Transcutaneous electrical nerve stimulation (TENS) for chronic pain - an overview of Cochrane Reviews

Transcutaneous electrical acupoint stimulation for cancer-related pain management in patients receiving chronic opioid therapy: a randomized clinical trial

PURPOSE

The opioid crisis resulting from its use disorder and overdose poses additional challenges for cancer pain management. The American Society of Clinical Oncology Practice Guideline recommends acupuncture therapy for the management of adult cancer-related pain (CRP), but the effectiveness of transcutaneous electrical acupoint stimulation (TEAS) on CRP remains uncertain.

METHODS

This 5-week prospective randomized clinical trial was conducted at 2 hospitals in China, and participants with CRP receiving chronic opioid therapy were randomized 1:1 into two groups between December 2014 and June 2018. The true TEAS group underwent 15 sessions of TEAS treatments over 3 consecutive weeks, while the control group received sham stimulation. The primary outcome was the numerical rating scale (NRS) score in the past 24h at week 3. The secondary outcomes included morphine equivalent daily dose, quality of life and adverse events.

RESULTS

A total of 159 participants were included in the modified intention-to-treat population. The baseline characteristics were similar in both groups. The mean NRS scores were 0.98 points at week 3 in the true TEAS group and 1.41 points in the sham group, with the mean difference between groups of -0.43 points (P < 0.001; OR = 0.68, P < 0.05). The proportion of patients with NRS reduction more than thirty percentage at week 3 was 50.00% in the true TEAS group and 35.44% in the sham group (RD = 0.15, P > 0.05; RR = 1.41, P > 0.05). No significant difference in pain intensity between the two groups was observed during the follow-up period without TEAS intervention (week 4, OR = 0.83, P > 0.05; week 5, OR = 0.83, P > 0.05). The Karnofsky Performance Status value suggested that patients in the true TEAS group experienced an improved quality of life (Between-group differences: week 3, 3.5%, P < 0.05; week 4, 4.6%, P < 0.001; week 5, 5.6%, P < 0.001).

CONCLUSIONS

The 3-week application of TEAS in patients with CRP receiving chronic opioid therapy resulted in a statistically significant reduction in pain scores, but the observed reduction was of uncertain clinical significance. The prolonged analgesic effect of TEAS was not confirmed in this trial.

CLINICALTRIAL

GOV: ChiCTR-TRC-13003803.

Neurosurgical Treatment of Pain

The aim of this review is to draw attention to neurosurgical approaches for treating chronic and opioid-resistant pain. In a first chapter, an up-to-date overview of the main pathophysiological mechanisms of pain has been carried out, with special emphasis on the details in which the surgical treatment is based. In a second part, the principal indications and results of different surgical approaches are reviewed. Cordotomy, Myelotomy, DREZ lesions, Trigeminal Nucleotomy, Mesencephalotomy, and Cingulotomy are revisited. Ablative procedures have a limited role in the management of chronic non-cancer pain, but they continues to help patients with refractory cancer-related pain. Another ablation lesion has been named and excluded, due to lack of current relevance. Peripheral Nerve, Spine Cord, and the principal possibilities of Deep Brain and Motor Cortex Stimulation are also revisited. Regarding electrical neuromodulation, patient selection remains a challenge.

Analgesic effects of high-frequency and low-frequency TENS currents in patients with distal neuropathy

Currently, diabetes mellitus (DM) is relevant problem, both for its prevalence and complications, including distal polyneuropathy (DPNP). At the same time, discussions continue on analgesic efficacy of transcutaneous electrical nerve stimulation (TENS) in DPNP. Aim of this study was to conduct a multi-faceted assessment of pain syndrome in these patients before and after TENS, taking into account levels of polyneuropathy, its severity and age of patients. The study was conducted in accordance with the research of the Federal State Budgetary Institution of the National Medical Research Center for Rehabilitation and Balneology of the Ministry of Health of the Russian Federation (CTR No. 121040100062-3) and with the permission of the Local Ethics Committee (IRB No. 2 dated 14.01.2021). The study included 75 patients with DM type II with DPNP, which are distributed into 3 groups of 25 people: Group 1a, patients received high–frequency TENS (HF); Group Ib, patients received low-frequency TENS (LF); as control, Group C received a standard method of pharmacological therapy without physiotherapy. Intensity of DPNP was evaluated before and after the course of treatment using a visual analog scale (VAS), the McGill Pain Questionnaire (MPQ), and a graphical linear analysis of pain on the neuropathic pain diagnostic questionnaire 4 (DN4) scale. TENS provides an analgesic effect that may exceed pharmacotherapy in terms of efficacy and safety. There was a 65.9% reduction in neuropathic pain according to VAS after a course of application, with the effects remaining up to 34% during the 6-month follow-up. HF TENS provided a higher significant analgesic effects than LF TENS, as it ensures the reduction of pain syndrome according to VAS by 25.8% (p <0.01), and total estimated characteristics - 35.5% (p <0.01), and touch - in at 58.1% (p = 0.001) and according to the scales of the MPQ (S) and DN4 - by 21% (p = 0.007). The observed differences in analgesic effects between HF TENS and LF TENS are based on analyses of pain in the immediate and long-term follow-up periods of type II DM patients with DPNP. These results, based on summation of the estimated parameters of the international pain scales support expectation of an expansion of the the use of analgesic TENS in aging patients suffering with DM of varying severity and extent of DPNP damage, a goal of great scientific and practical importance.

Efficacy and safety of transcutaneous electrical nerve stimulation (TENS) for acute and chronic pain in adults: a systematic review and meta-analysis of 381 studies (the meta-TENS study)

OBJECTIVE

To investigate the efficacy and safety of transcutaneous electrical nerve stimulation (TENS) for relief of pain in adults.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Medline, Cochrane Central, Embase (and others) from inception to July 2019 and updated on 17 May 2020.

ELIGIBILITY CRITERIA FOR STUDY SELECTION

Randomised controlled trials (RCTs) comparing strong non-painful TENS at or close to the site of pain versus placebo or other treatments in adults with pain, irrespective of diagnosis.

DATA EXTRACTION AND SYNTHESIS

Reviewers independently screened, extracted data and assessed risk of bias (RoB, Cochrane tool) and certainty of evidence (Grading and Recommendations, Assessment, Development and Evaluation). Mean pain intensity and proportions of participants achieving reductions of pain intensity (≥30% or >50%) during or immediately after TENS. Random effect models were used to calculate standardised mean differences (SMD) and risk ratios. Subgroup analyses were related to trial methodology and characteristics of pain.

RESULTS

The review included 381 RCTs (24 532 participants). Pain intensity was lower during or immediately after TENS compared with placebo (91 RCTs, 92 samples, n=4841, SMD=-0·96 (95% CI -1·14 to -0·78), moderate-certainty evidence). Methodological (eg, RoB, sample size) and pain characteristics (eg, acute vs chronic, diagnosis) did not modify the effect. Pain intensity was lower during or immediately after TENS compared with pharmacological and non-pharmacological treatments used as part of standard of care (61 RCTs, 61 samples, n=3155, SMD = -0·72 (95% CI -0·95 to -0·50], low-certainty evidence). Levels of evidence were downgraded because of small-sized trials contributing to imprecision in magnitude estimates. Data were limited for other outcomes including adverse events which were poorly reported, generally mild and not different to comparators.

CONCLUSION

There was moderate-certainty evidence that pain intensity is lower during or immediately after TENS compared with placebo and without serious adverse events.

PROSPERO REGISTRATION NUMBER

CRD42019125054.

Clinical Experience of High Frequency and Low Frequency TENS in Treatment of Diabetic Neuropathic Pain in Russia

Background: Transcutaneous electrical nerve stimulation (TENS) is presently one of the main methods of treatment for neuropathic pain in type II diabetes mellitus. The discussion about which TENS frequency is more effective in the treatment of neuropathic pain has been ongoing for many years. Despite this, the response of different aspects of neuropathic pain to various TENS modalities has not been sufficiently studied. Aim: To analyze changes in characteristics of neuropathic pain depending on the frequency of TENS. Materials and methods: Seventy-five Russian diabetic patients with painful distal axonal neuropathy were enrolled in the study. Patients were assigned to three groups: in the HF TENS group, 25 patients received standard drug therapy (Alpha-lipoic acid, Pentoxifylline, Vitamin B12, Gabapentin) + high-frequency TENS (HF); in the LF TENS group, 25 patients received standard drug therapy (Alpha-lipoic acid, Pentoxifylline, Vitamin B12, Gabapentin) + low-frequency TENS (LF); in the control group, 25 patients underwent just standard drug therapy (Alpha-lipoic acid, Pentoxifylline, Vitamin B12, Gabapentin). Pain intensity was calculated before and after treatment with visual analogue scale (VAS), McGill pain questionnaire (MPQ), Douleur Neuropathique 4 Questions (DN4) and Pain Drawing. Results: TENS increased the therapeutic effect of standard drug therapy, in the treatment of neuropathic pain, by 65.9% and prolonged its efficacy by 31% for up to 6 months after treatment. HF TENS had a more pronounced analgesic effect than LF TENS based on VAS (34.7%), sensory (57.6%) MPQ dimensions and DN4 (21%). Affective MPQ dimension with the use of LF TENS was lower than HF TENS by 34.7% immediately after treatment, by 47.3% after 2 months and by 34.8% after 6 months of the follow-up period. Conclusion: There are significant differences between HF and LF TENS based on pain assessment using various pain scales. This reflects the distinctive effects of different TENS modalities on different aspects of neuropathic pain.

Foundational Research Could Improve Future Transcutaneous Electrical Nerve Stimulation Evaluations

Background and objectives: There is a lack of good quality evidence regarding the effectiveness of transcutaneous electrical nerve stimulation (TENS) for chronic musculoskeletal pain, including chronic low back pain. High quality randomised controlled trials (RCTs) have been called for to establish effectiveness over and above placebo and some guidance has already been offered regarding the design of such trials. This article expands the discussion regarding the design of future TENS trials. There is qualitative evidence of the complexity of TENS as an intervention which should be considered in future TENS evaluations. This complexity includes multiple benefits reported by patients, depending on their chosen contexts of TENS use. The ideal content and delivery of support for patients to optimise TENS use also lacks consensus. There is no evidence that a TENS education package has been designed to support the complex set of behaviours and choices which experienced users suggest are required to optimise TENS benefits. Finally, clinical and research outcomes have not been contextualised and related to the specific strategies of use. Conclusions: We suggest that research is required to develop consensus about the content and delivery of training in TENS use for patients who live with pain, informed by the experience of patients, clinicians, and researchers. Once a consensus about the content of TENS training has been reached, there is then a need to develop a TENS training course (TTC) based on this content. An effective and acceptable TTC is needed to develop the knowledge and skills required to optimise TENS use, supporting patients to build confidence in using TENS in everyday life situations with the aim of reducing the impact of chronic pain on function and quality of life. Further research is required to extend the evidence base regarding appropriate, contextualised TENS patient-reported outcomes.

Conolidine: A Novel Plant Extract for Chronic Pain

: Pain, the most common symptom reported among patients in the primary care setting, is complex to manage. Opioids are among the most potent analgesics agents for managing pain. Since the mid-1990s, the number of opioid prescriptions for the management of chronic non-cancer pain (CNCP) has increased by more than 400%, and this increased availability has significantly contributed to opioid diversion, overdose, tolerance, dependence, and addiction. Despite the questionable effectiveness of opioids in managing CNCP and their high rates of side effects, the absence of available alternative medications and their clinical limitations and slower onset of action has led to an overreliance on opioids. Conolidine is an indole alkaloid derived from the bark of the tropical flowering shrub Tabernaemontana divaricate used in traditional Chinese, Ayurvedic, and Thai medicine. Conolidine could represent the beginning of a new era of chronic pain management. It is now being investigated for its effects on the atypical chemokine receptor (ACK3). In a rat model, it was found that a competitor molecule binding to ACKR3 resulted in inhibition of ACKR3’s inhibitory activity, causing an overall increase in opiate receptor activity. Although the identification of conolidine as a potential novel analgesic agent provides an additional avenue to address the opioid crisis and manage CNCP, further studies are necessary to understand its mechanism of action and utility and efficacy in managing CNCP.

Wound Healing with Electrical Stimulation Technologies: A Review

Electrical stimulation (ES) is an attractive field among clinicians in the topic of wound healing, which is common yet complicated and requires multidisciplinary approaches. The conventional dressing and skin graft showed no promise on complete wound closure. These urge the need for the exploration of electrical stimulation to supplement current wound care management. This review aims to provide an overview of electrical stimulation in wound healing. The mechanism of galvanotaxis related to wound repair will be reviewed at the cellular and molecular levels. Meanwhile, different modalities of externally applied electricity mimicking a physiologic electric field will be discussed and compared in vitro, in vivo, and clinically. With the emerging of tissue engineering and regenerative medicine, the integration of electroconductive biomaterials into modern miniaturised dressing is of interest and has become possible with the advancing understanding of smart biomaterials.

Does TENS Reduce the Intensity of Acute and Chronic Pain? A Comprehensive Appraisal of the Characteristics and Outcomes of 169 Reviews and 49 Meta-Analyses

Background and Objectives: Uncertainty about the clinical efficacy of transcutaneous electric nerve stimulation (TENS) to alleviate pain spans half a century. There has been no attempt to synthesise the entire body of systematic review evidence. The aim of this comprehensive review was to critically appraise the characteristics and outcomes of systematic reviews evaluating the clinical efficacy of TENS for any type of acute and chronic pain in adults. Materials and Methods: We searched electronic databases for full reports of systematic reviews of studies, overviews of systematic reviews, and hybrid reviews that evaluated the efficacy of TENS for any type of clinical pain in adults. We screened reports against eligibility criteria and extracted data related to the characteristics and outcomes of the review, including effect size estimates. We conducted a descriptive analysis of extracted data. Results: We included 169 reviews consisting of eight overviews, seven hybrid reviews and 154 systematic reviews with 49 meta-analyses. A tally of authors' conclusions found a tendency toward benefits from TENS in 69/169 reviews, no benefits in 13/169 reviews, and inconclusive evidence in 87/169 reviews. Only three meta-analyses pooled sufficient data to have confidence in the effect size estimate (i.e., pooled analysis of >500 events). Lower pain intensity was found during TENS compared with control for chronic musculoskeletal pain and labour pain, and lower analgesic consumption was found post-surgery during TENS. The appraisal revealed repeated shortcomings in RCTs that have hindered confident judgements about efficacy, resulting in stagnation of evidence. Conclusions: Our appraisal reveals examples of meta-analyses with 'sufficient data' demonstrating benefit. There were no examples of meta-analyses with 'sufficient data' demonstrating no benefit. Therefore, we recommend that TENS should be considered as a treatment option. The considerable quantity of reviews with 'insufficient data' and meaningless findings have clouded the issue of efficacy. We offer solutions to these issues going forward.

Resolving Long-Standing Uncertainty about the Clinical Efficacy of Transcutaneous Electrical Nerve Stimulation (TENS) to Relieve Pain: A Comprehensive Review of Factors Influencing Outcome

Pain is managed using a biopsychosocial approach and pharmacological and non-pharmacological treatments. Transcutaneous electrical nerve stimulation (TENS) is a technique whereby pulsed electrical currents are administered through the intact surface of the skin with the intention of alleviating pain, akin to 'electrically rubbing pain away'. Despite over 50 years of published research, uncertainty about the clinical efficacy of TENS remains. The purpose of this comprehensive review is to critically appraise clinical research on TENS to inform future strategies to resolve the 'efficacy-impasse'. The principles and practices of TENS are described to provide context for readers unfamiliar with TENS treatment. The findings of systematic reviews evaluating TENS are described from a historical perspective to provide context for a critical evaluation of factors influencing the outcomes of randomized controlled trials (RCTs); including sample populations, outcome measures, TENS techniques, and comparator interventions. Three possibilities are offered to resolve the impasse. Firstly, to conduct large multi-centered RCTs using an enriched enrolment with randomized withdrawal design, that incorporates a 'run-in phase' to screen for potential TENS responders and to optimise TENS treatment according to individual need. Secondly, to meta-analyze published RCT data, irrespective of type of pain, to determine whether TENS reduces the intensity of pain during stimulation, and to include a detailed assessment of levels of certainty and precision. Thirdly, to concede that it may be impossible to determine efficacy due to insurmountable methodological, logistical and financial challenges. The consequences to clinicians, policy makers and funders of this third scenario are discussed. I argue that patients will continue to use TENS irrespective of the views of clinicians, policy makers, funders or guideline panel recommendations, because TENS is readily available without prescription; TENS generates a pleasant sensory experience that is similar to easing pain using warming and cooling techniques; and technological developments such as smart wearable TENS devices will improve usability in the future. Thus, research is needed on how best to integrate TENS into existing pain management strategies by analyzing data of TENS usage by expert-patients in real-world settings.

Neuromodulation Techniques in Phantom Limb Pain: A Systematic Review and Meta-analysis

OBJECTIVE

To evaluate the effects of neuromodulation techniques in adults with phantom limb pain (PLP).

METHODS

A systematic search was performed, comprising randomized controlled trials (RCTs) and quasi-experimental (QE) studies that were published from database inception to February 2019 and that measured the effects of neuromodulation in adults with PLP. Hedge's g effect size (ES) and 95% confidence intervals were calculated, and random-effects meta-analyses were performed.

RESULTS

Fourteen studies (nine RCTs and five QE noncontrolled studies) were included. The meta-analysis of RCTs showed significant effects for i) excitatory primary motor cortex (M1) stimulation in reducing pain after stimulation (ES = -1.36, 95% confidence interval [CI] = -2.26 to -0.45); ii) anodal M1 transcranial direct current stimulation (tDCS) in lowering pain after stimulation (ES = -1.50, 95% CI = -2.05 to 0.95), and one-week follow-up (ES = -1.04, 95% CI = -1.64 to 0.45). The meta-analysis of noncontrolled QE studies demonstrated a high rate of pain reduction after stimulation with transcutaneous electrical nerve stimulation (rate = 67%, 95% CI = 60% to 73%) and at one-year follow-up with deep brain stimulation (rate = 73%, 95% CI = 63% to 82%).

CONCLUSIONS

The evidence from RCTs suggests that excitatory M1 stimulation-specifically, anodal M1 tDCS-has a significant short-term effect in reducing pain scale scores in PLP. Various neuromodulation techniques appear to have a significant and positive impact on PLP, but due to the limited amount of data, it is not possible to draw more definite conclusions.

Enhanced transcutaneous electrical nerve stimulation achieved by a localized virtual bipole: a computational study of human tibial nerve stimulation

OBJECTIVE

Electrical neuromodulation is a clinically effective therapeutic instrument, currently expanding into newer indications and larger patient populations. Neuromodulation technologies are also moving towards less invasive approaches to nerve stimulation. In this study, we investigated an enhanced transcutaneous electrical nerve stimulation (eTENS) system that electrically couples a conductive nerve cuff with a conventional TENS electrode. The objectives were to better understand how eTENS achieves lower nerve activation thresholds, and to test the feasibility of applying eTENS in a human model of peripheral nerve stimulation.

APPROACH

A finite element model (FEM) of the human lower leg was constructed to simulate electrical stimulation of the tibial nerve, comparing TENS and eTENS. Key variables included surface electrode diameter, nerve cuff properties (conductivity, length, thickness), and cuff location. Enhanced neural excitability was predicted by relative excitability (RE > 1), derived using either the activating function (AF) or the nerve activation threshold (MRG model).

MAIN RESULTS

Simulations revealed that a localized 'virtual bipole' was created on the target nerve, where the isopotential surface of the cuff resulted in large potential differences with the surrounding tissue. The cathodic part (nerve depolarization) of the bipole enhanced neural excitability, predicted by RE values of up to 2.2 (MRG) and 5.5 (AF) when compared to TENS. The MRG model confirmed that action potentials were initiated at the cathodic edge of the nerve cuff. Factors contributing to eTENS were larger surface electrodes, longer cuffs, cuff conductivity (>1×10³ S m^-1), and cuff position relative to the cathodic surface electrode.

SIGNIFICANCE

This study provides a theoretical basis for designing and testing eTENS applied to various neural targets and data suggesting function of eTENS in large models of nerve stimulation. Although eTENS carries key advantages over existing technologies, further work is needed to translate this approach into effective clinical applications.

Transcutaneous electrical nerve stimulation (TENS) for chronic neck pain

BACKGROUND

Chronic neck pain is a highly prevalent condition, affecting 10% to 24% of the general population. Transcutaneous electrical nerve stimulation (TENS) is the noninvasive, transcutaneous use of electrical stimulation to produce analgesia. It is a simple, low-cost and safe intervention used in clinical practice as an adjunct treatment for painful musculoskeletal conditions that have a considerable impact on daily activities, such as chronic neck pain. This review is a split from a Cochrane Review on electrotherapy for neck pain, published in 2013, and focuses specifically on TENS for chronic neck pain.

OBJECTIVES

To evaluate the effectiveness of transcutaneous electrical nerve stimulation (TENS) (alone or in association with other interventions) compared with sham and other clinical interventions for the treatment of chronic neck pain.

SEARCH METHODS

We searched Cochrane Back and Neck Trials Register, CENTRAL, MEDLINE, Embase, five other databases and two trials registers to 9 November 2018. We also screened the reference lists of relevant studies to identify additional trials. There were no language, source, or publication date restrictions.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) involving adults (≥ 18 years of age) with chronic neck pain (lasting > 12 weeks) that compared TENS alone or in combination with other treatments versus active or inactive treatments. The primary outcomes were pain, disability and adverse events.

DATA COLLECTION AND ANALYSIS

Two independent review authors selected the trials, extracted data and assessed the risk of bias of included studies. A third review author was consulted in case of disagreements. We used the Cochrane 'Risk of bias' tool (adapted by Cochrane Back and Neck), to assess the risk of bias of individual trials and GRADE to assess the certainty of evidence. We used risk ratios (RRs) to measure treatment effects for dichotomous outcomes, and mean differences (MDs) for continuous outcomes, with their respective 95% confidence intervals (CIs).

MAIN RESULTS

We included seven RCTs with a total of 651 participants, mean age 31.7 to 55.5 years, conducted in three different countries (Turkey, Jordan and China). The length of follow-up ranged from one week to six months. Most RCTs used continuous TENS, with a frequency of 60 Hz to 100 Hz, pulse width of 40 μs to 250 μs and tolerable intensity, described as a tingling sensation without contraction, in daily sessions lasting 20 to 60 minutes. Due to heterogeneity in interventions and outcomes, we did not pool individual study data into meta-analyses. Overall, we judged most studies as being at low risk for selection bias and high risk for performance and detection bias. Based on the GRADE approach, there was very low-certainty evidence from two trials about the effects of conventional TENS when compared to sham TENS at short-term (up to 3 months after treatment) follow-up, on pain (assessed by the Visual Analogue Scale (VAS)) (MD -0.10, 95% CI -0.97 to 0.77) and the percentage of participants presenting improvement of pain (RR 1.57, 95% CI 0.84 to 2.92). None of the included studies reported on disability or adverse events.

AUTHORS' CONCLUSIONS

This review found very low-certainty evidence of a difference between TENS compared to sham TENS on reducing neck pain; therefore, we are unsure about the effect estimate. At present, there is insufficient evidence regarding the use of TENS in patients with chronic neck pain. Additional well-designed, -conducted and -reported RCTs are needed to reach robust conclusions.

The clinical efficacy of transcutaneous electrical nerve stimulation (TENS) for acute and chronic pain: a protocol for a meta-analysis of randomised controlled trials (RCTs)

INTRODUCTION

The aim of this systematic review with meta-analysis is to evaluate the clinical efficacy of transcutaneous electrical nerve stimulation (TENS) for any type of acute and chronic pain in adults.

METHODS AND ANALYSIS

We intend to search electronic databases (Cochrane Library, MEDLINE, Embase, CINAHL, PsycINFO, LILACS, PEDRO, Web of Science, AMED and SPORTDiscus) from inception to the present day to identify all randomised controlled trials (RCT) on the use of TENS in adults for any type of pain including acute pain, chronic pain and cancer-related pain. We will screen the RCTs against eligibility criteria for inclusion in our review. Two reviewers will independently undertake RCT selection, data extraction and risk of bias assessment. Primary outcomes will be: (i) participant-reported pain relief of ≥30% expressed as frequency (dichotomous) data; and (ii) participant-reported pain intensity expressed as mean (continuous) data. We will conduct meta-analyses to determine risk ratio for dichotomous data, and mean difference (MD) or standardised MD for continuous data for TENS versus placebo TENS, no treatment or waiting list control, standard of care, and other treatments. Subgroup analyses will include different pain conditions (eg, acute vs chronic), TENS intensity, during versus after TENS, TENS as a sole treatment versus TENS in combination with other treatments and TENS administered as a single dose versus repetitive dose.

ETHICS AND DISSEMINATION

This systematic review will not use data from individual participants, and the results will be disseminated in a peer-reviewed publication and presented at a conference.

PROSPERO REGISTRATION NUMBER

CRD42019125054.

Transcutaneous electrical nerve stimulation (TENS) for fibromyalgia in adults

BACKGROUND

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.

OBJECTIVES

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.

SEARCH METHODS

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.

SELECTION CRITERIA

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.

DATA COLLECTION AND ANALYSIS

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.

MAIN RESULTS

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.

AUTHORS' CONCLUSIONS

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.