How neuroimaging studies have challenged us to rethink: is chronic pain a disease?

The onset of widespread musculoskeletal pain is associated with a decrease in healthy ageing in older people: a population-based prospective study

OBJECTIVE

Chronic musculoskeletal pain is common in older adults but the nature of its relationship with ageing is unclear. The objective for this study was to test the hypothesis that the onset of widespread pain would be associated with a decrease in healthy ageing.

METHODS

Population-based prospective cohort study. A "healthy ageing" index was constructed across biomedical, physical, psychosocial and lay components. Analysis was performed with 2949 adults aged 50 years and over who had complete index scores at baseline, 3 and 6-year follow-ups.

RESULTS

At three and six year follow-up, 365 (16.8%) and 259 (14.3%) experienced the onset of widespread pain. The onset of widespread pain during the six-year period was associated with a 25% and a 46% decrease in healthy ageing index scores; this decrease was independent of age, sex, education, social networks, smoking status, alcohol consumption and physical inactivity. The decrease in healthy ageing attenuated to 20% and 39% following adjustment for diagnosed musculoskeletal conditions and analgesic and non-steroidal use.

CONCLUSIONS

The onset of widespread pain was associated with a decrease in healthy ageing throughout the six-year period. When pain increased over time, the markers of unhealthy ageing increased also. Strong analgesia was associated with unhealthy ageing. Research could now usefully test whether early identification, improved treatment and prevention of pain prior to old age may facilitate healthy ageing.

Transition to persistent orofacial pain after nerve injury involves supraspinal serotonin mechanisms

The orofacial region is a major focus of chronic neuropathic pain conditions characterized by primary hyperalgesia at the site of injury and secondary hyperalgesia outside the injured zone. We have used a rat model of injury to the maxillary branch (V2) of the trigeminal nerve to produce constant and long-lasting primary hyperalgesia in the V2 territory and secondary hyperalgesia in territories innervated by the mandibular branch (V3). Our findings indicate that the induction of primary and secondary hyperalgesia depended on peripheral input from the injured nerve. In contrast, the maintenance of secondary hyperalgesia depended on central mechanisms. The centralization of the secondary hyperalgesia involved descending 5-HT drive from the rostral ventromedial medulla and the contribution of 5-HT3 receptors in the trigeminal nucleus caudalis (Vc), the homolog of the spinal dorsal horn. Electrophysiological studies further indicate that after nerve injury spontaneous responses and enhanced poststimulus discharges in Vc nociresponsive neurons were time-dependent on descending 5-HT drive and peripheral input. The induction phase of secondary hyperalgesia involved central sensitization mechanisms in Vc neurons that were dependent on peripheral input, whereas the maintenance phase of secondary hyperalgesia involved central sensitization in Vc neurons conducted by a delayed descending 5-HT drive and a persistence of peripheral inputs. Our results are the first to show that the maintenance of secondary hyperalgesia and underlying central sensitization associated with persistent pain depend on a transition to supraspinal mechanisms involving the serotonin system in rostral ventromedial medulla-dorsal horn circuits.

Brain structural and psychometric alterations in chronic low back pain

PURPOSE

Chronic low back pain (CLBP) is one of the most important pain disorders with increasing social and economic implications. Given that CLBP is a multidimensional process associated with comorbidities such as anxiety and depression, treatment of chronic low back pain is still a challenge. Advancement of in vivo brain imaging technologies has revealed increasing insights into the etiology and pathogenesis of chronic pain; however, the exact mechanisms of chronification of LBP remain still unclear. The purpose of the present study was to analyse the neurostructural alterations in CLBP and to evaluate the role of comorbidities and their neurostructural underpinnings.

METHODS

In the present study we investigated a well-characterized group of 14 patients with CLBP and 14 healthy controls applying structural MRI and psychometric measures. Using an improved algorithm for brain normalization (DARTEL) we performed a voxel-based morphometry (VBM) approach. Correlation analyses were performed to evaluate the role of anxiety and depression in neurostructural alterations observed in CLBP.

RESULTS

The psychometric measures revealed significantly higher scores on depression and anxiety in the patient population. VBM analysis showed significant decreases in grey matter density in areas associated with pain processing and modulation, i.e. the dorsolateral prefrontal cortex, the thalamus and the middle cingulate cortex. With respect to anxiety and depression scores, we did not observe any correlations to the structural data.

CONCLUSIONS

In the present study we found compelling evidence for alterations of grey matter architecture in CLBP in brain regions playing a major role in pain modulation and control. Our results fit the hypothesis of a "brain signature" in chronic pain conditions. The results of the psychometric assessment underline the importance of an interdisciplinary therapeutic approach including orthopedic, neurological and psychological evaluation and treatment.

Structural brain changes in chronic pain reflect probably neither damage nor atrophy

Chronic pain appears to be associated with brain gray matter reduction in areas ascribable to the transmission of pain. The morphological processes underlying these structural changes, probably following functional reorganisation and central plasticity in the brain, remain unclear. The pain in hip osteoarthritis is one of the few chronic pain syndromes which are principally curable. We investigated 20 patients with chronic pain due to unilateral coxarthrosis (mean age 63.25±9.46 (SD) years, 10 female) before hip joint endoprosthetic surgery (pain state) and monitored brain structural changes up to 1 year after surgery: 6–8 weeks, 12–18 weeks and 10–14 month when completely pain free. Patients with chronic pain due to unilateral coxarthrosis had significantly less gray matter compared to controls in the anterior cingulate cortex (ACC), insular cortex and operculum, dorsolateral prefrontal cortex (DLPFC) and orbitofrontal cortex. These regions function as multi-integrative structures during the experience and the anticipation of pain. When the patients were pain free after recovery from endoprosthetic surgery, a gray matter increase in nearly the same areas was found. We also found a progressive increase of brain gray matter in the premotor cortex and the supplementary motor area (SMA). We conclude that gray matter abnormalities in chronic pain are not the cause, but secondary to the disease and are at least in part due to changes in motor function and bodily integration.

Peripheral nerve injury is associated with chronic, reversible changes in global DNA methylation in the mouse prefrontal cortex

Changes in brain structure and cortical function are associated with many chronic pain conditions including low back pain and fibromyalgia. The magnitude of these changes correlates with the duration and/or the intensity of chronic pain. Most studies report changes in common areas involved in pain modulation, including the prefrontal cortex (PFC), and pain-related pathological changes in the PFC can be reversed with effective treatment. While the mechanisms underlying these changes are unknown, they must be dynamically regulated. Epigenetic modulation of gene expression in response to experience and environment is reversible and dynamic. Epigenetic modulation by DNA methylation is associated with abnormal behavior and pathological gene expression in the central nervous system. DNA methylation might also be involved in mediating the pathologies associated with chronic pain in the brain. We therefore tested a) whether alterations in DNA methylation are found in the brain long after chronic neuropathic pain is induced in the periphery using the spared nerve injury modal and b) whether these injury-associated changes are reversible by interventions that reverse the pathologies associated with chronic pain. Six months following peripheral nerve injury, abnormal sensory thresholds and increased anxiety were accompanied by decreased global methylation in the PFC and the amygdala but not in the visual cortex or the thalamus. Environmental enrichment attenuated nerve injury-induced hypersensitivity and reversed the changes in global PFC methylation. Furthermore, global PFC methylation correlated with mechanical and thermal sensitivity in neuropathic mice. In summary, induction of chronic pain by peripheral nerve injury is associated with epigenetic changes in the brain. These changes are detected long after the original injury, at a long distance from the site of injury and are reversible with environmental manipulation. Changes in brain structure and cortical function that are associated with chronic pain conditions may therefore be mediated by epigenetic mechanisms.

Quantifying the test-retest reliability of cerebral blood flow measurements in a clinical model of on-going post-surgical pain: A study using pseudo-continuous arterial spin labelling

Arterial spin labelling (ASL) is increasingly being applied to study the cerebral response to pain in both experimental human models and patients with persistent pain. Despite its advantages, scanning time and reliability remain important issues in the clinical applicability of ASL. Here we present the test–retest analysis of concurrent pseudo-continuous ASL (pCASL) and visual analogue scale (VAS), in a clinical model of on-going pain following third molar extraction (TME). Using ICC performance measures, we were able to quantify the reliability of the post-surgical pain state and ΔCBF (change in CBF), both at the group and individual case level. Within-subject, the inter- and intra-session reliability of the post-surgical pain state was ranked good-to-excellent (ICC > 0.6) across both pCASL and VAS modalities. The parameter ΔCBF (change in CBF between pre- and post-surgical states) performed reliably (ICC > 0.4), provided that a single baseline condition (or the mean of more than one baseline) was used for subtraction. Between-subjects, the pCASL measurements in the post-surgical pain state and ΔCBF were both characterised as reliable (ICC > 0.4). However, the subjective VAS pain ratings demonstrated a significant contribution of pain state variability, which suggests diminished utility for interindividual comparisons. These analyses indicate that the pCASL imaging technique has considerable potential for the comparison of within- and between-subjects differences associated with pain-induced state changes and baseline differences in regional CBF. They also suggest that differences in baseline perfusion and functional lateralisation characteristics may play an important role in the overall reliability of the estimated changes in CBF. Repeated measures designs have the important advantage that they provide good reliability for comparing condition effects because all sources of variability between subjects are excluded from the experimental error. The ability to elicit reliable neural correlates of on-going pain using quantitative perfusion imaging may help support the conclusions derived from subjective self-report.

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Test-retest reliability of pCASL is considered in a post-surgical pain model.

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Pain-state and ∆CBF measurements were reliable at the group and individual level.

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Single or average baseline measurements improve reliability of ∆CBF.

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pCASL is a reliable technique for detecting cerebral responses to on-going pain.

Default mode network connectivity encodes clinical pain: an arterial spin labeling study

Neuroimaging studies have suggested the presence of alterations in the anatomo-functional properties of the brain of patients with chronic pain. However, investigation of the brain circuitry supporting the perception of clinical pain presents significant challenges, particularly when using traditional neuroimaging approaches. While potential neuroimaging markers for clinical pain have included resting brain connectivity, these cross-sectional studies have not examined sensitivity to within-subject exacerbation of pain. We used the dual regression probabilistic Independent Component Analysis approach to investigate resting-state connectivity on arterial spin labeling data. Brain connectivity was compared between patients with chronic low back pain (cLBP) and healthy controls, before and after the performance of maneuvers aimed at exacerbating clinical pain levels in the patients. Our analyses identified multiple resting state networks, including the default mode network (DMN). At baseline, patients demonstrated stronger DMN connectivity to the pregenual anterior cingulate cortex (pgACC), left inferior parietal lobule, and right insula (rINS). Patients' baseline clinical pain correlated positively with connectivity strength between the DMN and right insula (DMN-rINS). The performance of calibrated physical maneuvers induced changes in pain, which were paralleled by changes in DMN-rINS connectivity. Maneuvers also disrupted the DMN-pgACC connectivity, which at baseline was anticorrelated with pain. Finally, baseline DMN connectivity predicted maneuver-induced changes in both pain and DMN-rINS connectivity. Our results support the use of arterial spin labeling to evaluate clinical pain, and the use of resting DMN connectivity as a potential neuroimaging biomarker for chronic pain perception.

Nerve injury causes long-term attentional deficits in rats

Human chronic pain sufferers frequently report problems with attention and concentration that affect daily functioning and quality of life. Chronic pain is also commonly associated with anxiety and depression. It is currently not known if the pain causes these co-morbidities, or if they are pre-disposing risk factors for the development of chronic pain. Animal studies suggest a possible causative effect of pain on cognition, but usually tests are conducted during acute ongoing pain when the pain may act as a distracter to normal cognitive and emotional processing. Here we examine long-term effects of nerve injury on cognitive functioning in a rat model, which contributes to better understanding of the relationship between cognitive impairment and chronic pain experience in human populations. This study investigated attentional capability, anxiety-like behavior and sensory functioning 6 months after spared nerve injury (SNI) surgery-a time-point well beyond the acute pain phase and akin to decades of pain experience in humans. Male Long Evans rats subjected to nerve injury remained hypersensitive to sensory stimuli from the time of injury to the 6-month post-injury assessment. At 6 months they were impaired on a visual non-selective, non-sustained attention task and displayed anxiety-like behaviors in the elevated plus maze. These findings show that cognitive disturbances observed during acute pain persist for months in a rodent chronic pain model and suggest that cognitive alterations in chronic pain patients are at least partially caused by the chronic pain state.

Medically unexplained symptoms and pain: misunderstanding and myth

PURPOSE OF REVIEW

The recent resurgence of the notion of psychosomatic disorders, grouping together as 'medically unexplained symptoms' all those without organic diagnosis and associated with distress, has included all chronic (persistent) pain within its remit. As pain is reasonably well explained, within an integrated biopsychosocial model, critical analysis of the position is required.

RECENT FINDINGS

Neuroscientific and translational studies of pain mechanisms have strengthened the understanding of pain, providing stronger connections between abstract psychological concepts corresponding to observation and studies of human clinical populations, neuroscientific findings in clinical and analogue studies, and animal research. This situation is contrasted with even the most recent reviews of medically unexplained symptoms providing only vague and patchily supported mechanisms, with little cognate human analogue or animal research.

SUMMARY

The implication of subsuming chronic pain under medically unexplained symptoms is that the primary care/community physician will try to persuade the patient that the symptoms indicate underlying depression, which her or she may offer to treat. When pain is instead recognized as a problem in its own right, it would be referred for specialist opinion and care, or treated directly with evidence-based pain interventions.

Visualizing the complex brain dynamics of chronic pain

Chronic pain is now recognized as a disease state that involves changes in brain function. This concept is reinforced by data that document structural and morphological remapping of brain circuitry under conditions of chronic pain. Evidence for aberrant neurophysiology in the brain further confirms neuroplasticity at cellular and molecular levels. Proper detection of pain-induced changes using emerging non-invasive and cost-effective technologies, such as analytical electroencephalography methods, could yield objective diagnostic measures and may guide therapeutic interventions targeting the brain for effective management of chronic pain.

The recurrent pain and sexual sequelae of provoked vestibulodynia: a perpetuating cycle

INTRODUCTION

Optimal management of provoked vestibulodynia (PVD), thought to be the most common form of chronic dyspareunia, is unclear.

AIM

To integrate recent brain data on chronic pain circuitry with stress-induced neuroendocrine mechanisms in the skin and the stress burden (allostatic load) of women with PVD; to also clarify the typical chronicity and negative sexual sequelae associated with PVD; and then review modulation of pain circuitry by cognitive therapy and mindfulness practice and apply to PVD management. Methods.  Review of scientific publications in the areas of sexual medicine, pain, brain imaging, gynecology, stress response, mindfulness, and cognitive behavioral therapy (CBT).

MAIN OUTCOME MEASURES

(i) A model of PVD to reflect its etiology, typical chronicity, and the detrimental effects on sexual function; (ii) Interventions of sexual rehabilitation based on principles underlying changes associated with CBT and mindfulness practice.

RESULTS

A model emerges which reflects how stress-induced changes of pain amplification (central sensitization), characteristic of chronic pain conditions, may impair sexual response in addition to sexual dysfunction that arises from conscious pain avoidance and/or fear-related inattention to sexual cues. Stress from low self-acceptance may be a major component of the allostatic load present in women with PVD, only to be exacerbated by the sexual dysfunction precipitated by the pain of intercourse. Mindfulness-based CBT appears promising to target both the pain and sexual suffering from PVD.

CONCLUSION

New findings on brain activity associated with recurrent clinical pain, functional brain changes associated with CBT and mindfulness, plus new data on stress systems within the skin along with data on increased stress load in women with PVD, support the use of mindfulness-based CBT for the recurrent pain and sexual suffering from PVD.

Brain structure and joint hypermobility: relevance to the expression of psychiatric symptoms

Joint hypermobility is overrepresented among people with anxiety and can be associated with abnormal autonomic reactivity. We tested for associations between regional cerebral grey matter and hypermobility in 72 healthy volunteers using voxel-based morphometry of structural brain scans. Strikingly, bilateral amygdala volume distinguished those with from those without hypermobility. The hypermobility group scored higher for interoceptive sensitivity yet were not significantly more anxious. Our findings specifically link hypermobility to the structural integrity of a brain centre implicated in normal and abnormal emotions and physiological responses. Our observations endorse hypermobility as a multisystem phenotype and suggest potential mechanisms mediating clinical vulnerability to neuropsychiatric symptoms.

Detecting the emergence of chronic pain in sickle cell disease

CONTEXT

Sickle cell disease (SCD) is an inherited hematological disease marked by intense pain. Early in life the pain is episodic, but it becomes increasingly chronic in many cases. Little is known about this emergence of a chronic pain state.

OBJECTIVES

The goal of this study was to determine whether adult SCD patients whose pain is still largely episodic show early signs of the disturbed pain processing (hyperalgesia and increased temporal summation) and cognition (hypervigilance and catastrophizing) that are characteristic of a chronic pain state.

METHODS

SCD patients (n=22) and healthy controls (n=52) received noxious pressure stimulation for up to three minutes and periodically reported pain intensity and unpleasantness on 0-10 scales, allowing the rate of pain increase (temporal summation) to be determined. Pain intensity discrimination also was measured, and attitudes toward pain were assessed.

RESULTS

There were no overall differences in pain ratings or temporal summation between patient and control groups. However, patients' experimental pain ratings tended to increase with age and those reporting a history of very painful episodes showed particularly rapid temporal summation of pain unpleasantness. Patients were significantly impaired at discriminating intensities of noxious stimulation. Patients were more hypervigilant than controls, but catastrophizing was elevated only during pain episodes.

CONCLUSION

Most SCD patients whose pain remits entirely between episodes are not in a chronic pain state, but some--those who are older and have a history of highly painful episodes--appear to be transitioning into it. These early signs of disturbed processing may aid clinicians seeking to forestall disease progression.

Engaging consumers living in remote areas of Western Australia in the self-management of back pain: a prospective cohort study

Background

In Western Australia (WA), health policy recommends encouraging the use of active self-management strategies as part of the co-care of consumers with persistent low back pain (LBP). As many areas in WA are geographically isolated and health services are limited, implementing this policy into practice is critical if health outcomes for consumers living in geographically-isolated areas are to be improved.

Methods

In this prospective cohort study, 51 consumers (mean (SD) age 62.3 (±15.1) years) participated in an evidence-based interdisciplinary pain education program (modified Self Training Educative Pain Sessions: mSTEPS) delivered at three geographically isolated WA sites. Self report measures included LBP beliefs and attitudes (Back Pain Beliefs Questionnaire (BBQ); Fear Avoidance Beliefs Questionnaire (FABQ)), use of active and passive self-management strategies, and health literacy, and global perceived impression of usefulness (GPIU) recorded immediately pre-intervention (n = 51), same day post-intervention (BBQ; GPIU, n = 49) and 3 months post-intervention (n = 25).

Results

At baseline, consumers demonstrated adequate health literacy and elements of positive health behaviours, reflected by the use of more active than passive strategies in self-managing their persistent LBP. Immediately post-intervention, there was strong evidence for improvement in consumers’ general beliefs about LBP as demonstrated by an increase in BBQ scores (baseline [mean (SD): 25.8 (7.6)] to same day post-intervention [28.8 (7.2); P < 0.005], however this improvement was not sustained at 3 months post-intervention. The majority of consumers (86.4%) reported the intervention as very useful [rated on NRS as 7–10].

Conclusions

To sustain improved consumer beliefs regarding LBP and encourage the adoption of more positive health behaviours, additional reinforcement strategies for consumers living in remote areas where service access and skilled workforce are limited are recommended. This study highlights the need for aligning health services and skilled workforce to improve the delivery of co-care for consumers living in geographically isolated areas.

Contribution of PKMζ-dependent and independent amplification to components of experimental neuropathic pain

Injuries can induce adaptations in pain processing that result in amplification of signaling. One mechanism may be analogous to long-term potentiation and involve the atypical protein kinase C, PKMζ. The possible contribution of PKMζ-dependent and independent amplification mechanisms to experimental neuropathic pain was explored in rats with spinal nerve ligation (SNL) injury. SNL increased p-PKMζ in the rostral anterior cingulate cortex (rACC), a site that mediates, in part, the unpleasant aspects of pain. Inhibition of PKMζ within the rACC by a single administration of ζ-pseudosubstrate inhibitory peptide (ZIP) reversed SNL-induced aversiveness within 24 hours, whereas N-methyl-d-aspartate receptor blockade with MK-801 had no effects. The SNL-induced aversive state (reflecting "spontaneous" pain), was re-established in a time-dependent manner, with full recovery observed 7 days post-ZIP administration. Neither rACC ZIP nor MK-801 altered evoked responses. In contrast, spinal ZIP or MK-801, but not scrambled peptide, transiently reversed evoked hypersensitivity, but had no effect on nerve injury-induced spontaneous pain. PKMζ phosphorylation was not altered by SNL in the spinal dorsal horn. These data suggest that amplification mechanisms contribute to different aspects of neuropathic pain at different levels of the neuraxis. Thus, PKMζ-dependent amplification contributes to nerve injury-induced aversiveness within the rACC. Moreover, unlike mechanisms maintaining memory, the consequences of PKMζ inhibition within the rACC are not permanent in neuropathic pain, possibly reflecting the re-establishment of amplification mechanisms by ongoing activity of injured nerves. In the spinal cord, however, both PKMζ-dependent and independent mechanisms contribute to amplification of evoked responses, but apparently not spontaneous pain.

Rodent functional and anatomical imaging of pain

Human brain imaging has provided much information about pain processing and pain modulation, but brain imaging in rodents can provide information not attainable in human studies. First, the short lifespan of rats and mice, as well as the ability to have homogenous genetics and environments, allows for longitudinal studies of the effects of chronic pain on the brain. Second, brain imaging in animals allows for the testing of central actions of novel pharmacological and nonpharmacological analgesics before they can be tested in humans. The two most commonly used brain imaging methods in rodents are magnetic resonance imaging (MRI) and positron emission tomography (PET). MRI provides better spatial and temporal resolution than PET, but PET allows for the imaging of neurotransmitters and non-neuronal cells, such as astrocytes, in addition to functional imaging. One problem with rodent brain imaging involves methods for keeping the subject still in the scanner. Both anesthetic agents and restraint techniques have potential confounds. Some PET methods allow for tracer uptake before the animal is anesthetized, but imaging a moving animal also has potential confounds. Despite the challenges associated with the various techniques, the 31 studies using either functional MRI or PET to image pain processing in rodents have yielded surprisingly consistent results, with brain regions commonly activated in human pain imaging studies (somatosensory cortex, cingulate cortex, thalamus) also being activated in the majority of these studies. Pharmacological imaging in rodents shows overlapping activation patterns with pain and opiate analgesics, similar to what is found in humans. Despite the many structural imaging studies in human chronic pain patients, only one study has been performed in rodents, but that study confirmed human findings of decreased cortical thickness associated with chronic pain. Future directions in rodent pain imaging include miniaturized PET for the freely moving animal, as well as new MRI techniques that enable ongoing chronic pain imaging.

Real-time fMRI applied to pain management

Current views recognize the brain as playing a pivotal role in the arising and maintenance of pain experience. Real-time fMRI (rtfMRI) feedback is a potential tool for pain modulation that directly targets the brain with the goal of restoring regulatory function. Though still relatively new, rtfMRI is a rapidly developing technology that has evolved in the last 15 years from simple proof of concept experiments to demonstrations of learned control of single and multiple brain areas. Numerous studies indicate rtfMRI feedback assisted control over specific brain areas may have applications including mood regulation, language processing, neurorehabilitation in stroke, enhancement of perception and learning, and pain management. We discuss in detail earlier work from our lab in which rtfMRI feedback was used to train both healthy controls and chronic pain patients to modulate anterior cingulate cortex (ACC) activation for the purposes of altering pain experience. Both groups improved in their ability to control ACC activation and modulate their pain with rtfMRI feedback training. Furthermore, the degree to which participants were able to modulate their pain correlated with the degree of control over ACC activation. We additionally review current advances in rtfMRI feedback, such as real-time pattern classification, that bring the technology closer to more comprehensive control over neural function. Finally, remaining methodological questions concerning the further development of rtfMRI feedback and its implications for the future of pain research are also discussed.

Managing pain in high-risk patients within a patient-centered medical home

Chronic pain remains a major healthcare problem despite noteworthy advancements in diagnostics, pharmacotherapy, and invasive and non-invasive interventions. The prevalence of chronic pain in the United States is staggering and continues to grow, and the personal and societal costs are not inconsequential. The etiology of pain is complex, and individuals suffering from chronic pain tend to have significant medical and psychiatric comorbidities such as depression, anxiety, and in some cases, substance use disorders. There is great concern regarding the burgeoning rate of prescription opioid misuse/abuse both for non-medical use and in pain patients receiving chronic opioid therapy. While there is ongoing debate about the "true" incidence of opioid abuse in the pain population, clearly, patients afflicted with both pain and substance use disorder are particularity challenging. The majority of patients with chronic pain including those with co-occurring substance use disorders are managed in the primary care setting. Primary care practitioners have scant time, resources and training to effectively assess, treat and monitor these complicated cases. A number of evidence- and expert consensus-based treatment guidelines on opioid therapy and risk mitigation have been developed but they have been underutilized in both specialty and primary care clinics. This article will discuss the utilization of new technologies and delivery systems for risk stratification, intervention and monitoring of patients with pain receiving opioid.

Imaging the neural correlates of neuropathic pain and pleasurable relief associated with inherited erythromelalgia in a single subject with quantitative arterial spin labelling

We identified a patient with severe inherited erythromelalgia secondary to an L858F mutation in the voltage-gated sodium channel Na_v1.7. The patient reported severe ongoing foot pain, which was exquisitely sensitive to limb cooling. We confirmed this heat hypersensitivity using quantitative sensory testing. Additionally, we employed a novel perfusion imaging technique in a simple block design to assess her baseline erythromelalgia pain vs cooling relief. Robust activations of key pain, pain-affect, and reward-related centres were observed. This combined approach allowed us to confirm the presence of a temperature-sensitive channelopathy of peripheral neurons and to investigate the neural correlates of tonic neuropathic pain and relief in a single subject.

Unpacking the burden: understanding the relationships between chronic pain and comorbidity in the general population

We investigated the association of chronic pain with physical and mental comorbidity in the New Zealand population by measuring chronic pain status separate from comorbid conditions. Models of allostatic load provided a conceptual basis for considering multi-morbidity as accumulated comorbid load and for using both discrete conditions and cumulative measures in analyses. The nationally representative cross-sectional survey data included self-reported doctor-diagnosed chronic physical and mental health conditions, Kessler 10-item scale scores, an independent measure of chronic pain, and sociodemographic characteristics. The population prevalence of chronic pain is 16.9%, and a quarter (26%) of the population report 2 or more comorbid physical conditions statistically associated with chronic pain (unadjusted P<0.01). Results indicate that accumulated comorbid load is independently associated with chronic pain. Six physical conditions independently associated with chronic pain (adjusted odds range from 1.4 to 3.9) increase the risk of chronic pain in an additive manner, and residual accumulated load further increases risk for 2 or more conditions (adjusted odds 1.6). Anxiety/depression interacts synergistically with arthritis and neck/back disorders to increase the odds of reporting chronic pain beyond an additive model. This synergistic effect is not apparent for other conditions or for additional comorbid load. Results imply that measurement of chronic pain independent of comorbid conditions and adjustment for comorbid conditions is important for more accurate prevalence estimates and understanding relationships between conditions. Future epidemiological research might usefully incorporate independent measurement of chronic pain alongside adjustment for specific physical and mental health conditions as well as accumulated comorbid load.

The brain in chronic pain: clinical implications

This article examines the present, and potential future, impact of brain imaging on chronic pain. It is argued that novel theories of chronic pain are coming to the fore, specifically through brain imaging of the human brain in chronic pain. Such studies show that the brain reorganizes in relation to chronic pain, in a pattern specific to the type of clinical pain, and that brain networks and receptor targets are being identified and reverse translated to animal studies of their efficacy and mechanisms. Future studies need to integrate across human brain imaging techniques, as well as more intensive reverse translational methods.

Functional brain activation during retrieval of visceral pain-conditioned passive avoidance in the rat

This study assessed functional brain activation in rats during expectation of visceral pain. Male rats were trained in step-down passive avoidance (PA) for 2 days. Upon stepping down from a platform, conditioned animals received noxious colorectal distension delivered through a colorectal balloon, whereas the balloon in control rats remained uninflated. On day 3, PA behavior was assessed while [(14)C]-iodoantipyrine was infused intravenously, followed by immediate euthanasia. Regional cerebral blood flow-related tissue radioactivity (rCBF) was analyzed by statistical parametric mapping using 3-dimensional brains reconstructed from autoradiographic brain slice images. Associated with retrieved PA behavior, conditioned rats compared with control subjects showed increases in rCBF in sensory (anterior insula, somatosensory cortex), limbic/paralimbic regions (anterior cingulate, prelimbic cortex, amygdala), all regions previously reported to show activation during acute visceral pain. Increases in rCBF were also noted in the dorsal hippocampus, nucleus accumbens, and caudate putamen, regions associated with retrieval of PA. Organization of the underlying brain network was further delineated by functional connectivity analysis. This revealed in conditioned rats a strongly and positively connected corticostriatal cluster (cingulate, prelimbic cortex, caudate putamen). The amygdala and cerebellar hemispheres formed another positively connected cluster, which was negatively connected with the corticostriatal cluster, suggesting corticolimbic modulation. Prelimbic cortex, nucleus accumbens, and anterior insula emerged in conditioned animals as hubs. Our results show that during retrieval of PA, brain areas implicated in PA expression as well as those implicated in acute visceral pain processing were recruited, in line with findings from human brain imaging studies on pain expectation.

High-frequency stimulation in the ventral posterolateral thalamus reverses electrophysiologic changes and hyperalgesia in a rat model of peripheral neuropathic pain

Chronic neuropathic pain is associated with long-term changes at multiple levels of the neuroaxis, including in the brain, where electrical stimulation has been used to manage severe pain conditions. However, the clinical outcome of deep brain stimulation is often mixed, and the mechanisms are poorly understood. By means of electrophysiologic methods, we sought to characterize the changes in neuronal activity in the ventral posterolateral nucleus of the thalamus (VPL) in a rat model of peripheral neuropathic pain, and to reverse these changes with low-voltage, high-frequency stimulation (HFS) in the VPL. Extracellular single-unit neuronal activity was recorded in naive rats and in those with sciatic chronic constriction injury (CCI). Seven days after CCI, brush- and pinch-evoked firing, as well as spontaneous firing and afterdischarge, were significantly increased compared to naive rats. Spontaneous rhythmic oscillation in neuronal firing was also observed in rats with CCI. HFS decreased neuronal firing rates in rats with CCI up to ~50% except for spontaneous activity, whereas low-frequency stimulation had no effect. Compared to naive rats, burst firing properties (burst events, percentage of spikes in burst, and mean interburst time) were altered in rats with CCI, whereas these changes were reversed to near normal after HFS. Thermal hyperalgesia in rats with CCI was significantly attenuated by HFS. Therefore, this study demonstrates that electrical stimulation within the VPL can effectively modulate some nociceptive phenomena associated with peripheral neuropathic pain.

Pelvic pain in women: clinical and scientific aspects

PURPOSE OF REVIEW

Pelvic pain is a common complaint of women that is frequently poorly managed. This review considers the current understanding of the mechanisms of pain perception and the development of chronic pain in the context of three gynaecological pain conditions. Recent advances in the management of these conditions are then discussed.

RECENT FINDINGS

Persistent pelvic pain is associated with central changes, reflected by alterations in psychology, brain structure and function, and dysfunction of the hypothalamic-pituitary-adrenal axis. The many similarities among the conditions support the notion that chronic pain should be treated as a symptom in its own right, however, obtaining a diagnosis remains important to patients. Few new treatments have been developed recently, however, older treatments are being subjected to more rigorous testing and improvements in phenotyping should lead to better design of clinical trials.

SUMMARY

Good quality, well designed clinical trials are urgently required to improve the treatment of pelvic pain in women. However, a variety of successful treatments exist and outcomes can be optimized by individualizing treatment strategies in the context of a multidisciplinary package.

Elevated pain sensitivity in chronic pain patients at risk for opioid misuse

This study employed quantitative sensory testing (QST) to evaluate pain responses in chronic spinal pain patients at low risk and high risk for opioid misuse, with risk classification based on scores on the Screener and Opioid Assessment for Patients with Pain-Revised (SOAPP-R). Patients were further subgrouped according to current use of prescription opioids. Of the 276 chronic pain patients tested, approximately 65% were taking opioids; a median split was used to further categorize these patients as being on lower or higher doses of opioids. The high-risk group (n = 161) reported higher levels of clinical pain, had lower pressure and thermal pain thresholds at multiple body sites, had lower heat pain tolerance, and rated repetitive mechanical stimuli as more painful relative to the low-risk group (n = 115; P's < .01). In contrast, QST measures did not differ across opioid groups. Multiple linear regression analysis suggested that indices of pain-related distress (ie, anxiety and catastrophizing about pain) were also predictive of hyperalgesia, particularly in patients taking opioids. Collectively, regardless of opioid status, the high-risk group was hyperalgesic relative to the low-risk group; future opioid treatment studies may benefit from the classification of opioid risk, and the examination of pain sensitivity and other factors that differentiate high- and low-risk groups.

PERSPECTIVE

This study demonstrates that chronic spinal pain patients at high risk for misuse of prescription opioids are more pain-sensitive than low-risk patients, whether or not they are currently taking opioids. Indices of pain-related distress were important predictors of pain sensitivity, particularly among those patients taking opioids for pain.

Lesion of the rostral anterior cingulate cortex eliminates the aversiveness of spontaneous neuropathic pain following partial or complete axotomy

Neuropathic pain is often "spontaneous" or "stimulus-independent." Such pain may result from spontaneous discharge in primary afferent nociceptors in injured peripheral nerves. However, whether axotomized primary afferent nociceptors give rise to pain is unclear. The rostral anterior cingulate cortex (rACC) mediates the negative affective component of inflammatory pain. Whether the rACC integrates the aversive component of chronic spontaneous pain arising from nerve injury is not known. Here, we used the principle of negative reinforcement to show that axotomy produces an aversive state reflecting spontaneous pain driven from injured nerves. Additionally, we investigated whether the rACC contributes to the aversiveness of nerve injury-induced spontaneous pain. Partial or complete hind paw denervation was produced by sciatic or sciatic/saphenous axotomy, respectively. Conditioned place preference resulting from presumed pain relief was observed following spinal clonidine in animals with sciatic axotomy but not in sham-operated controls. Similarly, lidocaine administration into the rostral ventromedial medulla (RVM) produced place preference selectively in animals with sciatic/saphenous axotomy. In rats with spinal nerve ligation (SNL) injury, lesion of the rACC blocked the reward elicited by RVM lidocaine but did not alter acute stimulus-evoked hypersensitivity. Lesion of the rACC did not block cocaine-induced reward, indicating that rACC blockade did not impair memory encoding or retrieval but did impair spontaneous aversiveness. These data indicate that spontaneous pain arising from injured nerve fibers produces a tonic aversive state that is mediated by the rACC. Identification of the circuits mediating aversiveness of chronic pain should facilitate the development of improved therapies.

Managing chronic nonspecific low back pain with a sensorimotor retraining approach: exploratory multiple-baseline study of 3 participants

BACKGROUND

Current approaches to the management of chronic nonspecific low back pain (CNSLBP) have shown limited effectiveness. It appears that disruption of cortical structure and function is a feature of CNSLBP and that these changes may contribute to current treatment failures. Sensorimotor retraining approaches have been shown to be effective in the management of other long-standing pain problems that are characterized by cortical dysfunction. Similar treatments may be an option for people with CNSLBP.

OBJECTIVE

The objectives of this study were to describe the effects of participation in a graded sensorimotor retraining program on pain intensity, interference of pain with daily life (pain interference), and self-reported disability and to evaluate the safety of the program.

DESIGN

A multiple-baseline, replicated, single-case design was used for this study.

METHODS

Three people with disabling CNSLBP were assessed weekly during a no-treatment baseline period. Each person then participated in a graded sensorimotor retraining program for a minimum of 10 weeks, during which clinical status was assessed weekly. Data collection continued weekly for 1 month after the end of formal treatment.

RESULTS

Pain intensity, pain interference, and disability all were reduced, and the improvements were maintained throughout the follow-up period. No adverse reactions to treatment were reported.

LIMITATIONS

The findings are preliminary and were based on a single-case design. The observed improvements in clinical status may have been attributable to the effects of factors other than treatment, such as the effect of time and other, nonspecific effects.

CONCLUSIONS

Positive outcomes were reported for 3 participants with CNSLBP after the completion of a graded sensorimotor retraining program. However, the findings are only preliminary and require replication with more-robust study designs.

End-to-end military pain management

The last three years have seen significant changes in the Defence Medical Services approach to trauma pain management. This article seeks to outline these changes that have occurred at every level of the casualty's journey along the chain of evacuation, from the point of injury to rehabilitation and either continued employment in the Services or to medical discharge. Particular attention is paid to the evidence for the interventions used for both acute pain and chronic pain management. Also highlighted are possible differences in pain management techniques between civilian and military casualties.

Beyond patient reported pain: perfusion magnetic resonance imaging demonstrates reproducible cerebral representation of ongoing post-surgical pain

Development of treatments for acute and chronic pain conditions remains a challenge, with an unmet need for improved sensitivity and reproducibility in measuring pain in patients. Here we used pulsed-continuous arterial spin-labelling [pCASL], a relatively novel perfusion magnetic-resonance imaging technique, in conjunction with a commonly-used post-surgical model, to measure changes in regional cerebral blood flow [rCBF] associated with the experience of being in ongoing pain. We demonstrate repeatable, reproducible assessment of ongoing pain that is independent of patient self-report. In a cross-over trial design, 16 participants requiring bilateral removal of lower-jaw third molars underwent pain-free pre-surgical pCASL scans. Following extraction of either left or right tooth, repeat scans were acquired during post-operative ongoing pain. When pain-free following surgical recovery, the pre/post-surgical scanning procedure was repeated for the remaining tooth. Voxelwise statistical comparison of pre and post-surgical scans was performed to reveal rCBF changes representing ongoing pain. In addition, rCBF values in predefined pain and control brain regions were obtained. rCBF increases (5–10%) representing post-surgical ongoing pain were identified bilaterally in a network including primary and secondary somatosensory, insula and cingulate cortices, thalamus, amygdala, hippocampus, midbrain and brainstem (including trigeminal ganglion and principal-sensory nucleus), but not in a control region in visual cortex. rCBF changes were reproducible, with no rCBF differences identified across scans within-session or between post-surgical pain sessions. This is the first report of the cerebral representation of ongoing post-surgical pain without the need for exogenous tracers. Regions of rCBF increases are plausibly associated with pain and the technique is reproducible, providing an attractive proposition for testing interventions for on-going pain that do not rely solely on patient self-report. Our findings have the potential to improve our understanding of the cerebral representation of persistent painful conditions, leading to improved identification of specific patient sub-types and implementation of mechanism-based treatments.

Maldynia: pathophysiology and management of neuropathic and maladaptive pain--a report of the AMA Council on Science and Public Health

BACKGROUND

Because of disparate taxonomic arrays for classification, the American Academy of Pain Medicine has proposed categorizing pain on a neurobiologic basis as eudynia (nociceptive pain), Greek for "good pain," or maldynia (maladaptive pain), Greek for "bad pain." The latter has been viewed as maladaptive because it may occur in the absence of ongoing noxious stimuli and does not promote healing and repair.

OBJECTIVE

To address recent findings on the pathogenesis of pain following neural injury and consider whether the development of maladaptive pain justifies its classification as a disease and to briefly discuss the scope of pharmacologic and non-pharmacologic approaches employed in patients with such pain.

METHODS

English language reports on studies using human subjects were selected from a PubMed search of the literature from 1995 to August 2010 and from the Cochrane Library. Further information was obtained from Internet sites of medical specialty and other societies devoted to pain management.

RESULTS

Neural damage to either the peripheral or central nervous system provokes multiple processes including peripheral and central sensitization, ectopic activity, neuronal cell death, disinhibition, altered gene expression, and abnormal sprouting and cellular connectivity. A series of neuro-immune interactions underlie many of these mechanisms. Imaging studies have shown that such damage is characterized by functional, structural, and chemical changes in the brain. Such pain is maladaptive in the sense that it occurs in the absence of ongoing noxious stimuli and does not promote healing and repair.

CONCLUSION

As defined, maldynia is a multidimensional process that may warrant consideration as a chronic disease not only affecting sensory and emotional processing but also producing an altered brain state based on both functional imaging and macroscopic measurements. However, the absolute clinical value of this definition is not established.

Can neuroimaging studies identify pain endophenotypes in humans?

Pain is a complex, multidimensional experience that has defied our understanding for centuries. Through the advent of noninvasive neuroimaging techniques, we have been able to examine the human brain and its response to nociceptive inputs. As a result, our knowledge of which brain regions are critical for generating an acute pain experience has grown, as has our understanding of how cognitive, emotional, contextual and various physiological factors influence the pain experience. Furthermore, we have been able to identify key processes within the brain that underpin the transition to and maintenance of chronic pain states, as well as highlight the dramatic consequences of chronic pain on the brain's structure and neurochemistry. Building upon this knowledge, we are now in a position to consider whether any of these brain imaging 'phenotypes' of acute or chronic pain should be considered as useful endophenotypes; thereby enabling us to relate the complex genetics that underpin everyday pain sensitivity or chronic pain states to intermediate biomarkers. This endophenotypic approach-the focus of this Review-simplifies the connection between genes and behavior and is needed for complex disorders like chronic pain.

The Role of the Mental Health Practitioner in the Assessment and Treatment of Child and Adolescent Chronic Pain

Chronic and recurrent benign pain complaints are common among children and adolescents. Although many young persons with chronic pain adapt well, a small, but significant, proportion experience marked functional deficits. Pain can produce life disruptions, e.g. impeding activities and maturation, and interferes with family functioning. Conventional medically-based approaches have been inadequate in addressing chronic pain and its sequelae. Instead, effective management requires an interdisciplinary approach involving paediatricians and mental health practitioners working collaboratively to treat psychiatric comorbidities, enhance the patient's functional adaptation, restore the child or adolescent's maturational and social capabilities and reduce family disruptions.

Carbamazepine for acute and chronic pain in adults

BACKGROUND

Carbamazepine is used to treat chronic neuropathic pain.

OBJECTIVES

Evaluation of analgesic efficacy and adverse effects of carbamazepine for acute and chronic pain management (except headaches).

SEARCH STRATEGY

Randomised controlled trials (RCTs) of carbamazepine in acute, chronic or cancer pain were identified, searching MEDLINE, EMBASE, SIGLE and Cochrane CENTRAL to June 2010, reference lists of retrieved papers, and reviews.

SELECTION CRITERIA

RCTs reporting the analgesic effects of carbamazepine.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted results and scored for quality. Numbers needed to treat to benefit (NNT) or harm (NNH) with 95% confidence intervals (CI) were calculated from dichotomous data for effectiveness, adverse effects and adverse event withdrawal. Issues of study quality, size, duration, and outcomes were examined.

MAIN RESULTS

Fifteen included studies (12 cross-over design; three parallel-group) with 629 participants.Carbamazepine was less effective than prednisolone in preventing postherpetic neuralgia following acute herpes zoster (1 study, 40 participants). No studies examined acute postoperative pain.Fourteen studies investigated chronic neuropathic pain: two lasted eight weeks, others were four weeks or less (mean 3 weeks, median 2 weeks). Five had low reporting quality. Ten involved fewer than 50 participants; mean and median maximum treatment group sizes were 34 and 29. Outcome reporting was inconsistent.Most placebo controlled studies indicated that carbamazepine was better than placebo. Five studies with 298 participants provided dichotomous results; 70% improved with carbamazepine and 12% with placebo. Carbamazepine at any dose, using any definition of improvement was significantly better than placebo (70% versus 12% improved; 5 studies, 298 participants); relative benefit 6.1 (3.9 to 9.7), NNT 1.7 (1.5 to 2.0). Four studies (188 participants) reporting outcomes equivalent to 50% pain reduction or more over baseline had a similar NNT.With carbamazepine, 66% of participants experienced at least one adverse event, and 27% with placebo; relative risk 2.4 (1.9 to 3.1), NNH 2.6 (2.1 to 3.5). Adverse event withdrawals occurred in12 of 323 participants (4%) with carbamazepine and 0 of 310 with placebo. Serious adverse events were not reported consistently; rashes were associated with carbamazepine. Five deaths occurred in patients on carbamazepine, with no obvious drug association.

AUTHORS' CONCLUSIONS

Carbamazepine is effective in chronic neuropathic pain, with caveats. No trial was longer than four weeks, of good reporting quality, using outcomes equivalent to at least moderate clinical benefit. In these circumstances, caution is needed in interpretation, and meaningful comparison with other interventions is not possible.

From atom to brain: applications of molecular imaging to neurosurgery

Molecular imaging is a field born out of the happy marriage of molecular biology and radiology. The first installment of this two-part series on molecular imaging demonstrated basic principles for practitioners in the field of the neurosciences. This installment seeks to provide some illustrative examples, insights, and specific applications to the neurosciences. The fields of functional neurosurgery including the treatment of neuropsychiatric disorders, novel treatments and imaging of tumors, neuroregenerative medicine, and nanotechnology in vascular disorders are covered. Finally, we give some parting thoughts on the future of molecular imaging, including advances in the imaging of neurodegenerative disorders.

Getting the pain you expect: mechanisms of placebo, nocebo and reappraisal effects in humans

The perception of pain is subject to powerful influences. Understanding how these are mediated at a neuroanatomical and neurobiological level provides us with valuable information that has a direct impact on our ability to harness positive and minimize negative effects therapeutically, as well as optimize clinical trial designs when developing new analgesics. This is particularly relevant for placebo and nocebo effects. New research findings have directly contributed to an increased understanding of how placebo and nocebo effects are produced and what biological and psychological factors influence variances in the magnitude of the effect. The findings have relevance for chronic pain states and other disorders, where abnormal functioning of crucial brain regions might affect analgesic outcome even in the normal therapeutic setting.

1H-MR spectroscopic detection of metabolic changes in pain processing brain regions in the presence of non-specific chronic low back pain

Reliable detection of metabolic changes in the brain in vivo induced by chronic low back pain may provide improved understanding of neurophysiological mechanisms underlying the manifestation of chronic pain. In the present study, absolute concentrations of N-acetyl-aspartate (NAA), creatine (Cr), total choline (tCho), myo-inositol (mI), glutamate (Glu) and glutamine (Gln) were measured in three different pain processing cortical regions (anterior insula, anterior cingulate cortex, and thalamus) of ten patients with non-specific chronic low back pain by means of proton MR spectroscopy ((1)H-MRS) and compared to matched healthy controls. Significant decrease of Glu was observed in the anterior cingulate cortex of patients. Patients also revealed a trend of decreasing Gln concentrations in all investigated brain areas. Reductions of NAA were observed in the patient group in anterior insula and in anterior cingulated cortex, whereas mI was reduced in anterior cingulated cortex and in thalamus of patients. Reduced concentrations of Glu and Gln may indicate disordered glutamatergic neurotransmission due to prolonged pain perception, whereas decrease of NAA and mI may be ascribed to neuron and glial cell loss. No significant changes were found for Cr. The morphological evaluation of anatomic brain data revealed a significantly decreased WM volume of 17% (p<0.05) as well as a non significant trend for GM volume increase in the anterior insula of patients.

Cortical changes in chronic low back pain: current state of the art and implications for clinical practice

There is increasing evidence that chronic pain problems are characterised by alterations in brain structure and function. Chronic back pain is no exception. There is a growing sentiment, with accompanying theory, that these brain changes contribute to chronic back pain, although empirical support is lacking. This paper reviews the structural and functional changes of the brain that have been observed in people with chronic back pain. We cast light on the clinical implications of these changes and the possibilities for new treatments but we also advise caution against concluding their efficacy in the absence of solid evidence to this effect.