Pain
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Substantial interindividual variability characterizes osteoarthritis (OA) pain. Previous findings identify quantitative sensory testing (QST), psychological factors, and health-related quality of life as contributors to OA pain and predictors of treatment outcomes. This exploratory study aimed to explain baseline OA pain intensity and predict OA pain after administration of a nonsteroidal anti-inflammatory drug in combination with paracetamol for 3 weeks. ⋯ When assessed separately, PCS was the strongest predictor (32.2% of baseline and 24.1% of follow-up pain), but QST, symptoms of anxiety and depression, PCS, and quality of life also explained some variability in baseline and follow-up knee OA pain. Further analyses revealed that only TSP and PCS were not mediated by any other included variables, highlighting their role as unique contributors to OA pain presentation. This study emphasizes the importance of embracing a multimodal approach to OA pain and highlights PCS and TSP as major contributors to the baseline OA pain experience and the OA pain experience after OA treatment.
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Facial grimacing is used to quantify spontaneous pain in mice and other mammals, but scoring relies on humans with different levels of proficiency. Here, we developed a cloud-based software platform called PainFace (http://painface.net) that uses machine learning to detect 4 facial action units of the mouse grimace scale (orbitals, nose, ears, whiskers) and score facial grimaces of black-coated C57BL/6 male and female mice on a 0 to 8 scale. ⋯ By analyzing the frequency distribution of grimace scores, we found that mice spent 7x more time in a "high grimace" state following laparotomy surgery relative to sham surgery controls. Our study shows that PainFace reproducibly quantifies facial grimaces indicative of nonevoked spontaneous pain and enables laboratories to standardize and scale-up facial grimace analyses.
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Our aim was to investigate relative contributions of central and peripheral mechanisms to knee osteoarthritis (OA) diagnosis and their independent causal association with knee OA. We performed longitudinal analysis using data from UK-Biobank participants. Knee OA was defined using International Classification of Diseases manual 10 codes from participants' hospital records. ⋯ Body mass index and MCP had independent causal effects on knee OA (OR 1.76 [95% CI, 1.64-1.88] and 1.83 [95% CI, 1.54-2.16] per unit change, respectively). In conclusion, peripheral risk factors (eg, BMI) contribute more to the development of knee OA than central risk factors (eg, MCP). Peripheral and central factors are independently causal on knee OA.
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Complex regional pain syndrome (CRPS) presents postinjury with disproportionate pain and neuropathic, autonomic, motor symptoms, and skin texture affection. However, the origin of these multiplex changes is unclear. Skin biopsies offer a window to analyze the somatosensory and vascular system as well as skin trophicity with their protecting barriers. ⋯ Barrier proteins in keratinocytes, perineurium of dermal nerves, Schwann cells, and papillary microvessels were not affected in early CRPS. Bilateral changes in the tissue architecture in early CRPS might indicate a predisposition for CRPS that manifests after injury. Further studies should evaluate whether these changes might be used to identify risk patients for CRPS after trauma and as biomarkers for outcome.
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People with chronic pain often attempt to manage pain and concurrent emotional distress with analgesic substances. Habitual use of such substances-even when not opioid-based-can pose side effect risks. A negative reinforcement model has been proposed whereby relief of pain and emotional distress following medication consumption increases the likelihood that the experience of elevated pain and distress will spur further medication use. ⋯ Primary results were as follows: (1) participants on average reported taking analgesic medication during 41.3% of the 3-hour reporting epochs (29 times over 14 days); (2) time 1 within-person increases in pain and NA predicted time 2 increases in the likelihood of ingesting analgesic medications; (3) time 1 within-person increases in medication use predicted time 2 decreases in pain and NA; and (4) lagged associations between time 1 pain/NA and time 2 medication use were strongest among women. Findings suggest that the use of analgesic medications for many people with chronic pain occurs frequently throughout the day. Results support the validity of a negative reinforcement model where pain and distress lead to pain medication use, which in turn leads to relief from pain and distress.