Differentiating adductor spasmodic dysphonia (ADSD) from muscle tension dysphonia (MTD) can be difficult. This investigation examined the precision of response to unilateral lidocaine block of the recurrent laryngeal nerve (RLN block) as a potential diagnostic test to discriminate ADSD from MTD.Methods:
Patients with ADSD (n = 23) and MTD (n = 20) were audio-recorded before and during RLN block. The patients completed self-ratings of dysphonia severity, vocal effort, and laryngeal tightness, and blinded listeners completed auditory-perceptual ratings of overall severity, breathiness, and strain of voice samples before and during the block.Results:
Repeated-measures analysis of variance, with “group” (ADSD/MTD) as the between-subjects variable and “time” (before block/during block) as the within-subjects variable, confirmed significant “time” effects, but no significant “group-by-time” interaction effects, indicating that both disorder groups responded favorably to RLN block, according to patient- and listener-based ratings. Furthermore, low estimates of sensitivity and specificity and weak receiver operating characteristic curves confirmed that a positive response to the RLN block test did not distinguish ADSD from MTD.Conclusions:
We conclude that RLN block offers little discriminatory value in the differential diagnosis of ADSD versus MTD, and a positive response to RLN block should not be considered confirmatory of ADSD.