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Original Article
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Janravee Vathakul, BNS*, Nanticha Kessava, M.D.*, Julaporn Pooliam, M.Sc.**, Madonna Damayanthie Datu,
M.D.***, anawut Jitsinthunun, M.D.*, Nantthasorn Zinboonyahgoon, M.D.*
*Department of Anesthesiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, ailand, **Clinical Epidemiology Unit, Oce
for Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, ailand, ***Department of Anesthesiolgy, Dr.
Wahidin Sudirohusodo-Hasanuddin University General Hospital, Makassar-Indonesia.
The Analgesic Effect of Transcutaneous Electrical
Nerve Stimulation (TENS) on the Opposite Side for
Phantom Limb Pain
ABSTRACT
Objective: To observe the eects of TENS on the contralateral limb and PLP reduction.
Materials and Methods: is was a single center retrospective study of 20 amputee participants with phantom limb
pain. e inclusion criteria were participants aged above 18, average pain of at least 4/10 on the numerical rating
scale (NRS), duration of pain longer than one week and treatment with TENS on the opposite side. We recorded
pain intensity before and aer TENS application, response time to treatment, satisfaction, and adverse eects.
Results: Of the 20 amputee participants, all patients suered from PLP and three also suered from residual limb
pain. e average pain score before use of TENS was 4.85/10 and aer was 1.15/10. e mean pain intensity score
was reduced by 3.7/10 (95% CI 2.95-4.45/10) or 76.28% (95% condence interval 63.61-89.47%). e average overall
satisfaction was 81.65%, and no adverse eects from application of TENS was reported.
Conclusion: e study shows that the application of TENS on the opposite side is a safe and eective treatment
method for intractable pain from PLP.
Keywords: Transcutaneous electrical nerve stimulation; amputee; phantom limb pain; contralateral; neuromodulation;
neuropathic pain (Siriraj Med J 2022; 74: 239-244)
Corresponding author: Nantthasorn Zinboonyahgoon
E-mail: nantthasorn@gmail.com
Received 8 October 2021 Revised 20 February 2022 Accepted 21 February 2022
ORCID ID: https://orcid.org/0000-0002-5946-7962
http://dx.doi.org/10.33192/Smj.2022.30
INTRODUCTION
Up to 80% of amputees experience pain sensation
to a limb aer amputation (phantom limb pain: PLP)
and/or pain at the stump (residual limb pain; RLP) that
negatively impacts their quality of life.
1-5
Although chronic
PLP is common, evidence evaluating the ecacy of
treatments remains scarce, and there is still no consensus
for a standard treatment in standard guidelines.
5,6
e
most common treatments are pharmacological. However,
strong evidence supporting the short and long-term
ecacy of pharmacological treatments for PLP is still
lacking.
6,7
In an eort to identify additional eective treatment
options for PLP, clinicians and investigators have examined
a variety of non-pharmacological treatments such as
application of mirror visual feedback
8,9
and transcutaneous
electrical nerve stimulation (TENS)
10-13
, especially for the
patients who had limited success from pharmacological
treatment. TENS delivers pulsed electrical currents across
the intact surface of the skin to stimulate the peripheral
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nerves and spinal cord, resulting in segmental and extra-
segmental analgesia.
14
Research indicates that the application
of TENS at the site of residual limb pain or projected
site of phantom pain is associated with decreases in pain
intensity, both at rest and during movement.
10
However,
residual limb application of TENS can be challenging in
certain situations because it may aggravate discomfort
in patients with pre-existing pain or cause skin irritation
that reduces stump integrity in recent amputees.
Contralateral TENS, by inhibiting the contralateral
segmental in the dorsal horn from another side
14
, potentially
alleviates PLP and can address the problems associated
with the stump. A number of reports and small case
series have reported successful outcomes of contralateral
TENS for PLP
11-13
, and we already apply this treatment
in our daily practice. As there is no data collection of
large series for such treatment, we conducted this study
to examine the eects in the ai population.
We hypothesized that patients with PLP who received
TENS on the contralateral limb would report signicant
pain reduction aer treatment. e primary objective
of this study was to observe the eects of TENS on the
contralateral limb and PLP reduction. e secondary
objectives included observing for adverse eects, satisfaction,
and the duration of contralateral TENS treatment for
PLP.
MATERIALS AND METHODS
In this retrospective observational study, in order to
compare the analgesic eect before and aer treatment, we
performed sample size calculations with the aim to detect
a 30% reduction in pain scores aer treatment, which is
a meaningful change. Using data from a pilot study, the
mean pain score of patient suering from phantom limb
pain in our center was 5.2/10 (SD=2). By using PASW
Statistics version 18 (Chicago, IL, USA), a sample size
of 16 patients was enough to detect a dierence, with an
alpha error of 0.05 and power of 90%. As the estimate of
incomplete data was 20%, the nal number of patients
needed for this study was adjusted to 20 patients.
Aer approval by the Mahidol University-IRB, the
research team identied the medical records of patients
who suered from phantom limb pain at the Siriraj
Pain Clinic and received contralateral TENS treatment
for pain relief at Siriraj Hospital from January 1, 2018
to December 31, 2018. e research team collected the
following data points:
1. General demographic and medical history, including
age, sex, and cause of amputation
2. Pain history, including pain diagnosis, past
medications and previous treatment(s) for PLP, and
pain-related interference assessed by a validated ai
version of a brief pain inventory questionnaire
15
3. NRS before and aer treatment
4. Side eects and patient satisfaction of treatment
In routine practice, we oer the treatment to adult
patients who have moderate to severe pain (average pain
intensity from numeric rating scale more than 3 out of
10) despite appropriate pharmacological treatment (the
patients had taken at least two analgesics). TENS was not
oered in contraindicated conditions such as pregnancy,
epilepsy, active malignancy, deep vein thrombosis, frail
or damaged skin or to patients with cardiac pacemakers
or implantable cardioverter debrillators.
We used commercially available TENS units in our
daily practice (Fig 1) due to their low cost and ease of use.
First, we applied TENS’ electrodes on the contralateral
limb, mimicking the pain area on the opposite side.
As the commercial TENS units were obtained from a
variety of brands and did not have measurable parameter
settings (frequency, pulse width, amplitude), we used
clinical response as our end point. We turned on the
stimulation and increased the intensity until the patient
felt pain-free paresthesia.
We recorded an initial pain score, then applied the
stimulation for at least 30 minutes and recorded their
subsequent pain score. If the patient did not report
any change, the session was extended to 45 minutes or
60 minutes. At the end of the session, we assessed the
patient satisfaction scale (0-100) and the presence of
any adverse eects. ere was no long-term follow-up
aer the session.
Fig 1. Commercially available TENS unit.
Vathakul et al.
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TABLE 1. Patient’s demographic data. PLP (phantom
limb pain), RLP (residual limb pain).
TABLE 2. Medication used for treatment of phantom limb pain.
Demographic data (n=20)
Sex
Male 10(50%)
Female 10(50%)
Age:mean(SD)years 57.1(15.63)
Pain
PLP 20(100%)
PLP+RLP 3(15%)
Levelofamputation
Transhumeral 5(25%)
Transfemoral 9(45%)
Transtibial 6(30%)
Cause
Vascular 8(40%)
Trauma 5(25%)
Tumor 7(35%)
Medication Number of patients (Percentage) Dose range (mg/day)
Gabapentin 20(100%) 600-3000
Tricyclicantidepressants(amitriptyline,nortriptyline) 15(75%) 10-25
Weakopioids(tramadol,codeine) 11(55%) Tramadol50-400mg/day
Strongopioids(morphine) 1(5%) 20mg/day
RESULTS
We collected data from a total of 21 patients who
received treatment. However, one patient was excluded
because of amputation on both legs. ere is no exclusion
due to unreliable reporting of pain score because of
psychological or physical morbidities. Finally, the data
of 20 patients were included in this analysis. All patients
had been suering from PLP, and three of them also
suered from residual limb pain (RLP). e demographic
data of all patients is shown in Table 1. e average pain
score was 4.85 out of 10 despite the use of at least two
analgesics such as gabapentin, tricyclic antidepressant,
or opioids (Table 2). e pain-related interferences were
evaluated by a brief pain inventory questionnaire.
15
e
average total score of pain-related interference (impact of
pain on general activity, mood, work, relationships, sleep,
and enjoyment of life) was 16.35 out of 60. e average
time elapsed since amputation before this treatment was
1.9 years.
Pain intensity
Pain intensity was rated by the average numeric rating
pain score (NRS). e average NRS before application of
TENS was 4.85/10 ±1.18, and it decreased to 1.15/10±1.38
aer the treatment. e dierence in average pain intensity
was 3.7±1.59 with a p-value of <0.001 for the paired
T-test (95% condence interval was 2.95-4.45). e NRS
ranged from 3-8 out of 10 before application of TENS
and decreased to 0-5 post-treatment.
Nineteen out of 20 patients reported clinically
signicant pain relief (pain score decreased by more than
30%). e mean percentage of pain reduction was 76.54
± 6.18% (95% condence interval was 63.61-89.47%).
e individual responses to treatment are shown in
Fig 2. Only one patient who had PLP aer a right elbow
amputation due to recurrent brosarcoma (number 12)
did not respond to treatment. is patient also did not
respond well to other treatments, including gabapentin
and tricyclic antidepressants.
Duration of treatment
In this study, we applied TENS on the contralateral
limb until the pain score decreased or for 60 minutes, if
pain did not improve. Sixteen participants responded
to treatment in the rst 30 minutes, and another three
responded aer it was extended to 45 minutes. Only one
participant (patient 12) reported no signicant change
in NRS aer 60 minutes. e median time required for
TENS to decrease pain was 30 minutes. e cumulative
number of responders over time is shown in Fig 3.
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Fig 2. Individual response to contralateral TENS stimulation.
Fig 3. Cumulative number of patient reporting pain relief over time.
Adverse eect and satisfaction
e application of transcutaneous electrical nerve
stimulation on the contralateral side was tolerated by
all participants without any adverse events during the
session. Participants reported no difficulty in using
TENS and titrating the amplitude. e average overall
satisfaction was 81.65% (0-100% and 0% for patient 12).
DISCUSSION
is study aimed to determine if the application of
TENS on the opposite limb could reduce pain intensity
in patients suering from PLP. Our ndings suggest a
signicant reduction of NRS immediately aer treatment.
Additionally, the treatment led to high satisfaction rates
and no report of adverse events.
Following amputation, up to 80% of patients reported
pain, either in the part that was amputated (phantom
pain) or at the site of amputation (residual limb pain), or
both.
1-4
is pain can aect their quality of life and prevent
proper rehabilitation and prosthetic usage. PLP is poorly
understood and one of the most dicult type of pain to
treat.
16
e underlying pathophysiology of PLP is unclear,
although it is generally accepted that nociceptive and
neuropathic processes are involved and that neuropathic
changes include reorganization and adaptation within the
peripheral and central nervous systems.
17
Additionally,
evidence evaluating the ecacy of treatments for chronic
PLP remains scarce.
6
Currently, multimodal treatment
strategies are used, including pharmacological treatments
(gabapentinoids, tricyclic antidepressants, and opioids),
pain intervention (sympathetic blocks, sympathectomies),
mirror box therapy, and TENS.
17
However, there is no
strong evidence that supports the long-term ecacy of
each treatment for PLP.
17,18
TENS delivers pulsed electric currents across the
intact surface of the skin to stimulate peripheral nerves
and the spinal cord, resulting in segmental and extra-
segmental analgesia.
14
Additionally, physiological and
clinical research suggest that TENS inhibits second-order
nociceptive neurons, may increase blood ow, reduces
muscle spasms, and selectively activates large diameter
aerent bers, which reduces nociceptor cell activity and
sensitization in the central nervous system,
17,19,20
all of
which are potential analgesic mechanisms for phantom
pain and/or residual limb pain. Mulvey et al, indicates that
TENS application at the site of residual limb pain or on
the site of phantom pain is associated with decreases in
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pain intensity, both at rest and with movement (frequency
100 hertz, pulse width 80 microseconds and the current
increased until the patient achieved strong non-painful
sensations).
10
However, residual limb application of
TENS can be challenging in certain situations because
this stimulation may aggravate pain in patients with
preexisting pain or allodynia. e application of TENS
on the residual limb can also cause skin irritation that
reduces stump integrity in recent amputees.
Contralateral TENS can address problems associated
with residual limb TENS. Moreover, a number of case
reports and small case series have reported successful
outcomes of contralateral TENS for PLP/ RLP and
phantom limb sensation.
11-13
Additionally, Carabelli
13
described a better response when TENS was applied
to the contralateral limb compared to residual limb
stimulation. e benecial eects may be the result of
stimulation on contralateral segmental inhibition in the
dorsal horn.
14
e case series of contralateral TENS were done
by Kawumara (10 cases), Katz (2 cases), and Carabelli
(3 cases).
11-13
e settings of TENS applications in these
studies varied from frequency 4-80 hertz, pulse width
90-225 microseconds and range of amplitude 50-80
MA depending on patients’ tolerance. Compared to
these previous studies, we use commercially available
machines without standard settings, but adjusted the
treatment by clinical response. Nevertheless, the results
from our larger series still conrmed that contralateral
TENS application successfully reduced pain signicantly
in 95% of patients. e NRS pain score decreased by an
average of 3.7/10 (from 4.85 to 1.15/10) or 76.28%. Since
almost all patients in this study experienced moderate
to severe pain despite the use of at least two analgesics
and suered a negative impact on their quality of life, the
population in this study were considered patients with
dicult to treat or intractable PLP. To the best of our
knowledge, this is the largest application of contralateral
TENS for intractable PLP. Moreover, the treatment is
associated with a high satisfaction rate as no adverse
events were reported and the method is inexpensive and
easy to use. is data demonstrates that TENS is one of
the logical options for treatment of phantom limb pain.
An additional interesting nding was the duration of
treatment in this study. Many studies of the application
of TENS for phantom limb pain treatment do not have an
exact duration to reduce pain.
17,18
Our study showed that
80% of patients responded aer 30 minutes of treatment
and 95% responded aer 45 minutes, with no additional
response aer 45 minutes. e data suggests that the
duration for application of TENS on the contralateral
limb for treating phantom limb pain should be at least
30 minutes, which can be extended to 45 minutes. For
treatments longer than 45 minutes, there is probably no
additional benet.
ere were several limitations to this study. First, the
design was an observational study and not a randomized
control trial, so it is possible that factors such as the placebo
eect or natural regression may have an eect. Second,
as we used commercially available TENS machines,
there was no standard treatment protocol. However,
commercially available machines were more practical
in clinical practice due to low cost and accessibility by
the patients. Although this research suggests short term
analgesic eect of the application of TENS in contralateral
limb for PLP, a randomized control trial is needed to
conrm this nding. Finally, as we only collected short
term data immediately aer treatment in this study,
long-term follow up regarding duration of the treatment
and its impact on quality of life and medication use aer
treatment is needed. Nevertheless, this study provides
useful information such as the eect of treatment on a
sample size and duration of application of treatment
for protocol design for a future prospective randomized
study.
CONCLUSION
is cohort study shows that the application of
TENS in the contralateral limb can lead to meaningful
reduction of pain in patients suering from dicult
to treat phantom limb pain. is treatment has a high
success rate and is associated with high satisfaction rates
and no reported adverse events. e suggested duration
of treatment is at least 30 minutes and may be extended
up to 45 minutes.
ACKNOWLEDGEMENTS
We would like to thank Ms. Nattaya Bunwatsana
for assistance with document preparation for the IRB
approval process. e authors have no conict of interest
to declare.
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