Objective: Adductor laryngeal dystonia (AdLD) is a neurogenic voice disorder in which laryngeal muscles adduct excessively and involuntarily, leading to breaks in phonation and a pressed or strained vocal quality. Past research has mainly examined the perceptual quality and acoustic characteristics of AdLD voices, but little research has been dedicated to specifically analyzing the spastic behaviors themselves. The present study utilizes perceptual voice quality assessment, acoustic voice analysis and high-speed videoendoscopy (HSV) during connected speech to study laryngeal spasms in AdLD.
Methods: Data collection included simultaneous recording of HSV and acoustic data from 5 subjects with AdLD (4 female and 1 male). The data were obtained during production of habitual, soft and hard glottal attacks, reading the Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V) sentences, and the first six sentences of the Rainbow Passage. Three SLPs came into consensus about the identification of laryngeal spasms based on perceptual evaluation of the voice data. The acoustic analysis focused on determining aperiodicity of acoustic waveforms, occurrence of creaks, and spectrum analysis to determine energy distribution across the formants and harmonics. The analysis focused on a time window surrounding the spasms, capturing data just before and after their occurrence. Additionally, high-speed videoendoscopy data were analyzed within the same time windows to assess periodicity of vocal fold vibration and any excessive laryngeal movement.
Results: Findings revealed that voice creaks commonly occurred before or at the onset of adductor-type spasms. These creaks were detected both perceptually, characterized by a low, breathy, or raspy sound, and through audio spectrograms, which displayed slow glottal pulses. The HSV analysis further indicated missing vibratory cycles and irregularity of vibratory patterns. In addition, excessive laryngeal movement was observed leading to the obstruction of the vocal folds by the epiglottis and sphincteric compression.
Conclusions: AdLD can often be difficult to diagnose in a clinical setting due to its similarities to other voice disorders. Identifying the specific characteristics of laryngeal spasms in AdLD through HSV and acoustic analysis in this study will facilitate the development of objective measures to distinguish spastic behaviors from other hyperfunctional vocal patterns as well as other neurological voice disorders, such as vocal tremor.