importance to move forward.

Adolescents' pain-related ontogeny shares a neural basis with adults' chronic pain in basothalamo-cortical organization

During late adolescence, the brain undergoes ontogenic organization altering subcortical-cortical circuitry. This includes regions implicated in pain chronicity, and thus alterations in the adolescent ontogenic organization could predispose to pain chronicity in adulthood - however, evidence is lacking. Using resting-state functional magnetic resonance imaging from a large European longitudinal adolescent cohort and an adult cohort with and without chronic pain, we examined links between painful symptoms and brain connectivity. During late adolescence, thalamo-, caudate-, and red nucleus-cortical connectivity were positively and subthalamo-cortical connectivity negatively associated with painful symptoms. Thalamo-cortical connectivity, but also subthalamo-cortical connectivity, was increased in adults with chronic pain compared to healthy controls. Our results indicate a shared basis in basothalamo-cortical circuitries between adolescent painful symptomatology and adult pain chronicity, with the subthalamic pathway being differentially involved, potentially due to a hyperconnected thalamo-cortical pathway in chronic pain and ontogeny-driven organization. This can inform neuromodulation-based prevention and early intervention.

Development, Insults and Predisposing Factors of the Brain's Predictive Coding System to Chronic Perceptual Disorders-A Life-Course Examination

The predictive coding theory is currently widely accepted as the theoretical basis of perception and chronic perceptual disorders are explained as the maladaptive compensation of the brain to a prediction error. Although this gives us a general framework to work with, it is still not clear who may be more susceptible and/or vulnerable to aberrations in this system. In this paper, we study changes in predictive coding through the lens of tinnitus and pain. We take a step back to understand how the predictive coding system develops from infancy, what are the different neural and bio markers that characterise this system in the acute, transition and chronic phases and what may be the factors that pose a risk to the aberration of this system. Through this paper, we aim to identify people who may be at a higher risk of developing chronic perceptual disorders as a reflection of aberrant predictive coding, thereby giving future studies more facets to incorporate in their investigation of early markers of tinnitus, pain and other disorders of predictive coding. We therefore view this paper to encourage the thinking behind the development of preclinical biomarkers to maladaptive predictive coding.

Treating persistent pain after breast cancer: practice gaps and future directions

This paper discusses the growing problem of persisting pain after successful treatment of breast cancer and presents recommendations for improving pain-related outcomes for this group. We discuss the dominant treatment approach for persisting pain post-breast cancer treatment and draw contrasts with contemporary treatment approaches to persistent pain in non-cancer-related populations. We discuss modern application of the biopsychosocial model of pain and the notion of variable sensitivity within the pain system, moment by moment and over time. We present the implications of increasing sensitivity over time for treatment selection and implementation. By drawing on transformative changes in treatment approaches to persistent non-cancer-related pain, we describe the potentially powerful role that an intervention called pain science education, which is now recommended in clinical guidelines for musculoskeletal pain, may play in improving pain and disability outcomes after successful breast cancer treatment. Finally, we present several research recommendations that centre around adaptation of the content and delivery models of contemporary pain science education, to the post-breast cancer context.

Chronic fatigue syndromes: real illnesses that people can recover from

The 'Oslo Chronic Fatigue Consortium' consists of researchers and clinicians who question the current narrative that chronic fatigue syndromes, including post-covid conditions, are incurable diseases. Instead, we propose an alternative view, based on research, which offers more hope to patients. Whilst we regard the symptoms of these conditions as real, we propose that they are more likely to reflect the brain's response to a range of biological, psychological, and social factors, rather than a specific disease process. Possible causes include persistent activation of the neurobiological stress response, accompanied by associated changes in immunological, hormonal, cognitive and behavioural domains. We further propose that the symptoms are more likely to persist if they are perceived as threatening, and all activities that are perceived to worsen them are avoided. We also question the idea that the best way to cope with the illness is by prolonged rest, social isolation, and sensory deprivation.Instead, we propose that recovery is often possible if patients are helped to adopt a less threatening understanding of their symptoms and are supported in a gradual return to normal activities. Finally, we call for a much more open and constructive dialogue about these conditions. This dialogue should include a wider range of views, including those of patients who have recovered from them.

Neural and Psychosocial Mechanisms Underlying Alcohol Use and Pain Interactions: Overview of Current Evidence and Future Directions

Purpose of Review

A growing body of research indicates bidirectional associations between alcohol use and pain. In this review, we highlight common neural and psychosocial mechanisms underlying pain and alcohol use and identify current gaps in the literature regarding alcohol/pain interactions. We also suggest future directions for the field moving forward, including more nuanced conceptualization of alcohol's negative reinforcing effects in the context of pain, broader use of clinically-relevant experimental pain induction modalities, and characterization of age, biological sex, gender, race, and ethnicity as moderators of pain/alcohol interactions.

Recent Findings

Acute alcohol intake has analgesic and negative-reinforcing effects in the context of pain, and chronic heavy alcohol use appears to increase risk for development of chronic pain. At the same time, pain, both acute and chronic, acts as a proximal antecedent for alcohol use and is associated with relapse risk for individuals in recovery from alcohol use disorder.

Summary

Although the links between alcohol use and pain are increasingly appreciated, significant gaps in understanding remain and systematic study of alcohol/pain interactions at all levels, including basic, preclinical, translational, and interventional, is needed.

Does Multisession Cathodal Transcranial Direct Current Stimulation of the Left Dorsolateral Prefrontal Cortex Prime the Effects of Cognitive Behavioral Therapy on Fear of Pain, Fear of Movement, and Disability in Patients with Nonspecific Low Back Pain? A Randomized Clinical Trial Study

Many studies have shown that low back pain (LBP) is associated with psychosomatic symptoms which may lead to brain changes. This study aimed to investigate the effect of the concurrent application of cognitive behavioral therapy (CBT) and transcranial direct electrical stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) on fear of pain, fear of movement, and disability in patients with nonspecific LBP. This study was performed on 45 LBP patients (23 women, 22 men; mean age 33.00 ± 1.77 years) in three groups: experimental (2 mA cathodal tDCS (c-tDCS)), sham (c-tDCS turned off after 30 s), and control (only received CBT). In all groups, CBT was conducted for 20 min per session, with two sessions per week for four weeks. Fear of pain, fear of movement, and disability were evaluated using questionnaires at baseline, immediately after, and one month after completion of interventions. Results indicated that all three different types of intervention could significantly reduce fear and disability immediately after intervention (p > 0.05). However, improvement in the experimental group was significantly higher than in the other groups immediately after and at the one-month follow-up after interventions (p < 0.05). DLPFC c-tDCS can prime the immediate effects of CBT and also the lasting effects on the reduction in the fear of pain, fear of movement, and disability in LBP patients.

Predicting chronic postsurgical pain: current evidence and a novel program to develop predictive biomarker signatures

ABSTRACT

Chronic pain affects more than 50 million Americans. Treatments remain inadequate, in large part, because the pathophysiological mechanisms underlying the development of chronic pain remain poorly understood. Pain biomarkers could potentially identify and measure biological pathways and phenotypical expressions that are altered by pain, provide insight into biological treatment targets, and help identify at-risk patients who might benefit from early intervention. Biomarkers are used to diagnose, track, and treat other diseases, but no validated clinical biomarkers exist yet for chronic pain. To address this problem, the National Institutes of Health Common Fund launched the Acute to Chronic Pain Signatures (A2CPS) program to evaluate candidate biomarkers, develop them into biosignatures, and discover novel biomarkers for chronification of pain after surgery. This article discusses candidate biomarkers identified by A2CPS for evaluation, including genomic, proteomic, metabolomic, lipidomic, neuroimaging, psychophysical, psychological, and behavioral measures. Acute to Chronic Pain Signatures will provide the most comprehensive investigation of biomarkers for the transition to chronic postsurgical pain undertaken to date. Data and analytic resources generatedby A2CPS will be shared with the scientific community in hopes that other investigators will extract valuable insights beyond A2CPS's initial findings. This article will review the identified biomarkers and rationale for including them, the current state of the science on biomarkers of the transition from acute to chronic pain, gaps in the literature, and how A2CPS will address these gaps.

Current Evidence for Biological Biomarkers and Mechanisms Underlying Acute to Chronic Pain Transition across the Pediatric Age Spectrum

Chronic pain is highly prevalent in the pediatric population. Many factors are involved in the transition from acute to chronic pain. Currently, there are conceptual models proposed, but they lack a mechanistically sound integrated theory considering the stages of child development. Objective biomarkers are critically needed for the diagnosis, risk stratification, and prognosis of the pathological stages of pain chronification. In this article, we summarize the current evidence on mechanisms and biomarkers of acute to chronic pain transitions in infants and children through the developmental lens. The goal is to identify gaps and outline future directions for basic and clinical research toward a developmentally informed theory of pain chronification in the pediatric population. At the outset, the importance of objective biomarkers for chronification of pain in children is outlined, followed by a summary of the current evidence on the mechanisms of acute to chronic pain transition in adults, in order to contrast with the developmental mechanisms of pain chronification in the pediatric population. Evidence is presented to show that chronic pain may have its origin from insults early in life, which prime the child for the development of chronic pain in later life. Furthermore, available genetic, epigenetic, psychophysical, electrophysiological, neuroimaging, neuroimmune, and sex mechanisms are described in infants and older children. In conclusion, future directions are discussed with a focus on research gaps, translational and clinical implications. Utilization of developmental mechanisms framework to inform clinical decision-making and strategies for prevention and management of acute to chronic pain transitions in children, is highlighted.

Exercise therapy for chronic pain: How does exercise change the limbic brain function?

We are exposed to various external and internal threats which might hurt us. The role of taking flexible and appropriate actions against threats is played by "the limbic system" and at the heart of it there is the ventral tegmental area and nucleus accumbens (brain reward system). Pain-related fear causes excessive excitation of amygdala, which in turn causes the suppression of medial prefrontal cortex, leading to chronification of pain. Since the limbic system of chronic pain patients is functionally impaired, they are maladaptive to their situations, unable to take goal-directed behavior and are easily caught by fear-avoidance thinking. We describe the neural mechanisms how exercise activates the brain reward system and enables chronic pain patients to take goal-directed behavior and overcome fear-avoidance thinking. A key to getting out from chronic pain state is to take advantage of the behavioral switching function of the basal nucleus of amygdala. We show that exercise activates positive neurons in this nucleus which project to the nucleus accumbens and promote reward behavior. We also describe fear conditioning and extinction are affected by exercise. In chronic pain patients, the fear response to pain is enhanced and the extinction of fear memories is impaired, so it is difficult to get out of "fear-avoidance thinking". Prolonged avoidance of movement and physical inactivity exacerbate pain and have detrimental effects on the musculoskeletal and cardiovascular systems. Based on the recent findings on multiple bran networks, we propose a well-balanced exercise prescription considering the adherence and pacing of exercise practice. We conclude that therapies targeting the mesocortico-limbic system, such as exercise therapy and cognitive behavioral therapy, may become promising tools in the fight against chronic pain.

Network targets for therapeutic brain stimulation: towards personalized therapy for pain

Precision neuromodulation of central brain circuits is a promising emerging therapeutic modality for a variety of neuropsychiatric disorders. Reliably identifying in whom, where, and in what context to provide brain stimulation for optimal pain relief are fundamental challenges limiting the widespread implementation of central neuromodulation treatments for chronic pain. Current approaches to brain stimulation target empirically derived regions of interest to the disorder or targets with strong connections to these regions. However, complex, multidimensional experiences like chronic pain are more closely linked to patterns of coordinated activity across distributed large-scale functional networks. Recent advances in precision network neuroscience indicate that these networks are highly variable in their neuroanatomical organization across individuals. Here we review accumulating evidence that variable central representations of pain will likely pose a major barrier to implementation of population-derived analgesic brain stimulation targets. We propose network-level estimates as a more valid, robust, and reliable way to stratify personalized candidate regions. Finally, we review key background, methods, and implications for developing network topology-informed brain stimulation targets for chronic pain.

Detection of brain regions responsible for chronic pain in osteoarthritis: an fMRI-based neuroimaging study using deep learning

Introduction

Chronic pain is a multifaceted condition that has yet to be fully comprehended. It is frequently linked with a range of disorders, particularly osteoarthritis (OA), which arises from the progressive deterioration of the protective cartilage that cushions the bone endings over time.

Methods

In this paper, we examine the impact of chronic pain on the brain using advanced deep learning (DL) algorithms that leverage resting-state functional magnetic resonance imaging (fMRI) data from both OA pain patients and healthy controls. Our study encompasses fMRI data from 51 pain patients and 20 healthy subjects. To differentiate chronic pain-affected OA patients from healthy controls, we introduce a DL-based computer-aided diagnosis framework that incorporates Multi-Layer Perceptron and Convolutional Neural Networks (CNN), separately.

Results

Among the examined algorithms, we discovered that CNN outperformed the others and achieved a notable accuracy rate of nearly 85%. In addition, our investigation scrutinized the brain regions affected by chronic pain and successfully identified several regions that have not been mentioned in previous literature, including the occipital lobe, the superior frontal gyrus, the cuneus, the middle occipital gyrus, and the culmen.

Discussion

This pioneering study explores the applicability of DL algorithms in pinpointing the differentiating brain regions in OA patients who experience chronic pain. The outcomes of our research could make a significant contribution to medical research on OA pain patients and facilitate fMRI-based pain recognition, ultimately leading to enhanced clinical intervention for chronic pain patients.

Classification and Diagnosis of Temporomandibular Disorders and Temporomandibular Disorder Pain

Designing classification systems and developing diagnostic criteria for temporomandibular disorders is difficult. An appreciation of the utility and applicability of these entities requires an understanding of the importance of each, the differences between the two, and how they may be optimally operationalized for both clinical and research activities in light of their inherent advantages and limitations. In addition, consideration for adopting newer approaches, such as following ontological and precision-based medicine principles, accounting for genetics/epigenetic and neurobiological factors, and the inclusion of biomarkers will potentially result in more thorough and comprehensive classification systems and diagnostic criteria.

The role of expectations, control and reward in the development of pain persistence based on a unified model

Chronic, or persistent pain affects more than 10% of adults in the general population. This makes it one of the major physical and mental health care problems. Although pain is an important acute warning signal that allows the organism to take action before tissue damage occurs, it can become persistent and its role as a warning signal thereby inadequate. Although per definition, pain can only be labeled as persistent after 3 months, the trajectory from acute to persistent pain is likely to be determined very early and might even start at the time of injury. The biopsychosocial model has revolutionized our understanding of chronic pain and paved the way for psychological treatments for persistent pain, which routinely outperform other forms of treatment. This suggests that psychological processes could also be important in shaping the very early trajectory from acute to persistent pain and that targeting these processes could prevent the development of persistent pain. In this review, we develop an integrative model and suggest novel interventions during early pain trajectories, based on predictions from this model.

A nigro-subthalamo-parabrachial pathway modulates pain-like behaviors

The basal ganglia including the subthalamic nucleus (STN) and substantia nigra pars reticulata (SNr) are involved in pain-related responses, but how they regulate pain processing remains unknown. Here, we identify a pathway, consisting of GABAergic neurons in the SNr (SNr^GABA) and glutamatergic neurons in the STN (STN^Glu) and the lateral parabrachial nucleus (LPB^Glu), that modulates acute and persistent pain states in both male and female mice. The activity of STN neurons was enhanced in acute and persistent pain states. This enhancement was accompanied by hypoactivity in SNr^GABA neurons and strengthening of the STN-LPB glutamatergic projection. Reversing the dysfunction in the SNr^GABA-STN^Glu-LPB^Glu pathway attenuated activity of LPB^Glu neurons and mitigated pain-like behaviors. Therefore, the SNr^GABA-STN^Glu-LPB^Glu pathway regulates pathological pain and is a potential target for pain management.

Relationship between behavioral and mood responses to monetary rewards in a sample of Indian students with and without reported pain

Physical pain has become a major health problem with many university students affected by it worldwide each year. Several studies have examined the prevalence of pain-related impairments in reward processing in Western, Educated, Industrialized, Rich, and Democratic (WEIRD) countries but none of the studies have replicated these findings in a non-western cultural setting. Here, we aimed to investigate the prevalence of physical pain symptoms in a sample of university students in India and replicate our previous study conducted on university students in Switzerland, which showed reduced mood and behavioral responses to reward in students with significant pain symptoms. We grouped students into a sub-clinical (N = 40) and a control group (N = 48) to test the association between pain symptoms and reward processes. We used the Fribourg reward task and the pain sub-scale of the Symptom Checklist (SCL-27-plus) to assess physical symptoms of pain. We found that 45% of the students reported high levels of physical symptoms of pain and interestingly, our ANOVA results did not show any significant interaction between reward and the groups either for mood scores or for outcomes related to performance. These results might yield the first insights that pain-related impairment is not a universal phenomenon and can vary across cultures.

Mindfulness-Based Stress Reduction, Cognitive Behavioral Therapy, and Acupuncture in Chronic Low Back Pain: Protocol for Two Linked Randomized Controlled Trials

BACKGROUND

Nonpharmacologic mind-body therapies have demonstrated efficacy in low back pain. However, the mechanisms underlying these therapies remain to be fully elucidated.

OBJECTIVE

In response to these knowledge gaps, the Stanford Center for Low Back Pain-a collaborative, National Institutes of Health P01-funded, multidisciplinary research center-was established to investigate the common and distinct biobehavioral mechanisms of three mind-body therapies for chronic low back pain: cognitive behavioral therapy (CBT) that is used to treat pain, mindfulness-based stress reduction (MBSR), and electroacupuncture. Here, we describe the design and implementation of the center structure and the associated randomized controlled trials for characterizing the mechanisms of chronic low back pain treatments.

METHODS

The multidisciplinary center is running two randomized controlled trials that share common resources for recruitment, enrollment, study execution, and data acquisition. We expect to recruit over 300 chronic low back pain participants across two projects and across different treatment arms within each project. The first project will examine pain-CBT compared with MBSR and a wait-list control group. The second project will examine real versus sham electroacupuncture. We will use behavioral, psychophysical, physical measure, and neuroimaging techniques to characterize the central pain modulatory and emotion regulatory systems in chronic low back pain at baseline and longitudinally. We will characterize how these interventions impact these systems, characterize the longitudinal treatment effects, and identify predictors of treatment efficacy.

RESULTS

Participant recruitment began on March 17, 2015, and will end in March 2023. Recruitment was halted in March 2020 due to COVID-19 and resumed in December 2021.

CONCLUSIONS

This center uses a comprehensive approach to study chronic low back pain. Findings are expected to significantly advance our understanding in (1) the baseline and longitudinal mechanisms of chronic low back pain, (2) the common and distinctive mechanisms of three mind-body therapies, and (3) predictors of treatment response, thereby informing future delivery of nonpharmacologic chronic low back pain treatments.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02503475; https://clinicaltrials.gov/ct2/show/NCT02503475.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/37823.

Pain "chronification": what is the problem with this model?

OBJECTIVES

There appears to be an unwarranted focus on all chronic pain being a "chronification" of acute pain. Despite a plethora of studies on mechanisms to prevent this "chronification" following surgery, the positive effects have been minimal. An alternate model to explain chronic pain is presented.

METHODS

Research in PUBMED and accessing data from the HUNTpain examination study.

RESULTS

Data from the HUNT pain examination study reveal that less than 25% of individuals with chronic pain in a general population can relate the onset to an acute event. Another theory explaining the origin of chronic pain is that of priming and the accumulation of events that can be predictors along a continuum before chronic pain is apparent. This theory is presented to refocus for better prevention and treatment of chronic pain.

CONCLUSIONS

"Chronification" cannot explain all cases of chronic/persistent pain. The plastic changes in the pain processing system can be seen as a continuum where at some point where an acute pain event is only one of several possible tipping points on this continuum that changes potential pain to perceived pain.

Structural, Functional and Neurochemical Cortical Brain Changes Associated with Chronic Low Back Pain

Chronic low back pain (CLBP) is one of the most prevalent musculoskeletal disorders, being one of the leading contributors to disability worldwide and involving an important economic and social burden. Up to 90% of CLBP is non-specific (not associated with specific injuries), with a chronicity expectation estimated at 10%. Currently, motivational and emotional central circuits are being investigated due to their role in CLBP persistency and chronification. Therefore, this narrative review aimed to summarize the evidence regarding the cortical brain changes described for proposing novel multidisciplinary approaches. Novel advances in neuroimaging techniques demonstrated structural (e.g., decrease in the grey matter located at the dorsolateral prefrontal cortex), functional (e.g., connectivity impairments in those areas involved in pain processing), and neurochemical changes (e.g., decrease in cerebral metabolites). In addition, significant changes were found in the primary somatosensory and motor cortex, contributing to the alteration of low back muscles activation and function.

Graph theory analysis identified two hubs that connect sensorimotor and cognitive and cortical and subcortical nociceptive networks in the non-human primate

Pain perception involves multiple brain regions and networks. Understanding how these brain networks work together is fundamental for appreciating network-wise changes reported in patients with chronic pain disorders. Parcellating pain related networks and understanding their causal relationships is the first step to understand how painful information is processed, integrated, and modulated, and it requires direct manipulation of specific brain regions. Nonhuman primates (NHP) offer an ideal model system to achieve these goals because cortical and subcortical regions in the NHP brain are established based on a variety of different types of data collected in a way that is not feasible or, at least, extremely difficult in humans (i.e., histology data, tract-tracing, intracerebral recordings). In addition, different methodological techniques can also help characterize and further understand these brain cortical and subcortical regions over the course of development. Here we used a heat nociceptive stimulation that is proven to elicit activity of nociceptive neurons in the cortex to refine and parcellate the whole brain nociceptive functional networks, to identify key network hubs, and to characterize network-wise temporal dynamic signatures using high-resolution fMRI. We first functionally localized 24 cortical and subcortical regions that responded to heat nociceptive stimuli (somatosensory area 1/2, area 3a/3b, S2, posterior insula (pIns), anterior insula, area 7b, posterior parietal cortex, anterior cingulate cortex (ACC), prefrontal cortex, caudate, and mediodorsal (MD) and ventral posterior lateral (VPL) thalamic nuclei) and used them as seeds in resting state fMRI (rsfMRI) data analysis. We applied both hierarchical clustering and graph-theory analyses of the pairwise rsfMRI correlation metrics and identified five cortical and one subcortical sub-networks: strong resting state functional connectivity (rsFC) between ACC and prefrontal regions, parietal cortex and area 7b, S2 and posterior insula, areas 3a/3b and 1/2 within the S1 cortex, and thalamic MD and caudate nuclei. The rsFC strengths between cortical areas within each subnetwork were significantly stronger than those between subcortical regions. Regions within each sub-network also exhibited highly correlated temporal dynamics at rest, but the overall dynamic patterns varied drastically across sub-networks. Graph-theory analysis identified the MD nucleus as a hub that connects subcortical and cortical nociceptive sub-networks. The S2-pIns connection joins the sensory and affective/cognitive sub-networks.

Impaired pain-related threat and safety learning in patients with chronic back pain

ABSTRACT

Pain-related learning mechanisms likely play a key role in the development and maintenance of chronic pain. Previous smaller-scale studies have suggested impaired pain-related learning in patients with chronic pain, but results are mixed, and chronic back pain (CBP) particularly has been poorly studied. In a differential conditioning paradigm with painful heat as unconditioned stimuli, we examined pain-related acquisition and extinction learning in 62 patients with CBP and 61 pain-free healthy male and female volunteers using valence and contingency ratings and skin conductance responses. Valence ratings indicate significantly reduced threat and safety learning in patients with CBP, whereas no significant differences were observed in contingency awareness and physiological responding. Moreover, threat learning in this group was more impaired the longer patients had been in pain. State anxiety was linked to increased safety learning in healthy volunteers but enhanced threat learning in the patient group. Our findings corroborate previous evidence of altered pain-related threat and safety learning in patients with chronic pain. Longitudinal studies exploring pain-related learning in (sub)acute and chronic pain are needed to further unravel the role of aberrant pain-related learning in the development and maintenance of chronic pain.

Prognostic Factors for Quality of Life After Interdisciplinary Pain Rehabilitation in Patients with Chronic Pain-A Systematic Review

BACKGROUND

Health-related quality of life (hrQoL) is a core outcome in evaluating interdisciplinary pain rehabilitation (IPR). This systematic review aimed to identify prognostic factors for hrQoL at least six months after IPR in chronic pain patients.

METHODS

A systematic search was conducted in MEDLINE, PsycINFO, EMBASE, CINAHL, Web of Science and Cochrane CENTRAL until September 2020. Included were prognostic studies on the outcome hrQoL in adults aged 18 to 67 years with chronic pain (excluding malignancies, systemic-, inflammatory or degenerative joint diseases) who had undergone IPR. Studies were assessed with The Quality in Prognostic Studies-tool. Potential prognostic factors at baseline for the domains pain, psychological and physical functioning were qualitatively synthesized for hrQoL. Grading of Recommendations Assessment, Development and Evaluation was used to evaluate the level of evidence.

RESULTS

Fourteen studies on 6,668 participants (mean age 37.4-52.8 y), with musculoskeletal pain/fibromyalgia and a pain duration ranging between 13.1 and 177.4 months were considered eligible. With a very low certainty of evidence, pain intensity, emotional distress, and physical functioning at baseline were inconsistent for prediction of hrQoL and pain duration was not predictive. With low certainty of evidence, fewer pain sites, lower levels of negative cognitive behavioral factors, and higher levels of positive cognitive behavioral factors predicted a better outcome.

CONCLUSIONS

The overall certainty of evidence was low to very low, making it difficult to reach definitive conclusions at present. Future studies with a predefined core set of predictors investigating hrQoL in patients with chronic pain after IPR are needed.

Dissociation between individual differences in self-reported pain intensity and underlying fMRI brain activation

Pain is an individual experience. Previous studies have highlighted changes in brain activation and morphology associated with within- and interindividual pain perception. In this study we sought to characterize brain mechanisms associated with between-individual differences in pain in a sample of healthy adolescent and adult participants (N = 101). Here we show that pain ratings varied widely across individuals and that individuals reported changes in pain evoked by small differences in stimulus intensity in a manner congruent with their pain sensitivity, further supporting the utility of subjective reporting as a measure of the true individual experience. Furthermore, brain activation related to interindividual differences in pain was not detected, despite clear sensitivity of the Blood Oxygenation Level-Dependent (BOLD) signal to small differences in noxious stimulus intensities within individuals. These findings suggest fMRI may not be a useful objective measure to infer reported pain intensity.

Differences in Quantitative Sensory Testing Outcomes Between Patients With Low Back Pain in Primary Care and Pain-free Controls

OBJECTIVES

Quantitative Sensory Testing (QST) is used to test somatosensory functioning in on people with chronic LBP in secondary/tertiary health care facilities. Studies using QST-testing on LBP populations in primary care are scarce. Central Sensitization Inventory (CSI) measures central sensitization (CS)-related symptoms and studies investigating the differences between QST-testing and participants with LBP with a positive and negative score on the CSI questionnaire are also rare. This case-control study investigates differences of an extensive QST-measurement between patients with acute, chronic LBP, and pain-free controls (PFCs) in primary care. Secondary aim is to investigate differences of an extensive QST-measurement between "CS" and "no-CS" group.

MATERIALS AND METHODS

Participants with LBP were recruited from November 2016 to October 2019. Demographic and clinical information was collected and a standardized QST protocol was taken. Data analysis involved determining differences between groups.

RESULTS

Data of 100 participants with LBP and 50 PFCs were analyzed. Heat pain thresholds, pressure pain threshold, and conditioned pain modulation local and remote were significantly moderately to relatively strongly affected by acute, chronic LBP and PFCs (P<0.001 to 0.001). Lumbar temporal summation was significantly moderately affected by acute, chronic LBP, and PFCs (P=0.001). Only pressure pain threshold showed significant difference between "CS" and "no-CS" group (P=0.001 to 0.002).

DISCUSSION

Signs of enhanced nociceptive processing and disturbed top-down nociceptive modulation are apparent in people with acute and chronic LBP in primary care. Results indicate existence of central mechanisms in LBP in primary care.

Toward Composite Pain Biomarkers of Neuropathic Pain-Focus on Peripheral Neuropathic Pain

Chronic pain affects ~10-20% of the U.S. population with an estimated annual cost of $600 billion, the most significant economic cost of any disease to-date. Neuropathic pain is a type of chronic pain that is particularly difficult to manage and leads to significant disability and poor quality of life. Pain biomarkers offer the possibility to develop objective pain-related indicators that may help diagnose, treat, and improve the understanding of neuropathic pain pathophysiology. We review neuropathic pain mechanisms related to opiates, inflammation, and endocannabinoids with the objective of identifying composite biomarkers of neuropathic pain. In the literature, pain biomarkers typically are divided into physiological non-imaging pain biomarkers and brain imaging pain biomarkers. We review both types of biomarker types with the goal of identifying composite pain biomarkers that may improve recognition and treatment of neuropathic pain.

Psychological interventions in preventing chronicity of sub-acute back pain: a systematic review

OBJECTIVES

There is scarce information on preventive psychological and behavioural methods applicable to sub-acute (4-12 weeks) back pain, a precursor to chronic back pain. We conducted a systematic literature review of the efficacy of psychological interventions in preventing chronicity of sub-acute back pain.

METHODS

A systematic literature search in CINAHL, CENTRAL, MEDLINE, PubMed®, PsychINFO, Scopus and Web of Science databases.

RESULTS

From a total of 271 records, only three studies met the eligibility criteria. In two of the reviewed studies, the interventions had an insignificant preventive impact on the chronification of back pain. In one study the CBT intervention proved promising in preventing back pain related disability. None of the studies reported a significant impact on pain intensity at follow-up.

CONCLUSIONS

The psychological interventions did not impact pain outcomes. There is a disproportion between novel knowledge on psychological factors involved in the transition to chronic pain and corresponding preventive treatments. Additional studies on psychological interventions on sub-acute back pain prevention are highly warranted due to the enormous burden that back pain creates when it becomes chronic. The research project has the ethical approval of the Research Ethical Committee at Helsinki University Hospital, HUS/2435/2017.

Multi-Site Observational Study to Assess Biomarkers for Susceptibility or Resilience to Chronic Pain: The Acute to Chronic Pain Signatures (A2CPS) Study Protocol

Chronic pain has become a global health problem contributing to years lived with disability and reduced quality of life. Advances in the clinical management of chronic pain have been limited due to incomplete understanding of the multiple risk factors and molecular mechanisms that contribute to the development of chronic pain. The Acute to Chronic Pain Signatures (A2CPS) Program aims to characterize the predictive nature of biomarkers (brain imaging, high-throughput molecular screening techniques, or "omics," quantitative sensory testing, patient-reported outcome assessments and functional assessments) to identify individuals who will develop chronic pain following surgical intervention. The A2CPS is a multisite observational study investigating biomarkers and collective biosignatures (a combination of several individual biomarkers) that predict susceptibility or resilience to the development of chronic pain following knee arthroplasty and thoracic surgery. This manuscript provides an overview of data collection methods and procedures designed to standardize data collection across multiple clinical sites and institutions. Pain-related biomarkers are evaluated before surgery and up to 3 months after surgery for use as predictors of patient reported outcomes 6 months after surgery. The dataset from this prospective observational study will be available for researchers internal and external to the A2CPS Consortium to advance understanding of the transition from acute to chronic postsurgical pain.

A vision for the future of wearable sensors in spine care and its challenges: narrative review

OBJECTIVE

This review aimed to: (I) provide a brief overview of some topical areas of current literature regarding applications of wearable sensors in the management of low back pain (LBP); (II) present a vision for a future comprehensive system that integrates wearable sensors to measure multiple parameters in the real world that contributes data to guide treatment selection (aided by artificial intelligence), uses wearables to aid treatment support, adherence and outcome monitoring, and interrogates the response of the individual patient to the prescribed treatment to guide future decision support for other individuals who present with LBP; and (III) consider the challenges that will need to be overcome to make such a system a reality.

BACKGROUND

Advances in wearable sensor technologies are opening new opportunities for the assessment and management of spinal conditions. Although evidence of improvements in outcomes for individuals with LBP from the use of sensors is limited, there is enormous future potential.

METHODS

Narrative review and literature synthesis.

CONCLUSIONS

Substantial research is underway by groups internationally to develop and test elements of this system, to design innovative new sensors that enable recording of new data in new ways, and to fuse data from multiple sources to provide rich information about an individual's experience of LBP. Together this system, incorporating data from wearable sensors has potential to personalise care in ways that were hitherto thought impossible. The potential is high but will require concerted effort to develop and ultimately will need to be feasible and more effective than existing management.

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

Supplemental Digital Content is Available in the Text.

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

Introduction:

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

Objectives:

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

Methods:

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

Results:

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

Conclusion:

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

Functional connectivity and neurotransmitter impairments of the salience brain network in chronic low back pain patients: a combined resting state functional MRI and 1H-MRS study

ABSTRACT

Functional re-organisation of the salience network (SN) has been proposed as one of the key pathomechanisms associated with central nociceptive processing in the chronic pain state. Being associated with an altered functional connectivity within the SN, these processes have been hypothesized to result from a loss of inhibitory function leading to node hyperexcitability and spontaneous pain. Combined resting-state (rs) BOLD fMRI and 1H-MR spectroscopy was applied to chronic back pain (CBP) patients and healthy subjects (HS) to assess deviations from functional integrity (weighted closeness centrality, wCC, derived from rs-fMRI), oscillatory BOLD characteristics (spectral power, SP), and neurotransmitter levels (GABA+, glutamate+glutamine) in two key SN nodes, anterior insular (aInsR) and anterior mid-cingulate (aMCC) cortices. In addition, examinations were repeated in CBP patients after a four week interdisciplinary multimodal pain treatment and in HS after four weeks to explore longitudinal, treatment-mediated changes in target variables. The aInsR and, to a lesser extent, the aMCC of patients exhibited significantly reduced wCC accompanied by a SP shift from a lower to a higher frequency band, indicating a desynchronization of their neuronal activity within the SN, possibly due to increased spontaneous activations. Without revealing neurotransmitter differences, patients alone showed significant positive associations between local GABA+ levels and wCC in aInsR, suggesting a stronger dependence of node synchronization on the inhibitory tone in the chronic pain state. However, this needs to be explored in future using MRS techniques that are more sensitive to detecting subtle neurotransmitter changes and also allow multifocal characterization of neurotransmitter tone.

Pain, negative affective states and opioid-based analgesics: Safer pain therapies to dampen addiction

Across centuries and civilizations opioids have been used to relieve pain. In our modern societies, opioid-based analgesics remain one of the most efficient treatments for acute pain. However, the long-term use of opioids can lead to the development of analgesic tolerance, opioid-induced hyperalgesia, opioid use disorders, and overdose, which can ultimately produce respiratory depressant effects with fatal consequences. In addition to the nociceptive sensory component of pain, negative affective states arising from persistent pain represent a risk factor for developing an opioid use disorder. Several studies have indicated that the increase in prescribed opioid analgesics since the 1990s represents the root of our current opioid epidemic. In this review, we will present our current knowledge on the endogenous opioid system within the pain neuroaxis and the plastic changes occurring in this system that may underlie the occurrence of pain-induced negative affect leading to misuse and abuse of opioid medications. Dissecting the allostatic neuronal changes occurring during pain is the most promising avenue to uncover novel targets for the development of safer pain medications. We will discuss this along with current and potential approaches to treat pain-induced negative affective states that lead to drug misuse. Moreover, this chapter will provide a discussion on potential avenues to reduce the abuse potential of new analgesic drugs and highlight a basis for future research and drug development based on recent advances in this field.

Pramipexole treatment attenuates mechanical hypersensitivity in male rats experiencing chronic inflammatory pain

Opioids are commonly prescribed for pain despite growing evidence of their low efficacy in the treatment of chronic inflammatory pain and the high potential for misuse. There is a clear need to investigate non-opioid alternatives for the treatment of pain. In the present study, we tested the hypothesis that acute and repeated dopamine agonist treatment would attenuate mechanical hypersensitivity in male Long-Evans rats experiencing chronic inflammatory pain. We used two clinically available therapeutics, l-DOPA (precursor of dopamine biosynthesis) and pramipexole (dopamine D2/3 receptor agonist), to examine the functional role of dopamine signaling on mechanical hypersensitivity using an animal model of chronic inflammatory pain (complete Freund's adjuvant, CFA). We found that both acute and repeated pramipexole treatment attenuated hyperalgesia-like behavior in CFA-treated animals but exhibited no analgesic effects in control animals. In contrast, there was no effect of acute or repeated l-DOPA treatment on mechanical hypersensitivity in either CFA- or saline-treated animals. Notably, we discovered some extended effects of l-DOPA and pramipexole on decreasing pain-like behavior at three days and one week post-drug treatment. We also examined the effects of pramipexole treatment on glutamatergic and presynaptic signaling in pain- and reward-related brain regions including the nucleus accumbens (NAc), dorsal striatum (DS), ventral tegmental area (VTA), cingulate cortex (CC), central amygdala (CeA), and periaqueductal gray (PAG). We found that pramipexole treatment decreased AMPA receptor phosphorylation (pGluR1845) in the NAc and DS but increased pGluR1845 in the CC and CeA. A marker of presynaptic vesicle release, pSynapsin, was also increased in the DS, VTA, CC, CeA, and PAG following pramipexole treatment. Interestingly, pramipexole increased pSynapsin in the NAc of saline-treated animals, but not CFA-treated animals, suggesting blunted presynaptic vesicle release in the NAc of CFA-treated animals following pramipexole treatment. To examine the functional implications of impaired presynaptic signaling in the NAc of CFA animals, we used ex vivo electrophysiology to examine the effects of pramipexole treatment on the intrinsic excitability of NAc neurons in CFA- and saline-treated animals. We found that pramipexole treatment reduced NAc intrinsic excitability in saline-treated animals but produced no change in NAc intrinsic excitability in CFA-treated animals. These findings indicate alterations in dopamine D2/3 receptor signaling in the NAc of animals with a history of chronic pain in association with the anti-hyperalgesic effects of pramipexole treatment.

Time-Dependent Changes in Protein Composition of Medial Prefrontal Cortex in Rats with Neuropathic Pain

Chronic pain is associated with time-dependent structural and functional reorganization of the prefrontal cortex that may reflect adaptive pain compensatory and/or maladaptive pain-promoting mechanisms. However, the molecular underpinnings of these changes and whether there are time-dependent relationships to pain progression are not well characterized. In this study, we analyzed protein composition in the medial prefrontal cortex (mPFC) of rats at two timepoints after spinal nerve ligation (SNL) using two-dimensional gel electrophoresis (2D-ELFO) and liquid chromatography with tandem mass spectrometry (LC–MS/MS). SNL, but not sham-operated, rats developed persistent tactile allodynia and thermal hyperalgesia, confirming the presence of experimental neuropathic pain. Two weeks after SNL (early timepoint), we identified 11 proteins involved in signal transduction, protein transport, cell homeostasis, metabolism, and apoptosis, as well as heat-shock proteins and chaperones that were upregulated by more than 1.5-fold compared to the sham-operated rats. Interestingly, there were only four significantly altered proteins identified at 8 weeks after SNL (late timepoint). These findings demonstrate extensive time-dependent modifications of protein expression in the rat mPFC under a chronic neuropathic pain state that might underlie the evolution of chronic pain characterized by early pain-compensatory and later aberrant mechanisms.

Shame Mediates the Relationship Between Pain Invalidation and Depression

The experience of pain is subjective, yet many people have their pain invalidated or not believed. Pain invalidation is associated with poor mental health, including depression and lower well-being. Qualitative investigations of invalidating experiences identify themes of depression, but also social withdrawal, self-criticism, and lower self-worth, all of which are core components of shame. Despite this, no studies have quantitatively assessed the interrelationship between pain invalidation, shame, and depression. To explore this relationship, participants recounted the frequency of experienced pain invalidation from family, friends, and medical professionals, as well as their feelings of internalized shame and depressive symptoms. As shame has been shown to be a precursor for depression, we further explored the role of shame as a mediator between pain invalidation and depressive symptoms. All sources of pain invalidation were positively associated with shame and depressive symptoms, and shame fully mediated the relationship between each source of pain invalidation and depression. Relative to other sources, pain invalidation from family was most closely tied to shame and depression. Overall, findings indicate that one mechanism by which pain invalidation may facilitate depression is via the experience of shame. Future research may explore shame as a potential upstream precursor to depression in the context of pain. Findings provide more insight into the harmful influence of pain invalidation on mental health and highlight the impact of interpersonal treatment on the experiences of people in pain.

Cognitive Reserve as a Protective Factor of Mental Health in Middle-Aged Adults Affected by Chronic Pain

Chronic pain is associated with worse mental health and cognitive impairment, which can be a cause or a consequence of brain structure and function alterations, e.g., maladaptive plasticity, antinociceptive system dysregulation. Cognitive reserve reflects the effectiveness of the internal connections of the brain and it has been shown to be a protective factor in brain damage, slowing cognitive aging or reducing the risk of mental health disorders. The current study explored the impact of chronic pain on psychosocial factors, mental health, and cognition. Furthermore, we aimed to examine the role of cognitive reserve in the relationship between mental health and chronic pain clinical characteristics in middle-aged adults. The study group consisted of 477 volunteers from the Barcelona Brain Health Initiative who completed online surveys on pain, mental health, cognitive reserve, and psychosocial factors (sleep and quality of life). We described the differences in sociodemographic data, psychosocial factors, mental health, and self-perceived cognitive impairment, and neuropsychological assessment, between participants reporting pain compared with those without pain, as well as the main characteristics of the chronic pain group. Finally, to study the role of cognitive reserve in the modulation of the relationship between chronic pain and mental health, we compared variables between subgroups of participants with high/low pain intensity and cognitive reserve. The results showed that chronic pain was reported by 45.5% of middle-aged adults. Our results revealed that participants with chronic pain were older and had worse health status than people without pain. The presence of chronic pain affected working memory, mental health, and daily life activities. Moreover, cognitive reserve moderated the influence of pain intensity on mental health, resulting in less mental health affection in people suffering from high pain intensity with high cognitive reserve. In conclusion, the construct of the cognitive reserve could explain differential susceptibility between chronic pain and its mental health association and be a powerful tool in chronic pain assessment and treatment, principally due to its modifiable nature.

Psychosocial predictors of persistent low back pain in patients presenting to the emergency department

OBJECTIVES

Chronic low back pain is an important public health problem, generating high financial and social costs. While most clinical guidelines stress the importance of managing low back pain in primary care, in practice a disproportionate amount of patients with low back pain present to emergency departments. Patients presenting to emergency departments may form a specific group with different factors leading to chronicity. This prospective cohort study aimed to determine the sociodemographic and psychological predictors of persistent low back pain and the length of sick leave due to pain in patients with acute symptoms visiting an emergency department.

METHODS

Patients with a first episode of non-specific acute low back pain in at least three months were qualified for this study. The participants filled a battery of questionnaires, including measures of pain, pain-related disability, depression, anxiety and pain coping strategies. A structured telephone interview was performed after three months with questions regarding pain and the length of sick leave.

RESULTS

110 patients participated in the study. 97 patients completed the follow-up, with 70.1% suffering from pain after three months. Lower self-rated health predicted pain after three months. Longer length of sick leave was predicted by lower self-rated health, distraction as a coping strategy and decreased behavioral activity.

CONCLUSION

Because of its simplicity, a measurement of self-rated health may be included in future clinical practice for assessing the risk of persistent pain.

Neuromuscular adaptations to experimentally induced pain in the lumbar region: protocol for a systematic review and meta-analysis

BACKGROUND

Numerous studies report changes in neuromuscular control in people with low back pain (LBP). However, the relationship between pain and altered neuromuscular control is challenging to unravel given the heterogeneity that exists in clinical populations. One approach commonly adopted to overcome this issue is the use of experimental pain models, but it is currently unclear if the effects of experimental pain are consistent between studies. Therefore, this planned study will systematically evaluate and summarise the effect of experimentally induced pain in the lumbar region on neuromuscular control at sites both locally and remote to the low back.

METHODS

This protocol has been developed following the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P). MEDLINE, EMBASE, CINAHL, ZETOC, Web of Science, and grey literature will be searched up to August 31, 2021. Screening processes (title/abstract and full-text), data extraction, and risk of bias assessment will be conducted by two independent reviewers. Studies investigating the effects of exogenous pain models delivered to the low back region on neuromuscular control in healthy individuals will be included. Muscle activity and body kinematics will be the outcomes of interest. The comparisons of interest will be between baseline or control conditions and the experimental pain condition, as well as between the experimental pain and post-pain conditions. Randomised crossover and non-randomised studies of interventions will be included and their risk of bias will be evaluated with the Cochrane Risk-of-Bias tool or with the Risk Of Bias In Non-randomised Studies of Interventions tool, respectively. A random-effect meta-analysis will be conducted for quantitative synthesis when clinical and methodological consistency is ensured. Quality of evidence will be evaluated using the Grading of Recommendations, Assessment, Development and Evaluation guidelines.

DISCUSSION

The current review will provide new insights to understand if and what neuromuscular adaptations are caused by pain experimentally induced in the lumbar region. Our findings will reveal which experimental pain model is able to better reproduce adaptations similar to those identified in people with low back pain, possibly contributing to improving our understanding of motor adaptation to low back pain in the long term.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42020220130.

Abnormal within- and cross-networks functional connectivity in different outcomes of herpes zoster patients

Neuroimaging studies have displayed aberrant brain activities in individual sensory- and emotional-linked regions in postherpetic neuralgia (PHN) patients. However, multi-dimensional dysfunction in chronic pain may rely on the interplay between networks. Little is known about the changes in the functional architecture of resting state networks (RSNs) in PHN. In this cross-sectional study, we recruited 31 PHN patients, 33 RHZ patients and 34 HCs; all participants underwent resting-state functional magnetic resonance imaging scans. We investigated the differences of within- and cross-network connectivities between different outcomes of HZ patients [including PHN and recuperation from herpes zoster (RHZ)] and healthy controls (HCs) so as to extract a characteristic network pattern of PHN. The abnormal network connectivities were then correlated with clinical variables in respective groups. PHN and RHZ patients could be similarly characterized by abnormal within-default mode network (DMN), DMN-salience network (SN) and SN-basal ganglia network (BGN) connectivity relative to HCs. Of note, compared with RHZ patients, PHN patients could be characterized by abnormal DMN-BGN and within-BGN connectivity. Furthermore, the within-DMN connectivity was associated with pain-induced emotional scores among PHN patients. Our study presented that network-level imbalance could account for the pain-related dysfunctions in different outcomes of herpes zoster patients. These insights are potentially useful for understanding neuromechanism of PHN and providing central therapeutic targets for PHN.