Postoperative vocal cord dysfunction despite normal intraoperative neuromonitoring: an unexpected complication with...

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.

We performed a retrospective analysis of all patients with false-negative IONM.

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.

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.