Adductor spasmodic dysphonia - Changes in dosing after prolonged injections

OBJECTIVES: Botulinum toxin therapy (BTX) for adductor spasmodic dysphonia (ADSD) requires re-injection. The dosing effects after prolonged treatment are not well reported. We report our ten-year experience in the utilization of BTX in ADSD STUDY DESIGN: Retrospective chart review METHODS: From a database of 182 ADSD patients from 1997-2008 treated with BTX, we pulled a subset of 87 patients receiving BTX for greater than 3 visits (average 10.27 visits, range 3-40). We analyzed duration of effect, dosing effects and changes in administration technique. RESULTS: This study group was predominantly female (3:1), presenting at mean age 60. All BTX was administered with laryngeal electromyographic guidance. The average starting dose was 2.28 units (range 1.25 - 3.75). The average dose per injection was 2.15 units (range 0.25-12.5) with an average time interval of 5.6 months between visits. Patients reached a stable dosing regimen at an average of 1.34 months, with 75% optimized after the first visit. There was a trend towards increased average dosage for patients during their 15th treatment visit and up (p=0.14), with increased variation in effect (SD 0.95 vs 1.36). Average time interval between visits tended to decrease over time. Patients who began treatment at older ages in the 6th and 7th tended to require decreasing dosages over time. 10 out of 87 patients progressed to unilateral injections after an average of 12.5 treatment visits, with 70% efficacy. CONCLUSIONS: Botulinum therapy in ADSD is stable and safe. Prolonged treatment over 15 visits may require changes in dosing and technique. Unilateral injections provide an effective alternative to bilateral injection.