Effect of Botulinum Toxin A (BTX-A) Injection into Denervated Muscles on Synkinesis and Symmetry in Patients with Facial Nerve Paralysis

Context: Synkinesis refers to an involuntary movement accompanying a voluntary one that is a consequence of facial paralysis. The cosmetic procedure is used for the management of synkinesis that results in facial symmetry. Botulinum A toxin (BTX-A) has been used for more than two decades for resolving asymmetry and synkinesis. However, the endpoints remain to be further explained. The purpose of this study was to analyze research trends in facial synkinesis and asymmetry after facial nerve palsy (FNP). Evidence Acquisition: The databases Medline, PubMed, ScienceDirect, CINHAL, Scopus, and ProQuest were searched for articles published between 1970 and 2017 using the keywords, ‘facial paralysis’, ‘Bell’s palsy’, ‘synkinesis’, and ‘Botulinum A toxin’. Results: In total, 13 eligible articles, cumulatively examining 332 patients, entered the analysis. They were divided into three groups as follows. Eight articles in group I were taken as case series with 181 patients. Two articles in group II compared BTX-A and neuromuscular rehabilitation with 61 patients. Both these groups concluded that BTX-A injection could help reduce synkinesis. In group III, only were three randomized clinical trials retrieved with 90 patients that reported disparate findings. Conclusions: BTX-A injection cannot yet be proposed as a solution for synkinesis reduction to achieve symmetry and overcome this complication of facial nerve palsy because of the small number of randomized clinical trials available on the subject. Further studies are recommended to be able to make a firm conclusion.