Blink reflex excitability recovery curves in patients with spasmodic dysphonia.

We studied 12 patients with spasmodic dysphonia (SD) and 12 healthy control subjects. The patients, who had no symptomatic involvement of the eyes, were evaluated for increased excitability of blink reflexes, which is characteristic of blepharospasm and generalized dystonia. We measured symptom severity from sound spectrograms of five sentences, including sentence production time, number of pitch phonatory breaks, and percentage of aperiodic phonation. We evoked blink reflexes by electrical and mechanical stimulation, and assessed excitability by obtaining excitability recovery curves and responses to trains of stimuli. Patients and controls differed from each other in test R2 amplitude attenuation across all intervals from 150 to 1,000 msec to electrical and mechanical stimulation. Our results indicate that patients with SD have increased excitability of blink reflexes, which suggests that the dystonia involves not only the larynx but also other anatomical structures.