Effect of Botulinum Toxin Injection on Airflow Stability in Spasmodic Dysphonia

Objectives: The aim of this study was to analyze the effects of botulinum toxin (BT) injection on mean phonatory airflow and its coefficient of variation (CV) in patients with adductor spasmodic dysphonia (SD). Methods: Mean oral airflow and its CV were measured in 15 SD patients (age, 31–78 years) and 23 controls (age, 29–63 years) during sustained emission of the vowel /a/. The measurement was repeated in the SD patients 3–4 weeks after BT injection. Results: Mean airflow increased in the SD patients after BT treatment (P = 0.02) but neither the pre- and posttreatment values were significantly different from those of controls. Airflow CV was much higher in the SD patients (P < 0.0001), but significantly decreased after BT treatment (P = 0.01) in 13 perceptually improved patients, including 3 showing an unchanged airflow. Conclusions: These results confirm that patients with SD have a highly unstable phonatory airflow and that airflow CV can be a valuable measure of treatment outcome after a BT injection. The reduction in airflow CV is not strictly related to increased airflow due to thyroarytenoid muscle paresis and may be a sign of a change in the activity of laryngeal motoneurons.