Modified arytenoid muscle electrode recording method for neuromonitoring during thyroidectomy

Intraoperative neuromonitoring (IONM) is an important application for protecting recurrent laryngeal nerve (RLN) during thyroid surgery. The method for recording arytenoid muscle electromyography (EMG) signals is reported to be feasible and reliable. However, the parameters of EMG signals are not provided. This study aimed to analyze the clinical characteristics of EMG signal parameters by modifying the insertion direction of needle electrodes.

A total of 92 patients who were scheduled to undergo thyroidectomy were recruited. Two paired needle electrodes were inserted in bilateral angle points between rectus cricothyroid muscle and inferior margin of thyroid cartilage (TC) intraoperatively, and then the information from the EMG signals was recorded according to four-step method (V1-R1-R2-V2). Pre-and post-operative laryngo-fiberoscopy was performed to confirm the vocal cord function.

A total of 122 RLNs were successfully recorded during thyroidectomy, with the mean EMG amplitude and latency were 1,857±1,718/2,347±2,323 µV and 3.89±1.12/2.26±0.05 ms for V1/R1 signals before resection, and 1,924±1,705/2,450±2,345 µV and 3.87±1.17/2.27±0.08 ms for R2/V2 signals after resection. There were no significant changes before and after resection, and a normal vocal cord movement was observed postoperatively. The amplitude of left nerves was higher than that of the right ones. Furthermore, the latency of the right vagus was shorter than the left ones, but there was no difference in the amplitude and latency between age, sex and pathological types.

Modified arytenoid muscle EMG recording method was considered to be safe, feasible and reliable. The latency of right vagus EMG signals were shorter than the left ones, and the amplitude of EMG signals might be related to different sides.