Factors influencing botulinum toxin dose instability in spasmodic dysphonia patients.

Objective: Many patients with spasmodic dysphonia (SD) see consistent effects from botulinum toxin (BTX) injections of the same dose, whereas others require dosage changes over time. We sought to determine whether demographics (age and gender) or environmental factors (smoking) affect the long-term stability of BTX dosing in these patients.

Study Design: Retrospective review.