On the relation between sensory deafferentation, pain and thalamic activity in Wallenberg's syndrome: A PET-scan study before and after motor cortex stimulation

[The EAN-NeuPSIG guideline on the diagnosis of neuropathic pain-a summary]

In this joint guideline of the scientific societies and working groups mentioned in the title, evidence-based recommendations for the use of screening questionnaires and diagnostic tests in patients with neuropathic pain were developed. The systematic literature search and meta-analysis yielded the following results: Of the screening questionnaires, Douleur Neuropathique en 4 Questions (DN4), I‑DN4 (self-administered DN4), and Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) received a strong recommendation, while S‑LANSS (self-administered LANSS) and PainDETECT received weak recommendations for their use in the diagnostic workup of patients with possible neuropathic pain. There was a strong recommendation for the use of skin biopsy and a weak recommendation for quantitative sensory testing and nociceptive evoked potentials. The role of confocal corneal microscopy is still unclear. Functional imaging and peripheral nerve blocks are helpful in elucidating the pathophysiology, but current literature does not support their use in diagnosing neuropathic pain. In selected cases, genetic testing in specialized centers may be considered.

Joint European Academy of Neurology-European Pain Federation-Neuropathic Pain Special Interest Group of the International Association for the Study of Pain guidelines on neuropathic pain assessment

BACKGROUND AND PURPOSE

In these guidelines, we aimed to develop evidence-based recommendations for the use of screening questionnaires and diagnostic tests in patients with neuropathic pain (NeP).

METHODS

We systematically reviewed studies providing information on the sensitivity and specificity of screening questionnaires, and quantitative sensory testing, neurophysiology, skin biopsy, and corneal confocal microscopy. We also analysed how functional neuroimaging, peripheral nerve blocks, and genetic testing might provide useful information in diagnosing NeP.

RESULTS

Of the screening questionnaires, Douleur Neuropathique en 4 Questions (DN4), I-DN4 (self-administered DN4), and Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) received a strong recommendation, and S-LANSS (self-administered LANSS) and PainDETECT weak recommendations for their use in the diagnostic pathway for patients with possible NeP. We devised a strong recommendation for the use of skin biopsy and a weak recommendation for quantitative sensory testing and nociceptive evoked potentials in the NeP diagnosis. Trigeminal reflex testing received a strong recommendation in diagnosing secondary trigeminal neuralgia. Although many studies support the usefulness of corneal confocal microscopy in diagnosing peripheral neuropathy, no study specifically investigated the diagnostic accuracy of this technique in patients with NeP. Functional neuroimaging and peripheral nerve blocks are helpful in disclosing pathophysiology and/or predicting outcomes, but current literature does not support their use for diagnosing NeP. Genetic testing may be considered at specialist centres, in selected cases.

CONCLUSIONS

These recommendations provide evidence-based clinical practice guidelines for NeP diagnosis. Due to the poor-to-moderate quality of evidence identified by this review, future large-scale, well-designed, multicentre studies assessing the accuracy of diagnostic tests for NeP are needed.

The Roles of Imaging Biomarkers in the Management of Chronic Neuropathic Pain

Chronic neuropathic pain (CNP) affects around 10% of the general population and has a significant social, emotional, and economic impact. Current diagnosis techniques rely mainly on patient-reported outcomes and symptoms, which leads to significant diagnostic heterogeneity and subsequent challenges in management and assessment of outcomes. As such, it is necessary to review the approach to a pathology that occurs so frequently, with such burdensome and complex implications. Recent research has shown that imaging methods can detect subtle neuroplastic changes in the central and peripheral nervous system, which can be correlated with neuropathic symptoms and may serve as potential markers. The aim of this paper is to review available imaging methods used for diagnosing and assessing therapeutic efficacy in CNP for both the preclinical and clinical setting. Of course, further research is required to standardize and improve detection accuracy, but available data indicate that imaging is a valuable tool that can impact the management of CNP.

Supraspinal Mechanisms Underlying Ocular Pain

Supraspinal mechanisms of pain are increasingly understood to underlie neuropathic ocular conditions previously thought to be exclusively peripheral in nature. Isolating individual causes of centralized chronic conditions and differentiating them is critical to understanding the mechanisms underlying neuropathic eye pain and ultimately its treatment. Though few functional imaging studies have focused on the eye as an end-organ for the transduction of noxious stimuli, the brain networks related to pain processing have been extensively studied with functional neuroimaging over the past 20 years. This article will review the supraspinal mechanisms that underlie pain as they relate to the eye.

Brain MRI-guided focused ultrasound conceptualised as a tool for brain network intervention

Magnetic resonance imaging guided high intensity focused ultrasound (HIFU) has emerged as a tool offering incisionless intervention on brain tissue. The low risk and rapid recovery from this procedure, in addition to the ability to assess for clinical benefit and adverse events intraprocedurally, makes it an ideal tool for intervention upon brain networks both for clinical and research applications. This review article proposes that conceptualising brain focused ultrasound as a tool for brain network intervention and adoption of methodology to complement this approach may result in better clinical outcomes, fewer adverse events and may unveil or allow treatment opportunities not otherwise possible. A brief introduction to network neuroscience is discussed before a description of pathological brain networks is provided for a number of conditions for which MRI-guided brain HIFU intervention has been implemented. Essential Tremor is discussed as the most advanced example of MRI-guided brain HIFU intervention adoption along with the issues that present with this treatment modality compared to alternatives. The brain network intervention paradigm is proposed to overcome these issues and a number of examples of implementation of this are discussed. The ability of low intensity MRI guided focussed ultrasound to neuromoduate brain tissue without lesioning is introduced. This tool is discussed with regards to its potential clinical application as well as its potential to further our understanding of network neuroscience via its ability to interrogate brain networks without damaging tissue. Finally, a number of current clinical trials utilising brain focused ultrasound are discussed, along with the additional applications available from the utilisation of low intensity focused ultrasound.

Repetitive transcranial magnetic stimulation alone and in combination with motor control exercise for the treatment of individuals with chronic non-specific low back pain (ExTraStim trial): study protocol for a randomised controlled trial

INTRODUCTION

While multiple pharmacological and non-pharmacological interventions treating chronic non-specific low back pain (CLBP) are available, they have been shown to produce at best modest effects. Interventions such as repetitive transcranial magnetic stimulation (rTMS), a form of non-invasive brain stimulation, have exhibited promising results to alleviate chronic pain. However, evidence on the effectiveness of rTMS for CLBP is scarce due to limited rigorous clinical trials. Combining rTMS with motor control exercises (MCE) may help to address both central and nociceptive factors contributing to the persistence of LBP. The primary aim of this randomised controlled trial is to compare the effectiveness of a combination of rTMS and MCE to repeated rTMS sessions alone, sham rTMS and a combination of sham rTMS and MCE on pain intensity.

METHODS AND ANALYSIS

One hundred and forty participants (35/group) with CLBP will be randomised into four groups (active rTMS+MCE, sham rTMS+MCE, active rTMS and sham rTMS) to receive 10 sessions of their allocated intervention. The primary outcome will be the pain intensity, assessed at baseline, 4, 8, 12 and 24 weeks. Secondary outcomes will include disability, fear of movement, quality of life and patient global rating of change.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the Comité d'éthique de la recherche sectoriel en réadaptation et intégration sociale, CIUSS de la Capitale Nationale in June 2019 (#2020-1844 - CER CIUSSS-CN). The results of the study will be submitted to a peer-reviewed journal and scientific meetings.

TRIAL REGISTRATION NUMBER

NCT04555278.

Long-term Effect and Predictive Factors of Motor Cortex and Spinal Cord Stimulation for Chronic Neuropathic Pain

The long-term effects of motor cortex stimulation (MCS) and spinal cord stimulation (SCS) remain unknown. To identify the long-term effects after MCS or SCS and determine any associated predictive factors for the outcomes. Fifty patients underwent MCS (n = 15) or SCS (n = 35) for chronic neuropathic pain. The degree of pain was assessed preoperatively, at 1, 6, and 12 months after surgery, and during the time of the last follow-up using Visual Analog Scale (VAS). Percentage of pain relief (PPR) was calculated, with “long-term effect” defined as PPR ≥ 30% and the presence of continued pain relief over 12 months. Outcomes were classified into excellent (PPR ≥ 70%) and good (PPR 30–69%) sub-categories. Long-term effects of MCS and SCS were observed in 53.3% and 57.1% of the patients, respectively. There were no predictive factors of long-term effects identified for any of the various preoperative conditions. However, the VAS at 1 month after surgery was significantly associated with the long-term effects in both MCS and SCS. All patients with an excellent outcome at 1 month after the surgery continued to exhibit these effects. In contrast, patients with the good outcome at 1 month exhibited a significant decrease in the effects at 6 months after surgery. The long-term effects of MCS and SCS were approximately 50% during the more than 8.5 and 3.5 years of follow-up, respectively. The VAS at 1 month after surgery may be a postoperative predictor of the long-term effects for both MCS and SCS.

Metabolic Changes in Central Poststroke Pain Following Thalamic Intracerebral Hemorrhage: An 18F-FDG PET Study

PURPOSE

Central poststroke pain (CPSP) is one of the most refractory neuropathic pains following stroke. Injury in the spinothalamic pathway appears crucial for the development of CPSP, but changes in activity in multiple brain regions may also be related. We investigated brain metabolic changes in patients with CPSP following thalamic intracerebral hemorrhage (ICH).

METHODS

Forty-three patients with thalamic ICH were examined. Overall brain metabolism was measured with F-FDG PET. Images were analyzed with statistical parametric mapping (SPM12). Patients with CPSP (n = 20) were compared with patients without CPSP (n = 23). In addition, the association between regional brain metabolism and the severity of CPSP was investigated.

RESULTS

In comparison to patients in the non-CPSP group, the CPSP group exhibited significant hypometabolism in the ipsilesional precentral, postcentral gyri, and the contralesional cuneus (Puncorrected < 0.001), whereas significant hypermetabolism was found in the medial dorsal nucleus of the contralesional thalamus (Puncorrected < 0.001). In addition, brain metabolism in the ipsilesional Crus I and Crus II of the cerebellum was positively correlated to pain intensity ratings (Puncorrected < 0.001).

CONCLUSION

Our findings suggested that an altered state of resting brain metabolism in various brain regions related to sensory processing and cognitive functioning may be involved in the underlying mechanism of CPSP following thalamic ICH.

Deep brain stimulation for stroke: Current uses and future directions

BACKGROUND

Survivors of stroke often experience significant disability and impaired quality of life related to ongoing maladaptive responses and persistent neurologic deficits. Novel therapeutic options are urgently needed to augment current approaches. One way to promote recovery and ameliorate symptoms may be to electrically stimulate the surviving brain. Various forms of brain stimulation have been investigated for use in stroke, including deep brain stimulation (DBS).

OBJECTIVE/METHODS

We conducted a comprehensive literature review in order to 1) review the use of DBS to treat post-stroke maladaptive responses including pain, dystonia, dyskinesias, and tremor and 2) assess the use and potential utility of DBS for enhancing plasticity and recovery from post-stroke neurologic deficits.

RESULTS/CONCLUSIONS

A large variety of brain structures have been targeted in post-stroke patients, including motor thalamus, sensory thalamus, basal ganglia nuclei, internal capsule, and periventricular/periaqueductal grey. Overall, the reviewed clinical literature suggests a role for DBS in the management of several post-stroke maladaptive responses. More limited evidence was identified regarding DBS for post-stroke motor deficits, although existing work tentatively suggests DBS-particularly DBS targeting the posterior limb of the internal capsule-may improve paresis in certain circumstances. Substantial future work is required both to establish optimal targets and parameters for treatment of maladapative responses and to further investigate the effectiveness of DBS for post-stroke paresis.

Reduction of chronic abdominal pain in patients with inflammatory bowel disease through transcranial direct current stimulation: a randomized controlled trial

Inflammatory bowel disease (IBD) is frequently associated with chronic abdominal pain (CAP). Transcranial direct current stimulation (tDCS) has been proven to reduce chronic pain. This study aimed to investigate the effects of tDCS in patients with CAP due to IBD. This randomized, sham-controlled, double blind, parallel-designed study included 20 patients with either Crohn disease or ulcerative colitis with CAP (≥3/10 on the visual analog scale (VAS) in 3/6 months). Anodal or sham tDCS was applied over the primary motor cortex for 5 consecutive days (2 mA, 20 minutes). Assessments included VAS, pressure pain threshold, inflammatory markers, and questionnaires on quality of life, functional and disease specific symptoms (Irritable Bowel Syndrome-Severity Scoring System [IBS-SSS]), disease activity, and pain catastrophizing. Follow-up data were collected 1 week after the end of the stimulation. Statistical analyses were performed using analysis of variance and t tests. There was a significant reduction of abdominal pain in the anodal tDCS group compared with sham tDCS. This effect was evident in changes in VAS and pressure pain threshold on the left and right sides of the abdomen. In addition, 1 week after stimulation, pain reduction remained significantly decreased in the right side of the abdomen. There was also a significant reduction in scores on pain catastrophizing and on IBS-SSS when comparing both groups. Inflammatory markers and disease activity did not differ significantly between groups throughout the experiment. Transcranial direct current stimulation proved to be an effective and clinically relevant therapeutic strategy for CAP in IBD. The analgesic effects observed are unrelated to inflammation and disease activity, which emphasizes central pain mechanisms in CAP.

Capturing brain metrics of neuropathic pain using nuclear magnetic resonance

SUMMARY Neuropathic pain is typically caused by a lesion or dysfunction in the nervous system that results in both negative (i.e., reduced sensitivity) and positive symptoms (i.e., paraesthesia, spontaneous ongoing pain with shooting, electric shock-like sensations and abnormal responses to evoked pain). Intriguingly, chronic pain disorders manifest profound alterations in brain structure and function, and thus, modern nuclear magnetic resonance (NMR) techniques have allowed us to begin to dissect the complexities of how neuropathic pain affects the brain. NMR approaches can be used as an independent measure to improve our understanding of key changes in brain structure, function and chemistry in chronic neuropathic pain. Accordingly, NMR techniques provide neurobiological metrics that allow us to understand the neurobiological basis of chronic neuropathic pain. Additionally, although at an early stage, NMR methods can also be useful to define clinical metrics to predict chronification of neuropathic pain and responses to drugs. This article provides a review of NMR techniques and their capacity to study spontaneous pain and evoked pain, as well as structural, functional and neurochemical alterations that have repeatedly been associated with chronic neuropathic pain. Finally, the importance for quantifying disease state and treatment efficacy in neuropathic pain using NMR techniques is discussed.

Therapeutic effects of non-invasive brain stimulation with direct currents (tDCS) in neuropsychiatric diseases

Neuroplasticity, which is the dynamic structural and functional reorganization of central nervous system connectivity due to environmental and internal demands, is recognized as a major physiological basis for adaption of cognition, and behavior, and thus of utmost importance for normal brain function. Pathological alterations of plasticity are increasingly explored as pathophysiological foundation of diverse neurological and psychiatric diseases. Non-invasive brain stimulation techniques (NIBS), such as repetitive transcranial magnetic stimulation (rTMS), and transcranial direct current stimulation (tDCS), are able to induce and modulate neuroplasticity in humans. Therefore, they have potential to alter pathological plasticity on the one hand, and foster physiological plasticity on the other, in neuropsychiatric diseases to reduce symptoms, and enhance rehabilitation. tDCS is an emerging NIBS tool, which induces glutamatergic plasticity via application of relatively weak currents through the scalp in humans. In the last years its efficacy to treat neuropsychiatric diseases has been explored increasingly. In this review, we will give an overview of pathological alterations of plasticity in neuropsychiatric diseases, gather clinical studies involving tDCS to ameliorate symptoms, and discuss future directions of application, with an emphasis on optimizing stimulation effects.

Motor cortex stimulation for facial chronic neuropathic pain: A review of the literature

Background:

Facial chronic neuropathic pain (FCNP) is a disabling clinical entity, its incidence is increasing within the chronic pain population. There is indication for neuromodulation when conservative treatment fails. Motor cortex stimulation (MCS) has emerged as an alternative in the advanced management of these patients. The aim of this work is to review the worldwide literature on MCS for FCNP.

Methods:

A PubMed search from 1990 to 2012 was conducted using established MeSH words. A total of 126 relevant articles on MCS focused on chronic pain were selected and analysed. Series of cases were divided in (1) series focused on MCS for FCNP, and (2) MCS series of FCNP mixed with other chronic pain entities.

Results:

A total of 118 patients have been trialed for MCS for FCNP, 100 (84.7%) pursued permanent implantation of the system, and 84% of them had good pain control at the end of the study. Male: female ratio was about 1:2 in the whole group of studies; mean age was 58 years (range, 28–83), and mean pain duration was 7 years (range, 0.6–25). Four randomized controlled studies have been reported, all of them not focused on MCS for FCNP. The most common complication was seizure followed by wound infection. Preoperative evaluation, surgical techniques, and final settings varied among the series.

Conclusion:

MCS for FNCP is a safe and efficacious treatment option when previous managements have failed; however, there is still lack of strong evidence (larger randomized controlled multicentre studies) that MCS can be offered in a regular basis to FNCP patients.

Dynamics of Circadian Thalamocortical Flow of Information during a Peripheral Neuropathic Pain Condition

It is known that the thalamocortical loop plays a crucial role in the encoding of sensory–discriminative features of painful stimuli. However, only a few studies have addressed the changes in thalamocortical dynamics that may occur after the onset of chronic pain. Our goal was to evaluate how the induction of chronic neuropathic pain affected the flow of information within the thalamocortical loop throughout the brain states of the sleep–wake cycle. To address this issue we recorded local field potentials (LFPs) – both before and after the establishment of neuropathic pain in awake freely moving adult rats chronically implanted with arrays of multielectrodes in the lateral thalamus and primary somatosensory cortex. Our results show that the neuropathic injury induced changes in the number of wake and slow-wave-sleep (SWS) state episodes, and especially in the total number of transitions between brain states. Moreover, partial directed coherence – analysis revealed that the amount of information flow between cortex and thalamus in neuropathic animals decreased significantly, indicating that the overall thalamic activity had less weight over the cortical activity. However, thalamocortical LFPs displayed higher phase-locking during awake and SWS episodes after the nerve lesion, suggesting faster transmission of relevant information along the thalamocortical loop. The observed changes are in agreement with the hypothesis of thalamic dysfunction after the onset of chronic pain, and may result from diminished inhibitory effect of the primary somatosensory cortex over the lateral thalamus.

Motor Cortex Stimulation Improves Local Cerebral Glucose Metabolism in the Ipsilateral Thalamus in Patients With Poststroke Pain: Case Report

BACKGROUND AND IMPORTANCE:

Motor cortex stimulation (MCS) is documented as an effective therapeutic option for patients with poststroke pain. However, its underlying mechanism is still unclear. This study aimed to evaluate local cerebral glucose metabolism before and after MCS in patients with poststroke pain.

CLINICAL PRESENTATION:

Using 18F-fluorodeoxyglucose positron emission tomography, cerebral metabolic rate for glucose (CMRGlu) was measured in 6 patients with poststroke pain before MCS. Their lesions were located in the corona radiata, internal capsule, and thalamus. An epidural electrode was implanted under the monitoring of intraoperative neuronavigation and somatosensory evoked/motor evoked potentials. 18F-fluorodeoxyglucose positron emission tomography was repeated in 4 patients (67%) who underwent successful MCS. Asymmetry of CMRGlu was semiquantitatively analyzed using an automated region of interest setting method. Before MCS, the ratio of CMRGlu in the ipsilateral to contralateral thalamus was 0.81 ± 0.13 (n = 6), (range, 0.63-0.97). However, there was no significant asymmetry of CMRGlu in other regions. Successful MCS significantly improved the asymmetry of CMRGlu in the ipsilateral thalamus from 0.81 ± 0.14 to 0.89 ± 0.17 (P &lt; .01, n = 4). The therapeutic effect was proportional to the improvement of CMRGlu asymmetry (R = 0.79, P = 0.28; single regression analysis).

CONCLUSION:

Poststroke pain is closely related to the reduced glucose use in the thalamus contralateral to the painful area. Successful MCS significantly improves glucose use in the thalamus ipsilateral to MCS, suggesting that electrical stimulation of the motor cortex may activate the corticothalamic connection from the motor cortex.

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

In this review, we present data from functional, structural, and molecular imaging studies in patients and animals supporting the notion that it might be time to reconsider chronic pain as a disease. Across a range of chronic pain conditions, similar observations have been made regarding changes in structure and function within the brains of patients. We discuss these observations within the framework of the current definition of a disease.

PERSPECTIVE

Neuroimaging studies have made a significant scientific impact in the study of pain. Knowledge of nociceptive processing in the noninjured and injured central nervous system has grown considerably over the past 2 decades. This review examines the information from these functional, structural, and molecular studies within the framework of a disease state.

Low-frequency BOLD fluctuations demonstrate altered thalamocortical connectivity in diabetic neuropathic pain

Background

In this paper we explored thalamocortical functional connectivity in a group of eight patients suffering from peripheral neuropathic pain (diabetic pain), and compared it with that of a group of healthy subjects. We hypothesized that functional interconnections between the thalamus and cortex can be altered after years of ongoing chronic neuropathic pain.

Results

Functional connectivity was studied through a resting state functional magnetic resonance imaging (fMRI) paradigm: temporal correlations between predefined regions of interest (primary somatosensory cortex, ventral posterior lateral thalamic nucleus, medial dorsal thalamic nucleus) and the rest of the brain were systematically investigated. The patient group showed decreased resting state functional connectivity between the thalamus and the cortex.

Conclusion

This supports the idea that chronic pain can alter thalamocortical connections causing a disruption of thalamic feedback, and the view of chronic pain as a thalamocortical dysrhythmia.

[Central post-stroke pain]

Central post-stroke pain (CPSP) is known since the famous Dejerine-Roussy syndrome and its description has not improved. The subject has however been revived over the last decade thanks to advances in central nervous system imaging with magnetic resonance imaging (MRI), the description of allodynia functional phenomena with fMRI, the study of opioid receptors, and above all, the analysis of pain pathways by laser-evoked potentials. Progress has also occurred in CPSP treatment with motor cortex stimulation, which probably opens a period of neuromodulation of the cortical areas controlling pain. The thalamus plays a prominent role in this disorder of central control of pain.

Fibromyalgia: a disorder of the brain?

This article presents evidence that fibromyalgia patients have alterations in CNS anatomy, physiology, and chemistry that potentially contribute to the symptoms experienced by these patients. There is substantial psychophysical evidence that fibromyalgia patients perceive pain and other noxious stimuli differently than healthy individuals and that normal pain modulatory systems, such as diffuse noxious inhibitory control mechanisms, are compromised in fibromyalgia. Furthermore, functional brain imaging studies revealing enhanced pain-related activations corroborate the patients' reports of increased pain. Neurotransmitter studies show that fibromyalgia patients have abnormalities in dopaminergic, opioidergic, and serotoninergic systems. Finally, studies of brain anatomy show structural differences between the brains of fibromyalgia patients and healthy individuals. The cerebral alterations offer a compelling explanation for the multiple symptoms of fibromyalgia, including widespread pain and affective disturbances. The frequent comorbidity of fibromyalgia with stress-related disorders, such as chronic fatigue, posttraumatic stress disorder, irritable bowel syndrome, and depression, as well as the similarity of many CNS abnormalities, suggests at least a partial common substrate for these disorders. Despite the numerous cerebral alterations, fibromyalgia might not be a primary disorder of the brain but may be a consequence of early life stress or prolonged or severe stress, affecting brain modulatory circuitry of pain and emotions in genetically susceptible individuals.

The cerebral signature for pain perception and its modulation

Our understanding of the neural correlates of pain perception in humans has increased significantly since the advent of neuroimaging. Relating neural activity changes to the varied pain experiences has led to an increased awareness of how factors (e.g., cognition, emotion, context, injury) can separately influence pain perception. Tying this body of knowledge in humans to work in animal models of pain provides an opportunity to determine common features that reliably contribute to pain perception and its modulation. One key system that underpins the ability to change pain intensity is the brainstem's descending modulatory network with its pro- and antinociceptive components. We discuss not only the latest data describing the cerebral signature of pain and its modulation in humans, but also suggest that the brainstem plays a pivotal role in gating the degree of nociceptive transmission so that the resultant pain experienced is appropriate for the particular situation of the individual.