Influence of neural monitoring during thyroid surgery on nerve integrity and postoperative vocal function

Background: Integrity of the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN) can be checked by intraoperative nerve monitoring (IONM) after visualization. The aim of this study was to determine the prevalence and nature of voice dysfunction following thyroid surgery with routine IONM. Methods: Thyroidectomies were performed with routine division of strap muscles and nerve monitoring to confirm integrity of the RLN and EBSLN following dissection. Patients were assessed for vocal function before surgery and at 1 and 3 months after operation. Assessment included use of the Voice Handicap Index (VHI) 10, maximum phonation time, fundamental frequency, pitch range, harmonic to noise ratio, cepstral peak prominence and smoothed cepstral peak prominence. Results: A total of 172 nerves at risk were analysed in 102 consecutive patients undergoing elective thyroid surgery. In 23.3 per cent of EBSLNs and 0.6 per cent of RLNs nerve identification required the assistance of IONM in addition to visualization. Nerve integrity was confirmed during surgery for 98.8 per cent of EBSLNs and 98.3 per cent of RLNs. There were no differences between preoperative and postoperative VHI-10 scores. Acoustic voice assessment showed small changes in maximum phonation time at 1 and 3 months after surgery. Conclusion: Where there is routine division of strap muscles, thyroidectomy using nerve monitoring confirmation of RLN and EBSLN function following dissection results in no clinically significant voice change.