A critical estimation of intraoperative neuromonitoring (IONM) in thyroid surgery

We investigated 238 patients with 431 nerves at risk (NAR) undergoing thyroid surgery. Positive identification of the recurrent laryngeal nerve was obtained in 99.3% of NAR with intraoperative neuromonitoring. 19 patients (4.4% NAR) suffered from unilateral vocal cord dysfunction in the early postoperative phase. A complete restitution of vocal cord function could be demonstrated in 18 of these patients, leaving one patient (0.23% NAR) with a permanent vocal cord dysfunction. Our data show that reliable predictions concerning the postoperative outcome of nerve function cannot always be made on the basis of the intraoperative findings. Thus, our own data show a specifity of 98.5% and a negative predictive value of 96.8%. On the other hand, sensitivity was 23.5% and positive predictive value was 40%. Misinterpretation of the intraoperative signal can lead to risky operative manoeuvres. Possible reasons for the misinterpretation of the intraoperative signal and a critical reflection on the possibilities and predictive values of neuromonitoring will be discussed.