Dissecting neuropathic from poststroke pain: the white matter within

Intraoperative recordings from the posterior superior insula in awake humans with peripheral neuropathic pain

BACKGROUND AND OBJECTIVES

The activity profile of the posterior insula in neuropathic pain (NeP) remains largely unexplored. To address this and examine its modulation by somatosensory stimulation, we recorded local field potentials (LFP) in awake patients with NeP undergoing deep brain stimulation (DBS) electrode implantation to the posterior-superior insula (PSI) for analgesic purposes.

MATERIALS AND METHODS

Six patients (one woman; 32-45 years), experiencing refractory peripheral NeP and having previously responded to non-invasive stimulation of the PSI underwent stereotactic implantation of DBS electrodes to the PSI as part of a phase II clinical trial. The averaged power of frequencies of LFP and their peaks were calculated during rest and under thermal painful and mechanical non-painful stimulation.

RESULTS

At rest, amplitude peaks within the delta (average min-max.: 2.2 Hz; 1.3-3.7) and theta (6.1 Hz, varying between 5.7 and 6.8 Hz) bands were identified. Compared to rest, both tonic thermal painful, and mechanical non-painful stimulation led to similar mean decreases in gamma power (-24.46 ± 70.56, and -19.56 ± 3.08; respectively). Painful stimuli caused an increase in all the other frequency bands, mainly in alpha and beta ranges, while non-painful stimulation led to decreases in power in all frequencies above 4Hz. Painful tonic stimulation was associated with a significantly greater power variability, both in amplitude and frequency, compared to nonpainful mechanical stimulation.

CONCLUSION

The posterior insula resting state activity in awake patients with chronic NeP was characterized by predominant theta oscillations. Painful and innocuous stimulation led to opposite spectral changes, with a much larger variability across the whole frequency spectrum for painful stimuli, relative to both resting state and non-painful stimulation.

Neuroimage Signature in Post-Stroke Pain: A Systematic Review

INTRODUCTION

Central Post-Stroke Pain (CPSP) is a debilitating condition with a significant prevalence in stroke survivors. Set apart by its refractory to treatment neuropathic pain, it appears to arise from lesions in the spino-thalamo-cortical pathways, particularly in the thalamus. Despite advances in neuroimaging techniques, the pathophysiology of CPSP remains poorly understood, with limited diagnostic criteria and therapeutic approaches.

OBJECTIVE

This systematic review aims to identify neuroimaging markers associated with CPSP, establish correlations between brain lesions and CPSP development, and explore the utility of neuroimaging techniques for diagnosis and prognosis. Secondary objectives involve establishing a link between CPSP and secondary brain area lesions and what type of pain patients with CPSP are more likely to experience.

METHODS

A systematic review was conducted following PRISMA guidelines. Relevant articles were sourced from PubMed, Embase, and Web of Science, using a predefined search strategy targeting CPSP and neuroimaging studies (MRI, PET, SPECT). Studies involving adult CPSP patients with post-stroke neuroimaging were included. Data from 14 studies was analyzed, focusing on lesion locations, neuroimaging findings, and functional connectivity. Risk of bias was assessed using the QUADAS-2 tool.

RESULTS

Key findings highlighted the association of CPSP with lesions in the ventral posterolateral and the ventral medial nuclei of the thalamus, spinothalamic pathway, and cortical areas like the insula and operculum. Functional connectivity studies highlighted the role of disrupted neural networks in pain perception. Limitations in the reviewed studies included small sample sizes, selection bias, and heterogeneity in study designs.

CONCLUSIONS

Neuroimaging findings confirm the significance of thalamic and spinothalamic pathway lesions in CPSP pathophysiology. Despite these insights, gaps in research underline the need for larger, multicenter trials to identify reliable biomarkers for diagnosis and therapeutic targets. Advanced neuroimaging combined with machine learning could be the key to understanding and managing CPSP.

Central post-stroke pain: advances in clinical and preclinical research

Central poststroke pain (CPSP) is a medical complication that arises poststroke and significantly impacts the quality of life and social functioning of affected individuals. Despite ongoing research, the exact pathomechanisms of CPSP remain unclear, and practical treatments are still unavailable. Our review aims to systematically analyse current clinical and preclinical studies on CPSP, which is critical for identifying gaps in knowledge and guiding the development of effective therapies. The review will clarify the clinical characteristics, evaluation scales and contemporary therapeutic approaches for CPSP based on clinical investigations. It will particularly emphasise the CPSP model initiated by stroke, shedding light on its underlying mechanisms and evaluating treatments validated in preclinical studies. Furthermore, the review will not only highlight methodological limitations in animal trials but also offer specific recommendations to researchers to improve the quality of future investigations and guide the development of effective therapies. This review is expected to provide valuable insights into the current knowledge regarding CPSP and can serve as a guide for future research and clinical practice. The review will contribute to the scientific understanding of CPSP and help develop effective clinical interventions.

Contributions of neuroimaging in central poststroke pain: a review

BACKGROUND

 Central neuropathic poststroke pain (CNPSP) affects up to 12% of patients with stroke in general and up to 18% of patients with sensory deficits. This pain syndrome is often incapacitating and refractory to treatment. Brain computed tomography and magnetic resonance imaging (MRI) are widely used methods in the evaluation of CNPSP.

OBJECTIVE

 The present study aims to review the role of neuroimaging methods in CNPSP.

METHODS

 We performed a literature review of the main clinical aspects of CNPSP and the contribution of neuroimaging methods to study its pathophysiology, commonly damaged brain sites, and possible differential diagnoses. Lastly, we briefly mention how neuroimaging can contribute to the non-pharmacological CNPSP treatment. Additionally, we used a series of MRI from our institution to illustrate this review.

RESULTS

 Imaging has been used to explain CNPSP pathogenesis based on spinothalamic pathway damage and connectome dysfunction. Imaging locations associated with CNPSP include the brainstem (mainly the dorsolateral medulla), thalamus (especially the ventral posterolateral/ventral posteromedial nuclei), cortical areas such as the posterior insula and the parietal operculum, and, more recently, the thalamocortical white matter in the posterior limb of the internal capsule. Imaging also brings the prospect of helping search for new targets for non-pharmacological treatments for CNPSP. Other neuropathic pain causes identified by imaging include syringomyelia, multiple sclerosis, and herniated intervertebral disc.

CONCLUSION

 Imaging is a valuable tool in the complimentary evaluation of CNPSP patients in clinical and research scenarios.

Role of Brain Derived Neurotrophic Factor and Related Therapeutic Strategies in Central Post-Stroke Pain

Brain-derived neurotrophic factor (BDNF) is vital for synaptic plasticity, cell persistence, and neuronal development in peripheral and central nervous systems (CNS). Numerous intracellular signalling pathways involving BDNF are well recognized to affect neurogenesis, synaptic function, cell viability, and cognitive function, which in turn affects pathological and physiological aspects of neurons. Stroke has a significant psycho-socioeconomic impact globally. Central post-stroke pain (CPSP), also known as a type of chronic neuropathic pain, is caused by injury to the CNS following a stroke, specifically damage to the somatosensory system. BDNF regulates a broad range of functions directly or via its biologically active isoforms, regulating multiple signalling pathways through interactions with different types of receptors. BDNF has been shown to play a major role in facilitating neuroplasticity during post-stroke recovery and a pro-nociceptive role in pain development in the nervous system. BDNF-tyrosine kinase receptors B (TrkB) pathway promotes neurite outgrowth, neurogenesis, and the prevention of apoptosis, which helps in stroke recovery. Meanwhile, BDNF overexpression plays a role in CPSP via the activation of purinergic receptors P2X4R and P2X7R. The neuronal hyperexcitability that causes CPSP is linked with BDNF-TrkB interactions, changes in ion channels and inflammatory reactions. This review provides an overview of BDNF synthesis, interactions with certain receptors, and potential functions in regulating signalling pathways associated with stroke and CPSP. The pathophysiological mechanisms underlying CPSP, the role of BDNF in CPSP, and the challenges and current treatment strategies targeting BDNF are also discussed.

Post stroke pain: Is there under-diagnosis in Black versus White patients?

Stroke incidence is higher and stroke outcomes are poorer in Black patients compared to White patients. Poststroke pain, however, is not a well understood stroke outcome. Using the National Institutes of Health All of Us Research Program database, we hypothesized that the dataset would demonstrate proportionately higher relative risk of poststroke pain in the Black poststroke patient population compared to the White poststroke patient population. However, our analysis showed that Black stroke patients were diagnosed with poststroke pain at a similar rate as White stroke patients. As our results are not consistent with other poststroke outcomes in the literature, this study identifies a potentially underdiagnosed patient population, highlighting the need for further research.

Electrostimulation of the white matter of the posterior insula and medial operculum: perception of vibrations, heat, and pain

ABSTRACT

This study aimed to characterize the sensory responses observed when electrically stimulating the white matter surrounding the posterior insula and medial operculum (PIMO). We reviewed patients operated on under awake conditions for a glioma located in the temporoparietal junction. Patients' perceptions were retrieved from operative reports. Stimulation points were registered in the Montreal Neurological Institute template. A total of 12 stimulation points in 8 patients were analyzed. Painful sensations in the contralateral leg were reported (5 sites in 5 patients) when stimulating the white matter close to the parcel OP2/3 of the Glasser atlas. Pain had diverse qualities: burning, tingling, crushing, or electric shock. More laterally, in the white matter of OP1, pain and heat sensations in the upper part of the body were described (5 sites in 2 patients). Intermingled with these sites, vibration sensations were also reported (3 sites in 2 patients). Based on the tractograms of 44 subjects from the Human Connectome Project data set, we built a template of the pathways linking the thalamus to OP2/3 and OP1. Pain sites were located in the thalamo-OP2/3 and thalamo-OP1 tracts. Heat sites were located in the thalamo-OP1 tract. In the 227 awake surgeries performed for a tumor located outside of the PIMO region, no patients ever reported pain or heat sensations when stimulating the white matter. Thus, we propose that the thalamo-PIMO connections constitute the main cortical inputs for nociception and thermoception and emphasize that preserving these fibers is of utmost importance to prevent the postoperative onset of a debilitating insulo-opercular pain syndrome.

Central neuropathic pain

Central neuropathic pain arises from a lesion or disease of the central somatosensory nervous system such as brain injury, spinal cord injury, stroke, multiple sclerosis or related neuroinflammatory conditions. The incidence of central neuropathic pain differs based on its underlying cause. Individuals with spinal cord injury are at the highest risk; however, central post-stroke pain is the most prevalent form of central neuropathic pain worldwide. The mechanisms that underlie central neuropathic pain are not fully understood, but the pathophysiology likely involves intricate interactions and maladaptive plasticity within spinal circuits and brain circuits associated with nociception and antinociception coupled with neuronal hyperexcitability. Modulation of neuronal activity, neuron-glia and neuro-immune interactions and targeting pain-related alterations in brain connectivity, represent potential therapeutic approaches. Current evidence-based pharmacological treatments include antidepressants and gabapentinoids as first-line options. Non-pharmacological pain management options include self-management strategies, exercise and neuromodulation. A comprehensive pain history and clinical examination form the foundation of central neuropathic pain classification, identification of potential risk factors and stratification of patients for clinical trials. Advanced neurophysiological and neuroimaging techniques hold promise to improve the understanding of mechanisms that underlie central neuropathic pain and as predictive biomarkers of treatment outcome.

Thermal Grill Illusion in Post-Stroke Patients: Analysis of Clinical Features and Lesion Areas

Purpose

In the thermal grill illusion, participants experience a feeling similar to burning pain. The illusion is induced by simultaneously touching warm and cool stimuli in alternating positions. In post-stroke pain, central sensitization is caused by a variety of factors, including damage to the spinothalamic tract and shoulder pain. Because the thermal grill illusion depends on central mechanisms, it has recently been suggested that it may be a useful indicator of central sensitization. Therefore, we hypothesized that post-stroke patients who are more likely to experience central sensitization may also be more likely to experience a thermal grill sensation of pain and discomfort than the likelihood among those who are less likely to experience central sensitization. However, the effects of the thermal grill illusion in post-stroke patients have not yet been reported. In this pilot study, we conducted the thermal grill illusion procedure in post-stroke patients and analyzed the relationship between clinical somatosensory functions and thermal grill sensations. We also conducted brain imaging analysis to identify brain lesion areas that were associated with thermal grill sensations.

Patients and Methods

Twenty patients (65.7 ± 11.9 years old) with post-stroke patients participated in this study. The thermal grill illusion procedure was performed as follows: patients simultaneously touched eight water-filled copper bars, with the water temperature adjusted to provide alternate warm (40°C) and cold (20°C) stimuli.

Results

Thermal grill sensation of pain and discomfort tended to be associated with the wind-up phenomenon in bedside quantitative sensory testing and thermal grill sensation of discomfort was also related to damage to the thalamic lateral nucleus.

Conclusion

These findings suggest that the thermal grill illusion might measure central sensitization, and that secondary brain hyperactivity might lead to increased thermal grill sensations.