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REVIEW ARTICLE
Efficacy of low-level laser therapy on management of Bell’spalsy:
a systematic review
Mohammad Javaherian
1
&Behrouz Attarbashi Moghaddam
1
&Siamak Bashardoust Tajali
1
&
Narges Dabbaghipour
1
Received: 1 June 2019 /Accepted: 9 March 2020
#Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract
The aim of this study is to evaluate the efficacy of low-level laser therapy (LLLT) in patients with Bell’s palsy (BP) through a
systematic review method. We systematically searched international databases including PubMed, Scopus, and Web of Science
to find eligible articles without language limitation. All relevant randomized controlled trials (RCTs) that compared the efficacy
of the LLLT with placebo laser, exercise, massage, or no intervention on BP patients were included. Four studies (out of 259) had
met our inclusion criteria involving171 patients and were entered to the systematic review. Full texts of the selected studies were
retrieved and critically appraised using Physiotherapy Evidence Database (PEDro) scale. The patients of all trials were in sub-
acute (less than 1 week) stage. Both of LLLT and control groups showed significant improvement after trials. Two authors
reported significant differences between the groups after 6 weeks of laser application (830 nm, 100 mW). In converse, two other
authors did not identify any effectiveness following 4 weeks and 15 days of LLLTapplication with 670 and 830 nm wavelength,
sequentially. There is clear lack of information lead to get and evidence-based suggestion for the LLLT application on Bells’
palsy; however, the LLLT irradiation with 830 nm and 100 mW power fora period of 6 weeks might be beneficial on recovery for
the patients with sub-acute Bell’s palsy. There were no reported adverse effects during treatment and/or follow-up sessions.
Keywords Low-level laser therapy .Facial palsy .Bell’spalsy .Physiotherapy
Introduction
Idiopathic peripheral facial palsy or Bell’s palsy (BP) is an
acute, unilateral common syndrome that affects half of facial
muscles and might lead to their paralysis [1,2]. Since the
facial muscles have major role in human communications,
BP may cause psychological and social problems [1].
Additionally, BP may cause many problems in eating, drink-
ing, speaking, and eye closure [3].
BP is associated with inflammation process of peripheral
part of facial nerve. Besides, it is different from other types of
facial palsies since it is categorized as an idiopathic disorder
[4,5]. Theoretically, it can be raised by infection,
compression, micro-trauma, autoimmune, or even genetic rea-
sons [6,7]. Some evidences suggested that herpes simplex
virus-1 reactivation at the cranial nerve is a most strongly
suspected cause of facial nerve inflammation in BP [8].
The annual incidence of BP is 23 to 35 cases per 100,000
with an equal gender ratio. It is thought that 50–75% of acute
unilateral facial paralysis appeared between 30 and 50 years
old [9,10]. The BP prognosis is relevant to the factors such as
time of recovery, age, pain behind of ear, taste distribution,
and genetics [9,11].
Several care methods have been suggested as treat-
ment approaches for the BP. Corticosteroid drugs and
acupuncture have been indicated as the effective modal-
ities for the BP treatment [12,13]. Turgeon et al. pro-
vided a relevant systematic review and reported that an-
tiviral agents might not be effective on the BP recovery
[14]. There are three other group of researchers who
systematically reviewed trials that report effects of elec-
trical stimulation, biofeedback, ultrasound, laser, and
short-wave diathermy on the BP treatment [2,10,15].
These researchers did not clarify clear distinct conclusion
*Siamak Bashardoust Tajali
s_bashardoust@sina.tums.ac.ir
1
Department of Physiotherapy, School of Rehabilitation, Tehran
University of Medical Sciences, Tehran, Iran
Lasers in Medical Science
https://doi.org/10.1007/s10103-020-02996-2
to suggest best effective physiotherapy methods of care
for the patients with the BP. Some of the selected trials
had been designed with a poor methodological concerns
such as lack of accepted facial function grading systems,
frequent failure to distinguish complete from functional
recovery, and inconsistent follow-up [15]. Pereira et al.
evaluated influence of exercise therapy associated or not
with mirror biofeedback. This researcher suggested this
method as an effective treatment for functional improve-
ment in patients with BP [2]. Teixeira et al. reviewed
efficacy of different physical therapy interventions for
the BP patients and concluded that there were no high-
quality evidences to support significant benefit or harm
for the identified interventions including acupuncture,
electrotherapy, and biofeedback. However, there were
low-quality evidences that show effects of exercise ther-
apy on functional improvement in patients with the BP
[10].
Some evidences suggested low-level laser therapy (LLLT)
as a useful modality for peripheral nerve anti-inflammation,
repair, regeneration, axonal growth, and myelination [16,17].
Also, specific dosages of LLLT were suggested to be applied
at nerve inflammation disorders such as trigeminal neuralgia
or carpal tunnel syndrome [18,19].
According to previous literatures, the LLLT provides
photons on the mitochondria in cells; the photon energy
will be absorbed by cytochrome c oxidase, which is the
last enzyme in the electron transportation chain, playing
an essential role in the oxygenation metabolism and pro-
duction of ATP. The more photons being absorbed by
cytochrome c oxidase, the more oxidized (activated) state
cytochrome c oxidase will be [20,21]. Therefore, the
accelerated oxygenation process and extra production of
ATP will then help the cells and tissues [22].
The LLLT has also been suggested for management of the
BP in some case reports, case series, clinical trials, and ran-
domized controlled trials (RCTs). All previous reviews, in-
cluding studies with the LLLT [10,15], can be categorized
as low-quality evidences. As a result, the authors did not
strongly suggest the LLLT application at patients with the
BP. Therefore, the need of a study with higher level of evi-
dence is felt in order to evaluate the effects of LLLT in BP
patients. Thus, the aim of this study is evaluating the efficacy
of the LLLT in patients with the BP through a systematic
review method.
Methods
Searching method
Two researchers independently searched three relevant inter-
national databases to identify potential relevant studies. The
authors searched PubMed (title/abstract), Scopus (title/ab-
stract/keyword), and Web of Science (topic) from 1980 to
July 2018. To identify suitable keywords, Bell’s palsy and
LLLT were searched in Medical Subject Heading (MeSH),
and their synonyms were applied for database searching.
The selected keywords were (“Laser”OR “phototherapy*”
OR “photo therap”) AND (“bells palsy”OR “bell’s palsy”
Fig. 1 Flowchart for the identification of the eligible studies evaluating the effect of the LLLTon BP
Lasers Med Sci
OR “facial neuropath”OR “facial paral”OR “Facial pals”).
The authors also provided hand search of the references of the
selected studies to identify other possible relevant studies.
Selection of studies
Two authors independently reviewed the title and abstract of
all identified articles from systematic and included potentially
relevant articles. The authors obtained full texts of all potential
relevant abstracts and independently reviewed them to identi-
fy inclusion/exclusion criteria. In the next stage, the authors
critically appraised the selected manuscripts by Physiotherapy
Evidence Database (PEDro) scale and provided a quality
score for each included study. There was an agreement session
that was held to resolve any disagreement between the
authors.
Inclusion/exclusion criteria
Type of studies
The published randomized controlled trials (RCTs) in any
language that report effects of the LLLT application on
Bell’s palsy were included in this systematic review. All se-
lected studies must have at least one control group receiving
placebo laser, exercise, massage, or no intervention.
Type of participants
The patients with idiopathic peripheral facial palsy (IPFP) in
any sex, gender, and age under the LLLT application were
considered as inclusion criteria in this systematic review. We
included studies with participants in all stages of the BP. The
BP diagnosis methods were not considered as an inclusion
criteria.
Type of intervention
The authors included all trials using any type of the LLLT
application with different wavelengths and output power less
than 500 mW, provided that the experimental groups did not
receive any further treatment such as corticosteroid therapy.
The studies compared the LLLT with exercise and/or massage
as control groups were entered into the systematic review.
Any laser acupuncture study was excluded from final results.
Outcome measurements
Any type of outcome measurement was accepted to the cur-
rent study.
Table 1 Summary of methodological properties for included studies
Author Study design Sample
size (T/C)
Age (years) Phase of disease Intervention/s of LLLTG Intervention/s of CG Duration
of Tx
Number of total
sessions/ frequency
(S/W)
Ordahan et al.
(2017) [32]
RCT 46 (23/23) Mean ± SD,
45 ±22
Sub-acute LLLT + facial exercise (active assistive,
resistive, and PNF exs. in front of mirror)
Facial exs. 6 weeks 30/5
Alayat et al. (2014)
[33]
Double-blind
RCT
31 (15/16) NM Sub-acute
(3–5days
after onset)
LLLT + facial massage + facial exs.
(active, active assistive, resistive, PNF,
and resisted exercise for neck muscles)
Sham laser, Facial massage,
Facial exs.
6 weeks 18/3
Delgado Castillo
et al. (2013) [31]
Simple-blind
RCT
73 (38/35) NM Sub-acute (less
than 1 week )
LLLT + facial massage + facial exs. Facial massage + Facial exs. 4 weeks 20/5
MacÍas-Hernández
et al. (2012) [34]
Double-blind
RCT
21 (11/10) Median
LLLTG 38,
CG 48
Sub-acute (less
than 1 week )
LLLT + facial massage + facial exs.
(stretching and re-education of facial
muscles in front of a mirror)
Sham laser + Superficial heat +
Facial massage + Facial exs.
15 days 15/7
RCT randomized controlled trial, Ttreatment, Ccontrol, NM not mentioned, LLLT low-level laser therapy, LLLTG low-level laser therapy group, CG control group, PNF proprioceptive neuromuscular
facilitation, exs exercise, S/W sessions per week
Lasers Med Sci
Quality assessment
Two researchers independently read the selected full texts,
appraised them critically, and scored their quality based on
PEDro quality assessment tool [23,24]. Any disagreement
was discussed between the authors, and final scores were
obtained.
Data collection
A data extraction form was designed to clarify the details for
each study. Two authors independently read full text ofinclud-
ed articles and extracted all obtainable characteristics for each
study, including design and blinding, sample size, phase of
disease, accompanying interventions both for laser and control
groups, number of sessions, period and frequency of treat-
ment, technical properties of laser, outcome measures, assess-
ment time, and final results. We used Google Translate online
software for data extraction of studies with non-English lan-
guage [25,26]. Alpha equal or less than 0.05 was considered
as significant difference in data extraction.
Results
We identified 259 abstracts based on the identified keywords
and the selected international databases. After the initial re-
view, there were 9 potentially relevant abstracts which were
selected to be fully retrieved. The selected 9 full manuscripts
were critically reviewed base on the inclusion/exclusion
criteria. Finally, there were 4 identified relevant manuscripts
that were critically appraised by two independent researchers.
In total, 250 studies did not meet the inclusion criteria and
were excluded. The most important reasons of exclusion of
studies were not meeting their type of patients to our criteria
[27–29], lack of proper control group [30], and combination
of two modalities in intervention group [31]. Finally, four
RCTs were included to our study [31–34].
There was no study added to the selected studies following
hand search. The flowchart of the database search and selec-
tion criteria is shown in Fig. 1.
Quality of the selected studies
The PEDro scales of included studies were varied from 7 to
10. Details of quality assessment are presented in Table 1.
Characteristics of the selected studies
Summaryofmethodologicalpropertiesofincludedstudiesis
presented in Table 2. There were two English [32,33] and two
Spanish [31,34] selected studies in our final review. Two
studies were designed as controlled, double-blinded RCTs that
one of them had patients and therapist blinding [33] and the
other had patients and assessor blinding [34]. Another group
of researchers followed simple blinding, but they did not iden-
tify who was blinded to their patient allocation [31].
Through the selected four studies, 87 and 84 patients were
consideredfor the LLLT and control groups, respectively. Two
studies had two parallel RCT design, the LLLT group and
control group [32,34]. One study had three parallel RCT
design including high-level laser therapy, LLLT group, and
Table 2 Quality assessment of included articles based on PEDro scale
Item Study ID
Ordahan et al. (2017)
[32]
Alayat et al. (2014)
[33]
Delgado Castillo et al.
(2013) [31]
MacÍas-
Hernández
et al. (2012)
[34]
Eligibility criteria specification Yes Yes Yes Yes
Proper random allocation Yes Yes Yes Yes
Allocation concealment Yes Yes No No
Groups similarity at baseline Yes Yes Yes Yes
Subjects blinding No Yes No Yes
Therapists blinding No Yes No No
Assessor blinding No No No Yes
Outcome measure obtaining from 85% subjects initially
allocated to groups
Yes Yes Yes Ye s
Use of intention to treat analysis Yes Yes Yes Yes
Reporting between group statistical comparisons Yes Yes Yes Yes
Reporting point measures and measures of variability Yes No Yes No
Total 8 10 7 8
Lasers Med Sci
control group [33]. There was one study using different inter-
ventions including conventional therapy (CT), magnetic field
therapy (MFT) + CT, LLLT + CT, and MFT + LLLT + CT
which we considered the LLLT + CT and CT groups as inter-
vention and control groups, respectively [31]. All studies
started treatment in sub-acute phase.
All researchers applied both exercise and massage therapy
in their control groups among all selected trials. The identified
exercise and massage therapy were accompanied as parts of
their care methods in the intervention groups. The period of
the treatment sessions were varied from 15 days to 6 weeks,
provided 15 to 30 sessions for the patient’streatment.
Laser properties of the selected studies
All identified researchers applied pencil-like method on facial
nerve roots, while most of them applied 830 nm wavelengths
for their laser application. Table 3summarizes laser properties
of included studies. Some variables like number of emitters,
emitter type, beam delivery system, central wavelength, spec-
tral bandwidth, energy per pulse, polarization, average radiant
power, and beam divergence were not reported in the included
studies [35].
Outcome measures and results
The only common outcome measure was facial disability in-
dex (FDI) which was divided to physical and social FDI
(PFDI and SFDI) and was reported in two studies [32,36].
Researchers of these studies reported significant improvement
(SI) on the FDI following laser therapy at the ending of their
treatment sessions (6 weeks).
Alayat et al. applied House-Brackmann scale for as-
sessment and showed similar results to the FDI scores.
However, they reported improvement of both scores over
time in the LLLT and control group, but their scores show
downward trend over time, unexpectedly. In total, laser
application was able to reduce downward trend of FDI
in the LLLT group; therefore, there is significant differ-
ence between the groups at 6 weeks. Table 4shows the
PFDI and SFDI scores which were extracted from the
studies by Ordahan et al. and Alayat et al.
Delgado Castillo et al. assessed patients by Sunnybrook
facial grading system at baseline, end of treatment (4 weeks),
and 12 weeks following the interventions [31]. He reported
that both groups had been improved following laser
application.
MacÍas-Hernández et al. used four outcome measures at
baseline, end of treatment sessions (15 days), and 30 and
60 days after interventions. This researcher reported muscle
and perception improvement following 15 sessions of LLLT
held through 15 days and also in control group. We did not
find statistical results of within group analysis in this study
Table 3 Technical properties of laser used in included articles
Study ID Type of laser Wavelength
(nm)
Frequency (Hz) Duty
cycle
(%)
Time of each point (s)/number
of points/total time (s)
Location of point(s) Set power (mW)/energy density
(J/cm
2
)/total energy (J)
Ordahan et al. (2017)
[32]
GaAlAs
(infrared)
diode
830 1000 NM 120/8/960 Superficial roots of the facial nerve on the
affected side
100/10/80
Alayat et al. (2014)
[33]
GaAs
(infrared)
830 1000 80 125/8/1000 Superficial roots of the facial nerve on the
affected side
100/NM/80
Delgado Castillo
et al. (2013) [31]
NM 670 NM, but mentioned
laser was pulsatile
NM starting with 30 s and increase
15 s every 5 sessions until
reachto1m/NM/NM
Through the course of facial nerve with
1.5-cm space between two points and
extra point at nerve exit locale
40/14/NM
MacÍas-Hernández
et al. (2012) [34]
GaAlAs 830 NM NM NM/NM/NM In the emergence of facial nerve 30/20/NM
GaAlAs gallium-aluminum-arsenide, GA gallium-arsenide, nm nanometer, NM not mentioned, Ssecond, Jjoule, mW milliwatt
Lasers Med Sci
between the baseline and end of treatment. There were no
significant differences between the groups, except improve-
ment of perception for the LLLT group after 60 days. All
patients in both groups had normal palpebral occultation with-
out any epiphora and dysgeusia following 30 days of inter-
ventions. All results of included studies are summarized in
Table 5.
Discussion
This study was designed as a systematic review to evaluate
effects of LLLT application on Bell’s palsy recovery. Totally,
four manuscripts met our inclusion criteria including 171 pa-
tients suffering sub-acute Bells’palsy. Two researchers had
been applied the GaAlAs laser (wavelength 830 nm) for a
period of 6 weeks and reported statistically significant effects
following the LLLT application on Bells’palsy. Conversely,
Delgado Castillo et al. did not identify any effectiveness fol-
lowing 4-week LLLT application (wavelength 670 nm) on
Bell’s palsy. The other identified researcher (Hernanzed
et al., 2012) did not report any difference between the groups
for all objective outcome measures following 15 days of the
LLLT application (wavelength 830 nm).
The researchers of all included trials had used facial exer-
cises in both LLLT and control groups. Although the presence
of exercise therapy is due to ethical aspects of studies, we
should pay attention to its major influence on patients’func-
tional improvement [2]. This effect might be the reason to lead
to levels of patient’s improvement in control groups.
Accordingly, between group analysis can show us a more
transparent effect of LLLT for BP in included studies.
Table 4 FDI scores of studies by Ordahan et al. and Alayat et al.
Study Groups PFDI SFDI
Before 3 weeks 6 weeks Before 3 weeks 6 weeks
Ordahan et al. (2017) [32] LLLTG 27.05± 14.13 37.42 ± 8.13 39.21 ± 9.08 22.80 ± 18.76 35.41 ± 10.12 37.53 ± 9.65
CG 26.52 ± 11.07 25.41 ± 13.12 29.06 ± 11.09 23.40 ± 15.23 23.25± 15.27 28.76 ± 12.14
Alayat et al. (2014) [33] * LLLTG 27.06 25.53 21.8 28.77 22.33 25.73
CG 26.84 9.81 10.84 23.25 10.91 8.5
PFDI, physical facial disability index; SFDI, social facial disability index; LLLTG, low-level laser therapy group; CG, control group
*
SD has not been reported
Table 5 Summary of results and finding of included studies
Study ID Outcome measurements Assessment times Summary of results
Ordahan et al. (2017)
[32]
•FDI (PFDI, SFDI) Before, 3 and
6weeks
LLLTG: SI at 3 and 6 weeks
CG: No improvement (exception BTW baseline
and 6 weeks)
Higher FDI at 3 and 6 weeks in LLLT
Alayat et al. (2014) [33]•FDI (PFDI, SFDI)
•HBS
Before, 3 weeks,
6weeks
LLLTG: SI of both scores at 3 and 6 weeks with greatest
improvement at 6 weeks.
CG: ↑FDI and HBS after 3 and 6 weeks
Higher FDI 3 and 6 weeks in the LLLT. Higher HBS 6
weeks in the LLLT (No effect on HBS after 3 weeks of irradiation)
Delgado Castillo et al.
(2013) [31]
•Sunnybrook facial
grading system
Before, 4 weeks,
12 weeks
LLLTG: SI at 4 and 12 weeks with greatest improvement at 12 weeks.
CG: SI at 4 and 12 weeks with greatest improvement at 12 weeks.
BGA: No significant difference between groups at 4 and 12 weeks.
MacÍas-Hernández
et al. (2012) [34]
•MMT of 18 facial
muscles
•Presence of epiphora
and dysgeusia
•Palpebral occlusion
capacity (mm)
•% of improvement
(self-assessment)
Before, 15, 30,
and 60 days
LLLTG: All outcomes improved at 60 days than baseline.
CG: All outcomes improved at 60 days than baseline.
BGA: NS for all outcome measures BTW groups (exception of improvement
perception for the LLLT after 60 days).
NS on palpebral occultation and no difference on number of patients
with epiphora and dysgeusia between the groups after 15 days.
All patients were fine 30 days following interventions.
FDI facial disability index, PFDI physical facial disability index, SFDI social facial disability index, HBS House-Brackmann scale, MMT manual muscle
testing, mm millimeter, VAS visual analogue scale, LLLTG low-level laser therapy group, CG control group, BGA between group analysis, SI significant
improvement
Lasers Med Sci
Current evidences show that it seems that the use of 830 nm
LLLT with 100 mWoutput and 120-s duration oneight points
of facial branches of affected site during6 weeks can positive-
ly influence on function of patients with BP in sub-acute stage.
However, generalization of the results of the current study
should be done with caution, because we could find only four
RCTs which two of them did not show statistically significant
difference between groups. None of included studies showed
any adverse effect of LLLT during treatment and follow-up.
Murakami et al. compared efficacy of stellate ganglion
block (SGB), infrared diode laser (830 nm), and combination
of both of them in patients with sub-acute BP in a clinical trial.
Their results showed that patients in LLLT group demonstrat-
ed faster initial recovery and slightly better final paralysis
scores than other groups [30]. Ladarlo et al. reported 4 patients
with BP who have undergone LLLTwith 780-nm wavelength
(GaAlAs) during 24 sessions with 2 sessions per week fre-
quency. They have mentioned the use of electrophysiology
examinations accompanying to HBS before and after of treat-
ment, but exact type of electrophysiology examination is not
reported. They indicated that all cases had abnormal blink
reflex before treatment, but all were normal after treatment
[37]. Fontana and Bagnato reported influence of LLLT on a
child patient with BP. They used GaAlAs diode laser (660 and
780 nm) during 11 sessions with 4 sessions per week frequen-
cy. The patient showed complete recovery after this treatment
method [38].
All included studies started treatments in sub-acute stage of
BP, and we do not have any information about its effective-
ness in chronic stage. NG and Shu reported two cases with
acute and chronic BP who have undergone 6 weeks treatment
by 890 nm LLLT and chiropractic techniques. Acute case
showed 95% improvement after 6 weeks, and chronic case
demonstrated 50% improvement after similar period [39].
Our study has some limitations which should be noted.
First, we only included RCTs that led to small number of
included studies, therefore made generalization of the results
difficult. Other relevant studies were mostly case report or
case series that rank lowly in level of evidences. From another
way, this limitation caused conducting meta-analysis impossi-
ble. Second, included studies mostly used non-parametric
tests for statistical analysis that reduce power of analysis. It
may be that this is due to small number of sample sizes of most
studies. Third, study by MacÍas-Hernández et al. did not men-
tion laser properties which had been used; therefore, we could
not find other reasons for insignificant results of between
group analysis except treatment duration [34]. Fourth, we
did not find a study with electrophysiology evaluation as a
reliable and accurate tool for assessment and prognosis of
patients with BP [40].
Further studies are needed in order to overcome limitations
with the following recommendations. First, more RCTs with
enlarged sample sizes compared LLLT with other standard
modalities. Second, studies should pay more attention to study
design, use sham laser, and perform blinding, allocation con-
cealment, proper randomization, and proper statistical analy-
sis. Moreover, explanation of complete properties of laser is
very important. Third, we need more studies evaluating effi-
cacy of LLLT on chronic BP. Fourth, other objective outcome
measures such as electrophysiological evaluation should be
assessed.
Conclusion
In summary, few available relevant evidences cautiously sug-
gested that the GaAlAs laser application (wavelength 830 nm,
80 J total energy per session, for a period of 6 weeks) can
effectively improve patients with sub-acute Bell’spalsy.
Limited number of eligible studies and lack of applied laser
characteristics did not let the authors to provide a meta-
analysis to reach better clarification.
Compliance with ethical standards
Conflict of interests The authors declare that they have no conflict
interest.
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