A Study of Time to Recovery Following Loss of Neuromonitoring Signal of the Recurrent Laryngeal Nerve in Thyroid Surgery

BACKGROUND: Injuries of the recurrent laryngeal nerve (RLN) during thyroidectomy although infrequent can lead to major morbidity. Permanent RLN injury is uncommon; however, temporary neurapraxia and loss of signal (LOS) during intraoperative neuromonitoring (IONM) are seen more frequently. This study aimed to identify factors associated with type I (segmental) and II (global) LOS of the RLN during thyroid surgery and to analyze time to recovery of vocal cord function. METHODS: This observational retrospective cohort study included 3806 patients (2924 female, 76.8% and 882 male, 23.2%) who underwent hemi or total thyroidectomy in a tertiary center between January 2015 and March 2021. Regression analyses determined factors associated with LOS. Postoperative fibreoptic laryngoscopy was used to measure time to recovery of vocal cord function. RESULTS: RLN LOS occurred in 167 (2.7%) of 5983 nerves at risk during surgery. The rate of Type I and Type II LOS per nerve at risk was 1.4% and 1.3%, respectively. Compared with an indication of malignancy, toxic nodule was associated with 96% increased odds of LOS independent of age and sex (P < 0.001). Time to recovery was reduced for those with a Type II LOS (median 4 weeks) compared to Type I LOS (median 8 weeks and p = 0.04). Female sex and increasing age were independently associated with a longer duration to return of vocal cord function. CONCLUSIONS: Time to recovery of RLN function is significantly reduced for patients with Type II LOS. Toxic thyroid nodules were associated with a higher risk of LOS, and female sex and age are significantly associated with a longer time to recovery.