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Fig. 1. Treatment algorithm for botulinum toxin use in vocal tremor.
performed too close to the hyoid bone due to toxin dif fusion into tongue base musculature; thus, it is essen tial to inject the strap muscles at the midportion of the thyroid lamina in the vertical plane. Development of blocking antibodies to botulinum toxin type A and sub sequent nonresponse is rare and can be overcome in these individuals by injecting with botulinum toxin type B, although this requires retitration and the dura tion of benefit is shorter lived. 22 With regard to dosing regimen, patients with pre dominantly horizontal laryngeal tremor are initially injected with 1 unit of botulinum toxin to each thyroary tenoid muscle via the transcricothyroid approach. Patients with predominantly vertical tremor are injected with 2.5 units to 5 units to each strap muscle, using the technique described in the methods section. Dosages are
then titrated up or down depending on individual patient response. Patients affected with both vertical and horizontal tremor are treated with injections, staged by at least 2 weeks, between the thyroarytenoid and strap muscles in order to minimize risk of dysphagia and aspiration due to the combined effects of weakening vocal fold closure and decreasing laryngeal elevation with swallowing. In previous studies, improvement or resolution of tremor symptoms with oral agents was between 50% to 70% for hand tremor and between 25% to 50% for voice tremor. 3,4,18–21,23,24 Our experience has been that most patients benefit from a combination of a centrally acting oral therapy (prescribed and monitored by a movement disorder neurologist) and peripherally acting botulinum toxin injection. Thus, the majority of our patients are
Laryngoscope 123: October 2013
Sinclair et al.: Botulinum Toxin Injection for Essential Vocal Tremor
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