Abstract
PurposeThe diagnostic accuracy of intraoperative recurrent laryngeal nerve (RLN) monitoring (IONM) remains controversial. The aim of this study was to evaluate IONM diagnostic accuracy in prognostication of postoperative nerve function in thyroid surgery.MethodsThis prospective study was conducted in 2011–2013. Five hundred consenting patients qualified for total thyroidectomy with IONM (1000 nerves at risk) using NIM 3.0 Response equipment were included. Laryngoscopy was used to evaluate and follow up RLN injury. The primary outcome was diagnostic accuracy of IONM. The receiver operating characteristics (ROC) were used for evaluation of IONM diagnostic accuracy.ResultsLoss of signal (LOS) occurred in 31 cases, including 25 patients with LOS and corresponding vocal fold paresis found in postoperative laryngoscopy (2.5 %), including 20 (2.0 %) temporary and 5 (0.5 %) permanent nerve lesions. The following diagnostic accuracy values were calculated for the criterion recommended by INMSG (V2 amplitude ≤ 100 μV): sensitivity 92.0 %, specificity 99.3 %, positive predictive value (PPV) 76.7 %, and negative predictive value (NPV) 99.8 %. The ROC curve analysis allowed for calculation of the most optimal criterion in prognostication of postoperative vocal fold paresis, namely, V2 amplitude ≤ 189 μV. For this criterion, PPV was 77.4 %, while NPV was 99.9 %.ConclusionsAdherence to the standardized protocol recommended by the International Neural Monitoring Study Group allows for optimizing predictive values of IONM in prognostication of postoperative RLN function. Any changes in the cutoff values for the definition of LOS only marginally improve PPV and NPV of IONM and need to be carefully assessed in multicenter studies.
Highlights
Stimulation techniques allow for certain identification of the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve [1,2,3]
Of 2034 patients referred for thyroid surgery during the study interval, 337 underwent hemithyroidectomy while 1697 were planned for total thyroidectomy and were potential candidates for the study
One thousand one hundred and sixty-four patients did not meet the inclusion criteria, as there was no plan for utilization of IONM during surgery, while 21 subjects refused to participate, leaving 512 eligible patients of which 12 patients were lost to follow-up at 6 months leaving 500 patients (1000 nerves at risk) who were included in the analysis
Summary
Stimulation techniques allow for certain identification of the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve [1,2,3]. RLN identification is often hindered due to neck anatomy altered by a largesize goiter, advanced-stage thyroid cancer, or scarring after previous procedures [2, 4]. In such situations, the neuromapping technique may be of high assistance, allowing for nerve localization prior to its visualization through repeated tissue stimulation in the surgical field [2, 4]. Neuromapping may help in evaluating mechanisms underlying RLN injuries, which is closely associated with its diagnostic value in prognostication of postoperative nerve function [2]. The assessment of qualitative (signal preservation or loss) or quantitative parameters (change of signal amplitude and/or latency) of electromyographic recording may be the basis for intraoperative
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