Objective: Cricothyroid (CT) muscle twitch inspection with neurostimulation is a widely accepted method to identify the external branch of the superior laryngeal nerve (EBSLN) and its integrity in thyroid surgery. However, there has been no large-scale research to evaluate the diagnostic values of CT muscle twitch inspection based on postoperative electromyography (EMG) results, which are considered the gold standard. In this study, we aimed to demonstrate the diagnostic value of CT muscle twitch inspection based on postoperative EMG.
Study design: Prospective cohort study.
Methods: A total of 454 patients underwent primary thyroid surgery. Among them, 55 patients were excluded because of preoperative vocal fold palsy, problems with the stimulator, or refusal to participate in the EMG study. Finally, 399 patients were prospectively enrolled in this study. Intraoperatively, CT muscle twitch was inspected with neurostimulation. Bilateral EMG examination of the CT muscle was performed 2 to 3 months postoperatively in all patients.
Results: A total of 712 EBSLNs at risk were analyzed in this study. Of these, 21 (2.9%) nerves were visually identified, and positive CT muscle twitch by neurostimulation was observed in 694 (97.5%). Normal results on postoperative EMG of the CT muscle were reported in 657 (92.3%). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 97.7%, 5.5%, 92.5%, and 16.7%, respectively.
Conclusion: CT muscle twitch inspection could be a useful intraoperative tool to determine EBSLN integrity considering its high sensitivity and PPV. However, the test may not completely replace EMG for evaluating EBSLN integrity due to its low specificity and NPV.
Level of evidence: 2b. Laryngoscope, 2654-2661, 2018.
Keywords: External branch of superior laryngeal nerve; cricothyroid muscle twitch; diagnostic value; neurostimulation; thyroid surgery.
© 2018 The American Laryngological, Rhinological and Otological Society, Inc.