Facial Paralysis Treatment and Facial Symmetrization with Botulinum Neurotoxin: A Narrative Review with Illustrative Clinical Cases
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Facial paralysis extends far beyond a clinical finding: it leads to static and dynamic asymmetry, hyperkinesis of the non-paralyzed side, and synkinesis, with significant consequences on quality of life, social interaction, and psychological well-being. Managing this condition requires a multidisciplinary approach and therapeutic tools capable of acting selectively and reversibly on the muscles involved.
In this context, botulinum neurotoxin type A (BoNT-A) has established itself as one of the most effective and versatile interventions, with a documented role in both the acute and chronic phases of facial paralysis.
This narrative review, recently published in Toxins (MDPI) and authored by Monica Renga, Roberta D'Emilio, Giovanni Salti, Selene Mogavero, Marco Papagni, Federico Biglioli, and Alessandro Lozza, with the support of Agorà – Italian Society of Aesthetic Medicine, synthesizes the available evidence on the use of BoNT-A in the treatment of facial paralysis and integrates it with three illustrative clinical cases, documented through standardized 3D photography and longitudinal functional grading scores.
Rationale for the use of BoNT-A in facial paralysis
Facial paralysis disrupts the balance of mimetic muscles innervated by the facial nerve, leading to compensatory hyperactivity on the healthy side and, in chronic cases, aberrant reinnervation phenomena responsible for synkinesis. BoNT-A acts by producing a reversible chemical denervation of overactive muscles, blocking presynaptic acetylcholine release at the neuromuscular junction for a period of 3–6 months. This mechanism allows selective weakening of hyperkinetic or synkinetic muscles while preserving the residual function of the paretic side.
Clinical series and long-term experience demonstrate that this approach is generally well tolerated, effectively reduces hyperkinesis and facial imbalance, and is associated with high patient satisfaction, including improvements in quality of life and emotional well-being.
Acute and chronic paralysis: Indications and differences
The review systematically addresses the distinction between acute and chronic facial paralysis, traditionally defined on the basis of an 18–24 month onset cut-off. In the acute phase, BoNT-A is primarily indicated for facial symmetrization: treatment of the healthy side reduces asymmetry, attenuating the aesthetic impact and social interaction difficulties experienced by patients. Recent evidence also suggests that this approach may improve and accelerate motor recovery of the paretic side by reducing the inhibitory feedback exerted by overactive healthy muscles.
In chronic paralysis, BoNT-A represents a fundamental tool for controlling synkinesis on the affected side and hyperkinesis on the contralateral side, improving symmetry both at rest and during movement. A systematic review identified three randomized trials, totaling 105 patients, in which BoNT-A improved objective measures of facial function and quality of life parameters, with effects that often extend beyond the expected 3–6 month pharmacological window.
Treatment plan and dosing
The review highlights that no internationally validated, evidence-based clinical practice guidelines currently exist for the use of BoNT-A in facial paralysis. The recommended approach involves a standardized pre-injection assessment, with photographic documentation in multiple positions and facial expressions, both static and dynamic, and the use of validated functional scales at each visit.
The treatment plan must be individualized according to the distribution and severity of facial dysfunction, disease chronicity, and clinical response. Target muscles vary depending on the side treated: on the affected side, the orbicularis oculi, platysma, mentalis, and other synkinetic muscles are addressed; on the healthy side, the zygomaticus major, levators, risorius, and depressor muscles are targeted, with the aim of reducing hyperkinesis and improving dynamic symmetry. The dosing strategy begins with low initial doses, with gradual increments at two-week intervals to define an individualized injection map.
Functional assessment scales
For outcome monitoring, the review recommends the systematic use of validated functional scales. The House-Brackmann (HB) scale is a rapid and widely used tool, but has limitations in detecting clinically meaningful differences and in separately assessing synkinesis. The Sunnybrook Facial Grading System (SB-FGS) offers a more detailed multidimensional assessment, with a composite score integrating resting symmetry, voluntary movement excursion, and synkinesis, proving more sensitive to clinical changes over time.
Complementary AI-based tools, such as Emotrics® and FaceReader™, are emerging as options for the objective assessment of facial symmetry, reducing the interobserver variability typical of manual scales.
Instrumental guidance: EMG and ultrasound
In complex cases, the review highlights the added value of instrumental guidance for BoNT-A injection. Electromyography (EMG) allows identification of muscle portions with abnormal activity, optimizing localization and dose titration across repeated sessions. Ultrasound provides real-time visualization of anatomical structures, enabling targeted toxin deposition and reducing the risk of complications related to involuntary diffusion, such as ptosis, diplopia, or dysphonia. Combined EMG-ultrasound modalities are particularly advantageous when both functional and anatomical guidance are required.
BoNT-A and functional microsurgery
A particularly relevant aspect concerns the role of BoNT-A as a preparatory tool for functional microsurgery. Its reversibility makes it ideal for simulating surgical outcomes, allowing patients to experience the reduction of synkinesis before a definitive decision. Furthermore, BoNT-A treatment has been shown to significantly improve outcomes in patients undergoing cross-facial nerve grafting, optimizing the environment for muscle reinnervation.
The clinical cases
The review is enriched by three illustrative clinical cases covering a broad range of clinical scenarios: a patient with chronic paralysis from Ramsay Hunt Syndrome, treated with a full face and neck protocol and followed for 18 months with standardized 3D photographic documentation; a young patient with a family history of facial paralysis, contralateral hyperkinesis, and synkinesis, managed with EMG-guided and landmark-guided injections; and the mother of the previous patient, with recurrent facial paralysis and chronic synkinesis, treated with a stepwise approach. All three cases demonstrated clinically meaningful improvements, documented through SB-FGS scores and standardized photography.
Conclusions
Overall, the review highlights how BoNT-A represents a clinically valuable tool in the management of facial paralysis, capable of acting on both aesthetic symmetry and motor recovery, with a potential role in promoting neuroplasticity. Its versatility, the reversibility of its effects, and the possibility of integrating it with neuromuscular rehabilitation and microsurgery make it a fundamental resource in the long-term management of this condition. For broader and more evidence-based adoption, however, the development of shared guidelines and randomized trials with validated outcome measures and extended follow-up remains a priority.
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