Review question
Does transcutaneous electrical nerve stimulation (TENS) relieve pain in adults with fibromyalgia?
Background
Fibromyalgia is a long-term medical condition that is characterised by long-lasting widespread pain throughout the body. TENS is a treatment that involves putting pulsed electrical currents across the surface of the skin using two or four electrodes. It is used to manage painful conditions. TENS is inexpensive, can be self-administered by people with fibromyalgia, and is not associated with any particular side effects. TENS reduces pain during movement so it may be useful in addition to other treatments to help people carry on their normal lives.
Study characteristics
In January 2017, we found eight clinical studies that examined 315 people. We included TENS administered to produce a non-painful 'tingling' sensation at the site of pain either as a treatment alone or combined with exercise treatment. All studies used TENS in comparison with 'fake' (called placebo or sham) TENS, no treatment, or other treatments such as medicine or hydrotherapy (treatment in water).
Key results
We did not find enough high-quality studies to allow us to come to any conclusions about the effectiveness of TENS for fibromyalgia pain. Even though seven studies concluded that TENS relieved pain associated with fibromyalgia, the studies were low quality and the findings for measures of pain were inconsistently reported. Studies did not measure most of our outcomes and it was not always clear what aspects of pain were being reported (e.g. present pain, remembered pain, pain severity, etc.). Only one small pilot study found that one 30-minute treatment of TENS reduced pain on movement during and immediately after treatment; however, there were too few participants observed and it is unknown whether this effect would be maintained over a longer course of TENS treatments. Overall, it is not possible to judge whether TENS reduces pain associated with fibromyalgia. There were no serious side events reported in any of the studies.
Quality of the evidence
We rated the quality of the evidence from studies using four levels: very low, low, moderate, or high. Very low-quality evidence means that we are very uncertain about the results. High-quality evidence means that we are very confident in the results. The quality of the evidence was very low overall because of a lack of data.
There was insufficient high-quality evidence to support or refute the use of TENS for fibromyalgia. We found a small number of inadequately powered studies with incomplete reporting of methodologies and treatment interventions.
Fibromyalgia is characterised by persistent, widespread pain; sleep problems; and fatigue. Transcutaneous electrical nerve stimulation (TENS) is the delivery of pulsed electrical currents across the intact surface of the skin to stimulate peripheral nerves and is used extensively to manage painful conditions. TENS is inexpensive, safe, and can be self-administered. TENS reduces pain during movement in some people so it may be a useful adjunct to assist participation in exercise and activities of daily living. To date, there has been only one systematic review in 2012 which included TENS, amongst other treatments, for fibromyalgia, and the authors concluded that TENS was not effective.
To assess the analgesic efficacy and adverse events of TENS alone or added to usual care (including exercise) compared with placebo (sham) TENS; no treatment; exercise alone; or other treatment including medication, electroacupuncture, warmth therapy, or hydrotherapy for fibromyalgia in adults.
We searched the following electronic databases up to 18 January 2017: CENTRAL (CRSO); MEDLINE (Ovid); Embase (Ovid); CINAHL (EBSCO); PsycINFO (Ovid); LILACS; PEDRO; Web of Science (ISI); AMED (Ovid); and SPORTDiscus (EBSCO). We also searched three trial registries. There were no language restrictions.
We included randomised controlled trials (RCTs) or quasi-randomised trials of TENS treatment for pain associated with fibromyalgia in adults. We included cross-over and parallel-group trial designs. We included studies that evaluated TENS administered using non-invasive techniques at intensities that produced perceptible TENS sensations during stimulation at either the site of pain or over nerve bundles proximal (or near) to the site of pain. We included TENS administered as a sole treatment or TENS in combination with other treatments, and TENS given as a single treatment or as a course of treatments.
Two review authors independently determined study eligibility by assessing each record and reaching agreement by discussion. A third review author acted as arbiter. We did not anonymise the records of studies before assessment. Two review authors independently extracted data and assessed risk of bias of included studies before entering information into a 'Characteristics of included studies' table. Primary outcomes were participant-reported pain relief from baseline of 30% or greater or 50% or greater, and Patient Global Impression of Change (PGIC). We assessed the evidence using GRADE and added 'Summary of findings' tables.
We included eight studies (seven RCTs, one quasi-RCT, 315 adults (299 women), aged 18 to 75 years): six used a parallel-group design and two used a cross-over design. Sample sizes of intervention arms were five to 43 participants.
Two studies, one of which was a cross-over design, compared TENS with placebo TENS (82 participants), one study compared TENS with no treatment (43 participants), and four studies compared TENS with other treatments (medication (two studies, 74 participants), electroacupuncture (one study, 44 participants), superficial warmth (one cross-over study, 32 participants), and hydrotherapy (one study, 10 participants)). Two studies compared TENS plus exercise with exercise alone (98 participants, 49 per treatment arm). None of the studies measured participant-reported pain relief of 50% or greater or PGIC. Overall, the studies were at unclear or high risk of bias, and in particular all were at high risk of bias for sample size.
Only one study (14 participants) measured the primary outcome participant-reported pain relief of 30% or greater. Thirty percent achieved 30% or greater reduction in pain with TENS and exercise compared with 13% with exercise alone. One study found 10/28 participants reported pain relief of 25% or greater with TENS compared with 10/24 participants using superficial warmth (42 °C). We judged that statistical pooling was not possible because there were insufficient data and outcomes were not homogeneous.
There were no data for the primary outcomes participant-reported pain relief from baseline of 50% or greater and PGIC.
There was a paucity of data for secondary outcomes. One pilot cross-over study of 43 participants found that the mean (95% confidence intervals (CI)) decrease in pain intensity on movement (100-mm visual analogue scale (VAS)) during one 30-minute treatment was 11.1 mm (95% CI 5.9 to 16.3) for TENS and 2.3 mm (95% CI 2.4 to 7.7) for placebo TENS. There were no significant differences between TENS and placebo for pain at rest. One parallel group study of 39 participants found that mean ± standard deviation (SD) pain intensity (100-mm VAS) decreased from 85 ± 20 mm at baseline to 43 ± 20 mm after one week of dual-site TENS; decreased from 85 ± 10 mm at baseline to 60 ± 10 mm after single-site TENS; and decreased from 82 ± 20 mm at baseline to 80 ± 20 mm after one week of placebo TENS. The authors of seven studies concluded that TENS relieved pain but the findings of single small studies are unlikely to be correct.
One study found clinically important improvements in Fibromyalgia Impact Questionnaire (FIQ) subscales for work performance, fatigue, stiffness, anxiety, and depression for TENS with exercise compared with exercise alone. One study found no additional improvements in FIQ scores when TENS was added to the first three weeks of a 12-week supervised exercise programme.
No serious adverse events were reported in any of the studies although there were reports of TENS causing minor discomfort in a total of 3 participants.
The quality of evidence was very low. We downgraded the GRADE rating mostly due to a lack of data; therefore, we have little confidence in the effect estimates where available.