Pain
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Comparative Study
Neural mechanisms mediating the effects of expectation in visceral placebo analgesia: an fMRI study in healthy placebo responders and nonresponders.
This functional magnetic resonance imaging study analysed the behavioural and neural responses during expectation-mediated placebo analgesia in a rectal pain model in healthy subjects. In N=36 healthy subjects, the blood oxygen level-dependent (BOLD) response during cued anticipation and painful rectal stimulation was measured. Using a within-subject design, placebo analgesia was induced by changing expectations regarding the probability of receiving an analgesic drug to 0%, 50%, and 100%. ⋯ Compared with nonresponders, responders demonstrated greater placebo-induced decreases in activation of dorsolateral prefrontal cortex during anticipation and in somatosensory cortex, posterior cingulate cortex, and thalamus during pain. In conclusion, the expectation of pain relief can substantially change perceived painfulness of visceral stimuli, which is associated with activity changes in the thalamus, prefrontal, and somatosensory cortices. Placebo analgesia constitutes a paradigm to elucidate psychological components of the pain response relevant to the pathophysiology and treatment of chronic abdominal pain.
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Randomized Controlled Trial Multicenter Study Comparative Study
Practice, practitioner, or placebo? A multifactorial, mixed-methods randomized controlled trial of acupuncture.
The nonspecific effects of acupuncture are well documented; we wished to quantify these factors in osteoarthritic (OA) pain, examining needling, the consultation, and the practitioner. In a prospective randomised, single-blind, placebo-controlled, multifactorial, mixed-methods trial, 221 patients with OA awaiting joint replacement surgery were recruited. Interventions were acupuncture, Streitberger placebo acupuncture, and mock electrical stimulation, each with empathic or nonempathic consultations. ⋯ Needle and nonneedle placebos are equivalent. An unknown characteristic of the treating practitioner predicts outcome, as does the patient's belief (independently). Beliefs about treatment veracity shape how patients self-report outcome, complicating and confounding study interpretation.
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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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Pain in cancer patients remains common and is often associated with insufficient prescribing of targeted analgesia. An explanation for undertreatment could be the failure to identify neuropathic pain mechanisms, which require additional prescribing strategies. We wanted to identify the prevalence of neuropathic mechanisms in patients with cancer pain to highlight the need for detailed assessment and to support the development of an international classification system for cancer pain. ⋯ The prevalence of pain with a neuropathic mechanism (95% confidence interval) ranged from a conservative estimate of 18.7% (15.3% to 22.1%) to a liberal estimate of 21.4% (15.2% to 27.6%) of all recorded cancer pains. The proportion of pain caused by cancer treatment was higher in neuropathic pain compared with all types of cancer pain. A standardised approach or taxonomy used for assessing neuropathic pain in patients with cancer is needed to improve treatment outcomes.