Task specificity in adductor spasmodic dysphonia versus muscle tension dysphonia.

OBJECTIVES: Adductor spasmodic dysphonia (ADSD) has been characterized as a "task specific" laryngeal dystonia, meaning that the severity of dysphonia varies depending on the demands of the vocal task. Voice produced in connected speech as compared with sustained vowels is said to provoke more frequent and severe laryngeal spasms. This study examined the diagnostic value of "task specificity" as a marker of ADSD and its potential to differentiate ADSD from muscle tension dysphonia (MTD), a functional voice disorder that can often masquerade as ADSD.

STUDY DESIGN: Case-control study.

METHODS: Five listeners, blinded to the purpose of the study, used a 10 cm visual analogue scale to rate dysphonia severity of subjects with ADSD (n = 36) and MTD (n = 45) producing either connected speech or a sustained vowel "ah."

RESULTS: In ADSD, dysphonia severity for connected speech (M = 6.22 cm, SD = 2.56) was rated significantly more severe than sustained vowel productions (M = 4.8 cm, SD = 2.8 [t (35) = 3.67, P < .001]). In MTD, however, no significant difference in severity was observed for the connected speech sample (M = 5.98 cm, SD = 2.83 versus the sustained vowel M = 5.86 cm, SD = 2.87 [t (44) = 0.378, P = .707]). The receiver operating characteristic (ROC) curve, an index of the accuracy of task specificity as a diagnostic marker, revealed that a 1 cm difference criterion correctly identified 53% of ADSD cases (sensitivity) and 76% of MTD cases (specificity) (chi2 (1) = 6.88, P = .0087).

CONCLUSIONS: Reduced dysphonia severity during sustained vowels supports task specificity in ADSD but not MTD and highlights a valuable diagnostic marker whose recognition should contribute to improved diagnostic precision.