Reliability of Subjective Endoscopic Parameters in the Differentiation of Essential Voice Tremor and Adductor Spasmodic Dysphonia Using High-Speed Videoendoscopy

Abstract

Certain neurogenic voice disorders present with similar or overlapping audio perceptual voice characteristics. Developing reliable and standardized perceptual measures of vocal fold vibratory characteristics for such voice disorders can enable accurate diagnosis and lead to faster, targeted treatment. In this study, subjective perceptual vocal fold vibratory characteristics and the presence and absence of supraglottic events during phonation were investigated to differentiate between Adductor Spasmodic Dysphonia (ADSD) and Essential Vocal Fold Tremor (EVT) using high-speed videoendoscopy (HSV). The specific aims of the study were to 1) assess which subjective endoscopic vocal fold vibratory measures differentiate EVT from AdSD; and 2) assess the inter-rater and intra-rater reliability of the ratings. High speed video recordings of vibratory vocal fold motion were selected to conduct a retrospective analysis on existing data. The participants were classified into three groups: 16 participants with a diagnosis of Adductor Spasmodic Dysphonia, 8 participants with a clinical diagnosis of Essential Vocal Tremor, and 10 participants with a diagnosis of Both (AdSD with Tremor). The inclusion criteria for HSV data was the presence of a full view of true vocal folds and supraglottic structures during vibration. It was hypothesized that HSV vocal fold vibratory measures and supraglottic events would distinguish EVT and ADSD and these measures would be reliable. In addition, the vocal fold vibratory features would be more reliable than supraglottic events in differentiating between the groups. Results demonstrated mixed reliability for supraglottic and vocal fold vibratory parameters. None of the hypothesized supraglottic parameters demonstrated any significant distinction between diagnostic groups given the three raters’ responses. While all four vocal fold vibratory parameters revealed distinctive patterns between the three diagnostic categories, only two, right/left TVF symmetry and anterior/posterior TVF symmetry, met the requirements for both reliability and differentiation. For these parameters, EVT demonstrated greater vocal fold symmetry in comparison to AdSD; however, those with a differential diagnosis of both demonstrated the highest vocal fold symmetry.