Synkinesis in primary and postparalytic hemifacial spasm: Clinical features and therapeutic outcomes of botulinum toxin A treatment

Botulinum Toxin Use in the Upper Third of the Face

Botulinum toxin (BTX) is one of the most frequent procedures performed in the United States for facial rhytids. It has become a mainstay aesthetic treatment of the upper third of the face. In addition to aesthetic indications, there are a multitude of functional disorders for which BTX has proved effective. Patient evaluation and selection are critical components to treatment success. A thorough understanding of patient anatomy is critical for prevention of complications when using BTX. The use of neuromodulators in the upper third of the face is continually evolving and its indications continue to expand.

Contribution of Single-Fiber Evaluation on Monitoring Outcomes Following Injection of Botulinum Toxin-A: A Narrative Review of the Literature

Botulinum toxin-A (BoNT-A) blocks acetylcholine release at the neuromuscular junction (NMJ) and is widely used for neuromuscular disorders (involuntary spasms, dystonic disorders and spasticity). However, its therapeutic effects are usually measured by clinical scales of questionable validity. Single-fiber electromyography (SFEMG) is a sensitive, validated diagnostic technique for NMJ impairment such as myasthenia. The jitter parameter (µs) represents the variability of interpotential intervals of two muscle fibers from the same motor unit. This narrative review reports SFEMG use in BoNT-A treatment. Twenty-four articles were selected from 175 eligible articles searched in Medline/Pubmed and Cochrane Library from their creation until May 2020. The results showed that jitter is sensitive to early NMJ modifications following BoNT-A injection, with an increase in the early days’ post-injection and a peak between Day 15 and 30, when symptoms diminish or disappear. The reappearance of symptoms accompanies a tendency for a decrease in jitter, but always precedes its normalization, either delayed or nonexistent. Increased jitter is observed in distant muscles from the injection site. No dose effect relationship was demonstrated. SFEMG could help physicians in their therapeutic evaluation according to the pathology considered. More data are needed to consider jitter as a predictor of BoNT-A clinical efficacy.