Purpose: To evaluate the reliability of intermittent intraoperative neuromonitoring (I-IONM) through recurrent laryngeal nerve (RLN) stimulation and laryngeal palpation in predicting postoperative vocal cord palsy and to examine the reliability of this technique in providing useful information in the decision to perform a staged surgery in initially planned total thyroidectomy.
Methods: This was a retrospective cohort study of patients who underwent thyroid surgery at the ENT Department of the University of Bologna from January 2014 to June 2017. In all cases, preoperative and postoperative laryngoscopy was performed. All surgeries were conducted with I-IONM and RLN simultaneous laryngeal palpation (NSLP) to detect contraction (laryngeal twitch) of the posterior crico-arytenoid muscle. The incidence of vocal cord palsy was calculated for nerves at risk. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV), positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio were calculated with a confidence interval determined at 95% level.
Results: Seven hundred and sixteen patients were enrolled in the study. The incidence of vocal cord palsy was 3.16%. Specificity of I-IONM in predicting vocal cord paralysis was 99.1% and sensitivity was 90%. The NPV was 99.7% and PPV 78.3%. Two-stage thyroidectomy (ST) was performed in 22 cases (22/570: 3.85%). Six patients (27.3%) were false positive and 16 true positive (72.7%) at I-IONM.
Conclusion: High sensitivity and specificity values confirm the validity of I-IONM with NSLP in predicting postoperative normal vocal cord function. Our results confirm that I-IONM may safely guide an ST overall in benign thyroid diseases and in low-grade malignancies.
Keywords: I-IONM; Neuromonitoring; Recurrent laryngeal nerve stimulation; Staged thyroidectomy; Thyroid.