|Year : 2013 | Volume
| Issue : 3 | Page : 132-141
Transcutaneous electrical nerve stimulation (TENS): A potential intervention for pain management in India?
Gourav Banerjee, Mark I Johnson
Centre for Pain Research, Faculty of Health and Social Sciences, Leeds Metropolitan University, Civic Quarter, England, United Kingdom
|Date of Web Publication||7-Jan-2014|
Faculty of Health and Social Sciences, Leeds Metropolitan University, Civic Quarter, Leeds LS1 3HE
Source of Support: None, Conflict of Interest: None
Globally, the burden of pain and consequent disability on healthcare and economy is significant. Given the pain prevalence, inconsistent, and inadequate specialist health care services in India, the burden is likely to be magnified. Analgesic medication is the mainstay treatment for most types of pain; however, its side effects and financial costs for prolonged periods of time have resulted in the search for safer, inexpensive treatment options. Transcutaneous Electrical Nerve Stimulation TENS is a non-invasive, self-administered and inexpensive analgesic technique used worldwide to manage pain. Evidence suggests that TENS is effective in relieving acute and chronic pain and can be used as a stand-alone treatment for mild to moderate pain or as an adjunct for moderate to severe pain. The purpose of this study is to overview the principles, techniques, and clinical research evidence when TENS is used to manage pain with reference to health care and research studies conducted in India. A summary of evidence was formed based on Cochrane reviews, systematic reviews and meta-analyses on TENS with respect to pain management.
Keywords: India, non-pharmacological analgesia, pain management, transcutaneous electrical nerve stimulation
|How to cite this article:|
Banerjee G, Johnson MI. Transcutaneous electrical nerve stimulation (TENS): A potential intervention for pain management in India?. Indian J Pain 2013;27:132-41
|How to cite this URL:|
Banerjee G, Johnson MI. Transcutaneous electrical nerve stimulation (TENS): A potential intervention for pain management in India?. Indian J Pain [serial online] 2013 [cited 2020 Feb 28];27:132-41. Available from: http://www.indianjpain.org/text.asp?2013/27/3/132/124590
| Pain as a Healthcare Problem in India|| |
A recent systematic review  estimated that the weighted mean ± SD prevalence of chronic pain worldwide was 30.3% ± 11.7% (19 studies, 65 surveys, 34 countries, 182,019 respondents) with no correlation between Human Development Index (HDI) and prevalence with insufficient reliable data to estimate with any certainty the prevalence of chronic pain in developing countries. Pain and consequent disability impose significant burden on a country's healthcare and economy. ,, Data on the prevalence of pain in India has not been established; however, a multinational study conducted by the World Health Organisation (WHO)  in 1998 estimated that prevalence of chronic pain in India was 19% sampled from a population of 398 members of the general public in Bangalore. India's population is above 1.2 billion, so it can be extrapolated that 0.32 billion people may be experiencing musculoskeletal pain at any given period. More recently, Bihari, et al  estimated that the prevalence of musculoskeletal pain in Gurgaon and Noida was 25.9% using a sample of 2086 people, with pain being more prevalent in females (31.3%) than males (20.9%). Thus, a significant proportion of the Indian population experiences chronic pain which jeopardizes India's growing but inadequate healthcare infrastructure  .
Similar approaches to pain management are taken in different regions of the world with medication being the mainstay treatment. , However, long-term analgesic medication has its problems including side effects and ongoing costs of buying drugs. For these reasons inexpensive, safe and easy to use non-drug alternatives are becoming popular. Ideally, treatments that can be self-administered by patients without the need of clinical supervision will reduce health care costs. The purpose of this review study is to overview the principles, techniques and clinical research evidence when Transcutaneous Electrical Nerve Stimulation (TENS) is used to manage pain with reference to health care and research studies conducted in India.
| Introduction to TENS|| |
During TENS pulsed electrical current is delivered across the intact surface of the skin to stimulate the underlying nerves. Current is generated by a portable TENS device powered by batteries (usually 9V) or A.C. mains and delivered to the skin via electrode leads and self-adhesive electrodes attached to the skin surface  [Figure 1]. If self-adhesive electrodes are not available, carbon-rubber electrodes smeared with conducting gel are used and secured to the skin using Velcro straps or medical adhesive tape.  Most TENS devices enable the user to vary amplitude (which affects subjective intensity of currents), frequency, pattern, and duration of the pulsed electrical current. TENS is used for symptomatic relief of mild to moderate pain of any origin, including nociceptive, neuropathic, and musculoskeletal.  TENS may be used on its own or as an adjunct to pharmacotherapy, especially for moderate to severe pain. , TENS can also be used to produce non-analgesic physiological effects and has been found to be beneficial in the management of dementia  , post-operative nausea and vomiting,  and wound healing. 
|Figure 1: TENS and accessories applied to the forearm using (a) carbon-rubber electrodes and (b) self- adhering electrodes|
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TENS devices and their accessories are inexpensive, easy to use, and can be purchased by individuals over the counter at pharmacies or over the internet. Individuals are able to self-administer TENS treatment and learn to titrate dosages accordingly to manage their painful condition. TENS effects are rapid in onset and there are few adverse effects or drug-interactions; TENS has no potential for toxicity or overdose and is economical when compared with long-term drug therapy. TENS is used throughout the world, although most commonly in countries with HDI of > 0.9 (i.e., developed countries). To date, there appears to have been little information about the use of TENS in developing countries. It is suspected that there is an awareness of the potential benefits of TENS for use in clinical settings in urban regions of developing countries although whether this translates into TENS being offered to patients by healthcare professionals is not clearly known.
| Historical Perspective of TENS|| |
The use of electricity to heal dates back over 4000 years; ancient Egyptians (2,500 BC  ) and Romans (46 AD  ) used fish to administer 'shocks' to treat a variety of painful ailments. These early practitioners were oblivious to the concept of electricity, but they found that the 'shock' administered by the fish caused numbness in painful body parts. It was not until the discovery of electricity in the 1700s that it was realized that the fish were in fact electrogenic. Devices were developed to generate electricity and this resulted in increased use of electricity in medicine until the late 19 th century when pharmacological interventions became popular. Interest in the use of medical electricity was rekindled in 1965 with the publication of 'Pain Gate' theory by Melzack and Wall  which offered a physiological rationale for electroanalgesia. Pioneering research on the use of electricity to relieve pain continued in late 1960s when Shealy and colleagues (1967)  and later, Reynolds (1969)  worked on invasive techniques of neuro-modulation of the spinal cord and brain, respectively. TENS was initially used to determine the success of dorsal column stimulation implants until it was realized that TENS could be a beneficial treatment when used on its own (Long, 1970's). ,
| TENS Techniques and Parameters|| |
A standard TENS device delivers repetitive biphasic pulsed currents with an amplitude ranging from 0 to 60 mA, pulse durations between 50 and 400 microseconds and pulse frequencies between 1 and 200 pulses per second (pps) [Figure 2]. Different TENS techniques are used to selectively activate different afferent nerve fibers [Table 1]. ,,, There are also several kinds of TENS-like devices which deliver current across the intact surface of the skin but are considered different to a standard TENS device because they have different technical output specifications. TENS-like devices include: Interferential therapy, microcurrent electrical therapy, transcutaneous spinal electroanalgesia and transcranial electrical stimulation. Their clinical evidence is, however, limited. ,
|Figure 2: Output characteristics of a standard TENS device. Circles represent dial controls for pulsed current amplitude (A), frequency (F) and duration (D). Pulsed current patterns are represented by B (burst mode), C (continuous mode) and M (amplitude modulation mode)|
Click here to view
| Physiological Rationale and Postulated Mechanisms of Action|| |
The mechanism of action of TENS-induced analgesia is consistent with pain gate theory. Conventional TENS (low intensity, high frequency) alleviates pain through selective activation of non noxious, low threshold, large diameter Aβ fibers which in turn inhibit ongoing central nociceptive cell activity and reduce central sensitization in the spinal cord (spinal mechanism resulting in segmental effects). ,, To achieve this effect, conventional TENS is administered to generate sensations of non-painful electrical paraesthesiae.
Acupuncture-like TENS (high intensity, low frequency) alleviates pain through selective activation of small diameter, (skin and muscles) high threshold Aδ peripheral afferents which in turn activates descending pain inhibitory pathways arising in the midbrain periaqueductal grey and the rostral ventromedial medulla (supraspinal mechanism resulting in segmental and extrasegmental effects). , AL-TENS is administered to generate sensations of electrical pulsing and muscle twitching. At intensities above pain threshold, AL-TENS may also activate diffuse noxious inhibitory controls producing counter irritant effects.
Intense-TENS (high intensity, high frequency) alleviates pain by stimulating high threshold small diameter cutaneous afferents leading to inhibition of central nociceptive transmission via spinal and supraspinal mechanisms. In addition, intense TENS causes nerve impulses travelling antidromically in cutaneous efferents resulting in blockade of orthodromic nociceptive impulses arising from nociceptor activity travelling in small diameter Aδ afferents toward the central nervous system., To achieve this effect, intense TENS is administered to generate sensations of painful electrical paraesthesiae, and can only be tolerated by the patient for short periods of time.
These TENS techniques cause the release of a variety of neurotransmitters in the central nervous system including opioids (endorphins), serotonin (5-HT), acetylcholine (ACh), norepinephrine, and gamma-amino-butyric-acid (GABA). In the rostral ventral medulla, high and low frequency TENS produces hypoalgesia by activation of Δ(delta) and μ(mu) opioid receptors, respectively. In addition, low-frequency TENS is associated with reduction of aspartate and glutamate levels in the spinal cord. ,, Further, it is thought that TENS induced pain relief may be augmented by dilation of local blood vessels  , although evidence is far from conclusive.
| Common Sites for TENS Electrodes in Pain Management|| |
Choosing an optimal electrode placement site at first may involve some degree of 'trial and error'. The order of priority of optimal electrode placement sites is:
- Painful area (over, close, or proximal to pain site, [Figure 3])
- Peripheral nerve (eg., over superficial radial nerve for pain on dorsum hand, 1 st 2 nd digits)
- Spinal nerve roots (parallel to vertebral column and over intervertebral foramen)
- Other specific sites: Acupuncture, Trigger and Motor points. Dermatome / Myotome
TENS should not be administered over the site of pain when there is a local contraindication (see below) or if the skin at that site is hypersensitive. For devices that use monophasic waveforms, or asymmetrical biphasic waveforms, it is best to apply the cathode proximal to the anode (i.e., toward the spinal cord) because it is the cathode that excites the axon to generate the action potential.
It is wise to use conventional TENS at the site of pain when TENS is tried on a patient for the first time as TENS sensations of 'tingling' or 'buzzing' are better tolerated than those of twitching. It is important that the patient understands that they need to use an intensity of TENS that is strong but not painful. If intensity is too weak then there will be insufficient afferent input to generate hypoalgesia. If intensity is too strong it will be uncomfortable and the patient would not be able to tolerate TENS for any appreciable length of time. Generally, conventional TENS can be administered regularly throughout the day although it is also advisable to take intermittent breaks from stimulation to reduce skin irritation. AL-TENS and intense TENS, which are administered using higher amplitudes of current should not be used for more than 20-30 minutes as longer duration may cause muscle fatigue and/or skin irritation. In addition, AL-TENS should not be used in cases of acute soft tissue injuries or over areas devoid of muscle tissues.
Skin and electrodes should be cleaned before and after application to reduce the possibility of surface lipids and dirt reducing conduction of electrical currents through the skin. ,
| Contraindications and Precautions|| |
All patients should have had their pain assessed before being given a trial of TENS. Comprehensive safety guidelines are available from the Canadian Physiotherapy Association  including a comprehensive list of contraindications. TENS is contraindicated at any site on the body for
- Patients using pacemakers or with cardiac conditions
- Impaired cognition, comprehension or other mental illnesses
The main situations where TENS is contraindicated locally and electrodes should not be applied over the region of concern are:
- The neck or head for patients with epilepsy and post-stroke patients
- The pelvis or abdomen including uterus during pregnancy (TENS is used on the back for labor pain)
- Areas where there has been recent hemorrhage, varicose veins, bleeding disorders (risk of further hemorrhage)
- Over ischemic tissue and thrombosis (risk of embolism)
- Transorbitally across the eyes (risk of increase in intraocular pressure)
- The anterior neck or carotid sinus (risk of hypotension, laryngeal spasm)
- Dysaesthetic skin or tactile allodynia (risk of skin irritation, burn, increased pain)
- Anterior or posterior areas of chest (risk of compromising pulmonary ventilation)
- Broken or frail, irritated or inflamed skin (apply over areas surrounding the wound)
- Areas of active malignancy (though TENS is found to be of help in cancer bone pain)
- Areas of active epiphyseal regions in children
Also, TENS should not be used:
- Internally (mouth)
- While driving or during operation of other hazardous machineries
- If the individual has an allergy to electrodes, gel or tape
- In water
| Previous TENS-related Studies Conducted in India|| |
Experimental TENS studies ,,, conducted in India have shown that AL-TENS increased experimental pain threshold in otherwise pain-free Indian participants. A case-report  suggested TENS was beneficial as an adjunct in the management of type 1 complex regional pain syndrome. We found 14 clinical studies on TENS that had been conducted in India on searching medical and physiotherapy electronic databases using relevant keywords (MEDLINE, PEDro, IndianJournals.com, up to September, 2013). The authors of most of the studies concluded that TENS was beneficial for pain relief in various conditions including trigeminal neuralgia, low back pain in labor, bruxism-associated masticatory pain, post-operative thoracic pain, cervical radiculopathy, low back pain specific to sacro-iliac joint dysfunction, fracture rib, diabetic neuropathy, temporomandibular joint dysfunction, and pain in frozen shoulder [Table 2].
| Clinical Effectiveness|| |
Meta-analyses and systematic reviews on TENS have yielded inconsistent results because several clinical trials were underpowered and lacked methodological rigor. This can be attributed in part to the fact that blinding and placebo intervention in electrophysical treatments is difficult. Recently, it has been shown that inadequate control groups, inappropriate TENS technique, suboptimal dose, poor adherence, and inappropriate outcome measures have contributed to negative findings on TENS.  A systematic review of TENS on experimental pain studies by Claydon et al  found that the efficacy of TENS depended on the selection of different combinations of intensity, frequency, and stimulation site. Evidence for TENS in acute pain and chronic pain has been conflicting, but more recently evidence is tending toward effects over and above that is seen with placebo (no current) TENS. Some guidelines recommend TENS for the management of pain in certain conditions while for others, they do not. For example, the United Kingdom's National Institute for Health and Clinical Excellence (NICE) guidelines recommend the use of TENS in osteoarthritis  but not in persistent non-specific low back pain.  A summary of the reviews and meta-analyses is provided below to demonstrate the conflicting evidence for TENS effectiveness as adapted from Johnson and Bjordal.  [Table 3].
There has been an on-going debate about the clinical effectiveness of TENS across the world, with evidence for efficacy changing over time leading to uncertainty about whether TENS should be offered. The use of TENS is supported by a vast quantity of case series and clinical studies without control groups. Large meta-analyses have found that TENS reduces chronic musculoskeletal pain and post-operative pain, although many systematic review findings are inconclusive because there is insufficient good-quality RCTs to make a judgement. Often evidence from RCTs is compromised because most RCTs are methodologically weak using inadequate sample sizes, inappropriate outcome measurement protocols and sub-optimal TENS technique.  Outcome tends to be positive if clear criteria for adequacy of TENS technique and dosage were set a priori. Recommendations about the use of TENS from professional and government bodies are also inconsistent. For example, in 2007 the American College of Physicians and the American Pain Society concluded that TENS had not been proven as effective for chronic low back pain  , yet 1 year later the North American Spine Society concluded that TENS reduced chronic low back pain in the immediate short term but not in the long term.  Recently, the USA Centers for Medicare and Medicaid Services withdrew coverage for TENS for chronic low back pain  because of insufficient evidence to judge effectiveness rather than evidence of a lack of effectiveness. Overall, TENS experts are confident that there is sufficient evidence from clinical research to suggest that TENS should remain an adjunct to core treatment for pain management and that negative outcome trials are due to methodological shortcomings rather than evidence of a lack of effect. ,
| Cost, Availability, and Usage of TENS in India|| |
In India, TENS is available without prescription either over-the-counter or from the internet. Standard TENS devices with accessories cost between Rs 1,800 and Rs 2,550 with more advanced TENS devices between Rs 22,000 and Rs 25,800. We conducted a survey  of attitudes and beliefs about the use of TENS for pain management by Indian physiotherapists and found that all physiotherapists in our survey reported that they used TENS on patients to relieve pain. They predominantly used it for musculoskeletal and neuropathic pain but did not regularly use it for post-operative, cancer, dysmenorrhoea pain. Furthermore, 76% of respondents reported that they did not recommend their patients to use TENS at home. This approach does not align with good practice guidelines which suggest that in most instances TENS should be used whenever pain is present and self-administered on an as needed basis.
| Issues Associated with Using TENS in India|| |
In India, it is likely that many health care professionals have not considered TENS as a possible treatment option for pain. Medical practitioners need to be aware of TENS as a viable treatment option so that they can encourage and support the use of TENS by nurses, physiotherapists, and other healthcare professionals. In the UK, it is often the physician who either recommends the use of TENS to their patients or refers them to a physiotherapist or a nurse who then recommends TENS and educates them on how to use it.
Technological developments in electronic gadgetry have touched lives of most urban dwellers including those of lower socioeconomic groups. Therefore, acceptance of TENS as part of a health care package should not be too difficult, especially where health care services adopt a modern (Western) model. Thus, in in-patient settings TENS devices could be loaned to patients for their duration of stay in hospital. Similar to the model of patient-controlled analgesia, patients could be trained on how to self-administer and use TENS for managing pain postoperatively or during early stages of labor. Costs to the clinic would be the initial outlay for TENS devices and then the running costs of replacing batteries and self-adhering electrodes. The latter may be moderately expensive as a new set of self-adhering electrodes would be necessary for each new patient to reduce any potential risk of cross infection. One way to overcome this problem would be to use carbon-rubber electrodes that can be sterilized and reused.
For out-patients with acute pain it may be possible to loan them a TENS device for a short duration. For patients with chronic pain who require TENS for a more prolonged period of time, it may be worth loaning them a TENS device for a month and if it proves beneficial then the patient can buy a TENS device for themselves, perhaps through a series of monthly instalments. This approach is used by some clinics in the UK.
Greater barriers to using TENS are more likely to exist in rural settings where healthcare services are resource limited and attitudes and approaches to pain management may be more traditional. The use of carbon-rubber electrodes smeared with conductive gel would be more appropriate not only because it would be less expensive but also because self-adhering electrodes deteriorate very rapidly if they are not kept in cool, dust free conditions which may not always be available. In addition, the cost of replacement batteries may also be prohibitive.
In rural settings, there may be socio-cultural barriers to accepting TENS as a viable treatment option including a lack of knowledge about TENS by the practitioner, and patients with negative attitudes and beliefs, a fear of electricity and of technology, inability to understand how to use TENS and a reluctance to try novel treatments. Not being able to attach the TENS device to an item of clothing (e.g., sarees) may also prove a barrier.
| Conclusions|| |
TENS is a safe, economical electrotherapeutic treatment used globally to relieve pain. Evidence to support effectiveness is generally positive and TENS is recommended in many good practice guidelines as a standalone treatment for mild to moderate pain and an adjunct to core treatment for managing moderate-severe pain. TENS has fewer adverse effects than analgesic drugs and can be self-administered for prolonged periods of time.
| Suggested Reading|| |
Johnson MI. Transcutaneous electrical nerve stimulation (TENS). Research to support clinical practice. Oxford University Press. Release date March 2014.
Johnson MI, Bjordal JM. Transcutaneous Electrical Nerve Stimulation for the management of painful conditions: Focus on neuropathic pain. Expert Reviews in Neurotherapeutics 2011;11:735-53.
Johnson MI. Transcutaneous electrical nerve stimulation. In: Watson T, editor. Electrotherapy: Evidence-based Practice. Edinburgh: Churchill Livingstone; 2008. p. 253-96.
Johnson MI. Transcutaneous electrical nerve stimulation: Mechanisms, Clinical Applications and Evidence. Reviews in Pain 2007;1:7.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]