title: The electrophysiology of thyroid surgery: electrophysiologic and muscular responses with stimulation of the vagus nerve, recurrent laryngeal nerve, and external branch of the superior laryngeal nerve.
abstract: Correlation of physiologically important electromyographic (EMG) waveforms with demonstrable muscle activation is important for the reliable interpretation of evoked waveforms during intraoperative neural monitoring (IONM) of the vagus nerve, recurrent laryngeal nerve (RLN), and external branch of the superior laryngeal nerve (EBSLN) in thyroid surgery.
  
  
  
  Retrospective chart review.
  
  
  
  Data were reviewed retrospectively for thyroid surgery patients with laryngeal nerve IONM from January to December, 2015. EMG responses to monopolar stimulation of the vagus/RLN and EBSLN were recorded in bilateral vocalis, cricothyroid (CTM), and strap muscles using endotracheal tube-based surface and intramuscular hook electrodes, respectively. Target muscles for vagal/RLN and EBSLN stimulation were the ipsilateral vocalis and CTM, respectively. All other recording channels were nontarget muscles.
  
  
  
  Fifty surgical sides were identified in 37 subjects. All target muscle mean amplitudes were significantly higher than in nontarget muscles. With vagal/RLN stimulation, target ipsilateral vocalis mean amplitude was 1,095.7 μV (mean difference range = -814.1 to -1,078 μV, P < .0001). For EBSLN stimulation, target ipsilateral CTM mean amplitude was 6,379.3 μV (mean difference range = -6,222.6 to -6,362.3 μV, P < .0001). Target muscle large-amplitude EMG responses correlated with meaningful visual or palpable muscular responses, whereas nontarget EMG responses showed no meaningful muscle activation.
  
  
  
  Target and nontarget laryngeal muscles are differentiated based on divergence of EMG response directly correlating with presence or absence of visual and palpable muscle activation. Low-amplitude EMG waveforms in nontarget muscles with neural stimulation can be explained by the concept of far-field artifactual waveforms and do not correspond to a true muscular response. The surgeon should be aware of these nonphysiologic waveforms when interpreting and applying IONM during thyroid surgery.
  
  
  
  4 Laryngoscope, 127:764-771, 2017.
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.|Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts, U.S.A.
authors.forename: Whitney
authors.initials: W
authors.lastname: Liddy
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Barber
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.|Surgery of Thyroid and Parathyroid Operative Unit, Sapienza University of Rome, S. Andrea Hospital, Rome, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Cinquepalmi
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.|Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts, U.S.A.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Lin
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Patricio
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.
authors.forename: Natalia
authors.initials: N
authors.lastname: Kyriazidis
authors.affiliation: Surgery of Thyroid and Parathyroid Operative Unit, Sapienza University of Rome, S. Andrea Hospital, Rome, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Bellotti
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.|Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts, U.S.A.
authors.forename: Dipti
authors.initials: D
authors.lastname: Kamani
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.
authors.forename: Sadhana
authors.initials: S
authors.lastname: Mahamad
authors.affiliation: Department of General, Visceral, and Vascular Surgery, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Dralle
authors.affiliation: Department of General, Visceral, and Vascular Surgery, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Rick
authors.initials: R
authors.lastname: Schneider
authors.affiliation: Endocrine Surgery Research Center, Department of Surgical Sciences, University of Insubria, Varese, Italy.
authors.forename: Gianlorenzo
authors.initials: G
authors.lastname: Dionigi
authors.affiliation: Department of Endocrine Surgery, Jagiellonian University College of Medicine, Krakow, Poland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Barczynski
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, Kaohsiung Medical University Hospital, 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 Otorhinolaryngology-Head and Neck Surgery, Kaohsiung Medical University Hospital, Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.|Institute of Clinical Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Feng Yu
authors.initials: FY
authors.lastname: Chiang
authors.affiliation: Division of Thyroid and Parathyroid Endocrine Surgery, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, U.S.A.|Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts, U.S.A.
authors.forename: Gregory
authors.initials: G
authors.lastname: Randolph
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D004558:Electric Stimulation / Q000379:methods*; D004576:Electromyography / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007821:Laryngeal Muscles / Q000294:innervation* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D011300:Preoperative Care / Q000379:methods; D011322:Primary Prevention / Q000379:methods; D012009:Recurrent Laryngeal Nerve / Q000502:physiology; D061226:Recurrent Laryngeal Nerve Injuries / Q000517:prevention & control*; D012189:Retrospective Studies; D013961:Thyroid Gland / Q000294:innervation / Q000601:surgery; D013965:Thyroidectomy / Q000009:adverse effects / Q000379:methods*; D016896:Treatment Outcome; D014630:Vagus Nerve / Q000502:physiology; D014826:Vocal Cord Paralysis / Q000517:prevention & control*
keywords: Thyroid surgery; electromyography; electrophysiology; external branch of the superior laryngeal nerve; intraoperative neural monitoring; recurrent laryngeal nerve; vagus