The role of laryngeal electromyography in vagus nerve stimulation-related vocal fold dysmotility

Vagus nerve stimulation (VNS) is a useful tool for drug-resistant epilepsy, but it induces known laryngeal side effects, with a significant role on patients' quality of life. VNS patients may show persistent left vocal fold (LVF) palsy at rest and/or recurrent LVF adduction during stimulation. This study aims at electromyographically evaluating laryngeal muscles abnormalities in VNS patients. We compared endoscopic laryngeal evaluation data in six VNS patients with laryngeal muscle electromyography (LMEMG) carried out on the thyroarytenoid, cricothyroid, posterior cricoarytenoid, and cricopharyngeal muscles. Endoscopy showed LVF palsy at rest in 3/6 patients in whom LMEMG documented a tonic spastic activity with reduced phasic modulation. In four out of six patients with recurrent LVF adduction during VNS activation, LMEMG showed a compound muscle action potential persisting for the whole stimulation. This is the first LMEMG report of VNS-induced motor unit activation via recurrent laryngeal nerve and upper laryngeal nerve stimulation. LMEMG data were could, therefore, be considered consistent with the endoscopic laryngeal examination in all patient.