EFFICACY OF REPEATED BOTULINUM TOXIN INJECTIONS AS A FUNCTION OF TIMING

This pilot study was designed to determine if the interval between rep eated botulinum toxin injections influenced physiologic and histologic effects on laryngeal muscles in a rat model. The physiologic measurem ents included digitized videomicroscopic recording of vocal fold movem ent and electromyography. The histologic measurements included muscle fiber size and digitized optical density of laryngeal muscles after gl ycogen depletion by electrical stimulation. The results demonstrated t hat the effect of timing of the second injection was strongly correlat ed to laryngeal changes. Most notable were results in the subjects tha t underwent injections 6 weeks apart. We hypothesize that these findin gs might be related to terminal axonal sprouting with reinnervation. T he results from this study help confirm and expand the validity of usi ng the rat laryngeal model to understand the effect of botulinum toxin . Moreover, we believe; that the data might be extrapolated to prove u seful in predicting human responses to botulinum toxin treatment for f unctional dystonias such as spasmodic dysphonia.