Pain
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The aim of this study was to examine whether irritable bowel syndrome (IBS) is associated with increased somatic pain sensitivity in a large population-based sample and to test whether this association was independent of sex, age, comorbid chronic pain, and psychological distress. Pain sensitivity tests included assessment of heat-pain threshold (N=4054) and pressure-pain threshold (N=4689) and of cold-pressor pain intensity and tolerance (N=10,487). Cox regression and analysis of variance (ANOVA) were used to assess the relationship between IBS and pain sensitivity in stepwise multivariate models. ⋯ Results for pressure-pain threshold were not significant. Heat- and cold-pressor pain sensitivity was greatest for the IBS reporting severe chronic abdominal pain, indicating that hyperalgesia in IBS is related to degree of clinical pain rather than to the diagnosis per se. Because all pain tests were all carried out on the upper extremities, our findings indicate the presence of widespread hyperalgesia in IBS, which may be a contributing factor to the high rate of comorbid pain seen in this patient group.
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This meta-analysis investigated whether attentional bias, that is, the preferential allocation of attention to information that is related to pain, is a ubiquitous phenomenon. We also investigated whether attentional bias effects are related to the methodological quality of the study, to procedural differences in their measurement, or to individual differences in pain severity, pain-related fear, anxiety, and depression. Results indicated that individuals who experience chronic pain (n=1023) display an attentional bias towards pain-related words or pictures, but this bias was of a small effect size (d=0.134), and did not differ from that in control groups (d=0.082; n=1398). ⋯ Moderator analyses in the chronic pain group identified important procedural variables that affected the presence and magnitude of an attentional bias towards pain-related words and pictures, that is, type and exposure time of pain-related information. None of the individual difference variables affected the magnitude of the attentional bias. Implications of current findings and future directions are discussed.
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Little is known about the central mechanisms underlying the transition from local or regional to widespread pain in low back pain patients. The aim of the study was to find out if muscle input induced by injection of nerve growth factor (NGF) can be used as an animal model for studying spinal mechanisms involved in widespread myofascial low back pain. Electrophysiological recordings from rat dorsal horn neurons were made in vivo to study alterations in their responsiveness caused by 2 injections of NGF into the multifidus muscle at an interval of 5 days. ⋯ Important findings were that the proportion of neurons having multiple receptive fields (RFs) in various tissues was significantly higher after 2 NGF injections, and new RFs appeared on the distal hind limb. The new RFs were located not in the skin but in deep tissues (muscles, thoracolumbar fascia). If similar changes occur in patients, the data might explain the diffuse nature and spread of myofascial low back pain.
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Migraine is a highly prevalent, disabling and complex episodic brain disorder whose pathogenesis is poorly understood, due in part to the lack of valid animal models. Here we report behavioral evidence of hallmark migraine features, photophobia and unilateral head pain, in transgenic knock-in mice bearing human familial hemiplegic migraine, type 1 (FHM-1) gain-of-function missense mutations (R192Q or S218L) in the Cacna1a gene encoding the CaV2.1 calcium channel α1 subunit. Photophobia was demonstrated using a modified elevated plus maze in which the safe closed arms were brightly illuminated; mutant mice avoided the light despite showing no differences in the standard (anxiety) version of the test. ⋯ These behaviors were: (1) more frequent in mutant versus wildtype mice; (2) lateralized in mutant but not in wildtype mice; (3) more frequent in females versus males; and (4) dose-dependently normalized by systemic administration of 2 different acute analgesics, rizatriptan and morphine. Furthermore, some of these behaviors were found to be more frequent and severe in 218L compared to 192Q mutants, consistent with the clinical presentation in humans. We suggest that Cacna1a transgenic mice can experience migraine-related head pain and can thus serve as unique tools to study the pathogenesis of migraine and test novel antimigraine agents.
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Randomized Controlled Trial
Single vs composite measures of pain intensity: relative sensitivity for detecting treatment effects.
Assay sensitivity remains a significant issue in pain clinical trials. One possible method for increasing assay sensitivity for detecting changes in pain intensity is to increase the reliability of pain intensity assessment by increasing the number of intensity ratings obtained, and combining these ratings into composite scores. The current study performed secondary analyses from a published clinical trial to test this possibility. ⋯ If this finding replicates in other pain populations, it has significant implications for the design and conduct of pain clinical trials. Specifically, it suggests the possibility that assessment burden (and associated costs and problems related to missing data) might be greatly reduced by specifying a single recall rating as the primary outcome variable. Research is needed to explore this possibility further.