The journal of pain : official journal of the American Pain Society
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Item Response Theory (IRT) is being increasingly used to develop and evaluate outcome measures. However, many pain measures, including those that assess pain quality, have yet to be evaluated from the IRT perspective. The current study evaluated the scales of a commonly used measure of pain quality (the Pain Quality Assessment Scale, or PQAS) using IRT analyses in 3 samples of patients with chronic pain. The findings indicated variability in the precision of the scales, suggesting that all 3 of the PQAS scales are precise when pain is severe and that the Paroxysmal and Deep scales but not necessarily the Surface scale are precise when pain is of moderate or lower severity. In addition, 2 potential problems with the 11 (ie, 0 to 10) response levels used for the PQAS items were identified: (1) a high degree of overlap between adjacent response levels and (2) a lack of interval scaling. Research is needed to determine the extent to which these problems do, or do not, threaten the validity of the PQAS items and scales as outcome measures in pain clinical trials. ⋯ IRT analyses provide important information about the psychometric and practical qualities of pain measures that is not provided by standard (classical test theory) analyses. IRT analyses of the PQAS subscales indicate that some of the scales are more precise than others at different levels of pain severity and provide important directions for further research to better understand the PQAS. IRT analyses would probably similarly provide important information concerning the utility of other measures commonly used in pain research.
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Randomized Controlled Trial
A new transient sham TENS device allows for investigator blinding while delivering a true placebo treatment.
This study compared a new transient sham transcutaneous electrical nerve stimulation (TENS) that delivers current for 45 seconds to an inactive sham and active TENS to determine the degree of blinding and influence on pain reduction. Pressure-pain thresholds (PPT), heat-pain thresholds (HPT), and pain intensities to tonic heat and pressure were measured in 69 healthy adults before and after randomization. Allocation investigators and subjects were asked to identify the treatment administered. The transient sham blinded investigators 100% of the time and 40% of subjects compared to the inactive sham that blinded investigators 0% of the time and 21% of subjects. Investigators and subjects were blinded only 7% and 13% of the time, respectively, with active TENS. Neither placebo treatment resulted in significant changes in PPT, HPT, or pain intensities. Subjects using higher active TENS amplitudes (> or =17 mAs) had significantly higher PPTs and lower pain intensities to tonic pressure than subjects using lower amplitudes (<17 mAs). HPTs and pain intensities to tonic heat were not significantly changed. The transient TENS completely blinds investigators to treatment and does not reduce pain, thereby providing a true placebo treatment. ⋯ This article presents the benefits of a new transient sham TENS device for use in prospective, randomized, clinical trials. This device facilitates blinding of subjects and investigators to eliminate expectation bias and determine the true efficacy of TENS for use in clinical populations.
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Most previous studies indicated that patients suffering from major depressive disorder (MDD) showed a decreased sensitivity for external or skin surface pain, eg, for heat or electrical stimuli, as compared to healthy controls. Here, we investigated cold-pain thresholds in 20 unmedicated patients suffering from MDD and 20 matched controls. We applied the ascending method of limits which has previously been used for heat-pain assessment in patients with depression. Similar to previous results for heat-pain thresholds we found a decreased sensitivity for cold pain in patients with MDD as indicated by increased cold-pain thresholds. This difference was significant on the right arm, whereas only a trend was obtained on the left arm, thus suggesting a certain degree of lateralization, similar to that seen in heat-pain perception in patients suffering from MDD or adjustment disorder. The study confirms our previous results of a lower sensitivity for externally induced pain in patients with MDD. Moreover, it adds weight to the assumption of a lateralized perception of thermal pain in depression. ⋯ This investigation provides further evidence for reduced pain perception of externally applied stimuli in major depression. Thus, central-nervous correlates for this altered pain perception in major depression are worth examining in future studies in order to gain more insight into mechanisms of pain perception on the one hand, and pathology of depression on the other.
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Acid-sensing ion channels (ASICs) respond to acidosis that normally occurs after inflammation. We examined the expression of ASIC1, ASIC2, and ASIC3 mRNAs in lumbar dorsal root ganglion neurons before and 24 hours after carrageenan-induced muscle inflammation. Muscle inflammation causes bilateral increases of ASIC2 and ASIC3 but not ASIC1 (neither ASIC1a nor ASIC1b) mRNA, suggesting differential regulation of ASIC1 versus ASIC2 and ASIC3 mRNA. Similar mRNA increases were observed after inflammation in knockout mice: ASIC2 mRNA increases in ASIC3-/- mice; ASIC2 and ASIC3 mRNAs increase in ASIC1-/- mice. Prior behavioral studies in ASIC3-/- mice showed deficits in secondary hyperalgesia (increased response to noxious stimuli outside the site of injury) but not primary hyperalgesia (increased response to noxious stimuli at the site of injury). In this study, we show that ASIC1-/- mice do not develop primary muscle hyperalgesia but develop secondary paw hyperalgesia. In contrast, and as expected, ASIC3-/- mice develop primary muscle hyperalgesia but do not develop secondary paw hyperalgesia. The pharmacological utility of the nonselective ASIC inhibitor A-317567, given locally, was tested. A-317567 reverses both the primary and the secondary hyperalgesia induced by carrageenan muscle inflammation. Thus, peripherally located ASIC1 and ASIC3 play different roles in the development of hyperalgesia after muscle inflammation. ⋯ This study shows changes in ASIC mRNA expression and behavioral hyperalgesia of C57Bl/6 (wild type), ASIC1-/-, and ASIC3-/- mice before and after the induction of muscle inflammation. A-317567 was effective in reversing hyperalgesia in these animals, suggesting the potential of ASICs as therapeutic targets for muscle inflammatory pain.
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Clinical observations suggest that the perceived intensity of a painful event increases as the unpredictability of its occurrence increases. We examined the effect of varying stimulus predictability on the Somatosensory Evoked Potential (SEP), Pupil Diameter Response (PDR), Pain Report (PR), and Fear Report (FR) in 25 healthy female volunteers experiencing repeated noxious fingertip shocks. Each volunteer underwent high- and low-stimulus intensities in 4 stimulus patterns defined by stimulus sequence (SEQ) and interstimulus interval (ISI) as follows: A) serial stimulus intensity SEQ with fixed ISI; B) serial stimulus intensity SEQ with varied ISI; C) random stimulus intensity SEQ with fixed ISI; and D) random stimulus intensity SEQ with varied ISI. Results revealed that: (1) lower stimulus predictability led to higher PR and FR, greater PDR magnitude, and greater SEP amplitude; and (2) the 4 dependent measures showed the same response pattern across levels of stimulus predictability. These findings support the hypothesis that lower stimulus predictability is associated with higher reported pain and fear as well as greater physiological arousal. ⋯ Patients undergoing painful procedures experience more distress when the occurrence of a painful event is unpredictable. Poor predictability increases pain, fear, and associated physiological arousal. Maximizing the predictability of painful events may improve the quality of patient care by minimizing associated levels of pain and fear.