Pain
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Randomized Controlled Trial
Side effects can enhance treatment response through expectancy effects: an experimental analgesic randomized controlled trial.
In randomized controlled trials, medication side effects may lead to beliefs that one is receiving the active intervention and enhance active treatment responses, thereby increasing drug-placebo differences. We tested these hypotheses with an experimental double-blind randomized controlled trial of a nonsteroidal anti-inflammatory drug with and without the addition of atropine to induce side effects. One hundred healthy volunteers were told they would be randomized to either combined analgesics that might produce dry mouth or inert placebos. ⋯ A chain of mediation analysis demonstrated that the addition of atropine increased dry mouth symptoms, which increased beliefs that one had received the active medication, which, in turn, increased analgesia. In addition to this indirect effect of atropine on analgesia (via dry mouth and beliefs), analyses suggest that among those who received diclofenac, atropine directly increased analgesia. This possible synergistic effect between diclofenac and atropine might warrant future research.
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Effective assessment and management of pain in patients with cancer is strengthened by the patient's report of how much pain interferes with daily functioning. This requires a clear delineation of different levels of pain interference. We derived optimal cutpoints for differentiating between mild, moderate, and severe pain interference assessed by the Brief Pain Inventory (BPI) and describe the prevalence and characteristics of pain-induced functional impairment in patients with cancer. ⋯ The mild (<2), moderate (2-5 or 2-6), and severe (>5 or >6) pain interference groups were significantly concordant with ECOG-PS levels (P < 0.0001). We empirically derived patient-reported pain interference categories in relation to clinician-rated performance status. These cutpoints may facilitate the conduct and interpretation of clinical evaluation, symptom epidemiology, and clinical trials.
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Spatial summation of pain (SSP) is the increase of perceived intensity that occurs as the stimulated area increases. Spatial summation of pain is subadditive in that increasing the stimulus area produces a disproportionately small increase in the perceived intensity of pain. A possible explanation for subadditive summation may be that convergent excitatory information is modulated by lateral inhibition. ⋯ Thus, the stimulation of the skin region between the endpoints of the lines appears to produce inhibition. These findings indicate that lateral inhibition limits SSP and is an intrinsic component of nociceptive information processing. Disruption of such lateral inhibition may contribute substantially to the radiation of some types of chronic pain.