Latencies Shorter than 3.5 ms After Vagus Nerve Stimulation Signify a Nonrecurrent Inferior Laryngeal Nerve Before Dissection

Objective: Quantitative electromyographic signals recorded after vagus nerve stimulation during intraoperative neuromonitoring (IONM) were analyzed for their clinical usefulness to identify and track a nonrecurrent inferior laryngeal nerve (NRLN) before dissection. Background: A NRLN is anatomically shorter than a recurrent inferior laryngeal nerve (RLN). This disparity should cause differential latencies after vagus nerve stimulation during IONM, which may aid in distinguishing a NRLN from a RLN. Failure to identify a NRLN early on entails a great risk of nerve injury. Methods: Included in this IONM case-control study were 18 cases with a NRLN and 36 controls with RLN anatomy matched for gender, age, body size, and underlying thyroid and parathyroid disease. Results: All 18 NRLN were found in the right neck only. Cases with a NRLN had significantly shorter latencies than controls (medians of 2.7 vs. 4.6 ms; P < 0.001) but comparable amplitude and duration after stimulation of the right vagus nerve. With a latency threshold of < 3.5 ms, sensitivity, specificity, positive and negative predictive value, and accuracy, respectively, were 100%, 94%, 100%, 97%, and 98% for diagnosis of a NRLN. Conclusions: A latency threshold of 3.5 ms after ipsilateral vagus nerve stimulation during IONM was able to discriminate well between a NRLN and a RLN in adults, helping avoid injury to the aberrant nerve. Additional studies should explore latency thresholds in children and adolescents who have shorter inferior laryngeal nerves and conceivably shorter latencies than adults.