Pain
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Randomized Controlled Trial
Learning potentiates neurophysiological and behavioral placebo analgesic responses.
Expectation and conditioning are supposed to be the two main psychological mechanisms for inducing a placebo response. Here, we further investigate the effects of both expectation, which was induced by verbal suggestion alone, and conditioning at the level of N1 and N2-P2 components of CO2 laser-evoked potentials (LEPs) and subjective pain reports. Forty-four healthy volunteers were pseudorandomly assigned to one of three experimental groups: Group 1 was tested with verbal suggestion alone, Group 2 was tested with a conditioning procedure, whereby the intensity of painful stimulation was reduced surreptitiously, so as to make the volunteers believe that the treatment was effective, Group 3 was a control group that allowed us to rule out phenomena of sensitization and/or habituation. ⋯ Conversely, the N2-P2 amplitude changes that were induced by the conditioning procedure were associated with the subjective perception of pain reduction. Compared to natural history, conditioning produced more robust reductions of LEP amplitudes than verbal suggestions alone. Overall, these findings indicate that prior positive experience plays a key role in maximizing both behavioral and neurophysiological placebo responses, emphasizing that the placebo effect is a learning phenomenon which affects the early central nociceptive processing.
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Controlled Clinical Trial
Oral opioid use alters DNIC but not cold pain perception in patients with chronic pain - new perspective of opioid-induced hyperalgesia.
Opioids can elicit unexpected changes in pain sensitivity, known as opioid-induced hyperalgesia (OIH). The aim of this study was to explore whether OIH exists in patients with chronic pain treated with oral opioids (OP) versus non-opioid (NOP) analgesics. The sensitivity to cold pain and the magnitude of diffuse noxious inhibitory control (DNIC) were evaluated in 73 OP and 37 NOP treated patients. ⋯ A regression analysis showed that opioid dosage and treatment duration had a significant negative effect on the magnitude of DNIC in OP treated men (beta=-2.175, p=0.036 and beta=-2.061, p=0.047, respectively). In conclusion, oral opioids usage for the treatment of chronic pain does not result in abnormal sensitivity to cold pain, but seems to alter pain modulation. The use of 'advanced' psychophysics tests such as evaluation of DNIC can help understanding the phenomenon of OIH.
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Previous research supports the fear-avoidance model in explaining the transition from acute to chronic non-specific musculoskeletal pain. However, there is still little knowledge on when this vicious circle of pain, disability, pain catastrophizing and fear of movement starts. We performed a daily diary study in 42 patients with acute whiplash injury. ⋯ We also examined the reverse association, that is, whether the changes in pain predict changes in the next day's fear of movement and pain catastrophizing. Although for the fear of movement the model reached significance, the amount of explained variance was negligible. In conclusion, this study provides evidence that already in the early stages of whiplash-related complaints, significant associations between fear of movement and pain intensity and disability occur, and that this association may be predictive of the persistence of pain.