The journal of pain : official journal of the American Pain Society
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Randomized Controlled Trial Multicenter Study
Lenalidomide for complex regional pain syndrome type 1: lack of efficacy in a phase II randomized study.
Complex regional pain syndrome (CRPS) is a potentially debilitating chronic pain syndrome with a poorly understood but likely neuroimmune/multifactorial pathophysiology associated with axonal injury. Based on the potential contribution of proinflammatory cytokines to CRPS pathogenesis and prior research with thalidomide, we investigated lenalidomide, a thalidomide derivative, for CRPS treatment. We conducted a phase II, randomized, double-blind, placebo-controlled study to evaluate the efficacy of oral lenalidomide 10 mg once daily in consenting patients with unilateral or bilateral CRPS type 1. The study comprised 12 weeks of treatment followed by a long-term extension. The primary efficacy outcome was reduced pain in the index limb, defined as ≥30% improvement from baseline using an 11-point numeric rating scale. One hundred eighty-four subjects enrolled. The primary endpoint was not met because equal proportions of treated (16.1%) and control (16.1%) subjects achieved the outcome; however, lenalidomide was well tolerated, with no evidence of neuropathy or major adverse effects. This study is the largest controlled, blinded clinical trial in subjects with chronic CRPS using the Budapest research criteria. It demonstrates the feasibility of conducting high-quality clinical trials in CRPS type 1 and provides considerations for designing future trials. ⋯ This article reports an adequately powered, controlled clinical trial in subjects with CRPS. Treatment and placebo were equally effective, but the study demonstrated that lenalidomide treatment is feasible in this population. The study provides examples to consider in designing future CRPS trials.
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Randomized Controlled Trial
Repetitive transcranial magnetic stimulation of the left premotor/dorsolateral prefrontal cortex does not have analgesic effect on central poststroke pain.
Central poststroke pain (CPSP) is caused by an encephalic vascular lesion of the somatosensory pathways and is commonly refractory to current pharmacologic treatments. Repetitive transcranial magnetic stimulation (rTMS) of the premotor cortex/dorsolateral prefrontal cortex (PMC/DLPFC) can change thermal pain threshold toward analgesia in healthy subjects and has analgesic effects in acute postoperative pain as well as in fibromyalgia patients. However, its effect on neuropathic pain and in CPSP, in particular, has not been assessed. The aim of this prospective, double-blind, placebo-controlled study was to evaluate the analgesic effect of PMC/DLPFC rTMS in CPSP patients. Patients were randomized into 2 groups, active (a-) rTMS and sham (s-) rTMS, and were treated with 10 daily sessions of rTMS over the left PMC/DLPFC (10 Hz, 1,250 pulses/d). Outcomes were assessed at baseline, during the stimulation phase, and at 1, 2, and 4 weeks after the last stimulation. The main outcome was pain intensity changes measured by the visual analog scale on the last stimulation day compared to baseline. Interim analysis was scheduled when the first half of the patients completed the study. The study was terminated because of a significant lack of efficacy of the active arm after 21 patients completed the whole treatment and follow-up phases. rTMS of the left PMC/DLPFC did not improve pain in CPSP. ⋯ The aim of this double-blind, placebo-controlled study was to evaluate the analgesic effects of rTMS to the PMC/DLPFC in CPSP patients. An interim analysis showed a consistent lack of analgesic effect, and the study was terminated. rTMS of the PMC/DLPFC is not effective in relieving CPSP.
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The amygdala contributes to the generation of pain affect, and the amygdaloid central nucleus (CeA) receives nociceptive input that is mediated by glutamatergic neurotransmission. The present study compared the contribution of N-methyl-d-aspartate (NMDA) receptor agonism and antagonism in the CeA to generation of the affective response of rats to an acute noxious stimulus. Vocalizations that occur following a brief tail shock (vocalization afterdischarges) are a validated rodent model of pain affect and were preferentially suppressed, in a dose-dependent manner, by bilateral injection into the CeA of NMDA (.1, .25, .5, or 1 μg/side) or the NMDA receptor antagonist d-(-)-2-amino-5-phosphopentanoic acid (AP5; 1, 2, or 4 μg/side). Vocalizations that occur during tail shock were suppressed to a lesser degree, whereas spinal motor reflexes (tail flick and hind limb movements) were unaffected by injection of NMDA or AP5 into the CeA. Injection of NMDA, but not AP5, into the CeA increased c-Fos immunoreactivity in the ventrolateral periaqueductal gray, and unilateral injection of the μ-opiate receptor antagonist H-d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP; .25 μg) into ventrolateral periaqueductal gray prevented the antinociception generated by injection of NMDA into the CeA. These findings demonstrate that although NMDA receptor agonism and antagonism in the CeA produce similar suppression of pain behaviors, they do so via different neurobiologic mechanisms. ⋯ The amygdala contributes to production of the emotional dimension of pain. NMDA receptor agonism and antagonism within the CeA suppressed rats' emotional response to acute painful stimulation. Understanding the neurobiology underlying emotional responses to pain will provide insights into new treatments for pain and its associated affective disorders.
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Chronic pain represents an immense clinical problem. With tens of millions of people in the United States alone suffering from the burden of debilitating chronic pain, there is a moral obligation to reduce this burden by improving the understanding of pain and treatment mechanisms, developing new therapies, optimizing and testing existing therapies, and improving access to evidence-based pain care. Here, we present a goal-oriented research agenda describing the American Pain Society's vision for pain research aimed at tackling the most pressing issues in the field. ⋯ This article presents the American Pain Society's view of some of the most important research questions that need to be addressed to advance pain science and to improve care of patients with chronic pain.
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Most clinically used opioids are mu-opioid receptor agonists. Therefore, genetic variation of the OPRM1 gene that encodes the mu-opioid receptor is of great interest for understanding pain management. A polymorphism 118A>G (rs1799971) within the OPRM1 gene results in a missense mutation and affects the function of the receptor. We studied the association between the 118A>G polymorphism and oxycodone analgesia and pain sensitivity in 1,000 women undergoing breast cancer surgery. Preoperatively, experimental cold and heat pain sensitivities were tested. Postoperative pain was assessed at rest and during motion. Intravenous oxycodone analgesia was titrated first by a research nurse and on the ward using a patient-controlled analgesia device. The primary endpoint was the amount of oxycodone needed for the first state of adequate analgesia. For each patient, the 118A>G polymorphism was genotyped using the Sequenom MassARRAY (Sequenom, San Diego, CA). The association between this variant and the pain phenotypes was tested using linear regression. The 118A>G variant was associated significantly with the amount of oxycodone requested for adequate analgesia (P = .003, β = .016). Collectively, oxycodone consumption was highest in individuals having the GG genotype (.16 mg/kg), lowest for those with the AA genotype (.12 mg/kg), and moderate for those having the AG genotype (.13 mg/kg). Furthermore, the G allele was associated with higher postoperative baseline pain ratings (P = .001, β = .44). No evidence of association with other pain phenotypes examined was observed. ⋯ This study demonstrates that the OPRM1 118A>G polymorphism was associated with the amount of oxycodone required in the immediate postoperative period. Although a significant factor for determining oxycodone requirement, the 118A>G polymorphism alone explained less than 1% of the variance. No association was found between 118A>G and experimental pain