Botulinum toxin injection and airflow stability in spasmodic dysphonia

OBJECTIVE: The aim of this study was to analyze the effects of botulinum toxin (BT) injection on airflow stability, by measuring mean phonatory oral airflow and its coefficient of variation (CV), in subjects with adductor spasmodic dysphonia (SD). STUDY DESIGN AND SETTING: Twenty-four subjects with SD (aged 31-78 years) and 23 controls (aged 29-63 years) were evaluated for mean airflow and its CV during sustained phonation. Fifteen of the subjects with SD were also evaluated within 3 weeks after BT injection. RESULTS: BT increased airflow in subjects (P = 0.0130) but neither the preinjection nor postinjection values differed significantly from those of controls. Conversely, airflow CV was invariably higher in subjects than in controls (P < 0.0001). In 13 subjects in whom phonation perceptually improved, including 3 in whom airflow did not increase, airflow CV decreased significantly after BT treatment (P = 0.0232). CONCLUSIONS: Subjects with SD have highly unstable phonatory airflow; its CV is a valid measure for assessing the outcome of a BT injection. A reduced airflow CV probably does not depend solely on increased airflow due to thyroarytenoid muscle paresis, and may indicate a change in laryngeal motoneuronal activity. EBM rating: B-3b.