Pain
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To compare the prevalence of disabling low back pain (DLBP) and disabling wrist/hand pain (DWHP) among groups of workers carrying out similar physical activities in different cultural environments, and to explore explanations for observed differences, we conducted a cross-sectional survey in 18 countries. Standardised questionnaires were used to ascertain pain that interfered with everyday activities and exposure to possible risk factors in 12,426 participants from 47 occupational groups (mostly nurses and office workers). Associations with risk factors were assessed by Poisson regression. ⋯ However, after allowance for these risk factors, an up-to 8-fold difference in prevalence remained. Systems of compensation for work-related illness and financial support for health-related incapacity for work appeared to have little influence on the occurrence of symptoms. Our findings indicate large international variation in the prevalence of disabling forearm and back pain among occupational groups carrying out similar tasks, which is only partially explained by the personal and socioeconomic risk factors that were analysed.
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Despite similar behavioral hypersensitivity, acute and chronic pain have distinct neural bases. We used intraplantar injection of complete Freund's adjuvant to directly compare activity of pain-modulating neurons in the rostral ventromedial medulla (RVM) in acute vs chronic inflammation. Heat-evoked and von Frey-evoked withdrawal reflexes and corresponding RVM neuronal activity were recorded in lightly anesthetized animals either during the first hour after complete Freund's adjuvant injection (acute) or 3 to 10 days later (chronic). ⋯ During early immune-mediated inflammation, ON-cell spontaneous activity promotes hyperalgesia. After inflammation is established, the antinociceptive influence of OFF-cells is dominant, yet the lowered threshold for the OFF-cell pause allows behavioral responses to stimuli that would normally be considered innocuous. The efficacy of OFF-cells in counteracting sensitization of ascending transmission pathways could therefore be an important determining factor in development of chronic inflammatory pain.
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Altered gray matter volume in the frontal pain modulation network in patients with cluster headache.
Previous functional imaging studies in episodic cluster headache (CH) patients revealed altered brain metabolism concentrated on the central descending pain control system. However, it remains unclear whether changes in brain metabolism during the "in bout" period are due to structural changes and whether these structural changes vary between the "in bout" and "out of bout" periods. To quantify brain structural changes in CH patients, the regional gray matter volume (GMV) was compared among 49 episodic CH patients during the "in bout" period and 49 age- and sex-matched controls. ⋯ Compared to "out of bout" scans, the "in bout" scans revealed significant GMV increases in the left anterior cingulate, insula, and fusiform gyrus. Additionally, compared to healthy controls, the "out of bout" scans revealed a trend of GMV reduction in the left middle frontal gyrus. These affected regions primarily belong to frontal pain modulation areas, and thus these GMV changes may reflect insufficient pain-modulating capacity in the frontal areas of CH patients.