Acoustic changes in spasmodic dysphonia after botulinum toxin injection

Abstract

Summary Botulinum toxin A injections in the left thyroarytenoid muscle were performed in 19 patients with adductor spasmodic dysphonia. Acoustic recordings were taken prior to and 1 week after injection and in a 2-week interval for a normal control group of 11 subjects. Fundamental frequency, standard deviation of fundamental frequency, jitter, shimmer, signal-to-noise ratio, and the voice break factor were studied. Each of the variables were measured from each subject's longest sustained phonation sample of the vowel quality /a/. Findings of the present study indicated: (a) Spasmodic dysphonia patients had significantly higher mean values of standard deviation of fundamental frequency, jitter, shimmer, and voice break factor and significantly lower mean values of signal-to-noise ratio when compared with normal controls; (b) a significant reduction post botulinum toxin injection was found for standard deviation of fundamental frequency and the voice break factor only