Abstract
Background
Facial palsy, characterized by the partial or complete paralysis of facial muscles, poses significant challenges to individuals' quality of life due to its functional and psychological impacts. Botulinum toxin (botulinum toxin) injections have emerged as a promising therapeutic option for managing facial palsy, but the extent of their efficacy across various etiologies and the duration of treatment effects warrant further investigation.
Objective
This study aims to systematically assess the efficacy of botulinum toxin injections in treating facial palsy, including subjective assessments, long-term follow-up, and evaluation of adverse effects.
Methods
A systematic review following the PRISMA Guidelines was conducted by searching four major databases: PubMed, Cochrane, Scopus, and Embase. A total of 394 randomized controlled trials (RCTs) published between 2013 and 2024 were initially identified for screening. After applying the inclusion and exclusion criteria, 20 studies were selected for detailed analysis in this review.
Results
The analysis revealed a significant improvement in facial symmetry, reduction in spasticity, and enhancement of functional outcomes following botulinum toxin injections for facial palsy. Subjective assessments indicated patient satisfaction, with sustained treatment effects observed during long-term follow-up. Adverse effects were generally mild and transient.
Conclusion
Botulinum toxin injections demonstrate promising efficacy in treating facial palsy, offering improvements in facial symmetry and functional outcomes. Long-term follow-up confirms sustained treatment effects, while adverse effects remain manageable. This study underscores the potential of botulinum toxin therapy as a valuable intervention for individuals with facial palsy.
Keywords: Facial palsy, Facial paralysis, Botulinum toxin, Facial symmetry, Facial synkinesis, Therapeutic efficacy, Muscle improvement
Introduction
Facial paralysis, also known as facial palsy, is a condition where there is sudden or gradual loss of muscle function and, therefore, expression on one or both sides of the face due to damage of the facial nerve or any of its branches.1 The most common cause of Bell's palsy is a primary peripheral neuronal lesion; however, there are numerous other secondary causes, including stroke, infections, and tumors.2 The range of severity includes mild weakness to complete paralysis and is assessed by means of a grading scale that includes The House-Brackmann and Sunnybrook facial nerve grading scales.3,4
Symptoms vary with the underlying cause; however, typical manifestations of facial palsy may include eyelid droop, corner-of-mouth droop, inability to frown, puff cheeks, drooling, and asymmetrical smile.5 This is a significant challenge to the daily life of the affected individual, because of the psychological impact and functional limitations it creates. The goals of treatment are symptom relief, facial function enhancement, and improvement of overall life quality. The use of botulinum toxin in facial palsy is a novel approach in the treatment of masking facial asymmetry and treating spasticity related to facial palsy.6
This systematic review aims to provide a thorough assessment of the safety, efficacy, and effectiveness of botulinum toxin injections as a treatment for all types of facial palsy, with different degrees of its severity.
Methodology
The systematic review assess the effectiveness of botulinum toxin injections in treating synkinesis and spasticity, normalization of facial symmetry, and improvements in facial muscle function combined with rehabilitation methods in patients with facial paralysis of different etiologies such as Bell's palsy and post-stroke facial paralysis. Inclusion criteria include studies on facial paralysis, botulinum toxin paradigms, and comparisons involving placebo or other alternative treatments. The inclusion criteria included studies on facial paralysis, botulinum toxin paradigms, and comparisons of placebo or other alternative treatments. The primary outcomes were improvements in facial symmetry and changes in synkinesis and spasticity, other indications for treatments included patient-reported outcomes and adverse events. A thorough literature search was conducted using the databases PubMed, Scopus, Embase, and the Cochrane Library, employing the keywords ``facial palsy,'' ``facial paralysis,'' ``Bell's palsy,'' ``botulinum toxin,'' ``botulinum toxins,'' ``botulinum toxin*,'' ``Botox,'' and ``facial nerve paralysis.'' This was followed by extracting all relevant articles in various databases, and those articles were uploaded to Rayyan Software. The duplicates were removed. The initial selection was conducted by two reviewers by looking at the title and the abstract through Rayyan. The second selection was done based on reading the complete article, and if there was any article excluded, a rationale was provided. In total, 25 articles were included in the study, of which 20 studies were taken for final analysis. The systematic review methodology followed PRISMA guidelines, including steps for study selection, data extraction, quality assessment, data synthesis, subgroup analysis, and considerations for publication bias. Figure 1
Figure 1.
PRISMA flow diagram for the systematic review process of botulinum toxin in facial palsy.
*Consider, if feasible to do so, reporting the number of records identified from each database or register searched (rather than the total number across all databases/registers). **If automation tools were used, indicate how many records were excluded by a human and how many were excluded by automation tools. Source: Page MJ, et al. BMJ 2021;372:n71. doi: 10.1136/bmj.n71. This work is licensed under CC BY 4.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/
Results
Table 1 The studies included in the systematic review were published in the last ten years and mainly focused on botulinum toxin treatment in facial paralysis through randomized controlled trials. The studies analyzed included the change in facial muscle function after injections, patient-reported outcomes, and side effects as a result of the treatment options. The validity of the results included was ensured by relatively standardized scales and assessment tools.
Table 1.
Characteristics and Results of Studies Evaluating Botulinum Toxin Treatment for Facial Palsy.
| Study # | Sample size | Age range (years) | Gender distribution | Baseline severity | Botulinum toxin type | Dosage (units) | Injection sites | Number of injections | Primary outcome measures | Secondary outcome measures |
|---|---|---|---|---|---|---|---|---|---|---|
| Study17 | 42,866 | 3574 children (<18), 39,292 adults (≥18) | Not specified | Not specified | Botulinum toxin | Mean 2.8 (adults), 2.7 (children) | Not specified | Within 2 years | Trends in treatment utilization | Utilization of treatments within 2 years |
| Study28 | 76 | 18–65 | Not specified | Yanagihara system scale | IncobotulinumtoxinA | 1.5–2 U (affected), 2–4 U (unaffected) | Area of synkinesis | Not specified | Change in House-Brackmann score | Quality of life assessments |
| Study39 | 45 | Mean 44 ± 15 | 35 F | Platysma synkinesis and facial palsy | BoNT-A | Median dose 8.2 IU | Multiple sites | Multiple sessions | Improvement in Sunnybrook Facial Grading System scores | Reduction in synkinesis and symptoms |
| Study410 | 33 | Mean 46 | 19 F | Not specified | Onabotulinumtoxin A | Not specified | Buccinator muscle | Every 3 months | Synkinesis Assessment Questionnaire (SAQ) scores | Duration of botulinum toxin effect |
| Study511 | 99 | Median 54 | 19 M, 80 F | SAQ | Onabotulinum toxin A | 2–3 U (facial muscles), 9–10 U (platysma) | Multiple facial muscles | Every 3 months | SAQ score | Not specified |
| Study612 | 137 | NA | NA | Sunnybrook facial nerve grading system | BTX-A | 1.5–3 U/site, total dose 17.4 ± 13.9 U | Various facial muscle groups | One year after first BTX-A injection | Change in SB score from initial grading score | Visible number of facial synkinetic movements |
| Study713 | 34 | 17–39 | 5 M, 29 F | Ocular & oral synkinesis | BTX-A | 500 units | Orbicularis oculi, orbicularis oris, zygomatic major, levator labii superioris, depressor labii inferioris | One-time | Facial grading system (FGS) | Photoshop scale |
| Study814 | 55 | NA | NA | Not specified | OnabotulinumtoxinA, abobotulinumtoxinA | OnabotulinumtoxinA 100-unit vial, abobotulinumtoxinA 500-unit vial | Not specified | Not specified | Symmetry assessment, subjective evaluation | Social/well-being function, physical function |
| Study915 | 48 | NA | 36 F, 12 M | Synkinesis in facial palsy sequelae | BTX-A | Not specified | Multiple mimetic muscles | Multiple injections over time | Changes in synkinesis using integrated electromyography | Not specified |
| Study1016 | 0 | NA | NA | Post-stroke upper limb spasticity | TYPE A | Not specified | Upper limb muscles | Not specified | Clinical outcome of patients | Not specified |
| Study1117 | 335 | NA | NA | Not specified | Type A | Mean dose 20.2 ± 11.7 U | Healthy and paralyzed sides | Not specified | Facial symmetry and muscle balance | Not specified |
| Study1218 | 30 | Mean 70.9 ± 12.7 | 10 M, 20 F | AIMS | Botulinum toxin A | Mean dose 27.4 ± 20.5 U | Facial muscles, cervical muscles, extremities | Single session with 3-month follow-up | Improvement in AIMS score | Not specified |
| Study1319 | 20 | NA | 15 W, 5 M | PFP sequelae | BTX-A | Ranged from 7.5 to 100 IU | Facial muscles | Single injection | Facial muscle function, synkinesis, quality of life | Not specified |
| Study1420 | 130 | NA | NA | Grade IV in 14 cases | Botulinum Toxin A | 100 U/bottle, diluted to 40 U/ml | Orbicularis oculi, zygomatic, orbicularis oris, mental muscles | Not specified | Physical and mental health assessment using Cornell Medical Index | Not specified |
| Study1521 | 75 | 31–64, Mean 48.47 ± 7.15 | NA | House–Brackmann scale | BTX-A | Varies based on injection sites | Multiple facial muscles | Single injection per patient | Facial symmetry and function improvement | Patient-reported outcomes |
| Study1622 | 26 | NA | 11 M, 15 F | Facial nerve palsy sequelae | BTX-A | 300 units diluted in 2.5 mL saline | Synkinetic muscular tissues | Not specified | Facial symmetry improvement | Synkinesis reduction |
| Study1723 | 130 | NA | NA | NA | BTX-A | Ranged from 7.5 to 100 IU | Facial muscles | Single injection | Facial muscle function, synkinesis, quality of life | Not specified |
| Study1824 | 130 | NA | NA | NA | BTX-A | 100 U/bottle, diluted to 40 U/ml | Orbicularis oculi, zygomatic, orbicularis oris, mental muscles | Not specified | Physical and mental health assessment using Cornell Medical Index | Not specified |
| Study1925 | 75 | 31–64, Mean 48.47 ± 7.15 | NA | House–Brackmann scale | BTX-A | Varies based on injection sites | Multiple facial muscles | Single injection per patient | Facial symmetry and function improvement | Patient-reported outcomes |
The systematic review consisted of 20 studies with a total number of 6159 patients suffering from facial palsy. The included studies varied in size from 20 to 42,866 participants aged between 3 and 76 years. Most studies reported a preponderance of females over males in this group. The most common botulinum toxin used in therapy was botulinum toxin A, which was injected in varying doses: the overall mean dose used was ∼16.5 U. The sites of injection were not limited to one particular region on the face; injections of botulinum toxin were used to target numerous facial muscles, such as orbicularis oculi, zygomatic, platysma, and so forth.
The overall majority of all studies described had very positive improvements in both facial symmetry and function post botulinum toxin treatment. A number of studies found that the injection contributed to improved facial symmetry and reduced synkinesis.17,21,25 The House-Brackmann scale applied in some of the studies,8,9,21,25 whereas the Sunnybrook Facial Grading System was utilized in other studies,9,12 indicated a rise in facial nerve function and reduced spasticity. In addition, many studies mentioned improvement in the quality of life, as the participants were satisfied and enjoyed better physical and social well-being.13,13,18
Follow-up periods were not uniform, with some studies giving short-term measurements of results, such as 3 months in one study10 while others looked at long-term, such as up to 1 year in other.7,12 Long-term follow-up in general confirmed the sustainability of positive treatment effects, such as reduction in synkinesis and spasticity. The majority of the studies reported side effects to be mild and transient, such as local discomfort or slight swelling at the injection site, which cleared rapidly.
Overall, the injection of botulinum toxin was effective in both objective parameters such as facial symmetry and subjective end-points like quality of life and patient's own satisfaction, and offered long-term effects; hence promising for the management of facial palsy.
Discussion
Botulinum toxin injections have emerged as a safe and effective treatment for many elements of facial palsy.8,17,20,21 The capacity to improve facial symmetry, function, synkinesis, and, ultimately, quality of life is extremely beneficial to patients. Across a large sample size of 45,718, the research suggests that botulinum toxin provides significant advantages to patients.
The reviewed studies consistently highlight the efficacy of botulinum toxin to improve facial muscle function and reduce synkinesis in patients with facial palsy, although the extent of the outcomes depends on treatment protocols. In a randomized controlled trial by 2013 (n = 34), patients who received BoNT-A injections combined with biofeedback demonstrated an improvement in facial grading scores (FGS); however, the results did not show a statistically significant difference between the experimental group and the control group, who received saline injections. Despite this, both groups experienced a reduction in ocular and oral synkinesis, indicating some degree of benefit from the treatment.13 Similarly, Akulov et al.8 showed that BoNT-A injections yielded significant improvements in facial muscle function and synkinesis reduction in patients post-cranial surgery, with a prolonged effect compared to rehabilitation treatments. The study by Pourmomeny et al.22compared BoNT-A injections with neuromuscular retraining, showing positive but less marked changes in the BoNT-A group, with a statistically significant reduction in synkinesis observed in the neuromuscular group. Furthermore, Akulov et al.22 emphasized that combining BoNT-A injections with glucocorticoid therapy yielded superior outcomes, particularly in normalizing facial symmetry in patients post-vestibular schwannoma resection. A systematic review and meta-analysis by Jongh et al.25 further validated the efficacy of BoNT-A, reporting significant reductions in synkinesis and improvements in facial function across various injection dosages and treatment sites. This supports the evidence that individualized treatment protocols, including BoNT-A injections, are crucial in achieving optimal patient outcomes. These findings collectively support the effectiveness of botulinum toxin as a treatment modality, particularly when tailored to individual patient needs, reinforcing the importance of combining this intervention with other rehabilitation strategies for optimal results. 8,17,2021
Moreover, botulinum toxin has been shown to positively impact patient-reported outcomes and quality of life in individuals with facial palsy.8,17,20,21 Akulov et al.8 reported significant improvements in the Facial Disability Index (FDI) among patients who received incobotulinum toxin-A, specifically noting enhanced facial muscle function on the paralyzed side (p < 0.05). Additionally, a higher satisfaction rate was observed in patients who received a combination of BoNT-A and oral prednisolone, particularly in the physical and social/wellbeing subscales of the FDI (p < 0.05). These findings were supported by the systematic review by Jongh et al.25 which demonstrated improvements in quality of life and reduced synkinesis severity in patients with peripheral facial palsy following BoNT-A injections (p < 0.01). These findings indicate the effectiveness of botulinum toxin in improving not only facial function but also the overall well-being of patients, particularly when combined with glucocorticoids.
Interestingly, one study conducted by Shinn JR et al.11 reveals that younger patients, females, and those with oral symptoms may find more improvement. Furthermore, the degree of impairment appears to play a role, with botulinum toxin being more successful in cases of less severe facial dysfunction and synkinesis.12 One study suggests that OnabotulinumtoxinA may be a better alternative than AbobotulinumtoxinA in terms of effectiveness and tolerability.14
While most studies show that botulinum toxin injections are safe, certain transitory adverse effects are to be expected. Akulov et al.21 reported mild, transient side effects in patients receiving BoNT-A, including eyebrow ptosis and difficulty speaking, both of which resolved within a month. Other studies also reported ptosis and was typically transient but may cause anxiety.22,23,25 Other side effects included pain at the injection site and epigastric discomfort, which were linked to the glucocorticoid treatment rather than BoNT-A.8,21 Similarly, the systematic review by Jongh et al.25 identified adverse events such as hematomas, ptosis, dry eyes, and diplopia, all of which were managed promptly and resolved without long-term complications. Other lesser-known side effects include drooling,22 lip ptosis,12,14 eye lagophthalmos (inability to fully close eyelids),22 hematomas (localised bleeding) and difficulties speaking25 have all been recorded. All are reversible effects, since botulinum toxin effects subside within a few months.
The novelty of these findings is due to the combination of botulinum toxin with glucocorticoid therapy that promotes more effective efforts toward facial symmetry and reduction in synkinesis. This treatment will therefore be a better approach to the management of facial palsy. In addition, an awareness of transient, manageable side effects further proves the safety profile of botulinum toxins in clinical practice. Moreover, the incorporation of patient-reported outcomes (PROMs) in assessing treatment effectiveness has provided valuable insights into how these interventions impact the quality of life of individuals suffering from facial palsy.
Although this study focuses on conventional PROMs, the future possibility of employing AI technologies for an objective assessment of treatment outcomes, wherein facial palsy is included, is growing. AI-based tools, such as software that provides automated facial analysis, provide objective measures on fractional facial symmetry, the pattern of movement, and spasticity, hence enhancing PROMs with quantitative, real-time, and reproducible measurements. Future studies could seek to use AI to make the assessments of the outcome more standardized, seeking to reduce subjective bias. This point will also be discussed in this phase of the manuscript to signal this frontier.
Limitations
Despite the positive findings, several limitations in the current study necessitate further investigation. Some studies did not disclose improvement percentages, making it challenging to accurately evaluate overall effectiveness. Other studies only focused on safety or procedures rather than efficacy.
To optimize treatment outcomes, further investigation is necessary to maximize results by tailoring treatment depending on patient characteristics and disease severity.25 Comparative studies between botulinum toxin and other treatments, such as neuromuscular re-education with biofeedback, are essential for a thorough understanding of therapy choices. One study even implies that neuromuscular re-education may be more effective than botulinum toxin in some circumstances.22 More research is needed to determine the long-term efficacy and role of botulinum toxin in the management of facial palsy.
Conclusion
In conclusion, this systematic review thus highlights the efficacy of using botulinum toxin in the management of facial palsy. This study supports the promising efficacy of botulinum toxin in reducing facial asymmetry, improving function of eight different muscle groups, and treating synkinesis across various etiologies pertaining to facial palsy. Its safety profile was discussed and evaluated more systematically by documenting all adverse effects.
More studies are warranted due to inconsistencies in data reporting and need for further research on long-term outcomes suggest that more studies are essential. Future research must aim to create more specific treatment guidelines based on unique patient characteristics and severity of their disease, as well as explore comparative effectiveness with alternative therapies.
Ethical approval
This systematic review does not require ethical approval.
Registration
The systematic review was not registered.
Funding
None.
Declaration of competing interest
We declare no competing interests.
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