Pain
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Randomized Controlled Trial
Perceptual bias in pain: A switch looks closer when it will relieve pain than when it won't.
Pain is fundamental to survival, as are our perceptions of the environment. It is often assumed that we see our world as a read-out of the sensory information that we receive; yet despite the same physical makeup of our surroundings, individuals perceive differently. What if we "see" our world differently when we experience pain? Until now, the causal effect of experimental pain on the perception of an external stimulus has not been investigated. ⋯ The critical result was a strong interaction between reaching and pain [F(1,181)=4.8, P=0.03], such that when participants experienced pain and were required to reach for a switch that would turn off the experimental stimulus, they judged the distance to that switch to be closer, as compared to the other 3 conditions (mean of the true distance 92.6%, 95% confidence interval 89.7%-95.6%). The judged distance was smaller than estimates in the other 3 conditions (mean±SD difference >5.7%±2.1%, t(181) >3.5, P<0.01 for all 3 comparisons). We conclude that the perception of distance to an object is modulated by the behavioural relevance of the object to ongoing pain.
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Randomized Controlled Trial Comparative Study
Modulation of the human nociceptive flexion reflex by pleasant and unpleasant odors.
The nociceptive withdrawal reflex (NWR), a defensive response that allows withdrawal from a noxious stimulus, is a reliable index of spinal nociception in humans. It has been shown that various kinds of stimuli (emotional, visual, auditory) can modulate the transmission and perception of pain. The aim of the present study was to evaluate, by means of the NWR, the modulatory effect on the spinal circuitry of olfactory stimuli with different emotional valence. ⋯ A significant effect of olfactory stimuli on subjective pain ratings were found at both ISIs for pleasant vs unpleasant odors (P<.000), and for both pleasant and unpleasant odors vs neutral and basal conditions (P<.000). No statistical differences in subjective pain ratings at different ISIs were found. Consistent with the notion that NWR magnitude and pain perception can be modulated by stimuli with different emotional valence, these results show that olfactory stimuli, too, can modulate spinal nociception in humans.
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Vision is important for avoiding encounters with objects in the environment that may imperil physical integrity. We tested whether, in the absence of vision, a lower pain threshold would arise from an adaptive shift to other sensory channels. We therefore measured heat and cold pain thresholds and responses to suprathreshold heat stimuli in 2 groups of congenitally blind and matched normal-sighted participants. ⋯ Thresholds for nonpainful thermal stimulation did not differ between groups. The results of the pain questionnaires further indicated that blind subjects are more attentive to signals of external threats. These findings indicate that the absence of vision from birth induces a hypersensitivity to painful stimuli, lending new support to a model of sensory integration of vision and pain processing.
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Randomized Controlled Trial
Specifying the nonspecific components of acupuncture analgesia.
It is well known that acupuncture has pain-relieving effects, but the contribution of specific and especially nonspecific factors to acupuncture analgesia is less clear. One hundred one patients who developed pain of ≥ 3 on a visual analog scale (VAS, 0 to 10) after third molar surgery were randomized to receive active acupuncture, placebo acupuncture, or no treatment for 30 min with acupuncture needles with potential for double-blinding. Patients' perception of the treatment (active or placebo) and expected pain levels (VAS) were assessed before and halfway through the treatment. ⋯ Expected pain levels accounted for significant and progressively larger amounts of the variance in pain ratings after both active and placebo acupuncture (up to 69.8%). This is the first study to show that under optimized blinding conditions, nonspecific factors such as patients' perception of and expectations toward treatment are central to the efficacy of acupuncture analgesia and that these factors may contribute to self-reinforcing effects in acupuncture treatment. To obtain an effect of acupuncture in clinical practice, it may therefore be important to incorporate and optimize these factors.
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Randomized Controlled Trial
A phase III placebo- and oxycodone-controlled study of tanezumab in adults with osteoarthritis pain of the hip or knee.
Tanezumab is a humanized monoclonal antinerve growth factor antibody in development for treatment of chronic pain. In a phase III, placebo- and active-controlled study, we investigated the efficacy and safety of tanezumab for osteoarthritis (OA) hip or knee pain. Patients (N=610) received up to 2 doses of intravenous tanezumab (5 or 10mg in 8-week intervals), controlled-release oral oxycodone (10 to 40 mg every 12 hours), or placebo. ⋯ Adverse event frequency was higher with oxycodone (63.3%) than tanezumab (40.7% to 44.7%) or placebo (35.5%); serious adverse event frequency was similar among treatments. The adverse event profile for tanezumab was similar to previous tanezumab studies. Results indicate that tanezumab is efficacious in the treatment of OA pain; no new safety signals were identified.