Pain
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Observational Study
National Breakthrough Pain Study: prevalence, characteristics, and associations with health outcomes.
The National Breakthrough Pain Study is a large observational study that assessed breakthrough pain (BTP) in a population of commercially insured community-dwelling patients with opioid-treated chronic pain. Eligible patients were identified from an administrative claims database, and consenting patients were asked to complete a structured telephone interview and several validated questionnaires. Questionnaires assessed pain interference with function (Brief Pain Inventory-Short Form), health status (Short Form 12 [SF-12] Health Survey), disability (Sheehan Disability Scale), work performance (World Health Organization Health and Work Performance Questionnaire), and mood (Generalized Anxiety Disorder-7 Screener [GAD-7] and Patient Health Questionnaire-2 [PHQ-2]). ⋯ Compared with patients without BTP, patients with BTP had more pain-related interference in function (Brief Pain Inventory, mean ± SD: 34.2 ± 15.6 vs 25.0 ± 15.7 [P < 0.001]), worse physical health (SF-12 physical component score: 29.9 ± 9.6 vs 35.1 ± 10.4 [P < 0.001]) and mental health (SF-12 mental component score: 47.4 ± 11.3 vs 49.3 ± 10.4 [P < 0.001]), more disability (Sheehan Disability Scale global impairment score: 15.1 ± 9.1 vs 10.6 ± 8.5; World Health Organization Health and Work Performance Questionnaire absolute absenteeism: 12.4 ± 59.9 vs 7.7 ± 44.9 hours [both P < 0.001]), and worse mood (GAD-7 score: 7.4 ± 5.9 vs 5.9 ± 5.4; PHQ-2 anhedonia score: 1.2 ± 1.1 vs 0.9 ± 1.0 [both P < 0.001]). In this population of community-dwelling patients with opioid-treated chronic pain, BTP was highly prevalent and associated with negative outcomes. This burden of illness suggests the need for specific treatment plans.
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Osteoarthritis (OA) of the knee is a progressive disease that is associated with inflammation of the joints and lower extremity pain. Total knee arthroplasty (TKA) is a surgical procedure that aims to reduce pain and restore motor function in patients suffering from OA. The immediate postoperative period can be intensely painful leading to extended recovery times including persistent pain. ⋯ Similarly, synovial fluid levels of the anti-inflammatory lipid palmitoylethanolamide correlated with functional disability in OA. Taken together, our results are the first to reveal associations between central and peripheral endocannabinoid levels and postoperative pain. This suggests that endocannabinoid metabolism may serve as a target for the development of novel analgesics both for systemic or local delivery into the joint.
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Ankylosing spondylitis is associated with back pain and fatigue and impacts mobility but can be treated with tumor necrosis factor inhibitors (TNFi). The differential effects of TNFi treatment on multiple symptoms and the brain is not well delineated. Thus, we conducted a 2-part study. ⋯ Pain intensity reduction was associated with cortical thinning of the secondary somatosensory cortex, and pain unpleasantness reduction was associated with the cortical thinning of motor areas. In contrast, fatigue reduction correlated with cortical thinning of the insula, primary sensory cortex/inferior parietal sulcus, and superior temporal polysensory areas. This indicates that TNFi treatment produces changes in brain areas implicated in sensory, motor, affective, and cognitive functions.
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Neuropathic pain is an important public health problem for which only a few treatments are available. Preclinical studies show that melatonin (MLT), a neurohormone acting on MT1 and MT2 receptors, has analgesic properties, likely through MT2 receptors. Here, we determined the effects of the novel selective MLT MT2 receptor partial agonist N-{2-([3-bromophenyl]-4-fluorophenylamino)ethyl}acetamide (UCM924) in 2 neuropathic pain models in rats and examined its supraspinal mechanism of action. ⋯ Using double staining immunohistochemistry, we found that MT2 receptors are expressed by glutamatergic neurons in the rostral ventrolateral periaqueductal gray. Using in vivo electrophysiology combined with tail flick, we observed that microinjection of UCM924 into the ventrolateral periaqueductal gray decreased tail flick responses, depressed the firing activity of ON cells, and activated the firing of OFF cells; all effects were MT2 receptor-dependent. Altogether, these data demonstrate that selective MT2 receptor partial agonists have analgesic properties through modulation of brainstem descending antinociceptive pathways, and MT2 receptors may represent a novel target in the treatment of neuropathic pain.
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Central dopamine and norepinephrine regulate behavioral and physiological responses during rewarding and aversive stimuli. Here, we investigated and compared norepinephrine and dopamine transmission in 2 limbic structures, the ventral bed nucleus of the stria terminalis and the nucleus accumbens shell of anesthetized rats, respectively, in response to acute tail pinch, a noxious stimulus. Norepinephrine release in the ventral bed nucleus of the stria terminalis responded monophasically, increasing at the time of the tail pinch and remaining elevated for a period after its cessation. ⋯ At the termination of the stimuli, however, extracellular dopamine either recovered back to or spiked above the initial baseline concentration. These signaling patterns were more clearly observed after administration of selective catecholamine autoreceptor and transporter inhibitors. The results suggest that the opposing responses of these catecholamines can provide integration of noxious inputs to influence behavioral outputs appropriate for survival such as escape or fighting.