Utility of continuous vagal neuromonitoring in thyroid and parathyroid gland surgery: a retrospective study of 500 cases.

Background: Injury to the recurrent laryngeal nerve (RLN) during thyroid and parathyroid surgery can cause vocal cord paralysis (VCP), with severe consequences, particularly in bilateral cases. Intraoperative neuromonitoring (IONM) is useful for identifying the nerve, but there are discrepancies regarding its effectiveness in preventing neural damage. Continuous monitoring, which provides real-time information, could improve postoperative outcomes, yet its adoption has been modest. Although over 90% of endocrine surgeons use some form of monitoring, this procedure has not been fully standardized. This study aims to evaluate the utility of continuous IONM (CIONM) to determine its effectiveness in clinical practice and justify its standardized adoption in other centers within our field. Methods: This is a retrospective observational study with 500 patients who underwent thyroid and parathyroid surgery with CIONM at the General University Hospital of Alicante, Spain. Patients undergoing hemithyroidectomy, total thyroidectomy, and parathyroidectomy were included, excluding those with neurological diseases or under 18 years of age. Laryngeal morbidity data were analyzed using the IBM SPSS® statistical software, version 29.0. Results: Of 477 patients who underwent CIONM, conduction blocks were observed in 92 cases, resulting in 27.6% of transient VCP and 1.1% permanent paralysis. Severe blocks were more frequent in patients with neoplasia and intrathoracic thyroid extension, and most temporary paralysis cases resolved within the first six months. The surgical plan was altered in 31.3% of severe block cases, with traction being the most frequent mechanism of injury. IONM demonstrated high diagnostic accuracy, with a negative predictive value (NPV) of 99% for permanent paralysis and 93% for transient paralysis. Surgical duration over 120 minutes and lymphadenectomy were independent risk factors for nerve injury. Conclusions: CIONM helps reduce recurrent nerve injuries by facilitating their identification and correction during complex surgeries. Additionally, continuous electromyography (EMG) is useful for assessing the functional prognosis of paralysis and allows for early initiation of rehabilitative treatments. However, standardized guidelines and meta-analysis methodology are needed to validate its effectiveness and cost-effectiveness.