Botulinum Toxin Type A Injection in the Treatment of Postparetic Facial Synkinesis: An Integrative Review

This study aimed to review the recent literature about botulinum toxin type A treatment patterns, including muscle targets, doses, duration of effect, adverse effects, and clinical outcomes in patients with postparetic synkinesis. A bibliographic research of studies published in the last 10 yrs was carried out on PubMed database, using the medical subject heading terms: botulinum toxin and synkinesis. English-language cohort studies or randomized controlled trials about botulinum toxin type A treatment on patients with postparetic synkinesis were eligible for inclusion. Ten studies met the inclusion criteria, seven prospective studies, two retrospective studies, and one randomized controlled trial, involving 23-99 patients. The target facial muscles included frontalis, corrugator supercilli, orbicularis oculi, levator labii superioris, zygomaticus major, orbicularis oris, risorius, buccinator, depressor anguli oris, depressor labii inferioris, mentalis, and platysma. The dose of onabotulinumtoxinA administered per injection site ranged between 0.5 and 10 U. Adverse effects were rare and temporary. The mean duration of onabotulinumtoxinA effect ranges from 66 days to 4 mos. There was a statistically significant improvement in posttreatment evaluation, both in objective and subjective assessments. There is scientific evidence of the benefit of botulinum toxin type A treatment for postparetic synkinesis, but there is lack of standardized treatment protocols.