Laryngeal-EMG: frequency of superior laryngeal nerve involvement in iatrogenic and non-iatrogenic vocal fold paralysis

Aim: Damage to the superior laryngeal nerve (SLN) is more difficult to diagnose clinically than a recurrent laryngeal nerve (RLN) lesion. But in many routine laryngeal EMG (LEMG) examinations this nerve is not regularly tested. According to the guides lines for LEMG of the European Laryngological Society we measure all relevant intrinsic laryngeal muscles to evaluate a vocal fold paralysis. In this study we looked at the SLN involvement in vocal fold paralysis patients who attended our neurolaryngology clinic. Method: LEMG results of 339 patients who attended our neurolaryngology clinic between 2008 and 2016 were evaluated. Results were stratified into iatrogenic and non-iatrogenic lesions, and further according to the kind of surgery that led to the paralysis. Cancer related cases were excluded. Results: There were a total of 179 paretic vocal folds with ipsilateral EMG of thyroarytenoid muscle (RLN) and cricothyroid muscles (SLN) EMG that could be evaluated. Patients with vocal fold paralysis after thyroid surgery and surgery of the carotid artery showed a relevant ipsilateral SLN involvement in 50% of cases. In cervical spine surgery it was 36.4%. In 43.5% of non-iatrogenic cases we saw an isolated RLN damage, while 56.5% had a lesion of the vagal stem (SLN + RLN). Conclusions: There was an unexpectedly high share of SLN involvement in iatrogenic paralysis. Therefore we recommend the routine measurement of the cricothyroid muscle during an LEMG examination. Not all idiopathic or viral vocal fold paralysis cases were due to vagal stem lesions but could be limited to the RLN portion. Publication History Publication Date: 18 April 2018 (online) © 2018. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/). Georg Thieme Verlag KG Stuttgart · New York