EFFECTS OF BOTULINUM TOXIN ON VOCAL-TRACT STEADINESS IN PATIENTS WITHSPASMODIC DYSPHONIA

Since laryngeal botulinum toxin (BTX) injections have become the treat ment of choice for spasmodic dysphonia, the purpose of this study was to examine its effects on the stability of the upper vocal tract as co mpared to the effects on glottic stability. Two different acoustic met hods were used to analyze voice samples from 16 patients with adductor -type spasmodic dysphonias before and after BTX therapy and from a nor mal control group. Independent acoustic analyses were used to determin e laryngeal and upper vocal tract stability. The results showed signif icantly higher values for the standard deviation of fundamental freque ncy (SDFO), reflecting laryngeal instability, for the patient group th an for the control group and an impressive improvement for the patient s after BTX therapy. Further, the equally high values of SDFO for the initial second and a second from the midsegment of phonation were diff erentially reduced by BTX therapy, resulting in a normal pattern of la ryngeal stability during sustained phonation. The variability of the f irst and second formants, reflecting upper vocal tract instability, sh owed higher values for the patients compared with the control group, b ut this difference was not statistically significant. The present find ings showed that BTX injections to the thyroarytenoid muscle had no di scernible effect on stability of the upper vocal tract.