Does the pulse frequency of transcutaneous electrical nerve stimulation (TENS) influence hypoalgesia?

Transcutaneous electrical nerve stimulation for pelvic pain: A scoping review of treatment protocols, practical indications, and caveats

BACKGROUND

Neuromodulation (NM) is a family of therapies based on electrical stimulation to target specific nerves that control LUTS (Lower Urinary Tract Symptoms) and pain. The aim is to modulate what is happening within the nervous system to achieve therapeutic effects. A particular type of neuromodulation, called TENS (Transcutaneous Electrical Nerve Stimulation), has proven effective for treating pelvic pain. The available evidence provides indications regarding the many aspects of TENS that influence therapeutic effects, but a comprehensive review has yet to be conducted.

METHODS

Scoping review on Pubmed, CINAHL, Embase, Scopus, and Web of Science, including clinical trials, reviews, case studies or series, and other descriptive studies, according to the Joanna Briggs and PRISMA methodology.

RESULTS

The 31 papers retrieved allowed the formulation of precise indications about the DOs and DON'Ts of electrode placement, waveform, pulse duration, pulse frequency, amplitude, session duration, and frequency of sessions. This paper also discusses the biochemical and neuro urological mechanisms of TENS.

CONCLUSION

TENS effectiveness is influenced by many factors, some self-evident, others subtle, which this paper elucidates. Pelvic pain requires a multimodal approach, of which TENS is just a part. TENS should therefore be viewed as one of the components of the rehabilitation program in the frame of thorough and continuous patient assessment.

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.

Parameterization of physical properties of layered body structure into equivalent circuit model

Background

This study presents a novel technique to develop an equivalent circuit model (ECM) for analyzing the responses of the layered body structure to transcutaneous electrical nerve stimulation (TENS) by parameterizing electrical and geometrical properties.Many classical ECMs are non-parametric because of the difficulty in projecting intrapersonal variability in the physical properties into ECM. However, not considering the intrapersonal variability hampers patient-specifically analyzing the body response to TENS and personal optimization of TENS parameter design. To overcome this limitation, we propose a tissue property-based (TPB) approach for the direct parameterization of the physical properties in the layered body structure and thus enable to quantify the effects of intrapersonal variability.

Results

The proposed method was first validated through in vitro phantom studies and then was applied in-vivo to analyze the TENS on the forearm. The TPB-ECM calculated the impedance network in the forearm and corresponding responses to TENS. In addition, the modelled impedance was in good agreement with well-known impedance properties that have been achieved empirically.

Conclusions

The TPB approach uses the parameterized circuit components compared to non-parametric conventional ECMs, thus overcoming the intrapersonal variability problem of the conventional ECMs. Therefore, the TPB-ECM has a potential for widely-applicable TENS analysis and could provide impactful guidance in the TENS parameter design.

Supplementary Information

The online version contains supplementary material available at (10.1186/s42490-021-00054-8).

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.

Efficacy of different-frequency TEAS on acute pain after the total knee arthroplasty: a study protocol for a parallel group randomized trial

BACKGROUND

Total knee arthroplasty (TKA) is an optimal option for patients with middle-to-end-stage knee osteoarthritis. However, the management of postoperative acute pain remains inefficient. Transcutaneous electrical acupoint stimulation (TEAS) is a nonpharmacological method to manage postoperative acute pain. Different frequencies of TEAS have been tested using varying parameters, but the optimal analgesic frequency remains controversial. The aim of this study was to explore the optimal analgesic frequency of TEAS for treating acute pain after the primary unilateral TKA.

METHODS/DESIGN

This is a double-blind, randomized controlled trial. A total of 156 patients are randomly assigned to: G1, 5 Hz TEAS; G2, 100 Hz TEAS; G3, mixed TEAS (alternative use of daily 5 Hz and 100 Hz TEAS) and G4, placebo TEAS. In the G1, G2 and G3 groups, TEAS is conducted at acupoints SP9 and GB34 of the leg that was operated on (at a wave of continuous, balanced and asymmetrical biphasic square, with a pulse width of 200 μs, and a strong but comfortable current) for 30 min prior to a 30-min rehabilitation session per day for 2 weeks. In G4 group, TEAS is delivered at a strong but comfortable current for 30 s, then the current is gradually decreased to none over the next 15 s. The primary outcomes are measured before surgery, at baseline (POD 3, before TEAS intervention), week 1 and 2 after TEAS intervention with the Numeric Pain Rating Scale and The American Knee Society Score. The secondary outcomes include: (1) Active range of motion of the knee that was operated on; (2) Surface electromyography of both quadriceps; (3) Modified 30-s sit to stand test; (4) Additional usage of analgesia; and (5) SF-36. The additional outcomes include: (1) Patients' satisfaction rate; (2) Patient's expectation rate; and (3) Incidence of analgesia-related side effects. To test the blinding of participants and assessors, they are asked to guess whether the subjects received active or placebo TEAS within 5 min after the latest intervention. The safety and financial cost of TEAS are assessed.

DISCUSSION

Mixed TEAS has more favorable effect on acute pain control than the placebo or 5 Hz or 100 Hz TEAS.

TRIAL REGISTRATION

ChiCTR1800016347 . Date of registration was 26 May 2018. Retrospectively registered.

Prolonged Reduction in Shoulder Strength after Transcutaneous Electrical Nerve Stimulation Treatment of Exercise-Induced Acute Muscle Pain

OBJECTIVES

Transcutaneous electrical nerve stimulation (TENS) is commonly used for reducing musculoskeletal pain to improve function. However, peripheral nerve stimulation using TENS can alter muscle motor output. Few studies examine motor outcomes following TENS in a human pain model. Therefore, this study investigated the influence of TENS sensory stimulation primarily on motor output (strength) and secondarily on pain and disability following exercise-induced delayed-onset muscle soreness (DOMS).

METHODS

Thirty-six participants were randomized to a TENS treatment, TENS placebo, or control group after completing a standardized DOMS protocol. Measures included shoulder strength, pain, mechanical pain sensitivity, and disability. TENS treatment and TENS placebo groups received 90 minutes of active or sham treatment 24, 48, and 72 hours post-DOMS. All participants were assessed daily.

RESULTS

A repeated measures analysis of variance and post-hoc analysis indicated that, compared to the control group, strength remained reduced in the TENS treatment group (48 hours post-DOMS, P < 0.05) and TENS placebo group (48 hours post-DOMS, P < 0.05; 72 hours post-DOMS, P < 0.05). A mixed-linear modeling analysis was conducted to examine the strength (motor) change. Randomization group explained 5.6% of between-subject strength variance (P < 0.05). Independent of randomization group, pain explained 8.9% of within-subject strength variance and disability explained 3.3% of between-subject strength variance (both P < 0.05).

DISCUSSION

While active and placebo TENS resulted in prolonged strength inhibition, the results were nonsignificant for pain. Results indicated that higher pain and higher disability were independently related to decreased strength. Regardless of the impact on pain, TENS, or even the perception of TENS, may act as a nocebo for motor output.

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.

Electro-analgesia for sheep husbandry practices: a review

Several sheep-husbandry practices such as mulesing, castration, ear-tagging and tail-docking are currently performed with no, or little, anaesthesia or analgesia. The potential for using electrotherapies to provide analgesia during and after these operations is examined in this review. The most common electrotherapy is transcutaneous electrical nerve stimulation (TENS). TENS is the application of an electrical current from electrodes placed on the skin. Analysis of a large number of trials in humans and in animal models indicates that TENS provides effective relief from acute and chronic pain, including pain associated with surgery. There is strong evidence now that TENS analgesia operates at the levels of the periphery, the spinal cord and in the brain. The mechanisms involve the autonomic nervous system, the opioid pathways and neurotransmitters involved in descending inhibitory pathways from the brain. Centrally operating pathways mean the current does not have to be applied near the injured site and there is evidence of sustained pain relief lasting hours, days or even weeks post-treatment, particularly after very high-frequency, randomly variable current applications. Treatment of sheep during painful operations with such a current has the potential to provide immediate and possibly sustained pain relief. Combining such a treatment with electro-immobilisation of the animal would be advantageous for sheep-husbandry operations, but there is considerable evidence that high-intensity currents producing tetanic contractions are aversive and probably painful for sheep. Investigations of the application and efficacy of electrotherapies for painful sheep operations should be undertaken.

Transcutaneous electrical nerve stimulation for acute pain

BACKGROUND

This is a second update of a Cochrane Review originally published in Issue 2, 2009. Transcutaneous Electrical Nerve Stimulation (TENS) is a non-pharmacological agent, based on delivering low voltage electrical currents to the skin. TENS is used by people to treat a variety of pain conditions.

OBJECTIVES

To assess the analgesic effectiveness of TENS, as a sole treatment, for acute pain in adults.

SEARCH METHODS

We searched the following databases up to 3 December 2014: the Cochrane Central Register of Controlled Trials (CENTRAL), in the Cochrane Library; MEDLINE; EMBASE; CINAHL; and AMED. We also checked the reference lists of included trials.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of adults with acute pain (< 12 weeks) if they examined TENS given as a sole treatment and assessed pain with subjective pain scales. Trials were eligible if they compared TENS to placebo TENS, no treatment controls, pharmacological interventions or non-pharmacological interventions. We excluded trials on experimental pain, case reports, clinical observations, letters, abstracts or reviews. Also we excluded trials investigating the effect of TENS on pain during childbirth (labour), primary dysmenorrhoea or dental procedures. Studies where TENS was given with another treatment as part of the formal trial design were excluded. We did not restrict any articles based on language of publication.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study eligibility and carried out study selection, data extraction, 'Risk of bias' assessment and analyses of data. We extracted data on the following: types of participants and pain condition, trial design and methods, treatment parameters, adverse effects, and outcome measures. We contacted trial authors for additional information if necessary.

MAIN RESULTS

We included 12 trials in the original review (2009) and included no further trials in the first update (2011). An additional seven new trials met the inclusion criteria in this second update. In total, we included 19 RCTs involving 1346 participants at entry, with 11 trials awaiting classification either because the full text was unavailable or information in the full text failed to clarify eligibility. We excluded most trials because TENS was given in combination with another treatment as part of the formal study design or TENS was not delivered using appropriate TENS technique. The types of acute pain included in this Cochrane Review were procedural pain, e.g. cervical laser treatment, venepuncture, screening flexible sigmoidoscopy and non-procedural pain, e.g. postpartum uterine contractions and rib fractures. We pooled data for pain intensity for six trials (seven comparisons) comparing TENS with placebo but the I(2) statistic suggested substantial heterogeneity. Mean difference (MD) with 95% confidence intervals (CIs) on a visual analogue scale (VAS, 100 mm) was -24.62 mm (95% CI -31.79 to -17.46) in favour of TENS. Data for the proportion of participants achieving ≥ 50% reduction in pain was pooled for four trials (seven comparisons) and relative risk was 3.91 (95% CI 2.42 to 6.32) in favour of TENS over placebo. We pooled data for pain intensity from five trials (seven comparisons) but the I(2) statistic suggested considerable heterogeneity. MD was -19.05 mm (95% CI -27.30 to -10.79) in favour of TENS using a random-effects model. It was not possible to pool other data. There was a high risk of bias associated with inadequate sample sizes in treatment arms and unsuccessful blinding of treatment interventions. Seven trials reported minor adverse effects, such as mild erythema and itching underneath the electrodes and participants disliking TENS sensation.

AUTHORS' CONCLUSIONS

This Cochrane Review update includes seven new trials, in addition to the 12 trials reviewed in the first update in 2011. The analysis provides tentative evidence that TENS reduces pain intensity over and above that seen with placebo (no current) TENS when administered as a stand-alone treatment for acute pain in adults. The high risk of bias associated with inadequate sample sizes in treatment arms and unsuccessful blinding of treatment interventions makes definitive conclusions impossible. There was incomplete reporting of treatment in many reports making replication of trials impossible.

Transcutaneous electrical nerve stimulation as an adjunct to education and exercise for knee osteoarthritis: a randomized controlled trial

OBJECTIVE

To determine the additional effects of transcutaneous electrical nerve stimulation (TENS) for knee osteoarthritis (OA) when combined with a group education and exercise program (knee group).

METHODS

The study was a randomized, sham-controlled clinical trial. Patients referred for physiotherapy with suspected knee OA (confirmed using the American College of Rheumatology clinical criteria) were invited. Exclusion criteria included comorbidities preventing exercise, previous TENS experience, and TENS contraindications. Prospective sample size calculations required 67 participants in each trial arm. A total of 224 participants (mean age 61 years, 37% men) were randomized to 3 arms: TENS and knee group (n = 73), sham TENS and knee group (n = 74), and knee group (n = 77). All patients entered an evidence-based 6-week group education and exercise program (knee group). Active TENS produced a "strong but comfortable" paraesthesia within the painful area and was used as much as needed during the 6-week period. Sham TENS used dummy devices with no electrical output. Blinded assessment took place at baseline and 3, 6, 12, and 24 weeks. The primary outcome was the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) function subscale at 6 weeks. Secondary outcomes included WOMAC pain, stiffness, and total scores; extensor muscle torque; global assessment of change; exercise adherence; and exercise self-efficacy. Data analysis was by intent to treat.

RESULTS

All outcomes improved over time (P < 0.05), but there were no differences between trial arms (P > 0.05). All improvements were maintained at 24-week followup.

CONCLUSION

There were no additional benefits of TENS, failing to support its use as a treatment adjunct within this context.

An investigation into the magnitude of the current window and perception of transcutaneous electrical nerve stimulation (TENS) sensation at various frequencies and body sites in healthy human participants

INTRODUCTION

Strong nonpainful transcutaneous electrical nerve stimulation (TENS) is prerequisite to a successful analgesic outcome although the ease with which this sensation is achieved is likely to depend on the magnitude of current amplitude (mA) between sensory detection threshold (SDT) and pain threshold, that is, the current window.

OBJECTIVES

To measure the current window and participant's perception of the comfort of the TENS sensation at different body sites.

METHODS

A repeated measure cross-over study was conducted using 30 healthy adult volunteers. Current amplitudes (mA) of TENS [2 pulses per second (pps); 30 pps; 80 pps] at SDT, pain threshold, and strong nonpainful intensities were measured at the tibia (bone), knee joint (connective tissue), lower back [paraspinal (skeletal) muscle], volar surface of forearm (nerve) and waist (fat). The amplitude to achieve a strong nonpainful intensity was represented as a percentage of the current window. Data were analyzed using repeated measures analysis of variance.

RESULTS

Effects were detected for body site and frequency for SDT (P<0.001, P=0.018, respectively), current window (P<0.001, P<0.001, respectively), and strong nonpainful TENS as a percentage of the current window (P=0.002, P<0.001, respectively). The current window was larger for the knee joint compared with tibia (difference [95% confidence interval]=12.76 mA [4.25, 21.28]; P=0.001) and forearm (10.33 mA [2.62, 18.40]; P=0.006), and for the lower back compared with tibia (12.10 mA [1.65, 22.52]; P=0.015) and forearm (9.65 mA [1.06, 18.24]; P=0.019). The current window was larger for 2 pps compared with 30 pps (P<0.001) and 80 pps (P<0.001). Participants rated strong nonpainful TENS as most comfortable at the lower back (P<0.001) and least comfortable at the tibia and forearm (P<0.001).

CONCLUSIONS

TENS is most comfortable and easiest to titrate to a strong nonpainful intensity when applied over areas of muscle and soft tissue.

High-frequency transcutaneous electrical nerve stimulation reduces pain and cardio-respiratory parameters in an animal model of acute pain: participation of peripheral serotonin

The objective of this study was to investigate the effect of high-frequency transcutaneous electrical nerve stimulation (HF-TENS) in antihyperalgesia, assessed through changes of sciatic nerve activity and its effects on cardiorespiratory parameters, using formalin-induced nociception in anesthetized rats. The animals were divided into formalin (FORM) and HF-TENS groups. All rats received injections of 5% formalin (50 μl, right hind-paw). The sciatic nerve activity and cardiopulmonary parameters (mean arterial pressure, heart rate, and respiratory frequency) were measured, and then the serum levels of serotonin (5-HT) were determined by an enzyme-linked immunosorbent assay kit. The formalin injection was able to increase the sciatic nerve activity, heart rate, and respiratory frequency. The treatment with HF-TENS significantly reduced the sciatic nerve activity and respiratory frequency 20 minutes after formalin injection and was able to increase serum 5-HT. Furthermore, when comparing the groups, reductions in the mean arterial pressure, heart rate, respiratory frequency, and sciatic nerve activity were shown at different times. Thus, we concluded that HF-TENS was capable of inducing analgesia, which was most likely related to increased serotonin release. Moreover, we demonstrated that TENS was able to block the adverse cardiovascular and respiratory changes induced by pain. Further neurophysiological studies are necessary to clarify the intrinsic mechanisms underlying HF-TENS-induced analgesia.

Transcutaneous electrical nerve stimulation for the management of painful conditions: focus on neuropathic pain

The management of neuropathic pain is challenging, with medication being the first-line treatment. Transcutaneous electrical nerve stimulation (TENS) is an inexpensive, noninvasive, self-administered technique that is used as an adjunct to medication. Clinical experience suggests that TENS is beneficial providing it is administered at a sufficiently strong intensity, close to the site of pain. At present, there are too few randomized controlled trials on TENS for neuropathic pain to judge effectiveness. The findings of systematic reviews of TENS for other pain syndromes are inconclusive because trials have a low fidelity associated with inadequate TENS technique and infrequent treatments of insufficient duration. The use of electrode arrays to spatially target stimulation more precisely may improve the efficacy of TENS in the future.

Conventional versus acupuncture-like transcutaneous electrical nerve stimulation on cold-induced pain in healthy human participants: effects during stimulation

OBJECTIVES

  To compare the hypoalgesic effects of conventional transcutaneous electrical nerve stimulation (TENS) (high frequency, low intensity) and acupuncture-like TENS (AL-TENS, low frequency, high intensity) on cold-induced pain.

DESIGN

Randomized controlled parallel group study comparing the effects of strong non-painful AL-TENS, conventional TENS and placebo (no current) TENS on cold-pressor pain threshold (CPT) and pain intensity. Two baseline (pre-intervention) measures and three during intervention measures of CPT and cold pain intensity (four point category scale) were recorded.

SETTING

Physiology laboratory in Leeds Metropolitan University.

PARTICIPANTS

One hundred and twenty-one healthy participants.

INTERVENTIONS

Each participant received one of three TENS interventions over their flexor digitorum profundus: (i) high pulse rate TENS with a strong non-painful paraesthesia (conventional), (ii) low-rate burst mode TENS that caused strong non-painful phasic muscle twitching (acupuncture like) or (iii) no current (placebo) TENS.

MAIN OUTCOME MEASURE

Difference between conventional TENS and AL-TENS in cold pain threshold relative to pre-TENS baseline after 25 min of stimulation.

RESULTS

No differences were detected for CPT or cold pain intensity during conventional TENS compared with AL-TENS. When compared with placebo TENS, the confidence intervals for the ratio of intervention CPT to baseline CPT, for both AL-TENS (0·966, 1·424) and conventional TENS (0·948, 1·401), were close to the positive side of one, although neither reached statistical significance.

CONCLUSIONS

Unlike some previous studies, the present study detected no differences in hypoalgesia between AL-TENS, conventional TENS and placebo (no current) TENS during stimulation.

Could acupuncture needle sensation be a predictor of analgesic response?

During acupuncture some patients experience distinct sensations which are often referred to as needle sensation. Needle sensation may be related to treatment outcome, although what constitutes adequate acupuncture needle sensation is not known. In this paper, we debate the possibility of using the self-report of the overall intensity of needle sensation as a predictor of analgesic outcome to acupuncture. We describe how our approach to establish criteria to determine adequacy of transcutaneous electrical nerve stimulation interventions in clinical trials has been used to inform our search for markers of adequacy of procedural technique for acupuncture. We describe previous research which has focused on developing tools to capture the nature of the descriptors used by patients when they self-report needle sensation and reveal that little attention has been given to its role in outcome. We demonstrate that needle sensation is a complex phenomenon with subjects using multiple descriptors to report their experience. We argue that the intensity of the overall experience of needle sensation may prove useful as a gross marker of the adequacy of acupuncture. We briefly describe our research which isolates individual components of needling technique, such as depth of needle penetration and bidirectional needle rotation, in order to assess their contribution to overall needle sensation intensity.

Electrical acustimulation of the wrist for chronic neck pain: a randomized, sham-controlled trial using a wrist-ankle acustimulation device

OBJECTIVES

Chronic neck pain is a common problem and is treated using a variety of conservative treatments. This single-blind, randomized, sham-controlled trial investigated the value of adding electrical stimulation of acupuncture points on the wrist to a standardized program of neck exercises for chronic neck pain.

METHODS

At initial recruitment 60 patients were randomly assigned to receive either active or sham electrical stimulation of acupuncture points on the wrist in addition to standardized neck exercise. Active or sham wrist acustimulation was given for 30 minutes 2 times/wk over a period of 4 weeks. A 30 minutes program of standardized neck exercises was also performed simultaneously.

RESULTS

Forty-nine patients completed the study (22 active, 27 sham). Statistically significant improvements were found for acustimulation when compared with sham at immediate posttreatment and 1-month posttreatment for Numerical Rating Scale, Northwick Park Neck Pain Questionnaire and Pain Self-Efficacy Questionnaire. In active and sham electrical stimulation group 38.9% and 8.3% of patients reported a reduction of Numerical Rating Scale > 50% at 1-month posttreatment follow-up, respectively. All patients tolerated acustimulation and no adverse effects were reported.

DISCUSSION

Electrical acustimulation of the wrist administered as two, 30 minutes sessions /wk added value to standardized neck exercise for chronic neck pain. A 4-week course of treatment produced effects lasting 1-month posttreatment.

Transcutaneous electrical nerve stimulation for acute pain

BACKGROUND

Transcutaneous Electrical Nerve Stimulation (TENS) is a non-pharmacological agent, based on delivering low voltage electrical currents to the skin. TENS is used for the treatment of a variety of pain conditions.

OBJECTIVES

To assess the analgesic effectiveness of TENS for acute pain in adults to see if it had any clear analgesic effect in its own right.

SEARCH STRATEGY

The following databases were searched: Cochrane Pain, Palliative and Supportive Care Group Specialised Register; the Cochrane Central Register of Controlled Trials, CENTRAL (in The Cochrane Library); MEDLINE; EMBASE; CINAHL; AMED; PEDro; OTseeker; OpenSIGLE; and, reference lists of included studies. The most recent search was undertaken in August 2008.

SELECTION CRITERIA

Randomised controlled trials (RCTs) of adults with acute pain (less than 12 weeks) were included if they examined TENS given as a sole treatment and assessed pain with subjective pain scales. Studies were eligible if they compared TENS to placebo TENS, no treatment controls, pharmacological interventions or non-pharmacological interventions. Studies on experimental pain, case reports, clinical observations, letters, abstracts or reviews were excluded. Studies on TENS and labour pain, pain due to dental procedures and primary dysmenorrhoea were excluded. Studies where TENS was given with another treatment as part of the formal study design were also excluded. No restrictions were made regarding language.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial eligibility and extracted data. Data were extracted on the following: types of participants and pain condition, study design and methods, treatment parameters, adverse effects, and outcome measures. Study authors were contacted for additional information if necessary.

MAIN RESULTS

Of 1479 studies identified in the search, 132 were identified as relevant. Of these, 116 were excluded; the vast majority of these were excluded due to TENS being given with another treatment. Four studies were categorised as awaiting classification as the information provided in the full text failed to clarify their eligibility. Twelve RCTs involving 919 participants at entry were included. The types of acute pain conditions included procedural pain, e.g. cervical laser treatment, venipuncture, screening flexible sigmoidoscopy and non-procedural pain, e.g. postpartum uterine contractions, rib fractures. It was not possible to perform a meta-analysis due to insufficient data.

AUTHORS' CONCLUSIONS

Due to insufficient extractable data in the studies included in this review, we are unable to make any definitive conclusions about the effectiveness of TENS as an isolated treatment for acute pain in adults.

Effectiveness of transcutaneous electrical nerve stimulation for treatment of hyperalgesia and pain

Transcutaneous electrical nerve stimulation (TENS) is a nonpharmacologic treatment for pain relief. TENS has been used to treat a variety of painful conditions. This review updates the basic and clinical science regarding the use of TENS that has been published in the past 3 years (ie, 2005-2008). Basic science studies using animal models of inflammation show changes in the peripheral nervous system, as well as in the spinal cord and descending inhibitory pathways, in response to TENS. Translational studies show mechanisms to prevent analgesic tolerance to repeated application of TENS. This review also highlights data from recent randomized, placebo-controlled trials and current systematic reviews. Clinical trials suggest that adequate dosing, particularly intensity, is critical to obtaining pain relief with TENS. Thus, evidence continues to emerge from both basic science and clinical trials supporting the use of TENS for the treatment of a variety of painful conditions while identifying strategies to increase TENS effectiveness.