Pain
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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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Facial expressions of pain play an important role in pain diagnostics and social interactions. Given the prominent impact of sex on various aspects of pain, it is not surprising that sex differences have also been explored regarding facial expressions of pain; however, with inconclusive findings. We aim to further investigate sex differences in facial expressions of pain by using a large, combined sample to maximize statistical power. ⋯ Additionally, facial and subjective responses to pain were significantly associated across sexes, with females showing slightly stronger associations. Although variations in facial expressions of pain are very large even within each sex, our findings demonstrate that women facially communicate pain more intensively and with a better match to their subjective experience compared with men. This indicates that women might be better in using facial communication of pain in an intensity-discriminative manner.
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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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Although multisite pain can markedly reduce work ability, the relevance of the bodily pain distribution as a predictor of long-term sick leave is still unknown. This study aimed to investigate the association between musculoskeletal pain distributions and long-term sick leave in the general working population of Denmark and included 66,177 currently employed wage earners without long-term sick leave during the prior 52 weeks. Participants reported whether they had pain in the lower extremity (hips/knees), upper extremity (neck/shoulders), or the low back. ⋯ Workers reporting pain in all 3 regions experienced a 72% increased risk (HR [95% CI]: 1.72 [1.55-1.91]). Thus, the number of pain regions seems to matter more than the exact pain location. The spatial extension of musculoskeletal pain in workers functions as a gradient system, where pain spread throughout the body is an independent indicator of the high risk of long-term sick leave.
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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.