Intraoperative EMG recovery patterns and outcomes after RLN traction-related amplitude decrease during monitored thyroidectomy

Kuan-Lin Chiu; Ching-Feng Lien; Chih-Chun Wang; Chien-Chung Wang; Tzer-Zen Hwang; Yu-Chen Shih; Wing-Hei Viola Yu; Che-Wei Wu; Gianlorenzo Dionigi; Tzu-Yen Huang; Feng-Yu Chiang

doi:10.3389/fendo.2022.888381

Intraoperative EMG recovery patterns and outcomes after RLN traction-related amplitude decrease during monitored thyroidectomy

Front Endocrinol (Lausanne). 2022 Aug 11:13:888381. doi: 10.3389/fendo.2022.888381. eCollection 2022.

Authors

Kuan-Lin Chiu¹, Ching-Feng Lien^{1

2}, Chih-Chun Wang^{1

2}, Chien-Chung Wang¹, Tzer-Zen Hwang^{1

2}, Yu-Chen Shih³, Wing-Hei Viola Yu⁴, Che-Wei Wu⁴, Gianlorenzo Dionigi^{5

6}, Tzu-Yen Huang⁴, Feng-Yu Chiang^{1

2}

Affiliations

¹ Department of Otolaryngology-Head and Neck Surgery, E-Da Hospital, Kaohsiung, Taiwan.
² School of Medicine, College of Medicine, I-Shou University, Kaohsiung, Taiwan.
³ Department of Otolaryngology, E-Da Cancer Hospital, Kaohsiung, Taiwan.
⁴ Department of Otorhinolaryngology-Head and Neck Surgery, International Thyroid Surgery Center, Kaohsiung Medical University Hospital, Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
⁵ Division of General Surgery, Endocrine Surgery Section, Istituto Auxologico Italiano IRCCS, Milan, Italy.
⁶ Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy.

Abstract

Objectives: Traction injury is the most common type of recurrent laryngeal nerve (RLN) injury in thyroid surgery. Intraoperative neuromonitoring (IONM) facilitates early detection of adverse electromyography (EMG) effect, and this corrective maneuver can reduce severe and repeated nerve injury. This study aimed to evaluate intraoperative patterns and outcomes of EMG decrease and recovery by traction injury.

Methods: 644 patients received nerve monitored thyroidectomy with 1142 RLNs at risk were enrolled. Intermittent IONM with stimulating dissecting instrument (real-time during surgical procedure) and trans-thyroid cartilage EMG recording method (without electrode malpositioning issue) were used for nerve stimulation and signal recording. When an EMG amplitude showed a decrease of >50% during RLN dissection, the surgical maneuver was paused immediately. Nerve dissection was restarted when the EMG amplitude was stable.

Results: 44/1142 (3.9%) RLNs exhibited a >50% EMG amplitude decrease during RLN dissection and all (100%) showed gradual progressive amplitude recovery within a few minutes after releasing thyroid traction (10 recovered from LOS; 34 recovered from a 51-90% amplitude decrease). Three EMG recovery patterns were noted, A-complete EMG recovery (n=14, 32%); B-incomplete EMG recovery with an injury point (n=16, 36%); C-incomplete EMG recovery without an injury point (n=14, 32%). Patients with postoperative weak or fixed vocal cord mobility in A, B, and C were 0(0%), 7(44%), and 2(14%), respectively. Complete EMG recovery was found in 14 nerves, and incomplete recovery was found in another 30 nerves. Temporary vocal cord palsy was found in 6 nerves due to unavoidable repeated traction.

Conclusion: Early detection of traction-related RLN amplitude decrease allows monitoring of intraoperative EMG signal recovery during thyroid surgery. Different recovery patterns show different vocal cord function outcomes. To elucidate the recovery patterns can assist surgeons in the intraoperative decision making and postoperative management.

Keywords: electromyography (EMG); intraoperative neuromonitoring (IONM); recurrent laryngeal nerve (RLN); thyroid surgery; traction injury.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Electromyography
Humans
Recurrent Laryngeal Nerve Injuries*
Thyroidectomy
Traction
Vocal Cord Paralysis*