An Electromyographic Study of the Vocal and Cricothyroid Muscles in Functional Dysphonia

Abstract

Eighteen patients with dysphonia without any signs of organic lesions as determined by phoniatric and general physical examination, and consequently diagnosed as having a functional dysphonia were subjected to EMG examination of the vocal and cricothyroid muscles. In all cases indirect laryngoscopy showed the vocal cords to be symmetrical and to have a normal appearance and mobility during quiet breathing. During phonation there was an incomplete closure in the posterior part of the vccal cords in 4 patients, a minor oval shaped adduction insufficiency (“internus paresis”) in 5 patients and in the remaining 9 patients the vocal cords completely closed the rima glottidis. Motor unit action potentials were sampled from each investigated muscle by means of a transcutaneous approach and an analysis made by comparison with the muscle action potentials of healthy vocal and cricothyroid muscles. The EMG study gave conclusive evidence of neurogenic lesions in 10 cases whereas in 8 patients there were no significant deviations from normal EMG pattern. In patients with signs of neurogenic lesions, EMG indicated partial paresis in most investigated muscles. In two muscles an almost complete conduction block was found. Three of the patients had an upper respiratory tract infection preceding their dysphonia, a history frequently found in idiopathic vocal cord paresis.