A New Electromyographic Definition of Laryngeal Synkinesis

Abstract

Laryngeal synkinesis involves the misdirected reinnervation of an injured recurrent laryngeal nerve to vocal fold abductor and adductor musculature. The resultant laryngeal dyscoordination can cause vocal fold immobility and airway compromise. Although this entity is sometimes considered in the differential diagnosis, it is only demonstrable with laryngeal electromyography (EMG). We propose a new EMG definition of synkinesis to assist in its identification during workup of vocal fold immobility. A retrospective chart review from 1992 to 1997 in the Voice Disorders Clinic identified 10 patients with laryngeal synkinesis. Five patients had bilateral immobility, and 5 had unilateral immobility. Monopolar EMG was performed on all patients. Fine-wire EMG was performed when monopolar EMG did not elucidate the cause of the immobility. The EMG studies revealed synkinetic reinnervation in all subjects. On the basis of the EMG results, 7 of the 10 patients were treated with botulinum toxin to weaken the undesired reinnervation. Three of the 7 patients had benefit from this therapy. Laryngeal synkinesis should be considered as part of the differential diagnosis of vocal fold immobility. Awake laryngeal EMG is the only method to demonstrate synkinesis of the larynx. The diagnosis of synkinesis is clinically significant in cases of immobility to identify patients who might benefit from botulinum toxin therapy. Additionally, the presence of synkinesis in cases of unilateral immobility may be a contraindication to laryngeal reinnervation procedures. The benefit of botulinum toxin therapy is likely greater in the treatment of bilateral as opposed to unilateral immobility.