The journal of pain : official journal of the American Pain Society
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Glia are now recognized as important contributors in pathological pain creation and maintenance. Spinal cord glia exhibit extensive gap junctional connectivity, raising the possibility that glia are involved in the contralateral spread of excitation resulting in mirror image pain. In the present experiments, the gap junction decoupler carbenoxolone was administered intrathecally after induction of neuropathic pain in response to sciatic nerve inflammation (sciatic inflammatory neuropathy) or partial nerve injury (chronic constriction injury). In both neuropathic pain models, a low dose of carbenoxolone reversed mirror image mechanical allodynia, while leaving ipsilateral mechanical allodynia unaffected. Ipsilateral thermal hyperalgesia was briefly attenuated. Critically, blockade of mechanical allodynia and thermal hyperalgesia was not observed in response to intrathecal glycyrrhizic acid, a compound similar to carbenoxolone in all respects but it does not decouple gap junctions. Thus, blockade of mechanical allodynia and thermal hyperalgesia by carbenoxolone does appear to reflect an effect on gap junctions. Examination of carbenoxolone's effects on intrathecal human immunodeficiency virus type 1 gp120 showed that blockade of pain facilitation might result, at least in part, via suppression of interleukin-1 and, in turn, interleukin-6. These data provide the first suggestion that spread of excitation via gap junctions might contribute importantly to inflammatory and traumatic neuropathic pain. ⋯ The current studies provide evidence for involvement of gap junctions in spinal cord pain facilitation. Intrathecal carbenoxolone, a gap junction decoupler, reversed neuropathy-induced mirror image pain and intrathecal gp120-induced allodynia. In addition, it decreased gp120-induced proinflammatory cytokines. This suggests gap junction activation might lead to proinflammatory cytokine release by distantly activated glia.
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Comparative Study
Development of a measure of the burden of pain due to herpes zoster and postherpetic neuralgia for prevention trials: adaptation of the brief pain inventory.
In preparation for clinical trials of a vaccine against herpes zoster (HZ), we conducted a prospective, observational study to evaluate (1) the Zoster Brief Pain Inventory (ZBPI), an HZ-specific questionnaire to quantify HZ pain and discomfort, (2) an operational definition of postherpetic neuralgia (PHN), and (3) a severity-duration measure of the burden of illness caused by HZ. HZ patients aged 60 years or older (n = 121) were enrolled within 14 days of rash onset and completed ZBPI, McGill Pain Questionnaire Present Pain Intensity (PPI), quality of life (QoL), and activities of daily living (ADL) questionnaires on a predetermined schedule. Reliability, measured by intraclass correlation coefficients within 14 days of rash onset, ranged between 0.63 and 0.78. ZBPI pain scores were strongly correlated with other pain measures, interference with ADL, and worsening QoL. The operational definition of PHN, a ZBPI pain score of 3 or greater occurring 90 or more days after rash onset, had high agreement with pain worse than mild on the PPI (kappa = 0.72). The ZBPI pain severity-duration measure had high correlations with severity-duration measures of ADL interference, worsening QoL, and other pain scales. These findings support the validity and utility of the ZBPI, the definition of PHN, and the severity-duration measure of the burden of HZ illness. ⋯ Herpes zoster pain, as measured by the ZBPI severity-duration measure, is associated with impairment in daily living activities and quality of life. The ZBPI measure appears useful for quantifying herpes zoster pain, postherpetic neuralgia, and impairment in daily living activities for clinical trials of herpes zoster prevention.
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Comparative Study
Ethnic differences in pain coping: factor structure of the coping strategies questionnaire and coping strategies questionnaire-revised.
Coping has been examined extensively in the pain literature, although coping instruments have been typically validated in clinical populations with little ethnic diversity. This study examined the factor structure of the Coping Strategies Questionnaire (CSQ) and the CSQ-Revised (CSQ-R) in 650 healthy male and female African American (44%) and white (56%) subjects and explored associations of coping to health and pain-related measures. Factor analyses revealed 6 components for each ethnic group, accounting for comparable amounts of variance and resembling previously reported CSQ subscales. Internal consistency for both ethnic groups was acceptable (0.72-0.91). There were significant main effects for ethnicity on 4 of the CSQ-R scales (P < .05). No ethnic differences in pain or health variables emerged, although when split into high-pain versus minimal-pain groups, differences were revealed on catastrophizing. Results indicate that the factor structure of the CSQ-R in healthy adults is similar to clinical populations and is comparable across African American and white subjects. Group differences on CSQ-R scales suggest potentially important ethnic influences on pain coping. These findings support the use of the CSQ-R to assess coping in African Americans and in healthy young adults. Additional clinical research is needed to determine the practical importance of group differences in pain coping. ⋯ Coping has been examined extensively in the pain literature, although coping instruments typically have been validated in clinical populations with little ethnic diversity. This study examines the factor structure of the CSQ-Revised in an ethnically diverse population and supports the use of the CSQ-R to assess coping in African Americans and in healthy young adults.
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Comparative Study
Population-based survey of pain in the United States: differences among white, African American, and Hispanic subjects.
A cross-sectional telephone survey was conducted in nationally representative probability sample of non-Hispanic white subjects, non-Hispanic African American subjects, and Hispanic subjects of any race to explore relationships between chronic pain and race or ethnicity. Approximately one third in each group reported "frequent or persistent pain" for 3 months or longer during the past year, and approximately one third of the 454 white subjects, 447 African American subjects, and 434 Hispanic subjects in the final sample experienced "disabling pain" (defined as both high severity and high functional interference). White subjects had pain longer but with lesser intensity than the other groups, and pain-related life interference did not vary. Significantly fewer Hispanic subjects (68%) than white subjects (82%) or African American subjects (85%) had visited a physician for pain, and African American subjects (81%) were more likely than white subjects (75%) or Hispanic subjects (63%) to have used prescription medications. Disabling pain was positively associated with female sex (odds ratio [OR], 1.45), income of $25,000 or less (OR, 1.71), less than a high school education (OR, 1.72), and divorce (OR, 1.69) and was negatively associated with younger age (18-34 years; OR, 0.68), income between $25,000 and $74,999 (OR, 0.64) or $75,000 or more (OR, 0.37), being employed (OR, 0.48), suburban residence (OR, 0.64), and having a college (OR, 0.51) or graduate (OR, 0.32) degree. Multivariate logistic regression found that income of $25,000 or less (OR, 2.54), less than a high school education (OR, 1.59), and being unemployed (OR, 1.50) remained significant when other factors were controlled. Neither race nor ethnicity predicted disabling pain, but the minorities had more characteristics identified as predictors. The data suggest that race and ethnicity contribute to clinical diversity, but socioeconomic disadvantage is the more important predictor of disabling pain. ⋯ Race and ethnicity influence the presentation and treatment of chronic pain. This study evaluated community-dwelling white, African American, and Hispanic subjects by using a sophisticated telephone survey methodology. Pain was highly prevalent across groups, and there were racial and ethnic differences in pain experience and treatment preferences. Race and ethnicity were not independently associated with severe pain, but both minorities were more likely to possess the socioeconomic and educational characteristics that were associated.
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Comparative Study
Body pain area and pain-related negative affect predict clinical pain intensity in patients with fibromyalgia.
Patients with fibromyalgia (FM) report widespread chronic musculoskeletal pain. Palpation of 9 paired tender points (TPs) is commonly used for the diagnosis of FM according to criteria specified by the American College of Rheumatology. Although TP palpation can be used to assess deep tissue hypersensitivity, it has failed as a reliable indicator of clinical pain intensity in FM. The sum of local areas of pain (SLAP) obtained from a body pain diagram represents a relevant measure of the spatial extent of clinical pain, a feature most likely important for FM pain. Because spatial summation of pain can be an important determinant of clinical pain intensity, we hypothesized that this measure would predict clinical pain intensity in FM patients. Because pain is strongly associated with negative emotions, we evaluated the relationship of pain-related negative affect (PRNA) with clinical pain intensity in FM. The independent contributions of SLAP, PRNA, and TP count to the variance of clinical pain intensity were assessed in 280 FM patients. Clinical pain intensity of 280 FM patients was measured by using a visual analogue scale. FM patients shaded all painful body areas on body pain diagrams. Dolorimetry was used for TP evaluations. PRNA was assessed with the Medical College of Virginia Pain Questionnaire. Hierarchical linear regression was used to test the association of SLAP, TPs, and PRNA with clinical pain intensity. FM patients' mean visual analogue scale rating (0 to 100) of usual clinical pain was 50.1. Mean SLAP, TP count, and PRNA were 11.4, 16.0, and 44.3, respectively. Hierarchical linear regression analysis identified SLAP, TP count, and PRNA as independent predictors of clinical pain that accounted for 45% of the variance in clinical pain intensity ratings in FM patients. Consistent with the literature, TP count predicted only a small part (4%) of this variance. Our statistical model of body pain areas and negative affect predicts a large portion of the variance of pain intensity in FM. This result suggests that the extent of pain areas and negative emotions are uniquely associated with clinical pain intensity in FM. ⋯ The number of painful body areas obtained by body pain diagrams is a better predictor of clinical pain intensity than TPs in FM patients. The combination of painful body areas, TP counts, and PRNA predicts 45% of the clinical pain intensity of FM patients. This finding might be useful for clinical evaluations of FM patients.