The effect of total thyroidectomy on the speech production

Voice and speech alternations that can occur after total thyroidectomy are usually due to recurrent or superior laryngeal nerve injury. These alterations may also be associated with other extralaryngeal factors, such as neck muscle dysfunction and scar contracture of the neck. We performed a prospective acoustic analysis on speech changes after surgery, in the absence of laryngeal nerve injury.

Patients aged 19 to 58 years undergoing total thyroidectomy, in the absence of laryngeal/pulmonary disease, previous neck surgery, or other malignant diseases, were recruited prospectively. For the running speech analysis, the speaking fundamental frequencies (SFo), range of SFo and speaking intensity were evaluated before surgery, 7 days, and 1 and 3 months after surgery. For consonant analysis, the acoustic distinctions of stop consonant, the voice onset time (VOT), vowel duration and closure duration were evaluated at the same periods.

SFo and range of SFo were specifically diminished after surgery, while speaking intensities were not changed significantly after surgery. The thyroidectomized speakers displayed systematically varied VOT for the consonant production, which was phonetically representative. However, VOT after surgery could be longer in the strong aspirated and glottalized stops, but not in the lax stop than before surgery. The vowel and closure durations were not affected before and after surgery.

Patients with thyroidectomy have some difficulty of pitch control and consonant articulation during speaking. VOT is also one of the meaningful acoustic parameters and provide a reference for comparing acoustic measures before and after thyroidectomy.