The journal of pain : official journal of the American Pain Society
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Central sensitization is one form of long-term plasticity in the central nervous system. Sustained activation of primary sensory fibers supplying dorsal horn can induce long-lasting increases in the discharge amplitude of primary afferent synapses. This is similar to the long-term potentiation that occurs in many other CNS regions. Drugs that limit the short-duration wind-up component of central sensitization include sodium channel blockers, NMDA antagonists, fast-acting opioids and the calcium-channel ligands gabapentin and pregabalin (S-3-(aminomethyl)-5-methylhexanoic acid). Pregabalin, like gabapentin, binds selectively to the Ca(V)α₂δ auxiliary subunit of presynaptic voltage-gated calcium channels. The conformational changes induced by this binding inhibit abnormally intense neuronal activity by reducing the synaptic release of glutamate and other neurotransmitters. Recent identification in animal models of increased Ca(V)α₂δ protein expression in chronic pain, allodynia, and hyperalgesia have drawn additional interest to drugs that bind the Ca(V)α₂δ site. Experimental studies with animal models and healthy human volunteers have shown that pregabalin reduces nociceptive responses, particularly in conditions involving central sensitization. Since these actions occur with relatively modest effects on physiological and cognitive functions, pregabalin may be an important consideration in the pharmacotherapy of otherwise difficult-to-treat pain syndromes. ⋯ This focus article discusses how the central nervous system plasticity phenomenon, central sensitization, is established in the induction and maintenance of chronic pain, allodynia, and hyperalgesia. In addition, it explores the neurophysiologic actions of the calcium-channel ligands gabapentin and pregabalin in limiting pathological manifestations of central sensitization.
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Emotional states have been shown to influence resilient behavior in conditions of loss, bereavement, and stress. Positive affect has been associated with better health outcomes, including chronic pain. Extant research suggests that positive emotions help buffer against stress, suggesting that positive emotions provide an important protective and adaptive significance. This study examined the role of positive versus negative emotions in the association between pain-related coping efficacy and interference with social functioning in a sample of chronic pain patients. Mediational analyses revealed that positive emotions partially mediated the relationship between control and coping efficacy and pain-related interference in social activities. Negative emotions were not found to mediate this relationship. Implications for research on the role of positive emotions in chronic pain are discussed. ⋯ The findings from this study demonstrate the mediating role of positive affect in explaining the relationship between pain-related coping efficacy and interference in social functioning in a sample of chronic pain patients. This could potentially assist clinicians who seek to enhance coping efficacy and social functioning in pain patients.
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Endogenous cannabinoids and peripheral cannabinoid CB2 receptors (CB2Rs) are involved in the antinociceptive effect of electroacupuncture (EA) on inflammatory pain. However, it remains unclear about how EA affects the expression and distribution patterns of peripheral CB2Rs in inflamed skin tissues. To study this, inflammatory pain was induced by local injection of complete Freund's adjuvant into the hindpaw of rats. The mRNA and protein levels of CB2Rs were quantified by using RTPCR and Western blotting, respectively. The distribution of CB2Rs on keratinocytes and immune cells recruited to the inflamed skin tissues was determined by using double-immunofluorescence labeling. Induction of tissue inflammation significantly increased the mRNA and protein levels of CB2Rs in the skin tissue. Also, both 2 Hz and 100 Hz EA, applied to GB30 and GB34, significantly increased the mRNA and protein levels of CB2Rs in inflamed tissues compared to the sham EA group. CB2Rimmunoreactivities were mainly distributed in keratinocytes, macrophages, and T-lymphocytes in the epidermis and dermis of the inflamed skin tissue. Inflammation caused a significant increase in the number of CB2R-immunoreactive keratinocytes, macrophages, and T-lymphocytes. Furthermore, compared to the sham EA group, EA at 2 or 100 Hz significantly increased the number of keratinocytes, macrophages, and T-lymphocytes with CB2R-immunoreactivity in the inflamed skin tissue. Therefore, our findings suggest that EA is associated with upregulation of local CB2Rs in the inflamed skin tissue. EA primarily potentiates the expression of CB2Rs on keratinocytes and infiltrating inflammatory cells at the site of inflammation. ⋯ This study shows that electroacupuncture increases the CB2 receptor expression on keratinocytes and infiltrating inflammatory cells in inflammatory skin tissues. This finding provides new evidence showing the potential role of CB2 receptors in the analgesic effect of acupuncture on inflammatory pain.
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Randomized Controlled Trial Multicenter Study
Duloxetine versus placebo in patients with chronic low back pain: a 12-week, fixed-dose, randomized, double-blind trial.
This randomized, double-blind, placebo-controlled study assessed efficacy and safety of duloxetine in patients with chronic low back pain (CLBP). Adults (n = 401) with a nonneuropathic CLBP and average pain intensity of ≥ 4 on an 11-point numerical scale (Brief Pain Inventory [BPI]) were treated with either duloxetine 60 mg once daily or placebo for 12 weeks. The primary measure was BPI average pain. Secondary endpoints included Patient's Global Impressions of Improvement (PGI-I), Roland Morris Disability Questionnaire (RMDQ-24), BPI-Severity (BPI-S), BPI-Interference (BPI-I), and response rates (either ≥ 30% or ≥ 50% BPI average pain reduction at endpoint). Health outcomes included Short Form-36, European Quality of Life-5 Dimensions, and the Work Productivity and Activity Impairment questionnaire. Safety and tolerability were assessed. Compared with placebo-treated patients, duloxetine-treated patients reported a significantly greater reduction in BPI average pain (P ≤ .001). Similarly, duloxetine-treated patients reported significantly greater improvements in PGI-I, BPI-S, BPI-I, 50% response rates, and some health outcomes. The RMDQ and 30% response rate showed numerical improvements with duloxetine treatment. Significantly more patients in the duloxetine group (15.2%) than patients in the placebo group (5.4%) discontinued because of adverse events (P = .002). Nausea and dry mouth were the most common treatment-emergent adverse events with rates significantly higher in duloxetine-treated patients. ⋯ This study provides clinical evidence of the efficacy and safety of duloxetine at a fixed dose of 60 mg once daily in the treatment of chronic low back pain (CLBP). As of December 2009, duloxetine has not received regulatory approval for the treatment of CLBP.
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Multicenter Study Clinical Trial
Initial Psychometric Properties of the Pain Care Quality Survey (PainCQ).
This study examined the psychometric properties of the Pain Care Quality (PainCQ) survey, a new instrument to measure the quality of nursing and interdisciplinary care related to pain management. Hospitalized medical/surgical oncology patients with pain from 3 states completed the 44-item version of the PainCQ survey following completion of a nursing shift. Interdisciplinary items were evaluated over the entire hospital stay; nursing care was evaluated during the previous shift. The sample included 109 patients ranging in age from 20 to 84 (mean = 53.09). The sample was 58.7% female, 88% non-Hispanic white. Principal Axis Factoring with an oblimin rotation was used as factors were correlated. Two scales resulted. The PainCQ-Interdisciplinary scale included 11 items representing 2 constructs and explaining 47.1% of shared item variance: partnership with the health care team (k = 6 items; α = .85) and comprehensive interdisciplinary pain care (k = 5 items; α = .76). The PainCQ-Nursing scale measured three constructs and explained 60.8 % of shared item variance: being treated right (k = 15 items; α = .95), comprehensive nursing pain care (k = 3 items; α = .77), and efficacy of pain management (k =4 items; α = .87). Results supported the internal consistency reliability and structural validity of the PainCQ survey with 33 items. ⋯ This article presents the psychometric properties of a new tool to measure interdisciplinary and nursing care quality related to pain management from the patient's perspective. This tool can be used for research and as a clinical performance measure to monitor and improve quality of care and patient outcomes.