Pain
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Clinical Trial
On the repeatability of brush-evoked allodynia using a novel semi-quantitative method in patients with peripheral neuropathic pain.
Using a semi-quantitative method the repeatability of brush-evoked allodynia was examined within and between days in nine patients with spontaneous ongoing pain and dynamic mechanical allodynia due to peripheral neuropathy. In addition, the relationship between the intensity of spontaneous ongoing pain and the total brush-evoked pain intensity was addressed. The brush stimulus was applied in the innervation territory of the lesioned nervous structure by lightly stroking 60 mm of the skin four times with an 8 mm wide brush. ⋯ The patients were examined 4 days during one month, i.e. at day 1, 3, 28 and 30 and each study day the stimulus was repeated four times with an inter-stimulus interval of 10 min. The variation between repeated assessments was analyzed using the intraclass correlation coefficient and the total brush-evoked pain intensity within days ranged from 0.89 to 0.95 ("very good repeatability") and between days from 0.77 to 0.97 ("very good repeatability"). A significant positive correlation was demonstrated between the mean intensity of spontaneous ongoing pain and the mean total brush-evoked pain intensity (r(s)=0.68, P<0.042, "a moderate to good correlation").
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Prior studies evaluating predictors of pain-related outcomes following treatment for sciatica have been limited by methodological problems, including retrospective study design, use of unvalidated outcome measures, and short-term follow-up periods. Despite these limitations, some reports have suggested that symptoms of psychological distress may predict individual differences in pain treatment-related outcomes (e.g., higher levels of depressive and anxious symptomatology are associated with greater pain and disability after treatment). In this study, we sought to determine whether acute symptoms of depression and anxiety were prospectively associated with treatment outcomes over a 3-year follow-up period in surgically treated and non-surgically treated patients with sciatica. ⋯ In most analyses, symptoms of depression and anxiety, both at baseline and at the preceding time point, were significant independent predictors of worse pain and function after controlling for relevant covariates. Collectively, elevated distress appears to be a significant risk factor for reduced treatment benefit (i.e., less improvement in pain and disability) over short and medium-term follow-up periods in patients with sciatica. Future research should determine whether the prospective identification and treatment of patients with high levels of distress (a "yellow flag") is associated with improved treatment outcomes.
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Pain is a complex human trait. It is likely that the interaction of multiple genes, each with a small individual effect, along with the effect of environmental factors, influences the clinical efficacy of opioids rather than a single gene alone. Polymorphisms in genes coding for the mu-opioid receptor (A118G) and catechol-O-methyl transferase (Val158Met) may be important modulators of opioid efficacy. ⋯ When we explored for joint effects, we found that carriers of the OPRM1 AA and COMT Met/Met genotype required the lowest morphine dose to achieve pain relief (87 mg/24 h; 95%CI=57,116) and those with neither Met/Met nor AA genotype needed the highest morphine dose (147 mg/24 h; 95%CI=100,180). The significant joint effects for the Met/Met and AA genotypes (p<0.012) persisted, even after controlling for demographic and clinical variables in the multivariable analyses. Future studies are needed to further characterize the joint effects of multiple genes, along with demographic and clinical variables, in predicting opioid dose.
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Provoked vestibulodynia is a common cause of superficial dyspareunia in young women. Recent evidence has pointed out the importance of studying endogenous pain modulation in these women. An impairment of diffuse noxious inhibitory controls (DNIC) has been suggested in chronic pain conditions with a female predominance such as fibromyalgia and temporomandibular disorder. ⋯ No differences related to the intake of COC were observed between the healthy women. In conclusion, women with provoked vestibulodynia as well as healthy women irrespective of COC status display a DNIC response indicating an endogenous pain inhibition. However, the results imply a systemic hypersensitivity in women with vestibulodynia with low general pain thresholds as compared to healthy women.
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Impulse frequency and number of recruited central neurons are relevant for pain encoding and temporal as well as spatial summation of pain (SSP). Whereas SSP of heat-induced pain is well characterized, mechanical SSP (MSSP) has been less studied. MSSP may be relevant for chronic pain conditions like fibromyalgia (FM) and play an important role in the pathogenesis of this chronic pain syndrome. ⋯ Furthermore, muscle stimuli elicited more MSSP when separated by 8 cm than 4 cm and this finding was not different between NC and FM subjects. Thus, mechanisms of MSSP were similar for both FM and NC subjects. The important role of MSSP for pain encoding suggests that decreasing pain in some muscle areas by local anesthetics or other means may improve overall clinical pain of FM patients.