Pain
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Randomized Controlled Trial
Analgesic tolerance without demonstrable opioid-induced hyperalgesia: a double-blinded, randomized, placebo-controlled trial of sustained-release morphine for treatment of chronic nonradicular low-back pain.
Although often successful in acute settings, long-term use of opioid pain medications may be accompanied by waning levels of analgesic response not readily attributable to advancing underlying disease, necessitating dose escalation to attain pain relief. Analgesic tolerance, and more recently opioid-induced hyperalgesia, have been invoked to explain such declines in opioid effectiveness over time. Because both phenomena result in inadequate analgesia, they are difficult to distinguish in a clinical setting. ⋯ The differences in visual analogue scale pain levels (P = .003) and self-reported disability (P = .03) between both treatment groups were statistically significant. After 1 month of oral morphine therapy, patients with chronic low-back pain developed tolerance but not opioid-induced hyperalgesia. Improvements in pain and functional ability were observed.
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Multicenter Study
Assessment and validation of prognostic models for poor functional recovery 12 months after whiplash injury: a multicentre inception cohort study.
Uncertainty surrounds prognostic factors after whiplash injury. Previously we identified a prognostic model for 6-month pain-related disability in a cohort of 80 participants with acute whiplash. Predictors included initial disability, older age, decreased cold pain thresholds, decreased neck rotation movement, posttraumatic stress symptoms and decreased sympathetic vasoconstriction. ⋯ After adjusting for site, age and Impact of Events Scale scores regained significance (r(2) = 0.56, 95% confidence interval 0.48 to 0.64). The tested model was not precise in predicting NDI as a continuous variable. However, it found good accuracy to discriminate participants with moderate to severe disability at 12 months (area under the receiver operating characteristic curve 0.89 [95% confidence interval 0.84-0.94], P<.001) which is clinically useful.
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Nerve growth factor (NGF) induces local hyperalgesia for a few days after intramuscular injection, but longer-lasting muscle pain upon systemic administration. As the muscle fascia is densely innervated by free nerve endings, we hypothesized a lasting sensitization of fascia nociceptors by NGF. We administered 1 μg NGF (dissolved in 100 μL saline) ultrasound-guided to the fascia of the Musculus erector spinae muscle at the lumbar level of 14 male volunteers and assessed hypersensitivity after 6 hours, and 1, 3, 7, 14, and 21 days. ⋯ Pain upon injected protons was significantly elevated (P<0.04) for 2 weeks. NGF induced a sensitization of the muscle fascia to mechanical and chemical stimuli lasting for up to 2 weeks. As nociceptors in the fascia appear to be particularly prone to sensitization, they may contribute to acute or chronic muscle pain.
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Randomized Controlled Trial
Ethnicity interacts with the OPRM1 gene in experimental pain sensitivity.
Robust interindividual variation in pain sensitivity has been observed, and recent evidence suggests that some of the variability may be genetically mediated. Our previous data revealed significantly higher pressure pain thresholds among individuals possessing the minor G allele of the A118G SNP of the mu-opioid receptor gene (OPRM1) compared with those with 2 consensus alleles. Moreover, ethnic differences in pain sensitivity have been widely reported. ⋯ The reasons for this dichotomy are unclear; they may involve ethnic differences in haplotypic structure, or A118G may be a tag-SNP linked to other functional polymorphisms. These findings demonstrate an ethnicity-dependent association of OPRM1 genotype with pain sensitivity. Additional research is warranted to uncover the mechanisms influencing these relationships.
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Comparative Study
A comparison of four self-report scales of pain intensity in 6- to 8-year-old children.
There are many different instruments for assessing pain intensity in children, but the agreement between them is unclear. The aims of this study were to determine the 1-dimensionality of 4 widely used self-report scales for measuring the intensity of pediatric pain, and the agreement between them. A sample of 126 school children between 6 and 8 years of age (mean = 6.87 years; SD = 0.68 year) were interviewed individually and asked to identify the most frequent pain that they had experienced in the 3 months before the interview, and to report their maximum pain intensity using all 4 scales (Visual Analogue Scale, Coloured Analogue Scale, Faces Pain Scale-Revised and Numerical Rating Scale-11). ⋯ Our data show the 1-dimensionality of the scales. The 95% limits of agreement between each pair of measures were as follows: VAS/CAS (-23.8, 23.4); VAS/NRS-11 (-41, 31.1); VAS/FPS-R (-38.3, 33.6); CAS/NRS-11 (-35.6, 26.2); CAS/FPS-R (-36.4, 32.1), and FPS-R/NRS-11 (-36.3, 31). Our data suggest that these 4 instruments measure 1 common factor but that they are not concordant.