Effect of neuromuscular activity on the response to botulinum toxin injections in spasmodic dysphonia

Spasmodic dysphonia (SD), a neurologic disorder characterized by involuntary vocal spasms during speech, has been effectively treated by injections of botulinum toxin (BT) into the laryngeal muscles. The aim of the present study was to determine if the therapeutic response to BT is enhanced by immediate and continuous activation of the injected muscles. Twenty SD patients were randomized into two groups following bilateral injections: vocal rest for 30 minutes and continuous vocalization for 30 minutes. Evaluations consisted of voice ratings by expert observers, acoustic measurements using computer analyses, and laryngeal aerodynamic measurements. The findings suggest that vocal rest, rather than vocalization, produces a superior and longer lasting response in SD patients receiving BT injections. It is recommended that SD patients refrain from post-injection vocalization to maximize the therapeutic effects of BT.