Incidence of Injury to External Branch of Superior Laryngeal Nerve as Diagnosed by Acoustic Voice Analysis After Thyroidectomy.

Abstract

Voice related complications are a major cause of morbidity in patients undergoing thyroidectomy in the postoperative period in the modern world. EBSLN being a primary tensor of vocal cords via cricothyroid muscle is important to produce high pitched sound above 150 Hz and it is essential for professional voice users. This nerve is prone to injury during surgery because of its proximity to the upper pole of the thyroid and complex anatomical relationship with the superior thyroid vessels. We aimed to study the occurrence of injury to EBSLN during surgery via acoustic voice analysis and comparing it with the pre-operative values. Patients of benign thyroid swelling with Bethesda type I to III and normal thyroid function tests were taken up for surgery. Pre- and post-operatively acoustic voice analysis was done in a soundproof room. Fundamental frequency (F0), amplitude perturbation (shimmer), fundamental frequency perturbation (jitter), and harmonic/noise ratio (HNR) were calculated and analysed. Intraoperatively, EBSLN was identified in Joll's triangle and preserved. The acoustic voice analysis was performed on the postoperative day one and seven, and compared with the pre-operative values. The mean age of patients was 35.73 ± 9.13 years. Most common age group 36-45 with male to female ratio being 1:9. Cystic colloid goitre was seen in 85% patients. F0 decreased from the preoperative value (221.447 ± 45.981 Hz) on postoperative day one (217.283 ± 46.323 Hz), p-value < 0.01 and on day 7, F0 (219.872 ± 45.096 Hz) p = 0.46. Pitch sigma increase (p < 0.01) from pre-operative (16.791 ± 14.716 Hz) to postoperative day 1 (18.454 ± 15.088 Hz) and on day 7 (17.79 ± 15.315 Hz), p = 0.09. Jitter (%) pre-operatively (0.46%±0.17%), post-operative day 1 (0.45%±0.21%, p = 0.05) and postoperative day 7 (0.44%±0.19%, p = 0.11). Shimmer (dB) the pre-operative (0.582 ± 0.317 dB), post-operative day 1 (0.552 ± 0.301 dB), p = 0.08 and postoperative day 7 (0.566 ± 0.302 dB) p = 0.90 on day 7. HNR pre-operatively (19.009 ± 3.939 dB), postoperative day 1 (18.803 ± 4.14 dB, p = 0.58) and postoperative day 7 (18.740 ± 3.630 dB, p = 0.46). Acoustic voice analysis showed decreased pitch and increase in pitch sigma on postoperative day one which improved on day seven, and it shows that there was no permanent injury to ESBLN during surgery. Acoustic voice analysis being a non-invasive objective procedure, can be used to diagnose EBSLN injury post-thyroidectomy. However, research with large sample size is required to conclusively study the diagnostic efficacy of acoustic voice analysis to diagnose injury to EBSLN.