Quantitative study of voice dysfunction after thyroidectomy.

BACKGROUND Up to 80% of patients without a recurrent laryngeal nerve palsy report alteration in their voice after a thyroid procedure. The aims of this study were (1) to quantify voice changes after thyroid operation; (2) to correlate the changes to the extent of operation; and (3) to correlate voice changes to intraoperative recurrent laryngeal nerve swelling. METHODS Patients undergoing total and hemithyroidectomy were recruited prospectively from the Monash University Endocrine Surgery Unit during a 12-month period. Voice quality was scored subjectively using the Voice Disorder Index (score 0-40, from best to worst) and objectively using the Dysphonia Severity Index (score -5 to 5, from worst to best), before and after operation. These assessments were carried out by 2 speech pathologists. Recurrent laryngeal nerve diameter was measured intraoperatively at the commencement and conclusion of the lobectomy, using Vernier calipers with a resolution of 0.1 mm. Statistical methods used included Student t test, χ2, Wilcoxon signed-rank test, and linear regression. RESULTS A total of 62 patients were included in the study, with a mean age of 48 ± 16 years and a female preponderance (6:1). Overall, the voice quality deteriorated both subjectively (mean Voice Disorder Index 4.2 ± 0.8-9.4 ± 1.2, P < .01) and objectively (mean Dysphonia Severity Index 3.9 ± 0.3-2.8 ± 0.3, P < .01) with thyroid operation. Patients who underwent either hemi- or total thyroidectomy both reported significant deterioration of voice (mean Voice Disorder Index 5.4 ± 1.5-7.9 ± 1.4, P = .02 and 3.4 ± 0.7-10.4 ± 1.8, P < .01 respectively). However, on objective assessment, only total thyroidectomy patients showed significant deterioration (Mean Dysphonia Severity Index 4.0 ± 0.3-2.5 ± 0.3, P < .01). At 6-12 months, both Voice Disorder Index and DSI returned to preoperative levels. Intraoperatively, the recurrent laryngeal nerve diameter increased by 0.58 ± 0.05 mm (1.82 ± 0.05 mm-2.40 ± 0.05 mm; P < .01). In hemithyroidectomy patients, the degree of nerve swelling correlated with the degree of deterioration in objective voice assessment, in that the greater the increase in recurrent laryngeal nerve diameter, the worse the Dysphonia Severity Index score (coefficient -0.4, P = .03). This was not the case in the total thyroidectomy patients. CONCLUSION Voice quality deteriorates with thyroid operation despite functionally intact recurrent laryngeal nerve. While likely multifactorial, the degree of deterioration is related to the extent of operation and may also be related to the degree of recurrent laryngeal nerve swelling. Spontaneous resolution is expected in the majority of patients.