Pain
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Comparative Study
Severity and specificity of neglect-like symptoms in patients with complex regional pain syndrome (CRPS) compared to chronic limb pain of other origins.
In the literature, the neglect-like syndrome is described as an additional phenomenon of CRPS. The perception of the affected limb as strange, disordered and not belonging to the body is typical of and characterises this syndrome. Since this phenomenon has never been studied in other pain conditions, we assessed occurrence and extent of neglect-like symptoms in patients with CRPS of the upper and lower limb (n = 123) and in a control group with chronic limb pain of other origins (n = 117). ⋯ The only difference between these two localisations concerning the neglect-like syndrome was the symptom of 'involuntary movements', which occurs significantly more often in affected legs. In conclusion, we recommend to evaluate neglect-like symptoms and to use them as an additional criterion in the diagnosis of CRPS. High scores of > or = 5 confirm the diagnosis of CRPS, whereas lower scores must not be used for disease classification.
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Comparative Study
Explaining sex differences in chronic musculoskeletal pain in a general population.
Many studies report a female predominance in the prevalence of chronic musculoskeletal pain (CMP) but the mechanisms explaining these sex differences are poorly understood. Data from a random postal questionnaire survey in the Dutch general population were used to examine whether sex differences in the prevalences of CMP are due to sex differences in the distribution of known potential risk factors for CMP (exposure model) and/or to the different importance of risk factors for CMP (i.e. show different strength of association) in men and women (vulnerability model). In the present analyses, 909 men and 1178 women aged 25-65 were included. ⋯ In conclusion, sex differences in prevalence of CMP may partly be explained by sex differences in vulnerability to risk factors for CMP. Future research towards sex-specific identification of risk factors for CMP is warranted. Eventually this may lead to sex-specific prevention and management of CMP.
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Some studies indicate that placebo analgesia is stronger when pre-conditioning with effective analgesic treatments is performed, thereby suggesting that the placebo response is a learning phenomenon. Here we further tested this hypothesis in order to better understand when and how previous experience affects the placebo analgesic response. To do this, we used a conditioning procedure whereby the intensity of painful stimulation was reduced surreptitiously, so as to make the subjects believe that an analgesic treatment was effective. ⋯ We also ran extinction trials, and found that these effects did not undergo extinction in a time span of several minutes. These findings indicate that placebo analgesia is finely tuned by prior experience and these effects may last, albeit reduced, several days. These results emphasize that the placebo effect is a learning phenomenon in which many factors come into play, and may explain the large variability of the placebo responses that is found in many studies.
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We investigated effects of topical application of ketanserin, a 5-HT2A receptor antagonist, on hyperalgesia and edema in the arthritic rat, a chronic pain model with inflammation. Unilateral, but not bilateral, arthritis was induced with intra-articular injection of a mixture of kaolin and carrageenan in one side, as indicated by the shortened paw withdrawal latency and an increase in the circumference of the knee joint. Topical application of ketanserin onto skin over the arthritic joint delivered in a mixture of gelatin, glycerol and kaolin produced dose-dependent attenuation of nociceptive and inflammatory effects resulting from intra-articularly injected kaolin/carrageenan. ⋯ In contrast, 3% ketanserin applied to skin of the knee joint on the non-inflamed side for 2 weeks did not alter nociceptive thresholds of the paw and the size of the knee joint in both the inflamed and non-inflamed limbs. These results indicate that 5-HT2A receptors in the periphery play a significant role in the maintenance and/or development of inflammatory pain. The present study suggests that topical ketanserin is a promising direction for potential clinical exploration to relieve established hyperalgesia and inflammation in arthritis without adverse effects and tolerance.
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Comparative Study
Attenuation of capsaicin-evoked mechanical allodynia by peripheral neuropeptide Y Y1 receptors.
Neuropeptide Y (NPY) and its cognate receptors are important modulators of nociception and their expression is significantly altered following injury. In particular, previous studies have demonstrated that the Y1 subtype of NPY receptors inhibits nociceptive transmission from capsaicin-sensitive terminals in the dorsal horn of the spinal cord. The present study evaluated the function of the Y1 receptor on peripheral terminals of primary afferent neurons by testing whether peripherally administered Y1 agonists and antagonists alter capsaicin-evoked mechanical allodynia in rats and capsaicin-evoked immunoreactive calcitonin gene-related peptide (iCGRP) release from isolated superfused rat skin. ⋯ In isolated skin, application of [Leu31,Pro34]-NPY (300 nM) significantly inhibited capsaicin-evoked CGRP release. BIBO3304 reversed this inhibition, having itself no effect on capsaicin-evoked iCGRP release. These studies indicate that the activation of peripheral Y1 receptors produces anti-allodynia, possibly via the direct inhibition of capsaicin-sensitive fibers.