Comparison of Vocal Fold Vibratory Characteristics in Adductor Spasmodic Dysphonia and Muscle Tension Dysphonia Using High-Speed Videolaryngoscopy with 2D and Line Digital Kymography.

Background/Objectives: Differentiating adductor spasmodic dysphonia (AdSD) from muscle tension dysphonia (MTD) is challenging because their auditory-perceptual features often overlap. We examined whether high-speed videolaryngoscopy (HSV) combined with two-dimensional digital kymography (2D-DKG) and line DKG yields qualitative signs and quantitative metrics that distinguish AdSD from MTD. Methods: We analyzed vocal fold vibration in eight patients with AdSD, eight with primary MTD, and eleven vocally healthy controls using a multifunctional system integrating HSV, 2D-DKG, and line DKG. Qualitative features (glottal closure, mucosal wave, phase and amplitude symmetry, oscillatory breaks, and supraglottic hyperfunction) and quantitative indices (closed quotient [CQ], speed quotient [SQ], phase symmetry index [PSI], amplitude symmetry index [ASI]) were assessed. Group differences were tested with one-way ANOVA and Scheffé post hoc comparisons. Results: Oscillatory breaks were observed in 75% of AdSD cases and in 0% of MTD and controls, whereas supraglottic hyperfunction occurred in 100% of MTD and in 0% of AdSD and controls. Quantitatively, CQ, SQ, PSI, and ASI differed between dysphonic groups and controls (p < 0.05), but no quantitative index discriminated against AdSD from MTD. Conclusions: HSV with 2D-/line-DKG provides complementary, objective information on vibratory patterns and supraglottic behavior, supporting targeted qualitative assessment in the clinical differentiation between AdSD and MTD, and highlighting the need for its incorporation into clinical practice as a procedure to assist in the complex diagnostic distinction between these conditions.