Factors Associated with Failure of Botulinum Toxin Injection in Adductor Spasmodic Dysphonia.

Failure rate was 12% and associated with patients' first injection with a physician, professional voice user, and lack of breathiness. Dosage change occurred in 29% of injections and was associated with injection side effects, bilateral injections, BTX dose, professional voice user, and shorter duration of good effect.Level of evidence: 3.