The journal of pain : official journal of the American Pain Society
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Temporal summation of second pain (TSSP) is a psychophysical indication of a central pain encoding mechanism, potentially enhanced in pathological pain conditions. Low-frequency repetitive stimulation of unmyelinated (C) nociceptors results in a progressive increase of pain intensity when thermal stimulation intensity remains constant. However, when using different methods of nociceptive delivery to the skin, regularity as well as rate of pain enhancement with repetition varies between experiments. ⋯ In the present study, TSSP by the intermittent contact with a preheated thermode and constant contact, ramp and hold methods were compared during 10 iterations of stimulation of glabrous skin of the hand or hairy forearm skin, with an onset to onset interval of 3.3 seconds and stimulus interval of .8 seconds. Significantly greater TSSP was observed for intermittent contact stimulation at both sites (P < .001). Differential activation of myelinated and unmyelinated nociceptors by ramping and tapping may account for different rates of temporal summation of heat pain.
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An age-related decline in endogenous pain inhibitory processes likely places older adults at an increased risk for chronic pain. Limited research indicates that older adults may be characterized by deficient offset analgesia, an inhibitory temporal sharpening mechanism that increases the detectability of minor decreases in noxious stimulus intensity. The primary purpose of the study was to examine age differences in offset analgesia in community-dwelling younger, middle-aged, and older adults. ⋯ The results indicated that older and middle-aged adults showed reduced offset analgesia compared with younger adults in the 1.0°C and .4°C offset trials. Furthermore, the magnitude of offset analgesia predicted self-reported bodily pain, with those exhibiting reduced offset analgesia reporting greater bodily pain. Dysfunction of this endogenous inhibitory system could increase the risk of developing chronic pain for middle-aged and older adults.
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The Acquisition and Extinction of Fear of Painful Touch: a Novel Tactile Fear Conditioning Paradigm.
Fear of touch, due to allodynia and spontaneous pain, is not well understood. Experimental methods to advance this topic are lacking, and therefore we propose a novel tactile conditioning paradigm. Seventy-six pain-free participants underwent acquisition in a predictable as well as an unpredictable pain context. ⋯ Cue exposure reduced fear of touch, whereas context exposure reduced contextual fear. Thus, painful touch leads to increased fear, as does touch in the same context as unpredictable pain, and extinction protocols can reduce this fear. We conclude that tactile conditioning is valuable for investigating fear of touch and can advance our understanding of chronic pain.
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The U.S. National Pain Strategy calls for increased population research on "high-impact chronic pain" (ie, longstanding pain that substantially limits participation in daily activities). Using data from the nationally-representative Health and Retirement Study (HRS), we investigated the prevalence of high-impact chronic pain in U.S. adults older than age 50 overall and within population subgroups. We also explored sociodemographic variation in pain-related disability within specific activity domains. Data are from a subsample of HRS respondents (n = 1,925) who were randomly selected for a supplementary pain module in 2010. Our outcome was operationalized as pain duration of ≥7 months and a disability rating of ≥7 (0-10 scale) in at least 1 domain: family/home, leisure, social activities, work, or basic activities. Overall, 8.2% (95% confidence interval = 6.7-10.1%) of adults older than age 50 met criteria for high-impact chronic pain. This proportion rose to 17.1% (95% confidence interval = 12.3-23.4%) among individuals in the lowest wealth quartile. Prevalence differences according to education, race/ethnicity, and age were not significant. Arthritis and depression were significantly associated with high-impact pain in multivariable analysis. Among adults with any chronic pain, African American and individuals in the lowest wealth quartile reported more pain-related disability across activity domains. ⋯ High-impact chronic pain is unequally distributed among midlife and older U.S. adults. Efforts to reduce the burden of disabling chronic pain should prioritize socioeconomically vulnerable groups, who may have the least access to multimodal pain treatment to improve function.
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Chronic pain is a common condition associated with psychological distress, functional impairments, and age-associated comorbidity. Preliminary studies, on the basis of relatively small sample sizes, suggest that the combination of chronic pain and stress is associated with telomere shortening, a widely recognized marker of cellular aging. We sought to determine the cross-sectional association of chronic pain with telomere length in 7,816 community-dwelling adults ages 20 years and older who participated in the 1999 to 2002 National Health and Nutrition Examination Survey. ⋯ The age-adjusted means (standard error) of telomere length telomere to single copy gene ratios were 1.04 (.02), 1.03 (.02), and 1.02 (.02) in participants with no chronic pain, chronic regional pain, and chronic widespread pain, respectively (P = .69). In addition, chronic pain did not modify the effects of age, sex, race/ethnicity, education, or psychological distress on telomere length. In summary, chronic regional and widespread pain were not associated with telomere length in this nationally representative study; however, we could not determine associations of pain duration and severity with telomere length because of limitations in pain assessment data.