Objectives/Hypothesis

To report normative electromyography (EMG) data on the external branch of the superior laryngeal nerve (EBSLN) and to compare this to analogous data of the recurrent laryngeal nerve (RLN) and vagus nerve (VN) during intraoperative neural monitoring (IONM) using both the standard monopolar stimulator probe and a novel bipolar stimulator probe.

Study Design

Prospective multiple tertiary care center study.

Method

A prospective study of EBSLN, RLN and VN EMG data in 22 thyroid surgeries was performed. Subjects with preoperative vocal fold paralysis were excluded. Postoperative laryngoscopy was normal in all subjects. Normative EMG data were acquired using both a standard monopolar and a novel bipolar stimulator probe, as well as a novel endotracheal tube. Cricothyroid muscle (CTM) twitch response during EBSLN stimulation was analyzed.

Results

In 100% of cases, EBSLN was identified and quantifiable EMG response was observed. EMG amplitude did not change despite extensive nerve dissection and multiple nerve stimulations. EBSLN amplitude was similar for left and right sides for patients under age 50 and aged 50 or older, for both genders, and with monopolar and bipolar stimulators.

Conclusions

Intraoperative neural monitoring may be used to safely assist in EBSLN identification during thyroid surgery in 100% of patients. A novel endotracheal tube allows for quantifiable EBSLN EMG activity in 100% of cases. Monopolar and bipolar stimulator probes produce similar EMG data.

Level of Evidence 4. Laryngoscope, 124:1035-1041, 2014