The journal of pain : official journal of the American Pain Society
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Randomized Controlled Trial
Adjusting pulse amplitude during transcutaneous electrical nerve stimulation (TENS) application produces greater hypoalgesia.
Transcutaneous electrical nerve stimulation (TENS) is a noninvasive technique used for pain modulation. During application of TENS there is a fading of current sensation. Textbooks of electrophysical agents recommend that pulse amplitude should be constantly adjusted. This seems to be accepted clinically despite the fact that there is no direct experimental evidence. The aim of the current study was to investigate the hypoalgesic effect of adjusting TENS pulse amplitude on pressure pain thresholds (PPTs) in healthy humans. Fifty-six healthy TENS naïve participants were recruited and randomly assigned to 1 of 4 groups (n = 14 per group): control, placebo TENS, fixed pulse amplitude TENS, and adjusted pulse amplitude TENS. Both active and placebo TENS were applied to the dominant forearm. PPTs were recorded from 2 points on the dominant forearm and hand before, during, and after 40 minutes of TENS. TENS increased the PPTs on the forearm (P = .003) and hand (P = .003) in the group that received the adjusted pulse amplitude when compared to all other groups. The mean final pulse amplitude for the adjusted pulse amplitude TENS group was 35.51 mA when compared to the fixed pulse amplitude TENS group, which averaged 31.37 mA (P = .0318). ⋯ These results suggest that it is important to adjust the pulse amplitude during TENS application to get the maximal analgesic effect. We propose that the fading of current sensation allows the use of higher pulse amplitudes, which would activate a greater number of and deeper tissue afferents to produce greater analgesia.
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Randomized Controlled Trial Multicenter Study
Subcutaneous methylnaltrexone for treatment of opioid-induced constipation in patients with chronic, nonmalignant pain: a randomized controlled study.
Methylnaltrexone is effective for opioid-induced constipation (OIC) in advanced illness patients. This 4-week, double-blind, randomized, placebo-controlled study investigated the effect of subcutaneous methylnaltrexone on OIC in patients receiving opioids for chronic, nonmalignant pain. Patients (N = 460) received subcutaneous methylnaltrexone 12 mg once daily (QD) or every other day (alternating with placebo) compared with placebo. Assessments included bowel movement count, time of bowel movement, straining, sense of complete evacuation, Bristol Stool Form Scales, and quality of life. Within 4 hours of first dose, 34.2% of patients in both methylnaltrexone groups had rescue-free bowel movements (RFBMs) versus 9.9% on placebo (P < .001). The estimated number needed to treat was about 4. On average, 28.9% of methylnaltrexone QD and 30.2% of methylnaltrexone alternate-day dosing resulted in RFBMs within 4 hours versus 9.4% QD and 9.3% alternate-day placebo injections (both P < .001). Both methylnaltrexone groups had significantly shorter time to first RFBM (P < .001) and greater increase in number of weekly RFBMs (P < .05) versus placebo. Adverse events included abdominal pain, diarrhea, nausea, and hyperhidrosis. Bristol Stool Form Scale scores (P = .002) and sensation of complete evacuation (P < .04) were significantly superior with methylnaltrexone QD; both methylnaltrexone groups reported no or mild straining during RFBMs in the first 2 weeks (P < .02). At 4 weeks, a significantly greater improvement in patient-reported, constipation-specific quality of life was seen in the alternate-day dosing (P < .05) and QD (P < .001) groups. ⋯ We present data demonstrating that subcutaneous methylnaltrexone 12 mg given once daily (QD) or every other day provides significant relief of OIC and was generally well tolerated in patients with chronic, nonmalignant pain. These results expand on prior effectiveness observed for the treatment of OIC in advanced illness patients to a broader population.
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Randomized Controlled Trial
Transcranial DC stimulation in fibromyalgia: optimized cortical target supported by high-resolution computational models.
In this study we aimed to determine current distribution and short-term analgesic effects of transcranial direct current stimulation (tDCS) in fibromyalgia using different electrode montages. For each electrode montage, clinical effects were correlated with predictions of induced cortical current flow using magnetic resonance imaging-derived finite element method head model. Thirty patients were randomized into 5 groups (Cathodal-M1 [primary motor cortex], Cathodal-SO [supra-orbital area], Anodal-M1, Anodal-SO, and Sham) to receive tDCS application (2 mA, 20 minutes) using an extracephalic montage. Pain was measured using a visual numerical scale (VNS), pressure pain threshold (PPT), and a body diagram (BD) evaluating pain area. There was significant pain reduction in cathodal-SO and anodal-SO groups indexed by VNS. For PPT there was a trend for a similar effect in anodal-SO group. Computer simulation indicated that the M1-extracephalic montage produced dominantly temporo-parietal current flow, consistent with lack of clinical effects with this montage. Conversely, the SO-extracephalic montage produced current flow across anterior prefrontal structures, thus supporting the observed analgesic effects. Our clinical and modeling findings suggest that electrode montage, considering both electrodes, is critical for the clinical effects of M1-tDCS as electric current needs to be induced in areas associated with the pain matrix. These results should be taken into consideration for the design of pain tDCS studies. ⋯ Results in this article support that electrode montage is a critical factor to consider for the clinical application of tDCS for pain control, as there is an important correlation between the location of induced electrical current and tDCS-induced analgesic effects.