European journal of pain : EJP
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In subgroups of patients with localised musculoskeletal pain spread of pain and signs of altered somatosensory processing at painful sites, both focal and referred areas have been reported. The purpose of the study was to examine somatosensory processing in patients with mainly unilateral long-term (> or =1 year) trapezius myalgia with ongoing pain for the last 3 months in the trapezius muscle in conjunction with ongoing or recurrent referral of pain to the ipsilateral arm. Ten patients with trapezius myalgia and 10 age- and sex-matched healthy controls participated. ⋯ Compared to controls a bilaterally decreased sensitivity to light touch was found in patients in the area of referred pain (p<0.01). No differences were found in the outcome of thermal testing. These findings suggest altered central processing of somatosensory input from the area of referred pain in patients with trapezius myalgia.
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Complex regional pain syndrome type I (CRPS-I), formerly reflex sympathetic dystrophy (RSD), is a chronic pain syndrome of unknown aetiology. Its diagnosis is a clinical one, for which several criteria systems have been defined. Despite their widespread use, the reliability of these criteria has never been studied. ⋯ The kappa values were higher, had physicians applied IASP criteria, but still insufficient. The application of Bruehl's criteria results in a fair kappa of 0.38, but then frequency of CRPS diagnosis in our study population decreased from 73% to 43% in comparison with physicians' own diagnosis. We conclude that, using current criteria systems, the diagnosis of CRPS is not reliable.
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Although the antinociceptive effect of NMDA antagonists in the formalin test is well recognised, these compounds can induce adverse motor effects. The aim of this study was to identify the systemic doses of NMDA antagonists that induce analgesia without causing side effects. Male Swiss mice (30-40g) received a subcutaneous (sc) injection of 1.25% formalin (50 micro l) in the dorsal surface of the right hind-paw and, 15min before or after formalin, an ip injection of one of the following NMDA receptor antagonists: MK 801 (0.01, 0.025, and 0.05mg/kg), memantine (0.1, 0.5, and 1mg/kg), ketamine (0.125, 0.25, and 0.5mg/kg), dextromethorphan (5, 10, and 20mg/kg), and CGP 37849 (4, 6, and 8mg/kg). ⋯ The rank order potency of antinociceptive activity of NMDA antagonists was: MK801>memantine>ketamine>dextromethorphan>CGP37849. The NMDA antagonists administered after formalin (during the analgesic interval) did not affect the late phase of the formalin test. In conclusion, systemic administration of NMDA receptor antagonists decreases the nociception observed during the late phase of the formalin test.
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L5 and L6 spinal nerve ligation (SNL) in rats leads to behavioral signs of neuropathic pain including mechanical allodynia. The purposes of this study were to investigate the role of the intact L4 spinal nerve in the development of mechanical allodynia following L5 and L6 SNL and, as a result, to develop a modified model of neuropathic pain. As a first set of experiments, in addition to tight ligation of the left L5 and L6 spinal nerves, the intact L4 spinal nerve was manipulated either (1) by gentle repeated stretching of the L4 spinal nerve immediately after L5 and L6 SNL or (2) by intermittent mechanical stimulation to the ipsilateral paw during the first week after SNL. ⋯ These results suggest that afferent activity of the intact L4 spinal nerve aids in the development of mechanical allodynia in the SNL model of neuropathic pain. The addition of a chromic gut loop around the intact L4 spinal nerve can augment the development of mechanical allodynia following SNL of L5. We propose this latter as a useful and practical animal model of neuropathic pain.
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Epidural opioids have been reported to provide superior analgesia in acute pain management. Despite the fact that the required doses are low, major side effects such as respiratory depression may still occur. In an effort to maximize analgesia and to minimize the rate of side effects, epidural NMDA receptor antagonists, especially ketamine, may be co-administered with opioids. ⋯ Moreover, increasing doses of ketamine tended to decrease the MPE of various doses of fentanyl. These data confirm that ketamine, contrary to opioids, does not possess important antinociceptive properties in an acute test such as the TWR test. Furthermore, these data indicate that additive drugs such as ketamine may have different effects on different opioids.