Evolution of recording methods in thyroid intraoperative neuromonitoring

Intraoperative neuromonitoring (IONM) has been increasingly adopted as an adjunct to visual identification of the recurrent laryngeal nerve during thyroid surgery. The endotracheal tube (ETT)-based surface electrode system is the most widely established recording method; however, its dependence on stable electrode-vocal fold contact makes it vulnerable to false-positive loss-of-signal caused by tube displacement or rotation. These recording-side limitations have driven the development of alternative electrode configurations. Transcartilage electrodes, either needle or adhesive surface types, provide recordings independent of ETT position with less signal variation during tracheal displacement, but require surgical exposure of the thyroid cartilage. More recently, transcutaneous adhesive skin electrodes placed on the anterior neck have been introduced. Preclinical and early clinical studies have shown that these electrodes can record evoked laryngeal electromyography, with lower amplitudes than ETT electrodes but less waveform variation during tracheal displacement. A normative study identified sex, age, body mass index, and surgical extent as factors influencing amplitude, providing initial reference values for clinical use. However, whether conventional loss-of-signal criteria apply to these lower-amplitude recordings remains uncertain. This review focuses on the technical rationale, current evidence, and remaining barriers to clinical adoption of alternative recording methods for thyroid IONM.