Abstract
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.
Highlights
IntroductionThere is not yet a general consensus on the best way to evaluate its efficacy
Anomalies of the neuromuscular junction (NMJ) have been noted at distance from the injected site according to jitter results [95,96,97,98,99] and in placebo side when contralateral Botulinum toxin-A (BoNT-A) injection was made [94,100]
Single-fiber electromyography (SFEMG) is an electromyographic technique, which has revealed the mechanisms of NMJ damage
Summary
There is not yet a general consensus on the best way to evaluate its efficacy. Clinical scales are used, for example the Frequency of Involuntary Movements score and the Severity Rating Scale. Western Spasmodic Torticollis Rating Scale is the most widely used and disseminated clinical scale according to a Cochrane review [3]. The Facial Grading System is employed in HSF assessment and is based on the evaluation of resting symmetry, degree of voluntary excursion of facial muscles, and degree of synkinesis associated with specified voluntary iations
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