Vibratory Onset of Adductor Spasmodic Dysphonia and Muscle Tension Dysphonia: A High-Speed Video Study

Objective. Adductor spasmodic dysphonia (AdSD) is a challenging voice disorder to diagnose, often erroneously diagnosed as muscle tension dysphonia (MTD) or vocal tremor, due to its similarity in auditory and perceptual presentation. Assessments using laryngoscopy or strobolaryngoscopy procedures have demon- strated limited utility in the diagnosis of spasmodic dysphonia. High-speed videoendoscopy (HSV) provides visu- alization of the precise vibratory pattern of phonatory onset and thus, offers an alternative to previous diagnostic strategies for visual diagnosis of AdSD. The purpose of this study was to examine vibratory onset of patients with AdSD and patients with MTD using HSV methodology. Methods. HSV of six adults with AdSD and five adults with MTD were captured during sustained phonation. Digital kymography was used to obtain precise vibrogram data at the mid -membranous region of the vocal fold prior to and at the onset of phonation. Voice onset delay was examined by (1) quantifying timing of prephona- tory delay and steady state delay and (2) describing vocal fold onset movements qualitatively in each diagnosis. Results. HSV adequately captured the phonatory onset of the vocal folds. Voice onset delay was not signi fi- cantly different between AdSD and MTD. However, there were distinct differences in voice onset gestures. Both AdSD and MTD patients presented with vocal hyperfunction during the onset of phonation. In a subset of AdSD patients, a rapid sustained adduction occurred following the initial vibratory motion. Vocal fold vibration then continued until steady phonation was achieved. This oscillatory break pattern was not observed in patients with MTD. Therefore, there appears to be differences in vocal fold vibratory onset motion between MTD and AdSD. Conclusion. HSV captures the precise vibratory onset in patients with MTD and AdSD. Differences were most notable after vibratory onset as opposed to vibratory delay measurements. Examination of voice onset gesture may offer an additional laryngeal parameter to assist in the differential diagnosis of spasmodic dysphonia.