The journal of pain : official journal of the American Pain Society
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This study investigated if conditioned pain modulation (CPM) varies across the menstrual cycle in healthy, normally menstruating women and investigated correlations between sex hormone levels and CPM across the menstrual cycle. Thirty-six normally menstruating women were tested during 3 phases of the menstrual cycle: early follicular, ovulatory, and midluteal, confirmed by hormone determinations. Mechanical pressure (test stimulus) was applied to the masseter muscle and the induced pain assessed before, during, and after immersion of the hand into ice water (conditioning stimulus) to activate CPM or tepid water (control). Conditioning pain, ie, pain in the hand during CPM/control experiment, and tolerance time were also measured. Test pain intensity was suppressed during CPM in all phases (P < .001), but with more effective suppression during the ovulatry than during the early follicular phase (P < .05). There were no changes in test pain intensity during the control experiment and no significant differences in conditioning pain, or tolerance time between phases. In conclusion, our results showed more effective pain modulation in the ovulatory phase of the menstrual cycle, when estradiol levels are high and progesterone levels are low, than in the early follicular phase when both these hormones are low. ⋯ Deficient pain modulation is believed to be an important pathogenic factor in many chronic pain conditions that affect women. This article shows that sex hormones modulate conditioned pain modulation, because pain inhibition was more effective in the ovulatory phase of the menstrual cycle than in the early follicular phase.
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Randomized Controlled Trial
"There's more to this pain than just pain": how patients' understanding of pain evolved during a randomized controlled trial for chronic pain.
Chronic pain is prevalent, is costly, and exerts an emotional toll on patients and providers. Little is known about chronic pain in veterans of the recent military conflicts in Afghanistan and Iraq (OEF/OIF/OND [Operation Enduring Freedom/Operation Iraqi Freedom/Operation New Dawn] veterans). This study's objective was to ascertain veterans' perceptions of a multicomponent intervention tested in a randomized controlled trial for OEF/OIF/OND veterans with chronic musculoskeletal pain (ESCAPE: Evaluation of Stepped Care for Chronic Pain). Qualitative interviews were conducted with patients in the intervention arm of ESCAPE. Questions related to veterans' experiences with trial components, overall perceptions of the intervention, strengths, and suggestions for improvement. Twenty-six veterans (21% of total intervention patients) participated. Patients were purposefully sampled to include treatment responders (defined as ≥30% reduction in pain-related disability or pain severity) and non-responders. Non-completers (completed <50% of the trial) were also sampled. Qualitative analysis was guided by grounded theory, using constant comparative methodology. Both responders and non-responders spoke about their evolving understanding of their pain experience during the trial, and how this new understanding helped them to manage their pain more effectively. This evolution is reported under 2 themes: 1) learning to recognize physical and psychosocial factors related to pain; and 2) learning to manage pain through actions and thoughts. ⋯ Responders and non-responders both described making connections between their pain and other factors in their lives, and how these connections positively influenced how they managed their pain. Traditional quantitative measures of response to pain interventions may not capture the full benefits that patients report experiencing.
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Patients with painful vertebral compression fractures produced by multiple myeloma (MM) often experience reduction in pain after spinal augmentation with kyphoplasty or vertebroplasty. Previous studies have shown pain reduction and improvement in functional status after augmentation, but no studies have examined the effect of augmentation on other cancer-related symptoms. We hypothesized that reduction in pain severity would be significantly associated with improvement in other reported symptoms. We retrospectively studied 79 patients who rated pain and symptom severity both before and after kyphoplasty or vertebroplasty. Pain was significantly reduced after spinal augmentation (1.3 on a 0 to 10 scale; effect size [ES] = .59; P < .001), as were anxiety (1.3; ES = .47), drowsiness (1.3; ES = .39), fatigue (1.1; ES = .32), depression (.7; ES = .28), and difficulty thinking clearly (.7; ES = .26) (all P < .05). Greater reduction in pain was associated with a greater number of symptoms being reduced. Interestingly, insomnia worsened regardless of any amount of improvement in pain. Because appropriate symptom control contributes to the overall well-being of cancer patients, future studies of pain reduction procedures should include measures of other symptoms to fully characterize the potential benefit of treating pain. ⋯ Appropriate symptom control contributes to overall well-being for cancer patients. This study demonstrated that pain reduction after spinal augmentation with vertebroplasty or kyphoplasty was positively associated with reduction in other patient-reported cancer-related symptoms. Future studies of these augmentation procedures should measure multiple symptoms, in addition to pain and functional status.
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The use of von Frey filaments, originally developed by Maximilian von Frey, has become the cornerstone for assaying mechanical sensitivity in animal models and is widely used for human assessment. While there are certain limitations associated with their use that make comparisons between studies not straightforward at times, such as stimulus duration and testing frequency, von Frey filaments provide a good measurement of mechanosensation. Here we describe the application of von Frey filaments to testing in animal models, specifically with respect to determining changes in sensory thresholds in a pain state using the Dixon up-down method. In a literature survey, we found that up to 75% of reports using this method analyze the data with parametric statistical analysis and of those that used nonparametric analysis, none took into account that mechanical sensation is perceived on a logarithmic scale (Weber's Law) when calculating efficacy. Here we outline a more rigorous analysis for calculating efficacy and ED(50)'s from von Frey data that incorporates Weber's Law. We show that this analysis makes statistical and biological sense and provide a specific example of how this change affects data analysis that brings results from animal models more in line with clinical observations. ⋯ This focus article argues that analyzing von Frey paw withdrawal threshold data obtained by using the Dixon up-down method without considering Weber's Law is inappropriate. An analysis method that incorporates how mechanical sensation is perceived and how its application brings results from animal models more in line with clinical data is presented.
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The aim of this present study was to test the hypothesis that tonic nociceptive stimulation of latent myofascial trigger points (MTPs) may induce a spatially enlarged area of pressure pain hyperalgesia. Painful glutamate (.2 mL, 1M) stimulation of latent MTPs and non-MTPs in the forearm was achieved by an electromyography-guided procedure. Pain intensity (as rated on the visual analog scale [VAS]) and referred pain area following glutamate injections were recorded. Pressure pain threshold (PPT) was measured over 12 points in the forearm muscles and at the mid-point of tibialis anterior muscle before and at .5 hour, 1 hour, and 24 hours after glutamate injections. The results showed that maximal pain intensity, the area under the VAS curve, and referred pain area were significantly higher and larger following glutamate injection into latent MTPs than non-MTPs (all, P < .05). A significantly lower PPT level was detected over time after glutamate injection into latent MTPs at .5 hour (at 4 points), 1 hour (at 7 points), and 24 hours (at 6 points) in the forearm muscles. However, a significantly lower PPT was observed only at 24 hours after glutamate injection into non-MTPs in the forearm muscles (at 4 points, P < .05) when compared to the pre-injection PPT. PPT at the mid-point of the tibialis anterior was significantly decreased at 1 hour only as compared to the pre-injection PPT in both groups (< .05). The results of the present study indicate that nociceptive stimulation of latent MTPs is associated with an early onset of locally enlarged area of mechanical hyperalgesia. ⋯ This study shows that MTPs are associated with an early occurrence of a locally enlarged area of pressure hyperalgesia associated with spreading central sensitization. Inactivation of MTPs may prevent spatial pain propagation.