Objective: Development of objective criteria for standardized diagnosis of spasmodic dysphonia (SD) and distinction between its adductor and abductor phenotypes.

Background: SD is a task-specific focal dystonia causing involuntary spasms in the laryngeal muscles and affecting speech production. Depending on the laryngeal muscle affected, adductor (ADSD) and abductor (ABSD) phenotypes lead to either strained and strangled or breathy quality of voice, with characteristic voice breaks on vowels and voiceless consonants, respectively. Due to the absence of diagnostic biomarkers, SD is often misdiagnosed, with patients receiving the accurate diagnosis on average 5.5 years after the first symptom onset.

Method: Audio recordings of voice samples of 52 ABSD or ADSD patients (range 25-78 years, 37 females, 14 males) were analysed for diagnostic classification based on their severity and phenotype. The severity degree was extracted using the mean confidence of pitch estimation. To distinguish between SD phenotypes, the pitch stability during the /h/ phase of symptomatic /ihi/ syllable was examined using standard deviation of the pitch and its confidence of estimation, as well as the location of instabilities during the /h/ phase.

Results: The severity degree determined by the mean confidence of pitch estimation showed a spearman correlation of -0.4, (p-value = 0.003) with the severity rated by perceptual analysis of voice samples.  The classification between ABSD and ADSD became apparent, where the abductor type was generally unstable in pitch or decreasing confidence indicated beginning instabilities, while the adductor type was either overall stable or showed instabilities only at the start of voicing, in 92% of the observed /ihi/ syllables.

Conclusion: The extraction of severity degree based on the mean confidence of pitch estimation is a promising step toward an objective marker of SD diagnosis. The definition of objective distinction criteria between the two SD phenotypes may be achieved using a specified for vowel – /h/- vowel combinations. These findings outline a scientific rationale for the development of a clinically useful discriminatory tool for objective diagnosis of SD.

References: [1] Mor, N., Simonyan, K., & Blitzer, A. (2018). Central voice production and pathophysiology of spasmodic dysphonia. Laryngoscope, 128(1). [2] Creighton, F. X., Hapner, E., Klein, A., Rosen, A., Jinnah, H. A., & Johns, M. M. (2015). Diagnostic Delays in Spasmodic Dysphonia: A Call for Clinician Education. Journal of Voice : Official Journal of the Voice Foundation, 29(5), 592–594.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/objective-evaluation-criteria-for-diagnosis-of-spasmodic-dysphonia/