For many patients who suffer from spasmodic dysphonia, botulinum toxin type A or Botox, injection to the vocal cords is a ritual treatment undergone several times a year to keep the spasms in their voice away. The amount of Botox injected varies from patient to patient. Regardless of the patient and their specific dose, it is intuitive to many patients and healthcare providers that larger doses of Botox injected results in greater side effects (breathy/hoarse voice, dysphagia) and perhaps a longer duration of normal voice. This assumption, logical as it may sound, may not be correct according to a new study published in the June 2007 edition of Otolaryngology-Head & Neck Surgery (Link). According to the study’s author Dr. Christopher Chang (Fauquier ENT Consultants, PLC in Warrenton, Virginia) and coauthors, they actually found that there is a bell curve response of normal voice duration to higher doses of Botox. In other words, at some tipping point, giving higher doses of Botox actually resulted in a decrease in duration of normal voice. The study also reported, not surprisingly, that higher doses of Botox does lead to more severe side effects that lasts longer before normal voice resumes. The impact of this finding is that for some patients, a better and longer response may occur with a LOWER dose of botox.
These results were obtained from 101 patients with adductor spasmodic dysphonia who collectively underwent 876 injections between March 1998 and August 2006. In this study population, the Botox dosage range went from as low as 0.25 Units to as high as 7.5 Units bilaterally. The average dose was 1.62 Units. Based on statistical models, the “ideal” dose was found to be 1.41 Units bilaterally which would give a theoretical zero days of side effects and 87.3 days of normal voice. Based on these same statistical models, giving Botox doses higher than 1.41 units bilaterally theoretically would result in a DECREASE in duration of normal voice while increasing the duration and severity of side effects.
Of course, theory doesn’t always play out in reality as many individuals obtain perfectly good results with Botox dosages much larger than 1.41 Units bilaterally. However, when looking over large numbers of patients with spasmodic dysphonia over many injections over time, the statistical models provided in the study does provide some insights into what may be happening inside the body with each Botox injection.
With larger doses of Botox injected, larger volumes are obviously required. With increased volumes injected, however, there is an increased risk of diffusion of the toxin beyond the vocal cord muscle. Such spread of the toxin beyond the vocal cord muscle would result in a decrease in toxin left behind to exert its effect. Another outcome of this diffusion would be increased side effects as other uninvolved muscles become affected by Botox. As an example stated another way, if 4.0 Units were injected into the vocal cord muscle, 1.5 Units may actually diffuse away affecting other muscles in the area causing side effects. This would leave only 2.5 Units (instead of 4.0 Units) behind to actually affect the vocal cord muscle.
What does this information mean? Well, it does suggest strategies to improve clinical efficacy while causing less severe and shorter duration of side effects. How? By using smaller volumes to decrease risk of diffusion. How can one use less volume, but maintain or even increase effective dosage amounts? By distributing a large dose over multiple injections instead of one injection. By using multiple injections, one is effectively using smaller volumes over multiple injection sites, a strategy known as “saturation of injection site”. Such a strategy may result in improved outcomes after Botox injections without resorting to large doses of Botox with its attendant side effects.
Though physicians throughout the world are investigating other experimental treatment options for spasmodic dysphonia such as selective laryngeal nerve denervation reinnervation, thyroarytenoid myectomy, thyroplasty, and carbon dioxide laser ablation, this study does bring to light that the old standard of Botox injection also has much room to become even better. Although the strategies based on this study have yet to be verified in clinical studies, it does bring up the that fact that even something as straightforward and simple as an injection can be further refined and improved upon.
Dr. Chang does provide Botox injections for patients with spasmodic dysphonia every Friday afternoon in Warrenton, Virignia.
Books on voice therapy found to be a useful ADJUNCT to botox injections:
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