title: Postoperative vocal cord dysfunction despite normal intraoperative neuromonitoring: an unexpected complication with the risk of bilateral palsy.
abstract: BACKGROUND
  Intraoperative neuromonitoring (IONM) has become standard practice in thyroid surgery for many surgeons. It reduces the risk of vocal cord palsy in high-risk patients and has led to two-stage operations to prevent bilateral palsies. The specificity of detecting nerve injuries is not 100 %, leading to patients with vocal cord dysfunction (VCD) despite regular neuromonitoring (false-negative IONM). We aimed to evaluate possible risk factors for this phenomenon and its importance regarding bilateral palsies.
  
  
  METHODS
  We performed a retrospective analysis of all patients with false-negative IONM.
  
  
  RESULTS
  A total of 2152 patients (3426 nerves at risk) underwent surgery for benign disease between January 2008 and October 2010. Sensitivity for predicting VCD was 85.4 % and specificity 99.0 %. The positive predictive value was 68.0 % and the negative predictive value 99.6 %. We were not able to identify risk factors for false-negative IONM. We found four patients with delayed occurrence of VCD after regular IONM (1-8 weeks). We registered two patients with bilateral VCD after false negative IONM on the first side of bilateral resections (2/7) and four patients with bilateral palsy after correct IONM (4/1256). The relative risk for bilateral VCD between patients with false-negative IONM on the primary resection side and patients with correct IONM was 89.7.
  
  
  CONCLUSIONS
  Although seldom, false-negative IONM is of clinical importance as it bears a high risk of bilateral VCD if it occurs on the first side of a bilateral resection. It can also have a latent occurrence after surgery.
authors.affiliation: Department of General, Visceral, Endocrine, Thoracic, and Vascular Surgery, Lukaskrankenhaus GmbH Neuss, 84 Preussenstrasse, 41464, Neuss, Germany, mmelin@lukasneuss.de.
authors.forename: Magnus
authors.initials: M
authors.lastname: Melin
authors.forename: Katharina
authors.initials: K
authors.lastname: Schwarz
authors.forename: Marc D
authors.initials: MD
authors.lastname: Pearson
authors.forename: Bernhard J
authors.initials: BJ
authors.lastname: Lammers
authors.forename: Peter E
authors.initials: PE
authors.lastname: Goretzki
mesh_terms: D000328:Adult; D000368:Aged; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D011184:Postoperative Period; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012307:Risk Factors; D013959:Thyroid Diseases / Q000601:surgery; D013965:Thyroidectomy / Q000009:adverse effects*; D064706:Vocal Cord Dysfunction / Q000209:etiology*; D014826:Vocal Cord Paralysis / Q000209:etiology*