Post-thyroidectomy dysphonia in patients with bilateral resection of the superior laryngeal nerve: a comparative spectrographic study

The most serious complications of total thyroidectomy, in cases of widespread and invasive diseases, are mainly hypoparathyroidism and laryngeal inferior nerve palsy. Lesions of the external branch of superior laryngeal nerve instead, although less obvious than the those caused by the recurrent laryngeal nerve lesions, have been taken less into consideration. The frequency of this lesion varies from 14% to 20% of cases, although in reality it is underestimated; in fact, on the one hand it is difficult to assess this, and on the other, post-thyroidectomy dysphonia is often considered inevitable. In the present retrospective research, 15 thyroidectomized patients (4 male, 11 female), have been subjected to qualitative and quantitative evaluation of the voice. Of these, 7 had a nerve lesion, while 8 did not. All the patients received a self-evaluation voice questionnaire (VHI). In all cases, a videolaryngostroboscopy has been carried out and the voice acoustic features examined through a spectrographic analysis. The results showed that removal of the thyroid, at the end of a 12-month post-surgery period, still causes an impact on the qualitative and quantitative aspects of the vocal function, whether the superior larynx nerve was injured or not. The majority of the patients, in both groups, reported that their voice had worsened in quality and durability. Hence, we have shown that the patients with upper larynx nerve lesion have an alteration of F0, show a lower energy level and a modified spectrographic quality compared to patients without injury. This low voice is often considered by patients as a normal consequence of thyroid surgery. The present research confirms that the attempt to identify and protect the superior laryngeal nerve is essential to prevent post-thyroidectomy dysphonia, but this is not sufficient to obtain the best results because of the existence of muscular and psychogenic factors that reduce the still voice capacity of the patient.