Pain
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Two studies that assess fear and avoidance in patients with chronic pain are presented. In the first study, 200 patients with chronic back pain were classified, using the Multidimensional Pain Inventory (Kerns et al., 1985) clustering procedure, as dysfunctional (n = 53), interpersonally distressed (n = 37), and adaptive copers (n = 62). Groups were compared on common measures of anxiety, fear and avoidance. ⋯ In the second study, pain-specific fear and avoidance measures were used in a discriminant function analysis to predict the MPI classification of an independent sample of 55 patients with chronic pain. The measures correctly classified 76.5% of the dysfunctional group and 71.1% of a composite group of interpersonally distressed and adaptive copers. The implications of these findings are discussed.
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Duration of acute herpetic pain (AHP) in 1431 patients for whom treatment was begun within 14 days after the onset of herpes zoster (HZ) was analyzed with respect to age, involved region, and severity of skin lesions. All patients were treated with repeated sympathetic nerve blocks until their pain was almost nil. Severity of the skin lesions at the worst phase was defined as mild when they covered less than one-quarter of the primary dermatome, as severe when they covered more than three-quarters of the primary dermatome, and moderate if they were between mild and severe. ⋯ Multiple stepwise regression analysis revealed that the most important factors influencing the duration of AHP were the severity of skin lesions of HZ at the worst phase (r = 0.412), age (r = 0.277) and the involved region (r = -0.101). Thus, AHP in the elderly and in cases of trigeminal involvement is longer because of higher frequencies of severe HZ in the elderly and in trigeminal involvement rather than "being aged' and "trigeminal involvement' itself. We propose that one needs to analyze the results of treatment of AHP with respect to the severity of skin lesions at the worst phase.
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The mechanical allodynia and edema related to a subcutaneous carrageenin injection are increased by a conditioning carrageenin injection 7 days before (Guilbaud et al., 1992). In the present study, the possibility of preventing this by bupivacaine infiltration was tested. In the first part of the experiment, the time course of a carrageenin induced inflammation of the right hind paw was assessed in animals receiving local anesthetic injection (0.2 ml of bupivacaine 0.5% solution with epinephrine) either 5 min before (BUPI PRE group) or 60 min after (BUPI POST group) the carrageenin injection (0.2 ml of 1% solution). ⋯ In contrast, the increase in allodynia and edema was less intense in the BUPI PRE group than in the other groups (P < 0.0001 and P < 0.02 respectively). Bupivacaine injections had no effect on allodynia and edema related to a second contra-lateral carrageenin injection. These results suggest that bupivacaine infiltration, when administered before the first conditioning injection of carrageenin, can prevent the reinforcement of mechanical allodynia and edema related to a second ipsilateral injection of carrageenin 7 days later.
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Randomized Controlled Trial Clinical Trial
Effect of adrenergic receptor activation on post-herpetic neuralgia pain and sensory disturbances.
Patients with acute herpes zoster, and to a lesser extent post-herpetic neuralgia (PHN), have been reported to respond to local anesthetic blockade of the sympathetic nervous system. In animal models of nerve injury, local injection of adrenergic agonists after nerve injury, but not before, excites nociceptors. In some patients with chronic neuropathic pain, local application of norepinephrine evokes pain. ⋯ After injection of the adrenergic agonist into PHN skin, both overall PHN pain and allodynia severity were significantly greater than after saline injection, peaking at 10-15 min post-injection. Even when PHN has been present for years, adrenergic receptor stimulation in PHN skin increases pain, most likely through direct activation of C-nociceptors in the painful skin. Increased allodynia is most likely mediated centrally and driven by the increase in C-nociceptor input.
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Injection of formalin in the rat hindpaw produces two phases of nociceptive behavior. Although it is generally agreed that the first phase results from direct chemical activation of nociceptive primary afferent fibers, the factors that contribute to the second phase are not established. In the present study, we monitored the expression of the c-fos protein to evaluate whether the pattern of activity of dorsal horn neurons differs as a result of ongoing afferent activity during the two phases. ⋯ We did not observe further significant decreases when both remifentanil and lidocaine, or bupivacaine and lidocaine were injected (69.7% and 74.6%, respectively). Our results not only provide strong evidence that activity during the second phase is necessary for maintaining the maximal expression of c-fos in the spinal cord, but also reveal significant regional differences in the central patterns of activity generated during the two phases. These results also confirm our previous reports that c-fos expression is not eliminated when the behavioral manifestation of the noxious stimulus is completely blocked.