The journal of pain : official journal of the American Pain Society
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Persistent pain following breast cancer surgery is a significant clinical problem. Although immune mechanisms may play a role in the development and maintenance of persistent pain, few studies have evaluated for associations between persistent breast pain following breast cancer surgery and variations in cytokine genes. In this study, associations between previously identified extreme persistent breast pain phenotypes (ie, no pain vs severe pain) and single nucleotide polymorphisms (SNPs) spanning 15 cytokine genes were evaluated. In unadjusted analyses, the frequency of 13 SNPs and 3 haplotypes in 7 genes differed significantly between the no pain and severe pain classes. After adjustment for preoperative breast pain and the severity of average postoperative pain, 1 SNP (ie, interleukin [IL] 1 receptor 2 rs11674595) and 1 haplotype (ie, IL10 haplotype A8) were associated with pain group membership. These findings suggest a role for cytokine gene polymorphisms in the development of persistent breast pain following breast cancer surgery. ⋯ This study evaluated for associations between cytokine gene variations and the severity of persistent breast pain in women following breast cancer surgery. Variations in 2 cytokine genes were associated with severe breast pain. The results suggest that cytokines play a role in the development of persistent postsurgical pain.
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Randomized Controlled Trial
Spinal manipulative therapy-specific changes in pain sensitivity in individuals with low back pain (NCT01168999).
Spinal manipulative therapy (SMT) is effective for some individuals experiencing low back pain; however, the mechanisms are not established regarding the role of placebo. SMT is associated with changes in pain sensitivity, suggesting related altered central nervous system response or processing of afferent nociceptive input. Placebo is also associated with changes in pain sensitivity, and the efficacy of SMT for changes in pain sensitivity beyond placebo has not been adequately considered. We randomly assigned 110 participants with low back pain to receive SMT, placebo SMT, placebo SMT with the instructional set "The manual therapy technique you will receive has been shown to significantly reduce low back pain in some people," or no intervention. Participants receiving the SMT and placebo SMT received their assigned intervention 6 times over 2 weeks. Pain sensitivity was assessed prior to and immediately following the assigned intervention during the first session. Clinical outcomes were assessed at baseline and following 2 weeks of participation in the study. Immediate attenuation of suprathreshold heat response was greatest following SMT (P = .05, partial η(2) = .07). Group-dependent differences were not observed for changes in pain intensity and disability at 2 weeks. Participant satisfaction was greatest following the enhanced placebo SMT. This study was registered at www.clinicaltrials.gov under the identifier NCT01168999. ⋯ The results of this study indicate attenuation of pain sensitivity is greater in response to SMT than the expectation of receiving an SMT. These findings suggest a potential mechanism of SMT related to lessening of central sensitization and may indicate a preclinical effect beyond the expectations of receiving SMT.
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Randomized Controlled Trial
Latent myofascial trigger points are associated with an increased intramuscular electromyographic activity during synergistic muscle activation.
The aim of this study was to evaluate intramuscular muscle activity from a latent myofascial trigger point (MTP) in a synergistic muscle during isometric muscle contraction. Intramuscular activity was recorded with an intramuscular electromyographic (EMG) needle inserted into a latent MTP or a non-MTP in the upper trapezius at rest and during isometric shoulder abduction at 90° performed at 25% of maximum voluntary contraction in 15 healthy subjects. Surface EMG activities were recorded from the middle deltoid muscle and the upper, middle, and lower parts of the trapezius muscle. Maximal pain intensity and referred pain induced by EMG needle insertion and maximal pain intensity during contraction were recorded on a visual analog scale. The results showed that higher visual analog scale scores were observed following needle insertion and during muscle contraction for latent MTPs than non-MTPs (P < .01). The intramuscular EMG activity in the upper trapezius muscle was significantly higher at rest and during shoulder abduction at latent MTPs compared with non-MTPs (P < .001). This study provides evidence that latent MTPs are associated with increased intramuscular, but not surface, EMG amplitude of synergist activation. The increased amplitude of synergistic muscle activation may result in incoherent muscle activation pattern of synergists inducing spatial development of new MTPs and the progress to active MTPs. ⋯ This article presents evidence of increased intramuscular, but not surface, muscle activity of latent MTPs during synergistic muscle activation. This incoherent muscle activation pattern may overload muscle fibers in synergists during muscle contraction and may contribute to spatial pain propagation.
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Postherpetic neuralgia (PHN) is one of the most severe sequelae of herpes zoster events. Several risk factors have been reported for PHN, including old age, severe skin rash, and intense pain. This study therefore aims to evaluate the usefulness of the Self-completed Leeds Assessment of Neuropathic Symptoms and Signs pain scale (S-LANSS) in conjunction with previously reported risk factors for predicting PHN. A group of herpes zoster patients (N = 305) were included in the cohort study. Subjects were asked for their demographic information, clinical symptoms and signs, intensity of pain by visual analog scale (VAS), and S-LANSS. They were followed up in clinical visits or via telephone for 12 months. Nineteen patients (6.2%) suffered from PHN in this study. Using logistic regression, 3 risk factors for PHN were identified: age ≥70 years, high VAS scores, and high S-LANSS scores. Prediction of PHN using VAS (≥8) and S-LANSS (≥15) criteria achieved a sensitivity of 78.9% and specificity of 78.0%. Prediction of PHN in elderly patients (≥70 years), using the criteria of VAS (≥6) and S-LANSS (≥15) as well, achieved 100% sensitivity and 57.1% specificity. S-LANSS could be a useful prediction tool for PHN, particularly if combined with previously well-known risk factors and VAS. ⋯ Among acute herpes zoster patients, subjects with characteristics of neuropathic pain showed high frequency of PHN. The tools for screening neuropathic pain like S-LANSS could be helpful for predicting PHN and enabling early intervention of pain management.
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Neurobiological evidence points to altered central nervous system processing of nociceptive stimuli in fibromyalgia. Enzymes like catechol-O-methyl-transferase (COMT) are involved in the elimination of catecholamines playing a possible role in central sensitization and pain. We used quantitative sensory testing to evidence central sensitization in fibromyalgia patients and test whether COMTVal158Met polymorphism, associated with a reduction in enzyme activity, plays a role in sensitized patients. Pain evaluation and quantitative sensory testing were performed including the spinal nociceptive flexion reflex, a physiologic correlate for the evaluation of central nociceptive pathways. Quality of life and distress questionnaires were used. A total of 137 fibromyalgia patients were assessed and compared to 99 matched controls. Central sensitization (nociceptive flexion reflex <27 mA) was present in 95/134 (71%) patients. Among them, COMT p.Val158Met polymorphism displayed a significant linear "genotype effect" (P = .033), with the Met/Met (mean = 17.8 ± 4.8 mA) and Val/Val (mean = 21.4 ± 4.6 mA) subgroups at the opposite ends of the nociceptive flexion reflex threshold (Met/Met vs Val/Val P = .015) and the Val/Met subgroup (mean = 19 ± 4.9 mA) in between (Val/Met vs Val/Val P = .041). Spontaneous moderate to severe pain was more likely to be associated with COMT Met/Met genotype. Patients showed important emotional distress compared to controls. In sensitized patients, the COMT Met/Met subgroup showed systematically-though not significantly-worse scores for all psychological variables. ⋯ The association between COMT p.Val158Met polymorphism and central sensitization in fibromyalgia is essential as it refers to the severity of central sensitization and may be a risk factor for treatment outcome.