title: Recurrent laryngeal nerve injury with incomplete loss of electromyography signal during monitored thyroidectomy-evaluation and outcome.
abstract: OBJECTIVE
  During monitored thyroidectomy, a partially or completely disrupted point of nerve conduction on the exposed recurrent laryngeal nerve (RLN) indicates true electrophysiologic nerve injury. Complete loss of signal (LOS; absolute threshold value <100 μV) at the end of operation often indicates a postoperative vocal cord (VC) palsy. However, the evaluation for the injured RLN with incomplete LOS and its functional outcome has not been well described.
  
  
  METHODS
  Three hundred twenty-three patients with 522 RLNs at risk who underwent standardized monitored thyroidectomy were enrolled. The RLN was routinely stimulated at the most proximal (R2psignal) and distal (R2dsignal) ends of exposure after thyroid resection to determine if there was an injured point on the RLN. Pre- and postoperative VC function was routinely examined.
  
  
  RESULTS
  Twenty-nine RLNs (5.6 %) were detected with an injury point. Five nerves had complete LOS and other 24 nerves had incomplete LOS where the R2p/R2dreduction (% of amplitude reduction compared with proximal to distal RLN stimulation) ranged from 22 to 79 %. Postoperative temporary VC palsy was noted in those five RLNs with complete LOS (final vagal signal, V2< 100 μV) and four RLNs with incomplete LOS (R2p/R2dreduction 62-79 %; V2181-490 μV). In the remaining 20 nerves with R2p/R2dreduction ≤53 % (V2373-1623 μV), all showed normal VC mobility. Overall, false negative results were found in two RLNs (0.4 %) featuring unchanged V2and R2p/R2dbut developed VC palsy.
  
  
  CONCLUSIONS
  Testing and comparing the R2p/R2dsignal is a simple and useful procedure to evaluate RLN injury after its dissection and predict functional outcome. When the relative threshold value R2p/R2dreduction reaches over 60 %, surgeon should consider the possibility of postoperative VC palsy.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Kaohsiung Medical University Hospital, Kaohsiung Medical University, 100 TzYou 1st Road, Kaohsiung City, 807, Taiwan.|Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Che-Wei
authors.initials: CW
authors.lastname: Wu
authors.affiliation: Department of Breast Thyroid Surgery, The People's Hospital of Dong Ying, Shan Dong province, China.
authors.forename: Min
authors.initials: M
authors.lastname: Hao
authors.affiliation: Department of Breast Thyroid Surgery, The People's Hospital of Dong Ying, Shan Dong province, China.
authors.forename: Mengzi
authors.initials: M
authors.lastname: Tian
authors.affiliation: 1st Division of Surgery, Research Center for Endocrine Surgery, Department of Surgical Sciences and Human Morphology, University of Insubria (Como-Varese), Varese, Italy.
authors.forename: Gianlorenzo
authors.initials: G
authors.lastname: Dionigi
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Ralph P
authors.initials: RP
authors.lastname: Tufano
authors.affiliation: Department of Surgery, Korea University College of Medicine, Seoul, South Korea.
authors.forename: Hoon Yub
authors.initials: HY
authors.lastname: Kim
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, South Korea.
authors.forename: Kwang Yoon
authors.initials: KY
authors.lastname: Jung
authors.affiliation: Department of Thyroid and Parathyroid Surgery, China-Japan Union Hospital, Jilin Provincial Key Laboratory of Surgical Translational Medicine, Jilin University, Changchun, Jilin, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Thyroid and Parathyroid Surgery, China-Japan Union Hospital, Jilin Provincial Key Laboratory of Surgical Translational Medicine, Jilin University, Changchun, Jilin, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Sun
authors.affiliation: Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.|Department of Anesthesiology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: I-Cheng
authors.initials: IC
authors.lastname: Lu
authors.affiliation: Department of Anesthesiology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Pi-Ying
authors.initials: PY
authors.lastname: Chang
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Kaohsiung Medical University Hospital, Kaohsiung Medical University, 100 TzYou 1st Road, Kaohsiung City, 807, Taiwan. fychiang@kmu.edu.tw.|Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan. fychiang@kmu.edu.tw.
authors.forename: Feng-Yu
authors.identifier: http://orcid.org/0000-0003-1052-5348
authors.initials: FY
authors.lastname: Chiang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004576:Electromyography; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D009431:Neural Conduction / Q000502:physiology; D011183:Postoperative Complications / Q000175:diagnosis / Q000209:etiology*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D020127:Recovery of Function; D061226:Recurrent Laryngeal Nerve Injuries / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D013959:Thyroid Diseases / Q000503:physiopathology / Q000601:surgery; D013965:Thyroidectomy / Q000009:adverse effects*; D016896:Treatment Outcome; D014826:Vocal Cord Paralysis / Q000175:diagnosis / Q000209:etiology*; D055815:Young Adult
keywords: Electromyography; Intraoperative neuromonitoring; Loss of signal; Recurrent laryngeal nerve; Thyroid surgery