Androgenic and anabolic hcrmones have often been used in treating various diseases. The treatment for dysphonia, one of their side effects, has not yet been ascertained. We have employed a new surgical procedure and have obtained successful results.
It may be said that when the cricothyroid muscle is more dominant than the thyroarytenoid (TA) muscle, voice will be high-pitched.
Based on this concept, a method of weakening the activity of the TA muscle was assumed to be effective for eliminating abncrmal high-pitched voice. Prior to clinical application, we designed electrophysiological and histochemical experiments.
Using canine larynx, a portion of the terminal branch of the recurrent nerve in the TA muscle was severed by making an incision onto the vocal cord parallel to its free edge. By deepening the incision, evoked electromyographic activity was gradually decreased presumably due to reduction in action potentials of the muscle fibers to be picked up by the electrodes. Similar results were also obtained in chronic experiments using canine larynx.
A histochemical study revealed that motor end-plates were remarkably degenerated one month after ncision. This finding would indicate that the incision has severed the branch in the TA muscle.
This method have been successfully employed for 8 clinical cases. In this paper, the results were reported and descussed from the viewpoint of phoniatric examinations.
