The journal of pain : official journal of the American Pain Society
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Several brain stimulation technologies are beginning to evidence promise as pain treatments. However, traditional versions of 1 specific technique, transcranial direct current stimulation (tDCS), stimulate broad regions of cortex with poor spatial precision. A new tDCS design, called high definition tDCS (HD-tDCS), allows for focal delivery of the charge to discrete regions of the cortex. We sought to preliminarily test the safety and tolerability of the HD-tDCS technique as well as to evaluate whether HD-tDCS over the motor cortex would decrease pain and sensory experience. Twenty-four healthy adult volunteers underwent quantitative sensory testing before and after 20 minutes of real (n = 13) or sham (n = 11) 2 mA HD-tDCS over the motor cortex. No adverse events occurred and no side effects were reported. Real HD-tDCS was associated with significantly decreased heat and cold sensory thresholds, decreased thermal wind-up pain, and a marginal analgesic effect for cold pain thresholds. No significant effects were observed for mechanical pain thresholds or heat pain thresholds. HD-tDCS appears well tolerated, and produced changes in underlying cortex that are associated with changes in pain perception. Future studies are warranted to investigate HD-tDCS in other applications, and to examine further its potential to affect pain perception. ⋯ This article presents preliminary tolerability and efficacy data for a new focal brain stimulation technique called high definition transcranial direct current stimulation. This technique may have applications in the management of pain.
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Little is known about whether patients with chronic pain treated with opioids experience craving for their medications, whether contextual cues may influence craving, or if there is a relationship between craving and medication compliance. We hypothesized that craving for prescription opioids would be significantly correlated with the urge for more medication, preoccupation with the next dose, and current mood symptoms. We studied craving in 62 patients with chronic pain who were at low or high risk for opioid misuse, while they were enrolled in an RCT to improve prescription opioid medication compliance. Using electronic diaries, patients completed ratings of craving at monthly clinic visits and daily during a 14-day take-home period. Both groups consistently endorsed craving, whose levels were highly correlated (P < .001) with urge, preoccupation, and mood. The intervention to improve opioid compliance in the high-risk group was significantly associated with a rate of decrease in craving over time in comparison to a high-risk control group (P < .05). These findings indicate that craving is a potentially important psychological construct in pain patients prescribed opioids, regardless of their level of risk to misuse opioids. Targeting craving may be an important intervention to decrease misuse and improve prescription opioid compliance. ⋯ Patients with noncancer pain can crave their prescription opioids, regardless of their risk for opioid misuse. We found craving to be highly correlated with the urge to take more medication, fluctuations in mood, and preoccupation with the next dose, and to diminish with a behavioral intervention to improve opioid compliance.
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Clinical Trial
Muscle pain differentially modulates short interval intracortical inhibition and intracortical facilitation in primary motor cortex.
Excitability of the motor cortex can be suppressed during muscle pain. Yet the mechanisms are largely unknown. Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were examined as possible candidate mechanisms to underpin this change. SICI and ICF were investigated in 11 healthy individuals before, during and after infusion of hypertonic saline into right first dorsal interosseous (FDI). Using paired-pulse transcranial magnetic stimulation (TMS), interstimulus intervals of 2, 3, and 13 ms were investigated. Pain intensity and quality were recorded using a 10-cm visual analogue scale and the McGill Pain Questionnaire. Resting motor threshold and motor-evoked potentials (MEPs) to single TMS stimuli were recorded before and after pain. Electromyographic recordings were made from right FDI and abductor digiti minimi. Participants reported an average pain intensity of 5.8 (1.6) cm. MEP amplitudes decreased in both muscles. Compared with the pre-pain condition, SICI was increased following pain, but not during. ICF was decreased both during and after pain when compared with the pre-pain condition. These findings suggest that muscle pain differentially modulates SICI and ICF. Although the functional relevance is unknown, we hypothesize decreased facilitation and increased inhibition may contribute to the restriction of movement of a painful body part. ⋯ This article provides evidence for decreased intracortical facilitation and increased short interval intracortical inhibition in response to muscle pain. This finding is relevant to clinicians as a mechanism which may underlie restricted movement in acute and chronic pain.
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We previously demonstrated that a single injection of diluted bee venom (DBV) temporarily alleviates thermal hyperalgesia, but not mechanical allodynia, in neuropathic rats. The present study was designed to determine whether repetitive injection of DBV produces more potent analgesic effects on neuropathy-induced nociception and whether those effects are associated with increased neuronal activity in the locus coeruleus (LC) and with the suppression of spinal NMDA receptor NR1 subunit phosphorylation (pNR1). DBV (.25 mg/kg) was administered subcutaneously twice a day for 2 weeks beginning on day 15 post-chronic constrictive injury surgery. Pain responses were examined and potential changes in LC Fos expression and spinal pNR1 expression were determined. Repetitive DBV administration significantly reduced mechanical allodynia, as well as thermal hyperalgesia. The activity of LC noradrenergic neurons was increased and spinal pNR1 expression was significantly suppressed by repetitive DBV as compared with those of vehicle or single DBV injection. These suppressive effects of repetitive DBV on neuropathic pain and spinal pNR1 were prevented by intrathecal pretreatment of idazoxan, an alpha-2 adrenoceptor antagonist. These results indicate that repetitive DBV produces potent analgesic effects on neuropathic pain and this is associated with the activation of the LC noradrenergic system and with a reduction in spinal pNR1. ⋯ The results of current study demonstrate that repetitive administration of DBV significantly suppresses neuropathic pain. Furthermore, this study provides mechanistic information that repetitive treatment of DBV can produce more potent analgesic effect than single DBV treatment, indicating a potential novel strategy for the management of chronic pain.
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Randomized Controlled Trial
The interruptive effect of pain in a multitask environment: an experimental investigation.
Daily life is characterized by the need to stop, start, repeat, and switch between multiple tasks. Here, we experimentally investigate the effects of pain, and its anticipation, in a multitask environment. Using a task-switching paradigm, participants repeated and switched between 3 tasks, of which 1 predicted the possible occurrence of pain. Half of the participants received low intensity pain (N = 30), and half high intensity pain (N = 30). Results showed that pain interferes with the performance of a simultaneous task, independent of the pain intensity. Furthermore, pain interferes with the performance on a subsequent task. These effects are stronger with high intensity pain than with low intensity pain. Finally, and of particular importance in this study, interference of pain on a subsequent task was larger when participants switched to another task than when participants repeated the same task. ⋯ This article is concerned with the interruptive effect of pain on people's task performance by using an adapted task-switching paradigm. This adapted paradigm may offer unique possibilities to investigate how pain interferes with task performance while people repeat and switch between multiple tasks in a multitask environment.