Pain
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Review Meta Analysis
The effect of bodily illusions on clinical pain: A systematic review and meta-analysis.
This systematic review and meta-analysis critically examined the evidence for bodily illusions to modulate pain. Six databases were searched; 2 independent reviewers completed study inclusion, risk of bias assessment, and data extraction. Included studies evaluated the effect of a bodily illusion on pain, comparing results with a control group/condition. ⋯ Conflicting results were found for virtual walking illusions (both active and inactive control comparisons). Single studies suggest no effect of resizing illusions on pain evoked by noxious stimuli, no effect of embodiment illusions, but a significant pain decrease with synchronous mirrored stroking in nonresponders to traditional mirror therapy. There is limited evidence to suggest that bodily illusions can alter pain, but some illusions, namely mirror therapy, bodily resizing, and use of functional prostheses show therapeutic promise.
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In treating Major Depressive Disorder with associated painful physical symptoms (PPS), the effect of duloxetine on PPS has been shown to decompose into a direct effect on PPS and an indirect effect on PPS via depressive symptoms (DS) improvement. To evaluate the changes in relative contributions of the direct and indirect effects over time, we analyzed pooled data from 3 randomized double-blind studies comparing duloxetine 60 mg/d with placebo in patients with major depressive disorder and PPS. Changes from baseline in Montgomery-Åsberg Depression Rating Scale total and Brief Pain Inventory-Short Form average pain score were assessed over 8 weeks. ⋯ Initially, the direct effect of duloxetine on PPS was markedly greater than its indirect effect, whereas later the indirect effect predominated. Conversely, at week 1, the direct effect of treatment on DS (46.4%) was less than the indirect effect (53.6%), and by week 8 it superseded (62.6%) the indirect effect (37.4%). Thus, duloxetine would relieve PPS directly in the initial phase and indirectly via improving DS in the later phase.
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Hand disabilities are frequent causes of pain and disability in older people, yet knowledge regarding the characteristics and patterns of hand pain and problems over time is lacking. The main aim of this study was to identify subgroups of older individuals with distinct presentations (phenotypes) of hand pain and function, investigate how these might change over a 6-year period, and explore what characteristics and factors are associated with long-term status. The study population stemmed from the North Staffordshire Osteoarthritis Project, a large, general population-based, prospective, cohort study of adults aged 50 years and older. ⋯ There was a high level of stability in individuals in the "least-affected" or "severely affected" group at baseline. Individuals with widespread body pain, nodes, sleep problems, and pain in both hands at baseline were more likely to be in a severe hand phenotype at 6 years. The results provide clinically relevant information regarding the pattern of hand pain and problems over time and factors that predict transition to more severe hand phenotypes.
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Predictions which invoke evolutionary mechanisms are hard to test. Agent-based modeling in artificial life offers a way to simulate behaviors and interactions in specific physical or social environments over many generations. The outcomes have implications for understanding adaptive value of behaviors in context. ⋯ Allowing exploitation of injured agents decreased expression of pain to near zero, but altruists remained. Decreasing costs or increasing benefits of helping hardly changed its frequency, whereas increasing interaction rate between injured agents and helpers diminished the benefits to both. Agent-based modeling allows simulation of complex behaviors and environmental pressures over evolutionary time.
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The spinal dorsal horn contains numerous inhibitory interneurons that control transmission of somatosensory information. Although these cells have important roles in modulating pain, we still have limited information about how they are incorporated into neuronal circuits, and this is partly due to difficulty in assigning them to functional populations. Around 15% of inhibitory interneurons in laminae I-III express neuropeptide Y (NPY), but little is known about this population. ⋯ Our results suggest that this input originates from a small subset of NPY-expressing interneurons, with the projection cells representing only a minority of their output. Taken together with results of previous studies, our findings indicate that somatodendritic morphology is of limited value in classifying functional populations among inhibitory interneurons in the dorsal horn. Because many NPY-expressing cells respond to noxious stimuli, these are likely to have a role in attenuating pain and limiting its spread.