Changes of VKG picture and objective voice analysis in the application of minimal invasive technologies and NM in thyroid gland surgery
Abstract
Present trends in the thyroid gland and parathyroid gland surgery head towards minimization of morbidity and mortality, and the effort is therefore oriented to higher safety of surgical interventions. Thanks to technological progress the minimally invasive video-assisted intraoperative approach to thyroid gland develops in considerable dynamism and the intraoperative NM (IONM) of laryngeal recurrent nerve (nervus laryngeus recurrens - NLR is used as well.
The external branch of upper laryngeal nerve (nervus laryngeus superior- NLS) is monitored less frequently. The present study is intended to verify a hypothesis, whether IONM of NLR and NLS can decrease the incidence of iatrogenic nervous damage.
Moreover we investigated whether certain laryngoscopic examinations, subjective evaluation of voice or objective voice analysis can improve the detection of laryngeal nerves. 150 patients having undergone surgery in a minimum extent of hymithyroidectomy were enrolled into the study. Unilateral paresis of recurrent nerve was determined three times and one of these proved to be transient.
Video kymography examination verified suspect damage of motor branch of NLS in 11 other patients. In five of these patients their condition returned to normal during the observation.
The changes in video kymography well correlated with subjective evaluation of voice by the patients according to the GRBAS (Grade-Roughness-Breathiness-Asthenicity-Strain) scale. In the objective voice analysis the only significantly different parameter related to surgery was the mean basic voice frequency, which significantly decreased after the surgery.
This kind of phenomenon was detected in all the examined groups of patients irrespective of the type and extent of surgical intervention. Psychometric examination using the Voice Handicap Index (VHI) clearly correlates with a significant disorder of vocal cord motility in unilateral paresis.
In less significant changes in innervation and in patients with subjective voice changes the point changes in the questionnaire proved to be a tool of low sensitivity.