Int J Thyroidol IJT International Journal of Thyroidology 2384-3799 2466-1899 Korean Thyroid Association 10.11106/ijt.2018.11.2.130 Original Article Efficacy of Intraoperative Neural Monitoring (IONM) in Thyroid Surgery: the Learning Curve Kwak Min Kyu Lee Song Jae Song Chang Myeon Ji Yong Bae Tae Kyung Department of Otorhinolaryngology-Head and Neck Surgery, Hanyang University College of Medicine, Seoul, Korea. Correspondence: Kyung Tae, MD, PhD, Department of Otorhinolaryngology-Head and Neck Surgery, Hanyang University College of Medicine, 222-1 Wangsimni-ro, Seongdong-gu, Seoul 04763, Korea. Tel: 82-2-2290-8585, Fax: 82-2-2293-3335, kytae@hanyang.ac.kr 11 2018 30 11 2018 11 2 130 136 15 10 2018 29 10 2018 29 10 2018 Copyright © 2018. the Korean Thyroid Association 2018 The Korean Thyroid Association This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Background and Objectives

Intraoperative neural monitoring (IONM) of recurrent laryngeal nerve (RLN) in thyroid surgery has been employed worldwide to identify and preserve the nerve as an adjunct to visual identification. The aims of this study was to evaluate the efficacy of IONM and difficulties in the learning curve.

 Materials and Methods

We studied 63 patients who underwent thyroidectomy with IONM during last 2 years. The standard IONM procedure was performed using NIM 3.0 or C2 Nerve Monitoring System. Patients were divided into two chronological groups based on the success rate of IONM (33 cases in the early period and 30 cases in the late period), and the outcomes were compared between the two groups.

 Results

Of 63 patients, 32 underwent total thyroidectomy and 31 thyroid lobectomy. Failure of IONM occurred in 9 cases: 8 cases in the early period and 1 case in the late period. Loss of signal occurred in 8 nerves of 82 nerves at risk. The positive predictive value increased from 16.7% in the early period to 50% in the late period. The mean amplitude of the late period was higher than that of the early period (p<0.001).

 Conclusion

IONM in thyroid surgery is effective to preserve the RLN and to predict postoperative nerve function. However, failure of IONM and high false positive rate can occur in the learning curve, and the learning curve was about 30 cases based on the results of this study.

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BMI: body mass index, N: number

 Correlation of postoperative vocal cord paralysis and loss of signal in intraoperative neural monitoring according to the period

LOS: loss of signal, VCP: vocal cord paralysis

 Validation of the performance of intraoperative neural monitoring for predicting postoperative recurrent laryngeal nerve function according to the period

NPV: negative predictive value, PPV: positive predictive value

 Mean electromyographic amplitude according to the period

NAR: nerve at risk

 Mean electromyographic amplitude according to neuromonitoring devices

C2: C2 Nerve Monitoring System (Inomed, Teningen, Germany), NAR: nerve at risk, NIM 3.0: NIM 3.0 Nerve Monitoring System (Medtronic Xomed, Jacksonville, FL, USA)