Comparison of botulinum toxin injection procedures in adductor spasmodic dysphonia

This study compares the effects of unilateral and bilateral thyroarytenoid muscle injections of botulinum toxin in 50 patients with adductor spasmodic dysphonia. Patients were randomly assigned to two treatment groups of 25 patients each and a group of 15 normal control subjects was also included. Using a standard electromyographic guidance procedure, one patient group received unilateral thyroarytenoid muscle injections of 15 units of botulinum toxin, while the second patient group received bilateral thyroarytenoid muscle injections of 2.5 units of botulinum toxin on each side. Follow-up data were obtained at 2- and 6-week intervals. Acoustic and perceptual measures of vocal performance included maximum phonation time, fundamental frequency, standard deviation of fundamental frequency, jitter, shimmer, signal/noise ratio, voice break frequency, spasm severity rating, and vocal breathiness rating. Unilateral and bilateral group comparisons at 2-weeks postinjection revealed no significant difference on any of the measures examined. At 6-weeks postinjection, maximum phonation time was significantly lower in the bilateral group. All other measures failed to differentiate the two patient groups. These results suggest that standard unilateral and bilateral botulinum toxin injections provide equivalent degrees of improvement in the symptoms of spasmodic dysphonia. However, bilateral injections appear to be associated with a longer period of excessive phonatory airflow than do unilateral injections.