Diagnosis and treatment of unilateral cricothyroid muscle paralysis with a modified Isshiki type 4 thyroplasty

Cricothyroid adduction increases tension to the vocal folds, thus increasing fundamental frequency and upper pitch range. We treated 10 patients with cricothyroid muscle dysfunction using this technique. Preoperative electromyographic, acoustic, and perceptual analysis was performed. Intraoperatively the effect of increasing tension on the fundamental, falsetto, and basal frequencies was measured by using a strain gauge to the adducting suture at several tensions and a cervical microphone connected to a pitch meter. Postoperative acoustic and perceptual analysis was then performed up to 18 months later. Analysis of pitch vs. tension curves indicates a near-linear relationship until very high tensions are applied. Statistically significant improvement was achieved in both acoustic and perceptual analysis, although some deterioration was noted between early and late results. Cricothyroid adduction is indicated for a large range of vocal fold tension problems.