VAGAL NERVE STIMULATION: CLINICAL AND ELECTROPHYSIOLOGICAL EFFECTS ON VOCAL FOLD FUNCTION.

More than 16.000 vagal nerve stimulators (VNSs) have been implanted for refractory epileptic seizures. The most commonly reported side effect is hoarseness. This study examines the effects of VNS placement on vocal fold function. level patients who had undergone VNS placement at our institution were recruited. Subjective evaluation by a panel of speed and language athologists of both connected speech and videolaryngoscopy recordings were used both at rest and during VNS activation. Additional ubjective evaluation included use of the Voice Handicap Index for the study group. These results were compared to data from age- and sexmatched controls. Objective data included maximum phonation time iti the study and control groups, as well as laryngeal electromyography perft>mied on the VNS-implanted patients only. Motor unit potential morphology and recruitment, as well as spontaneous activity, were analyzed bilaterally for the cricothyroid and thyroarytenoid muscles. Significant differences were ound between the study and control groups subjectively for vocal quality and videolaryngoscopy parameters. Vocal fold tension, supragtoltic muscular hyperfunction. and reduced vocal fold mobility were the most common findings during VNS activation. Two of 10 patients had inmiohile left vocal folds in the absence of active stiniulatit>n. The maximum phonation time was generally reduced in the subject group, bul this reductitin did not reach statistical significance. Finally, 6 of 10 patients had abnormal electromy graphic results, including large-amplilude poiyphasic motor unit potentials and decreased recruitment. We conclude that implantation of a VNS can affect local fold function. The effects are magnified during periods of active stimulation. There is the potential for nerve degeneration after prolonged repetitive stimulation, and there may be a trend toward greater vocal fold dysfunction with higher stimulation parameters. [ABSTRACT FROM AUTHOR]