Adductor spasmodic dysphonia involves an overadduction of the vocal folds during speech causing uncontrolled voice and pitch breaks and slow, effortful speech. The disorder is resistant to speech therapy and often recurs following initial benefit from unilateral recurrent laryngeal nerve resection. Botulinum toxin injections into multiple sites of the thyroarytenoid muscle on one side were performed in 16 patients. Speech was recorded prior to injection and three times post-injection. Symptoms were measured by two examiners from speech spectrograms without knowledge of speaker identity or recording session. Significant (p less than or equal to 0.03) reductions in pitch and voice breaks, phonatory aperiodicity, and sentence time occurred only when injections resulted in unilateral vocal fold paralysis. Symptoms returned with the restoration of vocal fold movement, 3 months later. Reduction in speed of swallowing without aspiration was reported in 80% of cases. Although speech volume was reduced, there were no instances of aphonia.

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Ten patients with abductor spasmodic dysphonia, who exhibited spasmodic bursts and heightened activity of the cricothyroid muscle during speech, were selected for participation. Between 5 and 20 U of botulinum toxin type A were injected into both right and left cricothyroid muscles. Six patients benefited substantially, whereas four did not. Acoustic analyses of voice patterns showed similar changes to the clinical impressions. Significant group improvements were found in sentence duration while selected patients improved in the proportion of their speech that was voiced and the duration of their voiceless consonants. Those patients with abductor spasmodic dysphonia and other muscle abnormalities in addition to the cricothyroid and with constant breathiness did not benefit.

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