Botulinum toxin in peripheral facial paralysis: systematic review and rehabilitation perspectives

Peripheral facial paralysis (PFP) causes both static and dynamic facial dysfunctions, leading to synkinesis, hypertonia, and aesthetic asymmetry that significantly affect quality of life. Botulinum toxin type A (BTX-A) has become an effective adjunct in rehabilitation, improving facial balance and function. However, there is no consensus regarding optimal injection patterns, dosage, or the therapeutic role of contralateral treatment.

A systematic review of the literature was conducted in accordance with the PRISMA 2020 guidelines. The MEDLINE (PubMed) database was searched for studies published between January 2013 and January 2024 using the terms "Facial Paralysis" AND "Botulinum Toxin." Randomized controlled trials, cohort, and observational studies in English or Spanish analyzing BTX-A treatment in peripheral facial paralysis were included. Data on toxin formulation, injection site, dosage, and outcomes were extracted and qualitatively analyzed.

Thirteen studies met the inclusion criteria, encompassing 1821 patients. OnabotulinumtoxinA was the most frequently used formulation. Injections on the affected side were mainly indicated for synkinesis, while contralateral injections aimed to reduce hypertonia and restore facial symmetry. Reported doses ranged from 0.6 to 7.5 U per point. Across studies, BTX-A improved facial symmetry, reduced synkinesis, and enhanced quality of life, with only mild and transient adverse effects.

Botulinum toxin is a safe and effective therapeutic tool within the multidisciplinary rehabilitation of peripheral facial paralysis. Despite consistent clinical benefits, heterogeneity in dosing and injection protocols persists. Future randomized studies combining BTX-A therapy with structured neuromuscular rehabilitation are needed to establish standardized evidence-based guidelines.