424 Journal of Pain and Symptom Management Vol. 37 No. 3 March 2009

Palliative Care Rounds

Transcutaneous Electrical Nerve Stimulation(TENS) for Cancer Bone PainRobert D. Searle, FRCA, Michael I. Bennett, MB ChB, MD, FRCP,Mark I. Johnson, PhD, Sarah Callin, MRCP, and Helen Radford, BScAcademic Unit of Anaesthesia (R.D.S.), Leeds General Infirmary, Leeds; Institute for Health Research

(M.I.B.), Lancaster University, Lancaster; Faculty of Health (M.I.J.), Leeds Metropolitan University,

Leeds; and St. Gemma’s Hospice (S.C., H.R.), Leeds, United Kingdom

Abstract

In the cancer population, painful bony metastases are common, difficult to treat andsignificantly reduce quality of life. Common treatments include opioid analgesics,bisphosphonates, and radiotherapy; yet these have significant side effects and are notuniversally effective. Transcutaneous electrical nerve stimulation (TENS) is inexpensive,relatively free from side effects, and widely available. We present a case study of successfulTENS therapy in a patient with cancer bone pain and discuss the rationale for using TENSin this setting. J Pain Symptom Manage 2009;37:424e428. � 2009 U.S. Cancer PainRelief Committee. Published by Elsevier Inc. All rights reserved.

Key Words

Transcutaneous electrical nerve stimulation, TENS, cancer, metastatic, bone, pain

IntroductionApproximately one-third of patients with

cancer will develop bone metastases duringthe course of their disease, and painful bonemetastases remain the most common cause ofcancer-related pain.1 Cancer bone pain oftencan be severe. Of the 108 patients with this con-dition who were referred to an oncology clinic,23% rated their average pain as severe (be-tween 7 and 10 on a 0e10 numerical pain rat-ing scale) and 78% rated their worst pain assevere.2 Furthermore, a survey of 518 patientswith bone metastases found that one-third ofthose with moderate to severe pain still sufferedfrom painful symptoms despite treatment.3 A

Address correspondence to: Robert D. Searle, FRCA, Aca-demic Unit of Anaesthesia, Leeds General Infirmary,Great George Street, Leeds, LS1 3EX, United King-dom. E-mail: rdsearle@hotmail.com

Accepted for publication: April 3, 2008.

� 2009 U.S. Cancer Pain Relief CommitteePublished by Elsevier Inc. All rights reserved.

large international survey of over 1000 patientswith cancer pain found that cancer bone painsignificantly reduced quality of life and was as-sociated with poorer outcomes, comparedwith other pain types.4

Transcutaneous electrical nerve stimulation(TENS) is used throughout the world to man-age painful conditions because it is inexpen-sive, noninvasive, safe, and is simple to use.TENS is becoming more widely used in oncol-ogy and palliative care settings.5,6 However, ev-idence to judge whether TENS is beneficial forcancer pain is lacking. We present a case studyof TENS used in cancer bone pain and discussthe rationale for using TENS in this setting.

Case StudyA 63-year-old woman with a history of meta-

static lung cancer and an Eastern CooperativeOncology Group (ECOG) performance status

0885-3924/09/$esee front matterdoi:10.1016/j.jpainsymman.2008.03.017

Vol. 37 No. 3 March 2009 425TENS Therapy for Cancer Bone Pain

of 3 presented to clinic with persistent upperarm pain from a bony deposit in her proximalhumerus. The metastatic deposit had beenconfirmed by radiograph and bone scintigra-phy, and the patient had undergone a courseof radiotherapy and bisphosphonate treat-ment for symptom control in the past. The pa-tient continued to have pain, and at the timeof consultation, her analgesic requirementswere: modified-release morphine sulfate1200 mg daily, ketamine 400 mg daily, gaba-pentin 1800 mg daily, and oral morphine forbreakthrough pain.

Bone pain often results in pain both at restand particularly on movement. The latterpain may be short-lived but can have signifi-cant impact on patient activity. After consent,this patient agreed to undergo an hour ofTENS therapy to assess its acceptability in diffi-cult-to-treat cancer bone pain. Baseline painscores were taken (visual analog score, numer-ical rating scale [NRS] and verbal rating scale),both at rest and on painful movement (in thiscase, putting on a shirt). In addition, a short-form McGill multidimensional pain score wascompleted.

After completing baseline pain scores, theUltima XL-A1 TENS device (TensCare LTD,Epsom, UK) was applied to the site of bonepain. A single channel with two self-adheringgel pads was used. The gel pads were initiallyplaced six inches apart over the proximal hu-merus and adjusted to achieve paresthesiaover the site of pain. The TENS device was ad-justed to deliver a pulse width of 200 microsec-onds at 80 Hz. Intensity was increased until thesensation was ‘‘strong but comfortable.’’ After30 minutes, pain intensity and pain reliefmeasurements were completed at rest andwhile performing the painful movement.This process was then repeated at one hour(including a final short-form McGill question-naire), immediately before the TENS devicewas switched off and removed.

The overall pain scores improved with TENStherapy, both at rest and especially duringpainful movement. The NRS fell from a base-line of 4 at rest and 7 on painful movementto 1 at rest and 2 on painful movement after60 minutes of TENS therapy. Similar changeswere recorded with the verbal rating scaleand visual analog score. The short-form McGillpain score fell from a baseline of 8 to a score of

1 after 60 minutes of TENS therapy. The pa-tient found the sensation from TENS accept-able and was prescribed a TENS device totake home. Follow-up after 48 hours showedno adverse events to the TENS therapy.

DiscussionRationale for the Use of TENS in Cancer BonePain

The mechanisms of cancer bone pain arecomplex, but research suggests that sensoryand sympathetic neuronal changes withinbone marrow, mineralized bone, and perios-teum drive changes in the neurophysiology ofthe dorsal horn, which may represent a uniquepain state.7,8

Animal research suggests that tumor cellswithin bone initiate not only inflammatorybut also neuropathic pain mechanisms. Mousestudies have shown that pain is generatedthrough destruction of bone (by osteoclasts)and acidotic stimulation of pH sensitive recep-tors.9 The neuropathic component of bonepain is supported by studies that show thatbone tumor cells injure and destroy sensory fi-bers that innervate bone marrow and mineral-ized bone.7 In addition, ATF-3, a transcriptionfactor strongly expressed by sensory neuronsin neuropathic (but not inflammatory) painstates, is expressed by sensory neurons of tu-mor-bearing animals, probably as a result ofperipheral nerve destruction.7

Although cancer bone pain seems to bedriven by both inflammatory and neuropathicinitiators, changes in the neurophysiology ofthe dorsal horn in rat cancer bone painmodels seem to be unlike those found in in-flammatory or neuropathic models, suggestinga unique pain state.8 Research has shown thatin rat models of cancer bone pain, the dorsalhorn is both hyperexcitable and very dy-namic.8 Because of these changes to the dorsalhorn, cancer bone pain may be amenable toTENS therapy.

TENS is thought to reduce hyperalgesiathrough activation of receptor-mediated path-ways at the level of the spinal cord andsupraspinally.10e12 In animal models of inflam-matory pain states, high-frequency TENS actsby stimulating large-diameter primary afferentnerve fibers from deep tissue and by increasingthe extracellular concentration of gamma-

426 Vol. 37 No. 3 March 2009Searle et al.

aminobutyric acid (GABA) in the spinalcord.10,13 This leads to a reduction in centralsensitization and primary hyperalgesia.14 Stud-ies using chronic constriction injuries in ratssuggest that daily TENS can reduce the devel-opment of mechanical allodynia and thermalallodynia, although this may depend in parton electrode location and neurotransmittercontent of the dorsal horn.15e17 It is possiblethat by stimulating primary afferent nerve fi-bers, TENS may reduce the hyperexcitableand dynamic dorsal horn changes seen in ani-mal models of cancer bone pain. However, it isequally possible that stimulation analgesia mayprovoke increased pain by an enhanced spinalneuronal response to electrical stimuli.

Recent systematic reviews conclude thatTENS is beneficial for musculoskeletal painand osteoarthritis of the knee.18,19 Clinical trialson peripheral neuropathic pain are promising,although a systematic review on post-stroke painwas inconclusive.20 Overall clinical research onTENS for neuropathic pain is lacking.

To date, there are no systematic reviews onTENS for cancer-related pain. A systematic re-view of complementary therapies for symptomsin patients near the end of life included one‘‘pilot’’ randomized controlled trial (RCT) onTENS (n¼ 15), one non-RCT (n¼ 60) andtwo case series.21e24 The reviewers concludedthat TENS may relieve intractable pain in dyingpatients with cancer.25 Likewise, narrative re-views conclude that TENS could be particularlyuseful in the management of pain caused bymetastatic bone disease and neoplasm.5,6 Wehave recently completed a Cochrane systematicreview of TENS in cancer pain.26

Practical Considerations When Using TENSA variety of TENS devices are commercially

available. Users manipulate the electricaloutput characteristics of TENS to selectively ac-tivate different nerve fibers. The most com-monly used TENS technique is conventionalTENS.27 The aim of conventional TENS is toselectively stimulate large-diameter Ab nerve fi-bers without stimulating Ad and C nerve fibersand motor efferents. In theory, high-frequencyand low-intensity pulsed currents would bemost effective in achieving this type of stimula-tion. Large-diameter nerve fibers have shortrefractory periods and can generate nerve im-pulses at high frequencies. For this reason,

pulse frequencies between 10 and 200 pulsesper second (p.p.s) are shown to be consistentlyeffective and popular with patients.28 The pat-tern of TENS delivery is usually continuousand initial pulse width should be set between100 and 200 microseconds. However, the theo-retical relationship between pulse frequency,duration, and pattern may break down as cur-rents follow the path of lowest resistancethrough tissue. In practice, therefore, patientsshould experiment with different settings withthe aim of producing strong non-painful elec-trical paresthesia in the area of pain (a ‘‘strongbut comfortable sensation’’) without musclecontraction.27

Conventional TENS operates by way of a seg-mental mechanism, and electrodes are ideallyplaced to stimulate Ab fibers that enter thesame spinal segment as the nociceptive fibers as-sociated with the origin of the pain. Electrodesare usually applied to straddle the painful area.However, if this is not possible (because of a skinlesion, for example), electrodes can be triedproximally over the nerve trunk arising fromthe site of pain, over the spinal cord at the levelof the spinal segments related to the origin ofthe pain, or even at a site that is contralateralto the site of pain. In cases of tactile allodynia,TENS pads can be tried proximal to the site ofpain and altered sensitivity.

Following an initial supervised trial of TENS(to ensure acceptability, electrode placement,and patient education), patients should be in-structed to administer TENS in 30 minute ses-sions at first until they become familiar withthe equipment. After this, they should be en-couraged to use TENS as often as they like. Al-though some TENS users report decliningeffectiveness of TENS over time, the exactextent of this problem is unknown.27 Thereis some evidence to suggest that, in some pa-tients, the nervous system habituates to TENSstimuli. If patients are complaining of reducedeffectiveness of TENS over time, changing theelectrical characteristics of the TENS machineand the electrode placement may help.27

Acupuncture-like TENS (AL-TENS) delivershigh-intensity and low-frequency currents toactivate small-diameter afferents. AL-TENS isa form of hyperstimulation and has beenused for patients who do not respond to con-ventional TENS. Some patients are unable totolerate the higher intensity of AL-TENS, and

Vol. 37 No. 3 March 2009 427TENS Therapy for Cancer Bone Pain

until more evidence is available to guide prac-tice, we advise caution when using this therapyfor cancer bone pain. Some manufacturershave tried to overcome the problem of habitu-ation by including random pulse delivery orfrequency modulated pulse delivery settingsto their standard TENS devices. However,these devices have met with varied success.

Although contraindications to TENS ther-apy are few and mostly hypothetical, cautionshould be exercised when giving TENS to cer-tain groups of patients. These include patientswith epilepsy, women in the first trimester ofpregnancy, and patients with cardiac pace-makers.27 In addition, TENS should not be ap-plied over the carotid sinus, internally, or onbroken or dysesthetic skin. Complications ofTENS are few, but can include sensitivity toelectrode pads, resulting in contact dermatitis.In addition, patients whose activities have beenrestricted by pain should be warned that unac-customed increased mobility while using TENScould lead to muscular strains.

In conclusion, TENS may be a novel treat-ment for cancer bone pain, especially thepain caused by movement, and is probably un-derused in palliative care. However, further re-search is necessary to investigate and quantifyany analgesic effects of TENS in this context.

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