Pain
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Randomized Controlled Trial Comparative Study
Lidocaine patch (5%) produces a selective, but incomplete block of Aδ and C fibers.
Topical lidocaine (5%) leads to sufficient pain relief in only 29%-80% of treated patients, presumably by small-fiber block. The reasons for nonresponse are unclear; it may be due to different underlying pain mechanisms or partly insufficient anesthetic effect. Using quantitative sensory testing (QST) following the protocol of the DFNS (German Research Network on Neuropathic Pain), this study aims to assess the type and extent of somatosensory changes after lidocaine application in healthy volunteers. ⋯ Interindividually, the extent of the small-fiber block varied widely (eg, thermal detection thresholds: in 54% of the subjects there were only minimal changes; in only 8% were there changes of >60% of the maximal achievable value). Topical lidocaine (5%) induces thermal hypoesthesia and pinprick hypoalgesia, suggesting an isolated but only partial block of Aδ and C fibers of unpredictable extent. Further studies must analyze the influencing factors and determine whether patients with poor analgesic effect, in particular, are those with insufficient small-fiber block.
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Randomized Controlled Trial
Experimental characterization of the effects of acute stresslike doses of hydrocortisone in human neurogenic hyperalgesia models.
Relative hypothalamic-pituitary-adrenal axis dysfunction has been described as a common feature of several dysfunctional pain syndromes, and its end hormone cortisol may thus constitute a protective factor against the development of chronic pain. We investigated the potential influence of experimentally induced stress-like hypercortisolism on the induction of neurogenic hyperalgesia using 2 human surrogate models: secondary hyperalgesia after intradermal capsaicin injection into the volar forearm, and perceptual windup in normal skin. In a double-blind, placebo-controlled, randomized, crossover study, a psychophysical study was performed in 10 healthy subjects (median age 23 years) examining the effects of 40 mg orally administered hydrocortisone. ⋯ Temporal summation (windup) to mechanical pain stimuli and electrically induced windup of second pain (tested in an independent cohort of 10 other subjects) were also unchanged. The selective effects of hydrocortisone on pinprick hyperalgesia but not pinprick pain suggest an antihyperalgesic rather than analgesic effect. The findings suggest that hypothalamic-pituitary-adrenal axis reactivity might be an important mechanism in resilience to dysfunctional pain syndromes.
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Randomized Controlled Trial
Effect of intravenous tropisetron on modulation of pain and central hypersensitivity in chronic low back pain patients.
The activation of 5-hydroxytryptamine-3 (5-HT-3) receptors in spinal cord can enhance intrinsic spinal mechanisms of central hypersensitivity, possibly leading to exaggerated pain responses. Clinical studies suggest that 5-HT-3 receptor antagonists may have an analgesic effect. This randomized, double-blind, placebo-controlled crossover study tested the hypothesis that the 5-HT-3 receptor antagonist tropisetron attenuates pain and central hypersensitivity in patients with chronic low back pain. ⋯ However, there was no statistically significant difference between tropisetron and placebo in VAS scores. Compared to placebo, tropisetron produced a statistically significant increase in pain threshold after single electrical stimulation, but no difference in all other secondary outcomes was found. A single-dose intravenous administration of tropisetron in patients with chronic low back pain had no significant specific effect on intensity of pain and most parameters of central hypersensitivity.
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Multicenter Study
Patient perspective on herpes zoster and its complications: an observational prospective study in patients aged over 50 years in general practice.
Understanding the effect of herpes zoster and zoster-related pain should inform care to improve health-related quality of life in elderly patients. A 12-month, longitudinal, prospective, multicenter observational study conducted in primary care in France enrolled patients aged ≥ 50 years with acute eruptive herpes zoster. Patient-reported zoster-related pain was assessed by validated questionnaires (Douleur Neuropathique en 4 Questions [DN4], Zoster Brief Pain Inventory [ZBPI], and Neuropathic Pain Symptom Inventory [NPSI]) on days 0 and 15, and at months 1, 3, 6, 9, and 12. ⋯ Patients with persistent pain had lower scores on the physical and mental component summaries of the SF-12 and the ZBPI interference score than those without pain. By logistic regression analysis, main predictive factors on day 0 for postherpetic neuralgia at month 3 were age, male sex, ZBPI interference score, Physical Component Summary score of the SF-12, and neuropathic quality of pain (DN4 score ≥ 4). Despite early diagnosis and treatment with antiviral agents, many patients with herpes zoster experience persistent pain and marked long-term reduction in health-related quality of life.
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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.