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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Randomized Controlled Trial
The Effect of Preoperative Intra-Articular Methylprednisolone on Pain after TKA: a Randomized Double-Blinded Placebo Controlled Trial in Patients with High-Pain Knee Osteoarthritis and Sensitization.
In a randomized, double-blind, placebo controlled trial, we investigated the postoperative analgesic effect of a single intra-articular injection of 40 mg methylprednisolone acetate (MP) administered 1 week before total knee arthroplasty (TKA). Forty-eight patients with high pain osteoarthritis (≥5 on a numeric rating scale during walk) and sensitization (pressure pain threshold <250 kPa), aged 50 to 80 years and scheduled for primary unilateral TKA under spinal anaesthesia were included. ⋯ No difference in the proportion of patients with moderate/severe pain was found between MP/placebo groups at 24 hours (67% and 74%, χ2 = .2, P = .63, odds ratio = .7, 95% confidence interval = .2-2.8) or at 48 hours (57% and 68%, χ2 = .5, P = .46, odds ratio = .6, 95% confidence interval = .2-2.3), and no difference between groups in postoperative sensitization was found (P > .4) despite reduced preoperative intra-articular inflammation (IL-6) in the MP group versus placebo (median change in IL-6 = -70 pg/mL, interquartile range = -466 to 0 vs. 32 pg/mL, interquartile range = -26 to 75, P = .029). Alternative central or peripheral analgesic interventions in this high-risk group are required.
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Randomized Controlled Trial
Chronic opioid therapy modifies QST changes following ketamine infusion in chronic pain patients.
The long-term effects of opioids on sensitization processes are believed to be mediated through the N-methyl-D-aspartate receptor. Quantitative sensory testing (QST) changes observed after a ketamine infusion have been previously described but the effect that chronic opioids will have is not known. The results of this prospective randomized factorial trial compared the thermal QST changes observed after a .05 mg/kg ketamine infusion or a saline placebo in chronic pain subjects who were either opioid-naive or were chronically using opioids for chronic noncancer pain are presented. No baseline QST differences were noted between the 4 groups at baseline. Comparison of changes preinfusion with postinfusion QST measurements resulted in decreased average change in temporal summation response between opioid subjects who received a placebo compared with those who received a ketamine infusion (-5.22, SD = 9.96 vs 13.81, SD = 19.55; P = .004). Additionally, the average change in temporal summation was decreased among subjects who received a ketamine infusion and were not chronically using opioids compared with subjects who were using chronic opioids and received a placebo infusion (-1.91, SD = 13.25 vs 13.81, SD = 19.55; P = .007). The results indicate that low-dose ketamine infusions produce subtle changes in QST phenotypes that are modified by the chronic use of opioids. This illustrates the potential diagnostic and therapeutic value of ketamine in the setting of chronic opioid use. ⋯ The presented data further our understanding of modulation of sensory perception in the setting of chronic opioid use and the role of the N-methyl-D-aspartate receptor. The use of low-dose ketamine infusions may be useful for the treatment as well as diagnosis of opioid-related neuropathic conditions.
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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.
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Review
Using Screening Tests to Predict Aberrant Use of Opioids in Chronic Pain Patients: Caveat Emptor.
Screening tests represent a critical tool in chronic pain treatment for predicting aberrant opioid use, which has emerged as a significant public health issue. Nevertheless, there remains a significant potential for the misapplication of screeners in this context. The potential difficulties in evaluating the diagnostic efficiency of screeners have been well established, particularly with regard to the effect that the prevalence of a disorder has on predictive value. ⋯ Given the prevalence of opioid problems, however, formulating clear clinical guidelines on such screeners appears highly important. The aims of the present report include: 1) providing a review of the salient issues necessary for interpreting diagnostic efficiency statistics of screening tests, 2) identifying the critical differences between sensitivity, specificity, and predictive value, and 3) discussing the characteristic effects that disease prevalence has on statistical prediction. The article also reviews key processes in screening measure development and highlights several key considerations relevant to their appropriate use in clinical decision-making.