Brief Report

Acute Effect of Transcutaneous ElectricalNerve Stimulation on Tremor

Renato P. Munhoz, MD, Ritsuko Hanajima, MD, PhD, Peter Ashby, MD, FRCPC,and Anthony E. Lang, MD, FRCPC*

Movement Disorders Centre, Toronto Western Hospital, University of Toronto, Toronto, Canada

Abstract: Based on the claims that transcutaneous electricalnerve stimulation is effective in myoclonic dystonia andessential tremor, we evaluated its acute effects in 5 patientswith essential tremor and 2 patients with tremor attributed toperipheral neuropathy using as parameters the WashingtonHeights-Inwood Genetic Study of Essential Tremor rating

scale, self-reported impression, and recording of electro-myographic activity. We found no significant improvementin any of the parameters tested. © 2003 Movement DisorderSociety

Key words: WHIGET rating scale; TENS; myoclonic dys-tonia; essential tremor; neuropathic tremor

Transcutaneous electrical nerve stimulation (TENS) iscurrently used for analgesia in a broad range of medicalconditions such as peripheral nerve lesions, angina, dys-menorrhea, labor and delivery, osteoarticular diseases,burns, and some kinds of postoperative pain.1 Despite itswidespread clinical use, the physiological mechanism ofaction is not known, stimulating parameters are subjec-tive, electrode placement is empirical, and most of all, itseffectiveness is a subject of controversy.2 Regardless ofthese uncertainties, the use of TENS has been reported tobe effective in certain movement disorders, namely myo-clonic dystonia3 and essential tremor (ET) (J. Toglia,personal communication, 2001). We evaluated, undersubjective and objective parameters, the acute effects ofTENS on tremor.

PATIENTS AND METHODS

Five patients with ET (1 associated with oro-mandib-ular-lingual dystonia) and 2 patients with tremor attrib-

uted to peripheral neuropathy (PNT) volunteered for thestudy after providing informed consent. The patients arefollowed by the Movement Disorders Centre of the To-ronto Western Hospital, and the study had the approvalof the University Heath Network Research Ethics Board.Tremor was clinically assessed and quantified by usingthe Washington Heights-Inwood Genetic Study of Es-sential Tremor (WHIGET) rating scale,4 electromyo-graphic (EMG) activity, and accelerometers.

Recordings

Recordings were made while the patients sat comfort-ably in a chair. EMG activity was recorded with surfaceelectrodes 5 cm apart placed over the forearm extensorand flexor muscles bilaterally. The signals were ampli-fied with a band pass of 100 Hz to 1 kHz, digitized at �2kHz and analyzed with CED software (Cambridge Elec-tronic Devices, Cambridge, UK). An accelerometer(EGAXT-10; Entran, Fairfield, NJ) was taped to thedorsum of the wrist, and the signals were amplified witha band pass of 0 to 50 Hz and analyzed with CEDsoftware.

Stimulation

TENS was generated with a commercially availabledevice (Selectra, Dual Channel TENS 7720; Medtronic,

*Correspondence to: Anthony E. Lang, MD, FRCPC, 399 BathurstStreet, MP-11, Toronto Western Hospital, Toronto, Ontario, CanadaM5T 2S8. E-mail: lang@uhnres.utoronto.ca

Received 14 March 2002; Revised 28 June 2002; Accepted 9 July2002

Movement DisordersVol. 18, No. 2, 2003, pp. 191–194© 2002 Movement Disorder Society

191

Tempe, AZ). One electrode was placed over the brachialplexus at the inferior lateral corner of the posterior tri-angle of the neck bordered inferiorly by the clavicle andlaterally by the trapezius. The other electrode was placedover the C7 spinous process (as described by Toglia andIzzo).3 The brachial plexus electrode was initially used asthe cathode in all patients. The stimulus was first set at 2Hz, 250-�sec pulse width, and the intensity graduallyincreased until muscle twitching was observed. Thisintensity was called motor threshold (MT). The rate wasthen increased to 50 Hz. At 1 MT, such stimulationproduces an odd sensation of proprioceptive distortionand tightness of the arm.

Procedure

Recordings were made in 80-second segments in whichthe patients (1) relaxed with the hands in the lap for 20seconds (“rest”); (2) extended their forearms in front ofthem for 20 seconds (“posture”); (3) carried out the finger–nose test; and (4) carried out a task such as writing orholding a cup of water each for 20 seconds. In all 7 patients,three such recordings were made at 5-minute intervals be-fore (baseline), during a 15-minute period of TENS stimu-lation at 50 Hz, 250 msec, 1 MT (in one patient 0.8 MT wasthe maximum tolerated), and immediately after stimulation(TENS turned off). The whole sequence could then berepeated with different stimulus parameters: 5, 10, and 100Hz; intensities up to 2 MT; one side, the other side, or bothsides simultaneously.

Analysis

WHIGET rating scale was performed before, during, andafter stimulation and compared for each patient by nonpara-metric comparison using the Kruskal-Wallis test. For eachstate (e.g., posture) the mean amplitude of the tremor was

determined for each of six contiguous 3-second segments ofthe accelerometer trace (total 18 seconds) for the three trials(total 18 segments over 54 seconds) before, during, andafter stimulation. The means of 18 segments were com-pared with Student’s t test for each individual patient, andthe grand mean from all 7 patients for each state was alsocompared with the t test.

RESULTS

The clinical profile, rating scale results, and subjectiveimpression for each individual patient is shown in Table1. The mean WHIGET scale rating score for ET patientsbefore TENS was 15.4 (15.0 during and 14.8 after). Thecomparison of the values for each patient was not statis-tically significantly different (P � 0.858). This findingwas also true for the same comparison for each patientamong the whole group where the mean rating score was15.7 before, 15.3 during, and 14.9 after (P � 0.855).Patients ET2, ET4, and PNT2 showed a small decreasein WHIGET scale rating scores, and 2 of these (ET4,PNT2) reported a modest subjective improvement inspecific tasks. The other patients denied any improve-ment during and after stimulation. None of the patientspresented an increase in WHIGET scale score or wors-ening of symptoms after stimulation.

The mean values of the accelerometer recordings werecompared for each of the 7 patients before, during, andafter TENS (50 Hz, 250 msec, 0.8–1 MT). There was nosignificant change (Table 2). The overall means for theET patients were 1.24 during stimulation and 0.97 after,neither significantly different from baseline (Table 2). In1 patient with PNT (PNT1), the mean accelerometerdisplacement was significantly less during stimulation(P � 0.0068) (Table 2). This patient, however, did notreport any benefit and her WHIGET scale scoring re-

TABLE 1. Clinical profile, WHIGET scale rating (before, during, and after TENS), and subjective impression after TENS trialfor each individual patient

Patientno. Sex

Age(yr) Diagnosis

Durationof tremor

(yr)Locationof tremor

OtherMD

Response to drugs/alcohol

WHIGET scalerating before/during/after

TENSSubjective

improvement

ET 1 F 75 ET 20 UL/jaw OMLD No 16/16/16 NoET 2 M 73 ET 40 UL No Propanolol 12/11/11 NoET 3 F 69 ET 10 UL/head No No 15/15/15 NoET 4 F 69 ET 30 UL/head No Propanolol/Alcohol 16/15/14 DiscreteET 5 M 64 ET 40 UL No Primidone/Alcohol 18/18/18 NoPNT 1 F 68 CIDP for

7 yr6 UL No No 12/12/12 No

PNT 2 F 67 CMTD for61 yr

6 UL/head No No 21/20/18 Yes, action/writing

WHIGET, Washington Heights-Inwood Genetic Study of Essential Tremor rating scale; TENS, transcutaneous electrical nerve stimulation; MD,movement disorder; ET, essential tremor; UL, upper limbs; OMLD, oro-mandibulo-ligual dystonia; PNT, peripheral neuropathy tremor; CIDP,chronic inflammatory demyelinating polyneuropathy; CMTD, Charcot-Marie Tooth disease.

192 R.P. MUNHOZ ET AL.

Movement Disorders, Vol. 18, No. 2, 2003

mained unchanged after the procedure. These results areshown in Table 2 and Figure 1.

Recordings were made before, during, and after stim-ulation at 5 Hz (n � 1), 10 Hz (n � 3), 100 Hz (n � 3),and at intensities of 1.3 MT (n � 3), 1.5 MT (n � 1), and2 MT (n � 3). In 5 patients, stimulation was also appliedon both sides simultaneously. No significant changeswere observed in any of these trials.

DISCUSSION

We investigated the efficacy of TENS in a smallnumber of typical ET and PNT patients comparing sub-jective and objective parameters before, during, and afterstimulus. These comparisons did not reveal any signifi-cant improvement in the WHIGET scale scores, nor didthey show any statistically significant difference in theamplitudes of the accelerometer tracings.

The understanding of the pathophysiology of tremor isstill incomplete; however, it is well accepted that ET is acentral tremor influenced by peripheral factors, i.e., it iscaused by a central oscillator that is influenced by so-matosensory feedback loops. Therefore, studies of Elbleand colleagues5 and Britton and associates6 demonstratedthat mechanical perturbation of a tremulous upper limbsuch as a sudden muscle stretch or electrical stimulationof the median nerve could cause tremor resetting andinterfere with amplitude.

High-frequency stimulation of the Vim nucleus of thethalamus is very effective in controlling tremor.7 Themechanism is unknown. Stimulation has been postulatedto cause “depolarization block,”8 synaptic decay,9 or todisrupt the firing of thalamic cells reducing the degree ofsynchrony.10

We were unable to show that TENS reduced tremoracutely. We used a variety of stimulus parameters andthe maximum tolerable intensities of stimulation. It ispossible that by using such a small number of patients,especially those with tremor associated with peripheralneuropathy, caused us to miss a mild but significantbeneficial effect. However, previous claims of effects ofTENS in myoclonic dystonia and ET have indicatedprofound and consistent clinical benefit, which shouldhave been evident even with the small number assessedhere.

Why does this afferent barrage differ from that of tha-lamic stimulation? First, TENS may be stimulating thewrong fiber system. Thalamic DBS is delivered to the Vimnucleus of the thalamus, which receives mainly afferentsfrom the cerebellum. TENS, as applied here, probably ac-tivates local cutaneous afferents and the large muscle andcutaneous afferents traveling in the upper brachial plexus.Second, the TENS stimulation may not be powerfulenough. Stimulation in the Vim may be able to activate alarge proportion of the cerebellothalamic fibers withoutactivating cutaneous or pain afferents and without spread tothe internal capsule. With TENS, the intensity of stimulithat can be delivered is limited by the recruitment of painfibers and muscle efferents. With dorsal column stimulationpowerful afferent volleys can be created without recruit-ment of afferents or the activation of motor neurons.11 Itwould be interesting to know the effect of dorsal columnstimulation on tremor. We have been unable to find anyreports on this topic. It is also possible that frequencycould have been a factor limiting the efficacy of thestimulation procedures presented here. However, weevaluated the maximum stimulation frequency permit-

FIG. 1. Pooled data from 7 patients showing the mean amplitude ofthe accelerometer signal during and after stimulation compared withbaseline (arbitrarily defined as 1). Stimulation was applied over theipsilateral brachial plexus at 50 Hz, with a pulse width of 250 msec, andan intensity of 1 motor threshold (0.8 motor threshold on one patient).ET, essential tremor; PNT, peripheral neuropathy tremor. Filled circles,ET mean; open squares, PNT mean; filled triangles, PNT1; diamonds,PNT2.

TABLE 2. Comparison of accelerometer signals analyzedwith the CED software before (arbitrarily defined as 1),

during, and after TENS

Patient

Ratio Statistics

Before During After b-d b-a

ET 1 1 0.949804 1.128981 ns nsET 2 1 0.88131 0.778525 ns nsET 3 1 0.833367 0.83889 ns nsET 4 1 1.764865 1.416047 ns nsET 5 1 1.781418 0.707746 ns nsMean 1 1.242153 0.974038 ns nsSE 0.217579 0.131678

PNT 1 1 0.744802 0.834269 0.0068 nsPNT 2 1 0.602157 0.784785 ns nsMean 1 0.67348 0.809527 ns nsSE 0.071322 0.024742

Mean values compared using Student’s t test.b-d, before-during; b-a, before-after; ns, nonsignificant; CED, Cam-

bridge Electronic Devices; TENS, transcutaneous electrical nerve stim-ulation; ET, essential tremor; PNT, peripheral neuropathy tremor.

TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION 193

Movement Disorders, Vol. 18, No. 2, 2003

ted by the TENS device used (100 Hz), and becausethe rates used for the treatment of pain generally rangefrom 60 to 100 Hz and 3 to 80 Hz has been reported tobe effective for movement disorders3 (J. Toglia, per-sonal communication, 2001), we believe it is unlikelythat the use of higher stimulation frequencies wouldhave provided significantly greater clinical benefitthan demonstrated in our study. Finally, TENS mayrequire chronic application for beneficial effects, es-pecially if it operates by changing levels of neuro-transmitters within spinal chord or supraspinal path-ways. If this is the case, our treatment paradigm mighthave missed potential benefit by exclusively studyingpatients during and after relatively brief exposures.However, both central and peripheral perturbationsknown to affect tremor do so acutely and previoustherapeutic claims for TENS have suggested that thebeneficial effects have a relatively rapid onset.

Acknowledgment: Partially supported by a Centre of Ex-cellence grant from the National Parkinson Foundation (Mi-ami).

REFERENCES

1. Basford JR. Physical agents. In: DeLisa JA, Gans BM, editors.Rehabilitation medicine. 3rd ed. Philadelphia: Lippincott-Raven;1998. p 404–424.

2. Carroll D, Moore RA, McQuay HJ, Fairman F, Leijon G. Trans-cutaneous electrical nerve stimulation for chronic pain. CochraneDatabase Syst Rev 2001:CD003222.

3. Toglia JU, Izzo K. Treatment of myoclonic dystonia with trans-cutaneous electrical nerve stimulation. Ital J Neurol Sci 1985;6:75–78.

4. Louis ED, Barnes L, Wendt KJ, Ford B, Sangiorgio M, Tabbal S,Lewis L, Kaufmann P, Moskowitz C, Comella CL, Goetz CC,Lang AE. A teaching videotape for the assessment of essentialtremor. Mov Disord 2001;16:89–93.

5. Elble RJ, Higgins C, Leffler K, Hughes L. Factors influencing theamplitude and frequency of essential tremor. Mov Disord 1994;9:589–596.

6. Britton TC, Thompson PD, Day BL, Rothwell JC, Findley LJ,Marsden CD. Modulation of postural wrist tremors by magneticstimulation of the motor cortex in patients with Parkinson’s diseaseor essential tremor and in normal subjects mimicking tremor. AnnNeurol 1993;33:473–479.

7. Koller WC, Pahwa PR, Lyons KE, Wilkinson SB. Deep brainstimulation of the Vim nucleus of the thalamus for the treatment oftremor. Neurology 2000;55(Suppl. 6):S29–S33.

8. Benazzouz A, Hallett M. Mechanism of action of deep brainstimulation. Neurology 2000;55(Suppl 6):S13–S16.

9. Ashby P, Rothwell JC. Neurophysiologic aspects of deep brainstimulation. Neurology 2000;55(Suppl. 6):S17–S20.

10 Strafella A, Ashby P, Munz M, Dostrovsky JO, Lozano AM, LangAE. Inhibition of voluntary activity by thalamic stimulation inhumans: relevance for the control of tremor. Mov Disord 1997;12:727–737.

11. Hunter JP, Ashby P. Segmental effects of epidural spinal cordstimulation in humans. J Physiol 1994;474:407–419.

194 R.P. MUNHOZ ET AL.

Movement Disorders, Vol. 18, No. 2, 2003