Pain
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Randomized Controlled Trial
Open-label placebo vs double-blind placebo for irritable bowel syndrome: a randomized clinical trial.
It is commonly believed that blinding to treatment assignment is necessary for placebos to have an effect. However, placebos administered without concealment (ie, open-label placebos [OLPs]) have recently been shown to be effective in some conditions. This study had 2 objectives: first, to determine whether OLP treatment is superior to no-pill control (NPC) in irritable bowel syndrome (IBS) and, second, to compare the efficacy of OLP against double-blind placebo (DBP). ⋯ Standardized effect sizes were moderate for OLP vs NPC (d = 0.43) and small for OLP vs DBP (d = 0.10). Participants treated with OLP reported clinically meaningful improvements in IBS symptoms that were significantly greater than those on NPC. Open-label placebo and DBP had similar effects that did not differ significantly, suggesting that blinding may not be necessary for placebos to be effective and that OLP could play a role in the management of patients with refractory IBS.
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Meta Analysis
Efficacy of ketamine in relieving neuropathic pain: a systematic review and meta-analysis of animal studies.
In humans, proof of long-term efficacy of ketamine treatment in neuropathic pain is lacking. To improve our understanding of ketamine behavior under various administration conditions, we performed a systematic review and meta-analyses of controlled studies on the efficacy of ketamine in mice and rats with a disease model of nerve injury on relief of allodynia. Searches in PubMed and EMBASE identified 31 unique studies. ⋯ No subgroups analyses were possible in the last 3 meta-analyses due to small group sizes. These results indicate long-term ketamine anti-allodynic effects after chronic exposure (>3 days) but not after a single administration. Given several limitations, extrapolation of the animal data to the human condition is tenuous.
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Pain is a subjective experience with significant individual differences. Laboratory studies investigating pain thresholds and experimental acute pain have identified structural and functional neural correlates. However, these types of pain stimuli have limited ecological validity to real-life pain experiences. ⋯ Peak pain did, however, positively correlate with baseline resting-state functional connectivity between the thalamus contralateral to the separator and bilateral insula, and negatively correlated with connectivity between the periaqueductal gray (PAG) and core nodes of the default mode network (medial prefrontal and posterior cingulate cortices). The ascending (thalamic) nociceptive and the descending (PAG) pain modulatory pathways at baseline each explained unique variation in peak pain intensity ratings. In sum, preinterventional functional neural architecture of both systems determined the individual pain experience to a subsequent ecologically valid pain stimulus.
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Migraine pathophysiology has been suggested to include dysregulation of the endocannabinoid system (ES). We simultaneously evaluated plasma anandamide (AEA) and palmitoylethanolamide (PEA) levels and spinal sensitization in a validated human model of migraine based on systemic nitroglycerin (NTG) administration. Twenty-four subjects with episodic migraine (MIG) and 19 healthy controls (HC) underwent blood sampling and investigation of nociceptive withdrawal reflex thresholds (RTh: single-stimulus threshold; TST: temporal summation threshold) before and 30 (T30), 60 (T60), and 120 (T120) minutes after sublingual NTG administration (0.9 mg). ⋯ We found no significant correlations between the ES and neurophysiological parameters. Our findings suggest a role for PEA in the ictal phase of episodic migraine. The ES does not seem to be directly involved in the modulation of NTG-induced central sensitization, which suggests that the observed PEA increase and spinal sensitization are parallel, probably unrelated, phenomena.