Botulinum toxin for relief of bilateral abductor paralysis of the larynx: histologic study in an animal model.

We previously reported the effectiveness of botulinum toxin injections in the cricothyroid muscle under electromyographic guidance for lateralization of the true vocal cord in the mongrel dog. These additional experiments were performed to substantiate the effectiveness of botulinum toxin injections in laryngeal muscle to overcome airway obstruction produced by bilateral abductor vocal cord paralysis. A predetermined aliquot of the toxin was injected into the cricothyroid muscle of ten dogs, the duration of its effectiveness was noted, and repeated injections were given the animals. Biopsies of the injected muscles were obtained in three of the animals for routine histologic and electron microscopic studies. The effects of the toxin were recorded by cinelaryngoscopy and videotape documentation. In all the dogs, the true vocal cord was lateralized effectively and there was no morbidity, dysphagia, aspiration, or deaths. This study also confirms that the effects of the toxin in the canine larynx are spontaneously reversed and that multiple injections do not cause irreparable damage to the laryngeal muscles.