Influence of Transcutaneous Electrical Nerve Stimulation (TENS) on Pressure Pain Thresholds and Conditioned Pain Modulation in a Randomized Controlled Trial in Women With Fibromyalgia

Abstract

Transcutaneous electrical nerve stimulation (TENS) effectively reduces pain in fibromyalgia (FM). The purpose of this study was to examine the influence of TENS use on pressure pain thresholds (PPT) and conditioned pain modulation (CPM) in individuals with FM using data from the Fibromyalgia Activity Study with TENS trial (NCT01888640). Individuals with FM were randomly assigned to receive active TENS, placebo TENS, or no TENS for 4 weeks. A total of 238 females satisfied the per-protocol analysis among the active TENS (n = 76), placebo TENS (n = 68), and no TENS (n = 94) groups. Following 4 weeks of group allocation, the active TENS group continued for an additional 4 weeks of active TENS totaling 8 weeks (n = 66), the placebo and no TENS groups transitioned to receive 4 weeks of active TENS (delayed TENS, n = 161). Assessment of resting pain, movement-evoked pain (MEP), PPT, and CPM occurred prior to and following active, placebo, or no TENS. There were no significant changes in PPT or CPM among the active TENS, placebo TENS, or no TENS groups after 4 weeks. Individuals who reported clinically relevant improvements in MEP (≥30% decrease) demonstrated increases in PPT (P < .001), but not CPM, when compared to MEP non-responders. There were no significant correlations among the change in PPT or CPM compared to MEP and resting pain following active TENS use (active TENS + delayed TENS). PPT and CPM may provide insight to underlying mechanisms contributing to pain; however, these measures may not relate to self-reported pain symptoms. PERSPECTIVE: Pressure pain threshold increased in individuals with clinically relevant improvement (≥30%) in MEP, indicating the clinical relevance of PPT for understanding mechanisms contributing to pain. CPM was not a reliable indicator of treatment response in MEP responders.

Keywords: Conditioned pain modulation; Fibromyalgia; Pain; Pressure pain threshold; Transcutaneous electrical nerve stimulation.

Figure 1.

Study protocol. HC = healthy control, TENS = transcutaneous electrical nerve stimulation, PPT = pressure pain threshold, CPM = conditioned pain modulation

Figure 2.

Baseline pressure pain thresholds (PPT) and conditioned pain modulation (CPM) in fibromyalgia (Active, Placebo, No TENS) and healthy control (HC) groups. A) Lumbar PPT prior to and during the first TENS application in FM. B) Baseline CPM measured as the percent change in PPT from baseline to post-conditioning stimulus. Error bars indicate standard error. * = p<.001

Figure 3.

Change in PPT and CPM comparing 4 weeks of active, placebo, and No TENS use. A) Lumbar PPT and B) CPM assessed prior to and after 4 weeks of TENS allocation. Error bars indicate standard error.

Figure 4.

Change in PPT and CPM with 4 weeks of active TENS use in the Active TENS and Delayed TENS groups. A) Lumbar PPT assessed prior to and after 4 weeks of active TENS use. B) CPM assessed prior to and after 4 weeks of active TENS. C) Percent change in PPT in movement-evoked pain responders. D) Percent change in CPM in movement-evoked pain responders. Error bars indicate standard error.

Figure 5.

Change in PPT and CPM over 8 weeks in the Active TENS group only. A) Lumbar PPT assessed at baseline, 4 weeks, and 8 weeks. B) CPM assessed at baseline, 4 weeks, and 8 weeks. C) Percent change in PPT and CPM in the Active TENS group according to movement-evoked pain responders at 4 weeks, and D) 8 weeks. Error bars indicate standard error.