Pain
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The hypothesis that the pain and allodynia associated with post-herpetic neuralgia (PHN) is maintained by a combination of input from preserved primary afferent nociceptors and sensitization of central pain transmitting neurons was examined in 17 subjects with PHN. Pain, allodynia, thermal sensory function, cutaneous innervation, and response to controlled application of 0.075% capsaicin were measured. ⋯ In three of the 'capsaicin responders' the area of allodynia expanded into previously non-allodynic and non-painful skin that had normal sensory function and cutaneous innervation. These observations support the hypothesis that allodynia in some PHN patients is a form of chronic secondary hyperalgesia maintained by input from intact and possibly 'irritable' primary afferent nociceptors to a sensitized CNS.
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Clinical Trial
Intradermal injection of norepinephrine evokes pain in patients with sympathetically maintained pain.
Tissue injuries, with or without involvement of nerves, may lead to ongoing pain and hyperalgesia to external stimuli. In a subset of patients, the pain is maintained by sympathetic efferent activity (SMP). We investigated if the peripheral administration of the alpha-adrenergic agonist, norepinephrine (NE), in physiologically relevant doses resulted in pain in patients with SMP. ⋯ Two of the three patients who did not receive pain relief following phentolamine infusion also did not report pain to the NE injections. We conclude that NE injections produce pain in SMP patients at doses that are at the threshold for producing vasoconstriction. These studies support a role for cutaneous adrenoceptors in the mechanisms of sympathetically maintained pain.
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We investigated the effects of acute and of chronic morphine treatment on T-lymphocyte function and natural killer (NK) cell activity in rats receiving chronic constriction injury (CCI) of the sciatic nerve. T-Lymphocyte function was evaluated based on concanavalin-A (ConA)- and phytohemagglutinin (PHA)-induced splenocyte proliferation. The effects of morphine on thermal hyperalgesia were also assessed by measuring paw withdrawal latency (PWL) in rats. ⋯ No tolerance to the suppression of NK cell activity and splenocyte proliferation was observed after chronic morphine treatment. These data suggest that both acute and chronic morphine treatment can cause a dose-dependent reversal of thermal hyperalgesia and inhibition of NK cell activity and splenocyte proliferation in rats with sciatic CCI, without concomitant development of tolerance. Opioid therapy for chronic neuropathic pain should be used cautiously, especially in immune-compromised cases.
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Comparative Study
Barriers to the analgesic management of cancer pain: a comparison of attitudes of Taiwanese patients and their family caregivers.
The purposes of this study were as follows: (1) to compare the attitudes which were considered to be barriers to cancer pain management held by Taiwanese cancer patients and their family caregivers; (2) to determine if these barriers were related to patient hesitancy to take analgesics and/or family caregiver hesitancy to administer analgesics: and (3) to determine if attitudinal barriers by patients and/or family caregivers predicted the adequacy of analgesics that patients used. A total of 159 dyads of oncology outpatients and their primary family caregivers (n = 318) participated in this study. The instruments completed by patients consisted of the Barriers Questionnaire-Taiwan form, the Brief Pain Inventory-Chinese version, the ECOG performance status scale, and a demographic and medication questionnaire. ⋯ Patient concerns were related to their hesitancy to take analgesics and, similarly, caregiver concerns were related to their hesitancy to administer analgesics. Most importantly, patient and caregiver concerns had an impact on how the patients' pain was managed: (1) patients and their family caregivers with higher levels of concerns used inadequate analgesics as compared to patients using adequate analgesics; (2) family caregiver barriers (concerns) were a significant predictor of inadequate management of cancer pain (after controlling for demographic and disease variables). Therefore, educational interventions for overcoming these barriers for both patients and their family caregivers may have potential for improving the management of cancer pain in Taiwan.
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Ovariohysterectomy in the rat led to the induction of abdominal postures and referred mechanical allodynia in the hind paws. The latter was differentiated into static and dynamic subtypes. The abdominal postures were present up to 4-5 h, whilst the two types of allodynia lasted for at least 2 days. ⋯ In contrast, administration of three doses of morphine (3 mg/kg) in a similar dosing regime but starting 24 h after surgery, only blocked the two types of allodynia for 4 h. These data indicate the importance of blocking the induction phase of surgical pain and support the concept of pre-emptive analgesia. It is suggested that the ovariohysterectomy model should prove to be useful for studying mechanisms and designing novel therapeutic strategies for the treatment of post-operative pain.