Articles: hyperalgesia.
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Comparative Study
Psychophysical and cerebral responses to heat stimulation in patients with central pain, painless central sensory loss, and in healthy persons.
Patients with central pain (CP) typically have chronic pain within an area of reduced pain and temperature sensation, suggesting an impairment of endogenous pain modulation mechanisms. We tested the hypothesis that some brain structures normally activated by cutaneous heat stimulation would be hyperresponsive among patients with CP but not among patients with a central nervous system lesion causing a loss of heat or nociceptive sensation with no pain (NP). We used H(2)(15)O positron emission tomography to measure, in 15 healthy control participants, 10 NP patients, and 10 CP patients, increases in regional cerebral blood flow among volumes of interest (VOI) from the resting (no stimulus) condition during bilateral contact heat stimulation at heat detection, heat pain threshold, and heat pain tolerance levels. ⋯ Compared with NP patients, CP patients had more hyperresponsive VOI in the intralaminar thalamus and sensory-motor cortex during heat stimulation. Our results show that focal CNS lesions produce bilateral sensory deficits and widespread changes in the nociceptive excitability of the brain. The increased nociceptive excitability within the intralaminar thalamus and sensory-motor cortex of our sample of CP patients suggests an underlying pathophysiology for the pain in some central pain syndromes.
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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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Though triptans are considered the standard of acute therapy for migraine attacks with headache-related disability, they are used by the minority of potentially eligible persons. Understanding the socio-demographic and headache features that predict triptan use may help to clarify barriers to optimal treatment. ⋯ Less than 1 in 5 persons with migraine in the United States who were respondents to this survey used triptans for acute headache treatment over the course of a year. Several markers of severe headache, including disability and allodynia,were associated with increased triptan use. Groups less likely to get triptans included males, African Americans, older adults, and the uninsured. Predictors of use provide insight into groups with unmet treatment needs.
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Painful diabetic neuropathy is a common complication of diabetes mellitus and can affect many aspects of life and severely limit patients' daily functions. Signals of painful diabetic neuropathy are believed to originate in the peripheral nervous system. However, its peripheral mechanism of hyperalgesia has remained elusive. ⋯ Delivery of low concentrations of tetrodotoxin and Nav1.8 selective blocker, A-803467 on the main axon of C-fibres was found to markedly enhance the conduction failure in a dose-dependent manner in diabetic rats. Upregulated expression of sodium channel subunits Nav1.7 and Nav1.8 in both small dorsal root ganglion neurons and peripheral C-fibres as well as enhanced transient and persistent sodium current and increased excitability in small dorsal root ganglion neurons from diabetic rats might underlie the reduced conduction failure in the diabetic high-firing-frequency polymodal nociceptive C-fibres. This study shed new light on the functional capability in the pain signals processing for the main axon of polymodal nociceptive C-fibres and revealed a novel mechanism underlying diabetic hyperalgesia.