Dose-specific Effects of Transcutaneous Electrical Nerve Stimulation (TENS) on Experimental Pain: A Systematic Review

High-frequency, high-intensity transcutaneous electrical nerve stimulation compared with opioids for pain relief after gynecological surgery: a systematic review and meta-analysis

OBJECTIVES

Opioids are important for postoperative analgesia but their use can be associated with numerous side effects. Transcutaneous electrical nerve stimulation (TENS) has been used for acute pain treatment and has dose-dependent analgesic effects, and therefore presents an alternative to intravenous (iv) opioids for postoperative pain relief. The aim of this meta-analysis was to compare high-frequency, high-intensity (HFHI or intense) TENS to iv opioids with regard to postoperative pain intensity, recovery time in the Post Anesthesia Care Unit (PACU) and opioid consumption after elective gynecological surgery.

METHODS

We searched Medline, Embase, Web of Science, Cochrane, Amed and Cinahl for RCTs and quasi-experimental studies (2010-2022), and WHO and ClinicalTrials.gov for ongoing/unpublished studies. Meta-analysis and subsequent Trial Sequential Analysis (TSA) was performed for all stated outcomes. Quality of evidence was assessed according to GRADE.

RESULTS

Only three RCTs met the inclusion criteria (362 participants). The surgical procedures involved surgical abortion, gynecologic laparoscopy and hysteroscopy. The applied TENS frequency was 80 Hz and intensity 40-60 mA. There was no difference in pain intensity according to Visual Analogue Scale (VAS) at discharge from PACU between the TENS and opioid group (MD VAS -0.15, 95 % CI -0.38 to 0.09) (moderate level of evidence). Time in PACU was significantly shorter in the TENS group (MD -15.2, 95 % -22.75 to -7.67), and this finding was manifested by TSA (high-level of evidence). Opioid consumption in PACU was lower in the TENS group (MD Morphine equivalents per patient mg -3.42, 95 % -4.67 to -2.17) (high-level of evidence).

CONCLUSIONS

There was no detectable difference in postoperative pain relief between HFHI TENS and iv opioids after gynecological surgery. Moreover, HFHI TENS decreases recovery time and opioid consumption in PACU. HFHI TENS may be considered an opioid-sparing alternative for postoperative pain relief after gynecological surgery.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021231048.

Effect of Transcutaneous Electrical Nerve Stimulation on Pain-related Quantitative Sensory Tests in Chronic Musculoskeletal Pain and Acute Experimental Pain: Systematic Review and Meta-analysis

This report provides a systematic review of the literature to analyze the effects of transcutaneous electrical nerve stimulation (TENS) on analgesia on sensitization measures, in studies with chronic musculoskeletal pain and in studies with acute experimental pain. The protocol was registered at PROSPERO (CRD42020213473). The authors searched Cochrane Central Register of Controlled Trials, Cumulative Index to Nursing and Allied Health Literature, EMBASE, Latin American and Caribbean Health Sciences Literature via Biblioteca Virtual de Saúde, Physiotherapy Evidence Database, PubMed, ScienceDirect, Web of Science, Google Scholar, and hand-searched reference lists were also conducted. Among 22,252 manuscripts found, 58 studies were included in the systematic review and 35 in the meta-analysis. Thirty-four studies assessed pain intensity; 24 studies investigated hyperalgesia; temporal summation was only evaluated in 2 studies; and conditioned pain modulation was not observed in the included studies. Meta-analyses favored TENS, despite its limitations and heterogeneity. Primary hyperalgesia in studies with musculoskeletal pain presented a high level of evidence, while other outcomes presented moderate evidence in the studies that were included. It is not possible to infer results about both temporal summation and conditioned pain modulation. Moderate evidence suggests that TENS promotes analgesia by reducing both central and peripheral sensitization, as shown by the reduction in primary and secondary hyperalgesia, pain intensity at rest, and during movement in experimental acute pain and chronic musculoskeletal pain. Overall, both types of studies analyzed in this review presented meta-analyses favorable to the use of TENS (compared to placebo TENS), showing reductions in both primary and secondary hyperalgesia, as well as decreases in pain intensity at rest and in motion. PERSPECTIVE: This article presents data from the literature on the effect of TENS through sensitization assessments in individuals with chronic musculoskeletal pain, or acute experimental pain. These data contribute to knowledge about pain neuroscience research, using TENS technology.

The dose-dependent effects of transcutaneous electrical nerve stimulation for pain relief in individuals with fibromyalgia: a systematic review and meta-analysis

ABSTRACT

Transcutaneous electrical nerve stimulation (TENS) is a nonpharmacological modality widely used to manage pain; however, its effectiveness for individuals with fibromyalgia (FM) has been questioned. In previous studies and systematic reviews, variables related to dose of TENS application have not been considered. The objectives of this meta-analysis were (1) to determine the effect of TENS on pain in individuals with FM and (2) determine the dose-dependent effect of TENS dose parameters on pain relief in individuals with FM. We searched the PubMed, PEDro, Cochrane, and EMBASE databases for relevant manuscripts. Data were extracted from 11 of the 1575 studies. The quality of the studies was assessed using the PEDro scale and RoB-2 assessment. This meta-analysis was performed using a random-effects model that, when not considering the TENS dosage applied, showed that the treatment had no overall effect on pain (d+ = 0.51, P > 0.050, k = 14). However, the moderator analyses, which were performed assuming a mixed-effect model, revealed that 3 of the categorical variables were significantly associated with effect sizes: the number of sessions (P = 0.005), the frequency (P = 0.014), and the intensity (P = 0.047). The electrode placement was not significantly associated with any effect sizes. Thus, there is evidence that TENS can effectively reduce pain in individuals with FM when applied at high or at mixed frequencies, a high intensity, or in long-term interventions involving 10 or more sessions. This review protocol was registered at PROSPERO (CRD42021252113).

Mechanism of Action of Peripheral Nerve Stimulation for Chronic Pain: A Narrative Review

The use of stimulation of peripheral nerves to test or treat various medical disorders has been prevalent for a long time. Over the last few years, there has been growing evidence for the use of peripheral nerve stimulation (PNS) for treating a myriad of chronic pain conditions such as limb mononeuropathies, nerve entrapments, peripheral nerve injuries, phantom limb pain, complex regional pain syndrome, back pain, and even fibromyalgia. The ease of placement of a minimally invasive electrode via percutaneous approach in the close vicinity of the nerve and the ability to target various nerves have led to its widespread use and compliance. While most of the mechanism behind its role in neuromodulation is largely unknown, the gate control theory proposed by Melzack and Wall in the 1960s has been the mainstay for understanding its mechanism of action. In this review article, the authors performed a literature review to discuss the mechanism of action of PNS and discuss its safety and usefulness in treating chronic pain. The authors also discuss current PNS devices available in the market today.

High-frequency electrical stimulation attenuates neuronal release of inflammatory mediators and ameliorates neuropathic pain

BACKGROUND

Neuroinflammation is an important driver of acute and chronic pain states. Therefore, targeting molecular mediators of neuroinflammation may present an opportunity for developing novel pain therapies. In preclinical models of neuroinflammatory pain, calcitonin gene-related peptide (CGRP), substance P and high mobility group box 1 protein (HMGB1) are molecules synthesized and released by sensory neurons which activate inflammation and pain. High-frequency electrical nerve stimulation (HFES) has achieved clinical success as an analgesic modality, but the underlying mechanism is unknown. Here, we reasoned that HFES inhibits neuroinflammatory mediator release by sensory neurons to reduce pain.

METHODS

Utilizing in vitro and in vivo assays, we assessed the modulating effects of HFES on neuroinflammatory mediator release by activated sensory neurons. Dorsal root ganglia (DRG) neurons harvested from wildtype or transgenic mice expressing channelrhodopsin-2 (ChR2) were cultured on micro-electrode arrays, and effect of HFES on optogenetic- or capsaicin-induced neuroinflammatory mediator release was determined. Additionally, the effects of HFES on local neuroinflammatory mediator release and hyperalgesia was assessed in vivo using optogenetic paw stimulation and the neuropathic pain model of chronic constriction injury (CCI) of the sciatic nerve.

RESULTS

Light- or capsaicin-evoked neuroinflammatory mediator release from cultured transgenic DRG sensory neurons was significantly reduced by concurrent HFES (10 kHz). In agreement with these findings, elevated levels of neuroinflammatory mediators were detected in the affected paw following optogenetic stimulation or CCI and were significantly attenuated using HFES (20.6 kHz for 10 min) delivered once daily for 3 days.

CONCLUSION

These studies reveal a previously unidentified mechanism for the pain-modulating effect of HFES in the setting of acute and chronic nerve injury. The results support the mechanistic insight that HFES may reset sensory neurons into a less pro-inflammatory state via inhibiting the release of neuroinflammatory mediators resulting in reduced inflammation and pain.

How to gain evidence for causation in disease and therapeutic intervention: from Koch’s postulates to counter-counterfactuals

Researchers, clinicians, and patients have good reasons for wanting answers to causal questions of disease and therapeutic intervention. This paper uses microbiologist Robert Koch’s pioneering work and famous postulates to extrapolate a logical sequence of evidence for confirming the causes of disease: association between individuals with and without a disease; isolation of causal agents; and the creation of a counterfactual (demonstrating that an agent is sufficient to reproduce the disease anew). This paper formally introduces counter-counterfactuals, which appear to have been used, perhaps intuitively, since the time of Koch and possibly earlier. An argument is presented that counter-counterfactuals (disease-preventers) are a useful tool for identifying necessary causes of disease, and sometimes must be used in place of isolation which is not always possible. In addition, a logical sequence of causal evidence for a therapeutic intervention is presented: creating a counterfactual (demonstrating that the intervention is sufficient to change the natural course of a disease), comparisons between subjects in receipt of treatment versus those who are not (typically within a randomised controlled trial, which can quantify effects of intervention), and counter-counterfactuals (treatment-preventers, which can identify the intervention’s mechanisms of action).

Comparing an e-Health program vs home rehabilitation program in patients with non-specific low back pain: A study protocol randomized feasibility trial

BACKGROUND

There is little evidence on the reliability of the web application-based rehabilitation systems to treat chronic low back pain (CLBP).

METHODS

This protocol describes a double-blind, randomized controlled feasibility trial of an e-Health intervention developed to support the self-management of people with CLBP in primary care physiotherapy. Three Hospitals with primary care for outpatients will be the units of randomisation, in each Hospital the participants will be randomized to one of two groups, a pragmatic control group receiving either the usual home program based on electrostimulation and McKenzie Therapy and e-Health intervention. Patients are followed up at 2 and 6 months. The primary outcomes are (1) acceptability and demand of the intervention by GPs, physiotherapists and patients and (2) feasibility and optimal study design/methods for a definitive trial. Secondary outcomes will include analysis in the clinical outcomes of pain, disability, fear of movement, quality of life, isometric resistance of the trunk flexors, lumbar anteflexion and lumbar segmental range of motion.

DISCUSSION

The specific e-Health programs to home could increase adherence to treatment, prevent stages of greater pain and disability, and improve the painful symptomatology.

CONCLUSIONS

The e-Health programs could be an effective healthcare tool that can reach a large number of people living in rural or remote areas.

Comparison of the effectiveness of an e-health program versus a home rehabilitation program in patients with chronic low back pain: A double blind randomized controlled trial

OBJETIVE

We conducted a randomized double blind clinical trial, to compare the effectiveness of McKenzie exercises and electroanalgesia via an e-Health program versus a home rehabilitation program on functionality, pain, fear of movement and quality of life in patients with non-specific chronic low back pain.

METHODS

Seventy-four participants with non-specific chronic low back pain were randomized to either the e- Health program group (n = 39) or the home rehabilitation program group (n = 35). The interventions consisted of the e-Health program group performing McKenzie exercises and received transcutaneous electrical nerve stimulation, while the home rehabilitation group attended an information session to explain the exercises, which they then performed at home with printed instructions. Both groups performed 3 weekly sessions for 8 weeks. The following were analyzed main measures: pain, disability, fear of movement, quality of life, trunk muscle endurance and trunk anteflexion motion were assessed at baseline and at 2 months.

RESULTS

Independent samples Student's t-tests showed that although the patients who followed the e-Health program showed significantly greater improvement than those who followed the home disability rehabilitation program in terms of intensity of pain, lumbar flexion mobility (P < 0.001), and the following dimensions of quality of life (P < 0.005), both groups improved significantly in the immediate post-treatment follow up compared with baseline scores.

CONCLUSIONS

Patients with chronic low back pain who followed an unsupervised home intervention supported by an individualized video exercise program showed greater post-treatment improvement than those who followed the same program with printed instructions.

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.

Hypoalgesic Effects of Transcutaneous Electrical Nerve Stimulation Combined With Joint Manipulation: A Randomized Clinical Trial

OBJECTIVE

The objective of this study was to compare the hypoalgesic effects of isolated or combined use of transcutaneous electrical nerve stimulation (TENS) and cervical joint manipulation (JM) in asymptomatic participants.

METHODS

One hundred and forty-four healthy participants aged 18 to 30 years old were randomly assigned to 1 of 4 groups (n = 36 per group): active TENS + active JM, active TENS + placebo JM, placebo TENS + active JM, and placebo TENS + placebo JM. Active or placebo TENS was applied to the dominant forearm. JM was applied to the C6-7 segments. The pressure pain threshold was measured pre- and postintervention and after 20 minutes on the forearm and tibialis anterior of the dominant side.

RESULTS

Segmental hypoalgesia was greater in the group active TENS + active JM compared with active TENS + placebo JM (P = .002), placebo TENS + active JM (P < .0001), and placebo TENS + placebo JM (P < .0001). For the extrasegmental hypoalgesia, active TENS + active JM had greater hypoalgesic effect compared with active TENS + placebo JM (P = .033), placebo TENS + active JM (P = .002), and placebo TENS + placebo JM (P < .0001).

CONCLUSION

TENS and JM produced hypoalgesia when used alone and, when the treatments were combined, a higher segmental and extrasegmental hypoalgesic effect was obtained in asymptomatic participants.

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.

Cervical Interferential Current Transcutaneous Electrical Sensory Stimulation for Patients with Dysphagia and Dementia in Nursing Homes

Purpose

We aimed to determine the efficacy of interferential current transcutaneous electrical sensory stimulation (IFC-TESS) in patients with dementia who were being treated for dysphagia in nursing homes under normal living conditions.

Patients and Methods

This study recruited 54 nursing home residents (13 males, 41 females; mean age, 84.5 ± 10.7 years) with dysphagia and dementia. IFC-TESS was performed with Gentle Stim^® (Careido Co. Ltd., Kanagawa, Japan) for 15 minutes. Two sessions per day were administered 5 days per week, for 3 weeks. The outcomes included the improvement of the patients' cough reflexes and nutritional states across the 3 weeks of intervention; the former was evaluated with the cough test based on the changes in cough latency time and cough frequency, while the latter was assessed based on changes in the functional oral intake scale (FOIS) score and oral calorie intake.

Results

The cough latency times before and after the 3-week intervention were 15.8 (7.0-60.0) and 6.7 (3.6-30.7) s/min, respectively; the cough frequencies were 5.0 (0.0-5.0) and 5.0 (5.0-5.0) t/min, respectively; the FOIS scores were 5.0 (5.0-6.0) and 5.0 (5.0-6.0), respectively; and oral calorie intakes were 1300.0 (862.5-1420.0) and 1300.0 (1005.0-1462.5) kcal/day, respectively. All parameters significantly improved across the intervention (p < 0.05). When the results were adjusted for age, sex, body mass index, mini nutritional assessment results, Barthel index, and mini-mental state examination scores, IFC-TESS improved the cough reflex and oral calorie intake in older nursing home residents with dementia.

Conclusion

Cervical IFC-TESS can improve the cough reflexes and nutritional states of patients with dysphagia and dementia in nursing homes. As it has previously been difficult to perform active rehabilitation with dementia patients, IFC-TESS may be effective and practicable for the rehabilitation of this patient population.

The Predictive Value of Transcutaneous Electrical Nerve Stimulation for Patient Selection in Peripheral Nerve Field Stimulation for Chronic Low Back Pain: A Prospective Study

OBJECTIVE

Peripheral nerve field stimulation (PNFS) is an effective alternative treatment for patients with chronic low back pain. Transcutaneous electrical nerve stimulation (TENS) is frequently used in pain therapy. Aim of this prospective study was to examine the predictive value of TENS for later PNFS treatment.

MATERIALS AND METHODS

Between 2014 and 2019, a prospective cohort study of 41 patients with chronic lumbar pain was conducted. Pain intensity (NRS) was assessed before and after TENS use, preoperatively/postoperatively and in the follow-up after three and six months, SF12v2 questionnaires with physical (PCS) and mental component summary (MCS) scores, and Oswestry disability index (ODI) questionnaire at baseline as well as three and six months after PNFS implantation. Implantation of the PNFS-system with two percutaneous leads was performed after four to seven days of positive testing. Statistical analysis was performed using depending t-test, ANOVA, and Spearman correlation.

RESULTS

The cohort consisted of 41 patients (19 females, 22 males) with a median age of 60.5 years (IQR^25-75 52-67). Two patients were lost to follow-up. After positive PNFS testing a pulse generator (IPG) was implanted in 15 patients with positive TENS effect and 15 patients without TENS effect. Leads were explanted in nine patients after negative PNFS trial phase. TENS positive patients showed significant correlation to a positive effect in the PNFS trial phase in NRS reduction (p = 0.042) indicating that TENS responders will also respond to PNFS (94% patients). After three and six months follow-up median NRS and SF12v2 (PCS) improved significantly in both cohorts, SF12v2 (MCS) and ODI only in the TENS positive cohort, respectively.

CONCLUSION

TENS can be predictive for patient selection in PNFS, as TENS positive patients showed significant correlation with a positive PNFS trial period. Therefore, TENS positive patients might be justifiable to be directly implanted with leads and IPG. TENS positive patients further tend to show a better improvement in the follow-up.

Mechanism of Peripheral Nerve Stimulation in Chronic Pain

INTRODUCTION

With the advancement of technology, peripheral nerve stimulation (PNS) has been increasingly used to treat various chronic pain conditions. Its origin is based on the gate control theory postulated by Wall and Melzack in 1965. However, the exact mechanism behind PNS' analgesic effect is largely unknown. In this article, we performed a comprehensive literature review to overview the PNS mechanism of action.

DESIGN

A comprehensive literature review on the mechanism of PNS in chronic pain.

METHODS

Comprehensive review of the available literature on the mechanism of PNS in chronic pain. Data were derived from database searches of PubMed, Scopus, and the Cochrane Library and manual searches of bibliographies and known primary or review articles.

RESULTS

Animal, human, and imaging studies have demonstrated the peripheral and central analgesic mechanisms of PNS by modulating the inflammatory pathways, the autonomic nervous system, the endogenous pain inhibition pathways, and involvement of the cortical and subcortical areas.

CONCLUSIONS

Peripheral nerve stimulation exhibits its neuromodulatory effect both peripherally and centrally. Further understanding of the mechanism of PNS can help guide stimulation approaches and parameters to optimize the use of PNS.

Transcutaneous electrical nerve stimulation is superior than placebo and control for postoperative pain relief

Aim: To determine whether transcutaneous electrical nerve stimulation (TENS) is more efficient than placebo TENS and control groups for pain relief. Design: Randomized, single-blinded, placebo-controlled trial. Setting & participants: A total of 78 adults with postoperative pain, after cholecystectomy, at the University Hospital. They were randomized into active TENS, placebo TENS and control. Intervention: A total of 30-min interventions applied in the first 24 h after the surgery. Outcome: Pain intensity. Results: Pain significantly decreased for both TENS; however, the active TENS was better. A decrease of 2 points or more on the visual analog scale for 53.8% active TENS and 11.5% placebo. Conclusion: There was a greater reduction in pain of important clinical relevance in the active TENS group.

Clinical Trial registration: Brazilian Clinical Trial (REBEC): RBR-6cgx2k.

Repeated and patterned stimulation of cutaneous reflex pathways amplifies spinal cord excitability

Priming with patterned stimulation of antagonist muscle afferents induces modulation of spinal cord excitability as evidenced by changes in group Ia reciprocal inhibition. When assessed transiently with a condition-test pulse paradigm, stimulating cutaneous afferents innervating the foot reduces Ia presynaptic inhibition and facilitates soleus Hoffmann (H)-reflex amplitudes. Modulatory effects (i.e., priming) of longer lasting sensory stimulation of cutaneous afferents innervating the foot have yet to be examined. As a first step, we examined how priming with 20 min of patterned and alternating stimulation between the left and right foot affects spinal cord excitability. During priming, stimulus trains (550 ms; consisting of twenty-eight 1-ms pulses at 51 Hz, 1.2 times the radiating threshold) were applied simultaneously to the sural and plantar nerves of the ankle. Stimulation to the left and right ankle was out of phase by 500 ms. We evoked soleus H-reflexes and muscle compound action potentials (M waves) before and following priming stimulation to provide a proxy measure of spinal cord excitability. H-reflex and M-wave recruitment curves were recorded at rest, during brief (<2 min) arm cycling, and with sural conditioning [train of five 1-ms pulses at 2 times the radiating threshold (RT) with a condition-test interval (C-T) = 80 ms]. Data indicate an increase in H-reflex excitability following priming via patterned sensory stimulation. Transient sural conditioning was less effective following priming, indicating that the increased excitability of the H-reflex is partially attributable to reductions in group Ia presynaptic inhibition. Sensory stimulation to cutaneous afferents, which enhances spinal cord excitability, may prove useful in both rehabilitation and performance settings.NEW & NOTEWORTHY Priming via patterned stimulation of the nervous system induces neuroplasticity. Yet, accessing previously known cutaneous reflex pathways to alter muscle reflex excitability has not yet been examined. Here, we show that sensory stimulation of the cutaneous afferents that innervate the foot sole can amplify spinal cord excitability, which, in this case, is attributed to reductions in presynaptic inhibition.

EEG alpha activity increased in response to transcutaneous electrical nervous stimulation in young healthy subjects but not in the healthy elderly

Transcutaneous Electrical Nerve Stimulation (TENS) is used not only in the treatment of pain but also in the examination of sensory functions. With aging, there is decreased sensitivity to somatosensory stimuli. It is essential to examine the effect of TENS application on the sensory functions in the brain by recording the spontaneous electroencephalogram (EEG) activity and the effect of aging on the sensory functions of the brain during the application. The present study aimed to investigate the effect of the application of TENS on the brain’s electrical activity and the effect of aging on the sensory functions of the brain during application of TENS. A total of 15 young (24.2 ± 3.59) and 14 elderly (65.64 ± 4.92) subjects were included in the study. Spontaneous EEG was recorded from 32 channels during TENS application. Power spectrum analysis was performed by Fast Fourier Transform in the alpha frequency band (8–13 Hz) for all subjects. Repeated measures of analysis of variance was used for statistical analysis (p < 0.05). Young subjects had increased alpha power during the TENS application and had gradually increased alpha power by increasing the current intensity of TENS (p = 0.035). Young subjects had higher alpha power than elderly subjects in the occipital and parietal locations (p = 0.073). We can, therefore, conclude that TENS indicated increased alpha activity in young subjects. Young subjects had higher alpha activity than elderly subjects in the occipital and somatosensory areas. To our knowledge, the present study is one of the first studies examining the effect of TENS on spontaneous EEG in healthy subjects. Based on the results of the present study, TENS may be used as an objective method for the examination of sensory impairments, and in the evaluative efficiency of the treatment of pain conditions.

Investigation of the Involvement of the Endocannabinoid System in TENS-Induced Antinociception

Transcutaneous electrical nerve stimulation (TENS) promotes antinociception by activating the descending pain modulation pathway and consequently releasing endogenous analgesic substances. In addition, recent studies have shown that the endocannabinoid system controls pain. Thus, the present study investigated the involvement of the endocannabinoid system in TENS-induced antinociception of cancer pain using a cancer pain model induced by intraplantar (i.pl.) injections of Ehrlich tumor cells in male Swiss mice. Low- and high-frequency TENS was applied for 20 minutes to the mice's paws, and to investigate the involvement of the endocannabinoid system were used the N-(peperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pitazole-3-carboixamide (AM251), a cannabinoid CB₁ receptor antagonist and (5Z,8Z,11Z,14Z)-5,8,11,14-eicosatetraenyl-methylester phosphonofluoridic acid (MAFP), an inhibitor of the endocannabinoid metabolizing enzyme fatty acid amide hydrolase, injected by via i.pl., intrathecal (i.t.), and intradorsolateral periaqueductal gray matter (i.dl.PAG). Furthermore, liquid chromatography-tandem mass spectrometry, western blot, and immunofluorescence assays were used to evaluate the endocannabinoid anandamide levels, cannabinoid CB₁ receptor protein levels, and cannabinoid CB₁ receptor immunoreactivity, respectively. Low- and high-frequency TENS reduced the mechanical allodynia induced by Ehrlich tumor cells and this effect was reversed by AM251 and potentiated by MAFP at the peripheral and central levels. In addition, TENS increased the endocannabinoid anandamide levels and the cannabinoid CB₁ receptor protein levels and immunoreactivity in the paw, spinal cord, and dorsolateral periaqueductal gray matter. These results suggest that low- and high-frequency TENS is effective in controlling cancer pain, and the endocannabinoid system is involved in this effect at both the peripheral and central levels. PERSPECTIVE: TENS is a nonpharmacological strategy that may be used to control cancer pain. Identification of a new mechanism involved in its analgesic effect could lead to the development of clinical studies as well as an increase in its application, lessening the need for pharmacological treatments.

Segmental and extrasegmental hypoalgesic effects of low-frequency pulsed current and modulated kilohertz-frequency currents in healthy subjects: randomized clinical trial

Objective: To compare the segmental and extrasegmental hypoalgesic effects of TENS, IFC and Aussie current on pressure pain threshold (PPT) during and after stimulation in healthy subjects. The second objective was to compare the sensory comfort related to electrical stimulation.Material and Methods: 120 healthy subjects were randomized in TENS, IFC, Aussie current or placebo groups. The electrical stimulation was administered on the forearm. The PPT was measured on the forearm (segmental measure) and on the lower leg (extrasegmental measure) by an algometer at baseline, during and after stimulation of the forearm, and the sensory comfort in relation to electrical stimulation was measured with a visual analogue scale. Statistical analysis was performed using linear mixed models for PPT analysis and one-way ANOVA for sensory comfort analysis.Results: The TENS, IFC and Aussie current increased the segmental and extrasegmental PPTs during application of current compared to the placebo. The PPTs measures and sensory comfort were not significantly different between the TENS, IFC and Aussie current groups.Conclusions: Segmental and extrasegmental hypoalgesic effects may be produced using TENS, IFC or Aussie currents in healthy subjects. Furthermore, all of them presented a similar sensory comfort.

Does Frequency Modulation of Transcutaneous Electrical Nerve Stimulation Affect Habituation and Mechanical Hypoalgesia? A Randomized, Double-Blind, Sham-Controlled Crossover Trial

BACKGROUND

Devices for applying transcutaneous electrical nerve stimulation (TENS) use numerous frequency modulation patterns for decreasing habituation to currents. However, there is no evidence supporting the use of an optimal pattern instead of the others, or even modulated frequencies instead of a fixed frequency.

OBJECTIVE

The objectives of this study were to determine the effects of 3 TENS patterns (fixed frequency, random modulation, and 6-second-6-second [6s-6s] modulation) on habituation, to examine the subjective perception of habituation and comfort, and to determine their effects on the mechanical pain threshold (MPT).

DESIGN

This study was a randomized, double-blind, sham-controlled crossover trial.

SETTING

The study took place in a university research laboratory under attenuated noise conditions at a regulated temperature of 22°C to 26°C.

PARTICIPANTS

Thirty-nine volunteers who were healthy participated in this trial.

INTERVENTION

The participants received 4 different TENS interventions (fixed frequency, random modulation, 6s-6s modulation, and sham) in random order, with a 24-hour washout period, on the radial nerve.

MEASUREMENTS

The main outcome-habituation-was quantified by the increase in current density and the number of times the intensity had to be increased during the session. Secondary outcome variables were subjective perception of habituation and comfort and MPT.

RESULTS

Random modulation reduced the number of times the intensity had to be increased because of habituation compared with no modulation (1.6 times; 95% confidence interval [CI] = 0.7-2.6) and 6s-6s modulation (0.8 times; 95% CI = 0.01-1.6). No differences were observed between interventions in terms of an increase in current density, self-perceived habituation, or self-perceived comfort. MPT increased during the intervention in the random-modulation group (4.4 N; 95% CI = 1.8-7.0) and the no-modulation group (5.9 N; 95% CI = 1.9-10.0); there were no significant changes in the other 2 groups.

LIMITATIONS

The success of masking or blinding procedures of the participants was not assessed.

CONCLUSIONS

Randomly modulated frequencies caused less habituation than nonmodulated frequencies or 6s-6s modulation. Further research on more prolonged (hours-long) interventions in participants with pain is required.

Efficiency of Tissue Penetration by Currents Induced by 3 Electrotherapeutic Techniques: A Comparative Study Using a Novel Deep-Tissue Measuring Technique

BACKGROUND

Electrotherapy provides a wide range of treatment alternatives for musculoskeletal pathologies. However, for the electrical stimulation to exert a significant therapeutic effect, the induced current must often penetrate deep inside the target tissue.

OBJECTIVE

The objective was to systematically compare the penetration efficiency of 3 electrotherapeutic stimulation modalities: transcutaneous electrical nerve stimulation (TENS), interferential (IF) stimulation, and combined therapy with pulsed ultrasound and IF current (CTPI).

DESIGN

This was a comparative, experimental laboratory study.

METHODS

The penetration efficiency was evaluated as a voltage difference between 2 of an 8-contact spinal cord stimulation array. Each of 20 participants with a preimplanted spinal cord stimulation array was stimulated with TENS (3 different electrode configurations), IF current (3 configurations), and CTPI (1 configuration).

RESULTS

Significant differences in penetration efficiency were found between the various stimulation conditions and electrode configurations. CTPI showed the highest penetration efficiency, followed by IF, and finally TENS. Penetration efficiency was inversely and significantly correlated with skinfold thickness in all conditions, but this correlation was lowest for the CTPI stimulation.

LIMITATIONS

Our study design did not include a condition of combined therapy with pulsed ultrasound and TENS, and it did not directly control for current or voltage density under the stimulating electrodes. In addition, further research is required to determine whether a higher stimulation intensity of the target tissue is advantageous clinically.

CONCLUSIONS

Pending further testing, CTPI stimulation could prove more effective than IF and TENS in reaching deeper tissues, especially considering the variability in adipose tissue thickness in the population, for example, in cases of patients with obesity.

Contralateral segmental transcutaneous electrical nerve stimulation inhibits nociceptive flexion reflex in healthy participants

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive treatment to relieve pain. Contralateral TENS (i.e. TENS administered to the contralateral side of a painful body part) is beneficial when TENS cannot be directly applied to pain site, such as in cases of trauma. Although TENS produces segmental analgesia in an ipsilateral limb, it has been unclear whether TENS produces higher analgesic effects in the contralateral segmental area. The aim of the present study was to investigate the analgesic effects of TENS in contralateral segmental or extra-segmental areas on physiological and subjective pain outcomes, using a nociceptive flexion reflex (NFR) method.

METHODS

We randomly allocated 60 healthy participants to three groups: contralateral segmental TENS (CS-TENS); contralateral extra-segmental TENS (CE-TENS); and contralateral placebo TENS (CP-TENS). CS-TENS was applied to right superficial sural nerve and CE-TENS was applied to the right superficial femoral nerve, each for 30 minutes. The magnitude of the NFR elicited by electrical stimulation of the left sural nerve was measured at baseline and at three subsequent 10-minute intervals. Subjective pain intensity was measured simultaneously with a visual analogue scale (VAS).

RESULTS

At 30 min, the NFR magnitude of CS-TENS group was significantly lower than that of the CP-TENS group (p = 0.021). There were no significant differences in VAS scores among the groups at any time point.

CONCLUSIONS

Our findings suggest that CS-TENS inhibited NFR. Although there was no significant between-group difference in subjective pain intensity, factors such as a placebo effect probably impacted it.

SIGNIFICANCE

Our findings provide support for the contralateral approach at stimulation sites when TENS cannot be directly administered to a pain site (e.g. due to disease or trauma).

Effectiveness of fixed-site high-frequency transcutaneous electrical nerve stimulation in chronic pain: a large-scale, observational study

Objective

The objective of this study was to assess the effectiveness of fixed-site high-frequency transcutaneous electrical nerve stimulation (FS-TENS) in a real-world chronic pain sample.

Background

There is a need for nonpharmacological treatment options for chronic pain. FS-TENS improved multisite chronic pain in a previous interventional study. Large observational studies are needed to further characterize its effectiveness.

Methods

This retrospective observational cohort study examined changes in chronic pain measures following 60 days of FS-TENS use. The study data were obtained from FS-TENS users who uploaded their device utilization and clinical data to an online database. The primary outcome measures were changes in pain intensity and pain interference with sleep, activity, and mood on an 11-point numerical rating scale. Dose-response associations were evaluated by stratifying subjects into low (≤30 days), intermediate (31-56 days), and high (≥57 days) utilization subgroups. FS-TENS effectiveness was quantified by baseline to follow-up group differences and a responder analysis (≥30% improvement in pain intensity or ≥2-point improvement in pain interference domains).

Results

Utilization and clinical data were collected from 11,900 people using FS-TENS for chronic pain, with 713 device users meeting the inclusion and exclusion criteria. Study subjects were generally older, overweight adults. Subjects reported multisite pain with a mean of 4.8 (standard deviation [SD] 2.5) pain sites. A total of 97.2% of subjects identified low back and/or lower extremity pain, and 72.9% of subjects reported upper body pain. All pain measures exhibited statistically significant group differences from baseline to 60-day follow-up. The largest changes were pain interference with activity (-0.99±2.69 points) and mood (-1.02±2.78 points). A total of 48.7% of subjects exhibited a clinically meaningful reduction in pain interference with activity or mood. This proportion increased to 57.1% for the high utilization subgroup.

Conclusion

FS-TENS is a practical option for treating multisite chronic pain. The greatest impact is on pain interference with activity and mood. FS-TENS utilization and effectiveness exhibit a dose-response association, suggesting that daily use maximizes pain relief.

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.

Study protocol of hypoalgesic effects of low frequency and burst-modulated alternating currents on healthy individuals

The aim of the study will be to compare different types of analgesic electrical currents in relation to the pressure pain threshold and sensory comfort in healthy individuals. A total of 100 individuals will be randomly assigned to four groups: transcutaneous electrical nerve stimulation, interferential current, Aussie current or placebo. The electrical stimulation will be administered with a strong level for 30 min and to the placebo group, the electrodes will be positioned while the equipment will remain switched off. The pressure pain threshold and sensory comfort will be measured with an algometer and the visual analogue scale, respectively. The level of significance will be p < 0.05. Study registration: NCT01950728 (clinical trials).

Intensity matters: Therapist-dependent dose of spinal transcutaneous electrical nerve stimulation

The intensity used during transcutaneous electrical nerve stimulation (TENS) in both, clinical practice and research studies, is often based on subjective commands such as “strong but comfortable sensation”. There is no consensus regarding the effectiveness dose of TENS. The objective was to determine the difference in the effect of spinal TENS on soleus H-reflex modulation when applied by two therapists instructed to apply the stimulation at a “strong but comfortable” intensity. Twenty healthy volunteers divided into two groups: Therapist 1 (n = 10) and Therapist 2 (n = 10). Both therapist applied spinal TENS and sham stimulation at the T10–12 spinal level for 40min in random order to each subject, at an intensity designed to produce a “strong but comfortable” sensation. To avoid habituation, the intensity was adjusted every 2min. Soleus H-reflex was recorded before, during, and 10min after TENS by an observer blinded to the stimulus applied. Despite the instruction to apply TENS at a “strong comfortable” level, a significant difference in current density was identified: Therapist 1 (0.67mA/cm², SD 0.54) applied more than Therapist 2 (0.53mA/cm², SD 0.57; p<0.001) at the onset of the intervention. Maximal peak-to-peak H-reflex amplitude was inhibited significantly more 10min following TENS applied by Therapist 1 (-0.15mV, SD 0.16) compared with Therapist 2 (0.04mV, SD 0.16; p = 0.03). Furthermore, current density significantly correlated with the inhibitory effect on peak-to-peak Soleus H-reflex amplitude 10 min after stimulation (Rho = -0.38; p = 0.04). TENS intensity dosage by the therapist based on the subjective perception of the participants alone is unreliable and requires objective standardization. In addition, higher current density TENS produced greater inhibition of the Soleus H-reflex.

Review of devices used in neuromuscular electrical stimulation for stroke rehabilitation

Neuromuscular electrical stimulation (NMES), specifically functional electrical stimulation (FES) that compensates for voluntary motion, and therapeutic electrical stimulation (TES) aimed at muscle strengthening and recovery from paralysis are widely used in stroke rehabilitation. The electrical stimulation of muscle contraction should be synchronized with intended motion to restore paralysis. Therefore, NMES devices, which monitor electromyogram (EMG) or electroencephalogram (EEG) changes with motor intention and use them as a trigger, have been developed. Devices that modify the current intensity of NMES, based on EMG or EEG, have also been proposed. Given the diversity in devices and stimulation methods of NMES, the aim of the current review was to introduce some commercial FES and TES devices and application methods, which depend on the condition of the patient with stroke, including the degree of paralysis.

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.

Fixed-site high-frequency transcutaneous electrical nerve stimulation for treatment of chronic low back and lower extremity pain

Objective

The objective of this study was to determine if fixed-site high-frequency transcutaneous electrical nerve stimulation (FS-TENS) is effective in treating chronic low back and lower extremity pain.

Background

Transcutaneous electrical nerve stimulation is widely used for treatment of chronic pain. General-purpose transcutaneous electrical nerve stimulation devices are designed for stimulation anywhere on the body and often cannot be used while the user is active or sleeping. FS-TENS devices are designed for placement at a pre-determined location, which enables development of a wearable device for use over extended time periods.

Methods

Study participants with chronic low back and/or lower extremity pain self-administered an FS-TENS device for 60 days. Baseline, 30-, and 60-day follow-up data were obtained through an online questionnaire. The primary outcome measure was the patient global impression of change. Pain intensity and interference were assessed using the Brief Pain Inventory. Changes in use of concomitant pain medications were evaluated with a single-item global self-rating.

Results

One hundred and thirty participants were enrolled, with 88 completing the 60-day follow-up questionnaire. Most participants (73.9%) were 50 years of age or older. At baseline, low back pain was identified by 85.3%, lower extremity pain by 71.6%, and upper extremity pain by 62.5%. Participants reported widespread pain, at baseline, with a mean of 3.4 (standard deviation 1.1) pain sites. At the 60-day follow-up, 80.7% of participants reported that their chronic pain had improved and they were classified as responders. Baseline characteristics did not differentiate non-responders from responders. There were numerical trends toward reduced pain interference with walking ability and sleep, and greater pain relief in responders. There was a large difference in use of concomitant pain medications, with 80.3% of responders reporting a reduction compared to 11.8% of non-responders.

Conclusion

FS-TENS is a safe and effective option for treating chronic low back and lower extremity pain. These results motivate the use of FS-TENS in development of wearable analgesic devices.

High- and low-frequency transcutaneous electrical nerve stimulation does not reduce experimental pain in elderly individuals

High- and low-frequency transcutaneous electrical nerve stimulation is effective for reducing experimental heat pain in young individuals but not in older individuals.

Despite its widespread clinical use, the efficacy of transcutaneous electrical nerve stimulation (TENS) remains poorly documented in elderly individuals. In this randomized, double-blind crossover study, we compared the efficacy of high-frequency (HF), low-frequency (LF), and placebo (P) TENS in a group of 15 elderly adults (mean age: 67 ± 5 years). The effect of HF-, LF-, and P-TENS was also evaluated in a group of 15 young individuals (26 ± 5 years; same study design) to validate the effectiveness of the TENS protocols that were used in the elderly group. Each participant came to the laboratory on 3 separate occasions to receive, in random order, HF-, LF-, and P-TENS. Pain intensity and pain perception thresholds were assessed before, during, and after TENS, using an experimental heat pain paradigm. For the young group, there was a significant decrease in pain intensity during and after HF- and LF-TENS when compared with baseline, with both HF- and LF-TENS being superior to P-TENS. In the older group, HF- and LF-TENS did not reduce pain when compared with baseline and no difference was observed between the 2 active TENS sessions and P-TENS. High-frequency, LF-, and P-TENS all increased pain thresholds in young individuals, whereas in older individuals, only LF-TENS increased pain thresholds. Taken together, these results suggest that TENS is effective in young, but not in older, individuals. Future studies should be conducted to confirm these results in pain populations and to identify strategies that could enhance the effect of TENS in the elderly.

Effect of Fixed Versus Adjusted Transcutaneous Electrical Nerve Stimulation Amplitude on Chronic Mechanical Low Back Pain

OBJECTIVES

This study aimed to investigate the effect of adjusting pulse amplitude of transcutaneous electrical nerve stimulation versus fixed pulse amplitude in treatment of chronic mechanical low back pain.

DESIGN

Randomized clinical trial.

SETTING

El-sahel Teaching Hospital, Egypt.

PARTICIPANTS

Forty-five patients with chronic low back pain assigned to three equal groups. Their ages ranged from 20 to 50 years.

INTERVENTION

The three groups received the same exercise program. Group A received transcutaneous electrical nerve stimulation with fixed pulse amplitude for 40 minutes. Group B received transcutaneous electrical nerve stimulation with adjusted pulse amplitude for 40 minutes, with the pulse amplitude adjusted every 5 minutes. Group C received exercises only. Treatment sessions were applied three times per week for 4 weeks for the three groups.

OUTCOME MEASURES

A visual analogue scale was used to assess pain severity, the Oswestry Disability Index was used to assess functional level, and a dual inclinometer was used to measure lumbar range of motion. Evaluations were performed before and after treatment.

RESULTS

Visual analogue scale, Oswestry Disability Index, and back range of motion significantly differed between the two groups that received transcutaneous electrical nerve stimulation and the control group and did not significantly differ between fixed and adjusted pulse amplitude of transcutaneous electrical nerve stimulation.

CONCLUSION

Adjusting pulse amplitude of transcutaneous electrical nerve stimulation does not produce a difference in the effect of transcutaneous electrical nerve stimulation used to treat chronic low back pain.

Effect of pulsed electromagnetic field therapy on experimental pain: A double-blind, randomized study in healthy young adults

Previous studies suggested that pulsed electromagnetic field (PEMF) therapy can decrease pain. To date, however, it remains difficult to determine whether the analgesic effect observed in patients are attributable to a direct effect of PEMF on pain or to an indirect effect of PEMF on inflammation and healing. In the present study, we used an experimental pain paradigm to evaluate the direct effect of PEMF on pain intensity, pain unpleasantness, and temporal summation of pain. Twenty-four healthy subjects (mean age 22 ± 2 years; 9 males) participated in the experiment. Both real and sham PEMF were administered to every participant using a randomized, double-blind, cross-over design. For each visit, PEMF was applied for 10 minutes on the right forearm using a portable device. Experimental pain was evoked before (baseline) and after PEMF with a 9 cm(2) Pelletier-type thermode, applied on the right forearm (120 s stimulation; temperature individually adjusted to produce moderate baseline pain). Pain intensity and unpleasantness were evaluated using a 0-100 numerical pain rating scale. Temporal summation was evaluated by comparing pain intensity ratings obtained at the end of tonic nociceptive stimulation (120 s) with pain intensity ratings obtained after 60 s of stimulation. When compared to baseline, there was no change in pain intensity and unpleasantness following the application of real or sham PEMF. PEMF did not affect temporal summation. The present observations suggest that PEMF does not directly influence heat pain perception in healthy individuals.

The use of conventional transcutaneous electrical nerve stimulation in chronic facial myalgia patients

OBJECTIVES

The aim of this study was to evaluate the efficacy of conventional TENS in women affected by chronic facial myalgia.

MATERIALS AND METHODS

The study was performed on 49 women affected by chronic facial myalgia randomly allocated in the TENS group (34 women) and the control group (15 women). The subjective level of pain was assessed by the Visual Analogue Scale indicating the mean (VAS MEAN), the maximum (VAS MAX) and the current intensity of pain (VAS NOW). The level of pain at the muscular palpation sites was assessed by the Pericranial Muscle Tenderness Score (PTS) and the Cervical Muscle Tenderness Score (CTS). The TENS therapy lasted for 10 weeks, and data were collected at baseline, after 5, 10, 15 and 25 weeks. The differences between groups before and after treatment were compared with the Mann-Whitney and the Kolmogorov-Smirnov tests. The intra-group differences were compared with the one-way ANOVA test.

RESULTS

The results showed that the VAS MEAN, VAS MAX, PTS and CTS were significantly reduced in the TENS group compared to the control group after 10 weeks of TENS (p < 0.05). The intra-group analysis revealed a decreasing tendency of VAS MEAN, VAS MAX, VAS NOW, PTS and CTS in the TENS group in a 25-week period (p < 0.05).

CONCLUSIONS

The study demonstrated the efficacy of conventional TENS in patients with chronic facial myalgia and the decrease in both subjective and objective pain.

CLINICAL RELEVANCE

Conventional TENS is a safe, non-invasive, easy-to-administer therapy for chronic facial myalgia.

Associating high intensity and modulated frequency of TENS delays analgesic tolerance in rats

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive analgesic resource extensively used in painful conditions. However, preclinical studies suggest that the prolonged use of TENS results in the development of tolerance to its analgesic effect. The present study investigated the analgesic effect and development of tolerance to TENS with four different stimulation protocols.

METHODS

Male Wistar rats induced with joint inflammation were divided into four groups: sensory intensity, low motor intensity, high motor intensity and sham groups. TENS was applied daily for 20 min with alternating frequency between 4 and 100 Hz until tolerance development was evidenced. Mechanical hyperalgesia was measured before and after each TENS daily application.

RESULTS

After TENS, tolerance was evidenced There was a significant reduction in the mechanical withdrawal threshold in all groups 24 h after induction of inflammation (p  <  0.01). We observed a loss of analgesic efficacy of TENS around the 12th, 19th and 19th days in the groups treated with sensory intensity, low motor intensity and high motor intensity, respectively (p < 0.02) when analysed using paired measurements and compared with the control.

CONCLUSIONS

The association between frequency variation and intensity at motor level promotes a delay in the development of analgesic tolerance to TENS, optimizing and extending its therapeutic effectiveness.

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.

Brain mechanisms of pain relief by transcutaneous electrical nerve stimulation: A functional magnetic resonance imaging study

BACKGROUND

Although the exact mechanism of TENS pain relief is unknown, it is believed that TENS impulses interrupt nociceptive signals at the dorsal horn of the spinal cord.

AIMS

To evaluate the hypotheses that during pain caused by noxious stimuli, brain responses, temporal summation and brain functional connectivity are modulated by TENS, and that mechanisms of pain relief by TENS differ between men and women.

METHODS

During fMRI scanning, the same noxious stimuli were delivered to each participant in pain-only and pain+TENS conditions. In the pain-only condition, noxious stimuli were presented without TENS. In the pain+TENS condition, participants received noxious stimuli and TENS concurrently. Participants were initially presented with TENS at an intensity that was just below that causing discomfort. TENS intensity was presented in a step-wise fashion to prevent temporal summation from repetitive noxious stimuli.

RESULTS

Pain and unpleasantness ratings were significantly higher in the pain-only than the pain+TENS condition. With non-painful TENS, primary and secondary somatosensory and parietal cortices were activated, and temporal summation from repetitive noxious stimuli was prevented. Periaqueductal gray (PAG) and lateral prefrontal cortex functional connectivity was increased by TENS, and modulated by testosterone and cortisol. Women reported greater pain during TENS than men, and showed greater activation in the temporoparietal junction cortex and increased PAG functional connectivity with the orbitofrontal cortex.

CONCLUSION

TENS led to pain reduction, probably due to activation of the descending pain-inhibitory pathway, indicating that this TENS method may be applied in clinical practice.

Influence of different frequencies of transcutaneous electrical nerve stimulation on the threshold and pain intensity in young subjects

Objective

To investigate the effects of different transcutaneous electrical nerve stimulation frequencies in nociception front of a pressure pain threshold and cold in healthy individuals.

Methods

Twenty healthy subjects were divided into four groups, all of which have gone through all forms of electrical stimulation at different weeks.

Assessments were

pre and post-therapy, 20 and 60 minutes after stimulation. To evaluate the pressure pain threshold, an algometer was used with one tapered tip, pressing the hypothenar region until voluntary report the word “pain”. Cold pain intensity was assessed by immersion in water at 5°C for 30 seconds; at the end, the subject was asked to quantify the pain intensity on a Visual Analog Scale for Pain. For electrical stimulation, two electrodes were used near the elbow, for 20 minutes, with an intensity strong, but not painful. The frequency was in accordance with the group: 0Hz (placebo); 7Hz; 100Hz; and 255Hz.

Results

Both for the assessment of pressure pain threshold as the cold pain intensity, there was no significant difference (p>0.05).

Conclusion

We conclude that the use of transcutaneous electrical nerve stimulation on dermatomes C6 to C8 produced no significant change in pressure pain threshold or cold discomfort.

Contralateral antalgic effect of high-frequency transcutaneous peripheral nerve stimulation

OBJECTIVE

To investigate the analgesic effect of high-frequency transcutaneous peripheral nerve stimulation (HF-TPNS) in the ipsilateral and contralateral skin territory of the stimulated nerve.

DESIGN

Prospective, cross-over study.

SETTING

Clinical neurophysiology unit, institutional care, rehabilitation center.

PARTICIPANTS

Ten healthy volunteers (5 male, 5 female).

METHODS

Participants underwent 3 different sessions. In the first, heat pain thresholds (HPTs) were measured on the left dorsal hand skin without stimulation; in the second and third sessions, HPTs were measured, respectively, in the territory of the left and right radial nerve before, during, and after an electrical stimulation (10 minutes, 100 Hz, 0.1 ms) of the left superficial radial nerve.

MAIN OUTCOME MEASUREMENT

Heat pain threshold.

RESULTS

An increase of HPTs was observed in the skin territory of both right and left radial nerve during and after the left radial nerve stimulation.

CONCLUSION

The present study demonstrates an analgesic effect of HF-TPNS not only in the ipsilateral but also in the contralateral side of stimulation, suggesting a possible role of contralateral HF-TPNS in the treatment by physical therapy of patients with unilateral pain syndromes.

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.

A preliminary report on adjuvant analgesic efficacy of HANS in opioid tolerant patients with cancer pain

OBJECTIVE

To observe the adjuvant analgesic efficacy of Han's Acupoint Nerve Stimulator (HANS) in opioid tolerant patients with cancer pain.

METHODS

A prospective non-controlled study was conducted. Opioid tolerant patients with cancer pain were enrolled and treated with both routinely analgesics and adjuvant HANS (2/100 Hz for 30 min/d, 5 d on and 2 d off for two weeks). Cancer pain, quality of life (QOL), anxiety and depression were assessed before enrollment and on d 8 and d 15 with the BPI-C, EORTC QLQ-C30, and self-rating anxiety scale (SAS)/self-rating depression scale (SDS), respectively; the therapeutic frequency of breakthrough pain (BP) and daily opioid dose were also recorded.

RESULTS

Totally 47 patients meeting the inclusion criteria participated in this study; 43 patients completed the two-week treatment and assessment. The mean scores of patient's "worst" and "least" pain intensity assessed with BPI-C decreased significantly on d 8 and d 15; the therapeutic frequency of BP also significantly decreased; but the average daily dose of opioids did not change significantly. For the nine symptoms in EORTC QLQ-C30 assessment, the mean scores of pain, fatigue, constipation and insomnia were significantly lower on d 8 and d 15 compared with baseline; the mean scores of the overall health status, nausea/vomiting and the incidence rates of both anxiety and depression also decreased significantly on d 15.

CONCLUSIONS

To opioid tolerant patients with cancer pain, adjuvant treatment with HANS could improve pain release and patients' QOL by decreasing the severity of pain, fatigue, constipation, insomnia and other concomitant symptoms; it could also decrease the incidence rates of anxiety and depression.