Pain
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Combinations of analgesics with caffeine have been discussed as bearing a risk for headache chronicity. We investigated whether aspirin with caffeine (ASA+) increases headache frequency compared with aspirin alone in migraine, tension-type headache (TTH), and migraine + TTH (MigTTH). The population-based German Headache Consortium Study, which included participants aged 18 to 65 years, collected information about headache and analgesics at baseline (2003-2007, t0, response rate: 55.2%), first follow-up after 1.87 ± 0.39 years (t1, 37.2%), and second follow-up after 3.26 ± 0.60 years (t2, 38.8%). ⋯ Of 509 participants (56.0% women, 42.0 ± 11.8 years [mean ± SD]), 45.2% reported aspirin intake (41.3 ± 10.9 years, 59.6% women, headache days at t0: 2.8 ± 3.1 d/mo, t2: 3.6 ± 4.1 d/mo), 11.8% ASA+ intake (46.0 ± 9.8 years, 73.3%, t0: 4.8 ± 6.1 d/mo, t2: 5.3 ± 5.1 d/mo), and 43.0% no analgesics (41.6 ± 13.1 years, 47.5%, t0: 3.8 ± 6.2 d/mo, t2: 5.3 ± 6.6 d/mo). There was no increase in headache frequency in participants with ASA+ intake compared with aspirin (adjusted, all headache: -0.34 d/mo [95% confidence intervals: -2.50 to 1.82], migraine: -1.36 d/mo [-4.76 to 2.03], TTH: -0.57 d/mo [-4.97 to 3.84], MigTTH: 2.46 d/mo [-5.19 to 10.10]) or no analgesics (all headache: -2.24 d/mo [-4.54 to 0.07], migraine: -3.77 d/mo [-9.22 to 1.68], TTH: -4.68 d/mo [-9.62 to 0.27]; MigTTH: -3.22 d/mo [-10.16 to 3.71]). In our study, ASA+ intake did not increase headache frequency compared with aspirin or no analgesics.
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Glycine transporter 1 (GlyT1) plays a crucial role in regulating extracellular glycine concentrations and might thereby constitute a new drug target for the modulation of glycinergic inhibition in pain signaling. Consistent with this view, inhibition of GlyT1 has been found to induce antinociceptive effects in various animal pain models. We have shown previously that the lidocaine metabolite N-ethylglycine (EG) reduces GlyT1-dependent glycine uptake by functioning as an artificial substrate for this transporter. ⋯ Additionally, we found that EG reduced the increase in neuronal firing of wide-dynamic-range neurons caused by inflammatory pain induction. These findings suggest that systemically applied lidocaine exerts antihyperalgesic effects through its metabolite EG in vivo, by enhancing spinal inhibition of pain processing through GlyT1 modulation and subsequent increase of glycine concentrations at glycinergic inhibitory synapses. EG and other substrates of GlyT1, therefore, may be a useful therapeutic agent in chronic pain states involving spinal disinhibition.
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A large number of analgesics have failed to prove superiority over placebo in randomized controlled trials (RCTs), and as this has been related to increasing placebo responses, there is currently an interest in specifying predictors of the placebo response. The literature on placebo mechanisms suggests that factors related to patients' expectations of treatment efficacy are pivotal for the placebo response. Also, general characteristics of RCTs have been suggested to influence the placebo response. ⋯ Opioid trials, a high number of planned face-to-face visits, and randomization ratio predicted the magnitude of the placebo response, thereby supporting the expectancy hypothesis. Exploratory models with baseline pain intensity, age, washout length, and discontinuation because of adverse events accounted for approximately 10% of the variability in the placebo response. Based on these results and previous mechanisms studies, we think that patients' perception of treatment allocation and expectations toward treatment efficacy could potently predict outcomes of RCTs.
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Review
Transcranial Magnetic Stimulation (TMS) of the Brain: Guidelines for Pain Treatment Research.
Recognizing that electrically stimulating the motor cortex could relieve chronic pain sparked development of noninvasive technologies. In transcranial magnetic stimulation (TMS), electromagnetic coils held against the scalp influence underlying cortical firing. Multiday repetitive transcranial magnetic stimulation (rTMS) can induce long-lasting, potentially therapeutic brain plasticity. ⋯ Minimum required elements include sample sources, sizes, and demographics, recruitment methods, inclusion and exclusion criteria, baseline and posttreatment means and SD, adverse effects, safety concerns, discontinuations, and medication-usage records. Outcomes should be monitored for at least 3 months after initiation with prespecified statistical analyses. Multigroup collaborations or registry studies may be needed for pivotal trials.