Allodynia in Relation to Lesion Site in Central Post-Stroke Pain

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.

Site matters: Central neuropathic pain characteristics and somatosensory findings after brain and spinal cord lesions

BACKGROUND

It is unknown if different etiologies or lesion topographies influence central neuropathic pain (CNP) clinical manifestation.

METHODS

We explored the symptom-somatosensory profile relationships in CNP patients with different types of lesions to the central nervous system to gain insight into CNP mechanisms. We compared the CNP profile through pain descriptors, standardized bedside examination, and quantitative sensory test in two different etiologies with segregated lesion locations: the brain, central poststroke pain (CPSP, n = 39), and the spinal cord central pain due to spinal cord injury (CPSCI, n = 40) in neuromyelitis optica.

RESULTS

Results are expressed as median (25th to 75th percentiles). CPSP presented higher evoked and paroxysmal pain scores compared to CPSCI (p < 0.001), and lower cold thermal limen (5.6°C [0.0-12.9]) compared to CPSCI (20.0°C [4.2-22.9]; p = 0.004). CPSCI also had higher mechanical pain thresholds (784.5 mN [255.0-1078.0]) compared to CPSP (235.2 mN [81.4-1078.0], p = 0.006) and higher mechanical detection threshold compared to control areas (2.7 [1.5-6.2] vs. 1.0 [1.0-3.3], p = 0.007). Evoked pain scores negatively correlated with mechanical pain thresholds (r = -0.38, p < 0.001) and wind-up ratio (r = -0.57, p < 0.001).

CONCLUSIONS

CNP of different etiologies may present different pain descriptors and somatosensory profiles, which is likely due to injury site differences within the neuroaxis. This information may help better design phenotype mechanism correlations and impact trial designs for the main etiologies of CNP, namely stroke and spinal cord lesions. This study provides evidence that topography may influence pain symptoms and sensory profile. The findings suggest that CNP mechanisms might vary according to pain etiology or lesion topography, impacting future mechanism-based treatment choices.

The Management of Poststroke Thalamic Pain: Update in Clinical Practice

Poststroke thalamic pain (PS-TP), a type of central poststroke pain, has been challenged to improve the rehabilitation outcomes and quality of life after a stroke. It has been shown in 2.7–25% of stroke survivors; however, the treatment of PS-TP remains difficult, and in majority of them it often failed to manage the pain and hypersensitivity effectively, despite the different pharmacotherapies as well as invasive interventions. Central imbalance, central disinhibition, central sensitization, other thalamic adaptative changes, and local inflammatory responses have been considered as its possible pathogenesis. Allodynia and hyperalgesia, as well as the chronic sensitization of pain, are mainly targeted in the management of PS-TP. Commonly recommended first- and second-lines of pharmacological therapies, including traditional medications, e.g., antidepressants, anticonvulsants, opioid analgesics, and lamotrigine, were more effective than others. Nonpharmacological interventions, such as transcranial magnetic or direct current brain stimulations, vestibular caloric stimulation, epidural motor cortex stimulation, and deep brain stimulation, were effective in some cases/small-sized studies and can be recommended in the management of therapy-resistant PS-TP. Interestingly, the stimulation to other areas, e.g., the motor cortex, periventricular/periaqueductal gray matter, and thalamus/internal capsule, showed more effect than the stimulation to the thalamus alone. Further studies on brain or spinal stimulation are required for evidence.

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.

Dissecting central post-stroke pain: a controlled symptom-psychophysical characterization

Central post-stroke pain affects up to 12% of stroke survivors and is notoriously refractory to treatment. However, stroke patients often suffer from other types of pain of non- neuropathic nature (musculoskeletal, inflammatory, complex regional) and no head-to-head comparison of their respective clinical and somatosensory profiles has been performed so far.

We compared 39 patients with definite central neuropathic post-stroke pain with two matched- control groups: 32 patients with exclusively non-neuropathic pain developed after stroke and 31 stroke patients not complaining of pain. Patients underwent deep phenotyping via a comprehensive assessment including clinical exam, questionnaires and quantitative sensory testing to dissect central post-stroke pain from chronic pain in general and stroke.

While central post-stroke pain was mostly located in the face and limbs, non-neuropathic pain was predominantly axial and located in neck, shoulders and knees (p&lt;0.05). Neuropathic Pain Symptom Inventory clusters burning (82.1%, n=32, p&lt;0.001), tingling (66.7%, n= 26, p&lt;0.001) and evoked by cold (64.1%, n=25, p&lt;0.001) occurred more frequently in central post-stroke pain. Hyperpathia, thermal and mechanical allodynia also occurred more commonly in this group (p&lt;0.001), which also presented higher levels of deafferentation (p&lt;0.012) with more asymmetric cold and warm detection thresholds compared to controls. In particular, cold hypoesthesia (considered when the threshold of the affected side was less than 41% of the contralateral threshold) odds ratio was 12 (95%CI: 3.8-41.6) for neuropathic pain. Additionally, cold detection threshold/ warm detection threshold ratio correlated with the presence of neuropathic pain (ρ=-0.4, p&lt; 0.001). Correlations were found between specific neuropathic pain symptom clusters and quantitative sensory testing: paroxysmal pain with cold (ρ=-0.4; p=0.008) and heat pain thresholds (ρ=0.5; p=0.003), burning pain with mechanical detection (ρ= -0.4; p=0.015) and mechanical pain thresholds (ρ=-0.4, p&lt;0.013), evoked pain with mechanical pain threshold (ρ= -0.3; p=0.047). Logistic regression showed that the combination of cold hypoesthesia on quantitative sensory testing, the Neuropathic Pain Symptom Inventory, and the allodynia intensity on bedside examination explained 77% of the occurrence of neuropathic pain.

These findings provide insights into the clinical-psychophysics relationships in central post-stroke pain and may assist more precise distinction of neuropathic from non-neuropathic post-stroke pain in clinical practice and in future trials.

Microglia in the Pathophysiology of Hemorrhagic Stroke and the Relationship Between Microglia and Pain After Stroke: A Narrative Review

Stroke is a leading cause of death worldwide, and about a quarter of stroke patients are dead within 1 month. The prognosis is even worse for those with hemorrhagic stroke because the 1-month mortality approaches 50%. Besides, most patients who survive experience complications such as nausea, vomiting, and chronic pain. These adverse experiences, especially the existence of chronic pain, can lead to a decline in the patient's quality of life. In order to improve the treatment and prognosis of hemorrhagic stroke, there is an urgent need to understand its pathophysiological mechanism as well as the chronic pain it induces. This paper reviews studies of the molecular mechanisms of hemorrhagic stroke, especially the activation of microglia and the relationship between microglia and pain after stroke, which could shed new light on hemorrhagic stroke treatment.

Molecular mechanisms of cold pain

The sensation of cooling is essential for survival. Extreme cold is a noxious stimulus that drives protective behaviour and that we thus perceive as pain. However, chronic pain patients suffering from cold allodynia paradoxically experience innocuous cooling as excruciating pain. Peripheral sensory neurons that detect decreasing temperature express numerous cold-sensitive and voltage-gated ion channels that govern their response to cooling in health and disease. In this review, we discuss how these ion channels control the sense of cooling and cold pain under physiological conditions, before focusing on the molecular mechanisms by which ion channels can trigger pathological cold pain. With the ever-rising number of patients burdened by chronic pain, we end by highlighting the pressing need to define the cells and molecules involved in cold allodynia and so identify new, rational drug targets for the analgesic treatment of cold pain.

Effects of Non-Invasive Brain Stimulation on Clinical Pain Intensity and Experimental Pain Sensitivity Among Individuals with Central Post-Stroke Pain: A Systematic Review

Purpose

Central post-stroke pain (CPSP) is a neuropathic disorder resulting in pain and disability. An emerging treatment for CPSP is non-invasive brain stimulation including direct current stimulation [tDCS] and repetitive transcranial magnetic stimulation [rTMS]. This systematic review analyzes the efficacy and quality of non-invasive brain stimulation intervention studies for CPSP.

Methods

Studies were sought from three research databases published between 2007 and 2017. Studies were included if the sole intervention was non-invasive brain stimulation and the primary outcome either clinical or experimental pain intensity. Studies were qualitatively assessed for risk of bias.

Results

Of 1107 articles extracted, six met eligibility criteria. Five studies found a decrease in pain intensity (p<0.05) immediately and 3 weeks after rTMS or tDCS was delivered over the primary motor cortex. For experimental pain, one study found thermal pain thresholds improved for those receiving tDCS compared to sham (p<0.05), while another found normalization of the cold detection threshold only after rTMS (p<0.05). Qualitative assessment revealed only one study rated as "excellent/good" quality, while the other five were rated as "fair" or "poor".

Conclusion

Non-invasive brain stimulation may have a therapeutic effect on pain level for individuals with CPSP, as evidenced by significant decreases in clinical and experimental pain scores. However, despite the impact of CPSP and the promise of non-invasive brain stimulation, few rigorous studies have been performed in this area. Future studies should aim to standardize treatment parameters, measure both clinical and experimental pain, and include long-term follow-up.

Acupuncture-Analgesia-Mediated Alleviation of Central Sensitization

Pain can trigger central amplification called central sensitization, which ultimately results in hyperalgesia and/or allodynia. Many reports have showed acupuncture has an analgesic effect. We searched the related article on PubMed database and Cochrane database to discover central sensitization pathway in acupuncture analgesia. We summarized that acupuncture enhances the descending inhibitory effect and modulates the feeling of pain, thus modifying central sensitization. The possible mechanisms underlying the analgesic effects of acupuncture include segmental inhibition and the activation of the endogenous opioid, adrenergic, 5-hydroxytryptamine, and N-methyl-D-aspartic acid, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate pathways. Moreover, acupuncture can locally reduce the levels of inflammatory mediators. In clinical settings, acupuncture can be used to treat headache, neuropathic pain, low back pain, osteoarthritis, and irritable bowel syndrome. These mechanisms of acupuncture analgesia may be involved in the alleviation of central sensitization.

The role of NLRP3 inflammasome in stroke and central poststroke pain

BACKGROUND

NLRP3 inflammasome plays a prominent role in the pathogenesis and progression of many diseases, such as type 2 diabetes mellitus, obesity, atherosclerosis, and Alzheimer's disease. However, little knowledge is known about the role of NLRP3 inflammasome in central post-stroke pain (CPSP).

METHODS

We selected relevant studies by searching PubMed, Embase, and Medline from inception through February, 2018. We systematically reviewed available publications according to the terms "NLRP3 inflammasome" and "stroke" or "central post-stroke pain" in the title/abstract field.

RESULTS

We reviewed the articles and put forward two possible ways for NLRP3 inflammasome in CPSP. One way is that NLRP3 activation causes cerebral cortex injure, decreasing descending projection fiber to thalamus. Such condition may let GABAergic releases reduce, making the ventral basal (VB) neurons excitability increased. Finally, CPSP occur. Another way is that NLRP3 inflammasome leads to thalamic lesion and strengthens inflammatory response of microglia at the same time. Persistent inflammation causes GABAergic alteration in thalamus reticular neurons (TRN) to restrain VB interneurons functions, contributing to CPSP.

CONCLUSIONS

These possible mechanisms will help become knowledgeable about the occurrence CPSP and provide potential therapy for CPSP.

Central Poststroke Pain: Its Profile among Stroke Survivors in Kano, Nigeria

BACKGROUND

Central poststroke pain (CPSP) caused by sensory dysfunction of central origin is a disabling condition that significantly affects the quality of life of stroke patients.

AIM

The aim of this study is to determine the clinical profiles and pattern of CPSP among stroke patients in Kano, Nigeria.

METHODS

The study was a cross-sectional design involving stroke survivors who were ≥18 years old and with no significant cognitive impairment approved by the Research Ethics Committee of Aminu Kano Teaching Hospital. Participants were assessed using diagnostic criteria form, the douleur neuropathique 4 questions (DN4 questionnaire), and Leeds assessment of neuropathic symptoms and signs (LANNS).

RESULTS

A total of 120 stroke patients participated in the study, in which 6 (5%) were diagnosed with CPSP occurring within the first 3 months in 50% of the participants. The pain characteristics were mainly moderate (83.3%), burning (62.5%), and continuously experienced (66.7%). The frequently affected parts were extremities or occurring as hemisyndrome.

CONCLUSION

Prevalence of CPSP following stroke is low. The clinical features are variable and can occur at a varied time and different intensities and locations. However, it majorly occurs within the first few months post stroke.

Late-onset hypersensitivity after a lesion in the ventral posterolateral nucleus of the thalamus: A macaque model of central post-stroke pain

Central post-stroke pain (CPSP) can occur as a result of a cerebrovascular accident in the ventral posterolateral nucleus (VPL) of the thalamus. Developing therapeutic interventions for CPSP is difficult because its pathophysiology is unclear. Here we developed and characterized a macaque model of CPSP. The location of the VPL was determined by magnetic resonance imaging (MRI) and extracellular recording of neuronal activity during tactile stimulation, after which a hemorrhagic lesion was induced by injecting collagenase type IV. Histological analysis revealed that most of the lesion was localized within the VPL. Several weeks after the injection, the macaques displayed behavioral changes that were interpreted as reflecting the development of both mechanical allodynia and thermal hyperalgesia. Immunohistochemistry revealed that microglial and astrocytic activation in the perilesional areas lasted at least 3 months after injection. The present model reproduced the symptoms of patients suffering from CPSP, in which both mechanical allodynia and thermal hyperalgesia often develop several weeks after cerebrovascular accident. Further, the long-lasting glial activation revealed here may be characteristic of primate brains following injury. The present model will be useful not only for examining the neurological changes underlying CPSP, but also for testing therapeutic interventions for CPSP.

Central poststroke pain: A systematic review

Background Physical, psychological, and/or social impairment can result after a stroke and can be exacerbated by pain. One type of pain after stroke, central poststroke pain, is believed to be due to primary central nervous system mechanisms. Estimated prevalence of central poststroke pain ranges widely from 8% to 55% of stroke patients, suggesting a difficulty in reliably, accurately, and consistently identifying central poststroke pain. This may be due to the absence of a generally accepted definition. Aim We aimed to clarify the role of thalamic strokes and damage to the spinothalamic pathway in central poststroke pain patients. Also, we aimed to gain a current understanding of anatomic substrates, brain imaging, and treatment of central poststroke pain. Summary of review Two independent reviewers identified 10,144 publications. Based on Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines, we extracted data from 23 papers and categorized the articles' aims into four sections: somatosensory deficits, pathway stimulation, clinical trials, and brain imaging. Conclusions Our systematic review suggests that damage to the spinothalamic pathway is associated with central poststroke pain and this link could provide insights into mechanisms and treatment. Moreover, historical connection of strokes in the thalamic region of the brain and central poststroke pain should be reevaluated as many studies noted that strokes in other regions of the brain have high occurrence of central poststroke pain as well.

A Comprehensive Review of Central Post-Stroke Pain

Although central post-stroke pain is widely recognized as a severe chronic neuropathic pain condition, its consolidated definition, clinical characteristics, and diagnostic criteria have not been defined due to its clinically diverse features. The present study was undertaken to comprehensively review current literature and provide a more complete picture of central post-stroke pain with respect to its definition, prevalence, pathophysiology, clinical characteristics, and diagnostic problems, and to describe the range of therapies currently available. In particular, nursing care perspectives are addressed. It is hoped that this review will help nurses become knowledgeable about central post-stroke pain and provide valuable information for the drafting of effective nursing care plans that improve outcomes and quality of life for patients with central post-stroke pain.

Stroke syndromes and clinical management

The knowledge of brain syndromes is essential for stroke physicians and neurologists, particularly those that can be extremely difficult and challenging to diagnose due to the great variability of symptom presentation and yet of clinical significance in terms of potential devastating effect with poor outcome. The diagnosis and understanding of stroke syndromes has improved dramatically over the years with the advent of modern imaging, while the management is similar to general care as recommended by various guidelines in addition to care of such patients on specialized units with facilities for continuous monitoring of vital signs and dedicated stroke therapy. Such critical care can be provided either in the acute stroke unit, the medical intensive care unit or the neurological intensive care unit. There may be no definitive treatment at reversing stroke syndromes, but it is important to identify the signs and symptoms for an early diagnosis to prompt quick treatment, which can prevent further devastating complications following stroke. The aim of this article is to discuss some of the important clinical stroke syndromes encountered in clinical practice and discuss their management.

The nucleus accumbens as a potential target for central poststroke pain

Although deep brain stimulation (DBS) has been found to be efficacious for some chronic pain syndromes, its usefulness in patients with central poststroke pain (CPSP) has been disappointing. The most common DBS targets for pain are the periventricular gray region (PVG) and the ventralis caudalis of the thalamus. Despite the limited success of DBS for CPSP, few alternative targets have been explored. The nucleus accumbens (NAC), a limbic structure within the ventral striatum that is involved in reward and pain processing, has emerged as an effective target for psychiatric disease. There is also evidence that it may be an effective target for pain. We describe a 72-year-old woman with a large right hemisphere infarct who subsequently experienced refractory left hemibody pain. She underwent placement of 3 electrodes in the right PVG, ventralis caudalis of the thalamus, and NAC. Individual stimulation of the NAC and PVG provided substantial improvement in pain rating. The patient underwent implantation of permanent electrodes in both targets, and combined stimulation has provided sustained pain relief at nearly 1 year after the procedure. These results suggest that the NAC may be an effective DBS target for CPSP.

Vaginal allodynia as the presentation of a thalamic tumor

Central pain syndromes associated with damage to the thalamic sensory relay nuclei have been described predominantly in the stroke literature; however, pain syndromes associated with thalamic neoplasms are much less common. We describe a woman with dyspareunia secondary to vaginal allodynia as the presenting sign of a left thalamic juvenile pilocytic astrocytoma. Subsequent to an uneventful stereotactic biopsy, her vaginal allodynia progressed to hemi-body allodynia. We believe that this is the first reported case of isolated vaginal allodynia associated with a thalamic neoplasm or any other structural pathology of the central nervous system. Dyspareunia secondary to vaginal allodynia as the presenting sign of a left thalamic juvenile pilocytic astrocytoma is reported, in a rare case underscoring that thalamic pathology including neoplasms should be considered in evaluating patients with longstanding and unexplained pain syndromes.

Somatosensory symptoms and signs and conditioned pain modulation in chronic post-stroke shoulder pain

Persistent shoulder pain is a common complication after stroke. Its etiology and underlying mechanisms are not well understood and treatment is generally unsatisfactory. The objective of this study was to assess the role of central sensitization and disinhibition in chronic stroke patients with chronic PSSP (n = 19), pain-free stroke patients (n = 29), and healthy controls (n = 23). Positive and negative somatosensory symptoms and signs were assessed using clinical examination and electrical and mechanical quantitative sensory testing (QST). Conditioned pain modulation (CPM) was assessed by comparing QST thresholds before and after applying a cold pressor test. Sensory abnormalities were more frequently observed and more severe in patients with PSSP, including positive signs such as allodynia at the affected side and generalized hyperalgesia at the unaffected side. CPM was similar in stroke patients and healthy controls. This study showed that chronic PSSP was associated with several positive and negative somatosensory signs, implicating a role for central sensitization and possibly for disinhibition. Since the causal relationship remains unclear, and may be related to either neuroplasticity induced by ongoing nociception as well as to the neuropathic brain lesion, prospective studies are warranted.

PERSPECTIVE

The assessment of somatosensory symptoms and signs and endogenous pain modulation demonstrated a role for central sensitization and possibly for disinhibition in chronic PSSP. Prevention and treatment of PSSP could benefit from a more detailed analysis of both peripheral and central pain mechanisms.

Successful treatment of central pain in a multiple sclerosis patient with epidural stimulation of the dorsal root entry zone

OBJECTIVE

We report a case of central pain successfully treated by epidural placement of spinal cord stimulator electrodes. Neuromodulation of primary afferent fibers and the underlying dorsal root entry zone provided effective analgesia whereas traditional lead placement over the dorsal columns on a prior occasion had not been effective. The rationale for this technique based on current understanding of the mechanisms of central pain and the risk/benefit considerations are discussed.

CASE REPORT

A 52-year-old woman presented with a 2-year history of pain in the lateral hand secondary to a demyelinating episode in the C2-4 spinal cord secondary to multiple sclerosis. Medications, sympathetic blocks, and acupuncture had been ineffective. One year after an unsuccessful single-lead trial of spinal cord stimulation over the cervical dorsal columns, a dual-lead trial of spinal cord stimulation over the lateral cervical spinal cord and dorsal roots provided significant analgesia, prompting a successful permanent implant.

OUTCOME MEASURES

Responses on the Brief Pain Inventory short form and quantitative thermosensory testing data were collected at two timepoints 16 days apart under two conditions: no stimulation and single-lead stimulation of cervical primary afferents and underlying spinal cord.

RESULTS

The patient's questionnaire responses indicated significantly improved pain scores with lateral-lead neuromodulation that was associated with a reduction in her baseline heat hypoalgesia.

CONCLUSIONS

Lateral-lead spinal cord stimulation may be effective for some central pain syndromes through a partial restoration of homeostatic small-fiber signaling. Neuroanatomical and physiological data in a larger population of patients will be required to predict the best responders to this therapeutic modality.

Development and characterization of a hemorrhagic rat model of central post-stroke pain

Stroke is the leading cause of disability in the industrialized world and it is estimated that up to 8% of stroke victims suffer from some form of central post-stroke pain (CPSP). Thalamic syndrome is form of central pain that typically results from stroke in the thalamus. In the present study, we describe the development and characterization of a rat model of thalamic CPSP. This model is based on a hemorrhagic stroke lesion in the ventral posterolateral nucleus of the thalamus, one of the reported causes of thalamic syndrome in humans. Behavioral analysis showed that animals displayed hyperesthesia in response to mechanical pinch stimulation, with sensitivity localized to the hind limb. This response appeared within 7 days of the intra-thalamic hemorrhage. Animals also showed increased thermal sensitivity in the contralateral hind limb. Histopathology indicated the presence of activated microglia adjacent to the core of hemorrhagic lesions in the thalamus. Neutrophils were confined to the hemorrhage core, indicating that they entered in the initial bleed. By 7 days, bands of activated microglia and astrocytes separated the hematoma from surviving neurons at the edge of the lesion. We did not observe any terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive neurons beyond the immediate hematoma at 1, 3, or 7 days after hemorrhage. Surviving neurons were located in the vicinity of activated microglia and astrocytes at the outer edge of the hematoma. Thus, thalamic hemorrhage produces a confined lesion that destroys the tissue within the initial bleed, with little or no neuron death beyond the hemorrhage core. Surviving neurons surrounded by activated glial cells likely contribute to neuropathic pain in this model. This thalamic hemorrhage model is useful for studying the neuropathology and physiology of thalamic syndrome, and developing therapeutics for central post-stroke pain.

Central poststroke pain: an abstruse outcome

Central poststroke pain (CPSP), formerly known as thalamic pain syndrome of Déjerine and Roussy, is a central neuropathic pain occurring in patients affected by stroke. It is one manifestation of central pain, which is broadly defined as central neuropathic pain caused by lesions or dysfunction in the central nervous system. Thalamic pain was first described 100 years ago by Déjerine and Roussy and has been described as "among the most spectacular, distressing, and intractable of pain syndromes". CPSP is characterized by constant or intermittent pain and is associated with sensory abnormalities, particularly of thermal sensation. While the pain is frequently described as burning, scalding, or burning and freezing, other symptoms are usually vague and hard to characterize, making an early diagnosis particularly difficult. In fact, those who develop CPSP may no longer be under the care of health care professionals when their symptoms begin to manifest, resulting in misdiagnosis or a significant delay before treatment begins. Diagnosis is further complicated by cognitive and speech limitations that may occur following stroke, as well as by depression, anxiety and sleep disturbances. Patients may also exhibit spontaneous dysesthesia and the stimulus-evoked sensory disturbances of dysesthesia, allodynia and hyperalgesia. The present study offers a historical reference point for future clinical and basic research into this elusive type of debilitating pain.

Modeling pain circuits: how imaging may modify perception

Pain is the unpleasant sensory experience following tissue damage or the threat of damage. The activation of cortical regions during noxious stimulation is believed a result of the negative affect and sensations generated by the stimulus. How a noxious event is translated into pain experience remains uncertain, and pain that occurs in the absence of a noxious event remains mysterious. Acute pain and chronic pain depend on a categorization of feeling that occurs collectively rather than individually. Capturing that process inside a brain scan is problematic. Resolving this problem requires an approach to imaging that transgress the boundaries of physical and social concepts.

Imaging central pain syndromes

Anatomic, functional, and neurochemical imaging studies have provided new investigative tools in the study of central pain. High-resolution imaging studies allow for precise determination of lesion location, whereas functional neuroimaging studies measure pathophysiologic consequences of injury to the central nervous system. Additionally, magnetic resonance spectroscopy evaluates lesion-induced neurochemical changes in specific brain regions that may be related to central pain. The small number of studies to date precludes definitive conclusions, but the recent findings provide information that either supports or refutes current hypotheses and can serve to generate new ideas.