Pain
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Chronic fibromyalgia (FM) pain is prevalent (estimated as high as 13%), predominantly affects women, and is associated with a variety of focal pain conditions. Ongoing FM pain is referred to deep tissues and is described as widespread but usually is maximally located within a restricted region such as the shoulders. Palpation of deep tissues reveals an enhanced nociceptive sensitivity that is not restricted to regions of clinical pain. ⋯ Thus, it appears that central mechanisms of FM pain are dependent on abnormal peripheral input(s) for development and maintenance of this condition. A substantial literature defines peripheral-CNS-peripheral interactions that are integral to FM pain. These reciprocal actions and related phenomena of relevance to FM pain are reviewed here, leading to suggestions for testing of therapeutic approaches.
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Randomized Controlled Trial
Parental history of chronic pain may be associated with impairments in endogenous opioid analgesic systems.
A family history of chronic pain has previously been linked to increased incidence of spontaneous acute pain and risk for chronic pain. Mechanisms underlying these associations are unknown, although similar effects on both acute and chronic pain suggest that central endogenous analgesic system differences may be relevant. This study tested whether a positive parental chronic pain history (PH+) was associated with impaired endogenous opioid analgesic responses to acute pain. ⋯ A significant multivariate PHxSubject Type interaction (p<.05) indicated that opioid analgesic impairments were most prominent in PH+ LBP subjects. Similar analyses for finger pressure pain blockade effects were nonsignificant (p>.10). The possible heritability of endogenous opioid analgesic dysfunction observed in individuals with a positive parental chronic pain history remains to be investigated.
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Comparative Study Controlled Clinical Trial
Effects of subcutaneous administration of glutamate on pain, sensitization and vasomotor responses in healthy men and women.
The present study aimed to investigate if (1) subcutaneous injection of glutamate induces pain, sensitization and vasomotor responses in humans and (2) if sex differences exist in these responses. Thirty healthy volunteers (men-15 and women-15) were included. Each subject received four subcutaneous injections (0.1ml; glutamate 100, 10, 1mM and isotonic saline 0.9%) into the forehead skin in two sessions separated by one week. ⋯ Concentration-dependent local vasomotor responses were found following the subcutaneous injection of glutamate but there was no sex difference in this effect. Glutamate 100mM significantly reduced the PPT values (P<0.001) without sex-related differences. The present study demonstrates for the first time that subcutaneous injection of glutamate evokes pain, vasomotor responses and pinprick hyperalgesia in human volunteers and that there are sex-related differences in some of these responses.
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Clinical Trial
The evaluation of acute pain in individuals with cognitive impairment: a differential effect of the level of impairment.
The present study investigated whether the level of cognitive impairment (CI) affects acute pain behavior and how it is manifested. Participants were 159 individuals (mean age 42+/-12), 121 with CI (divided into four groups according to the level of CI: mild, moderate, severe, profound) and 38 with normal cognition (controls). The behavior of the participants before and during acute pain (influenza vaccination) was coded by two raters with the Facial Action Coding System (FACS - scores facial reactions to pain) and the Non-Communicating Children's Pain Checklist (NCCPC-R - scores both facial and general body reactions). ⋯ In contrast, individuals with severe-profound CI exhibited high rates of "freezing reaction" (stillness) during vaccination, manifested mainly in the face and therefore resulting in elevation of only NCCPC-R scores but not of FACS's. The results suggest that the level of CI affects baseline as well as pain behavior and it is therefore necessary to choose an appropriate behavioral tool to measure pain in these individuals accordingly. For example, tools based on facial reactions alone might provide the false impression that individuals with severe-profound CI are insensitive to pain (due to freezing).