Long-Term Changes in Botulinum Toxin Injection Dosage for Spasmodic Dysphonia and Associated Factors

Spasmodic dysphonia (SD), or laryngeal dystonia, is a chronic, task-specific, focal dystonia affecting the larynx and primarily interfering with voice production. It has been shown to profoundly affect communication-related quality of life. The injection of botulinum neurotoxin (BTX) into the intrinsic laryngeal muscles remains the standard of care for the management of SD. The benefits of BTX are temporary and last 2-5 months, necessitating repeated injections. However, effects may vary based on the patient and/or type of dysphonia. Patients with adductor SD, which is defined by hyperadduction of the vocal folds, account for the majority of SD while abductor SD, defined by hyperabduction of the vocal folds, is less common. BTX injection provides a longer duration of relief in adductor SD cases. Patients can develop immunoresistance to BTX injection over time, which among other reasons may cause physicians to consider surgical treatment for patients. Patients with progressively increasing BTX doses have been noted at the laryngology practice of the senior author and the characteristics of this population have not been previously characterized. Thus, the purpose of this study is to investigate the relationship between patients who have adequate symptom control with a stable dose of BTX to patients with a BTX dose that is progressively increased. These two patient populations will be compared to determine if factors such as age, sex, type of SD, autoimmune history, associated neurological disease, and family history help to predict whether a patient will have symptom control with a stable dose. Insight into predictors of changes to BTX dosage will improve the standard workup and treatment algorithm for otolaryngology patients presenting with SD.