Transcutaneous Electrical Nerve Stimulation (TENS) A Possible Aid for Pain Relief in Developing Countries?

Abstract

Transcutaneous electrical nerve stimulation (TENS) refers to the delivery of electrical currents through the skin to activate peripheral nerves. The technique is widely used in developed countries to relieve a wide range of acute and chronic pain conditions, including pain resulting from cancer and its treatment. There are many systematic reviews on TENS although evidence is often inconclusive because of shortcomings in randomised control trials methodology. In this overview the basic science behind TENS will be discussed, the evidence of its effectiveness in specific clinical conditions analysed and a case for its use in pain management in developing countries will be made.

Full text

DOI: 10.4176/090119
Review Article
Transcutaneous Electrical Nerve Stimulation (TENS)
A Possible Aid for Pain Relief in Developing Countries?
Tashani O, Johnson MI
Centre for Pain Research, Faculty of Health, Leeds Metropolitan University, UK, Leeds Pallium Research Group
Abstract: Transcutaneous electrical nerve stimulation (TENS) refers to the delivery of electrical currents through the skin to
activate peripheral nerves. The technique is widely used in developed countries to relieve a wide range of acute and chronic
pain conditions, including pain resulting from cancer and its treatment. There are many systematic reviews on TENS although
evidence is often inconclusive because of shortcomings in randomised control trials methodology. In this overview the basic
science behind TENS will be discussed, the evidence of its effectiveness in specific clinical conditions analysed and a case for
its use in pain management in developing countries will be made.
Key words:
Transcutaneous Electrical Nerve Stimulation (TENS), Pain, Analgesia, Pain relief, Pain management, Developing
countries, Pain gate theory
Introduction
Transcutaneous electrical nerve stimulation (TENS) is
widely used in western and developed countries to relieve
a wide range of painful conditions, including non-
malignant acute and chronic pain and pain resulting from
cancer and its treatment [1-3]. TENS is inexpensive, non-
invasive and safe with no major side effects. TENS can be
self administered by patients following simple training and
because there is no potential for toxicity, patients can
titrate the dosage on an as-needed basis. During TENS
pulsed electrical currents are generated by a small battery
operated TENS device that can be kept in the pocket or
attached to the user’s belt. Currents from the TENS device
are delivered through the skin by two self-adhering
electrode pads (Figure 1).
The purpose of TENS is to selectively activate nerve
fibers. Maximal pain relief is achieved when TENS
generates a strong non-painful electrical sensation
beneath the electrodes. Pain relief is usually rapid in onset
and stops shortly after TENS is turned off. For this reason
patients are encouraged to deliver TENS for as long as
needed, which may be for hours at a time and throughout
the day. The main contraindication is patients with
implanted stimulators such as pacemakers. In the UK,
TENS devices can be purchased without prescription,
although this is not the case in some European countries.
TENS devices, including electrode leads, pads and battery,
retail for approximately £30GBP although bulk buying can
markedly reduce cost. Interestingly, TENS does not appear
to be widely available for patient use in developing
countries.
In this review the basic science behind TENS will be
discussed, the evidence of its effectiveness in specific
clinical conditions will be provided and a case for its use in
pain management in developing countries will be made.
Physiological principle of TENS induced pain relief
The ancient Egyptians are usually acknowledged as the
first people who used electrogenic fish to apply electricity
for pain relief. Yet, the first documented use of this kind of
pain relief is of a Roman Physician in 46 AD [4]. In 1786,
Luigi Galvani, an Italian doctor, demonstrated that the leg
of a frog contained electricity. This observation and other
advancements in generating electricity lead to a
resurgence in the use of electricity to treat different
illnesses and relieve pain. However, increased use of
pharmacological agents to manage pain resulted in the
decline of the electrotherapy at the end of the 19th
century. In 1965, Ronald Melzack from McGill University
in Montreal Canada and Patrick Wall from University
College London UK, published their seminal paper which
proposed a gating mechanism in the central nervous
system to regulate the flow of nerve signals from
peripheral nerves en-route to the brain [5]. According to
this Gate-Control Theory of Pain, activity in large diameter
low threshold mechanoreceptive (touch-related) nerve
fibers could inhibit the transmission of action potentials
from small diameter higher threshold nociceptive (pain-
related) fibers through pre and post synaptic inhibition in
the dorsal horn of spinal cord. Humans utilise this
mechanism whenever they rub their skin to relieve pain.
Because nociceptive fibers (A-delta and C-fibers) have a
higher threshold of activation than mechanoreceptive
fibers (A-beta fibers) Melzack and Wall proposed that it
would be possible to selectively stimulate
mechanoreceptive fibers by titrating the amplitude of
electrical currents delivered across the surface of the skin
(ie TENS). This would prevent signals from nociceptive
fibers from reaching higher centres of the brain, thus
reducing pain (Figures 2). In essence, TENS electrically
rubs pain away.
In addition to interrupting nociceptive signals, at spinal
cord dorsal horn, we now know that TENS analgesia also
involves a descending inhibitory mechanism that could be
partially prevented by spinalization [6]. Activity in nerve
fibers descending from the brain can also block onward
transmission of peripheral nerve signals within the spinal
cord. Humans utilise this mechanism whenever they
mentally distract themselves to not feel pain despite the
presence of tissue damage (Figure 2)
Evidence gathered from animal studies suggested that
low frequency TENS effects may be due to release of
endogenous opioids [6]. This explains why analgesia may
persist for hours after electrical stimulation has stopped
because endorphins have long lasting effects in the central
nervous system. The released opioids may generate their
analgesic action at peripheral, spinal and supraspinal sites
[7,8]. However, other neurochemicals have been
implicated in TENS analgesia including GABA [9],
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Review Article
acetylcholine [10], 5-HT [11], noradrenaline [12] and
adenosine [13].
Figure 1 A standard TENS device.
TENS and TENS-like devices
In health care the term TENS refers to the delivery of
currents using a ‘standard TENS device’ (Table 1) [3].
However, there are a variety of devices that deliver
electrical currents through the skin but have technical
output characteristics that differ from a standard TENS
device. We have previously described these as “TENS-like
devices” and include Trancutaneous Spinal
Electroanalgesia, Interferential Therapy, Microcurrent
Stimulation and Pain Gone pens (see [3,14,15] for a
review of these devices). The remainder of this review will
focus on standard TENS devices.
Table 1 Technical output specifications of a standard TENS
device
Weight
Dimensions
50-250g
6 x 5 x 2 cm (small device)
12 x 9 x 4 cm (large device)
Cost Approximately £30
Pulse waveform
(usually fixed)
Monophasic symmetrical biphasic
asymmetrical biphasic
Pulse amplitude
(usually adjustable) 1-50mA into a 1 kΩ load
Pulse duration
(sometimes fixed,
sometimes adjustable)
10-1000µs
Pulse frequency
(usually adjustable) 1-250pps
Pulse pattern
usually continuous and burst
available (some devices have
modulated amplitude, modulated
frequency, modulated pulse
duration, random frequency)
Channels 1 or 2
Batteries PP3 (9V), rechargeable
Additional features Timer, most devices deliver
constant current output
TENS Techniques
TENS is a technique to stimulate different categories of
nerve fibers. The most commonly used TENS technique is
termed conventional TENS. During conventional TENS,
low-intensity pulsed currents are administered at high-
frequencies (between 10-200 pulses per second, pps) at
the site of pain. The user experiences a “strong, non-
painful TENS sensation often described as ‘’tingling’ or
pleasant ‘electrical paraesthesiae’. Physiologically,
conventional TENS activates large diameter non-noxious
afferents which has been shown to close the pain gate at
spinal segments related to the pain [6]. Another
technique, which is used less often is acupuncture-like
TENS (AL-TENS) using high-intensity and low-frequency
(less than 10pps, usually 2pps) administered over
muscles, acupuncture and trigger points [16]. The purpose
of AL-TENS is to activate small diameter afferents which
has been shown to close the pain gate using extra-
segmental mechanisms [2]. TENS can also be used as a
counter-irritant, termed intense TENS, using high-intensity
and high-frequency currents (Table 2, Figure 3).
Figure 2 Diagrammatic representation of the principle of
conventional TENS. By selectively activating A-beta fibers, TENS
shuts the Pain Gate on A-delta and C fibers preventing pain-
related signals reaching the brain.
Clinical effectiveness of TENS
In Western clinical practice TENS has been shown to
have a role in pain management [2]. There are many
systematic reviews on TENS although evidence is often
inconclusive because of shortcomings in RCT
methodology. Early systematic reviews suggested that
TENS was of limited benefit as a stand alone pain therapy
for acute pain. Carroll et al. judged there to be no benefit
of TENS for postoperative pain because 15 of 17 RCTs
found no differences in pain relief between active and
placebo TENS [17]. However, Bjordal et al. re-assessed
the evidence and concluded that TENS reduced post-
operative analgesic consumption if TENS was applied
using adequate TENS technique [18]. Systematic reviews
have also concluded that there was no evidence for TENS
producing beneficial analgesic effects during childbirth
[19,20] and insufficient evidence to determine the
effectiveness of TENS in reducing pain associated with
primary dysmenorrhoea [21]. RCTs suggest that TENS is
effective for acute orofacial pain, painful dental
procedures, fractured ribs and acute lower back pain (for
review see [22].
Previously, systematic reviews suggested that TENS
may be of benefit for chronic pain but definitive
conclusions were hindered by shortcomings in RCT
methodology [23,24]. Reviews on rheumatoid arthritis of
the hand [25], whiplash and mechanical neck disorders
[26], chronic low back pain [27], poststroke shoulder pain
[28] and chronic recurrent headache [29] were
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Table 2 TENS techniques
TENS parameters Patient
experience
Electrode
location
Physiological
Intention Regimen Analgesic
profile
Conventional
TENS
Low intensity
(amplitude), high
frequency (10-200 pps)
Strong, non-
painful TENS
paraesthesia with
minimal muscle
activity
Dermatomes
Site of pain
To stimulate
large diameter
non-noxious
afferents (A-
beta) to produce
segmental
analgesia
Use TENS
whenever
in pain
Usually
rapid
onset and
offset
AL-TENS
High intensity
(amplitude), low
frequency (1-5 bursts of
100 pps)
Strong
comfortable
muscle twitching
Myotomes
Site of pain
Muscles
Motor nerves
Acupuncture
points
To stimulate
small diameter
cutaneous and
motor afferents
(A-delta) to
produce
extrasegmental
analgesia
Use TENS
for 20-30
minutes at
a time
May be
delayed
onset and
offset
Intense
TENS
High amplitude
(uncomfortable/noxious
), high frequency (50-
200pps)
Uncomfortable
(painful)
electrical
paraesthesia
Dermatomes
Site of pain
Nerves
proximal to
pain
To stimulate
small diameter
cutaneous
afferents (A-
delta) to produce
counter irritation
Short
periods
only 5-15
minutes at
a time
Rapid
onset and
delayed
offset
inconclusive. In contrast, systematic reviews have
demonstrated TENS efficacy for knee osteoarthritis [30]
and chronic musculoskeletal pain [31]. RCTs have also
demonstrated effects for a range of other chronic pain
conditions including localized muscle pain, post-herpetic
neuralgia, trigeminal neuralgia, phantom limb and stump
pain and diabetic neuropathies (for review see [3]. A
recent Cochrane review by Robb et al. concluded that
there is insufficient available evidence to determine the
effectiveness of TENS in treating cancer-related pain
[32,33].
Pain Management in developing countries: Could
TENS help?
The International Association for The Study of Pain
(IASP) speculate that “the prevalence of most types of
pain may be much higher in developing countries than in
developed countries”, although epidemiological evidence is
lacking [34]. It is known that there is a higher incidence of
pain conditions associated with epidemics such as
HIV/aids in the developing world. An IASP Developing
Countries Task Force, which included Africa and the
Middle East reported that pain management in the general
population was inadequate, although there was
considerable variations between regions [35]. Limited
resources, ignorance by health care professionals and a
lack of pain specialists were contributing factors. This has
impacted significantly on pharmacological therapy with
many drugs commonly used in the developed world being
unavailable to the general public because of the weak
economy and limited purchasing power of citizens [36]. In
addition, drugs even when available may be fake,
adulterated, passed their expiry date or perished due to
inadequate storage.
TENS is advantageous in this regard. It is inexpensive
when compared to drug therapy. The cost of a TENS
device is £30GBP, although devices are available for less
than £15GBP if bought in bulk. Once purchased a TENS
device will not perish or deteriorate and devices in the
developed world are used for many decades without the
need for further servicing or repair. Often clinics purchase
TENS devices in bulk and loan them to patients for short
and long term use, on the proviso that the patient returns
the device to the clinic when it is no longer needed.
Running costs are minimal and include battery and
reusable electrode pad replacement. Manufacturers
recommend that individual pads have longevity of one
month on daily use, although patients often use them for
far greater lengths of time, especially if they take care to
store them carefully. Electrode costs can be reduced by
using carbon rubber electrodes which are smeared with
electrode gel and attached to the skin with micropore
tape, rather than using self adhering electrodes. In
general, battery and electrode use depends on how often
the patient uses TENS
TENS has no known drug interactions and so can be
used in combination with pharmacotherapy to reduce
medication, medication-related side effects and medication
costs. TENS has very few side effects with no incidents of
serious or adverse events reported in the literature. TENS
has a rapid onset of action, unlike medication, and there is
no potential for toxicity or overdose.
Clearly, there is a case to use TENS for pain
management in the developing world. However, research
is needed to determine the feasibility of TENS use in
developing countries. Perhaps health promotion
authorities should alert the public and heath care
practitioners to the role of TENS as an important aid in the
fight against pain.
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Figure 3 Output characteristics (settings) of a standard
TENS device. The user can control the amplitude
(intensity), duration (width), frequency (rate) and pattern
(mode) of the pulsed electrical currents.
References
1. Barlas, P. and T. Lundeberg, Transcutaneous electrical nerve
stimulation and acupuncture, in Melzack and Wall's Textbook of
Pain, S. McMahon and M. Koltzenburg, Editors. 2006, Elsevier
Churchill Livingstone: Philadelphia. p. 583-90.
2. Walsh, D., TENS. Clinical applications and related theory. 1st
ed. 1997, New York: Churchill Livingstone.
3. Johnson, M., Transcutaneous Electrical Nerve Stimulation, in
Electrotherapy: Evidence based practice, T. Watson, Editor.
2008, Churchill Livingstone: Edinburgh. p. 253-96.
4. Gildenberg, P.L., History of electrical neuromodulation for
chronic pain. Pain Med, 2006. 7 Suppl 1: p. S7-S13.
5. Melzack, R. and P. Wall, Pain mechanisms: A new theory.
Science, 1965. 150: p. 971-79.
6. Sluka, K.A. and D. Walsh, Transcutaneous electrical nerve
stimulation: basic science mechanisms and clinical
effectiveness. J Pain, 2003. 4(3): p. 109-21.
7. Sluka, K.A., et al., Spinal blockade of opioid receptors prevents
the analgesia produced by TENS in arthritic rats. J Pharmacol
Exp Ther, 1999. 289(2): p. 840-46.
8. Kalra, A., M.O. Urban, and K.A. Sluka, Blockade of opioid
receptors in rostral ventral medulla prevents antihyperalgesia
produced by transcutaneous electrical nerve stimulation
(TENS). J Pharmacol Exp Ther, 2001. 298(1): p. 257-63.
9. Maeda, Y., et al., Release of GABA and activation of GABA(A) in
the spinal cord mediates the effects of TENS in rats. Brain Res,
2007. 1136(1): p. 43-50.
10. Radhakrishnan, R. and K.A. Sluka, Spinal muscarinic receptors
are activated during low or high frequency TENS-induced
antihyperalgesia in rats. Neuropharmacology, 2003. 45(8): p.
1111-19.
11. Radhakrishnan, R., et al., Spinal 5-HT(2) and 5-HT(3)
receptors mediate low, but not high, frequency TENS-induced
antihyperalgesia in rats. Pain, 2003. 105(1-2): p. 205-13.
12. King, E.W., et al., Transcutaneous electrical nerve stimulation
activates peripherally located alpha-2A adrenergic receptors.
Pain, 2005. 115(3): p. 364-73.
13. Sawynok, J., Adenosine receptor activation and nociception.
Eur J Pharmacol, 1998. 347(1): p. 1-11.
14. Johnson, M., Transcutaneous Electrical Nerve Stimulation
(TENS) and TENS-like devices. Do they provide pain relief? Pain
Reviews, 2001. 8: p. 121-28.
15. Johnson, M.I., A critical review of the analgesic effects of
TENS-like devices. Physical Therapy Reviews, 2001. 6: p. 153-
73.
16. Johnson, M., The analgesic effects and clinical use of
Acupuncture-like TENS (AL-TENS). Physical therapy Reviews.,
1998. 3: p. 73-93.
17. Carroll, D., et al., Randomization is important in studies with
pain outcomes: systematic review of transcutaneous electrical
nerve stimulation in acute postoperative pain. Br J Anaesth,
1996. 77(6): p. 798-803.
18. Bjordal, J.M., M.I. Johnson, and A.E. Ljunggreen,
Transcutaneous electrical nerve stimulation (TENS) can reduce
postoperative analgesic consumption. A meta-analysis with
assessment of optimal treatment parameters for postoperative
pain. Eur J Pain, 2003. 7(2): p. 181-88.
19. Carroll, D., et al., Transcutaneous electrical nerve stimulation
does not relieve in labour pain: updated systematic review.
Contemporary Reviews in Obstetrics and Gynecology, 1997.
September 1997: p. 195-205.
20. Carroll, D., et al., Transcutaneous electrical nerve stimulation
in labour pain: a systematic review. Br J Obstet Gynaecol,
1997. 104(2): p. 169-75.
21. Proctor, M.L., et al., Transcutaneous electrical nerve
stimulation and acupuncture for primary dysmenorrhoea.
Cochrane Database Syst Rev, 2002(1): p. CD002123.
22. Johnson, M., S. Oxberry, and K. Simpson, Transcutaneous
Electrical Nerve Stimulation (TENS) and acupuncture for acute
pain, in Acute Pain. Clinical Pain Management Second Edition,
P. Macintyre, S. Walker, and D. Rowbotham, Editors. 2008,
Hodder Arnold: London. p. 271-90.
23. Carroll, D., et al., Transcutaneous electrical nerve stimulation
(TENS) for chronic pain. Cochrane Database of Systematic
Reviews (Online : Update Software), 2003(3): p. CD003222.
24. Nnoaham, K.E. and J. Kumbang, Transcutaneous electrical
nerve stimulation (TENS) for chronic pain. Cochrane Database
Syst Rev, 2008(3): p. CD003222.
25. Brosseau, L., et al., Transcutaneous electrical nerve
stimulation (TENS) for the treatment of rheumatoid arthritis in
the hand. Cochrane Database Syst Rev, 2003(3): p. CD004287.
26. Kroeling, P., A.R. Gross, and C.H. Goldsmith, A Cochrane
review of electrotherapy for mechanical neck disorders. Spine,
2005. 30(21): p. E641-8.
27. Khadilkar, A., et al., Transcutaneous electrical nerve
stimulation (TENS) versus placebo for chronic low-back pain.
Cochrane Database Syst Rev, 2008(4): p. CD003008.
28. Price, C.I. and A.D. Pandyan, Electrical stimulation for
preventing and treating post-stroke shoulder pain: a systematic
Cochrane review. Clin Rehabil, 2001. 15(1): p. 5-19.
29. Bronfort, G., et al., Non-invasive physical treatments for
chronic/recurrent headache. Cochrane Database Syst Rev,
2004(3): p. CD001878.
30. Bjordal, J.M., et al., Short-term efficacy of physical
interventions in osteoarthritic knee pain. A systematic review
and meta-analysis of randomised placebo-controlled trials. BMC
Musculoskelet Disord, 2007. 8: p. 51.
31. Johnson, M. and M. Martinson, Efficacy of electrical nerve
stimulation for chronic musculoskeletal pain: a meta-analysis of
randomized controlled trials. Pain, 2007. 130(1-2): p. 157-65.
32. Robb, K., et al., A Cochrane Systematic Review of
Transcutaneous Electrical Nerve Stimulation for Cancer Pain. J
Pain Symptom Manage, 2008.
33. Robb, K.A., et al., Transcutaneous electric nerve stimulation
(TENS) for cancer pain in adults. Cochrane Database Syst Rev,
2008(3): p. CD006276.
34. Woodruff, R., Pain and palliative care in the developing world
and marginalized populations: A global challenge. Indian J
Palliat Care, 2004. 10: p. 80.
35. Bond, M., et al., Education and Training for Pain management
in Developing Countries. 2007, WWW.IASP-PAIN.ORG acessed
on 3/10/2008.
36. Omoti, A.E. and C.E. Omoti, Pharmacological strategies for
the management of cancer pain in developing countries.
Pharmacy Practice, 2007. 5(3): p. 99-104.
www.ljm.org.ly
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