Dysphonia severity degree and phonation onset latency in laryngeal adductor dystonia

Although the latency between the initiation of thyroarytenoid electrical activity and the onset of phonation generally is increased in patients with adductor laryngeal dystonia, there is disagreement about whether there is overlap of latency values in these patients and normal subjects. The goal of this article was to compare the severity of dysphonia with the latency between electrophysiological activation of the thyroarytenoid muscle (TA) and the onset of phonation in patients with adductor laryngeal dystonia and compare the values with normal controls. Twenty-one patients with adductor dystonia and 15 control patients underwent laryngeal electromyographic (EMG) examination of the left TA. We measured the latency from initiation spike of the electric activity of the TA muscle to the onset of phonation. Three speech-pathologists/voice specialists arrived at a consensus to rate the perceptual evaluation of voice quality for the study group. The average latency measured for patients with mild dysphonia was 332 milliseconds, for moderate dysphonia was 426 milliseconds, and for the severe dysphonia was 792 milliseconds. We used the Spearman's correlation test to compare the latency time values and the dysphonia's degree of severity (P<0.05). Latency was significantly and directly related to the degree of severity of dysphonia.