Central Poststroke Pain: A Review of Pathophysiology and Treatment

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.

The P2X7 Hypothesis of Central Post-Stroke Pain

The present study examined how P2X7 receptor knockout (KO) modulates central post-stroke pain (CPSP) induced by lesions of the ventrobasal complex (VBC) of the thalamus in behaviors, molecular levels, and electrical recording tests. Following the experimental procedure, the wild-type and P2X7 receptor KO mice were injected with 10 mU/0.2 μL type IV collagenase in the VBC of the thalamus to induce an animal model of stroke-like thalamic hemorrhage. Behavioral data showed that the CPSP group induced thermal and mechanical pain. The P2X7 receptor KO group showed reduced thermal and mechanical pain responses compared to the CPSP group. Molecular assessments revealed that the CPSP group had lower expression of NeuN and KCC2 and higher expression of GFAP, IBA1, and BDNF. The P2X7 KO group showed lower expression of GFAP, IBA1, and BDNF but nonsignificant differences in KCC2 expression than the CPSP group. The expression of NKCC1, GABAa receptor, and TrkB did not differ significantly between the control, CPSP, and P2X7 receptor KO groups. Muscimol, a GABAa agonist, application increased multiunit numbers for monitoring many neurons and [Cl-] outflux in the cytosol in the CPSP group, while P2X7 receptor KO reduced multiunit activity and increased [Cl-] influx compared to the CPSP group. P2X4 receptor expression was significantly decreased in the 100 kDa but not the 50 kDa site in the P2X7 receptor KO group. Altogether, the P2X7 hypothesis of CPSP was proposed, wherein P2X7 receptor KO altered the CPSP pain responses, numbers of astrocytes and microglia, CSD amplitude of the anterior cingulate cortex and the medial dorsal thalamus, BDNF expression, [Cl-] influx, and P2X4 expression in 100 kDa with P2X7 receptors. The present findings have implications for the clinical treatment of CPSP symptoms.

Repetitive transcranial magnetic stimulation in central post-stroke pain: a meta-analysis and systematic review of randomized controlled trials

Background

The rehabilitation of central post-stroke pain (CPSP) is a complex clinical challenge, and repetitive transcranial magnetic stimulation (rTMS) has been widely applied in the research of neurofunctional recovery following stroke. However, there is currently no reliable evidence-based medicine supporting the efficacy of rTMS in central post-stroke pain. This review aims to evaluate the effects of rTMS on central post-stroke pain.

Methods

Following the PRISMA guidelines, we conducted searches on PubMed, Cochrane Library, Embase, Web of Science, CNKI, and Wan Fang Data Knowledge Service Platform. We searched for randomized controlled trials (RCTs) investigating the use of rTMS in treating central post-stroke pain, and conducted screening based on inclusion and exclusion criteria. Characteristics of the included RCTs were extracted. The heterogeneity of the trials was assessed using the I2 statistic. Meta-analysis was performed using Stata 17 software. Bias risk and methodological quality were evaluated using the Cochrane RoB 2 tool and the Pedro scale.

Results

A total of six randomized controlled trials involving 288 patients met our inclusion criteria. In our analysis, rTMS was more effective in treating patients with CPSP compared to the placebo group (SMD=-1.15, 95% CI: -1.69, -0.61, P < 0.001). Furthermore, results from subgroup analysis indicated no statistically significant difference in the improvement of pain for durations exceeding 6 months when comparing rTMS to conventional treatment (SMD=-0.80, 95% CI: -1.63, 0.03, P = 0.059).

Conclusion

TMS can alleviate pain in CPSP patients and improve their motor function, but its effects on depression, anxiety, and MEP-latency are not significant.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, CRD42024497530.

Transcranial magnetic stimulation therapy for central post-stroke pain: systematic review and meta-analysis

Introduction

Although rare, central post-stroke pain remains one of the most refractory forms of neuropathic pain. It has been reported that repetitive transcranial magnetic stimulation (rTMS) may be effective in these cases of pain.

Aim

The aim of this study was to investigate the efficacy of rTMS in patients with central post-stroke pain (CPSP).

Methods

We included randomized controlled trials or Controlled Trials published until October 3rd, 2022, which studied the effect of rTMS compared to placebo in CPSP. We included studies of adult patients (>18 years) with a clinical diagnosis of stroke, in which the intervention consisted of the application of rTMS to treat CSP.

Results

Nine studies were included in the qualitative analysis; 6 studies (4 RCT and 2 non-RCT), with 180 participants, were included in the quantitative analysis. A significant reduction in CPSP was found in favor of rTMS compared with sham, with a large effect size (SMD: -1.45; 95% CI: -1.87; -1.03; p < 0.001; I2: 58%).

Conclusion

The findings of the present systematic review with meta-analysis suggest that there is low quality evidence for the effectiveness of rTMS in reducing CPSP.

Systematic review registration

Identifier (CRD42022365655).

Research Progress on the Mechanisms of Central Post-Stroke Pain: A Review

Central Post-Stroke Pain (CPSP) is a primary sequelae of stroke that can develop in the body part corresponding to the cerebrovascular lesion after stroke, most typically after ischemic stroke but also after hemorrhagic stroke. The pathogenesis of CPSP is currently unknown, and research into its mechanism is ongoing. To summarize current research on the CPSP mechanism and provide guidance for future studies. Use "central post-stroke pain," "stroke AND thalamic pain," "stroke AND neuropathic pain," "post-stroke thalamic pain" as the search term. The search was conducted in the PubMed and China National Knowledge Infrastructure databases, summarizing and classifying the retrieved mechanism studies. The mechanistic studies on CPSP are extensive, and we categorized the included mechanistic studies and summarized them in terms of relevant pathway studies, relevant signals and receptors, relevant neural tissues, and described endoplasmic reticulum stress and other relevant studies, as well as summarized the mechanisms of acupuncture treatment. Studies have shown that the pathogenesis of CPSP involves the entire spinal-thalamo-cortical pathway and that multiple substances in the nervous system are involved in the formation and development of CPSP. Among them, the relevant receptors and signals are the hotspot of research, and the discovery and exploration of different receptors and signals have provided a wide range of therapeutic ideas for CPSP. As a very effective treatment, acupuncture is less studied regarding the analgesic mechanism of CPSP, and further experimental studies are still needed.

NLR family pyrin domain containing 3 (NLRP3) inflammasomes and peripheral neuropathic pain - Emphasis on microRNAs (miRNAs) as important regulators

Neuropathic pain is caused by the lesion or disease of the somatosensory system and can be initiated and/or maintained by both central and peripheral mechanisms. Nerve injury leads to neuronal damage and apoptosis associated with the release of an array of pathogen- or damage-associated molecular patterns to activate inflammasomes. The activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome contributes to neuropathic pain and may represent a novel target for pain therapeutic development. In the current review, we provide an up-to-date summary of the recent findings on the involvement of NLRP3 inflammasome in modulating neuropathic pain development and maintenance, focusing on peripheral neuropathic conditions. Here we provide a detailed review of the mechanisms whereby NLRP3 inflammasomes contribute to neuropathic pain via (1) neuroinflammation, (2) apoptosis, (3) pyroptosis, (4) proinflammatory cytokine release, (5) mitochondrial dysfunction, and (6) oxidative stress. We then present the current research literature reporting on the antinociceptive effects of several natural products and pharmacological interventions that target activation, expression, and/or regulation of NLRP3 inflammasome. Furthermore, we emphasize the effects of microRNAs as another regulator of NLRP3 inflammasome. In conclusion, we summarize the possible caveats and future perspectives that might provide successful therapeutic approaches against NLRP3 inflammasome for treating or preventing neuropathic pain conditions.

Stroke-Induced Central Pain: Overview of the Mechanisms, Management, and Emerging Targets of Central Post-Stroke Pain

The incidence of stroke plays the foremost role in the genesis of central neuropathic pain. Central post-stroke pain (CPSP) is a central pain arising from a vascular lesion in the central nervous system that elicits somatosensory deficits, often contralateral to stroke lesions. It is expressed as continuous or intermittent pain accompanied by sensory abnormalities like dysesthesia and allodynia. CPSP remains de-emphasized due to the variation in onset and diversity in symptoms, besides the difficulty of distinguishing it from other post-stroke pains, often referred to as a diagnosis of exclusion. Spinothalamic dysfunction, disinhibition of the medial thalamus, and neuronal hyperexcitability combined with deafferentation in thalamocortical regions are the mechanisms underlying central pain, which play a significant role in the pathogenesis of CPSP. The treatment regimen for CPSP seems to be perplexed in nature; however, based on available studies, amitriptyline and lamotrigine are denoted as first-line medications and non-pharmacological choices may be accounted for cases intractable to pharmacotherapy. This review attempts to provide an overview of the mechanisms, existing management approaches, and emerging targets of CPSP. A profound understanding of CPSP aids in optimizing the quality of life among stroke sufferers and facilitates further research to develop newer therapeutic agents for managing CPSP.

A predictive model based on random forest for shoulder-hand syndrome

Objectives

The shoulder-hand syndrome (SHS) severely impedes the function recovery process of patients after stroke. It is incapable to identify the factors at high risk for its occurrence, and there is no effective treatment. This study intends to apply the random forest (RF) algorithm in ensemble learning to establish a predictive model for the occurrence of SHS after stroke, aiming to identify high-risk SHS in the first-stroke onset population and discuss possible therapeutic methods.

Methods

We retrospectively studied all the first-onset stroke patients with one-side hemiplegia, then 36 patients that met the criteria were included. The patients’ data concerning a wide spectrum of demographic, clinical, and laboratory data were analyzed. RF algorithms were built to predict the SHS occurrence, and the model’s reliability was measured with a confusion matrix and the area under the receiver operating curves (ROC).

Results

A binary classification model was trained based on 25 handpicked features. The area under the ROC curve of the prediction model was 0.8 and the out-of-bag accuracy rate was 72.73%. The confusion matrix indicated a sensitivity of 0.8 and a specificity of 0.5, respectively. And the feature importance scored the weights (top 3 from large to small) in the classification were D-dimer, C-reactive protein, and hemoglobin.

Conclusion

A reliable predictive model can be established based on post-stroke patients’ demographic, clinical, and laboratory data. Combining the results of RF and traditional statistical methods, our model found that D-dimer, CRP, and hemoglobin affected the occurrence of the SHS after stroke in a relatively small sample of data with tightly controlled inclusion criteria.

The Potential Role of Etanercept in the Management of Post-stroke Pain: A Literature Review

Strokes are the second leading cause of death and disability worldwide. The brain injury resulting from stroke produces a persistent neuroinflammatory response in the brain, resulting in a spectrum of neurologic dysfunction affecting stroke survivors chronically, also known as post-stroke pain. Excess production of tumor necrosis factor alpha (TNF alpha) in the cerebrospinal fluid (CSF) of stroke survivors has been implicated in post-stroke pain. Therefore, this literature review aims to assess and review the role of perispinal etanercept in the management of post-stroke pain. Several studies have shown statistically significant evidence that etanercept, a TNF alpha inhibitor, can reduce symptoms present in post-stroke syndrome by targeting the excess TNF alpha produced in the CSF. Studies have also shown improvements in not only post-stroke pain but also in traumatic brain injury and dementia. Further research is needed to explore the effects of TNF alpha on stroke prognosis and determine the optimal frequency and duration of etanercept treatment for post-stroke pain.

The mechanism and effect of repetitive transcranial magnetic stimulation for post-stroke pain

Post-stroke pain (PSP) is a common complication after stroke and affects patients' quality of life. Currently, drug therapy and non-invasive brain stimulation are common treatments for PSP. Given the poor efficacy of drug therapy and various side effects, non-invasive brain stimulation, such as repetitive transcranial magnetic stimulation (rTMS), has been accepted by many patients and attracted the attention of many researchers because of its non-invasive and painless nature. This article reviews the therapeutic effect of rTMS on PSP and discusses the possible mechanisms. In general, rTMS has a good therapeutic effect on PSP. Possible mechanisms of its analgesia include altering cortical excitability and synaptic plasticity, modulating the release of related neurotransmitters, and affecting the structural and functional connectivity of brain regions involved in pain processing and modulation. At present, studies on the mechanism of rTMS in the treatment of PSP are lacking, so we hope this review can provide a theoretical basis for future mechanism studies.

Relief of Central Poststroke Pain Affecting Both the Arm and Leg on One Side by Double-independent Dual-lead Spinal Cord Stimulation Using Fast-acting Subperception Therapy Stimulation: A Case Report

Central poststroke pain is a chronic, intractable, central neuropathic pain. Spinal cord stimulation is a neuromodulation therapy for chronic neuropathic pain. The conventional stimulation method induces a sense of paresthesia. Fast-acting subperception therapy is one of the latest new stimulation methods without paresthesia. A case of achieving pain relief of central poststroke pain affecting both the arm and leg on one side by double-independent dual-lead spinal cord stimulation using fast-acting subperception therapy stimulation is presented. A 67-year-old woman had central poststroke pain due to a right thalamic hemorrhage. The numerical rating scale scores of the left arm and leg were 6 and 7, respectively. Using dual-lead stimulation at the Th 9-11 levels, a spinal cord stimulation trial was performed. Fast-acting subperception therapy stimulation achieved pain reduction in the left leg from 7 to 3. Therefore, a pulse generator was implanted, and the pain relief continued for 6 months. Then, two additional leads were implanted at the C 3-5 levels, and pain in the arm decreased from 6 to 4. Independent setting and adjustments of the dual-lead stimulation were required because the thresholds of paresthesia perception were significantly different. To achieve pain relief in both the arm and leg, double-independent dual-lead stimulation placed at cervical and thoracic levels is an effective treatment. Fast-acting subperception therapy stimulation may be effective for central poststroke pain, especially in cases where the paresthesia is perceived as uncomfortable or the conventional stimulation itself is ineffective.

Avellis syndrome with ipsilateral prosopalgia, glossopharyngeal neuralgia, and central post-stroke pain: A case report and literature review

RATIONALE

Avellis syndrome is a rare bulbar syndrome. The main lesions may involve nucleus ambiguus and the lateral spinothalamic tract. The typical reported clinical manifestations are hoarseness, dysphagia, pain, and temperature disturbance of contralateral body. The manifestations, however, may vary. We aim to report new manifestations of Avellis syndrome in this report.

PATIENT CONCERNS

A 47-year-old Chinese peasant woman who felt sudden dizziness, nausea when she was doing the laundry was referred to our department from other hospital. She vomited the stomach contents once and complained numbness of the left trunk and limbs as well as coughing while drinking. The patient presented with palatopharyngeal paralysis, Horner syndrome, and diminished pain as well as temperature sensation in the contralateral face, trunk, and limbs. She also presented with ipsilateral prosopalgia, glossopharyngeal neuralgia, and central poststroke pain.

DIAGNOSES

T2-weighted MRI images demonstrated a high-signal intensity lesion in the right medulla oblongata which indicated a banded infarction site. The patient was diagnosed with medulla oblongata infarction, Avellis syndrome, Horner syndrome, dysphagia, hemiparesthesia, ipsilateral prosopalgia, glossopharyngeal neuralgia, and central poststroke pain.

INTERVENTIONS

The patient was administrated aspirin to prevent the aggregation of platelet and rosuvastatin tablets to regulate lipids as well as to stabilize vascular plaque. She was injected with butylphthalide sodium chloride to improve nerve nutritional status and carbamazepine was prescribed to deal with prosopalgia and glossopharyngeal neuralgia. Gabapentin and pregabalin were administrated to deal with the central poststroke pain.

OUTCOMES

The symptoms of prosopalgia as well as glossopharyngeal neuralgia were gone, and dizziness, dysphagia, and Horner syndrome were significantly alleviated when she was discharged from the hospital while the interventions showed little effect on central poststroke pain.

LESSONS

We reported a case of Avellis syndrome who manifested as the typical reported manifestations. The patient, what's more, presented with ipsilateral trigeminal, glossopharyngeal neuralgia, and central poststroke pain which were described for the first time. It is of great significance for clinicians to recognize the typical as well as other manifestations which helps to make a clear diagnosis.

Biological Mechanism on SIRT1/NLRP3/IL-18 Signaling Pathway of Acupuncture for Treatment of Ischemic Stroke with Center Poststroke Pain

Objective

To evaluate the effect of acupuncture on an animal model of ischemic stroke with central poststroke pain (CPSP) through Sirtuin 1 (SIRT1)/NOD-like receptor thermal protein domain associated protein 3 (NLRP3)/interleukin-18 (IL-18) signaling pathway.

Methods

Data mining was performed with R package “edgeR,” “limma,” “pathview,” etc., from NCBI Gene Expression Omnibus (GEO) database. Sprague Dawley (SD) rats were divided into 4 groups: sham operation group (Sham group, n = 5), poststroke central pain group (CPSP group, n = 5), poststroke central pain + acupuncture group (AP group, n = 5), central pain after stroke + acupuncture + SIRT1 inhibitor EX527 group (EX527 group, n = 5). Pain behavior testing was performed to determine the mechanical withdrawal threshold (MWT). Quantitative real-time PCR (qRT-PCR) was performed to verify the data mining results from the GEO database.

Results

The KEGG key pathway map was created using the R package “pathview” package, demonstrating that the expression levels of NLRP3's downstream inflammatory factors IL-18 were downregulated in both of siSIRT1 group compared to the control group and the NLRP3 reconstituted group compared to NLRP3 KO group. QRT-PCR results on animal models of CPSP ischemic stroke showed that the expression levels of SIRT1 were downregulated, the activation of the NLRP3 inflammasome was upregulated, and the expression levels of IL-18 were upregulated in the brain tissues of the surrounding area of the injury. As the pain threshold of CPSP rats was increased, the expression level of S1RT1 was upregulated, and the activation of NLRP3 inflammasome was downregulated. The expression level of IL-18 was downregulated after acupuncture treatment.

Conclusion

Acupuncture may inhibit CPSP in an animal model of ischemic stroke by upregulating SIRT1 expression levels, inhibition of the activation of the inflammasome, and downregulating IL-18 expression levels.

Secondary damage and neuroinflammation in the spinal dorsal horn mediate post-thalamic hemorrhagic stroke pain hypersensitivity: SDF1-CXCR4 signaling mediation

Central post-stroke pain (CPSP) is an intractable neuropathic pain, which can be caused by primary lesion of central somatosensory system. It is also a common sequelae of the thalamic hemorrhagic stroke (THS). So far, the underlying mechanisms of CPSP remain largely unknown. Our previous studies have demonstrated that SDF1-CXCR4 signaling in the hemorrhagic region contributes to the maintenance of the THS pain hypersensitivity via mediation of the thalamic neuroinflammation. But whether the spinal dorsal horn, an initial point of spinothalamic tract (STT), suffers from retrograde axonal degeneration from the THS region is still unknown. In this study, neuronal degeneration and loss in the spinal dorsal horn were detected 7 days after the THS caused by intra-thalamic collagenase (ITC) injection by immunohistochemistry, TUNEL staining, electron microscopy, and extracellular multi-electrode array (MEA) recordings, suggesting the occurrence of secondary apoptosis and death of the STT projecting neuronal cell bodies following primary THS via retrograde axonal degeneration. This retrograde degeneration was accompanied by secondary neuroinflammation characterized by an activation of microglial and astrocytic cells and upregulation of SDF1-CXCR4 signaling in the spinal dorsal horn. As a consequence, central sensitization was detected by extracellular MEA recordings of the spinal dorsal horn neurons, characterized by hyperexcitability of both wide dynamic range and nociceptive specific neurons to suprathreshold mechanical stimuli. Finally, it was shown that suppression of spinal neuroinflammation by intrathecal administration of inhibitors of microglia (minocycline) and astrocytes (fluorocitrate) and antagonist of CXCR4 (AMD3100) could block the increase in expression levels of Iba-1, GFAP, SDF1, and CXCR4 proteins in the dorsal spinal cord and ameliorate the THS-induced bilateral mechanical pain hypersensitivity, implicating that, besides the primary damage at the thalamus, spinal secondary damage and neuroinflammation also play the important roles in maintaining the central post-THS pain hypersensitivity. In conclusion, secondary neuronal death and neuroinflammation in the spinal dorsal horn can be induced by primary thalamic neural damage via retrograde axonal degeneration process. SDF1-CXCR4 signaling is involved in the mediation of secondary spinal neuroinflammation and THS pain hypersensitivity. This finding would provide a new therapeutic target for treatment of CPSP at the spinal level.

Changes in the Brain Metabolism Associated with Central Post-Stroke Pain in Hemorrhagic Pontine Stroke: An 18F-FDG-PET Study of the Brain

Central post-stroke pain (CPSP) is an intractable neuropathic pain that can occur following central nervous system injuries. Spino-thalamo-cortical pathway damage contributes to CPSP development. However, brain regions involved in CPSP are unknown and previous studies were limited to supratentorial strokes with cortical lesion involvement. We analyzed the brain metabolism changes associated with CPSP following pontine hemorrhage. Thirty-two patients with isolated pontine hemorrhage were examined; 14 had CPSP, while 18 did not. Brain glucose metabolism was evaluated using 18F-fluorodeoxyglucose-positron emission tomography images. Additionally, regions revealing metabolic correlation with CPSP severity were analyzed. Patients with CPSP showed changes in the brain metabolism in the cerebral cortices and cerebellum. Compared with the control group, the CPSP group showed significant hypometabolism in the contralesional rostral anterior cingulum and ipsilesional primary motor cortex (Puncorrected < 0.001). However, increased brain metabolism was observed in the ipsilesional cerebellum (VI) and contralesional cerebellum (lobule VIIB) (Puncorrected < 0.001). Moreover, increased pain intensity correlated with decreased metabolism in the ipsilesional supplementary motor area and contralesional angular gyrus. This study emphasizes the role of the many different areas of the cortex that are involved in affective and cognitive processing in the development of CPSP.

Quantitative and Fiber-Selective Evaluation for Central Poststroke Pain

The electrophysiological recording can be used to quantify the clinical features of central poststroke pain (CPSP) caused by different lesion locations. We aimed to explore the relationship between clinical features and lesion location in patients with CPSP using the current perception threshold (CPT) approach. Here, patients underwent the standardized CPT measure at five detection sites on both the contralesional and ipsilesional sides, using a constant alternating-current sinusoid waveform stimulus at three frequencies: 2000 Hz, 250 Hz, and 5 Hz. 57 CPSP patients were recruited in this cross-sectional study, including 13 patients with thalamic lesions and 44 patients with internal capsule lesions. Patients with a thalamic lesion had more frequent abnormal Aδ and C fibers than those with an internal capsule lesion (69.2% versus 36.4%, p value = 0.038; 53.8% versus 63.6%, p value = 0.038). The patients with internal capsule lesions had more frequent abnormal Aβ fibers than those with thalamic lesions (53.8% versus 63.6%, p value < 0.001). The sensory dysfunction in the patients with thalamic lesions was more likely to occur in the upper limbs (i.e., the shoulder (p value = 0.027) and the finger (p value = 0.040)). The lower limbs (i.e., the knee (p value = 0.040) and the toe (p value = 0.005)) were more likely to experience sensory dysfunction in the patients with internal capsule lesions. Hyperesthesia was more likely to occur in the thalamic patients, and hypoesthesia was more likely to occur in the patients with internal capsule lesions (p value < 0.001). In patients with thalamic lesions, Visual Analogue Scale (VAS) had a positive correlation with 5 Hz CPT on the shoulder (r = 0.010, p value = 0.005), 250 Hz CPT on the finger (r = 0.690, p value = 0.009) from the contralesional side, and 2000 Hz CPT on the knee (r = 0.690, p value = 0.009). In patients with internal capsule lesions, VAS had a positive correlation with 2000 Hz CPT on the knee (r = 0.312, p value = 0.039) and foot (r = 0.538, p value < 0.001). In conclusion, the abnormal fiber types, sensory dysfunction territory, and clinical signs of CPSP in thalamic stroke differ from those in internal capsule stroke. Implementation of the portable and convenient CPT protocol may help clarify the locations of different stroke lesions in various clinical settings.

A Randomized, Sham-Controlled Trial of Repetitive Transcranial Magnetic Stimulation Targeting M1 and S2 in Central Poststroke Pain: A Pilot Trial

OBJECTIVES

Central poststroke pain (CPSP), a neuropathic pain condition, is difficult to treat. Repetitive transcranial magnetic stimulation (rTMS) targeted to the primary motor cortex (M1) can alleviate the condition, but not all patients respond. We aimed to assess a promising alternative rTMS target, the secondary somatosensory cortex (S2), for CPSP treatment.

MATERIALS AND METHODS

This prospective, randomized, double-blind, sham-controlled three-arm crossover trial assessed navigated rTMS (nrTMS) targeted to M1 and S2 (10 sessions, 5050 pulses per session at 10 Hz). Participants were evaluated for pain, depression, anxiety, health-related quality of life, upper limb function, and three plasticity-related gene polymorphisms including Dopamine D2 Receptor (DRD2). We monitored pain intensity and interference before and during stimulations and at one month. A conditioned pain modulation test was performed using the cold pressor test. This assessed the efficacy of the descending inhibitory system, which may transmit TMS effects in pain control.

RESULTS

We prescreened 73 patients, screened 29, and included 21, of whom 17 completed the trial. NrTMS targeted to S2 resulted in long-term (from baseline to one-month follow-up) pain intensity reduction of ≥30% in 18% (3/17) of participants. All stimulations showed a short-term effect on pain (17-20% pain relief), with no difference between M1, S2, or sham stimulations, indicating a strong placebo effect. Only nrTMS targeted to S2 resulted in a significant long-term pain intensity reduction (15% pain relief). The cold pressor test reduced CPSP pain intensity significantly (p = 0.001), indicating functioning descending inhibitory controls. The homozygous DRD2 T/T genotype is associated with the M1 stimulation response.

CONCLUSIONS

S2 is a promising nrTMS target in the treatment of CPSP. The DRD2 T/T genotype might be a biomarker for M1 nrTMS response, but this needs confirmation from a larger study.

Central Neuropathic Pain Syndromes: Current and Emerging Pharmacological Strategies

Central neuropathic pain is caused by a disease or lesion of the brain or spinal cord. It is difficult to predict which patients will develop central pain syndromes after a central nervous system injury, but depending on the etiology, lifetime prevalence may be greater than 50%. The resulting pain is often highly distressing and difficult to treat, with no specific treatment guidelines currently available. This narrative review discusses mechanisms contributing to central neuropathic pain, and focuses on pharmacological approaches for managing common central neuropathic pain conditions such as central post-stroke pain, spinal cord injury-related pain, and multiple sclerosis-related neuropathic pain. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, and gabapentinoids have some evidence for efficacy in central neuropathic pain. Medications from other pharmacologic classes may also provide pain relief, but current evidence is limited. Certain non-pharmacologic approaches, neuromodulation in particular, may be helpful in refractory cases. Emerging data suggest that modulating the primary afferent input may open new horizons for the treatment of central neuropathic pain. For most patients, effective treatment will likely require a multimodal therapy approach.

miR‑223 ameliorates thalamus hemorrhage‑induced central poststroke pain via targeting NLRP3 in a mouse model

Central poststroke pain (CPSP) is a central neuropathic pain syndrome that occurs following a stroke and mainly manifests as pain and paresthesia in the body region corresponding to the brain injury area. At present, due to the lack of clinical attention given to CPSP, patients suffer from long-term pain that seriously affects their quality of life. Current literature indicates that microRNA (miR)-223 can impede inflammation and prevent collateral damage. The NLR family pyrin domain containing 3 (NLRP3) inflammasome induces IL-18 and IL-1β secretion and maturation and participates in the inflammatory response. Previous evidence has confirmed that miR-223 can negatively regulate NLRP3 in the development of inflammatory responses. However, whether the miR-223 targeting of NLRP3 is involved in CPSP remains unclear. In the present study, the expression of miR-223 was detected by reverse transcription-quantitative PCR analysis. The expression levels of NLRP3, caspase-1, ASC, IL-18, IL-1β, ERK1/2, p-ERK1/2 and GFAP were detected by western blot analysis. The results demonstrated that thalamic hemorrhagic stroke triggered by microinjection of collagenase Ⅳ (Coll IV) into the ventral posterior lateral (VPL) nucleus results in pain hypersensitivity. miR-223 expression level were significantly reduced in the CPSP model. The expression levels of NLRP3, caspase-1, ASC, IL-18 and IL-1β were significantly increased in the CPSP model. The expression level of GFAP was detected to determine astrocyte activation. The results demonstrated that astrocyte activation induced by Coll IV produced a CPSP model. The p-ERK1/2 expression level was demonstrated to be significantly increased in the CPSP model. The introduction of an miR-223 agomir significantly attenuated thalamic pain and significantly decreased the levels of NLRP3, caspase-1, ASC and proinflammatory cytokines (IL-18 and IL-1β). Furthermore, introducing a miR-223 antagomir into the VPL nucleus of naïve mice mimicked thalamic pain and significantly increased the levels of NLRP3, caspase-1, ASC and proinflammatory cytokine levels (IL-18 and IL-1β). These results indicated that miR-223 inhibited NLRP3 inflammasome activity (caspase-1, NLRP3 and ASC), which ameliorated thalamus hemorrhage-induced CPSP in mice via NLRP3 downregulation. In conclusion, these results may determine the mechanisms underlying CPSP and facilitate development of targeted therapy for CPSP.

MED1/BDNF/TrkB pathway is involved in thalamic hemorrhage-induced pain and depression by regulating microglia

Central post-stroke pain (CPSP) and associated depression remain poorly understood and pharmacological treatments are unsatisfactory. Recently, microglia activation was suggested to be involved in CPSP pathophysiology. The goal of this study was to investigate the effectiveness of a co-ultramicronized combination of N-palmitoylethanolamide and luteolin (PEALut) in a mouse model of thalamic hemorrhage (TH)-induced CPSP. TH was established through the collagenase-IV injection in thalamic ventral-posterolateral-nucleus. PEALut effects in CPSP-associated behaviors were evaluated during a 28-days observation period. We found that repeated administrations of co-ultra PEALut significantly reduced mechanical hypersensitivity after TH, as compared to vehicle, by reducing the early microglial activation in the perilesional site. Moreover, PEALut prevented the development of depressive-like behavior (21 days post-TH). These effects were associated with the restoration of synaptic plasticity in LEC-DG pathway and monoamines levels found impaired in TH mice. Hippocampal MED1 and TrkB expressions were significantly increased in TH compared to sham mice 21 days post-TH, whereas BDNF levels were decreased. PEALut restored MED1/TrkB/BDNF expression in mice. Remarkably, we found significant overexpression of MED1 in the human autoptic brain specimens after stroke, indicating a translational potential of our findings. These results pave the way for better-investigating depression in TH- induced CPSP, together with the involvement of MED1/TrkB/BDNF pathway, proposing PEALut as an adjuvant treatment.

Evidence Mapping Based on Systematic Reviews of Repetitive Transcranial Magnetic Stimulation on the Motor Cortex for Neuropathic Pain

BACKGROUND AND OBJECTIVE

There is vast published literature proposing repetitive transcranial magnetic stimulation (rTMS) technology on the motor cortex (M1) for the treatment of neuropathic pain (NP). Systematic reviews (SRs) focus on a specific problem and do not provide a comprehensive overview of a research area. This study aimed to summarize and analyze the evidence of rTMS on the M1 for NP treatment through a new synthesis method called evidence mapping.

METHODS

Searches were conducted in PubMed, EMBASE, Epistemonikos, and The Cochrane Library to identify the studies that summarized the effectiveness of rTMS for NP. The study type was restricted to SRs with or without meta-analysis. All literature published before January 23, 2021, was included. Two reviewers independently screened the literature, assessed the methodological quality, and extracted the data. The methodological quality of the included SRs was assessed by using the A Measurement Tool to Assess Systematic Reviews (AMSTAR-2). Data were extracted following a defined population, intervention, comparison, and outcome (PICO) framework from primary studies that included SRs. The same PICO was categorized into PICOs according to interventions [frequency, number of sessions (short: 1-5 sessions, medium: 5-10 sessions, and long: >10 sessions)] and compared. The evidence map was presented in tables and a bubble plot.

RESULTS

A total of 38 SRs met the eligibility criteria. After duplicate primary studies were removed, these reviews included 70 primary studies that met the scope of evidence mapping. According to the AMSTAR-2 assessment, the quality of the included SRs was critically low. Of these studies, 34 SRs scored "critically low" in terms of methodological quality, 2 SR scored "low," 1 SR scored "moderate," and 1 SR scored "high."

CONCLUSION

Evidence mapping is a useful methodology to provide a comprehensive and reliable overview of studies on rTMS for NP. Evidence mapping also shows that further investigations are necessary to highlight the optimal stimulation protocols and standardize all parameters to fill the evidence gaps of rTMS. Given that the methodological quality of most included SRs was "critically low," further investigations are advised to improve the methodological quality and the reporting process of SRs.

What is Operative? Conceptualizing Neuralgia: Neuroma, Compression Neuropathy, Painful Hyperalgesia, and Phantom Nerve Pain

Neuralgia, or nerve pain, is a common presenting complaint for the hand surgeon. When the nerve at play is easily localized, and the cause of the pain is clear (eg, carpal tunnel syndrome), the patient may be easily treated with excellent results. However, in more complex cases, the underlying pathophysiology and cause of neuralgia can be more difficult to interpret; if incorrectly managed, this leads to frustration for both the patient and surgeon. Here we offer a way to conceptualize neuralgia into 4 categories-compression neuropathy, neuroma, painful hyperalgesia, and phantom nerve pain-and offer an illustrative clinical vignette and strategies for optimal management of each. Further, we delineate the reasons why compression neuropathy and neuroma are amenable to surgery, while painful hyperalgesia and phantom nerve pain are not.

Tricyclic antidepressants and selective serotonin reuptake inhibitors but not anticonvulsants ameliorate pain, anxiety, and depression symptoms in an animal model of central post-stroke pain

Background

Central post-stroke pain (CPSP) is a type of neuropathic pain caused by dysfunction in the spinothalamocortical pathway. However, no animal studies have examined comorbid anxiety and depression symptoms. Whether the typical pharmacological treatments for CPSP, which include antidepressants, selective serotonin reuptake inhibitors (SSRIs), and anticonvulsants, can treat comorbid anxiety and depression symptoms in addition to pain remains unclear? The present study ablated the ventrobasal complex of the thalamus (VBC) to cause various CPSP symptoms. The effects of the tricyclic antidepressants amitriptyline and imipramine, the SSRI fluoxetine, and the anticonvulsant carbamazepine on pain, anxiety, and depression were examined.

Results

The results showed that VBC lesions induced sensitivity to thermal pain, measured using a hot water bath; mechanical pain, assessed by von Frey test; anxiety behavior, determined by the open-field test, elevated plus-maze test, and zero-maze test; and depression behavior, assessed by the forced swim test. No effect on motor activity in the open-field test was observed. Amitriptyline reduced thermal and mechanical pain sensitivity and anxiety but not depression. Imipramine suppressed thermal and mechanical pain sensitivity, anxiety, and depression. Fluoxetine blocked mechanical but not thermal pain sensitivity, anxiety, and depression. However, carbamazepine did not affect pain, anxiety, or depression.

Conclusion

In summary, antidepressants and SSRIs but not anticonvulsants can effectively ameliorate pain and comorbid anxiety and depression in CPSP. The present findings, including discrepancies in the effects observed following treatment with anticonvulsants, antidepressants, and SSRIs in this CPSP animal model, can be applied in the clinical setting to guide the pharmacological treatment of CPSP symptoms.

Non-human Primate Models to Explore the Adaptive Mechanisms After Stroke

The brain has the ability to reconstruct neural structures and functions to compensate for the brain lesions caused by stroke, although it is highly limited in primates including humans. Animal studies in which experimental lesions were induced in the brain have contributed to the current understanding of the neural mechanisms underlying functional recovery. Here, I have highlighted recent advances in non-human primate models using primate species such as macaques and marmosets, most of which have been developed to study the mechanisms underlying the recovery of motor functions after stroke. Cortical lesion models have been used to investigate motor recovery after lesions to the cortical areas involved in movements of specific body parts. Models of a focal stroke at the posterior internal capsule have also been developed to bridge the gap between the knowledge obtained by cortical lesion models and the development of intervention strategies because the severity and outcome of motor deficits depend on the degree of lesions to the region. This review will also introduce other stroke models designed to study the plastic changes associated with development and recovery from cognitive and sensory impairments. Although further validation and careful interpretation are required, considering the differences between non-human primate brains and human brains, studies using brain-lesioned non-human primates offer promise for improving translational outcomes.

Interaction of the Left-Right Somatosensory Pathways in Patients With Thalamic Hemorrhage: A Case Report

Neural plasticity compensates for the loss of motor function after stroke. However, whether neural plasticity occurs in the somatosensory pathways after stroke is unknown. We investigated the left–right somatosensory interaction in two hemorrhagic patients using a paired somatosensory evoked potentials (p-SEPs) recorded at CP3 and CP4, which was defined as an amplitude difference between the SEPs of paired median nerve stimulations to both sides and that of single stimulation to the affected side. Patient 1 (61-year-old, left thalamic hemorrhage) has a moderate motor impairment, severe sensory deficit, and complained of pain in the affected right upper limb. Patient 2 (72-year-old, right thalamic hemorrhage) had slight motor and sensory impairments with no complaints of pain. Single SEPs (s-SEPs) were obtained by stimulation of the right and left median nerves, respectively. For paired stimulations, 1 ms after the first stimulation to the non-affected side, followed by a second stimulation to the affected side. In patient 1, a s-SEP with stimulation to the non-affected side and a p-SEP were observed in CP4. However, a s-SEP was not observed in either hemisphere with stimulation to the affected side. On the other hand, in patient 2, a s-SEP in CP3 with stimulation to the non-affected side and in CP4 with stimulation to the affected side were observed; however, a p-SEP was not observed. In addition, to investigate the mechanism by which ipsilateral median nerve stimulation enhances contralateral p-SEP in patient 1, we compared the SEP averaged over the first 250 epochs with the SEP averaged over the second 250 epochs (total number of epochs recorded: 500). The results showed that in the patient 1, when the bilateral median nerve was stimulated continuously, the habituation did not occur and the response was larger than that of the s-SEP with unilateral median nerve stimulation. In the current case report, the damage to the thalamus may cause neuroplasticity in terms of the left–right interaction (e.g., left and right S1). The somatosensory input from the affected side may interfere with the habituation of the contralateral somatosensory system and conversely increase the response.

A Meta-Analysis and Meta-Regression of Frequency and Risk Factors for Poststroke Complex Regional Pain Syndrome

Background and Objectives: This article aimed to investigate the risk factors for poststroke complex regional pain syndrome (CRPS). Materials and Methods: We searched electronic databases including PubMed, Medline, Web of Science, Cochrane Library, and Embase up to 27 October 2021. We enrolled analytical epidemiological studies comprising cohort, case-control, and cross-sectional studies. A quality assessment was performed using the Newcastle–Ottawa Quality Assessment Scale for cohort and case-control studies and the Joanna Briggs Institute critical appraisal checklist for analytical cross-sectional studies. Binary outcomes were reported as odds ratios (ORs), and continuous outcomes were described as standardized mean differences (SMDs) with 95% confidence intervals. For the meta-regression, beta coefficient and p value were adopted. Results: We included 21 articles comprising 2225 participants. Individuals with shoulder subluxation and spasticity were found to have higher risks for poststroke CRPS. Spasticity with higher modified Ashworth scale score, lower Brunnstrom hand stage, and inferior Barthel index scores were observed in patients with poststroke CRPS. The pooled incidence proportion in nine articles was 31.7%, and a correlation was found between effect sizes and the ratio of women and the proportion of left hemiparesis. The summarized prevalence in nine cross-sectional studies was 33.1%, and a correlation was observed between prevalence and the subluxation ratio and Brunnstrom stage. Conclusions: Based on our meta-analysis, being female, left hemiparesis, shoulder subluxation, spasticity, a lower Brunnstrom stage of distal upper limb, and an inferior Barthel index are all features for poststroke CRPS. Larger studies with greater statistical power may confirm our findings and clarify some other unknown risk factors for poststroke CRPS.

EETs/sEHi alleviates nociception by blocking the crosslink between endoplasmic reticulum stress and neuroinflammation in a central poststroke pain model

Background

Central post-stroke pain (CPSP) is a chronic and intolerable neuropathic pain syndrome following a cerebral vascular insult, which negatively impacts the quality of life of stroke survivors but currently lacks efficacious treatments. Though its underlying mechanism remains unclear, clinical features of hyperalgesia and allodynia indicate central sensitization due to excessive neuroinflammation. Recently, the crosslink between neuroinflammation and endoplasmic reticulum (ER) stress has been identified in diverse types of diseases. Nevertheless, whether this interaction contributes to pain development remains unanswered. Epoxyeicosatrienoic acids (EETs)/soluble epoxy hydrolase inhibitors (sEHi) are emerging targets that play a significant role in pain and neuroinflammatory regulation. Moreover, recent studies have revealed that EETs are effective in attenuating ER stress. In this study, we hypothesized that ER stress around the stroke site may activate glial cells and lead to further inflammatory cascades, which constitute a positive feedback loop resulting in central sensitization and CPSP. Additionally, we tested whether EETs/sEHi could attenuate CPSP by suppressing ER stress and neuroinflammation, as well as their vicious cycle, in a rat model of CPSP.

Methods

Young male SD rats were used to induce CPSP using a model of thalamic hemorrhage and were then treated with TPPU (sEHi) alone or in combination with 14,15-EET or 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, the EET antagonist), tunicamycin (Tm, ER stress inducer), or 4-PBA (ER stress inhibitor). Nociceptive behaviors, ER stress markers, JNK and p38 (two well-recognized inflammatory kinases of mitogen-activated protein kinase (MAPK) signaling) expression, and glial cell activation were assessed. In addition, some healthy rats were intrathalamically microinjected with Tm or lipopolysaccharide (LPS) to test the interaction between ER stress and neuroinflammation in central pain.

Results

Analysis of the perithalamic lesion tissue from the brain of CPSP rats demonstrated decreased soluble epoxy hydrolase (sEH) expression, which was accompanied by increased expression of ER stress markers, including BIP, p-IRE, p-PERK, and ATF6. In addition, inflammatory kinases (p-p38 and p-JNK) were upregulated and glial cells were activated. Intrathalamic injection of sEHi (TPPU) increased the paw withdrawal mechanical threshold (PWMT), reduced hallmarks of ER stress and MAPK signaling, and restrained the activation of microglia and astrocytes around the lesion site. However, the analgesic effect of TPPU was completely abolished by 14,15-EEZE. Moreover, microinjection of Tm into the thalamic ventral posterior lateral (VPL) nucleus of healthy rats induced mechanical allodynia and activated MAPK-mediated neuroinflammatory signaling; lipopolysaccharide (LPS) administration led to activation of ER stress along the injected site in healthy rats.

Conclusions

The present study provides evidence that the interaction between ER stress and neuroinflammation is involved in the mechanism of CPSP. Combined with the previously reported EET/sEHi effects on antinociception and neuroprotection, therapy with agents that target EET signaling may serve as a multi-functional approach in central neuropathic pain by attenuating ER stress, excessive neuroinflammation, and subsequent central sensitization. The use of these agents within a proper time window could not only curtail further nerve injury but also produce an analgesic effect.

Central Post-Stroke Pain: An Integrative Review of Somatotopic Damage, Clinical Symptoms, and Neurophysiological Measures

Introduction: The physiopathology of central post-stroke pain (CPSP) is poorly understood, which may contribute to the limitations of diagnostic and therapeutic advancements. Thus, the current systematic review was conducted to examine, from an integrated perspective, the cortical neurophysiological changes observed via transcranial magnetic stimulation (TMS), focusing on the structural damage, and clinical symptoms in patients with CPSP. Methods: The literature review included the databases EMBASE, PubMed, and ScienceDirect using the following search terms by MeSH or Entree descriptors: [("Cerebral Stroke") AND ("Pain" OR "Transcranial Magnetic Stimulation") AND ("Transcranial Magnetic Stimulation")] (through September 29, 2020). A total of 297 articles related to CPSP were identified. Of these, only four quantitatively recorded cortical measurements. Results: We found four studies with different methodologies and results of the TMS measures. According to the National Institutes of Health (NIH) guidelines, two studies had low methodological quality and the other two studies had satisfactory methodological quality. The four studies compared the motor threshold (MT) of the stroke-affected hemisphere with the unaffected hemisphere or with healthy controls. Two studies assessed other cortical excitability measures, such as cortical silent period (CSP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). The main limitations in the interpretation of the results were the heterogeneity in parameter measurements, unknown cortical excitability measures as potential prognostic markers, the lack of a control group without pain, and the absence of consistent and validated diagnosis criteria. Conclusion: Despite the limited number of studies that prevented us from conducting a meta-analysis, the dataset of this systematic review provides evidence to improve the understanding of CPSP physiopathology. Additionally, these studies support the construction of a framework for diagnosis and will help improve the methodological quality of future research in somatosensory sequelae following stroke. Furthermore, they offer a way to integrate dysfunctional neuroplasticity markers that are indirectly assessed by neurophysiological measures with their correlated clinical symptoms.

Neuroanatomical correlates of poststroke complex regional pain syndrome: a voxel-based lesion symptom-mapping study

Complex regional pain syndrome (CRPS) is a common poststroke complication. However, the neural substrates associated with CRPS remain unclear. We investigated the neural correlates associated with poststroke CRPS using voxel-based lesion‒symptom mapping (VLSM) analysis. Among 145 patients with ischemic stroke, 35 were diagnosed with CRPS and categorized into the poststroke CRPS group, and the remaining 110 into the control group. We compared the clinical characteristics between the groups. VLSM analysis was performed to identify the brain region associated with the development of poststroke CRPS. The clinical findings suggested that the poststroke CRPS group had lower muscle strength; lower scores on Fugl‒Meyer assessment, Manual Function Test, Mini-Mental Status Examination; and higher incidence of absent somatosensory evoked potentials in the median nerve than the control group. The head of the caudate nucleus, putamen, and white matter complexes in the corona radiata were significantly associated with poststroke CRPS development in ischemic stroke patients. These results facilitate an understanding of poststroke CRPS pathophysiology. Monitoring patients with lesions in these structures may aid the prevention and early treatment of poststroke CRPS.

Alteration of White Matter in Patients with Central Post-Stroke Pain

A stroke may be followed by central post-stroke pain (CPSP), which is characterized by chronic neuropathic pain. The exact mechanism has not yet been fully uncovered. We investigated alterations in the white matters in patients with CPSP, compared with stroke patients without CPSP and normal controls. Our retrospective cross-sectional, case-control study participants were assigned to three groups: CPSP (stroke patients with CPSP (n = 17)); stroke control (stroke patients without CPSP (n = 26)); and normal control (normal subjects (n = 34)). The investigation of white matter for CPSP was focused on the values of fiber numbers (FN) and fractional anisotrophy (FA) for spinothalamic tract (STT), anterior thalamic radiation (ATR), superior thalamic radiation (STR) and posterior thalamic radiation (PTR), and corticospinal tract (CST) was measured. The FA for the STT and STR of the CPSP group were lower than those for the stroke control and normal control groups. The FA of CST and ATR did not differ between the CPSP and stroke groups, but both differed from the normal control. The FA of PTR in the stroke control group differed from the normal control group, but not from the CPSP group. The FN of CST, STT, ATR, and STR for the CPSP and stroke control groups did not differ from each other, but both differed from those of normal controls. FN of PTR did not differ between the CPSP and normal control groups. The alterations in the spinothalamic tract and superior thalamic radiation after stroke would play a role in the pathogenesis of CPSP.

Structural Plastic Changes of Cortical Gray Matter Revealed by Voxel-Based Morphometry and Histological Analyses in a Monkey Model of Central Post-Stroke Pain

Central post-stroke pain (CPSP) is a chronic pain caused by stroke lesions of somatosensory pathways. Several brain imaging studies among patients with CPSP demonstrate that the pathophysiological mechanism underlying this condition is the maladaptive plasticity of pain-related brain regions. However, the temporal profile of the regional plastic changes, as suggested by brain imaging of CPSP patients, as well as their cellular basis, is unknown. To investigate these issues, we performed voxel-based morphometry (VBM) using T1-weighted magnetic resonance imaging and immunohistochemical analysis with our established CPSP monkey model. From 8 weeks after a hemorrhagic lesion to the unilateral ventral posterolateral nucleus of the thalamus, the monkeys exhibited significant behavioral changes that were interpreted as reflecting allodynia. The present VBM results revealed a decrease in gray matter volume in the pain-related areas after several weeks following the lesion. Furthermore, immunohistochemical staining in the ipsilesional posterior insular cortex (ipsi-PIC) and secondary somatosensory cortex (ipsi-SII), where the significant reduction in gray matter volume was observed in the VBM result, displayed a significant reduction in both excitatory and inhibitory synaptic terminals compared to intact monkeys. Our results suggest that progressive changes in neuronal morphology, including synaptic loss in the ipsi-PIC/SII, are involved in theCPSP.

Repetitive transcranial magnetic stimulation restores altered functional connectivity of central poststroke pain model monkeys

Central poststroke pain (CPSP) develops after a stroke around the somatosensory pathway. CPSP is hypothesized to be caused by maladaptive reorganization between various brain regions. The treatment for CPSP has not been established; however, repetitive transcranial magnetic stimulation (rTMS) to the primary motor cortex has a clinical effect. To verify the functional reorganization hypothesis for CPSP development and rTMS therapeutic mechanism, we longitudinally pursued the structural and functional changes of the brain by using two male CPSP model monkeys (Macaca fuscata) developed by unilateral hemorrhage in the ventral posterolateral nucleus of the thalamus. Application of rTMS to the ipsilesional primary motor cortex relieved the induced pain of the model monkeys. A tractography analysis revealed a decrease in the structural connectivity in the ipsilesional thalamocortical tract, and rTMS had no effect on the structural connectivity. A region of interest analysis using resting-state functional magnetic resonance imaging revealed inappropriately strengthened functional connectivity between the ipsilesional mediodorsal nucleus of the thalamus and the amygdala, which are regions associated with emotion and memory, suggesting that this may be the cause of CPSP development. Moreover, rTMS normalizes this strengthened connectivity, which may be a possible therapeutic mechanism of rTMS for CPSP.

Glial and neuroimmune cell choreography in sexually dimorphic pain signaling

Chronic pain is a major global health issue that affects all populations regardless of sex, age, ethnicity/race, or country of origin, leading to persistent physical and emotional distress and to the loss of patients' autonomy and quality of life. Despite tremendous efforts in the elucidation of the mechanisms contributing to the pathogenesis of chronic pain, the identification of new potential pain targets, and the development of novel analgesics, the pharmacological treatment options available for pain management remain limited, and most novel pain medications have failed to achieve advanced clinical development, leaving many patients with unbearable and undermanaged pain. Sex-specific susceptibility to chronic pain conditions as well as sex differences in pain sensitivity, pain tolerance and analgesic efficacy are increasingly recognized in the literature and have thus prompted scientists to seek mechanistic explanations. Hence, recent findings have highlighted that the signaling mechanisms underlying pain hypersensitivity are sexually dimorphic, which sheds light on the importance of conducting preclinical and clinical pain research on both sexes and of developing sex-specific pain medications. This review thus focuses on the clinical and preclinical evidence supporting the existence of sex differences in pain neurobiology. Attention is drawn to the sexually dimorphic role of glial and immune cells, which are both recognized as key players in neuroglial maladaptive plasticity at the origin of the transition from acute pain to chronic pathological pain. Growing evidence notably attributes to microglial cells a pivotal role in the sexually dimorphic pain phenotype and in the sexually dimorphic analgesic efficacy of opioids. This review also summarizes the recent advances in understanding the pathobiology underpinning the development of pain hypersensitivity in both males and females in different types of pain conditions, with particular emphasis on the mechanistic signaling pathways driving sexually dimorphic pain responses.

[Central Post-Stroke Pain at the Tingandogo University Teaching Hospital of Ouagadougou (Burkina Faso): Frequency, Clinical Profile, Quality of Life of Patients and Associated Factors]

Objective

Few studies have been done on central post-stroke pain (CPSP) in Sub-Saharan Africa, while taking it into account would improve the quality of life of stroke survivors. The purpose of this study was to determine the prevalence of CPSP, to describe its clinical profile, to assess the quality of life of patients and to identify the factors associated with its occurrence, from a prospective hospital series in Ouagadougou, Burkina Faso.

Methodology

It was a prospective, descriptive and analytical longitudinal follow-up study, conducted from January 2015 to March 2020, at the Tingandogo University Hospital, in Ouagadougou, Burkina Faso. The study involved all patients over the age of 16, consecutively hospitalized for stroke confirmed by CT and / or brain MRI, then reviewed every three months in outpatient Neurology, during at least 9 months after their stroke. The sociodemographic and clinical characteristics of the patients, the nature of the stroke, the existence of CPSP and, if applicable, its clinical characteristics, its treatment and its impact on the quality of life of the patients were recorded; a bivariate then multivariate analysis with logistic regression step by step, made it possible to search for the factors associated with the occurrence of CPSP. The significance threshold used was p < 0.05.

Results

A total of 236 patients were collected, out of which 28 patients presented a CPSP (11.9%), after a mean duration of post-stroke follow-up of 12.9 months. Cerebral infarction, intracerebral hemorrhage and cerebral venous thrombosis accounted for 69.5%, 29.7% and 0.8% respectively. The mean age of patients with CPSP was 54.6 years, with a male predominance (53.6%). The mean time to onset for CPSP was 3.8 months after stroke. Pains such as burning (75%) and allodynia (67.8%) were the most common. The average CPSP intensity was 7.6 / 10 on the visual analog scale. Hypoaesthesia (96.4%) and paraesthesia (71.4%) were the signs or symptoms most commonly associated with CPSP. CPSP had a moderate to severe negative impact on usual work, general activity and mood of patients in 60.7%, 50% and 46.4% of patients, respectively. Amitriptyline (75%) and / or level II analgesics (60.7%,) were the most used molecules, and effective in 57% of cases. Only age ≤ 50 years was independently associated with the occurrence of CPSP (OR 2.86; p = 0.03).

Conclusion

CPSP affects more than 1 in 10 stroke patients and moderately to severely affects the quality of life for most of these patients. Screening and adequate management of CPSP as part of multidisciplinary post-stroke follow-up will contribute to improve the quality of life of stroke patients and will facilitate their social and professional reintegration.

The prevalence and management of central post-stroke pain at a hospital in Zimbabwe

Background

Central post-stroke pain (CPSP) is a poorly diagnosed chronic pain. It is under-treated and usually mismanaged.

Objective

To establish the prevalence of CPSP and its management in stroke clinics at a tertiary hospital.

Methods

This was a cross-sectional design with stroke patients and health professionals from the stroke clinic at the tertiary hospital in Zimbabwe.

Results

Out of 166 stroke survivors, 8% had CPSP. Younger age (<60 years) was significantly associated with CPSP (P<0.003). Pain characteristics of CPSP were hyperaesthesia (10, 71%), electric shocks (9, 64%), temperature allodynia (9, 64%) and allodynia (12, 86%). Ten health professionals participated in the study: one (10%) reported using Douleur Neuropathique 4 (to diagnose neuropathic pain) and two (20%) reported using sensory tests. Four patients (44%) were on paracetamol (acetaminophen) and on weak opiates such as codeine. None of the patients were on anticonvulsants or antidepressants. Two medical doctors (50%) used weak opiates as second-line management. Five patients (36%) reported receiving a combination of massage, stretching, general exercise and moist heat or cryotherapy.

Conclusion

The prevalence of CPSP in the study group is within international range. There is a need for appropriate management and use of tests and outcome measures for diagnosis of CPSP.

Poststroke Pain

Pain is common but often underrecognized after stroke. Poststroke pain (PSP) hinders recovery, impairs quality of life, and is associated with the psychological state of patients with stroke. The most common subtypes of PSP include central PSP, complex regional pain syndrome, shoulder pain, spasticity-related pain, and headache. The pathophysiologies of these PSP subtypes are not yet clearly understood, and PSP is refractory to conventional treatment in many patients. However, recent studies have proposed potential pathophysiologies of PSP subtypes, which may help prioritize therapies that target specific mechanisms.

Fgr contributes to hemorrhage-induced thalamic pain by activating NF-κB/ERK1/2 pathways

Thalamic pain, a type of central poststroke pain, frequently occurs following ischemia/hemorrhage in the thalamus. Current treatment of this disorder is often ineffective, at least in part due to largely unknown mechanisms that underlie thalamic pain genesis. Here, we report that hemorrhage caused by microinjection of type IV collagenase or autologous whole blood into unilateral ventral posterior lateral nucleus and ventral posterior medial nucleus of the thalamus increased the expression of Fgr, a member of the Src family nonreceptor tyrosine kinases, at both mRNA and protein levels in thalamic microglia. Pharmacological inhibition or genetic knockdown of thalamic Fgr attenuated the hemorrhage-induced thalamic injury on the ipsilateral side and the development and maintenance of mechanical, heat, and cold pain hypersensitivities on the contralateral side. Mechanistically, the increased Fgr participated in hemorrhage-induced microglial activation and subsequent production of TNF-α likely through activation of both NF-κB and ERK1/2 pathways in thalamic microglia. Our findings suggest that Fgr is a key player in thalamic pain and a potential target for the therapeutic management of this disorder.

Care for patients with musculoskeletal pain during the COVID-19 pandemic: Physical therapy and rehabilitation suggestions for pain management

Coronavirus disease 2019 has severely affected public health. Under social distancing and lockdown policies, patients with musculoskeletal pain have fewer opportunities than usual to receive routine medical care for pain management in hospitals. Therefore, we provided some suggestions for such patients to manage musculoskeletal pain and techniques that may be performed at home during this period.

Epoxyeicosatrienoic acids: Emerging therapeutic agents for central post-stroke pain

Central post-stroke pain (CPSP) is chronic neuropathic pain due to a lesion or dysfunction of the central nervous system following cerebrovascular insult. This syndrome is characterized by chronic somatosensory abnormalities including spontaneous pain, hyperalgesia and allodynia, which localize to body areas corresponding to the injured brain region. However, despite its potential to impair activities of daily life and cause mood disorders after stroke, it is probably the least recognized complication of stroke. All currently approved treatments for CPSP have limited efficacy but troublesome side effects. The detailed mechanism underlying CPSP is still under investigation; however, its diverse clinical features indicate excessive central neuronal excitability, which is attributed to loss of inhibition and excessive neuroinflammation. Recently, exogenous epoxyeicosatrienoic acids (EETs) have been used to attenuate the mechanical allodynia in CPSP rats and proven to provide a quicker onset and superior pain relief compared to the current first line drug gabapentin. This anti-nociceptive effect is mediated by reserving the normal thalamic inhibition state through neurosteroid-GABA signaling. Moreover, mounting evidence has revealed that EETs exert anti-inflammatory effects by inhibiting the expression of vascular adhesion molecules, activating NFκB, inflammatory cytokines secretion and COX-2 gene induction. The present review focuses on the extensive evidence supporting the potential of EETs to be a multi-functional therapeutic approach for CPSP. Additionally, the role of EETs in the crosstalk between anti-CPSP and the comorbid mood disorder is reviewed herein.

Treatment of Déjerine-Roussy syndrome pain with scrambler therapy

Aim: Déjerine-Roussy syndrome or central thalamic pain can be devastating, and treatment with drugs and even deep brain stimulation can be unsatisfactory. Scrambler therapy is a form of neuromodulation that uses external skin electrodes to send a 'non-pain' signal to the brain, with some success in difficult-to-treat syndromes such as neuromyelitis optica spectrum disorder. We used scrambler therapy to treat a patient with 6 years of disabling Déjerine-Roussy syndrome pain. Methods: A 56-year-old man received multiple daily then monthly treatments with electrode pairs placed just above the area of distal pain. Each treatment was for 40 min. Results: His allodynia and hyperalgesia resolved within 10 min, and his pain score fell to almost zero after 30 min. Months later, he resumed normal activity and is off all his pain medications. No side effects were noted. Conclusion: Scrambler therapy appeared to reverse 6 years of disabling pain safely and economically, and continues to be effective. Further multi-institutional trials are warranted for this rare syndrome.

Stroke in Pregnancy: A Focused Update

Ischemic stroke (IS) and hemorrhagic stroke (HS) can be devastating complications during pregnancy and the puerperium that are thought to occur in approximately 30 in 100,000 pregnancies. In high-risk groups, such as women with preeclampsia, the incidence of both stroke subtypes, combined, is up to 6-fold higher than in pregnant women without these disorders. IS or HS may present in young women with atypical symptoms including headache, seizure, extremity weakness, dizziness, nausea, behavioral changes, and visual symptoms. Obstetric anesthesiologists who recognize these signs and symptoms of pregnancy-related stroke are well positioned to facilitate timely care. Acute stroke of any type is an emergency that should prompt immediate coordination of care between obstetric anesthesiologists, stroke neurologists, high-risk obstetricians, nurses, and neonatologists. Historically, guidelines have not addressed the unique situation of maternal stroke, and pregnant women have been excluded from the large stroke trials. More recently, several publications and professional societies have highlighted that pregnant women suspected of having IS or HS should be evaluated for the same therapies as nonpregnant women. Vaginal delivery is generally preferred unless there are obstetric indications for cesarean delivery. Neuraxial analgesia and anesthesia are frequently safer than general anesthesia for cesarean delivery in the patient with a recent stroke. Potential exceptions include therapeutic anticoagulation or intracranial hypertension with risk of herniation. General anesthesia may be appropriate when cesarean delivery will be combined with intracranial neurosurgery.

Unmet Need for Social and Emotional Support and Lack of Recalled Screening Is Associated with Depression in the Long-Term Course After Stroke

Purpose

Details on adequate care and prevalence of depression in long-term stroke aftercare are limited. We aimed to determine long-term depression rates after stroke and to test for an association between depression and inadequate screening, socio-economic complications and lack of sub-optimal care.

Patients and Methods

In this cross-sectional study, 57 patients were re-invited into the clinic 2-3 years after stroke. Patients were interviewed about recalled screening concerning depression and unmet needs. Depression, the patient's social situation, and confounders were assessed by standardized scores.

Results

In our study, 20% (n = 11) of patients were classified as depressed by the HDRS-17 score result. However, only 36% of all patients recalled to have been previously screened for depression and only 43% of those patients also recalled out-patient screening. Patients classified as depressed reported significantly lower recalled screening rates (9% vs 43%; p = 0.036) and higher rates of self-reported unmet need with emotional problems (72% vs 18%; p < 0.001). Depression in our study was further associated with a worse socio-economic situation, fewer social contacts, unmet needs with regard to emotional problems and higher rates of recommendations to apply for additional social support.

Conclusion

Our data suggest that systematic out-patient screening for depression is lacking in stroke aftercare. Furthermore, the high rate of unmet emotional needs, the poor socio-economic situation and the higher rates of recommendations for social counselling and application for benefits suggest an undersupply of care in the out-patient setting that is more prominent in patients with depression and warrants further studies to investigate the underlying causes.

Repetitive transcranial magnetic stimulation in stroke rehabilitation: review of the current evidence and pitfalls

Acute brain ischemia causes changes in several neural networks and related cortico-subcortical excitability, both in the affected area and in the apparently spared contralateral hemisphere. The modulation of these processes through modern techniques of noninvasive brain stimulation, namely repetitive transcranial magnetic stimulation (rTMS), has been proposed as a viable intervention that could promote post-stroke clinical recovery and functional independence. This review provides a comprehensive summary of the current evidence from the literature on the efficacy of rTMS applied to different clinical and rehabilitative aspects of stroke patients. A total of 32 meta-analyses published until July 2019 were selected, focusing on the effects on motor function, manual dexterity, walking and balance, spasticity, dysphagia, aphasia, unilateral neglect, depression, and cognitive function after a stroke. Only conventional rTMS protocols were considered in this review, and meta-analyses focusing on theta burst stimulation only were excluded. Overall, both HF-rTMS and LF-rTMS have been shown to be safe and well-tolerated. In addition, the current literature converges on the positive effect of rTMS in the rehabilitation of all clinical manifestations of stroke, except for spasticity and cognitive impairment, where definitive evidence of efficacy cannot be drawn. However, routine use of a specific paradigm of stimulation cannot be recommended yet due to a significant level of heterogeneity of the studies in terms of protocols to be set and outcome measures that have to be used. Future studies need to preliminarily evaluate the most promising protocols before going on to multicenter studies with large cohorts of patients in order to achieve a definitive translation into daily clinical practice.

Repetitive transcranial magnetic stimulation in stroke rehabilitation: review of the current evidence and pitfalls

Acute brain ischemia causes changes in several neural networks and related cortico-subcortical excitability, both in the affected area and in the apparently spared contralateral hemisphere. The modulation of these processes through modern techniques of noninvasive brain stimulation, namely repetitive transcranial magnetic stimulation (rTMS), has been proposed as a viable intervention that could promote post-stroke clinical recovery and functional independence. This review provides a comprehensive summary of the current evidence from the literature on the efficacy of rTMS applied to different clinical and rehabilitative aspects of stroke patients. A total of 32 meta-analyses published until July 2019 were selected, focusing on the effects on motor function, manual dexterity, walking and balance, spasticity, dysphagia, aphasia, unilateral neglect, depression, and cognitive function after a stroke. Only conventional rTMS protocols were considered in this review, and meta-analyses focusing on theta burst stimulation only were excluded. Overall, both HF-rTMS and LF-rTMS have been shown to be safe and well-tolerated. In addition, the current literature converges on the positive effect of rTMS in the rehabilitation of all clinical manifestations of stroke, except for spasticity and cognitive impairment, where definitive evidence of efficacy cannot be drawn. However, routine use of a specific paradigm of stimulation cannot be recommended yet due to a significant level of heterogeneity of the studies in terms of protocols to be set and outcome measures that have to be used. Future studies need to preliminarily evaluate the most promising protocols before going on to multicenter studies with large cohorts of patients in order to achieve a definitive translation into daily clinical practice.