Prospective study of the impact of thyroid hormone replacement on objective voice parameters

Hypothyroidism has long been considered to have an impact on phonation. In this study, objective evaluation of vocal function in women with hypothyroidism was performed in order to characterize potential dysphonia; their subsequent response to thyroid hormone replacement was prospectively studied. It was hypothesized that thyroid hormone replacement therapy in this cohort would have an objectively measurable impact on vocal function.

Prospectiv evaluation of objective voice parameters and concurrent determination of serum thyroid status was executed both before and after thyroid hormone replacement in a cohort of patients who had had total thyroidectomy. Objective voice parameters before and after treatment were compared.

Twenty-four female subjects were recruited over an 18-month period. After surgery, all subjects were hypothyroid (mean thyroid-stimulating hormone level, 81.38 mIU/L; range, 25.26 to 100.00 mIU/L) before replacement. After hormone therapy, their mean thyroid-stimulating hormone level dropped to 1.20 mIU/L (range, 0.28 to 3.83 mIU/L). The mean fundamental frequency significantly increased from a pretreatment average of 223.48 +/- 36.10 Hz to 237.64 +/- 38.81 Hz. Other measured voice parameters (jitter, shimmer, amplitude perturbation quotient, pitch perturbation quotient, noise-to-harmonics ratio, and maximum phonation time) were not affected.

Thyroid hormone replacement therapy following total thyroidectomy has a measurable impact on mean fundamental frequency in female patients. The mechanism of this effect is not known.