Central post-stroke pain: a challenge for the scientist and the clinician

Modulation of melatonin to the thalamic lesion-induced pain and comorbid sleep disturbance in the animal model of the central post-stroke hemorrhage

The devastating chronic central post stroke pain is associated with variety of comorbidities. Disrupted sleep is a severe comorbidity, causing an increase in the suicide rate, due to CPSP’s pain symptom. Melatonin is a well-known jet-lag compound, which helps in entrainment of sleep cycle. Accordingly, whether melatonin as a therapeutic measurement for the regulation of sleep disturbance related to central post stroke pain remains unclear. Exogenous melatonin administration entrained the disrupted 24 h circadian cycle, more effectively after 2 and 3 week of administration. The effect of melatonin was persisted on 4th week too, when melatonin administration was discontinued. Also, melatonin ameliorated the pain due to distorted sleep-activity behavior after melatonin administration for 3 weeks. The low levels of melatonin in blood plasma due to CPSP were restored after 3 weeks of melatonin administration. After 30 mg/kg melatonin administrations for 3 weeks, all the disrupted resting and activity behaviors were reduced during light and dark periods. The results suggested that melatonin significantly ameliorated CPSP’s pain symptoms and comorbid sleep disturbance showing in activity behavior.

Effects of thalamic hemorrhagic lesions on explicit and implicit learning during the acquisition and retrieval phases in an animal model of central post-stroke pain

Hemorrhagic stroke has many symptoms, including central pain, learning and memory impairments, motor deficits, language problems, emotional disturbances, and social maladjustment. Lesions of the ventral basal complex (VBC) of the thalamus elicit thermal and mechanical hyperalgesia, forming an animal model of central post-stroke pain (CPSP). However, no research has yet examined the involvement of learning and memory in CPSP using an animal model. The present study examined whether VBC lesions affect motor function, conditioned place preference (CPP; implicit memory), and spatial learning (explicit memory) in the acquisition and retrieval phases. The results showed that rats with VBC lesions exhibited thermal hyperalgesia in the acquisition and retrieval phases, indicating that these lesions can induce CPSP. During these phases, the rats with VBC lesions exhibited enhanced (morphine-induced) CPP learning. These lesions did not affect the rats' total distance travelled, time spent, or velocity in the spatial learning tasks. The lesions also did not affect motor function in the rotarod task. Altogether, VBC lesions resulted in CPSP and facilitated CPP (implicit memory). However, the lesions did not affect spatial learning (explicit memory) or motor function. The relationship between CPSP and learning and memory is important for patients who suffer from such central pain. The implications of the present study may provide insights into helping reduce CPSP and its associated symptoms.

Pain anticipatory phenomena in patients with central poststroke pain: a magnetoencephalography study

Central poststroke pain (CPSP) is characterized by hemianesthesia associated with unrelenting chronic pain. The final pain experience stems from interactions between sensory, affective, and cognitive components of chronic pain. Hence, managing CPSP will require integrated approaches aimed not only at the sensory but also the affective-cognitive spheres. A better understanding of the brain's processing of pain anticipation is critical for the development of novel therapeutic approaches that target affective-cognitive networks and alleviate pain-related disability. We used magnetoencephalography (MEG) to characterize the neural substrates of pain anticipation in patients suffering from intractable CPSP. Simple visual cues evoked anticipation while patients awaited impending painful (PS), nonpainful (NPS), or no stimulus (NOS) to their nonaffected and affected extremities. MEG responses were studied at gradiometer level using event-related fields analysis and time-frequency oscillatory analysis upon source localization. On the nonaffected side, significantly greater responses were recorded during PS. PS (vs. NPS and NOS) exhibited significant parietal and frontal cortical activations in the beta and gamma bands, respectively, whereas NPS (vs. NOS) displayed greater activation in the orbitofrontal cortex. On the affected extremity, PS (vs. NPS) did not show significantly greater responses. These data suggest that anticipatory phenomena can modulate neural activity when painful stimuli are applied to the nonaffected extremity but not the affected extremity in CPSP patients. This dichotomy may stem from the chronic effects of pain on neural networks leading to habituation or saturation. Future clinically effective therapies will likely be associated with partial normalization of the neurophysiological correlates of pain anticipation.

Central Neuropathic Pain Syndromes

Chronic pain is common in patients with neurologic complications of a central nervous system insult such as stroke. The pain is most commonly musculoskeletal or related to obligatory overuse of neurologically unaffected limbs. However, neuropathic pain can result directly from the central nervous system injury. Impaired sensory discrimination can make it challenging to differentiate central neuropathic pain from other pain types or spasticity. Central neuropathic pain may also begin months to years after the injury, further obscuring recognition of its association with a past neurologic injury. This review focuses on unique clinical features that help distinguish central neuropathic pain. The most common clinical central pain syndromes-central poststroke pain, multiple sclerosis-related pain, and spinal cord injury-related pain-are reviewed in detail. Recent progress in understanding of the pathogenesis of central neuropathic pain is reviewed, and pharmacological, surgical, and neuromodulatory treatments of this notoriously difficult to treat pain syndrome are discussed.

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.

A [14C]iodoantipyrine study of inter-regional correlations of neural substrates following central post-stroke pain in rats

BACKGROUND

Central pain syndrome is characterized by a combination of abnormal pain sensations, and pain medications often provide little or no relief. Accumulating animal and clinical studies have shown that impairments of the spinothalamic tract (STT) and thalamocingulate pathway causes somatosensory dysfunction in central post-stroke pain (CPSP), but the involvement of other neuronal circuitries in CPSP has not yet been systematically examined. The aim of the present study was to evaluate changes in brain activity and neuronal circuitry using [(14)C]iodoantipyrine (IAP) in an animal model of CPSP.

RESULTS

Rats were subjected to lateral thalamic hemorrhage to investigate the characteristics of CPSP. Thermal and mechanical hyperalgesia developed in rats that were subjected to thalamic hemorrhagic lesion. The medial prefrontal cortex (mPFC), anterior cingulate cortex (ACC), striatum, thalamus, hypothalamus, and amygdala were more active in the CPSP group compared with rats that were not subjected to lateral thalamic hemorrhage. The inter-regional correlation analysis showed that regional cerebral blood flow in the mPFC was highly correlated with the amygdala in the right brain, and the right brain showed complex connections among subregions of the ACC. Rats with CPSP exhibited strong activation of the thalamocingulate and mPFC-amygdala pathways.

CONCLUSIONS

These results corroborate previous findings that the STT and thalamocingulate pathway are involved in the pathophysiological mechanisms of CPSP symptoms. The mPFC, amygdala, and periaqueductal gray emerged as having important correlations in pain processing in CPSP. The present data provide a basis for a neural correlation hypothesis of CPSP, with implications for CPSP treatment.

Post-stroke pain hypersensitivity induced by experimental thalamic hemorrhage in rats is region-specific and demonstrates limited efficacy of gabapentin

Intractable central post-stroke pain (CPSP) is one of the most common sequelae of stroke, but has been inadequately studied to date. In this study, we first determined the relationship between the lesion site and changes in mechanical or thermal pain sensitivity in a rat CPSP model with experimental thalamic hemorrhage produced by unilateral intra-thalamic collagenase IV (ITC) injection. Then, we evaluated the efficacy of gabapentin (GBP), an anticonvulsant that binds the voltage-gated Ca(2+) channel α2δ and a commonly used anti-neuropathic pain medication. Histological case-by-case analysis showed that only lesions confined to the medial lemniscus and the ventroposterior lateral/medial nuclei of the thalamus and/or the posterior thalamic nucleus resulted in bilateral mechanical pain hypersensitivity. All of the animals displaying CPSP also had impaired motor coordination, while control rats with intra-thalamic saline developed no central pain or motor deficits. GBP had a dose-related anti-allodynic effect after a single administration (1, 10, or 100 mg/kg) on day 7 post-ITC, with significant effects lasting at least 5 h for the higher doses. However, repeated treatment, once a day for two weeks, resulted in complete loss of effectiveness (drug tolerance) at 10 mg/kg, while effectiveness remained at 100 mg/kg, although the time period of efficacious analgesia was reduced. In addition, GBP did not change the basal pain sensitivity and the motor impairment caused by the ITC lesion, suggesting selective action of GBP on the somatosensory system.

Pharmacological management of central post-stroke pain: a practical guide

Pain is one of the most troublesome sequelae of stroke. Some of this post-stroke pain is caused by the brain lesion itself; this is called central post-stroke pain (CPSP). Although the prevalence of CPSP is low (1-8 %), persistent, often treatment-resistant, painful sensations are a major problem for stroke patients. The pathogenesis of CPSP remains unknown, but suggested underlying causes include hyperexcitation in the damaged sensory pathways, damage to the central inhibitory pathways, or a combination of the two. For pharmacological treatment, amitriptyline, an adrenergic antidepressant, is currently the first-line drug for CPSP. However, its effect is frequently incomplete and a high dose is commonly not tolerated in stroke patients. Lamotrigine, an antiepileptic, was also found to be effective in a controlled trial and can be used as an alternative or additive therapy. GABAergic drugs with potential calcium channel-blocking effects, such as gabapentin or pregabalin, have recently emerged as a potentially useful therapy. These drugs are effective in various neuropathic pain syndromes, but their effect on CPSP remains to be proven. Pregabalin may improve pain-related anxiety and sleep disturbances. Fluvoxamine and mexiletine may be used adjunctively in some patients. Non-pharmacological treatments such as motor cortex stimulation or deep brain stimulation are used in some centers, but are not proven to be effective. Further well designed clinical trials as well as basic research should be performed to improve our understanding of the pathophysiology of CPSP and to develop better treatment strategies.

Development and pharmacological verification of a new mouse model of central post-stroke pain

Central post-stroke pain (CPSP) including thalamic pain is one of the most troublesome sequelae that can occur after a cerebrovascular accident. Although the prevalence of CPSP among stroke patients is relatively low, the persistent, often treatment-refractory, painful sensations can be a major problem and decrease the affected patient's quality of life. To better understand of the pathophysiological basis of CPSP, we developed and characterized a new mouse model of thalamic CPSP. This model is based on a hemorrhagic stroke lesion with collagenase in the ventral posterolateral nucleus of the thalamus. Histopathological analysis indicated that the thalamic hemorrhage produced a relatively confined lesion that destroys the tissue within the initial bleed, and also showed the presence of activated microglia adjacent to the core of hemorrhagic lesions. Behavioral analysis demonstrated that the animals displayed diclofenac-, morphine- or pregabalin-resistant mechanical allodynia and thermal hyperalgesia of the hind paw contralateral to the lesion for over 112 days. However, we found that minocycline, a microglial inhibitor, significantly ameliorated mechanical allodynia and thermal hyperalgesia. These results suggest that this model might be proved as a useful animal model for studying the neuropathology of thalamic syndrome, and developing improved therapeutics for CPSP.

Psychophysical and cerebral responses to heat stimulation in patients with central pain, painless central sensory loss, and in healthy persons

Patients with central pain (CP) typically have chronic pain within an area of reduced pain and temperature sensation, suggesting an impairment of endogenous pain modulation mechanisms. We tested the hypothesis that some brain structures normally activated by cutaneous heat stimulation would be hyperresponsive among patients with CP but not among patients with a central nervous system lesion causing a loss of heat or nociceptive sensation with no pain (NP). We used H(2)(15)O positron emission tomography to measure, in 15 healthy control participants, 10 NP patients, and 10 CP patients, increases in regional cerebral blood flow among volumes of interest (VOI) from the resting (no stimulus) condition during bilateral contact heat stimulation at heat detection, heat pain threshold, and heat pain tolerance levels. Both patient groups had a reduced perception of heat intensity and unpleasantness on the clinically affected side and a bilateral impairment of heat detection. Compared with the HC group, both NP and CP patients had more hyperactive and hypoactive VOI in the resting state and more hyperresponsive and hyporesponsive VOI during heat stimulation. Compared with NP patients, CP patients had more hyperresponsive VOI in the intralaminar thalamus and sensory-motor cortex during heat stimulation. Our results show that focal CNS lesions produce bilateral sensory deficits and widespread changes in the nociceptive excitability of the brain. The increased nociceptive excitability within the intralaminar thalamus and sensory-motor cortex of our sample of CP patients suggests an underlying pathophysiology for the pain in some central pain syndromes.

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.

Challenges in using opioids to treat pain in persons with substance use disorders

Pain and substance abuse co-occur frequently, and each can make the other more difficult to treat. A knowledge of pain and its interrelationships with addiction enhances the addiction specialist's efficacy with many patients, both in the substance abuse setting and in collaboration with pain specialists. This article discusses the neurobiology and clinical presentation of pain and its synergies with substance use disorders, presents methodical approaches to the evaluation and treatment of pain that co-occurs with substance use disorders, and provides practical guidelines for the use of opioids to treat pain in individuals with histories of addiction. The authors consider that every pain complaint deserves careful investigation and every patient in pain has a right to effective treatment.

Caring and uncaring experiences as narrated by persons with long-term pain after a stroke

The aim of this study was to describe how persons with long-term pain after a stroke experience their care. The study is part of a larger research project concerning a group persons suffering from long-term pain after a stroke. Qualitative interviews were performed with 43 persons suffering from central poststroke pain, nociceptive pain or tension-type headache after their stroke incident. Content congruence emerged among the narratives (n = 43), and therefore the most information-rich ones (n = 23) were selected for deeper investigation by means of qualitative content analysis. The results reveal the patients' need for being respected, understood and supported, also for being given adequate time and information. Accessibility and continuity in the professional contacts and with regard to medical and physical treatment was emphasized. The participants' narratives highlight the importance of the professionals having knowledge of pain and pain management.

Effects of a cannabinoid agonist on spinal nociceptive neurons in a rodent model of neuropathic pain

The effects of the synthetic cannabinoid WIN 55,212-2 on heat-evoked firing of spinal wide dynamic range (WDR) neurons were examined in a rodent model of neuropathic pain. Fifty-eight WDR neurons (1 cell/animal) were recorded from the ipsilateral spinal dorsal horns of rats with chronic constriction injury (CCI) and sham-operated controls. Relative to sham-operated controls, neurons recorded in CCI rats showed elevations in spontaneous firing, noxious heat-evoked responses, and afterdischarge firing as well as increases in receptive field size. WIN 55,212-2 (0.0625, 0.125, and 0.25 mg/kg, intravenous) dose-dependently suppressed heat-evoked activity and decreased the receptive field areas of dorsal horn WDR neurons in both nerve injured and control rats with a greater inhibition in CCI rats. At the dose of 0.125 mg/kg iv, WIN 55,212-2 reversed the hyperalgesia produced by nerve injury. The effect of intravenous administration of WIN 55,212-2 appears to be centrally mediated because administration of the drug directly to the ligated nerve did not suppress the heat-evoked neuronal activity in CCI rats. Pretreatment with the cannabinoid CB(1) receptor antagonists SR141716A or AM251, but not the CB(2) antagonist SR144528, blocked the effects. These results provide a neural basis for reports of potent suppression by cannabinoids of the abnormal sensory responses that result from nerve injury.

Reward-aversion circuitry in analgesia and pain: implications for psychiatric disorders

Sensory and emotional systems normally interact in a manner that optimizes an organism's ability to survive using conscious and unconscious processing. Pain and analgesia are interpreted by the nervous system as aversive and rewarding processes that trigger specific behavioral responses. Under normal physiological conditions these processes are adaptive. However, under chronic pain conditions, functional alterations of the central nervous system frequently result in maladaptive behaviors. In this review, we examine: (a) the interactions between sensory and emotional systems involved in processing pain and analgesia in the physiological state; (b) the role of reward/aversion circuitry in pain and analgesia; and (c) the role of alterations in reward/aversion circuitry in the development of chronic pain and co-morbid psychiatric disorders. These underlying features have implications for understanding the neurobiology of functional illnesses such as depression and anxiety and for the development and evaluation of novel therapeutic interventions.

Transient attenuation of neuropathic manifestations in rats following lesion or reversible block of the lateral thalamic somatosensory nuclei

BACKGROUND AND AIMS

Nociceptive behavior in animal models for mononeuropathy has been shown to be altered by spinal tract lesions which suggest a possible supraspinal modulation. The thalamus constitutes a chief center for the processing of nociception. We have, therefore, investigated the effects of transient or permanent blocks of the lateral somatosensory thalamic nuclei (the ventrobasal complex) on the neuropathic manifestations in rats.

METHODS

Different groups of rats (n = 5-6) were subjected to mononeuropathy, following the spared nerve injury model, known to produce sustained heat hyperalgesia and tactile and cold allodynia which peaked about 2 weeks after nerve injury. This was followed by stereotaxic placement of either electrolytic or chemical lesions or implantation of mini osmotic pump for slow release of lidocaine in the ventrobasal complex.

RESULTS

Chronic electrolytic and chemical lesions or reversible block of the lateral somatosensory thalamus produced transient (1-2 weeks) attenuation of neuropathic manifestations along with a persistent decrease of the hot plate latency. The most pronounced effect was observed on heat hyperalgesia, and the least significant and short-lived effect was observed on cold allodynia.

CONCLUSION

We conclude that the lateral somatosensory thalamic complex is involved in the processing of neuropathic manifestations but cannot be considered as an obligatory or exclusive relay center for the neuropathic syndromes.

Allodynia in patients with post-stroke central pain (CPSP) studied by statistical quantitative sensory testing within individuals

The disinhibition hypothesis of post-stroke central pain (CPSP) suggests that 'the excessive response (dysesthesia/hyperalgesia/allodynia) is accompanied by a em leader loss of sensation' resulting from a lesion of a 'lateral nucleus' of thalamus or of 'cortico-thalamic paths' [Brain 34 (1911) 102]. One recent elaboration of this hypothesis proposes a submodality specific relationship, such that injury to a cool-signaling lateral thalamic pathway disinhibits a nociceptive medial thalamic pathway, thereby producing both burning, cold, ongoing pain and cold allodynia. The current study quantitatively evaluated the sensory loss and sensory abnormalities to discern submodality relationships between these sensory features of CPSP. The present results were statistically tested within individuals so that sensory loss and sensory abnormality are directly related by occurrence in the same individual. The results demonstrate that individuals with CPSP and normal tactile detection thresholds experience tactile allodynia significantly more often than those with tactile hypoesthesia. Most patients (11/13) exhibited hypoesthesia for the perception of cool stimuli, but few of these (2/11) showed cold allodynia. The most dramatic case of cold allodynia occurred in a patient who had a normal detection threshold for cold. Individuals with cold hypoesthesia, strictly contralateral to the cerebro-vascular accident (CVA or stroke), were often characterized by the presence of burning, cold, ongoing pain, and by the absence, not the presence, of cold allodynia. Overall, these results in CPSP suggest that tactile allodynia occurs in disturbances of thermal/pain pathways that spare the tactile-signaling pathways, and that cold hypoesthesia is neither necessary nor sufficient for cold allodynia.

Health-related quality of life in persons with long-term pain after a stroke

BACKGROUND

No study has, to our knowledge, previously been published on health-related quality of life (HRQoL) in a group suffering from long-term pain after a stroke.

AIM

The aim of the present study was to describe HRQoL in persons with long-term pain after a stroke, and to compare this with different types of pain conditions, age, gender and household status.

DESIGN

This study has a design combining qualitative and quantitative methods.

METHODS

Forty three participants suffering from long-term pain after a stroke were included. A qualitative interview was performed and then analysed by means of latent content analysis. In addition, two self-report questionnaires, SF-36 and the Hospital Anxiety and Depression Scale (HAD Scale), were used.

RESULTS

The qualitative data revealed that physical and cognitive functioning, economic security and good relationships, support and having the ability to be together with family and friends were important factors with regard to experienced HRQoL. No significant differences were found in SF-36 and the HAD Scale with regard to the different types of pain. The older age group had decreased physical functioning in SF-36. The men had more decreased vitality than the women.

CONCLUSION

The results show, that the participants in this study have a lower HRQoL due to their long-term pain than those in previous studies on stroke survivors. It is evident that further research is needed with longitudinal studies and larger populations to gain more knowledge and thereby provide better supportive care.

RELEVANCE TO CLINICAL PRACTICE

Awareness and understanding of the patients' perceptions and transitions with regard to their life situation and suffering from long-term pain after a stroke is important in order to support a maintained or increased HRQoL. This is also important after the acute stage and rehabilitation, including quality of life of the relatives, especially to older and dependent persons.

Spinal cord injury pain--mechanisms and treatment

In spinal cord injury (SCI), pain is a major cause of disability. A review of experimental and human studies, which provide insight into the mechanisms and treatment of SCI neuropathic pain are presented. Each of a series of pathophysiologic changes after SCI may be relevant for the development of SCI neuropathic pain. These changes are discussed in relation to neuropathic pain at and below the level of SCI. SCI neuropathic pain is difficult to treat. Experimental and human randomized, double-blind, placebo-controlled, clinical trials on pharmacologic treatment of SCI pain are summarized.

An East-West approach to the management of central post-stroke pain

The development of neuropathic pain following stroke is not uncommon. The consequences include significant disabilities and depression. Treatment can often be difficult and responses unsatisfactory. We report a patient with severe central post-stroke pain (CPSP) of the right leg benefiting from a combination of Western multidisciplinary therapies AND acupuncture. A literature search has revealed that relatively few studies have been done on the management of CPSP, compared with other types of neuropathic pain. Amitriptyline and carbamazepine were found to produce positive effects on post-stroke pain in one small study; lamotrigine and gabapentin are two newer drugs which appear promising. To the best of our knowledge, the use of acupuncture for the treatment of CPSP has not been previously reported.

Disability after a stroke and the influence of long-term pain on everyday life

Pain after a stroke is a symptom often forgotten, unnoticed although it is reported to be a great problem in care. The aim of this study was to describe disability after a stroke and how long-term pain influences everyday life according to the Multidimensional Pain Inventory - Swedish language version (MPI-S) and to test the reliability of this instrument. Forty-three persons were investigated 2 years after the stroke incident: 15 with central post-stroke pain (CPSP), 18 with nociceptive pain mainly in the shoulder and 10 with tension-type headache. Data collection was performed through the MPI-S and a questionnaire regarding assistive devices, also structured interviews based on the Activities of Daily Living (ADL) staircase and the Self-report impairment questionnaire. The results show that the persons suffered moderate to severe pain. Almost half were dependent in ADL. The most often reported impairments and use of assistive devices concerned mobility and/or motion. This was most frequent in persons with nociceptive pain. There were significant differences in persons with central pain and nociceptive pain compared with tension-type headache with regard to mobility- and/or motion-related activities. No statistical differences emerged between age, gender, different types of pain and the MPI-S scales, nor any significant differences in degree of pain as between different types of pain according to the Self-report impairment questionnaire. The reliability analysis of the MPI-S shows good homogeneity in all scales except Interference, Life Control and Affective Distress. This is the first study with MPI-S on mainly older persons and on stroke patients, thus further research is needed on this instrument as well as on which specific activities evoke the pain. This is in order to offer adequate treatment, care and support to persons with pain after a stroke.

The clinical picture of neuropathic pain

Neuropathic pains refer to a heterogeneous group of pain conditions characterised by lesion or dysfunction of the normal sensory pathways. Clinical characteristics include: delayed onset of pain after nervous system lesion, pain in area of sensory loss, spontaneous and different evoked types of pains. It has so far only been possible to classify these pains on basis of underlying cause or on anatomical location. The mechanisms underlying neuropathic pain are not yet clear, but neuronal hyperexcitability in those neurons that have lost their normal patterned input seems to be a common denominator for many, if not all types, of neuropathic pains. Along these lines, a mechanism-based classification has recently been proposed, which is an attractive approach because it provides a frame for a rationally based therapy of neuropathic pains. The clinical manifestations of neuronal hyperexcitability due to nervous system lesions is described.

Hemihyperaesthesia and hyperresponsiveness resembling central pain syndrome in a dog with a forebrain oligodendroglioma

A 4-year-old male Boxer was presented with neurological signs referable to a right forebrain lesion that was confirmed with computed tomography. Whilst characteristic signs of a unilateral forebrain lesion were observed, the dominant and striking finding was a right-sided hemisensory disturbance characterised by hyperaesthesia and hyperresponsiveness. Necropsy revealed a gelatinous mass confined to the right forebrain that was identified histologically as an oligodendroglioma. The lesion was centred on the internal capsule and involved ventral frontal and temporal lobes and the ventrolateral thalamus, including lateral and medial parts of the ventrocaudal nuclear region (ventrobasilar complex) of the thalamus. On clinical and neuroanatomical grounds, the case exhibited features in common with central pain syndrome in human patients with thalamic lesions. These included a somatosensory disorder of hyperaesthesia affecting an entire side of the head and body, behavioural manifestations consistent with spontaneous pain and a lesion involving the ventrobasilar complex. Of interest, the hemisensory abnormality was ipsilateral to the lesion, contrasting with central pain in humans, in which clinical signs are contralateral to analogous lesions. It is suggested that species-specific differences in spinal cord organisation of pain pathways, particularly the greater bilateral projection of nociceptive afferents to thalamic relay nuclei in carnivores, may account for this disparity. Notably, central pain is rare in human patients with brain tumours, even those affecting the thalamus, and this may also be the case in dogs.

Stereotactic treatment of central pain

In the present study, the effect of stereotactic treatment on central pain is briefly reviewed. Studies have shown that the spinothalamic tract projects to the shell zone of the principal sensory nucleus (Vc) and its rostral part (Vim), where it forms clusters. Recent anatomophysiological studies have revealed specific nociceptive neurons in the thalamic submedius and VMpo nucleus, from which fibers project to the insular and cingulate cortex. In the abnormal state of central pain, these structures may be subjected to excess excitation. Thalamic recording during the course of stereotactic thalamotomy strongly supports this hypothesis. Thus, Vim-Vcpc thalamotomy ameliorates the so-called deep pain after stroke.

Central pain and dysesthesia syndrome

This article presents recent observations about different recognized central pain syndromes (CPS) and discusses them in light of contemporary microelectrode and imaging findings. Different theories regarding the generation of CPS are reviewed, with an emphasis on difficulties in diagnosis and treatment. The author discourages destructive procedures for treatment of CPS, favoring, instead, reversible procedures such as stimulation techniques and drug delivery systems.

Opioids in the brain: supraspinal mechanisms in pain control

Systemically administered opioids produce a profound inhibition of noxious-evoked activity peripherally, spinally and supraspinally in several species, including man. The role of the brain in opioid mediated-pain control has been less well characterized than that occurring at lower levels in the nervous system. Yet, classical studies indicate that in morphine-induced analgesia the individual senses noxious stimuli, but the affective, motivational and aversive character of the stimulus is no longer present. This observation indicates that morphine probably exerts a specific action on those brain systems that control complex behaviors like aversion and motivation. The failure to document such effects in experimental studies may in part be explained by less suitable methods for assessing antinociception, e.g. measurements of simple reflex behaviors. Experimental animal studies show that supraspinal opioids may influence nociception by several distinct mechanisms, which differ from those seen in the spinal cord: Change of activity in descending bulbospinal pathways. Direct inhibition of noxious throughput at brainstem level. Indirect inhibition of noxious responding brainstem neurons projecting to supraspinal centers. Influence ascending forebrain systems. Direct cortical or thalamic inhibition. In humans, the antinociceptive actions of opioids occurring in the brain has until recently been like looking into a "black box". The introduction of new imaging techniques may provide new tools for directly measuring the antinociceptive action of opioids in the brain under normal and pathological conditions. In particular, the emotional-affective aspect of pain and how this is modulated by opioids will be of interest to study.

Effects of intrathecal vs. systemic clonidine in treating chronic allodynia-like response in spinally injured rats

A chronic pain-like response to innocuous mechanical stimuli (allodynia) was observed in rats after severe spinal cord ischemia, which resembled some painful conditions observed in spinally injured patients. The present studies examined the effects of clonidine, an alpha 2-adrenoceptor agonist, on this allodynia-like response. Intrathecal (i.t.) clonidine dose-dependently relieved allodynia and doses up to 10 micrograms did not induce motor deficits or sedation, but slightly increased systemic blood pressure. The anti-allodynic effect of i.t. clonidine was reversed by the selective alpha 2-adrenoceptor antagonist atipamezole. In contrast, 50 and 100 micrograms/kg intraperitoneal (i.p.) clonidine did not relieve the chronic allodynia, although the higher dose induced some motor deficits and sedation. Allodynic behavior was abolished after 200 micrograms/kg, i.p. clonidine, which, however, caused strong sedative and motor impairment. The present data suggested that spinal, but not systemic, alpha 2-adrenoceptor agonists may have therapeutic value in treating mechanical allodynia in patients with neuropathic pain of spinal origin.