Endocrine Abstracts

Vocal morbidity related to the external branch of the superior laryngeal nerve following thyroidectomy

Objectives: Damage to the external branch of the superior laryngeal nerve (EBSLN) can cause a vocal morbidity following thyroidectomy. However its diagnosis is challenging. Here we aim to determine the vocal, endoscopic and acoustic characteristics of a damage of the EBSLN as well as factors associated to its occurrence.

Materials and methods: We conducted a prospective study that included patients who underwent a partial or total thyroidectomy between September 2021 and January 2022 and who did not present a pre-operative laryngeal dysfunction. A vocal assessment was performed at pre-operatively and post-operatively at day1, one month and 6 months. We confirmed the diagnosis of EBSLN damage based on endoscopic findings and determined the vocal alterations related to its damage.

Results: We included 51 patients. We did not perform a systemic identification of the EBSLN. We observed endoscopic signs in favor of a damage of the EBSLN in 9 patients that included the following: shortening, thickening and bowing of the vocal fold in respectively 77.78%, 33.33% and 11.11% of cases as well as shortening of the ary-epiglottic fold (11,11%) and deviation of the glottis axe towards the paralyzed side (11,11%). We did not any vocal symptom in 6 patients while three patients presented a decrease of the habitual vocal pitch, vocal fatigue and dysphonia. Fundamental frequency (F0) deceased in 6 patients post-operatively with respective F0 values of 267 Hz, 238 Hz and 242 Hz at the pre-operative, one-day and one-month post-operative assessments. However the decrease was not significant. We did not record a significant difference of the degree of F0 decrease in patients with or without a damaged EBSLN. Jitter and shimmer increased in 5 patients with a damaged EBSLN but the increase was not significant. The used hemostasis technique for the ligature of the superior pedicle, operator experience and goiter size were not associated the EBSLN damage.

Conclusion: A damage of the EBSLN can cause a vocal alteration following thyroidectomy. Its clinical manifestation can remain unnoticed while endoscopic findings are neither constant no pathognomonic. Acoustic findings included a decrease of F0 and an increase of jitter. We did record any factor significantly associated with an increased risk of a damage of the EBSLN. Here we emphasize on the importance of suspecting a damage of the EBSLN in the case of a vocal alteration with normal vocal fold mobility.