Dosage changes in patients with long-term botulinum toxin use for laryngeal dystonia

Objective To investigate the dosage consistency of botulinum toxin injections in patients with long-term treatment for laryngeal dystonia. Study Design Chart review. Subjects and Methods Patients with laryngeal dystonia who had received at least 20 injections to the thyroarytenoid muscle were selected. Change of botulinum toxin dose, patient-reported effective weeks, and intervals between injections were investigated; data from the first five injections were excluded to eliminate initial dose titration. Results Fifty-five patients with an average follow-up of 12.5 years were identified. Mean dose of botulinum toxin was 2.37 ± 1.6 U at the sixth injection; there was a decrease in mean dose over time, which became statistically significant at the 13th injection with a mean dose of 2.02 ± 1.16 U. Mean duration of good effect and treatment intervals showed no significant change over time. Conclusion Botulinum toxin dose needed for a constant response in treatment of laryngeal dystonia decreases over time, without any accompanying change in effective weeks and intervals.