Correlation of final evoked potential amplitudes on intraoperative electromyography of the recurrent laryngeal nerve with immediate postoperative vocal fold function after thyroid and parathyroid surgery.

IMPORTANCE

Thyroid and parathyroid surgery are among the most common operations in the United States. Recurrent laryngeal nerve (RLN) injury is an infrequent but potentially detrimental complication.

OBJECTIVE

To correlate the final evoked potential amplitudes on intraoperative electromyography (EMG) after stimulation of the RLN with immediate postoperative vocal fold function after thyroid and parathyroid surgery.

DESIGN, SETTING, AND

PARTICIPANTS

Retrospective observational study at a tertiary academic medical center. We included 674 patients (with 1000 nerves at risk) undergoing thyroid or parathyroid surgery from July 1, 2008, through June 30, 2012.

INTERVENTIONS: Thyroid and parathyroid surgery.

MAIN OUTCOMES AND MEASURES: The association of final evoked potential amplitudes on EMG after thyroid and parathyroid surgery with vocal fold function as determined by postoperative fiberoptic laryngoscopy.

RESULTS

Three patients experienced permanent vocal fold paresis (VFP) secondary to intraoperative RLN transection. Of the remaining 997 RLNs at risk, 22 (2.2%) in 20 patients exhibited temporary VFP on fiberoptic laryngoscopy after extubation. Eighteen patients experienced unilateral temporary VFP, and 2 experienced bilateral VFP without the need for tracheostomy or reintubation. Of the 22 RLNs, postdissection EMG amplitudes were less than 200 µV (true-positive findings) in 21 and at least 200 µV (false-negative finding) in 1. Of the 975 RLNs (97.5%) with normal function, postdissection EMG amplitudes were at least 200 µV (true-negative findings) in 967 and less than 200 µV (false-positive findings) in 8. In regard to immediate postoperative VFP, sensitivity, specificity, positive and negative predictive values, and accuracy of postdissection EMG amplitudes of less than 200 µV were 95.5%, 99.2%, 72.4%, 99.9%, and 99.1%, respectively.

CONCLUSIONS AND RELEVANCE: Intraoperative nerve monitoring of the RLN with EMG provides real-time information regarding neurophysiologic function of the RLN and can predict immediate postoperative VFP reliably when a cutoff of 200 µV is used. The high negative predictive value means that the surgeon can presume with confidence that the RLN has not been injured in the presence of a potential of at least 200 µV. This information would be useful in patients for whom bilateral thyroid surgery is being considered.