Papers of the Week

Transcutaneous electrical nerve stimulation (TENS) uses endogenous opioids to produce analgesia, and effectiveness can be reduced in opioid-tolerant individuals. We examined TENS effectiveness (primary aim), and differences in fibromyalgia symptoms (secondary aim), in women with fibromyalgia regularly taking opioid (RTO) medications compared with women not- regularly taking opioids (not-RTO). Women (RTO n=79; not-RTO not-n=222) with fibromyalgia with daily pain levels ≥4 were enrolled and categorized into RTO (taking opioids at least 5 of 7 days in last 30 days) or not-RTO groups. For the RTO group, participants were categorized into tramadol n=52 (65.8%) and other opioids n=27 (34.2%). Participants were phenotyped across multiple domains including demographics, fibromyalgia characteristics pain, fatigue, sleep, psychosocial factors, and activity. Participants were randomized to active TENS (n=101), placebo TENS (n=99), or no TENS (n=99) for 1-month with randomization stratified by opioid use. Active TENS was equally effective in movement-evoked pain in those in the RTO and not-RTO groups. Women with fibromyalgia in the RTO group were older (p=0.002), lower income (p=0.035), more likely to smoke (p=0.014), and more likely to report depression (p=0.013), hypertension (p=0.005) or osteoarthritis (p=0.027). The RTO group demonstrated greater bodily pain on SF-36 (p=0.005), lower quality of life on the physical health component of the SF-36 (p=0.040), and greater fatigue (MAF-ADL p=0.047; fatigue with sit to stand test (p=0.047) These differences were small of and unclear clinical significance. In summary, regular use of opioid analgesics does not interfere with effectiveness of TENS for movement-evoked pain. Clinical Trial Registration Number: NCT01888640 Perspective: Individuals treated with mixed frequency TENS at strong but comfortable intensity that were taking prescription opioid analgesics showed a significant reduction in movement-evoked pain and fatigue. These data support the use of TENS, using appropriate parameters of stimulation, as an intervention for individuals with fibromyalgia taking opioid analgesics.