Evidence for the effectiveness of botulinum toxin for spasmodic dysphonia from high-quality research designs.

The practice of evidence-based medicine promotes use of the knowledge ascertained from high quality research designs. The objective of this review was to determine what evidence has been provided from high quality research designs (e.g., randomized control trials or high quality prospective, matched group cohort studies), through December of 2006, relative to the effectiveness of botulinum toxin for treating spasmodic dysphonia. Results of the review indicated that no new high quality (Class I or Class II) studies have been published since 2001. One Class I study has been published since 1973, which found significant treatment effects for acoustic and perceptual variables of vocal function. Four Class II studies have been published during this same time frame, all finding significant treatment effects, though the nature of studied factors was variable between investigations. Based on the quality of evidence scale used, botulinum toxin can be considered an effective treatment for adductor spasmodic dysphonia.