Transcutaneous Electrical Nerve Stimulator (TENS) is an electronic device that applies electrical stimulation to the surface of the skin and the site of pain and has been used to relieve chronic intractable pain, post surgical pain and pain associated with active or post trauma injury unresponsive to other standard pain therapies.
TENS consists of an electrical pulse generator, usually battery operated, connected by wire to two or more electrodes which are applied to the surface of the skin at the site of pain. The exact mechanism of action is unclear.
Percutaneous Neuromodulation Therapy is different from Percutaneous Electrical Nerve Stimulation, both in presumed mechanism of action and in the anatomical location and depth of the percutaneous electrodes. There is scant information regarding its efficacy, and it should be considered investigational.
The Micro-Z™ and The Micro-Z MINI™ is a small, lightweight stimulator that allows patients to receive electrotherapeutic treatment. The Micro-Z System may utilize an Electro-Mesh Garment electrode that covers the whole treatment area, alone with the first wearable High Volt Pulsed Galvanic (HVPG) Neuromusclar Stimulator.
On March 11, 2014, FDA granted de novo 510(k) approval for marketing to Cefaly® (STX-med, Herstal, Belgium), which is a TENS device for the prophylactic treatment of migraine in patients 18 years of age or older (USFDA, 2012).
The trial is monitored by a physician.
Continued use of transcutaneous electrical nerve stimulation (TENS) meets member benefit primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes for treatment of refractory chronic pain (e.g., chronic musculoskeletal or neuropathic pain) that causes significant disruption of function when efficacy has been demonstrated in an initial therapeutic trial.
*Note: CPT 64550 (application of surface transcutaneous electrical stimulator) is billed by the physician for instruction in the use of the TENS unit. This is allowed no more than twice. The trial is paid as a rental with that allowance applied toward the purchase of the device, if the device is effective.
The use of TENS does not meet member benefit primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes for the management of acute pain (e.g., postoperative or during labor and delivery), TMJ disorders, headache, migraine, headache and pain not originating from a defined anatomical source, treatment of dementia or any other condition.
For contracts without primary coverage criteria, the use of TENS for the management of acute pain (e.g., postoperative or during labor and delivery), TMJ disorders, headache, migraine, or generalized pain not originating from a defined anatomical source, treatment of dementia or any other condition is considered investigational. Investigational services are exclusions in most member benefit certificates of coverage.
The use of the Micro-Z System to treat acute or chronic pain does not meet member benefit certificate primary coverage criteria.
For members with contracts without primary coverage criteria, the use of the Micro-Z System to treat acute or chronic pain is considered investigational. Investigational services are specific contract exclusions in most member benefit certificates of coverage.
Transcutaneous Electrical Nerve Stimulator (TENS) meets primary coverage criteria for effectiveness and is covered for treatment of chronic intractable pain unresponsive to conservative medical therapy. This treatment is not covered for the treatment of TMJ disorders, headache or generalized pain not originating from a defined anatomical source. TENS is not appropriate for pain of internal, visceral origin (including that from the head, chest, abdomen or pelvis).
The TENS unit is used on a trial basis for a minimum of one month, not to exceed two months. The trial period is monitored by a physician for effectiveness. The trial is paid as a rental, with that allowance applied toward the purchase of the device, if the device is effective.
CPT 64550 (application of surface transcutaneous electrical stimulator) is billed by the physician for instruction in the use of the TENS unit. This is allowed no more than twice.
Services not meeting the above requirements are not covered based on benefit certificate primary coverage criteria that there be scientific evidence of effectiveness.
For contracts without primary coverage criteria, services not meeting the above requirements will be considered not medically necessary. Medically unnecessary services are an exclusion in the member benefit contract.
Transcutaneous Electrical Nerve Stimulator (TENS) is covered for treatment of chronic intractable pain unresponsive to conservative medical therapy. This treatment is not covered for the treatment of TMJ disorders, headache or generalized pain not originating from a defined anatomical source. TENS is not appropriate for pain of internal, visceral origin (including that from the head, chest, abdomen or pelvis).
Services not meeting the above requirements will be considered not medically necessary.
Transcutaneous Electrical Nerve Stimulator (TENS) is covered for treatment of chronic pain due to peripheral nerve injury when that pain is unresponsive to medication.
To treat chronic pain due to peripheral nerve injury as the choice of late/last resort on a PRN basis by the patient.
Review of literature through 1998, of TENS for the treatment of chronic and postoperative pain, concluded that the evidence did not clearly show that the effects of TENS exceeded placebo effects. An updated literature search in October 2002 identified several Cochrane reviews of TENS. One of the reviews, last amended in June 2000, addressed chronic pain due to a variety of conditions (e.g., osteoarthritis of the knee, rheumatoid arthritis of the wrist, pancreatic, myofascial trigger points, chronic back pain, temporomandibular joint pain, and a variety of nocioceptive and neuropathic causes of pain) (Carroll, 2002). A total of 19 randomized trials were judged as meeting study selection criteria, but due to heterogeneity of methods and inability to extract sufficient dichotomous pain outcomes data, it was concluded that meta-analysis was not possible, and the review of evidence was inconclusive. The trials reviewed did not indicate which stimulation parameters were most likely to provide pain relief, or answer questions about long-term effectiveness. The authors suggested a need for large, multicenter, randomized, controlled trials of TENS in chronic pain.
In a 2004 literature review update, two additional Cochrane Reviews were identified along with several randomized controlled trials (RCTs) on the use of TENS. Neither the Cochrane Reviews nor any of the RCTs identified were sufficient to alter the previous conclusions. The authors of the Cochrane reviews concluded that the evidence was inadequate to draw conclusions about the effects of TENS.
The update in 2007 examined the 10 Cochrane reviews on TENS that had been published over the previous 7 years. Overall, evidence for the efficacy of TENS for different pain conditions was weak. Two Cochrane reviews concluded that there is limited and inconsistent evidence for the use of TENS as an isolated treatment for low back pain, and that results in patients with rheumatoid arthritis of the hand were conflicting. Efficacy of TENS for neck pain, headache, shoulder pain after stroke, and dementia were considered inconclusive in 3 other reviews. One Cochrane review of 9 small, controlled trials found high-frequency TENS to be effective for the treatment of dysmenorrhea (Proctor, 2002). Another review found TENS and acupuncture-like TENS to be more effective than placebo for the treatment of knee osteoarthritis, but indicated that due to heterogeneity of the included studies, more well-designed trials with adequate numbers of participants were needed to conclude effectiveness (Osiri, 2002).
Two new systematic Cochrane reviews have been initiated to assess the use of TENS for cancer pain and acute pain. Factors that may influence efficacy, such as the type of pain, the type of TENS used, duration of treatment, and whether the study measures acute or chronic outcomes, will be addressed. Recent literature suggests that TENS may alleviate acute pain. For example, one double-blind randomized, sham-controlled trial found that during emergency transport of 101 patients, TENS reduced post-traumatic hip pain with a change in visual analog scale (VAS) from 89 to 59, whereas the sham-stimulated group remained relatively unchanged (86 to 79). Confirmation of these results is needed.
A search of the MEDLINE database from January 2007 to January 2008 identified several recent studies and 2 new meta-analyses on the use of TENS.
A randomized, controlled trial from Taiwan assessed the efficacy of TENS applied at bilateral acupuncture points (Li4: midpoint between the first and second carpal bones, and Sp 6: 5 cm above the medial malleolus) in 100 women in the first stage of labor (5% dropout due to precipitous labor) (Chao, 2007). Additional medication was allowed, but was not reported. At the end of 30 minutes of treatment, the median VAS score improved in the active TENS group from 8 to 4.5 (10 mm scale), the VAS of the placebo group changed from 8 to 7. Pain relief of greater than 3 points was obtained in 62% of patients in the active group and 14% of patients in the sham group. The median duration of relief from pain following TENS acupuncture was 75 minutes.
An industry-sponsored meta-analysis by Johnson and Martinson included 38 randomized controlled comparisons (1,227 patients from 29 publications) of trans- or percutaneous electrical nerve stimulation (ENS) for chronic musculoskeletal pain, using any stimulation parameters on any location (e.g., back, neck, hip, knee) (Johnson, 2007). The data were converted to a percentage improvement in VAS scores, then transformed into standardized mean differences (a continuous measure that adjusts for variability in different outcome measures). Based on the combined standardized difference, the authors concluded that TENS provided pain relief "nearly three times" the pain relief provided by placebo. There are a number of sources of bias in the analysis that seriously limit interpretation of the results. First, the heterogeneity of the individual study results (I2=82%) raises questions about the appropriateness of combining these studies in a meta-analysis (see previous discussion regarding the decision to not combine studies for the 2000 Cochrane review on chronic pain). Further limiting interpretation is the transformation of data to standardized effect size, which appears to have led to discrepant effect sizes of otherwise similar results. For example, comparison of the untransformed and transformed data shows that while two of the included trials (Deyo et al. 1990, and Machin et al. 1988), found similar percentage point differences in VAS between active and control groups (5% and 8%, respectively), the standardized effect sizes are not equivalent. Positive standardized effect sizes from data that are not statistically or clinically significant (e.g., 47% vs. 42% change from baseline in Deyo et al.) also raises concerns about the appropriateness of the data transformation. Inclusion of poor-quality studies is an additional concern, since several of the studies with the greatest effect sizes reported drop-out rates exceeding 25%. Furthermore, bias for publication of small positive studies may not have been adequately addressed, since the "Fail-safe N" method used to assess publication bias is problematic.
Another major limitation in interpretation of this meta-analysis is the absence of information about whether ENS results in a clinically meaningful improvement. For example, there was no discussion of the magnitude of the combined change in VAS scores or of the proportion of patients who achieved clinically meaningful improvements. Examination of the data indicates that there was less than a 15% difference between the ENS and placebo groups (with an average difference of 4%) for 13 of the 38 (34%) comparisons. The small effect observed in many of these small studies raises further questions about the contribution of publication bias to the meta-analysis. Also at issue is the relative contribution of percutaneous ENS (PENS), since meta-regression found PENS to be more effective than TENS. Given the substantial uncertainty regarding the appropriateness of the studies included and how the data were transformed, combined with questions regarding the clinical significance of the results, results from this meta-analysis are considered inconclusive.
Data regarding clinical significance were provided in a meta-analysis by Bjordal et al. on the short-term efficacy of physical interventions for osteoarthritic knee pain (Bjordal, 2007). Included in the review were 11 studies (259 subjects on active therapy) using TENS, acupuncture-like TENS (AL-TENS), or interferential stimulation; 9 of the 11 studies were included in the meta-analysis reviewed above. Combined data revealed a 19 mm improvement in VAS over placebo (a "slight improvement"), with a confidence interval ranging from 10 mm (a "minimal perceptible improvement") to 28 mm (above the 20 mm threshold of an "important improvement"). These results are similar to an earlier Cochrane review (overlap of 6 studies) on the use of TENS or AL-TENS for osteoarthritis of the knee (Osiri, 2002). The inclusion of 2 studies on interferential stimulation (with an unweighted average improvement in VAS of 34 mm over placebo) may also have increased the magnitude of the effect. Considering that the potential for publication bias is high when combining a number of small studies in a meta-analysis (particularly when the effect is small), evidence of short-term relief of chronic musculoskeletal pain remains weak. Results from these positive meta-analyses must also be balanced against other systematic reviews of musculoskeletal pain syndromes that found mixed and inconclusive results.
A recent randomized sham-controlled trial (n=163) reported that although no differences in VAS pain scores were observed, more patients were satisfied following 10 days (10-12 hours/day) of TENS (58%) than following use of a sham device (43%) (Oosterhof, 2006). Analysis of the results by type of pain (osteoarthritis-related, neuropathic, or bone/soft tissue/visceral) in a subsequent report showed no difference in patient satisfaction for the group with osteoarthritis and related disorders (39% vs. 31%, n = 31, 26) or in patients with neuropathic pain (63% vs. 48%, n = 16, 25), and greater satisfaction with TENS in the group of patients with injury of bone and soft tissue or visceral pain (74% vs. 48%, n = 34, 31). The nearly 50% patient satisfaction rating in the sham control group suggests a strong nonspecific effect with this treatment protocol.
Overall, evidence for the use of TENS remains inconclusive. Due to the inconsistency and uncertainty in the TENS literature, the policy is unchanged.
The Department of Defense, Veterans Health Administration, published clinical guidelines for the management of postoperative pain in May 2002. These guidelines indicate that TENS may be useful for postoperative pain relief for a variety of procedures and sites. Except for postoperative abdominal pain and pain from cholecystectomy, all of the recommendations are consensus based. For postoperative abdominal pain and pain from cholecystectomy, the recommendations are based on at least 1 RCT and general agreement that TENS is acceptable.
The AHRQ Guidelines Clearinghouse also lists several other guidelines that indicate TENS may be used for management of pain. However, none of these guidelines lists TENS as a major recommendation.
The American Pain Society and American College of Physicians published guidelines on therapies for acute and low back pain in 2007 (Chou, 2007). No recommendations for TENS were made; evidence was found to be insufficient to assess the efficacy of TENS in comparison with other interventions.
The European Federation of Neurological Societies published 2007 guidelines on neurostimulation for neuropathic pain Cruccu, 2007). The task force was not able to arrive at conclusive recommendations, with only about 200 patients with different diseases, in studies using different parameters and comparators, and with variable results. The task force concluded that standard high-frequency TENS is possibly (level C) better than placebo, and probably (level B) worse than acupuncture-like or any other kind of electrical stimulation.
Three additional Cochrane reviews were published in 2008, addressing the topics of TENS for cancer pain, chronic low back pain, and other chronic pain conditions (Robb, 2008) (Khadikar, 2008) Nnoaham, 2008). For cancer pain, only 2 RCTs (total of 64 participants) met the selection criteria for inclusion in the systematic review (Robb, 2008). There were no significant differences between TENS and placebo in the included studies, and results of the review were considered inconclusive due to a lack of suitable RCTs. For the treatment of chronic low back pain, 4 high-quality RCTs (585 patients) met the selection criteria (Khadikar, 2008). There was conflicting evidence about whether TENS reduced back pain and consistent evidence from 2 of the trials (410 patients) that it did not improve back-specific functional status. The review concluded that the evidence available at this time does not support the use of TENS in the routine management of chronic low back pain. An updated review of TENS for the treatment of various other chronic pain conditions including rheumatoid arthritis with wrist pain, temporomandibular joint dysfunction, multiple sclerosis with back pain, osteoarthritis with knee pain, neuropathy, pancreatitis, and myofascial trigger points included 25 RCTs (1281 patients) (Nnoaham, 2008). Due to heterogeneity, meta-analysis was not possible; slightly over half of the studies found a positive analgesic outcome in favor of active TENS treatments. The authors concluded that the 6 studies added since the last version of this review did not provide sufficient additional information to change the conclusions, and that the published literature lacks the methodological rigor needed to make confident assessments of the role of TENS in chronic pain management.
Recent literature suggests that TENS may alleviate acute pain. For example, one double-blind randomized, sham-controlled trial found that during emergency transport of 101 patients, TENS reduced post-traumatic hip pain with a change in visual analog scale (VAS) from 89 to 59, whereas the sham-stimulated group remained relatively unchanged (86 to 79) (Lang, 2007). In another double-blind study, 40 patients undergoing inguinal herniorrhaphy were randomized to active or placebo TENS for post-surgical pain (De Santana, 2008). Pain scores measured prior to the first treatment were 5.2 on a 10 point scale for the active TENS group and 5.3 for the placebo TENS group. Two 30-minute sessions of TENS at 2 and 4 hours after surgery reduced both analgesic use and pain scores measured up to 24 hours after surgery (mean pain score of 0 vs. 3.4). Blinding appears to have been maintained, as 95% of subjects from both groups reported that they would use TENS again in the future to treat their pain. Confirmation of these results is needed.
Overall, evidence for the use of TENS from high quality trials remains inconclusive. However, expert opinion received indicates that the use of TENS for the relief of chronic intractable pain has been beneficial in some patients. Therefore, the use of TENS meets primary coverage criteria of effectiveness for the treatment of chronic pain if shown to be effective during a 30 day therapeutic trial.
A small RCT from 2011 found no difference between microcurrent TENS (micro-TENS) compared to sham in 41 patients with diabetic peripheral neuropathy (Gossrau, 2011). In this study, current was applied at an intensity of 30-40 microAmps rather than the usual intensity of milliamps, and patients were treated for 30 minutes, 3 times per week. After 4 weeks of treatment, 29% of the micro-TENS group and 53% of the sham group showed a response to therapy, defined as a minimum of 30% reduction in the neuropathic pain score. The median Pain Disability Index was reduced to a similar extent in the TENS group (23%) and the sham group (25%).
A 2012 update of the Cochrane review identified one additional RCT (a feasibility study of 24 patients with cancer bone pain) that met selection criteria (Hurlow, 2012). The small sample sizes and differences in patient study populations of the 3 RCTs prevented meta-analysis. Results on TENS for cancer pain remain inconclusive.
A single-blinded randomized trial with 42 patients assessed the analgesic effect of TENS after laparoscopic cholecystectomy (Silva, 2012). Patients were treated with active or placebo TENS for 30 minutes within the first 24 hours after the operation. Pain, assessed by VAS before and immediately after treatment, improved by a median of 2.4 after TENS and 0.4 after placebo treatment. Pain, on an 11-point numerical scale, improved by a median of 3.0 after TENS and 0.7 after placebo. The relative risk of nausea and/or emesis was 2.17 times greater for patients from the placebo group.
A 2011 systematic review included 15 randomized or quasi-randomized studies (446 patients) on the use of TENS to enhance motor recovery follow stroke (Laufer, 2011). Although the methodological quality was considered generally good, only 4 studies were large RCTs. In the majority of studies (9/15), the number of subjects receiving TENS was less than 15. Stimulation targets for the various studies included nerves, muscles, acupuncture points, and the entire hand or foot. The majority of studies reported significant effects on at least 1 outcome measure, though the effect sizes were generally small and there were insignificant effects for many outcome measures. Meta-analysis could not be performed for most outcomes because of variability between studies and insufficient data. A moderate effect was determined for force production of ankle dorsiflexion (but not plantar flexion) and for the Timed Up and Go test (but not the 10-meter gait velocity test or the 6-minute walk test). Overall, results from studies of TENS after stroke are inconsistent.
Keskin et al. reported a randomized controlled trial of TENS for pregnancy-related low back pain in 2012 (Keskin, 2012). Seventy-nine patients were randomized to 6 TENS sessions over 3 weeks, a home exercise program, acetaminophen or a no-treatment control. In the control group, pain intensity increased in 57% of participants. Pain decreased in 95% of participants in the exercise group and all participants in the acetaminophen and TENS groups. VAS improved by a median of 4 points with TENS and by 1 point in the exercise and acetaminophen groups. In the control group, VAS worsened by 1 point. Roland-Morris Disability Questionnaire (RMDQ) scores indicated a significantly greater improvement in function in the TENS group (-8.5) compared to the control (+1), exercise (-3), and acetaminophen (-3) groups. This study is limited by the lack of a TENS-sham control.
A 2012 trial randomized 75 patients with osteoarthritis pain to a single session of high-frequency TENS, low-frequency TENS, or placebo TENS (Vance, 2012). Double-blind assessment during the treatment session found a significant increase in pressure pain threshold at the knee for both low- and high-frequency TENS. There was no effect of TENS on cutaneous mechanical pain threshold, heat pain threshold, or heat temporal summation. All 3 groups reported a reduction in pain at rest and during the timed up-and-go (TUG), and there were no differences in pain scores between groups. These results on pain scores suggest a strong placebo component of TENS treatment. There was no significant change in the time to perform the TUG in any of the groups.
A placebo-controlled crossover RCT from 2013 investigated the effect of a single treatment of TENS in 41 patients with fibromyalgia (Dailey, 2013). Patients were blindly allocated to either no treatment, active TENS treatment, or placebo treatment. Each of the treatment arms has therapy once per week for a 3-week period. Patients rated the average pain intensity before and after treatment on a 0 to 10 scale and found that pain with movement was less during active TENS when compared with placebo or no TENS (p<0.05). Patients also rated fatigue with movement and found that fatigue decreased with active TENS compared with placebo or no TENS, p<0.05 and p<0.01 respectively. Pressure pain threshold improvement was significantly greater in the active TENS group (30%, p<0.05) than placebo (11%) and no TENS (14%).
Another RCT published in 2013 investigated TENS in fibromyalgia. In this trial, 39 patients were randomized into 3 groups: a group with placebo devices at both lumbar and cervical sites, a group with a single active TENS device at the lumbar or cervical site and a placebo device at the second site, and a group with 2 active TENS devices at both lumbar and cervical sites (Lauretti, 2013). TENS was administered for 20 minutes at 12-hour intervals for 7 consecutive days. In the dual placebo group, VAS pain scores did not improve compared with baseline. Patients who had a single site of active TENS reported a reduction in pain of 2.5 cm (p<0.05), and patients in the dual TENS group experienced the greatest reduction in pain of 4.2 cm (p<0.02). Consumption of medication for pain was also decreased significantly in the single TENS and dual TENS groups (p<0.05 and p<0.02 respectively). Sleep improvements were reported by 10 patients in the dual TENS group, 8 in the single TENS group, and by 4 patients in the placebo group. Fatigue increased for 3 patients in the placebo group, but decreased in 7 patients in the dual TENS group and 5 patients in the single TENS group. No adverse events were reported.
An observational study of 60 men consecutively treated with TENS for refractory chronic pelvic pain syndrome was published in 2013 (Schneider, 2013). TENS was performed at home for 12 weeks with participants keeping a pain diary for the calculation of VAS score. A successful treatment response was defined as a 50% or greater reduction in VAS at the 12-week end point and absolute VAS of less than 3 at the end of treatment. TENS was successful in 29 (48%) of patients, and treatment response was sustained at a mean follow-up of 43.6 months (95% confidence interval [CI], 33.2 to 56). After 12 weeks of treatment the mean VAS score decreased significantly (p<0.001) from 6.6 to 3.9. The quality of life, as assessed by the National Institutes of Health Chronic Prostatitis Symptom Index improved significantly after 12 weeks of TENS treatment (p<0.001). No adverse events were reported.
An RCT comparing intra-articular hyaluronic acid (HA) injections with TENS for the management of knee osteoarthritis recruited 50 participants and was published in 2013 (Chen, 2013). Twenty-seven patients were randomized to HA and received 1 injection intra-articularly per week for 5 weeks. Twenty-three patients in the TENS group received a 20-minute session of TENS 3 times a week for 4 weeks. At 2 weeks follow-up, the TENS group exhibited a significantly greater improvement (p=0.03) than the HA group on the VAS pain scale (final score 4.17+-1.98 vs 5.31+-1.78, respectively). No difference between the 2 groups was found at 2 months after treatment or at 3 months after treatment. Similarly the TENS group had a greater improvement on the Lequesne index at 2 weeks follow-up compared with the HA group (final score 7.78+-2.08 vs 9.85+-3.54, respectively; p=0.01) and at 3 months follow-up (final score 7.07+-2.85 vs 9.24+-4.04, respectively; p=0.03). Both treatment groups had significant improvements from baseline to 3 month on scores in walking time, patient global assessment, and disability in activities in daily life. Only the TENS group improved in range, of motion for the target joint.
In 2014, an RCT of 224 participants with osteoarthritis of the knee assigned patients to 1 of 3 interventions: TENS (TouchTENS, TENScare, Surrey, United Kingdom) combined with education and exercise (n=73), sham TENS combined with education and exercise (n=74), or education and exercise alone (n=77) (Palmers, 2014). Investigators and participants were blinded to treatment. Participants were treated for 6 weeks and directed to use the TENS device as needed for pain relief. WOMAC pain, function and total score improved significantly over time from baseline to 24 weeks but did not vary between groups (p>0.05). TENS as an adjunct to exercise failed to elicit additional benefits.
A 2013 report by the Cochrane Collaboration reviewed the evidence on TENS for the treatment of chronic neck pain (Kroeling, 2013). Four studies (2 with a high risk of bias and 2 with a low risk of bias) compared TENS versus placebo for immediate pain relief. Three studies with a high risk of bias also compared TENS with electrical muscle stimulation, ultrasound, or manual therapy for the treatment of chronic neck pain. The treatment schedules and differing outcomes did not allow for pooling of results, and group sizes were very small (7-43 participants) with varied results for TENS therapy. Overall, the quality of this evidence is very low for TENS versus all comparators for the treatment of chronic neck pain.
The Cefaly device (Cefaly, STX-med, Herstal, Belgium) is a TENS headband device intended for the prophylactic treatment of migraine in patients 18 years of age or older (USFDA, 2012). The clinical information on Cefaly was supplied by 2 studies, the Prevention of Migraine using the STS Cefaly (PREMICE), (Schoenen, 2013), and a European postmarketing surveillance study (Magis, 2013). PREMICE was a double-blind sham-RCT conducted at 5 tertiary care headache clinics in Belgium. Sixty-seven patients were randomized to active (n=34) or sham (n=33) neurostimulation for 3 months and 59 (88%) completed the trial according to protocol. No serious adverse events occurred, although 1 patient discontinued the trial because of a reported device-caused headache. After a 1-month run-in period, patients were instructed to use the device daily for a 3-month period. Adherence was recorded by the TENS device. Ninety stimulation sessions were expected, but on average 55.5 sessions were completed by the active group and 49 were completed in the sham group. The primary outcome measures were changes in the number of migraine days and the percent of responders.
The authors present both intention-to-treat (ITT) and per-protocol analyses, but only the ITT will be discussed. The reduction in the number of migraine days (run-in compared with 3 month) was 2.06 (95% CI, -0.54 to -3.58) for the TENS group versus 0.32 (-0.63 to +1.27) for the sham group; this difference did not quite reach statistical significance (p=0.054). The proportion of responders (≥50% reduction in the number of migraine days/month) was 38% (95% CI, 22% to 55%) in the TENS groups versus 12% (95% CI, 1.0% to 23%) in the sham group (p=0.014). The number of migraine attacks from the run-in period to 3rd month was significantly lower for the active TENS group (decrease of 0.82 in the TENS groups versus 0.15 in the sham group, p=0.044). Number of headache days also was decreased in the TENS group compared with sham (decrease of 2.51 versus 0.15, p=0.041). Patients in the active TENS group reported a 36.6% reduced number of acute antimigraine drugs taken compared with the 0.5% reduction in the sham group (p=0.008).Severity of migraine days did not significantly differ between groups.
Participants rated their satisfaction with the treatment more highly in the active group (70.6%) than in the sham group (39%). During postmarketing surveillance 53% of 2313 participants were satisfied with the device and willing to continue using it. Ninety-nine participants (4%) reported a complaint with the device although none were serious adverse events. The most commonly reported adverse events included: insomnia in 4 participants (0.2%), reversible forehead skin irritation in 5 participants (0.2%), headache after a TENS session in 12 participants (0.52%), sleepiness during a Cefaly session (0.52%), and a dislike of how the device felt, leading to discontinuation in 29 participants (1.25%).
Another single-blinded randomized trial of 55 patients assessed the analgesic effect of TENS after pancreatic resection (Bjersa, 2014). All patients were treated according to a standard care protocol, which postoperatively gave thoracal epidural analgesia infusion of bupivacain of 1 mg/mL, fentanyl, 2μg/mL, and adrenaline, 2μg/mL. When the infusion was terminated patients were treated with either sham TENS or active TENS treatment which was regulated by the patient with the only rule being that each session's duration be at least 30 minutes. Most participants (64%) dropped out and only 9 active TENS and 11 sham TENS participants were available for analysis. No differences were identified in additional analgesic consumption or pain estimations 24 hours after discontinuing epidural analgesia.
This evidence for treatment of acute post-surgical pain is insufficient to determine whether TENS improves outcomes for this group; further high-quality trials are needed.
A placebo-controlled, randomized trial of TENS assessed 200 women who gave birth between January 2010 and July 2010 (Kayman-Kose, 2014). One hundred women who gave birth vaginally were allocated to either active TENS or sham TENS in a 1:1 ratio; this same assignment was performed for 100 women who gave birth by cesarean section. TENS was performed once for 30 minutes after childbirth was completed. After vaginal delivery or cesarean section but before administration of TENS, the placebo and active groups did not significantly differ in VAS score or verbal numeric scale (VNS) score. However, after active TENS in the cesarean group, there was a significant reduction in VAS score (p<0.001) and VNS score (p<0.001) compared with the placebo group. The same trend was observed in the vaginal delivery group with the active treatment showing a significant reduction in VAS (p=0.022) and VNS scores (Pp=0.005). The authors also assessed if TENS reduced the need for additional analgesia. There was no difference between the active TENS and placebo group for vaginal delivery (p=0.83), but in the cesarean arm, the active treatment group had a significant reduction in analgesic need (p=0.006).
A systematic review and meta-analysis of TENS for acute pain management in the prehospital setting was published in 2013 (Simpson, 2014). A literature search identified 4 sham-controlled RCTs of TENS including a total of 128 patients. On pooled analysis of these studies, TENS was superior to sham, with a clinically significant reduction in pain severity and a mean reduction of 38 mm on VAS (95% CI, 28 to 48; p<0.0001). The 4 studies were found to have significant heterogeneity (I2 = 94). The difference in mean final pain score compared with sham treatment was 33 mm (95% CI, 21 to 4; p<0.0001). The authors also found that TENS significantly reduced anxiety compared with the sham treatment with an overall 26 mm lower score on VAS for TENS (95% CI, 17 to 35; p<0.0001). No studies reported adverse events for TENS.
A multicenter RCT of TENS as an adjunct to primary care management for tennis elbow was identified. Thirty-eight general practices in the West Midlands, UK recruited 241 adults who had a new or first diagnosis of tennis elbow (Chesterton, 2013). Participants were randomized to TENS once per day for 45 minutes over 6 weeks or until resolution of pain plus primary care management (consultation with a general practitioner followed by information and advice on exercise) versus primary care management alone. Both groups saw a large (>25%) within group improvement in pain intensity, with the greatest improvement during the first 6 weeks of treatment. ITT analysis revealed no difference in improvement of pain (-0.33, 95% CI, -0.96 to 0.31; p=0.31) between the 2 groups at 6 weeks, 6 months (-0.20, 95% CI, -0.81 to 0.42; p=0.526), or 12 months (0.45, 95% CI, -0.15 to 1.06; p=0.139). However, adherence to exercise and TMS was very poor, with only 42 (35%) meeting a prior adherence criteria. Per protocol analyses did show a statistically significant difference in favor of TENS at 12 months (p=0.030) but not during other time periods.
A paired-sample randomized crossover trial of TENS for improving strength, proprioception, and balance was conducted with 29 mobile stroke survivors who had no pre-existing conditions which limited mobility (Tyson, 2013). Participants were given a single session of active TENS plus a session of control sham treatment with each session lasting approximately 1 hour. The authors found that all participants were able to tolerate the TENS treatment, although 1 participant did not feel the active treatment at maximum intensity. Participants improved in forward reach with a mean difference of 4.16 cm (p=0.009), velocity with a mean difference of 0.03ms (p=0.002), plantarflexor strength with a mean difference of 4.34 N/m, and joint position sense (JPS) plantar flexion with a mean difference of -1.8 degrees (p=0.029). The mean differences for JPS dorsiflexion and dorsiflexor strength did not vary significantly between the TENS and control arms.
The European Headache Federation, citing concerns about an ineffective sham procedure for TENS in headache methodology studies and the overall limited level of evidence, recommend that there is insufficient evidence for the use of TENS in headache prophylaxis and to abort an acute headache (Martelletti, 2013).
Guidelines from the Osteoarthritis Research Society International 2014 recommend that TENS is not appropriate for the use of multiple-joint osteoarthritis and is of uncertain value in the treatment of knee-only osteoarthritis (McAlindon, 2014).
A 2014 Cochrane review on non-pharmacologic interventions for chronic pain in individuals with spinal cord injury identified 1 RCT on TENS (Boldt, 2014). This study had a high risk of bias, and no conclusion could be drawn on the effectiveness of TENS compared with sham for reducing chronic pain in this population.
The largest RCT on TENS after surgery was published by Rakel and colleagues (Rakel, 2014). This double-blind study compared TENS once or twice daily for 6 weeks versus sham TENS versus standard care to reduce pain during rehabilitation in 317 patients who had undergone total knee arthroplasty (TKA). The primary outcome was pain intensity during range of motion (ROM) and during walking, measured by a 21-point numeric rating scale (NRS) on postoperative day 1 and week 6. Secondary outcomes were pain intensity at rest, hyperalgesia, and function. Intent-to-treat analysis showed that patients who used TENS during exercises had less pain when compared with standard care in the near postoperative period, but there was no significant difference in subjective pain when compared with patients who used sham TENS. There was also no significant difference between the active and control groups when tested at 6 weeks. This study, which found no benefit of TENS over placebo/sham, had good methodologic quality and a low risk of bias.
A patient-blinded study of TENS after abdominal surgery (n=55) found that application of TENS for 1 hour per day resulted in a significant reduction in pain, particularly at rest, measured both during and immediately after treatment compared with sham TENS (Tokuda, 2014). Pulmonary function (vital capacity, cough peak flow) was also significantly better in the active TENS arm. Another assessor-blinded study of TENS in 74 living kidney donors found a modest reduction in pain at rest and during the measurement of pulmonary function when measured 1 day postoperatively (Galli, 2015).
It is unclear whether the difference in findings between the RCT by Rakel et al and the smaller RCTs is due to increased risk of bias in small studies or in publication, or to differences in the time since surgery or the type of surgery. One can conclude with relative certainty that TENS has no greater effect than placebo on pain measured at least 1 day following total knee arthroplasty. Additional study is needed to determine the effect of TENS in the immediate post-operative period following other types of surgery.
For the treatment of pain after total knee arthroplasty, 1 large randomized controlled trial found no benefit of TENS compared with sham TENS.
Sawant and colleagues reported a meta-analysis of 4 RCTs of TENS for the management of central pain in multiple sclerosis (Sawant, 2015).Two of the studies had a sample size of 10, the other 2 studies had sample sizes of 59 and 60. One of the studies examined the effect of TENS on upper extremity pain and the other 3 studied the effect of TENS on low back pain. The exact electrode placement could not be identified. Effect sizes extracted from the 4 studies showed a medium sized effect of TENS (Heges' g = 0.35, p = 0.009). The overall level of evidence was considered to be GRADE 2.
A 2015 Cochrane review found no RCTs on TENS for phantom limb pain or stump pain after amputation (Johnson, 2015a). The authors concluded that the published literature on TENS for phantom limb pain in adults lacks the methodologic rigor and robust reporting needed to confidently assess its effectiveness and that RCT evidence is required.
Tucker and colleagues reported a double-blind RCT of TENS administered during bone marrow sampling in 70 patients (Tucker, 2015). There was no significant difference in a numeric pain score between patients who received strong TENS impulses and the control group that received TENS just above the sensory threshold as reported immediately after the procedure (5.6 vs 5.7, respectively). Over 94% of patients in both groups felt that they benefited from TENS.
A 2015 Cochrane review assessed the efficacy of TENS as a sole treatment for acute pain conditions that included procedural pain (eg, cervical laser treatment, venipuncture, screening flexible sigmoidoscopy) and nonprocedural pain (eg, postpartum uterine contractions, rib fractures) (Johnson, 2015b). Nineteen RCTs involving 1346 participants at entry were included. Data on pain intensity were pooled for six trials, showing a mean difference of -24.62 mm on a 100 mm VAS scale in favor of TENS, with significant heterogeneity between the trials. Data on the proportion of participants achieving at least 50% reduction in pain was pooled for 4 trials with a relative risk (RR) of 3.91 in favor of TENS over placebo. There was a high risk of bias associated with inadequate sample sizes in the treatment arms and unsuccessful blinding of treatment interventions. The authors concluded that the analysis provided tentative evidence that TENS reduces pain intensity over and above that seen with placebo, but the high risk of bias made definitive conclusions impossible.
(NCT01641471) an industry-sponsored or cosponsored trial. Prospective Evaluation of Transcutaneous Electrical Nerve Stimulation (TENS) for Pain Relief Following Total Knee Arthroplasty (TKA); planned enrollment 116; completion date June 2015 (completed).
Cherian et al published an RCT in 2016 comparing TENS with standard of care in the treatment for 70 patients with knee osteoarthritis; all patients had previously taken part in a prospective 3-month trial of TENS, allowing researchers to collect data on the long-term efficacy of TENS (mean follow-up time, 19 months) (Cherian, 2016). The follow-up study evaluated pain (using a VAS) and function (measured by new Knee Society Scale and lower-extremity functional scores) and a number of secondary outcomes, including medication usage, quality of life, device use, and conversion to total knee arthroplasty. For all outcomes, reviewers reported a general trend of improvement for the TENS group compared with the standard of care group; however, no statistical analyses were provided for secondary outcomes, and several differences were not significant among primary outcomes. When measured from pretreatment to final follow-up, Knee Society Scale and lower-extremity functional scores were significantly increased for the TENS group (p=0.002 and p<0.001 for the respective tests). The trial's limitations included a small sample size and possible variance in the amount of medication taken by each patient; also, the interviews were not conducted in person, meaning that some conclusions about functional improvement were not confirmed by a physical examination.
A 2017 RCT by De Giorgi et al evaluated the efficacy of TENS in treating subjective and objective pain in 49 women diagnosed with chronic facial myalgia; 34 patients received TENS treatment daily for 10 weeks but were evaluated for pain up to 25 weeks, and 15 patients received no treatment but were evaluated for pain up to 10 weeks (De Giorgi, 2017). TENS treatment consisted of daily 60-minute sessions at 50 Hz, and VAS scores were taken for average and maximum pain intensity in the previous 30 days, as well as the level of pain at examination. The other primary outcome was the assessment of pain at muscular palpation sites, measured by the Pericranial Muscle Tenderness Score and Cervical Muscle Tenderness Score; for this outcome and that of VAS (mean and maximum measurements), patients in the TENS group had significantly lower pain levels than those for the control group at 10 weeks (p<0.05). Within the TENS group, the authors found that VAS scores tended to decrease throughout the trial duration, as did Pericranial Muscle Tenderness and Cervical Muscle Tenderness scores (p<0.05); these differences were significant except for the period between 15 weeks and 25 weeks. Secondary outcomes included mandibular movement and range of motion, and the TENS group showed no significant improvement over the control group for either outcome. Although a limitation of the trial was that observation of control patients ended at 10 weeks, these results confirmed results of several similar studies of TENS in treating musculoskeletal pain. The trialists concluded that TENS is an effective treatment for chronic facial myalgia, although studies with more participants are needed.
A 2017 randomized placebo-controlled trial by Ferreira et al evaluated TENS in the treatment of individuals with temporomandibular disorder; 40 patients (30 female, 10 male) were randomized into 2 groups, receiving either placebo or active TENS (Ferreira, 2017). The trial used both high- and low-frequency TENS, allotting to the active TENS patients 25 minutes of 4 Hz followed by 25 minutes of 100 Hz; measuring pain intensity and pressure pain threshold immediately after treatment and again 48 hours later. When compared with baseline values, pain intensity was reduced for patients in the active TENS group, and pressure pain threshold was significantly increased (p<0.050); for those in the placebo group, there were no significant improvements for either primary outcome. A secondary outcome was electromyography activity in TENS-treated areas, measured in 3 positions (mandibular rest position, maximal voluntary contraction, habitual chewing); for this outcome, results varied among placebo and active TENS. Limitations of the trial included the short duration of the assessment, and the absence of control groups either receiving no treatment or evaluating the same treatment in patients without temporomandibular disorder. The authors concluded that longer term studies were needed, especially those evaluating the efficacy of both high- and low-frequency TENS.
Ramanathan et al published a prospective RCT of 66 patients having undergone total knee arthroplasty who were assigned to active or placebo TENS; patients used the device as needed for 2 hours with 30 minutes of rest afterward and had follow-up visits 2, 4, and 6 weeks after surgery (Ramanathan, 2017). For the primary outcome, reduction of opioid intake, no significant difference was observed between active and placebo TENS groups (p=0.60); this was also the case for secondary outcomes, which included assessment of pain, function, and clinical outcomes. The trial was limited by a high withdrawal rate (of 116 patients enrolled, only 66 completed) and a lack of uniformity in the device settings chosen by patients. The authors found no significant benefit of TENS treatment following total knee arthroplasty.
Lison et al published an RCT of the use of TENS to treat pain in women undergoing hysterectomy without sedation; the study included 138 women receiving active TENS, placebo TENS, or neither treatment during the procedure (Lison, 2017). Unlike previous studies of the use of TENS in hysterectomy, the trial used varying high-fixed TENS (fluctuating between 80 and 100 Hz) and isolated the relief of pain by prohibiting oral medications taken before the procedure. Women in the active TENS group reported significantly lower VAS scores than women in the control or placebo TENS groups reported; this was the case at each stage measured (entry, contact, biopsy [when necessary], and residual). To validate these measurements, the authors included a second pain scale (Likert scale), which found a significant correlation with the VAS results (p<0.001). For secondary end points (eg, procedure duration, vital parameters, vasovagal symptoms), the authors reported that differences between the groups were insignificant. However, patient satisfaction was significantly higher in the active TENS group than in either placebo TENS or control groups (p<0.001 and p=0.001, respectively). Limitations of the trial included that it did not account for the use of a flexible hysteroscope, instead using a rigid hysteroscope; this may limit the generalizability of its results. In addition, the study excluded patient anxiety as an outcome, focusing instead on pain and patient satisfaction.
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