Botulinum toxin for treating spasmodic dysphonia (laryngeal dystonia): a systematic Cochrane review.

BACKGROUND: Spasmodic dysphonia is a neurological voice disorder characterized by involuntary adductor (towards midline) or abductor (away from midline) vocal fold spasms during phonation which result in phonatory breaks. Botulinum toxin is currently the gold standard of treatment.

OBJECTIVE: To determine the efficacy of botulinum toxin therapy for the treatment of spasmodic dysphonia.

DESIGN: Systematic Cochrane review.

SEARCH STRATEGY: The search strategy for this review complied with Cochrane standards. We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1966 to February 2005), EMBASE (1974 to February 2005), CINAHL (through February 2005), Dissertation Abstracts International (1975 to February 2005) and PsycINFO (1975 to February 2005). The search engine FirstSearch was also used (February 2005). Reference lists for all the obtained studies and other review articles were examined for additional studies.

SELECTION CRITERIA: All randomized control trials where the participants were randomly allocated prior to intervention and in which botulinum toxin was compared to an alternative treatment, placebo or non-treated control group were included.

DATA COLLECTION AND ANALYSIS: Two reviewers independently evaluated all potential studies meeting the selection criteria noted above for inclusion.

MAIN RESULTS: Only one study in the literature met the inclusion criteria. This was the only study identified which reported a treatment/no treatment comparison. It reported significant beneficial effects for fundamental frequency (Fo), Fo range, spectrographic analysis, independent ratings of voice severity and patient ratings of voice improvement.

REVIEWER'S CONCLUSIONS: The evidence from randomized controlled trials supporting the effectiveness of botulinum toxin for management of spasmodic dysphonia is deficient. The lack of supporting evidence from randomized controlled trials results in an inability to draw unbiased generalized conclusions regarding the effectiveness of botulinum toxin for all types of spasmodic dysphonia.