Unilateral versus bilateral botulinum toxin injections in spasmodic dysphonia: acoustic and perceptual results

The present study compared the effects of unilateral and bilateral thyroarytenoid injections of botulinum toxin (botox) for the treatment of adductor spasmodic dysphonia. Using electromyographic guidance, 15 patients received unilateral botox injections of 15 units each and 11 patients received bilateral injections of 2.5 units in each site. Acoustic recordings of the patient's voice were made prior to injection and at two- and six-week intervals after injection. Both the unilateral and bilateral botox injections were associated with significant improvements in spasmodic dysphonia. This was determined by the acoustic measures of vocal shimmer and the number of voice breaks per second and by the perceptual measures of voice spasm severity. Both types of injections were also associated with a significant increase in vocal breathiness at two weeks post-injection. In addition, a number of acoustic measures including maximum phonation time, vocal jitter, and the number of voice breaks/second indicated that unilateral botox injections may provide both superior and longer lasting benefits than bilateral botox injections.