Effect of Intraoperative Nerve Monitorization on Predicting Vocal Cord Paralysis in Thyroid Surgery

Recurrent laryngeal nerve (RLN) paralysis is a distressing complication of thyroidectomy, and many methods have been investigated for prevention.

The aim of our study is to investigate to what extent intraoperative neuromonitoring (IONM) predicts postoperative RLN paralysis and what factors may be causing it.

Patients who underwent thyroidectomy in our clinic between January 2014 and December 2020 were included. Patient diagnoses, demographic characteristics, laboratory and imaging results, surgical information, and IONM results were evaluated.

Data from 287 patients and 523 RLNs were evaluated. Twenty-two (4.2%) of the RLNs were paralytic. The rate of paralysis was significantly higher in total thyroidectomies than in lobectomies ( p  = 0.046), permanent paralysis rate was higher in left RLNs. Malignancy was statistically associated with permanent paralysis ( p  = 0.017). The rate of overall and permanent paralysis was higher in patients with negative results of first, second response, first, and second laryngeal twitch examinations. The means of the first and second responses of the paralyzed RLNs were lower ( p  = 0.016, p  < 0.01, respectively). The sensitivity of the IONM increased when the new thresholds of the first and second responses were determined to be 155 and 170 µv, respectively, by ROC analysis.

This study demonstrates that voltage variation and magnitude obtained from IONM can be predictive and sensitivity can be increased by using a threshold higher than 100 µV and patients in this range may be at risk for RLN paralysis. Our results may guide future studies of IONM and risk scoring systems to be developed for RLN paralysis.