Incidence and risk factors for recurrent laryngeal nerve injury after thyroid surgery
Authors: Al-Hakami Hadi , Al Garni Mohammed 
Published: August 2024

Abstract
Objectives
Injury to the recurrent laryngeal nerve (RLNI) is a known possible morbidity after thyroid surgery. The clinical presentation varied in severity, from changes in voice quality and swallowing in unilateral cases to airway compromise in bilateral cases. In minor cases, vocal fold paralysis (VFP) may occur unnoticed. Although many intraoperative measures have been implemented to minimize nerve injury, the risk remains, either transient or permanent. This study evaluated the incidence and potential risk factors of recurrent laryngeal nerve injury after thyroidectomy.

Methods
Retrospective data analysis was conducted on 1368 patients who underwent thyroidectomy at the National Guard Hospital, King Abdul-Aziz Medical City, Jeddah, Saudi Arabia, between January 2008 and December 2021. Evaluations were conducted on the pathological features, surgical procedure type, and state of the recurrent laryngeal nerve during surgery as contributing to recurrent laryngeal nerve injury. All patients underwent preoperative and postoperative indirect laryngoscopy examinations with or without videostroboscopy. Physiological testing of the RLN using neurostimulation and laryngeal palpation (NSLP) or intraoperative neuromonitoring (IONM) was performed in all cases. VFP was considered present when vocal fold mobility was absent or significantly reduced.

Results
A total of 1368 patients (2177 nerves at risk) who underwent thyroidectomy and fulfilled the inclusive criteria (809 bilateral, 559 unilateral) were evaluated. A total of 62% of patients were more than 45 years old, and the mean age was 48.36 ± 13.03 with a male-to-female ratio of 1:3.6. Eight-hundred one (58.6%) patients underwent total or subtotal thyroidectomies (1602 nerves at risk). Two-hundred seventy-six patients underwent hemithyroidectomy (276 nerves at risk), and 291 patients underwent completion or redo surgeries (299 nerves at risk). Of these 1368 patients, post-surgery laryngoscopy showed reduced or absent vocal fold mobility in 47 (3.4%) patients. Forty-three out of 47 patients had unilateral vocal fold paralysis, and 4 had bilateral VFP. When we analyzed the three risk factors statistically significant for postoperative RLN palsy, age (OR, 1.01; 95% CI, 0.98–1.05; p = 0.365) became non-significant. The other risk factors (extent of surgery and histopathological diagnosis) remained statistically significant (p = 0.004 and 0.031). After adjustment, the extent of surgery, including total thyroidectomy and revision surgery, was strongly associated with a higher risk of odds of postoperative RLN palsy. Physiological RLN stimulation was performed in all cases with NSLP or INOM, and no significant association was observed in the incidence of VFP (p = 0.365). In most cases, symptoms were spontaneously resolved with recovery of vocal fold movement within a few months.

Conclusion
In this study, 3.4% of the recurrent laryngeal nerve showed postoperative dysfunction either transient or permanent VFP. Intraoperative identification of the nerve remains the gold standard of care during thyroidectomy. Neuromonitoring aids in detecting the nerve, particularly in severe cases, but does not reduce the nerve injury compared to NSLP.