The Clinical journal of pain
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Introduction of the term complex regional pain syndromes (CRPS) as a replacement of the older terminology, reflex sympathetic dystrophy (RSD) and causalgia, has achieved two goals: it has focused attention on the diagnosis and treatment, and sent basic scientists back to their laboratories. The relation of sympathetically maintained pain and sympatholysis is examined, particularly as a neuropathic process that is found in many conditions, including CRPS. This review also focuses on recent observations proposing a pathologic basis in support of diagnosis and treatment of these disorders.
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Our knowledge about the pathogenesis of neuropathic pain has grown significantly during last two decades. Basic research with animal models of neuropathic pain and human clinical trials with neuropathic pain have accumulated solid evidence that a number of pathophysiologic and biochemical changes take place in the nervous system at a peripheral or central level as a result of the insult or disease. Many similarities between the pathophysiologic phenomena observed in some epilepsy models and neuropathic pain models justify the rationale for the use of anticonvulsant drugs in the symptomatic management of neuropathic pain disorders. ⋯ One small clinical trial with lamotrigine demonstrated improved pain control in TN. Evidence in support of the efficacy of anticonvulsant drugs in the treatment of neuropathic pain continues to evolve, and benefits have been clearly demonstrated in the case of GBP and CBZ. More advances in our understanding of the mechanisms underlying neuropathic pain syndromes should further our opportunities to establish the role of anticonvulsants in the treatment of neuropathic pain.
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Studies on the psychosocial impact of neuropathic pain conditions, including postherpetic neuralgia, diabetic neuropathy, complex regional pain syndrome, post spinal cord injury, postamputation, and AIDS-related neuropathy, are reviewed. Although limited, data are consistent with the larger literature on chronic pain and indicate that neuropathic pain reduces quality of life, including mood and physical and social functioning. ⋯ Clinical trials of psychological interventions have not been reported, although some case series of successful treatment of neuropathic pain are reported, primarily in the area of biofeedback. Given the evidence indicating the broad impact of neuropathic pain on many areas of function, it is surprising that so few studies have investigated the impact of psychological interventions in these populations.
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Herpes zoster is a common and painful disease that is caused by reactivation of the varicella-zoster virus. Herpes zoster pain that persists after healing of the acute infection is termed postherpetic neuralgia (PHN), a chronic pain syndrome that is often refractory to all treatment. The prevalence of PHN is expected to increase substantially in the coming decades, because the incidence of herpes zoster and the risk of PHN will both increase as the population ages. Although the results of recent studies provide a basis for improved treatment of patients with PHN, as many as half of all PHN patients do not obtain relief of their pain. Research on the development of improved treatments is continuing, but it has not been generally recognized that an equally important goal should be the design of interventions to prevent PHN. The prevention of PHN would lead to major reductions in disability, suffering, and the use of health care resources. ⋯ This treatment approach would be expected to reduce the risk of PHN in herpes zoster patients by attenuating acute pain and thereby preventing the initiation of central mechanisms of chronic pain.
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Chronic pain can be maintained by a state of sensitization within the central nervous system that is mediated in part by the excitatory amino acids glutamate and aspartate binding to the N-methyl-D-aspartate (NMDA) receptor. A number of antagonists to the NMDA receptor are antinociceptive in animal models but are associated with significant dose-limiting side effects. ⋯ The NMDA-receptor antagonists have a significant impact on the development of tolerance to opioid analgesics. Consequently, NMDA-receptor antagonists may represent a new class of analgesics and may have potential as coanalgesics when used in combination with opioids.