F116. Correlation of laryngeal adductor reflex, vocal CoMEPs, and vagus nerve mapping during thyroid surgery with immediate and long-term outcome: Description of two cases

Abstract

Introduction The implementation of intraoperative neuromonitoring (IONM) during thyroid surgery has proven to place more emphasis on preserving neurological function, decreasing considerably unfavorable outcomes. Our purpose is to correlate the Laryngeal adductor reflex (LAR), vocal-CoMEPs and vagus-RLN nerve mapping IONM changes throughout thyroid surgery, with immediate and long-term outcome in two representative cases. Methods LAR, a novel method for assessing laryngeal and vagus nerve integrity, vocal-CoMEPs, and nerve mapping, were used for IONM. CoMEPs were elicited by TES (short trains of 5 stimuli of 0.5-ms; ISI of 2-ms; intensity up to 120-mA), and LAR by a single electrical stimulus of the laryngeal mucosa using electrodes attached to the ETT (of 0.1–1-ms; intensity up to 8-mA) on the contralateral side of the operative field. ETT-based electrodes were used to record both LAR and CoMEPs responses from vocal fold muscles. Facial-CoMEPs were elicited as a control parameter. RLN-vagus mapping was done using a hand-held monopolar stimulation probe. Videolaryngoscopy was used for initial intubation with tube position verification prior surgery. Significant changes in LAR amplitude responses were the critical parameters for IONM interpretation. Both patients underwent pre and postoperative direct laryngoscopy and thyroarytenoid (TA) EMG assessments. Results Case 1. – A 43-year-old female presented with a history of multinodular goiter. Total thyroidectomy was scheduled. Preoperative evaluation was normal. Bilateral LAR and vocal-CoMEPs responses were elicited at the onset of surgery. During transecting of the left-thyroid-gland, left vocal-CoMEPs and LAR responses were lost. Left RLN and vagus mapping did not elicit any response after the event. Postoperatively the patient presented with hoarseness. Laryngoscopic examination confirmed paralysis of the left vocal cord and left TA-EMG performed 4 weeks after surgery showed abnormal spontaneous activity; low amplitudes-polyphasic MUPs; and mildly decreased interference pattern, consistent with moderate left RLN dysfunction. Case 2. – A 63-year-old female patient who underwent total thyroidectomy for an intrathoracic multinodular goiter. Preoperative assessment was normal. LAR and vocal-CoMEPs responses were bilaterally elicited at the onset of surgery. During resection of the left thyroid lobe, left vocal-CoMEPs and LAR responses completely disappeared. Left RLN and vagus mapping did not elicit any response after the event. Postoperatively the patient presented with cough and hoarseness. The laryngoscopic examination confirmed paralysis of the left vocal cord and post-op left TA-EMG results were also consistent with moderate left RLN dysfunction. Conclusion There is a good correlation between LAR, vocal-CoMEPs and RLN-vagus mapping changes with immediate and long-term outcome in patients during thyroid surgery. LAR is a novel method for assessing laryngeal and vagus nerve integrity that can be useful for IONM during thyroid surgery.