Botulinum Toxin-A Dosing Trends for Adductor Spasmodic Dysphonia at a Single Institution Over 10 Years
Introduction
Adductor spasmodic dysphonia (ADSD) is a neurologic focal dystonia affecting the laryngeal musculature, which is characterized by task-specific involuntary spasms.1 It affects approximately 50,000 people in North America and is associated with marked reduction in quality of life for subjects.2, 3 The most common subtype, adductor, affects approximately 80% of all subjects with ADSD and demonstrates bursts of activity in the thyroarytenoid muscles during speech. Although ADSD has been well-known for more than a century, treatment for the condition proved mostly unsuccessful until Blitzer and colleagues demonstrated the use of botulinum toxin-A in successfully treating the disorder.1
As botulinum toxin-A began to be used more for a wide variety of focal dystonias, some subjects were noted to be developing resistance, manifested by increasing dosages needed to obtain the same treatment effect. In the mid-1990s, several studies that demonstrated the presence of neutralizing antibodies in up to 17% of subjects being treated with the original formulation of botulinum toxin-A for cervical dystonia were conducted.4, 5 After the release of a new formulation of botulinum toxin-A containing less complex protein per unit, a number of investigators have sought to better examine dosing patterns and for the presence of tachyphylaxis.6, 7
We sought to examine our own dosing patterns for botulinum toxin-A to (1) identify the presence of increasing dosages to suggest tachyphylaxis or resistance and (2) identify the point at which dosing seems to stabilize.
Section snippets
Methods
The Emory University School of Medicine Institutional Review Board gave approval for this study. Subjects treated for ADSD between 2003 and 2013 were identified through use of a clinical tracking base. Inclusion criteria included all males and females with ADSD who had been treated consistently for at least 3 years with more than 10 injections. Subjects were excluded from the study if they had abductor-type SD, ADSD mixed with tremor, muscle tension dysphonia, or received injections into the
Results
After querying our clinical database of more than 800 subjects, we identified 113 seen during the time frame of the study. Based on a previous study indicating a dosing titration period of five injections,8 we chose to examine those subjects who had received at least 10 injections to examine the longer trend without being confounded by early titration. This left 54 subjects for analysis. The average age of the subjects was 53.1 years, and 78% of them were female. The average starting dose for
Discussion
Early experience with the original formulation of botulinum toxin-A demonstrated some increased resistance and development of antibodies to the complex protein found.6 Despite the evidence of some increased tachyphylaxis in the treatment of cervical dystonia, its occurrence in the population with ADSD appears to be minimal and seems to have occurred with use of the original botulinum toxin-A formulation.9 Blitzer et al, in their 900-patient experience published in the late 1990s, showed no
Conclusions
Botulinum toxin-A dosing for laryngeal dystonia decreases consistently over time.
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Conflict of interest: None of the authors have any conflicts of interest to report.
Presented at the May 2014 Meeting of the American Laryngological Association, Las Vegas, Nevada.