TENS shows promise for women with fibromyalgia

Use of transcutaneous electrical nerve stimulation (TENS) led to a significant improvement in movement-evoked pain and fatigue in women with fibromyalgia, according to the FAST* study.

“Fibromyalgia is a complex condition characterized by widespread pain and fatigue,” said the researchers. Given the reported modest effects of pharmacologic interventions in this setting, [Pain Ther 2013;2:87-104; BMJ Open 2015;5:e006681] non-pharmacologic methods such as TENS may help improve activity-participation, resulting in a perceived global improvement, they added.

A total of 301 participants with stable medication were randomized 1:1:1 to receive daily active TENS, placebo TENS, or no TENS at home for 2 hours during activity for 4 weeks. TENS must be applied to the lumbar and cervicothoracic regions using a modulated frequency (2–125 Hz) at the highest tolerable intensity. [Arthritis Rheumatol 2019;doi:10.1002/art.41170]

At 4 weeks, active TENS recipients had a greater reduction in movement-evoked pain and fatigue vs placebo TENS (6MWT**, group mean difference [GMD], -1.0; p=0.008 [pain] and -1.4; p=0.001 [fatigue]) and no TENS (GMD, -1.8; p=0.001 and -1.9; p<0.0001, respectively).

Despite the minimal difference in pain between the active TENS and placebo TENS arms, the difference between the active TENS and no TENS arms should be taken into context, noted the researchers. “A 1.8-point decrease equates to >30 percent reduction for people with pain ratings of ≤6 … Some studies also suggest that a 2-point reduction in pain is the clinically relevant threshold.”

Among active TENS recipients, 44 percent demonstrated a clinically important 30-percent reduction in pain, 45 percent reported a reduction in fatigue, while 29 percent showed reductions in both pain and fatigue. “[These] suggest that a subpopulation of individuals with fibromyalgia responds well to TENS … [Moreover,] the responder rates for pain are similar to FDA-approved pharmaceutical agents for fibromyalgia such as duloxetine or pregabalin.”

A greater fraction of participants in the active TENS arm reported improvement in the global impression of change (GIC) vs those receiving placebo TENS and no TENS (70 percent vs 31 percent and 9 percent; p<0.0001 for both).

The researchers attributed the GIC improvements to the reductions in pain and fatigue, as both influence perceived disability and function. [Arthritis Res Ther 2016;18:68] “We showed … the relationship between global improvement and movement-evoked pain, with results similar to prior studies on pain and GIC. The magnitude of reduction in both pain and fatigue observed in the current study is likely to have a significant impact on the lived experience of fibromyalgia.”

Thirty patients reported TENS-related adverse events (AEs), the most common being pain and skin irritation with electrodes. No TENS-related serious AEs were reported, which further boosts the safety and suitability of TENS for home use.

“TENS is available over the counter, inexpensive, and safe and easy to use. It can provide a self-management option for people with chronic pain, particularly fibromyalgia, to provide an additional level of pain relief,” said senior author Professor Kathleen Sluka from the University of Iowa in Iowa, US, in a press release.

However, changes in other domains (ie, function, psychological factors, rescue medication usage, and quality of life) were not determined which, according to the researchers, could be due to the short duration of TENS use. “[F]unctional changes may take a longer period to change or are harder to achieve, particularly in long-standing conditions such as fibromyalgia,” they added, hence the need for longer treatment durations.

Furthermore, as the study was limited to women, the findings may not be extrapolated to men with fibromyalgia. Further exploration is warranted to validate the efficacy of TENS in the real-world setting.

Of note was the cumulative effect in the active TENS arm beyond 4 weeks which, according to the researchers, is important in light of reports of analgesic tolerance to repeated TENS use. The lack of tolerance in the study could be due to the mixed frequency used, following evidence reflecting decreased tolerance with mixed frequencies. [Arch Phys Med Rehabil 2008;89:754-780] Therefore, identifying mechanisms underlying the analgesia generated by non-pharmacologic interventions would be critical in designing a trial that would establish clinical effectiveness, they added.