The journal of pain : official journal of the American Pain Society
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Ischemic myalgia is a unique type of muscle pain in the patient population. The role that discrete muscle afferent subpopulations play in the generation of pain during ischemic events, however, has yet to be determined. Using 2 brachial artery occlusion models to compare prolonged ischemia or transient ischemia with reperfusion of the muscles, we found that both injuries caused behavioral decrements in grip strength, as well as increased spontaneous pain behaviors. Using our ex vivo forepaw muscles, median and ulnar nerves, dorsal root ganglion, and spinal cord recording preparation, we found after both prolonged and transient ischemia that there was a significant increase in the number of afferents that responded to both noxious and non-noxious chemical (lactate, adenosine triphosphate, varying pH) stimulation of the muscles compared to uninjured controls. However, we found an increase in firing to heat stimuli specifically in muscle afferents during prolonged ischemia, but a distinct increase in afferent firing to non-noxious chemicals and decreased mechanical thresholds after transient ischemia. The unique changes in afferent function observed also corresponded with distinct patterns of gene expression in the dorsal root ganglia. Thus, the development of ischemic myalgia may be generated by unique afferent-based mechanisms during prolonged and transient ischemia. ⋯ This study analyzed the response properties of thinly myelinated group III and unmyelinated group IV muscle afferents during prolonged and transient ischemia in addition to pain behaviors and alterations in DRG gene expression in the mouse. Results suggest that mechanisms of pain generation during prolonged ischemia may be different from ischemia/reperfusion.
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Fentanyl, introduced more than 50 years ago, has become the most often used opioid for intraoperative analgesia. Since the early 1990s the fentanyl patch has been available for management of chronic pain of all forms of cancer as well as the persistent, intense pain from many noncancerous maladies. ⋯ The purpose of this article is to describe why this opioid has become so important in the treatment of pain in modern clinical practice. The data indicate that fentanyl's popularity has occurred because it has minimal cardiovascular effects, does not result in increases in plasma histamine, is relatively short in onset of action and duration of effect, is easy and inexpensive to synthesize and prepare for the marketplace, and is now familiar to clinicians working in pain and perioperative medicine throughout the world.
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Randomized Controlled Trial
Repetitive transcranial magnetic stimulation of the left premotor/dorsolateral prefrontal cortex does not have analgesic effect on central poststroke pain.
Central poststroke pain (CPSP) is caused by an encephalic vascular lesion of the somatosensory pathways and is commonly refractory to current pharmacologic treatments. Repetitive transcranial magnetic stimulation (rTMS) of the premotor cortex/dorsolateral prefrontal cortex (PMC/DLPFC) can change thermal pain threshold toward analgesia in healthy subjects and has analgesic effects in acute postoperative pain as well as in fibromyalgia patients. However, its effect on neuropathic pain and in CPSP, in particular, has not been assessed. The aim of this prospective, double-blind, placebo-controlled study was to evaluate the analgesic effect of PMC/DLPFC rTMS in CPSP patients. Patients were randomized into 2 groups, active (a-) rTMS and sham (s-) rTMS, and were treated with 10 daily sessions of rTMS over the left PMC/DLPFC (10 Hz, 1,250 pulses/d). Outcomes were assessed at baseline, during the stimulation phase, and at 1, 2, and 4 weeks after the last stimulation. The main outcome was pain intensity changes measured by the visual analog scale on the last stimulation day compared to baseline. Interim analysis was scheduled when the first half of the patients completed the study. The study was terminated because of a significant lack of efficacy of the active arm after 21 patients completed the whole treatment and follow-up phases. rTMS of the left PMC/DLPFC did not improve pain in CPSP. ⋯ The aim of this double-blind, placebo-controlled study was to evaluate the analgesic effects of rTMS to the PMC/DLPFC in CPSP patients. An interim analysis showed a consistent lack of analgesic effect, and the study was terminated. rTMS of the PMC/DLPFC is not effective in relieving CPSP.
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Randomized Controlled Trial
Using multiple daily pain ratings to improve reliability and assay sensitivity: how many is enough?
The Initiative for Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) has reported diminished assay sensitivity in pain treatment trials and recommended investigation of the causes. Specific recommendations included examination of outcome measure reliability and lengthening the baseline measurement period to allow more measurements to be collected. This secondary data analysis evaluated the minimum number of daily pain intensity ratings required to obtain a reliability of at least .90 and whether a composite of this smaller number of ratings was interchangeable with the composite of all ratings. Veterans Affairs medical center patients made 14 daily calls to an automated telephone system to report their average daily pain intensity rating. A single daily rating produced less than adequate reliability (intraclass correlation coefficient = .65), but a composite of the average of 5 ratings resulted in reliability above .90. A Bland-Altman analysis revealed that the differences between a 5-day composite and the composite of all ratings were small (mean .09 points, standard deviation = .45; 95% confidence interval = -.05 to .23) and below the threshold for a clinically meaningful difference, indicating that the 2 measurements are interchangeable. Our results support the IMMPACT recommendations for improving assay sensitivity by collecting a multiple-day baseline of pain intensity ratings. ⋯ This study examined the minimum number of pain ratings required to achieve reliability of .90 and examined whether this smaller subset of ratings could be used interchangeably with a composite of all available ratings. Attention to measure reliability could enhance the assay sensitivity, power, and statistical precision of pain treatment trials.
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Physical function and functional recovery are important aspects of the acute pain experience in children and adolescents in hospitalized settings. Measures of function related to pediatric acute pain do not exist currently, limiting understanding of recovery in youth undergoing acute and procedural pain. To address this gap, we developed and assessed the clinical utility and preliminary validity of the Youth Acute Pain Functional Ability Questionnaire (YAPFAQ). We evaluated psychometric properties of this measure in 159 patients with sickle cell disease, ages 7 to 21 years, who were hospitalized for vaso-occlusive episodes at 4 urban children's hospitals. The YAPFAQ demonstrated strong internal reliability and test-retest reliability. An exploratory factor analysis was conducted to examine the preliminary factor structure and to help reduce the number of items for the final scale. Evidence for moderate construct validity was demonstrated among validated measures of pain burden, motor function, functional ability, and quality of life. The YAPFAQ is a new measure of youth functional ability in the acute pain setting. Further evaluation of this measure in additional pediatric populations is needed to understand applicability across a spectrum of youth experiencing acute pain related to illness, trauma, and medical/surgical procedures. ⋯ Measures of function in response to acute pain are needed in order to more comprehensively evaluate acute pain interventions in pediatrics; however, no specific measures are available. Our preliminary psychometric evaluation of an acute pain functional ability measure for youth indicates that it may be a promising tool for further refinement in additional pediatric acute pain populations.