Reduced cortical responses to noxious heat in patients with rheumatoid arthritis

Targeting Prefrontal Cortex Dysfunction in Pain

The prefrontal cortex (PFC) has justifiably become a significant focus of chronic pain research. Collectively, decades of rodent and human research have provided strong rationale for studying the dysfunction of the PFC as a contributing factor in the development and persistence of chronic pain and as a key supraspinal mechanism for pain-induced comorbidities such as anxiety, depression, and cognitive decline. Chronic pain alters the structure, chemistry, and connectivity of PFC in both humans and rodents. In this review, we broadly summarize the complexities of reported changes within both rodent and human PFC caused by pain and offer insight into potential pharmacological and nonpharmacological approaches for targeting PFC to treat chronic pain and pain-associated comorbidities. SIGNIFICANCE STATEMENT: Chronic pain is a significant unresolved medical problem causing detrimental changes to physiological, psychological, and behavioral aspects of life. Drawbacks of currently approved pain therapeutics include incomplete efficacy and potential for abuse producing a critical need for novel approaches to treat pain and comorbid disorders. This review provides insight into how manipulation of prefrontal cortex circuits could address this unmet need of more efficacious and safer pain therapeutics.

Causal relationship between rheumatoid arthritis and epilepsy in a European population: a univariate and multivariate Mendelian randomization study

Background

Several previous studies have reported an association between rheumatoid arthritis (RA) and epilepsy, but the causal relationship is unclear. The aim of this study was to assess the connection between RA and epilepsy in a European population using Mendelian randomization (MR).

Methods

Genome-wide association study summary data on RA and epilepsy from European populations were included. Univariate MR (UVMR) and multivariate MR were used to investigate the causal relationship between the two conditions. Three analysis methods were applied: inverse variance weight (IVW), MR-Egger, and weighted median, with IVW being the primary method. Cochran Q statistics, MR-PRESSO, MR-Egger intercept, leave-one-out test, and MR-Steiger test were combined for the sensitivity analysis.

Results

UVMR showed a positive association between RA and epilepsy risk (OR=1.038, 95% CI=1.007-1.038, p=0.017) that was supported by sensitivity analysis. Further MVMR after harmonizing the three covariates of hypertension, alcohol consumption, and smoking, confirmed the causal relationship between RA and epilepsy (OR=1.049, 95% CI=1.011-1.087, p=0.010).

Conclusion

This study demonstrated that RA is associated with an increased risk of epilepsy. It has emphasized that the monitoring of epilepsy risk in patients diagnosed with RA should be strengthened in clinical practice, and further studies are needed in the future to explore the potential mechanism of action connecting the two conditions.

Corticotropin-releasing hormone neurons control trigeminal neuralgia-induced anxiodepression via a hippocampus-to-prefrontal circuit

Anxiety and depression are frequently observed in patients suffering from trigeminal neuralgia (TN), but neural circuits and mechanisms underlying this association are poorly understood. Here, we identified a dedicated neural circuit from the ventral hippocampus (vHPC) to the medial prefrontal cortex (mPFC) that mediates TN-related anxiodepression. We found that TN caused an increase in excitatory synaptic transmission from vHPCCaMK2A neurons to mPFC inhibitory neurons marked by the expression of corticotropin-releasing hormone (CRH). Activation of CRH+ neurons subsequently led to feed-forward inhibition of layer V pyramidal neurons in the mPFC via activation of the CRH receptor 1 (CRHR1). Inhibition of the vHPCCaMK2A-mPFCCRH circuit ameliorated TN-induced anxiodepression, whereas activating this pathway sufficiently produced anxiodepressive-like behaviors. Thus, our studies identified a neural pathway driving pain-related anxiodepression and a molecular target for treating pain-related psychiatric disorders.

Alterations in brain structure and function in patients with osteonecrosis of the femoral head: a multimodal MRI study

Background

Pain, a major symptom of osteonecrosis of the femoral head (ONFH), is a complex sensory and emotional experience that presents therapeutic challenges. Pain can cause neuroplastic changes at the cortical level, leading to central sensitization and difficulties with curative treatments; however, whether changes in structural and functional plasticity occur in patients with ONFH remains unclear.

Methods

A total of 23 ONFH inpatients who did not undergo surgery (14 males, nine females; aged 55.61 ± 13.79 years) and 20 controls (12 males, eight females; aged 47.25 ± 19.35 years) were enrolled. Functional indices of the amplitude of low-frequency fluctuation (ALFF), regional homogeneity (ReHo), and a structural index of tract-based spatial statistics (TBSS) were calculated for each participant. The probability distribution of fiber direction was determined according to the ALFF results.

Results

ONFH patients demonstrated increased ALFF in the bilateral dorsolateral superior frontal gyrus, right medial superior frontal gyrus, right middle frontal gyrus, and right supplementary motor area. In contrast, ONFH patients showed decreased ReHo in the left superior parietal gyrus and right inferior temporal gyrus. There were no significant differences in TBSS or probabilistic tractography.

Conclusion

These results indicate cerebral pain processing in ONFH patients. It is advantageous to use functional magnetic resonance imaging to better understand pain pathogenesis and identify new therapeutic targets in ONFH patients.

A multidisciplinary assessment of pain in juvenile idiopathic arthritis

INTRODUCTION

Pain is prevalent in juvenile idiopathic arthritis (JIA). Unknowns regarding the biological drivers of pain complicate therapeutic targeting. We employed neuroimaging to define pain-related neurobiological features altered in JIA.

METHODS

16 male and female JIA patients (12.7 ± 2.8 years of age) on active treatment were enrolled, together with age- and sex-matched controls. Patients were assessed using physical examination, clinical questionnaires, musculoskeletal MRI, and structural neuroimaging. In addition, functional magnetic resonance imaging (fMRI) data were collected during the resting-state, hand-motor task performance, and cold stimulation of the hand and knee.

RESULTS

Patients with and without pain and with and without inflammation (joint and systemic) were evaluated.  Pain severity was associated with more physical stress and poorer cognitive function. Corrected for multiple comparisons, morphological analysis revealed decreased cortical thickness within the insula cortex and a negative correlation between caudate nucleus volume and pain severity. Functional neuroimaging findings suggested alteration within neurocircuitry structures regulating emotional pain processing (anterior insula) in addition to the default-mode and sensorimotor networks.

CONCLUSIONS

Patients with JIA may exhibit changes in neurobiological circuits related to pain. These preliminary findings suggest mechanisms by which pain could potentially become dissociated from detectable joint pathology and persist independently of inflammation or treatment status.

Changes in prefrontal cerebral hemodynamics during intermittent pain stimulation to gingiva: Preliminary study using functional near infrared spectroscopy

BACKGROUND/PURPOSE

Elucidating the transmission mechanism of pain signals from the orofacial area and the corresponding modification mechanism will not only aid in the understanding of pain mechanisms but also provide useful information regarding the development of pain mitigation methods. In this study, the involvement of the pain suppression system in the trigeminal area was investigated through an analysis of the activation status over time in the prefrontal cortex using functional near-infrared spectroscopy (fNIRS).

MATERIALS AND METHODS

In 28 healthy, right-handed male volunteers (average age, 30.1 ± 4.2 years) as subjects, a mild, intermittent, acute pain stimulus was administered through the implementation of pocket probing of the gingiva surrounding the right maxillary central incisor. In the prefrontal cortex, the levels of hemoglobin (Hb) were measured using the fNIRS measurement system. Average values of both oxy-Hb and deoxy-Hb were calculated at four stages: rest stage, 20 s prior to the pain stimulus application, and three stages at 20-s intervals within 1 min of stimulation. One-way analysis of variance and multiple comparisons were used to compare representative values to investigate the changes due to pain.

RESULTS

Oxy-Hb levels decreased the most during the 20 s stage directly after stimulus application. This change was seen mainly on the contralateral side, after which it returned to the resting baseline level before the stimulus application.

CONCLUSION

Our data demonstrate that in healthy males, a mechanism exists to mitigate pain involving the pain suppression system in the 20 s after feeling mild pain to the gingiva.

Pain: A Review of Interleukin-6 and Its Roles in the Pain of Rheumatoid Arthritis

Pain is a major and common symptom reported as a top priority in patients with rheumatoid arthritis (RA). Intuitively, RA-related pain is often considered to be a natural consequence of peripheral inflammation, so treatment of RA is expected to manage pain concurrently as part of inflammation control. However, pain in patients with RA can be poorly correlated with objective measures of inflammation, for example, in patients who are otherwise in remission. Joint damage appears to account for only a fraction of this residual pain. Emerging evidence suggests that alteration of peripheral and central pain processing contributes to RA-related pain; this is parallel to, but somewhat independent of, joint inflammation. Interleukin (IL)-6 is a proinflammatory cytokine that contributes to the pathogenesis of RA. It exerts systemic effects via signaling through soluble forms of the IL-6 receptor (“trans-signaling”). Evidence from preclinical studies demonstrates that intra-articular IL-6 can produce long-lasting peripheral sensitization to mechanical stimulation and suggests an important role for IL-6 in central pain sensitization. This may be partly explained by its ability to activate neurons through trans-signaling, affecting nociceptive plasticity and nerve fiber regrowth. Local activity at neuron endings may culminate in altered pain processing in the central nervous system because of persistent signaling from sensitized peripheral neurons. Peripheral and central sensitization can promote the development of chronic pain, which can have a significant impact on patients’ health and quality of life. A proportion of pain in RA may be more appropriately managed as an entity separate from inflammation. Both the peripheral and central nervous systems should be recognized as important potential systems targeted by RA. The substantial burden of RA-related chronic pain suggests that pain should be a key focus in RA management and should be assessed and addressed early and separately from the inflammatory component.

Brain Correlates of Continuous Pain in Rheumatoid Arthritis as Measured by Pulsed Arterial Spin Labeling

OBJECTIVE

Central nervous system pathways involving pain modulation shape the pain experience in patients with chronic pain. The aims of this study were to understand the mechanisms underlying pain in patients with rheumatoid arthritis (RA) and to identify brain signals that may serve as imaging markers for developing targeted treatments for RA-related pain.

METHODS

Patients with RA and matched control subjects underwent functional magnetic resonance imaging, using pulsed arterial spin labeling. The imaging conditions included 1) resting state, 2) low-intensity stimulus, and 3) high-intensity stimulus. Stimuli consisted of mechanical pressure applied to metacarpophalangeal (MCP) joints with an automated cuff inflator. The low-intensity stimulus was inflation to 30 mm Hg. The high-intensity stimulus was the amount of pressure required to achieve a pain intensity rating of 40 on a 100-point scale for each RA patient, with the same amount of pressure used in the matched control.

RESULTS

Among RA patients, regional cerebral blood flow (rCBF) in the medial frontal cortex and dorsolateral prefrontal cortex increased during both low-pressure and high-pressure stimulation. No rCBF changes were observed in pain-free controls. Region-of-interest analyses in RA patients showed that baseline rCBF in the medial frontal cortex was negatively correlated with the pressure required for the high-intensity stimulus and positively correlated with pain induced by the low-intensity stimulus. Baseline rCBF was also marginally correlated with disease activity). Regional CBF during high pain was positively correlated with pain severity and pain interference.

CONCLUSION

In response to clinically relevant joint pain evoked by pressure applied to the MCP joint, neural processing in the medial frontal cortex increases and is directly associated with clinical pain in patients with RA.

Altered cerebral pain processing of noxious stimuli from inflamed joints in rheumatoid arthritis: An event-related fMRI study

OBJECTIVE

To our knowledge, this is the first study assessing brain activation in response to painful stimulation over disease-relevant (finger joint) vs. neutral area (thumb nail) in patients suffering from rheumatoid arthritis (RA) compared to healthy controls (HC).

METHOD

Thirty-one RA patients and 23 HC underwent functional magnetic resonance imaging (fMRI) while stimulated with subjectively calibrated painful pressures corresponding to a pain sensation of 50 mm on a 100 mm VAS scale (P50) at disease-affected finger joint and thumbnail (left hand), and corresponding sites in HC.

RESULTS

Compared to controls, RA patients had significantly increased pain sensitivity (lower P50) at the inflamed joints but not at the thumbnail. RA patients exhibited significantly less activation in regions related to pain- and somatosensory processing (S1, M1, anterior insula, S2, SMG and MCC) during painful joint stimulation, compared to HC. No group difference in cerebral pain processing was found for the non-affected thumbnail. Within RA patients, significantly less brain activation was found in response to painful stimulation over disease-affected joint compared to non-affected thumbnail in bilateral S1, bilateral S2, and anterior insula. Further, RA patients exhibited a right-sided dlPFC deactivation, psycho-physiologically interacting (PPI) with the left dlPFC in response to painful stimulation at disease-affected joints.

CONCLUSION

The results indicate normal pain sensitivity and cerebral pain processing in RA for non-affected sites, while the increased sensitivity at inflamed joints indicate peripheral/spinal sensitization. Brain imaging data suggest that disease-relevant pain processing in RA is marked by aberrations and a failed initiation of cortical top-down regulation.

Altered Excitability and Local Connectivity of mPFC-PAG Neurons in a Mouse Model of Neuropathic Pain

The medial prefrontal cortex (mPFC) plays a major role in both sensory and affective aspects of pain. There is extensive evidence that chronic pain produces functional changes within the mPFC. However, our understanding of local circuit changes to defined subpopulations of mPFC neurons in chronic pain models remains unclear. A major subpopulation of mPFC neurons project to the periaqueductal gray (PAG), which is a key midbrain structure involved in endogenous pain suppression and facilitation. Here, we used laser scanning photostimulation of caged glutamate to map cortical circuits of retrogradely labeled cortico-PAG (CP) neurons in layer 5 (L5) of mPFC in brain slices prepared from male mice having undergone chronic constriction injury (CCI) of the sciatic nerve. Whole-cell recordings revealed a significant reduction in excitability for L5 CP neurons contralateral to CCI in the prelimbic (PL), but not infralimbic (IL), region of mPFC. Circuit mapping showed that excitatory inputs to L5 CP neurons in both PL and IL arose primarily from layer 2/3 (L2/3) and were significantly reduced in CCI mice. Glutamate stimulation of L2/3 and L5 elicited inhibitory inputs to CP neurons in both PL and IL, but only L2/3 input was significantly reduced in CP neurons of CCI mice. We also observed significant reduction in excitability and L2/3 inhibitory input to CP neurons ipsilateral to CCI. These results demonstrating region and laminar specific changes to mPFC-PAG neurons suggest that a unilateral CCI bilaterally alters cortical circuits upstream of the endogenous analgesic network, which may contribute to persistence of chronic pain.SIGNIFICANCE STATEMENT Chronic pain is a significant unresolved medical problem that is refractory to traditional analgesics and can negatively affect emotional health. The role of central circuits in mediating the persistent nature of chronic pain remains unclear. Local circuits within the medial prefrontal cortex (mPFC) process ascending pain inputs and can modulate endogenous analgesia via direct projections to the periaqueductal gray (PAG). However, the mechanisms by which chronic pain alters intracortical circuitry of mPFC-PAG neurons are unknown. Here, we report specific changes to local circuits of mPFC-PAG neurons in mice displaying chronic pain behavior after nerve injury. These findings provide evidence for a neural mechanism by which chronic pain disrupts the descending analgesic system via functional changes to cortical circuits.

A critical evaluation of validity and utility of translational imaging in pain and analgesia: Utilizing functional imaging to enhance the process

Assessing clinical pain and metrics related to function or quality of life predominantly relies on patient reported subjective measures. These outcome measures are generally not applicable to the preclinical setting where early signs pointing to analgesic value of a therapy are sought, thus introducing difficulties in animal to human translation in pain research. Evaluating brain function in patients and respective animal model(s) has the potential to characterize mechanisms associated with pain or pain-related phenotypes and thereby provide a means of laboratory to clinic translation. This review summarizes the progress made towards understanding of brain function in clinical and preclinical pain states elucidated using an imaging approach as well as the current level of validity of translational pain imaging. We hypothesize that neuroimaging can describe the central representation of pain or pain phenotypes and yields a basis for the development and selection of clinically relevant animal assays. This approach may increase the probability of finding meaningful new analgesics that can help satisfy the significant unmet medical needs of patients.

Brodmann area 10: Collating, integrating and high level processing of nociception and pain

Multiple frontal cortical brain regions have emerged as being important in pain processing, whether it be integrative, sensory, cognitive, or emotional. One such region, Brodmann Area 10 (BA 10), is the largest frontal brain region that has been shown to be involved in a wide variety of functions including risk and decision making, odor evaluation, reward and conflict, pain, and working memory. BA 10, also known as the anterior prefrontal cortex, frontopolar prefrontal cortex or rostral prefrontal cortex, is comprised of at least two cytoarchitectonic sub-regions, medial and lateral. To date, the explicit role of BA 10 in the processing of pain hasn't been fully elucidated. In this paper, we first review the anatomical pathways and functional connectivity of BA 10. Numerous functional imaging studies of experimental or clinical pain have also reported brain activations and/or deactivations in BA 10 in response to painful events. The evidence suggests that BA 10 may play a critical role in the collation, integration and high-level processing of nociception and pain, but also reveals possible functional distinctions between the subregions of BA 10 in this process.

Reduced local field potential power in the medial prefrontal cortex by noxious stimuli

Nociceptive signals produced by noxious stimuli at the periphery reach the brain through ascending pathways. These signals are processed by various brain areas and lead to activity changes in those areas. The medial prefrontal cortex (mPFC) is involved in higher cognitive functions and emotional processing. It receives projections from brain areas involved in nociception. In this study, we investigated how nociceptive input from the periphery changes the local field potential (LFP) activity in the mPFC. Three different types of noxious stimuli were applied to the hind paw contralateral to the LFP recording site. They were transcutaneous electrical stimulations, mechanical stimuli and a chemical stimulus (formalin injection). High intensity transcutaneous stimulations (10V to 50V) and noxious mechanical stimulus (pinch) significantly reduced the LFP power during the stimulating period (p<0.05), but not the low intensity subcutaneous stimulations (0.1V to 5V) and other innocuous mechanical stimuli (brush and pressure). More frequency bands were inhibited with increased intensity of transcutaneous electrical stimulation, and almost all frequency bands were inhibited by stimulations at or higher than 30v. Pinch significantly reduced the power for beta band and formalin injection significantly reduced the power of alpha and beta band. Our data demonstrated the noxious stimuli-induced reduction of LFP power in the mPFC, which indicates the active processing of nociceptive information by the mPFC.

Intrinsic Brain Connectivity in Chronic Pain: A Resting-State fMRI Study in Patients with Rheumatoid Arthritis

Background: Rheumatoid arthritis (RA) is commonly accompanied by pain that is discordant with the degree of peripheral pathology. Very little is known about the cerebral processes involved in pain processing in RA. Here we investigated resting-state brain connectivity associated with prolonged pain in RA.

Methods: 24 RA subjects and 19 matched controls were compared with regard to both behavioral measures of pain perception and resting-resting state fMRI data acquired subsequently to fMRI sessions involving pain stimuli. The resting-state fMRI brain connectivity was investigated using 159 seed regions located in cardinal pain processing brain regions. Additional principal component based multivariate pattern analysis of the whole brain connectivity pattern was carried out in a data driven analysis to localize group differences in functional connectivity.

Results: When RA patients were compared to controls, we observed significantly lower pain resilience for pressure on the affected finger joints (i.e., P50-joint) and an overall heightened level of perceived global pain in RA patients. Relative to controls, RA patients displayed increased brain connectivity predominately for the supplementary motor areas, mid-cingulate cortex, and the primary sensorimotor cortex. Additionally, we observed an increase in brain connectivity between the insula and prefrontal cortex as well as between anterior cingulate cortex and occipital areas for RA patients. None of the group differences in brain connectivity were significantly correlated with behavioral parameters.

Conclusion: Our study provides experimental evidence of increased connectivity between frontal midline regions that are implicated in affective pain processing and bilateral sensorimotor regions in RA patients.

Unexplained Painful Physical Symptoms in Patients with Major Depressive Disorder: Prevalence, Pathophysiology and Management

Patients with major depression often report pain. In this article, we review the current literature regarding the prevalence and consequences, as well as the pathophysiology, of unexplained painful physical symptoms (UPPS) in patients with major depressive disorder (MDD). UPPS are experienced by approximately two-thirds of depressed patients. The presence of UPPS makes a correct diagnosis of depression more difficult. Moreover, UPPS are a predictor of a poor response to treatment and a more chronic course of depression. Pain, in the course of depression, also has a negative impact on functioning and quality of life. Frequent comorbidity of depression and UPPS has inspired the formulation of an hypothesis regarding a shared neurobiological mechanism of both conditions. Evidence from neuroimaging studies has shown that frontal-limbic dysfunction in depression may explain abnormal pain processing, leading to the presence of UPPS. Increased levels of proinflamatory cytokines and substance P in patients with MDD may also clarify the pathophysiology of UPPS. Finally, dysfunction of the descending serotonergic and noradrenergic pathways that normally suppress ascending sensations has been proposed as a core mechanism of UPPS. Psychological factors such as catastrophizing also play a role in both depression and chronic pain. Therefore, pharmacological treatment and/or cognitive therapy are recommended in the treatment of depression with UPPS. Some data suggest that serotonin and noradrenaline reuptake inhibitors (SNRIs) are more effective than selective serotonin reuptake inhibitors (SSRIs) in the alleviation of depression and UPPS. However, the pooled analysis of eight randomised clinical trials showed similar efficacy of duloxetine (an SNRI) and paroxetine (an SSRI) in reducing UPPS in depression. Further integrative studies examining genetic factors (e.g. polymorphisms of genes for interleukins, serotonin transporter and receptors), molecular factors (e.g. cytokines, substance P) and neuroimaging findings (e.g. functional studies during painful stimulation) might provide further explanation of the pathophysiology of UPPS in MDD and therefore facilitate the development of more effective methods of treatment.

Pain in Times of Stress

Stress modulates pain perception, resulting in either stress-induced analgesia or stress-induced hyperalgesia, as reported in both animal and human studies. The responses to stress include neural, endocrine, and behavioural changes, and built-in coping strategies are in place to address stressors. Peculiar to humans are additional factors that modulate pain that are experienced in times of stress, notably psychological factors that potentially influence the directionality of pain perception.

Response to peripheral immune stimulation within the brain: magnetic resonance imaging perspective of treatment success

Chronic peripheral inflammation in diseases such as rheumatoid arthritis leads to alterations in central pain processing and consequently to mood disorders resulting from sensitization within the central nervous system and enhanced vulnerability of the medial pain pathway. Proinflammatory cytokines such as tumor necrosis factor (TNF) alpha play an important role herein, and therapies targeting their signaling (i.e., anti-TNF therapies) have been proven to achieve good results. However, the phenomenon of rapid improvement in the patients’ subjective feeling after the start of TNFα neutralization remained confusing, because it was observed long before any detectable signs of inflammation decline. Functional magnetic resonance imaging (fMRI), enabling visualization of brain activity upon peripheral immune stimulation with anti-TNF, has helped to clarify this discrepancy. Moreover, fMRI appeared to work as a reliable tool for predicting prospective success of anti-TNF therapy, which is valuable considering the side effects of the drugs and the high therapy costs. This review, which is mainly guided by neuroimaging studies of the brain, summarizes the state-of-the-art knowledge about communication between the immune system and the brain and its impact on subjective well-being, addresses in more detail the outcome of the abovementioned anti-TNF fMRI studies (rapid response to TNFα blockade within the brain pain matrix and differences in brain activation patterns between prospective therapy responders and nonresponders), and discusses possible mechanisms for the latter phenomena and the predictive power of fMRI.

A Large-Scale Study Indicates Increase in the Risk of Epilepsy in Patients With Different Risk Factors, Including Rheumatoid Arthritis

Peripheral neuropathy and inflammatory reactions of the central nervous system may accompany rheumatoid arthritis (RA). Inflammatory processes play a critical role in epilepsy. Therefore, we conducted this study to determine the risk of epilepsy in patients with RA.The RA cohort comprised patients ages 20 years and older who were newly diagnosed with RA between 2000 and 2011, with data obtained from the Registry of Catastrophic Illnesses Patient Database. Patients without RA were frequency matched with an RA cohort at a 1:1 ratio according to age, sex, and year of RA diagnosis.The overall crude hazard ratio (HR) for epilepsy was 1.27-fold higher in the RA cohort compared with that in the controls. After adjustment for age, sex, comorbidities, and medications, the patients with RA were associated with an increased risk of epilepsy compared with those without RA (adjusted HR [aHR] = 1.52, 95% confidence interval [CI] = 1.12-2.07). Compared with the RA patients with ≤ 560 days of nonsteroidal anti-inflammatory drug (NSAID) use, the RA patients with 1181 to 2145 and >2145 days of NSAID use had a significantly lower risk of epilepsy (aHR = 0.35, 95% CI = 0.24-0.52 and aHR = 0.15, 95% CI = 0.09-0.24, respectively).This study provides compelling evidence of an increased risk of epilepsy in patients with RA. The period of NSAID treatment is negatively associated with the risk of epilepsy in RA patients.

Mechanisms, impact and management of pain in rheumatoid arthritis

People with rheumatoid arthritis (RA) identify pain as their most important symptom, one that often persists despite optimal control of inflammatory disease. RA pain arises from multiple mechanisms, involving inflammation, peripheral and central pain processing and, with disease progression, structural change within the joint. Consequently, RA pain has a wide range of characteristics-constant or intermittent, localized or widespread-and is often associated with psychological distress and fatigue. Dominant pain mechanisms in an individual are identified by critical evaluation of clinical symptoms and signs, and by laboratory and imaging tests. Understanding these mechanisms is essential for effective management, although evidence from preclinical models should be interpreted with caution. A range of pharmacological analgesic and immunomodulatory agents, psychological interventions and surgery may help manage RA pain. Pain contributes importantly to the clinical assessment of inflammatory disease activity, and noninflammatory components of RA pain should be considered when gauging eligibility for or response to biologic agents. Further randomized controlled trials are required to determine the optimal usage of analgesics in RA, and novel agents with greater efficacy and lower propensity for adverse events are urgently needed. Meanwhile, targeted use of existing treatments could reduce pain in people with RA.

Diagnostic classification based on functional connectivity in chronic pain: model optimization in fibromyalgia and rheumatoid arthritis

RATIONALE AND OBJECTIVES

The combination of functional magnetic resonance imaging (fMRI) of the brain with multivariate pattern analysis (MVPA) has been proposed as a possible diagnostic tool. Goal of this investigation was to identify potential functional connectivity (FC) differences in the salience network (SN) and default mode network (DMN) between fibromyalgia syndrome (FMS), rheumatoid arthritis (RA), and controls (HC) and to evaluate the diagnostic applicability of derived pattern classification approaches.

MATERIALS AND METHODS

The resting period during an fMRI examination was retrospectively analyzed in women with FMS (n = 17), RA (n = 16), and HC (n = 17). FC was calculated for SN and DMN subregions. Classification accuracies of discriminative MVPA models were evaluated with cross-validation: (1) inferential test of a single method, (2) explorative model optimization.

RESULTS

No inferentially tested model was able to classify subjects with statistically significant accuracy. However, the diagnostic ability for the differential diagnostic problem exhibited a trend to significance (accuracy: 69.7%, P = .086). Optimized models in the explorative analysis reached accuracies up to 73.5% (FMS vs. HC), 78.8% (RA vs. HC), and 78.8% (FMS vs. RA) whereas other models performed at or below chance level. Comparable support vector machine approaches performed above average for all three problems.

CONCLUSIONS

Observed accuracies are not sufficient to reliably differentiate between FMS and RA for diagnostic purposes. However, some indirect evidence in support of the feasibility of this approach is provided. This exploratory analysis constitutes a fundamental model optimization effort to be based on in further investigations.

Imaging pain: a potent means for investigating pain mechanisms in patients

Chronic pain is a state of physical suffering strongly associated with feelings of anxiety, depression and despair. Disease pathophysiology, psychological state, and social milieu can influence chronic pain, but can be difficult to diagnose based solely on clinical presentation. Here, we review brain neuroimaging research that is shaping our understanding of pain mechanisms, and consider how such knowledge might lead to useful diagnostic tools for the management of persistent pain in individual patients.

Role of functional brain imaging in understanding rheumatic pain

Rheumatic pain and, in particular, rheumatoid arthritis, osteoarthritis and fibromyalgia, are common and debilitating chronic pain syndromes. Recently, human functional neuroimaging, for example EEG, fMRI, and PET has begun to reveal some of the crucial central nervous system mechanisms underlying these diseases. The purpose of this review is to summarise current knowledge on the brain mechanisms of rheumatic pain revealed by functional neuroimaging techniques. The evidence suggests that two mechanisms may be largely responsible for the clinical pain associated with these rheumatic diseases: abnormalities in the medial pain system and/or central nervous system sensitisation and inhibition. If we can understand how functioning of the central nociceptive system becomes altered, even in the absence of peripheral nociceptive input, by using functional neuroimaging techniques, in the future we may be able to develop improved, more effective treatments for patients with chronic rheumatic pain.

Imaging pain in arthritis: advances in structural and functional neuroimaging

Arthritis is a heterogeneous disease characterized by joint stiffness, swelling, and pain. Although primarily considered a peripheral joint disease, the severity of pain reported by arthritis patients does not always reflect the extent of joint pathology detectable by conventional means. Using structural and functional brain imaging techniques, a growing number of evolving neuroimaging methods are providing insight into these observed discrepancies at different time-scales. Of these methods, functional magnetic resonance imaging is exploited for short-term evoked pain examination and treatment evaluation; 'resting-state' approaches provide insight into fluctuations in pain; perfusion imaging captures elements of on-going clinical pain; and morphological brain assessment provides evidence for long-term structural changes in the brain associated with chronic pain. Further insight into arthritic pain processing at the brain-systems level could in the future be provided by combined neuroimaging approaches, specifically investigating the interactions between functional and structural alterations.

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.

The role of the central nervous system in the generation and maintenance of chronic pain in rheumatoid arthritis, osteoarthritis and fibromyalgia

Pain is a key component of most rheumatologic diseases. In fibromyalgia, the importance of central nervous system pain mechanisms (for example, loss of descending analgesic activity and central sensitization) is well documented. A few studies have also noted alterations in central pain processing in osteoarthritis, and some data, including the observation of widespread pain sensitivity, suggest that central pain-processing defects may alter the pain response in rheumatoid arthritis patients. When central pain is identified, different classes of analgesics (for example, serotonin-norepinephrine reuptake inhibitors, α2δ ligands) may be more effective than drugs that treat peripheral or nociceptive pain (for example, nonsteroidal anti-inflammatory drugs and opioids).

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 quantitative sensory testing in the evaluation of musculoskeletal pain conditions

Quantitative sensory testing (QST) is a noninvasive method of assessing sensory and pain perception that has been used in the past 30 years primarily for analysis of cutaneous and mucosal perception. In recent years, several published studies have demonstrated that QST may be useful in the analysis of painful musculoskeletal disorders as well. Based on the results of these studies, it can be postulated that QST may be useful in the analysis of the pathogenesis, classification, and differential diagnosis of musculoskeletal disorders. However, due to the diverse ethiopathogenetic basis of these disorders, a broad range of QST test batteries may be necessary to analyze the various musculoskeletal disease entities. This review analyzes published studies on this subject and summarizes current information on altered sensory and pain perception available for some of the most common musculoskeletal disorders. At present, QST remains primarily a research tool but may be useful in differential diagnosis in indicating the presence of central sensitization and for clinical monitoring of disease progression or treatment response.

Functional exploration for neuropathic pain

Neuropathic pain (NP) may become refractory to conservative medical management, necessitating neurosurgical procedures in carefully selected cases. In this context, the functional neurosurgeon must have suitable knowledge of the disease he or she intends to treat, especially its pathophysiology. This latter factor has been studied thanks to advances in the functional exploration of NP, which will be detailed in this review. The study of the flexion reflex is a useful tool for clinical and pharmacological pain assessment and for exploring the mechanisms of pain at multiple levels. The main use of evoked potentials is to confirm clinical, or detect subclinical, dysfunction in peripheral and central somato-sensory pain pathways. LEP and SEP techniques are especially useful when used in combination, allowing the exploration of both pain and somato-sensory pathways. PET scans and fMRI documented rCBF increases to noxious stimuli. In patients with chronic NP, a decreased resting rCBF is observed in the contralateral thalamus, which may be reversed using analgesic procedures. Abnormal pain evoked by innocuous stimuli (allodynia) has been associated with amplification of the thalamic, insular and SII responses, concomitant to a paradoxical CBF decrease in ACC. Multiple PET studies showed that endogenous opioid secretion is very likely to occur as a reaction to pain. In addition, brain opioid receptors (OR) remain relatively untouched in peripheral NP, while a loss of ORs is most likely to occur in central NP, within the medial nociceptive pathways. PET receptor studies have also proved that antalgic Motor Cortex Stimulation (MCS), indicated in severe refractory NP, induces endogenous opioid secretion in key areas of the endogenous opioid system, which may explain one of the mechanisms of action of this procedure, since the secretion is proportional to the analgesic effect.

Unravelling the mystery of pain, suffering, and relief with brain imaging

In humans, the experience of pain and suffering is conveyed specifically by language. Noninvasive neuroimaging techniques now provide an account of neural activity in the human brain when pain is experienced. Knowledge gleaned from neuroimaging experiments has shaped contemporaneous accounts of pain. Within the biopsychosocial framework, nociception is undoubtedly required for survival, but is neither necessary nor sufficient for the consciousness of pain in humans. Pain emerges from the brain, which also exerts a top-down influence on nociception. In the brains of patients with chronic pain, neuroimaging has revealed subtle but significant structural, functional, and neurochemical abnormalities. Converging evidence suggests that the chronic pain state may arise from dysfunction of the frontal-limbic system. Further research in the clinical pain population will continue to identify neural mechanisms that contribute to the experience and consequence of pain, which may then be targeted therapeutically.

A multi-scale view of skin thermal pain: from nociception to pain sensation

All biological bodies live in a thermal environment, including the human body, where skin is the interface with a protecting function. When the temperature is out of the normal physiological range, skin fails to protect, and the pain sensation is evoked. Furthermore, in medicine, with advances in laser, microwave and similar technologies, various thermal therapeutic methods have been widely used to cure disease/injury involving skin tissue. However, the corresponding problem of pain relief has limited further application and development of these thermal treatments. Skin thermal pain is induced through both direct (i.e. an increase/decrease in temperature) and indirect (e.g. thermomechanical and thermochemical) ways, and is governed by complicated thermomechanical-chemical-neurophysiological responses. However, a complete understanding of the underlying mechanisms is still far from clear. In this article, starting from an engineering perspective, we aim to recast the biological behaviour of skin in engineering system parlance. Then, by coupling the concepts of engineering with established methods in neuroscience, we attempt to establish multi-scale modelling of skin thermal pain through ion channel to pain sensation. The model takes into account skin morphological plausibility, the thermomechanical response of skin tissue and the biophysical and neurological mechanisms of pain sensation.

Fibromyalgia unique temporal brain activation during experimental pain: a controlled fMRI Study

Studies with functional neuroimaging support the hypothesis of central pain augmentation in fibromyalgia syndrome (FMS) with functional differences in areas of the medial pain system. To clarify whether these findings are unique to patients with FMS, BOLD-signal patterns during and before tonic experimental pain were compared to healthy controls and patients with rheumatoid arthritis (RA) as a chronic pain disorder of somatic origin. We expected different BOLD-signal patterns in areas of the medial pain system that were most pronounced in patients with FMS. An fMRI-block design before, during and after an incision was performed in patients with FMS (n = 17), RA (n = 16) and in healthy controls (n = 17). A 2-factorial model of BOLD-signal changes was designed to explore significant differences of brain activation between the groups during the pain stimulus. Additionally, the correlation of brain activity during the anticipation of pain with the amount of the impending pain was determined. We observed a FMS-unique temporal brain activation of the frontal cortex in patients with FMS. Moreover, areas of the motor cortex and the cingulate cortex presented a FMS-specific relation between brain activity during pain anticipation and the magnitude of the subsequent pain experience. Our results support the hypothesis that central mechanisms of pain processing in the frontal cortex and cingulate cortex may play an important role in patients with FMS.

The relationship between disease activity, sleep, psychiatric distress and pain sensitivity in rheumatoid arthritis: a cross-sectional study

Introduction

Despite recent advances in anti-inflammatory therapy, rheumatoid arthritis (RA) patients continue to rate pain as a priority. The etiology of RA pain is likely multifactorial, including both inflammatory and non-inflammatory components. In this study, we examine the association between disease activity, sleep, psychiatric distress and pain sensitivity in RA.

Methods

Fifty-nine female RA patients completed questionnaires and underwent pressure pain threshold testing to assess hyperalgesia/allodynia at joint and non-joint sites. Blood samples were taken to measure C-reactive protein (CRP). The association between disease activity, sleep problems, psychiatric distress and pain threshold was assessed using Pearson/Spearman correlations and multivariable linear regression. Disease activity levels, sleep problems and psychiatric distress were compared between RA patients with fibromyalgia and RA patients without fibromyalgia.

Results

In unadjusted analyses, CRP was not correlated with pain threshold, but tender joint count was inversely correlated with pain threshold at all sites (P ≤ 0.004). Sleep problems were associated with low pain threshold at all sites (P ≤ 0.0008). Psychiatric distress was associated with low pain threshold at the wrist and thumbnail (P ≤ 0.006). In multivariable linear regression models, CRP was inversely associated with wrist pain threshold (P = 0.003). Sleep problems were inversely associated with pain threshold at all sites (P ≤ 0.01), but psychiatric distress was not. Despite differences in pain threshold, CRP levels and sleep problems between RA patients with fibromyalgia and those without fibromyalgia, associations between these variables did not change when patients with fibromyalgia were excluded.

Conclusions

Multivariable models are essential in analyses of pain. Among RA patients, inflammation is associated with heightened pain sensitivity at joints. In contrast, poor sleep is associated with diffuse pain sensitivity, as noted in central pain conditions such as fibromyalgia. Future studies examining pain sensitivity at joint and non-joint sites may identify patients with different underlying pain mechanisms and suggest alternative approaches to treating RA pain.

Forebrain pain mechanisms

Emotional-affective and cognitive dimensions of pain are less well understood than nociceptive and nocifensive components, but the forebrain is believed to play an important role. Recent evidence suggests that subcortical and cortical brain areas outside the traditional pain processing network contribute critically to emotional-affective responses and cognitive deficits related to pain. These brain areas include different nuclei of the amygdala and certain prefrontal cortical areas. Their roles in various aspects of pain will be discussed. Biomarkers of cortical dysfunction are being identified that may evolve into therapeutic targets to modulate pain experience and improve pain-related cognitive impairment. Supporting data from preclinical studies in neuropathic pain models will be presented. Neuroimaging analysis provides evidence for plastic changes in the pain processing brain network. Results of clinical studies in neuropathic pain patients suggest that neuroimaging may help determine mechanisms of altered brain functions in pain as well as monitor the effects of pharmacologic interventions to optimize treatment in individual patients. Recent progress in the analysis of higher brain functions emphasizes the concept of pain as a multidimensional experience and the need for integrative approaches to determine the full spectrum of harmful or protective neurobiological changes in pain.

Imaging pain of fibromyalgia

Brain imaging studies have provided objective evidence of abnormal central regulation of pain in fibromyalgia (FM). Resting brain blood flow studies have reported mixed findings for several brain regions, whereas decreased thalamic blood flow has been noted by several investigators. Studies examining the function of the nociceptive system in FM have reported augmented brain responses to both painful and non-painful stimuli that may be influenced by psychologic dispositions such as depressed mood and catastrophizing. Treatment approaches are beginning to demonstrate the potential for brain imaging to improve our understanding of pain-alleviating mechanisms. Data from other chronic conditions suggest that idiopathic pain may be maintained by similar central abnormalities as in FM, whereas chronic pain conditions with a known nociceptive source may not be. Future neuroimaging research in FM is clearly warranted and should continue to improve our understanding of factors involved in pain maintenance and symptom exacerbation.

Arthritic pain is processed in brain areas concerned with emotions and fear

OBJECTIVE

Functional neuroimaging studies have shown that experimentally induced acute pain is processed within at least 2 parallel networks of brain structures collectively known as the pain matrix. The relevance of this finding to clinical pain is not known, because no direct comparisons of experimental and clinical pain have been performed in the same group of patients. The aim of this study was to compare directly the brain areas involved in processing arthritic pain and experimental pain in a group of patients with osteoarthritis (OA).

METHODS

Twelve patients with knee OA underwent positron emission tomography of the brain, using (18)F-fluorodeoxyglucose (FDG). Scanning was performed during 3 different pain states: arthritic knee pain, experimental knee pain, and pain-free. Significant differences in the neuronal uptake of FDG between different pain states were investigated using statistical parametric mapping software.

RESULTS

Both pain conditions activated the pain matrix, but arthritic pain was associated with increased activity in the cingulate cortex, the thalamus, and the amygdala; these areas are involved in the processing of fear, emotions, and in aversive conditioning.

CONCLUSION

Our results suggest that studies of experimental pain provide a relevant but quantitatively incomplete picture of brain activity during arthritic pain. The search for new analgesics for arthritis that act on the brain should focus on drugs that modify this circuitry.

Brain imaging of clinical pain states: a critical review and strategies for future studies

Research into brain imaging of pain is largely dominated by experimental acute-pain studies. Applied study paradigms have evolved a lot over past years and the ensuing results have furthered enormously our understanding of acute-pain processing. In sharp contrast, published work on brain-imaging in chronic pain remains scant. Furthermore, the results of these studies are highly incongruent, which could be explained by the fact that patient populations studied varied largely in terms of pain history, pain distribution, cause of pain, and psychological set-up. To circumvent these problems, several investigators have used surrogate models of neuropathic pain, but the validity of these models is highly questionable. In this Review we critically discuss the problems and shortcomings of most published reports on chronic pain and we propose some strategies for future studies. We argue that the post-operative pain model is highly appealing since it opens perspectives for prospective longitudinal studies with repeated assessments and it enables control for many confounding factors, which hamper the interpretation of most current studies. We also plead for a multimodal imaging approach in which classic brain-activation studies are supplemented with genetic, neurochemistry, brain morphometry, and transcranial magnetic stimulation studies.