Transcutaneous electrical nerve stimulation at both high and low frequencies reduces primary hyperalgesia in rats with joint inflammation in a time-dependent manner

Transcutaneous Electrical Nerve Stimulation Integrated into Pants for the Relief of Postoperative Pain in Hip Surgery Patients: A Randomized Trial

Background

The effect of transcutaneous electrical nerve stimulation (TENS) on pain and impression of change was assessed during a 2.5-hour intervention on the first postoperative days following hip surgery in a randomized, single-blinded, placebo-controlled trial involving 30 patients.

Methods

Mixed-frequency TENS (2 Hz/80 Hz) was administered using specially designed pants integrating modular textile electrodes to facilitate stimulation both at rest and during activity. The treatment outcome was assessed by self-reported pain Numerical Rating Scale (NRS) and Patient Global Impression of Change (PGIC) scores at four time points. The ability to perform a 3-meter walk test and the use of analgesics were also evaluated. Group comparison and repeated-measure analysis were carried out using nonparametric statistics.

Results

The active TENS group exhibited significantly higher PGIC scores after 30 minutes, which persisted throughout the intervention (all p ≤ 0.001). A reduction in NRS appeared after one hour of active TENS, persisting throughout the intervention (all p ≤ 0.05). The median group differences in pain ratings were greater than the minimum clinically important difference, and the analysis of pain trajectories confirmed clinical significance at the individual level. Moreover, patients in the active TENS group were more likely able to perform a 3-meter walk test by the end of the intervention (p = 0.04). Analysis of the opioid-sparing effect of TENS was inconclusive (p = 0.066). No postoperative surgical complications or TENS-related side effects were observed during the study.

Conclusion

Mixed-frequency TENS integrated in pants could potentially be an interesting addition to the arsenal of treatments for multimodal analgesia following hip surgery. This trial is registered with NCT05678101.

Transcutaneous Electric Nerve Stimulation in Animal Model Studies: From Neural Mechanisms to Biological Effects for Analgesia

OBJECTIVE

This systematic and meta-analysis review evaluated the transcutaneous electrical nerve stimulation (TENS)-induced action mechanisms for animal analgesia.

MATERIALS AND METHODS

Two independent investigators identified relevant articles published until February 2021 through a literature review, and a random-effects meta-analysis was performed to synthesize the results.

RESULTS

Of the 6984 studies found in the data base search, 53 full-text articles were selected and used in the systematic review. Most studies used Sprague Dawley rats (66.03%). High-frequency TENS was applied to at least one group in 47 studies, and most applications were performed for 20 minutes (64.15%). Mechanical hyperalgesia was analyzed as the primary outcome in 52.83% of the studies and thermal hyperalgesia in 23.07% of studies using a heated surface. More than 50% of the studies showed a low risk of bias on allocation concealment, random housing, selective outcome reporting, and acclimatization before the behavioral tests. Blinding was not performed in only one study and random outcome assessment in another study; acclimatization before the behavioral tests was not performed in just one study. Many studies had an uncertain risk of bias. Meta-analyses indicated no difference between low-frequency and high-frequency TENS with variations among the pain models.

CONCLUSIONS

This systematic review and meta-analysis suggests that TENS has presented a substantial scientific foundation for its hypoalgesic effect in preclinical studies for analgesia.

Efficiency of Direct Transcutaneous Electroneurostimulation of the Median Nerve in the Regression of Residual Neurological Symptoms after Carpal Tunnel Decompression Surgery

Carpal tunnel syndrome (CTS) is the most frequent entrapment neuropathy. CTS therapy includes wrist immobilization, kinesiotherapy, non-steroidal anti-inflammatory drugs, carpal tunnel steroid injection, acupuncture, and physical therapy. Carpal tunnel decompression surgery (CTDS) is recommended after failure of conservative therapy. In many cases, neurological disorders continue despite CTDS. The aim of this study was to investigate the efficiency of direct transcutaneous electroneurostimulation (TENS) of the median nerve in the regression of residual neurological symptoms after CTDS. Material and Methods: 60 patients aged 28-62 years with persisting sensory and motor disorders after CTDS were studied; 15 patients received sham stimulation with a duration 30 min.; 15 patients received high-frequency low-amplitude TENS (HF TENS) with a duration 30 min; 15 patients received low-frequency high-amplitude TENS (LF TENS) with a duration 30 min; and 15 patients received a co-administration of HF TENS (with a duration of15 min) and LF TENS (with a duration of 15 min). Results: Our research showed that TENS significantly decreased the pain syndrome, sensory disorders, and motor deficits in the patients after CTDS. Predominantly, negative and positive sensory symptoms and the pain syndrome improved after the HF TENS course. Motor deficits, reduction of fine motor skill performance, electromyography changes, and affective responses to chronic pain syndrome regressed significantly after the LF TENS course. Co-administration of HF TENS and LF TENS was significantly more effective than use of sham stimulation, HF TENS, or LF TENS in patients with residual neurological symptoms after CTDS.

Using TENS for Pain Control: Update on the State of the Evidence

Transcutaneous electrical nerve stimulation (TENS) is a non-pharmacological intervention used in the treatment of acute and chronic pain conditions. The first clinical studies on TENS were published over 50 years ago, when effective parameters of stimulation were unclear and clinical trial design was in its infancy. Over the last two decades, a better understanding of the mechanisms underlying TENS efficacy has led to the development of an adequate dose and has improved outcome measure utilization. The continued uncertainty about the clinical efficacy of TENS to alleviate pain, despite years of research, is related to the quality of the clinical trials included in systematic reviews. This summary of the evidence includes only trials with pain as the primary outcome. The outcomes will be rated as positive (+), negative (−), undecided (U), or equivalent to other effective interventions (=). In comparison with our 2014 review, there appears to be improvement in adverse events and parameter reporting. Importantly, stimulation intensity has been documented as critical to therapeutic success. Examinations of the outcomes beyond resting pain, analgesic tolerance, and identification of TENS responders remain less studied areas of research. This literature review supports the conclusion that TENS may have efficacy for a variety of acute and chronic pain conditions, although the magnitude of the effect remains uncertain due to the low quality of existing literature. In order to provide information to individuals with pain and to clinicians treating those with pain, we suggest that resources for research should target larger, high-quality clinical trials including an adequate TENS dose and adequate timing of the outcome and should monitor risks of bias. Systematic reviews and meta-analyses should focus only on areas with sufficiently strong clinical trials that will result in adequate sample size.

Electrical Stimulation of Muscle: Electrophysiology and Rehabilitation

The generation of action potentials in intramuscular motor and sensory axons in response to an imposed external current source can evoke muscle contractions and elicit widespread responses throughout the nervous system that impact sensorimotor function. The benefits experienced by individuals exposed to several weeks of treatment with electrical stimulation of muscle suggest that the underlying adaptations involve several physiological systems, but little is known about the specific changes elicited by such interventions.

Translingual Neurostimulation for the Treatment of Chronic Symptoms Due to Mild-to-Moderate Traumatic Brain Injury

OBJECTIVE

To compare the efficacy of high- and low-frequency noninvasive translingual neurostimulation (TLNS) plus targeted physical therapy (PT) for treating chronic balance and gait deficits due to mild-to-moderate traumatic brain injury (mmTBI).

DESIGN

Participants were randomized 1:1 in a 26-week double-blind phase 1/2 study (NCT02158494) with 3 consecutive treatment stages: in-clinic, at-home, and no treatment. Arms were high-frequency pulse (HFP) and low-frequency pulse (LFP) TLNS.

SETTING

TLNS plus PT training was initiated in-clinic and then continued at home.

PARTICIPANTS

Participants (N=44; 18-65y) from across the United States were randomized into the HFP and LFP (each plus PT) arms. Forty-three participants (28 women, 15 men) completed at least 1 stage of the study. Enrollment requirements included an mmTBI ≥1 year prior to screening, balance disorder due to mmTBI, a plateau in recovery with current PT, and a Sensory Organization Test (SOT) score ≥16 points below normal.

INTERVENTIONS

Participants received TLNS (HFP or LFP) plus PT for a total of 14 weeks (2 in-clinic and 12 at home), twice daily, followed by 12 weeks without treatment.

MAIN OUTCOME MEASURES

The primary endpoint was change in SOT composite score from baseline to week 14. Secondary variables (eg, Dynamic Gait Index [DGI], 6-minute walk test [6MWT]) were also collected.

RESULTS

Both arms had a significant (P<.0001) improvement in SOT scores from baseline at weeks 2, 5, 14 (primary endpoint), and 26. DGI scores had significant improvement (P<.001-.01) from baseline at the same test points; 6MWT evaluations after 2 weeks were significant. The SOT, DGI, and 6MWT scores did not significantly differ between arms at any test point. There were no treatment-related serious adverse events.

CONCLUSIONS

Both the HFP+PT and LFP+PT groups had significantly improved balance scores, and outcomes were sustained for 12 weeks after discontinuing TLNS treatment. Results between arms did not significantly differ from each other. Whether the 2 dosages are equally effective or whether improvements are because of provision of PT cannot be conclusively established at this time.

Coping with Phantom Limb Pain

Phantom limb pain is a chronic neuropathic pain that develops in 45-85% of patients who undergo major amputations of the upper and lower extremities and appears predominantly during two time frames following an amputation: the first month and later about 1 year. Although in most patients the frequency and intensity of pain diminish over time, severe pain persists in about 5-10%. It has been proposed that factors in both the peripheral and central nervous systems play major roles in triggering the development and maintenance of pain associated with extremity amputations. Chronic pain is physically and mentally debilitating, affecting an individual's capacity for self-care, but also diminishing an individual's daily capacity for personal and economic independence. In addition, the pain may lead to depression and feelings of hopelessness. A National Center for Biotechnology Information study found that in the USA alone, the annual cost of dealing with neuropathic pain is more than $600 billion, with an estimated 20 million people in the USA suffering from this condition. Although the pain can be reduced by antiepileptic drugs and analgesics, they are frequently ineffective or their side effects preclude their use. The optimal approach for eliminating neuropathic pain and improving individuals' quality of life is the development of novel techniques that permanently prevent the development and maintenance of neuropathic pain, or that eliminate the pain once it has developed. What is still required is understanding when and where an effective novel technique must be applied, such as onto the nerve stump of the transected peripheral axons, dorsal root ganglion neurons, spinal cord, or cortex to induce the desired influences. This review, the second of two in this journal volume, examines the techniques that may be capable of reducing or eliminating chronic neuropathic pain once it has developed. Such an understanding will improve amputees' quality of life by blocking the mechanisms that trigger and/or maintain PLP and chronic neuropathic pain.

Low-intensity muscle contraction exercise following the onset of arthritis improves hyperalgesia via reduction of joint inflammation and central sensitization in the spinal cord in a rat model

We examined the effect of immobilization, low-intensity muscle contraction exercise, and transcutaneous electrical nerve stimulation (TENS) on tissue inflammation and acute pain following the onset of arthritis in a rat model. Sixty Wistar rats were divided into five groups: (1) Arthritis group, (2) arthritis and immobilization (Immobilization group), (3) arthritis and low intensity muscle contraction (Exercise group), (4) arthritis and TENS (TENS group), and (5) sham arthritis (Sham group). Arthritis was induced in the right knee joints by single injection of 3% kaolin and carrageenan. Immobilization of the right hindlimb was conducted by full extension of the right knee joints and full plantar flexion of the ankle joints using a plaster cast for 7 days after injection. The right quadriceps muscles were subjected to electrical stimulation (frequency: 50 Hz; intensity: 2-3 mA) for 20 min/day as contraction exercise for one week. TENS was delivered at 20 min/day for one week (frequency: 50 Hz; intensity: 1 mA). The pressure pain threshold (PPT) and paw withdrawal response (PWR) were evaluated at 1 and 7 days after injection. We also analyzed the number of CD68-positive cells in the synovium by immunohistochemistry and determined the expression level of calcitonin gene-related peptide (CGRP) in the spinal dorsal horn with immunofluorescence. Improvements of both PPT and PWR were observed in the Exercise group at 7 days after injection compared to those of the Arthritis and Immobilization groups, although only improvement of PPT was observed in the TENS group. The number of CD68-positive cells in the synovium and CGRP expression in the dorsal horn decreased only in the Exercise group. These results suggested that low-intensity muscle contraction exercise might be a better treatment for reduction of arthritis-induced inflammation and acute pain compared to immobilization and TENS.

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.

Effect of electrical stimulation on motor nerve regeneration in sciatic nerve ligated-mice

The purpose of this study was to investigate the effect of electrical stimulation on sciatic nerve regeneration and functional recovery of target muscles. Mice were randomly divided into 3 groups: ligated without electrical stimulation, ligated with electrical stimulation and control (non-ligated). The unilateral peripheral mononeuropathy was produced on the right hind limb. Sciatic nerve was then electrically stimulated daily for a period of 2 weeks (duration: 0.2 msec, frequency: 100Hz, amplitude: 15mA). Evoked surface EMG was recorded from biceps femoris (BF) and gluteus maximus (GM) muscles on the 3rd, 7th, 10th and 14th day after sciatic nerve ligation. Muscle force and sensitivity was determined by processing of the recorded EMG signals in time and frequency domains respectively. The results showed electrical stimulation (ES) produced a significant increase in the EMG response of BF, and muscle force significantly increased on the 14th day (p<0.001), however no significant difference was found in GM muscle force between experimental groups. This may be due to possible innervation by inferior gluteal nerve. Frequency analysis of BF signals indicates that hyperalgesia remained after 14 days in both ligated groups. On the 14th day no difference in GM muscle sensitivity was found between groups. In conclusion, the results of this study have shown that the electrical stimulation of sciatic nerve accelerates nerve repair and indirectly improves BF muscle force to a comparable level with control without effect on muscle sensitivity. However, ES had no effect on GM muscle force and sensitivity.

Influence of transcutaneous electrical stimulation on heterotopic ossification: an experimental study in Wistar rats

Heterotopic ossification (HO) is a metaplastic biological process in which there is newly formed bone in soft tissues, resulting in joint mobility deficit and pain. Different treatment modalities have been tried to prevent HO development, but there is no consensus on a therapeutic approach. Since electrical stimulation is a widely used resource in physiotherapy practice to stimulate joint mobility, with analgesic and anti-inflammatory effects, its usefulness for HO treatment was investigated. We aimed to identify the influence of electrical stimulation on induced HO in Wistar rats. Thirty-six male rats (350-390 g) were used, and all animals were anesthetized for blood sampling before HO induction, to quantify the serum alkaline phosphatase. HO induction was performed by bone marrow implantation in both quadriceps of the animals, which were then divided into 3 groups: control (CG), transcutaneous electrical nerve stimulation (TENS) group (TG), and functional electrical stimulation (FES) group (FG) with 12 rats each. All animals were anesthetized and electrically stimulated twice per week, for 35 days from induction day. After this period, another blood sample was collected and quadriceps muscles were bilaterally removed for histological and calcium analysis and the rats were killed. Calcium levels in muscles showed significantly lower results when comparing TG and FG (P<0.001) and between TG and CG (P<0.001). Qualitative histological analyses confirmed 100% HO in FG and CG, while in TG the HO was detected in 54.5% of the animals. The effects of the muscle contractions caused by FES increased HO, while anti-inflammatory effects of TENS reduced HO.

Using TENS for pain control: the state of the evidence

Transcutaneous electrical nerve stimulation (TENS) is a nonpharmacological intervention that activates a complex neuronal network to reduce pain by activating descending inhibitory systems in the central nervous system to reduce hyperalgesia. The evidence for TENS efficacy is conflicting and requires not only description but also critique. Population-specific systemic reviews and meta-analyses are emerging, indicating both HF and LF TENS being shown to provide analgesia, specifically when applied at a strong, nonpainful intensity. The purpose of this article is to provide a critical review of the latest basic science and clinical evidence for TENS. Additional research is necessary to determine if TENS has effects specific to mechanical stimuli and/or beyond reduction of pain and will improve activity levels, function and quality of life.

Electrical stimulation as a treatment intervention to improve function, edema or pain following acute lateral ankle sprains: A systematic review

The purpose of this systematic review was to assess whether electrical stimulation (ES), when used in conjunction with a standard treatment, can reduce levels of functional impairment, edema, and pain compared to a standard treatment alone, in patients following a lateral ankle sprain. We searched PubMed, CINAHL, SportDiscus, and Medline (OVID) databases through June 2014 using the terms "ankle sprain or ankle sprains or ligament injury or ligamentous injury," and "electric stimulation or electric stimulation or electrotherapy." Our search identified four randomized control trials, of which, neuromuscular ES and high-voltage pulsed stimulation were the only two ES modalities utilized. Effect sizes and 95% confidence intervals (CI) were estimated using Cohen's d for comparison between treatment groups. Three of four effect sizes for function had 95% CI that crossed zero. Twenty-four of the thirty-two effect sizes for edema had 95% CI that crossed zero. All effect sizes for pain had 95% CI that crossed zero. Therefore, the use of ES is not recommended as a means to improve function, reduce edema, or decrease pain in the treatment of acute lateral ankle sprains.

Transcutaneous electrical nerve stimulation for the control of pain during rehabilitation after total knee arthroplasty: A randomized, blinded, placebo-controlled trial

This study evaluated the efficacy of transcutaneous electrical nerve stimulation (TENS) in reducing pain and hyperalgesia and increasing function after total knee arthroplasty (TKA). We hypothesized that participants using TENS during rehabilitation exercises would report significantly lower pain during range-of-motion (ROM) activity and fast walking but not at rest, would have less hyperalgesia, and would have better function than participants receiving placebo-TENS or standard care. We also hypothesized that change in ROM pain would differ based on psychological characteristics (trait anxiety, pain catastrophizing, and depression) and treatment group. This prospective, randomized study used intent-to-treat analyses in 317 participants after primary, unilateral TKA. Assessors, blinded to treatment allocation, measured pain, function (ROM and gait speed), and hyperalgesia (quantitative sensory tests) postoperatively and 6 weeks after surgery. Analgesic intake, anxiety, depression, and pain catastrophizing were also assessed. TENS participants used it 1 to 2 times per day at 42 mA (on average) and had less pain postoperatively during active knee extension (P=.019) and fast walking (P=.006) than standard care participants. TENS and placebo-TENS were not significantly different. TENS participants who scored low on anxiety and pain catastrophizing had a greater reduction in ROM pain at 6 weeks than those who scored high on these factors (P=.002 and P=.03). Both TENS and placebo-TENS participants had less postoperative mechanical hyperalgesia (P=.03-.01) than standard care participants. Supplementing pharmacologic analgesia with TENS during rehabilitation exercises reduces movement pain postoperatively, but a placebo influence exists and the effect is gone by 6 weeks. Patients with low anxiety and pain catastrophizing may benefit most from TENS.

Conventional and kilohertz-frequency spinal cord stimulation produces intensity- and frequency-dependent inhibition of mechanical hypersensitivity in a rat model of neuropathic pain

BACKGROUND

Spinal cord stimulation (SCS) is a useful neuromodulatory technique for treatment of certain neuropathic pain conditions. However, the optimal stimulation parameters remain unclear.

METHODS

In rats after L5 spinal nerve ligation, the authors compared the inhibitory effects on mechanical hypersensitivity from bipolar SCS of different intensities (20, 40, and 80% motor threshold) and frequencies (50, 1 kHz, and 10 kHz). The authors then compared the effects of 1 and 50 Hz dorsal column stimulation at high- and low-stimulus intensities on conduction properties of afferent Aα/β-fibers and spinal wide-dynamic-range neuronal excitability.

RESULTS

Three consecutive daily SCS at different frequencies progressively inhibited mechanical hypersensitivity in an intensity-dependent manner. At 80% motor threshold, the ipsilateral paw withdrawal threshold (% preinjury) increased significantly from pre-SCS measures, beginning with the first day of SCS at the frequencies of 1 kHz (50.2 ± 5.7% from 23.9 ± 2.6%, n = 19, mean ± SEM) and 10 kHz (50.8 ± 4.4% from 27.9 ± 2.3%, n = 17), whereas it was significantly increased beginning on the second day in the 50 Hz group (38.9 ± 4.6% from 23.8 ± 2.1%, n = 17). At high intensity, both 1 and 50 Hz dorsal column stimulation reduced Aα/β-compound action potential size recorded at the sciatic nerve, but only 1 kHz stimulation was partially effective at the lower intensity. The number of actions potentials in C-fiber component of wide-dynamic-range neuronal response to windup-inducing stimulation was significantly decreased after 50 Hz (147.4 ± 23.6 from 228.1 ± 39.0, n = 13), but not 1 kHz (n = 15), dorsal column stimulation.

CONCLUSIONS

Kilohertz SCS attenuated mechanical hypersensitivity in a time course and amplitude that differed from conventional 50 Hz SCS, and may involve different peripheral and spinal segmental mechanisms.

Transcutaneous electrical nerve stimulation attenuates CFA-induced hyperalgesia and inhibits spinal ERK1/2-COX-2 pathway activation in rats

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is a non-pharmacologic treatment for pain relief. In previous animal studies, TENS effectively alleviated Complete Freund's Adjuvant (CFA)- or carrageenan-induced inflammatory pain. Although TENS is known to produce analgesia via opioid activation in the brain and at the spinal level, few reports have investigated the signal transduction pathways mediated by TENS. Prior studies have verified the importance of the activation of extracellular signal-regulated kinase (ERK) signal transduction pathway in the spinal cord dorsal horn (SCDH) in acute and persistent inflammatory pains. Here, by using CFA rat model, we tested the efficacy of TENS on inhibiting the expressions of p-ERK1/2 and of its downstream cyclooxygenase-2 (COX-2) and the level of prostaglandin E2 (PGE2) at spinal level.

METHODS

Rats were randomly divided into control, model and TENS groups, and injected subcutaneously with 100 μl CFA or saline in the plantar surface of right hind paw. Rats in the TENS group were treated with TENS (constant aquare wave, 2 Hz and 100 Hz alternating frequencies, intensities ranging from 1 to 2 mA, lasting for 30 min each time) at 5 h and 24 h after injection. Paw withdrawal thresholds (PWTs) were measured with dynamic plantar aesthesiometer at 3d before modeling and 5 h, 6 h, and 25 h after CFA injection. The ipsilateral sides of the lumbar spinal cord dosral horns were harvested for detecting the expressions of p-ERK1/2 and COX-2 by western blot analysis and qPCR, and PGE2 by ELISA.

RESULTS

CFA-induced periphery inflammation decreased PWTs and increased paw volume of rats. TENS treatment significantly alleviated mechanical hyperalgesia caused by CFA. However, no anti-inflammatory effect of TENS was observed. Expression of p-ERK1/2 protein and COX-2 mRNA was significantly up-regualted at 5 h and 6 h after CFA injection, while COX-2 and PGE2 protein level only increased at 6 h after modeling. Furthermore, the high expression of p-ERK1/2 and COX-2, and over-production of PGE2 induced by CFA, were suppressed by TENS administration.

CONCLUSIONS

TENS may be an effective therapy in controlling inflammatory pain induced by CFA. Its analgesic effect may be associated with the inhibition of activation of the spinal ERK1/2-COX-2 pathway.

Effects of transcutaneous electrical nerve stimulation on pain, pain sensitivity, and function in people with knee osteoarthritis: a randomized controlled trial

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is commonly used for the management of pain; however, its effects on several pain and function measures are unclear.

OBJECTIVE

The purpose of this study was to determine the effects of high-frequency TENS (HF-TENS) and low-frequency TENS (LF-TENS) on several outcome measures (pain at rest, movement-evoked pain, and pain sensitivity) in people with knee osteoarthritis.

DESIGN

The study was a double-blind, randomized clinical trial.

SETTING

The setting was a tertiary care center.

PARTICIPANTS

Seventy-five participants with knee osteoarthritis (29 men and 46 women; 31-94 years of age) were assessed.

INTERVENTION

Participants were randomly assigned to receive HF-TENS (100 Hz) (n=25), LF-TENS (4 Hz) (n=25), or placebo TENS (n=25) (pulse duration=100 microseconds; intensity=10% below motor threshold).

MEASUREMENTS

The following measures were assessed before and after a single TENS treatment: cutaneous mechanical pain threshold, pressure pain threshold (PPT), heat pain threshold, heat temporal summation, Timed "Up & Go" Test (TUG), and pain intensity at rest and during the TUG. A linear mixed-model analysis of variance was used to compare differences before and after TENS and among groups (HF-TENS, LF-TENS, and placebo TENS).

RESULTS

Compared with placebo TENS, HF-TENS and LF-TENS increased PPT at the knee; HF-TENS also increased PPT over the tibialis anterior muscle. There was no effect on the cutaneous mechanical pain threshold, heat pain threshold, or heat temporal summation. Pain at rest and during the TUG was significantly reduced by HF-TENS, LF-TENS, and placebo TENS.

LIMITATIONS

This study tested only a single TENS treatment.

CONCLUSIONS

Both HF-TENS and LF-TENS increased PPT in people with knee osteoarthritis; placebo TENS had no significant effect on PPT. Cutaneous pain measures were unaffected by TENS. Subjective pain ratings at rest and during movement were similarly reduced by active TENS and placebo TENS, suggesting a strong placebo component of the effect of TENS.

Acid-sensing ion channel 3 mediates peripheral anti-hyperalgesia effects of acupuncture in mice inflammatory pain

Background

Peripheral tissue inflammation initiates hyperalgesia accompanied by tissue acidosis, nociceptor activation, and inflammation mediators. Recent studies have suggested a significantly increased expression of acid-sensing ion channel 3 (ASIC3) in both carrageenan- and complete Freund's adjuvant (CFA)-induced inflammation. This study tested the hypothesis that acupuncture is curative for mechanical hyperalgesia induced by peripheral inflammation.

Methods

Here we used mechanical stimuli to assess behavioral responses in paw and muscle inflammation induced by carrageenan or CFA. We also used immunohistochemistry staining and western blot methodology to evaluate the expression of ASIC3 in dorsal root ganglion (DRG) neurons.

Results

In comparison with the control, the inflammation group showed significant mechanical hyperalgesia with both intraplantar carrageenan and CFA-induced inflammation. Interestingly, both carrageenan- and CFA-induced hyperalgesia were accompanied by ASIC3 up-regulation in DRG neurons. Furthermore, electroacupuncture (EA) at the ST36 rescued mechanical hyperalgesia through down-regulation of ASIC3 overexpression in both carrageenan- and CFA-induced inflammation.

Conclusions

In addition, electrical stimulation at the ST36 acupoint can relieve mechanical hyperalgesia by attenuating ASIC3 overexpression.

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.

Quantitative assessment of physiological and behavioural parameters in healthy dairy cows evoked by transcutaneous electrical nerve stimulation of the udder

The pain and distress associated with transcutaneous electrical nerve stimulation (TENS) of the udder was evaluated by treating 20 healthy dairy cows with an electrical udder stimulator. This generated a sequence of pulses (frequency: 160±10% impulses per second, duration 250 μs) and provided voltage ranges from 0 to 10 volts (±10%). Trials took place on three consecutive days, twice daily after morning and evening milking. Daily sessions were divided into two periods: (1) control (sham treatment) and (2) treatment (real treatment). Physiological (heart rate, respiratory rate, and plasma cortisol concentration) as well as ethological parameters (kicking, weight shifting, and looking backwards to udder) were defined as pain-indicating parameters and observed. Evaluation of data showed that only one parameter (kicking) was significantly increased during real treatment compared to sham treatment. It is concluded that the TENS therapy tested in this study can evoke changes in behaviour (increased kicking) consistent with an experience of pain in some cows.

Cholecystokinin receptors mediate tolerance to the analgesic effect of TENS in arthritic rats

Transcutaneous electrical nerve stimulation (TENS) is a treatment for pain that involves placement of electrical stimulation through the skin for pain relief. Previous work from our laboratory shows that repeated application of TENS produces analgesic tolerance by the fourth day and a concomitant cross-tolerance at spinal opioid receptors. Prior pharmacological studies show that blockade of cholecystokinin (CCK) receptors systemically and spinally prevents the development of analgesic tolerance to repeated doses of opioid agonists. We therefore hypothesized that systemic and intrathecal blockade of CCK receptors would prevent the development of analgesic tolerance to TENS, and cross-tolerance at spinal opioid receptors. In animals with knee joint inflammation (3% kaolin/carrageenan), high (100Hz) or low frequency (4Hz) TENS was applied daily and the mechanical withdrawal thresholds of the muscle and paw were examined. We tested thresholds before and after inflammation, and before and after TENS. Animals treated systemically, prior to TENS, with the CCK antagonist, proglumide, did not develop tolerance to repeated application of TENS on the fourth day. Spinal blockade of CCK-A or CCK-B receptors blocked the development of tolerance to high and low frequency TENS, respectively. In the same animals we show that spinal blockade of CCK-A receptors prevents cross-tolerance at spinal delta-opioid receptors that normally occurs with high frequency TENS; and blockade of CCK-B receptors prevents cross-tolerance at spinal mu-opioid receptors that normally occurs with low frequency TENS. Thus, we conclude that blockade of CCK receptors prevents the development of analgesic tolerance to repeated application of TENS in a frequency-dependent manner.

Transcutaneous electrical nerve stimulation at both high and low frequencies activates ventrolateral periaqueductal grey to decrease mechanical hyperalgesia in arthritic rats

Transcutaneous electric nerve stimulation (TENS) is widely used for the treatment of pain. TENS produces an opioid-mediated antinociception that utilizes the rostroventromedial medulla (RVM). Similarly, antinociception evoked from the periaqueductal grey (PAG) is opioid-mediated and includes a relay in the RVM. Therefore, we investigated whether the ventrolateral or dorsolateral PAG mediates antinociception produced by TENS in rats. Paw and knee joint mechanical withdrawal thresholds were assessed before and after knee joint inflammation (3% kaolin/carrageenan), and after TENS stimulation (active or sham). Cobalt chloride (CoCl(2); 5 mM) or vehicle was microinjected into the ventrolateral periaqueductal grey (vlPAG) or dorsolateral periaqueductal grey (dlPAG) prior to treatment with TENS. Either high (100 Hz) or low (4 Hz) frequency TENS was then applied to the inflamed knee for 20 min. Active TENS significantly increased withdrawal thresholds of the paw and knee joint in the group microinjected with vehicle when compared to thresholds prior to TENS (P<0.001) or to sham TENS (P<0.001). The increases in withdrawal thresholds normally observed after TENS were prevented by microinjection of CoCl(2) into the vlPAG, but not the dlPAG prior to TENS and were significantly lower than controls treated with TENS (P<0.001). In a separate group of animals, microinjection of CoCl(2) into the vlPAG temporarily reversed the decreased mechanical withdrawal threshold suggesting a role for the vlPAG in the facilitation of joint pain. No significant difference was observed for dlPAG. We hypothesize that the effects of TENS are mediated through the vlPAG that sends projections through the RVM to the spinal cord to produce an opioid-mediated analgesia.

An investigation of the hypoalgesic effects of TENS delivered by a glove electrode

This randomized, placebo-controlled, blinded study investigated the hypoalgesic effects of high-frequency transcutaneous electrical nerve stimulation (TENS) delivered via a glove electrode compared with standard self-adhesive electrodes. Fifty-six TENS-naïve, healthy individuals (18 to 50 years old; 28 men, 28 women) were randomly allocated to 1 of 4 groups (n = 14 per group): glove electrode; placebo TENS using a glove electrode; standard electrode; and no treatment control. Active TENS (continuous stimulus, 100 Hz, strong but comfortable intensity) was applied to the dominant forearm/hand for 30 minutes. Placebo TENS was applied using a burst stimulus, 100-Hz frequency, 5-second cycle time for 42 seconds, after which the current amplitude was automatically reset to 0 mA. Pressure pain thresholds (PPTs) were recorded from 3 points on the dominant and nondominant upper limbs before and after TENS. Statistical analyses of dominant PPT data using between-within groups ANOVA showed significant differences between groups at all 3 recording points (P = .01). Post hoc Scheffe tests indicated no significant difference between the standard electrode and glove electrode groups. There was a significant hypoalgesic effect in the standard electrode group compared with the control group and between the glove electrode group and both the control and placebo TENS groups. There was no significant interactive effect between time and group at any of the recording points (P > .05).

PERSPECTIVE

This study presents a comparison of the hypoalgesic effects of 2 different types of TENS electrode, a novel glove electrode and standard self-adhesive rectangular electrodes. The glove electrode provides a larger contact area with the skin, thereby stimulating a greater number of nerve fibers. The results show that both electrodes have similar hypoalgesic effects and therefore give the clinician another choice in electrode.

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.

Low frequencies, but not high frequencies of bi-polar spinal cord stimulation reduce cutaneous and muscle hyperalgesia induced by nerve injury

Spinal cord stimulation (SCS) is an established treatment for neuropathic pain. However, SCS is not effective for all the patients and the mechanisms underlying the reduction in pain by SCS are not clearly understood. To elucidate the mechanisms of pain relief by SCS, we utilized the spared nerve injury model. Sprague-Dawley rats were anesthetized, the tibial and common peroneal nerves were tightly ligated, and an epidural SCS lead implanted in the upper lumbar spinal cord. SCS was delivered daily at one of 4 different frequencies (4Hz, 60Hz, 100Hz, and 250Hz) at approximately 85% of motor threshold 2 weeks after nerve injury for 4 days. Mechanical withdrawal threshold of the paw and compression withdrawal threshold of the hamstring muscles were measured before and after SCS on each day. All rats showed a decrease in withdrawal threshold of the paw and the muscle 2 weeks after nerve injury. Treatment with either 4Hz or 60Hz SCS significantly reversed the decreased withdrawal threshold of the paw and muscle. The effect was cumulative with a greater reversal by the fourth treatment when compared to the first treatment. Treatment with 100Hz, 250Hz or sham SCS had no significant effect on the decreased withdrawal threshold of the paw or muscle that normally occurs after nerve injury. In conclusion, SCS at 4Hz and 60Hz was more effective in reducing hyperalgesia than higher frequencies of SCS (100Hz and 250Hz); and repeated treatments result in a cumulative reduction in hyperalgesia.

Blockade of NMDA receptors prevents analgesic tolerance to repeated transcutaneous electrical nerve stimulation (TENS) in rats

Repeated daily application of transcutaneous electrical nerve stimulation (TENS) results in tolerance, at spinal opioid receptors, to the antihyperalgesia produced by TENS. Since N-methyl-D-aspartate (NMDA) receptor antagonists prevent analgesic tolerance to opioid agonists, we hypothesized that blockade of NMDA receptors will prevent tolerance to TENS. In rats with knee joint inflammation, TENS was applied for 20 minutes daily at high-frequency (100 Hz), low-frequency (4 Hz), or sham TENS. Rats were treated with the NMDA antagonist MK-801 (0.01 mg/kg to 0.1 mg/kg) or vehicle daily before TENS. Paw withdrawal thresholds were tested before and after inflammation and before and after TENS treatment for 4 days. On day 1, TENS reversed the decreased mechanical withdrawal threshold induced by joint inflammation. On day 4, TENS had no effect on the decreased withdrawal threshold in the group treated with vehicle, demonstrating development of tolerance. However, in the group treated with 0.1 mg/kg MK-801, TENS significantly reversed the mechanical withdrawal thresholds on day 4, demonstrating that tolerance did not develop. Vehicle-treated animals developed cross-tolerance at spinal opioid receptors. Treatment with MK-801 reversed this cross-tolerance at spinal opioid receptors. In summary, blockade of NMDA receptors prevents analgesic tolerance to daily TENS by preventing tolerance at spinal opioid receptors.

PERSPECTIVE

Observed tolerance to the clinical treatment of TENS could be prevented by administration of pharmaceutical agents with NMDA receptors activity such as ketamine or dextromethorphan.