Facial synkinesis, defined as the presence of unintentional muscle motion produced
during intentional movement in another area, is often described as one of the most
frustrating sequelae of facial palsy.[1] Postparalysis facial synkinesis (PPFS) can develop after any type of physical trauma
or condition associated with damage to or partial recovery of the facial nerve. The
proposed mechanism behind synkinesis is the aberrant regeneration of the facial nerve
when, for example, fascicles from the buccal branch erroneously regenerate along the
zygomatic branch, and the patient develops involuntary closure of their eye when they
smile[2] ([Fig. 1]). Alternative explanations focus on peripheral ephaptic transmissions between neighboring
regenerating axons or synaptic reorganization and hyperexcitability of the facial
nerve nucleus.[3] However, newer findings such as reduced intrinsic connectivity in subnetworks of
the central nervous system highlight that the full extent of the pathophysiology may
not yet be completely understood.[4] Synkinetic movements have an undeniable aesthetic impact and can, in severe cases,
be quite painful. Overall, PPFS can be socially debilitating, limit interpersonal
interactions, and has a significant impact on the quality of life of affected patients.[5]
[6]
Fig. 1 (A) Normal anatomy. (B) Aberrant regeneration of fascicles from the buccal branch along the zygomatic branch
after facial nerve injury. (C) As a result, the patient develops involuntary oculo–oral synkinesis.
Bell's Palsy is an idiopathic, acute-onset (typically less than 72 h), unilateral
facial nerve weakness. It is the most common cause of peripheral facial weakness,
and accounts for 60 to 75% of all cases of unilateral facial paralysis. Clinically,
it presents as a patient who is unable to properly close an eye, retract the angle
of the mouth, and/or raise an eyebrow/wrinkle the forehead.[7] It can also have accompanying retro-/auricular pain, changes in tearing, hyperacusis,
changes in sensation and taste, and/or other pain.[7]
[8]
[9]
[10] The etiology of Bell's Palsy remains unclear, but the belief is that most cases
are secondary to reactivation of latent herpes simplex virus infection.[7]
[11] Although the return to normal facial nerve function can range from 71 to 86%,[8]
[10] it is heavily dependent upon the initial severity of the paralysis (94% recovery
in partial; 61% in complete) and interval between onset and the beginning of remission.[10] Combined with an incidence of 20 to 43 cases per 100,000 person-years in the United
States, Bell's Palsy causes a great deal of morbidity.[8]
[9]
[11]
[12]
[13]
Following Bell's Palsy, synkinesis can develop in up to 21.3% of patients, with 6.6%
being moderate-to-severe cases.[14] However, in patients that develop long-term paralysis, some degree of synkinesis
is expected in almost all patients.[15] Interestingly, data suggest that PPFS affects significantly more females than male
patients and appears significantly more often in older patients.[15] While the roles of corticosteroids,[16] antivirals,[17] early surgical intervention,[18] and physical therapy[19] in the prevention of synkinesis after developing Bell's Palsy have been comparably
well examined, much less high-level evidence exists regarding the management of patients
with already established PPFS.[20] Therefore, the purpose of this review was to summarize the available literature
and to provide an overview of the current therapeutic options and level of evidence
in the treatment of facial palsy patients with established synkinesis.
Results
The initial search yielded 201 articles of which 38 fulfilled the study's inclusion
criteria ([Fig. 2]). [Table 1] shows the details of the studies included, as well as their characteristics.
Table 1
Characteristics of the included studies
Author
|
Year
|
Treatment
|
Study design
|
Prospective/Retrospective
|
Number of patients
|
Age focus
|
Principal synkinesis outcome measurement
|
Mountain et al[25]
|
1992
|
Chemodenervation
|
Cohort
|
Retrospective
|
4
|
Adults
|
Expert review of photographs + custom patient reported outcome
|
Toffola et al[26]
|
2010
|
Chemodenervation
|
Cohort
|
Prospective
|
30
|
Adults
|
Sunnybrook Facial Grading System
|
Filipo et al[29]
|
2012
|
Chemodenervation
|
Cohort
|
Retrospective
|
41
|
Adults
|
Sunnybrook Facial Grading System + Synkinesis Assessment Questionnaire
|
Dall'Angelo et al[31]
|
2014
|
Chemodenervation
|
Cohort
|
Retrospective
|
45
|
Adults
|
Sunnybrook Facial Grading System + custom platysma-specific evaluation of presence
and severity of synkinesis
|
Maria and Kim[27]
|
2017
|
Chemodenervation
|
Cohort
|
Retrospective
|
142
|
Adults
|
Sunnybrook Facial Grading System
|
Neville et al[30]
|
2017
|
Chemodenervation
|
Cohort
|
Prospective
|
51
|
Adults
|
Synkinesis Assessment Questionnaire
|
Patel et al[32]
|
2018
|
Chemodenervation
|
Cohort
|
Prospective
|
23
|
Adults
|
Synkinesis Assessment Questionnaire
|
Thomas et al[35]
|
2018
|
Chemodenervation
|
Randomized control trial
|
Prospective
|
28
|
Adults
|
Synkinesis Assessment Questionnaire
|
Kanerva[33]
|
2021
|
Chemodenervation
|
Cohort
|
Retrospective
|
83
|
Adults
|
Patient-reported symptoms (custom)
|
Pescarini et al[34]
|
2021
|
Chemodenervation
|
Cohort
|
Prospective
|
33
|
Adults
|
Synkinesis Assessment Questionnaire
|
Krag et al[66]
|
2021
|
Chemodenervation
|
Cohort
|
Prospective
|
36
|
Adults
|
Emotrics and FaceGram photographic analyses
|
Díaz-Aristizabal et al[28]
|
2023
|
Chemodenervation
|
Cohort
|
Prospective
|
20
|
Adults
|
Sunnybrook Facial Grading System + Synkinesis Assessment Questionnaire
|
Beurskens et al[48]
|
2006
|
Facial therapy
|
Randomized control trial
|
Prospective
|
48
|
Adults
|
Sunnybrook Facial Grading System
|
Fujiwara et al[50]
|
2018
|
Facial therapy
|
Cohort
|
Retrospective
|
37
|
Adults
|
Sunnybrook Facial Grading System
|
Micarelli et al[46]
|
2021
|
Facial therapy
|
Randomized control trial
|
Prospective
|
40
|
Adults
|
Sunnybrook Facial Grading System
|
Gil-Martínez et al[38]
|
2021
|
Facial therapy
|
Cohort
|
Prospective
|
5
|
Adults
|
Electromyographic feedback
|
Neville et al[65]
|
2022
|
Facial therapy
|
Cohort
|
Retrospective
|
75
|
Adults
|
Sunnybrook Facial Grading System
|
Guerrissi[51]
|
1991
|
Surgery
|
Cohort
|
Retrospective
|
6
|
Adults
|
Expert judgement
|
Bran et al[53]
|
2014
|
Surgery
|
Cohort
|
Retrospective
|
9
|
Adults
|
Custom adaptation of the Hemifacial spasm questionnaire (HFS-30)
|
Chuang et al[24]
|
2015
|
Surgery
|
Cohort
|
Retrospective
|
48
|
Adults
|
Sunnybrook Facial Grading System
|
Yoshioka[52]
|
2015
|
Surgery
|
Cohort
|
Retrospective
|
11
|
Adults
|
Sunnybrook Facial Grading System
|
Biglioli et al[56]
|
2017
|
Surgery
|
Cohort
|
Retrospective
|
18
|
Adults
|
Dichotomous clinical judgement (synkinesis present/not present)
|
van Veen et al[61]
|
2018
|
Surgery
|
Cohort
|
Retrospective
|
10
|
Adults
|
Palpebral fissure width + Mean units of botulinum toxin necessary pre- and postoperatively
|
Azizzadeh et al[59]
|
2019
|
Surgery
|
Cohort
|
Retrospective
|
63
|
Adults
|
eFACE
|
Gray et al[55]
|
2020
|
Surgery
|
Cohort
|
Retrospective
|
8
|
Adults
|
Emotrics software
|
Chuang et al[54]
|
2022
|
Surgery
|
Cohort
|
Retrospective
|
94
|
Adults
|
Sunnybrook Facial Grading System
|
Park et al[60]
|
2023
|
Surgery
|
Cohort
|
Retrospective
|
122
|
Adults
|
Synkinesis Assessment Questionnaire + palpebral fissure width
|
Monini et al[45]
|
2011
|
Chemodenervation + facial therapy versus facial therapy alone
|
Randomized control trial
|
Prospective
|
20
|
Adults
|
Sunnybrook Facial Grading System
|
Azuma et al[41]
|
2012
|
Chemodenervation + facial therapy
|
Cohort
|
Prospective
|
13
|
Adults
|
Palpebral fissure width
|
Pourmomeny et al[44]
|
2015
|
Chemodenervation + facial therapy versus facial therapy alone
|
Randomized control trial
|
Prospective
|
34
|
Adults
|
Sunnybrook Facial Grading System + custom measurements on photographs
|
Lee et al[42]
|
2015
|
Chemodenervation + facial therapy
|
Cohort
|
Prospective
|
17
|
Adults
|
Sunnybrook Facial Grading System
|
Mandrini et al[43]
|
2016
|
Chemodenervation + facial therapy
|
Cohort
|
Retrospective
|
27
|
Adults
|
Sunnybrook Facial Grading System
|
Pourmomeny et al[39]
|
2021
|
Chemodenervation versus facial therapy
|
Randomized control trial
|
Prospective
|
26
|
Adults
|
Sunnybrook Facial Grading System
|
Jeong et al[40]
|
2023
|
Chemodenervation + facial therapy
|
Cohort
|
Prospective
|
99
|
Adults
|
Computer-based numerical scoring system
|
Terzis and Karypidis[58]
|
2012
|
Surgery ± chemodenervation and facial therapy
|
Cohort
|
Retrospective
|
11
|
Children
|
Sunnybrook Facial Grading System
|
Terzis and Karypidis[57]
|
2012
|
Surgery ± chemodenervation and facial therapy
|
Cohort
|
Retrospective
|
31
|
Adults
|
Sunnybrook Facial Grading System
|
de Jongh et al[36]
|
2023
|
Chemodenervation
|
Meta-analysis
|
Retrospective
|
106
|
Adults
|
Synkinesis Assessment Questionnaire
|
Nakano et al[49]
|
2023
|
Facial therapy
|
Meta-analysis
|
Retrospective
|
179
|
Adults
|
Sunnybrook Facial Grading System
|
Fig. 2 Flow diagram of eligible studies. After screening and applying exclusion criteria,
38 studies from the initial 201 items were included in this systematic review.
Overall, the 36 original articles reported data on 1,408 patients. Articles were divided
into the following treatment categories: (1) chemodenervation (12 studies, 536 patients,
45 patients/study), (2) facial therapy (5 studies, 206 patients, 41 patients/study),
(3) surgical (10 studies, 389 patients, 39 patients/study), and (4) combination therapy
(9 studies, 278 patients, 31 patients/study). Only one of these studies was specifically
concerned with PPFS in the pediatric population.
Of the two meta-analyses, one examined the effect of chemodenervation (106 patients)
and one the success of facial therapy (179 patients).
The Sunnybrook Facial Grading System (FGS) was the most commonly used clinical assessment
tool to quantify the severity of synkinesis, reported in 20/38 (53%) of studies. Patient-reported
outcome measures (PROMs) were assessed in 11/38 (29%) of studies, most often using
the Synkinesis Assessment Questionnaire (SAQ). Other modalities, including expert
review or clinical judgement (3/38, 8%), were utilized in 14/38 (37%) of papers ([Table 1]).
Discussion
To date, there is no consensus on how PPFS is best treated. Although certain concepts
are common, the exact management varies greatly between centers and often relies on
expert opinion.[20] While there is ample literature on the treatment of facial palsy, most studies focus
on facial reanimation. Synkinesis is mostly mentioned as an adverse secondary outcome
and its prevention investigated. Comparably few articles examine the treatment of
patients with already established synkinesis and hence generate outcome data specific
to this population. Furthermore, no clinical tool for synkinesis assessment and therefore
outcome reporting is universally accepted. Most frequently, the Sunnybrook FGS is
used as the objective measurement because it allows for a separate quantification
of the degree of synkinesis. However, it was found that this assessment of synkinesis
is not consistent between examiners.[22] Subjective outcome measures in the form of PROMs are evaluated increasingly more
often. Yet, the most common tool, the SAQ[23] was still only used in 21% of studies.
Another key challenge is the clinical heterogeneity of patients suffering from PPFS.
There is a high level of variation in the number and extent of involved muscles as
well as the strength of synkinesis. Furthermore, in most cases, synkinesis does not
exist as a standalone symptom but as part of a more complex affliction involving varying
degrees of paresis, hyperkinesia, stiffness, and spasms of the facial musculature,
which also have to be addressed. Therefore, attempts have been made to classify synkinesis
based on the preservation of smile and degree of synkinesis and to target the therapy
accordingly.[24] However, no such classification has been widely adapted.
For the purpose of this review, we have separated articles based on intervention as
described below.
Management Strategies
Chemodenervation
Most of the included studies (58%) were focused on treating synkinesis with botulinum
toxin A (BTX-A) injections. Thirteen articles examined BTX-A alone and nine in combination
with surgery or facial therapy. BTX-A injections have been used to treat facial synkinesis
for over 30 years.[25] BTX-A, the most potent of the neurotoxins, produces paralysis by blocking presynaptic
release of the neurotransmitter (acetylcholine) at the neuromuscular junction, with
reversible chemical denervation of the muscle fiber, thereby inducing partial paralysis
and atrophy. Through targeting the synkinetic muscles on the affected side, as well
as hyperactive ones on the healthy side, the goal is to control synkinesis and restore
facial symmetry.
Although there are many reports examining the effect of BTX-A treatment on PPFS, the
studies are typically single cohorts comparing synkinetic complaints pre- and postinjection,
with no separate matched control group, making it difficult to draw any definitive
conclusions. Based on improved objective synkinesis measurements, these articles report
that BTX-A treatment is effective in reducing facial synkinesis and improving facial
symmetry both at rest and during voluntary movements.[26]
[27] Furthermore, improvement in subjective symptomatic burden and quality of life[28]
[29] have been documented, an effect that persists with repeated injections.[30]
Lately, focus has pivoted to further improving treatment success by not only targeting
the classic mimetic muscles, but also others that are innervated by the facial nerve.
Muscle tightness in the neck and banding may be addressed by targeting the platsyma,[31] residual facial tightness with buccinator[32]
[33] injections, and jaw discomfort by infiltrating the posterior belly of the digastric
muscle.[34] In properly selected cases, these individualized adaptations to the standard regimen
provided improved synkinesis scores and subjective symptom control.
While BTX-A is the most widely used neurotoxin to treat PPFS, other derivatives are
available, and usage appears to depend mainly on personal preference and regional
supply. Limited data exist on their respective efficacies: one randomized controlled
trial in 28 patients compared three types of BTX-A. Abobotulinumtoxin A (Dysport®),
onabotulinumtoxin A (Botox®), and incobotulinumtoxin A (Xeomin®)—all showed similar
effects during the first 4 weeks after injection. After that, incobotulinumtoxin A
(Xeomin®) had significantly less effect on the SAQ compared with onabotulinumtoxin
A (Botox®), due to a suspected shorter duration of action. The authors conclude that
shorter intervals between treatments or larger doses may be required when using incobotulinumtoxin
A (Xeomin®) for facial synkinesis.[35]
While rare, adverse events associated with BTX-A treatment mainly depend on location
and dosage as well as technique of infiltration. They include, but are not limited
to, hematomas, headache, stiff face, difficulty speaking, ptosis of both lip and eyes,
dry eyes, diplopia, and epiphora.[25]
[36] Unfortunately, studies seldomly report and elaborate on these adverse events and
those that do present heterogeneous data that are incomplete, making it impossible
to reliably estimate their incidence in PPFS patients treated with BTX-A in comparison
to the general population.[36]
A recent meta-analysis tried to objectify the benefit of BTX-A in patients with synkinesis.
Of the 4,299 articles screened, only three studies (covering 106 patients) met the
criteria for inclusion in the quantitative analysis. The evaluation showed a significant
effect of BTX-A treatment on the SAQ scores, and therefore patient reported outcomes,
2 weeks after injection. Due to inconsistencies in reporting, follow-up, and outcome
measurements, no other analysis was possible.[36]
Facial Therapy
Thirteen included studies evaluated the efficacy of physical therapy, six as their
main focus and seven in combinations with other treatment options.
Historically, various techniques have been used for facial palsy rehabilitation. Early
efforts focused on global activation and animation of the paralyzed face were later
adapted to minimize synkinetic motion.[37] One of these techniques, neuromuscular retraining therapy (NMRT), provides patients
with an individualized training program incorporating patient education, facial exercises,
massages, and typically some sort of feedback (surface electromyography [EMG], biofeedback,
mirroring). A proof-of-concept study analyzing electromyographic feedback pre- and
postmirror therapy with a computerized treatment system (Specular Face biofeedback)
showed that visual mirror feedback therapy changes the pattern of synkinesis and the
facial muscle function as well as improves involuntary discriminatory capacity of
the muscle activity in patients with PPFS.[38]
Clinical findings suggest that neuromuscular retraining not only leads to significant
improvements in facial symmetry but also allows patients to overcome synkinesis.[39] Although great differences in the exact regimen exist between centers, adaptations
of NMRT are nowadays in use worldwide, often in combination with BTX-A injections.
This combination has been shown to improve facial movements and synkinesis control
in patients with chronic PPFS regardless of the degrees of facial synkinesis and asymmetry
before treatment,[40] an effect that seems to last even long after the effect of BTX-A has faded.[41]
[42] Long-term facial therapy, supported by repeated BTX-A injections have therefore
become standard. However, evidence suggests that a certain plateau of improvement
is reached after four sessions of this combined therapy.[43]
Yet, the question as to what extent BTX-A contributes to the success of combination
therapy remains controversial. One study separated 34 participants into two groups:
one group (treatment) received a single BTX-A dose followed by 4 months of rehabilitation
with muscle stretching and EMG biofeedback sessions three times weekly as well as
mirror biofeedback at home, the second group (placebo) received a single saline injection
followed by the same rehab protocol. While both groups showed significant improvements
in facial symmetry, voluntary movements as well as synkinesis, multiple analysis modalities
failed to demonstrate any significant difference between the two groups.[44] Conversely, Monini et al demonstrated that BTX-A pretreatment resulted in significantly
better outcomes.[45]
Collagen “filler” injections have also been used to augment the effect of physical
therapy; however no significant improvement was demonstrated.[46]
Mime therapy has also gained increased popularity in recent years. This approach combines
elements of automassage, relaxation exercises, inhibition of synkinesis, coordination
exercises, and emotional expression exercises. One retrospective study of 155 patients
undergoing between 3 and 5 months of mime therapy demonstrated significant improvement
in facial impairment, disability, and quality of life. Interestingly, after therapy
the number of patients with synkinesis increased, however, the overall average of
synkinesis severity decreased significantly.[47] This was followed up with a randomized controlled trial involving 48 patients which
compared mime therapy with patient without any treatment. The results confirmed that
patients undergoing 3 months of mime therapy not only increased their facial symmetry
at rest and with voluntary movement, but also significantly decreased their synkinesis
score.[48]
Despite these findings, high-quality evidence regarding the overall efficacy of facial
therapy in patients with established PPFS remains sparse. In 2023, a meta-analysis
of randomized controlled trials showed that that physical therapy reduces nonrecovery
in patients with acute peripheral facial palsy. However, it also concluded that the
efficacy of facial therapy in reducing sequelae such as synkinesis remains uncertain.[49] Fujiwara et al noted that while physical rehabilitation, including mirror biofeedback
and massage, prevented worsening of synkinesis in female and younger patients, synkinesis
scores still deteriorated in older patients and especially in males.[50]
Surgery
Largely due to the success of facial therapy and chemodenervation, surgery has traditionally
only played a secondary role in treatment of synkinesis, with some questioning its
role at all.[37] Although a multitude of procedures have been described, two main surgical approaches
exist: selective neurectomy and myectomy. Our search yielded 10 studies reporting
surgery as the main treatment for synkinesis and two reporting surgical outcomes as
part of a multimodal approach in combination with BTX-A and biofeedback. All included
surgical papers described retrospective cohorts and often presented a new technique
pioneered at a particular center or even by a single surgeon.
In 1991, Guerrissi presented his experience resecting the zygomaticus major for treatment
of oculo–oral synkinesis.[51] The study proposed that selective myectomy yields superior outcomes over neurectomy
due to the complex and variable anastomoses between terminal nerve branches of the
facial nerve. Additionally, the study concluded that the upper part of the buccinator
and zygomaticus minor are sufficient to compensate for the loss of zygomaticus major,
hence the ability to elevate the corner of the mouth was unaffected following myectomy.[51]
Similarly, Yoshioka suggested partial orbicularis neuromyectomy.[52] The study describes resecting a peripheral 1-cm-wide strip of the lower orbicularis
oculi muscle to address synkinetic eye closure. The multitude of terminal facial nerve
branches in this region are resected together with the muscle, resulting in a definitive
neurectomy of the branches of the facial nerve that innervate the lower orbicularis
oculi muscle. However, the disadvantage of this procedure is that it results in complete
paralysis of the lower orbicularis muscle for several months. Furthermore, slight
recurrence of synkinesis has been observed 6 months after the operation.[52] Alternative procedures, such as endoscopic brow lifting, have also been explored
as a treatment option for periocular synkinesis and are reported to control synkinesis
symptoms more effectively than BTX-A.[53]
For patients with moderate-to-severe synkinesis, especially when combined with an
unacceptable smile, a more radical approach with combined myectomy and neurectomy
followed by free functioning muscle transplantation has been proposed.[54] Following extensive neuromyectomies of the synkinetic muscles and triggering facial
nerve branches in the cheek, nose, and neck regions, a free functioning gracilis flap
is used for hemifacial reanimation. Although reporting good outcomes for synkinesis
control and smile reanimation, revision surgery for secondary deformity was necessary
in 53%.[54]
In similar cases, other studies implement a single-stage masseteric–zygomatic nerve
transfer. The procedure aims to separate the innervation of the eyelids from that
of the zygomatic muscular complex which in turn becomes reinnervated by the masseteric
nerve. This technique corrects the synkinesis and simultaneously enhances muscle tone
at rest and smile excursion.[55] A cross-facial nerve graft (CFNG) can be added end-to-side to the zygomatic nerve
to enhance synchrony between the healthy and pathological side of the face and to
restore spontaneity.[56]
Alternatively, a two-stage procedure with CFNGs has also been used to directly innervate
the synkinetic muscle groups via their corresponding nerves from the healthy contralateral
side.[57]
[58]
Recently, the most common surgical approach to PPFS patients with some degree of remaining
active zygomatic muscle function has been selective neurectomy. Although various techniques
have been described, a standard rhytidectomy approach is usually chosen to access
the distal branches of the facial nerve. Once identified, the individual branches
are isolated and selectively transected to separate smile and eye closure ([Fig. 3]). It also aims at reducing the activity of antagonistic muscles while preserving
the neural input to key muscles, therefore effectively strengthening the smile mechanism.[59] Larger cohorts undergoing such procedures are now starting to appear. In 2023, Park
et al published their experience with selective neurectomy based on a retrospective
analysis of 122 cases. The findings demonstrate that selective neurectomy provides
satisfactory outcome regarding facial tightness as well as narrowing of the eyelid
aperture and improves the vertical inclination of the corner of the mouth, however,
the improvement of the horizontal angles remain suboptimal.[60]
Fig. 3 (A) Normal anatomy. (B) Aberrant regeneration of fascicles from the buccal branch along the zygomatic branch
after facial nerve injury resulting in oculo–oral synkinesis. (C) Selective neurectomy: individual branches are isolated and selectively transected
to separate smile and eye closure.
Currently, there is limited reporting regarding the longevity of these surgical interventions.
van Veen et al demonstrated that, although patients undergoing selective neurectomy
for periocular synkinesis usually experience a symptom-free interval after the surgery,
most required renewed BTX-A treatment later on. At 3.5 years postsurgery follow-up,
9 out of 10 patients required treatment with BTX-A. Additionally, the study noted
that patients maintained a larger palpebral fissure width long-term, and that previously
refractory patients now demonstrated good response to BTX-A.[61]
Limitations, Challenges, and Prospects
As discussed initially, there are many limitations encountered in this study. The
majority of included studies were either observational cohorts (79%) or of a retrospective
design (45%). Most of these studies were rated to be of poor quality according to
the Newcastle–Ottawa scale for cohort studies.[62] Only six papers (16%) represented prospective, randomized controlled trials, yet
with an average number of 32.7 participants (range 20–48)—they were small, leaving
on average only 16.3 participants per intervention group, and associated with a significant
risk of bias.
In general, most studies only involved a very limited number of patients, 47% less
than 30. While cohorts with more significant numbers of participants have been published
in recent years, the issue remains that many of these publications report on a center's
daily practice rather than investigate a specific scientific question. The significant
heterogeneity in study population and design, lack of control groups, differences
in postoperative follow-up as well as the use of a variety of subjective and objective
assessment tools to quantify synkinesis make comparison between studies difficult
and render quantitative meta-analysis almost impossible. The fact that 54% of all
included studies were published in the last 5 years (46% in the last 3 years) illustrates
that these issues are still very much ongoing.
The available clinical cohorts show that most patients with PPFS are treated in a
multimodal approach. While highlighting the success of such a combination of facial
therapy, chemodenervation and surgery, this also makes it almost impossible to determine
to what extent each modality contributed to the final outcome.[57]
[58] Comparing modalities based on the available single-therapy cohorts is prone to bias
as is obvious from the example of BTX-A versus selective neurectomy: Firstly, patients
referred for and willing to undergo selective neurectomy tend to represent more severe
cases. Secondly, these are usually patients that have exhausted or failed conservative
treatments such as BTX-A or facial rehabilitation.[60]
Selective chemodenervation with botulinum toxin and facial therapy remain the cornerstones
in the treatment of PPFS. BTX-A offers patients a quick symptomatic improvement, reduction
of synkinesis, and overall symmetrization of the face. There are few contraindications
and although adverse events occasionally occur, the effect is reversible within 3
to 4 months.[26] BTX-A has been used since 1984,[63] has an established safety profile and is a relatively cost-effective intervention.[64] Specialized facial therapy using forms of neuromuscular retraining or mime therapy
paired with a direct feedback mechanism not only enhance these effects but also achieve
stable long-term improvements for the patient. The combination of these two modalities
seems to be particularly successful and has led to many theories being postulated.
Perhaps the best explanation is that BTX-A injections allow patients to overcome aberrant
facial movements and concentrate on neuromuscular relearning of untargeted muscles
during the temporary chemodenervation, therefore basically creating a window of opportunity
for facial therapy.[41]
Surgical options are being refined and have shown promising results. Nevertheless,
a certain unpredictability, significant revision rate and steep learning curve remain.[59] Furthermore, surgical techniques and expertise vary greatly between centers. For
now, the use of these techniques primarily seems suitable for patients with severe
synkinesis or those who did not adequately respond to conservative measures.
In general, patients with established PPFS should be managed by an interdisciplinary
team able to offer all available options, tailored to the specific needs of the individual
patient. Such a multimodal approach not only reduces objective synkinesis scores but
also PROMs. Although even helpful in those with chronically neglected synkinesis,
it should be established as soon as possible to achieve the best possible outcome.[65]