Indirect laryngoscopic approach for injection of botulinum toxin in spasmodic dysphonia

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Abstract
Spasmodic dysphonia is a focal dystonia that causes a loss of the fine control of intrinsic laryngeal muscles and produces a strained staccato voice. Temporary relief from symptoms has been reported in patients treated with botulinum toxin percutaneously injected into the thyroarytenoid muscle. A newly developed method of treatment differs from reported methods by increasing the accuracy of botulinum toxin placement, reducing soft tissue trauma, and applying basic scientific information about the functional histology of intrinsic laryngeal musculature. Sixteen patients with primarily adductor spasmodic dysphonia were treated. Initial assessment included laryngeal examination by indirect laryngoscopy, videoendoscopy, and stroboscopy, neurology examination (Including laryngeal EMG), and vocal function studies with acoustic analysis and aerodynamic studies. A device originally designed for collagen injection allowed the precise microdelivery of toxin to the thyroarytenoid muscle. Indirect laryngoscopy was used to direct the needle, in an attempt to cover a broad area of motor end plates. The minimally effective dose was titrated for each patient, to avoid paralysis and preserve laryngeal function. All patients showed improved voices after treatment. There were no major complications. The basic technique can be performed in the otolaryngologist's office and does not require electromyography equipment or expertise.