Background: The vocal symptoms of spasmodic dysphonia (SD) are characterised by spasms of the laryngeal muscles and the objective of intervention is to reduce or eliminate these spasms. The purpose of this study is to assess the efficacy of botulinum toxin (BTX) in the treatment of SD by a meta-analytic review of existing research. Study Design A quantitative assessment of the efficacy of botulinum toxin injections (BTX) in the treatment of spasmodic dysphonia (SD) was conducted by a meta-analysis (or best synthesis) systematic summary of existing research.

Method: A MEDLINE and hand search of the published literature from 1988-1999 of BTX treatment for SD identified 61 studies. Of these, 27 studies provided sufficient data to be amenable to meta-analytic summary and constitute the database for this study. The magnitude of the experimental treatment effect, effect size (ES), was calculated comparing before and after measures of the dependent variables. Each study was coded in terms of subject characteristics, treatment characteristics, and outcome variables.

Results: The 27 studies contained 199 comparisons across 898 treated patients. The average treated SD patient experienced an effect size (ES = .983 representing an 84% improvement as a result of BTX treatment.

Conclusion: On the basis of this meta-analysis, botulinum toxin (BTX) injections was shown to be a highly effective treatment in the management of vocal symptoms in spasmodic dysphonia (SD).