Pain
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Carpal tunnel syndrome (CTS), a common entrapment neuropathy involving the median nerve at the wrist, frequently manifests with neuropathic pain. We sought information on pain mechanisms in CTS. We studied 70 patients with a diagnosis of CTS (117 CTS hands). ⋯ We sought possible correlations between neurophysiological data and the various qualities of neuropathic pain as assessed by the NPSI. We found that the median nerve sensory conduction velocity correlated with paroxysmal pain and abnormal sensations, whereas LEP amplitude correlated with spontaneous constant pain. Our findings suggest that whereas paroxysmal pain and abnormal sensations reflect demyelination of non-nociceptive Abeta-fibres, spontaneous constant pain arises from damage to nociceptive Adelta-fibres.
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In healthy adults, expectations can modulate the activity of inhibitory bulbo-spinal projections, and can even block the analgesic properties of counter-irritation - a phenomenon that triggers descending inhibition. Since descending inhibition is known to be deficient in fibromyalgia (FM) patients, we tested the possibility that expectancy-mediated analgesia would improve, or even kick-start, the deficient inhibitory responses of FM patients. By measuring subjective pain ratings, spinal withdrawal reflexes, and somatosensory evoked potentials (SEP), it was possible to test whether or not expectancy-mediated analgesia involved descending inhibition in FM patients. ⋯ However, even when analgesia was experienced, the spinal activity of FM patients was abnormal, showing heightened reflex responses. This demonstrates that, unlike healthy subjects, the modulation of pain by expectations in FM fails to influence spinal activity. These results indicate that FMs are capable of expectancy-induced analgesia but that, for them, this form of analgesia does not depend on the recruitment of descending inhibitory projections.
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The nociceptive flexion reflex (NFR) has been used as a psychophysiological tool to study spinal nociceptive processes in numerous clinical and experimental studies. Despite widespread use of the NFR, few attempts have been made to empirically test and compare different scoring criteria to detect the presence/absence of the reflex. The present studies were conducted to address this issue. ⋯ In both studies, receiver operating characteristics (ROCs) analyses were used to evaluate and compare different scoring methods. The results indicate that a number of different criteria were acceptable for defining an NFR threshold based on the area under the ROC curve and its statistical significance; however, NFR Interval z score [(NFR Interval Mean-baseline mean)/baseline SD] emerged as the scoring criterion with the greatest accuracy and with cut-points that are reliable across samples. These findings support the application of a common NFR scoring criterion to enhance direct comparison of results across different research laboratories and study samples.