Background: Thyroidectomy is a standard treatment for thyroid cancers. Hoarseness due to the paralysis of the recurrent laryngeal nerve is one of the most common postoperative complications, and has been studied by many investigators. However, voice quality after thyroidectomy in patients in whom recurrent laryngeal nerves were preserved and vocal cord morbidity was endoscopically normal has not been well studied. To understand voice quality after thyroidectomy further, we conducted a time-course analysis of voice quality in patients who had thyroidectomy with normal cord morbidity by various measures.
Methods: We evaluated voice parameters including the Voice Handicap Index-10 (VHI-10), the vocal efficacy index, the fundamental frequency (F0), the maximum phonation time (MPT), the mean air flow rate (MFR), jitter, shimmer, and the noise-to-harmonics ratio (NHR) before and after total thyroidectomy (TT) or lobectomy (LO) for thyroid cancers in 110 patients in whom the recurrent laryngeal nerves were preserved without apparent injury and normal vocal cord mobility was confirmed by endoscopic examination. Thirteen patients who underwent parotidectomy were enrolled as controls.
Results: Immediately after surgery, significant decreases in MPT (p=0.003) and significant increases in jitters, shimmers, and NHR (p=0.0002, 0.02, and 0.03, respectively) were observed in the patients who underwent TT. In comparison with the controls, jitters and NHR were significantly higher in the patients who had a TT (p=0.03, 0.04). MFR was significantly higher in the patients who had an LO than in the controls (p=0.02). As compared with the patients who had an LO, MPT was significantly shorter (p=0.0004) and MFR and NHR were significantly higher (p=0.004, 0.03) in the patients with a TT. In the patients who had a TT, the MPT immediately after the surgery was significantly longer in the patients who had simultaneously neck dissection (ND) in comparison with the patients who did not have ND. However, all these differences gradually decreased and were not significant at one month after surgery.
Conclusions: Our results suggest that TT and ND have a distinct impact on voice quality after surgical treatment for thyroid cancer, probably due to slight and transient nerve conduction disorders induced by the manipulation around recurrent laryngeal nerves and/or laryngeal edema induced by the disturbance of venous and lymphatic drainages. However, these changes appear to be temporary, lasting only a few weeks.