[Electromyography in function disorders of the cricothyroid muscle following trauma and strumectomy]

32 patients with a disturbed function of the cricothyroid muscle were examined electromyographically and some also electroneurographically. Thyroid surgery had preceded in 22 patients and a traumatic lesion in 10 patients. Clinical observation showed that all patients suffered from an instability and lowering of the speaking voice as well as a reduction of vocal range. This was caused by a deficient tension of the vocal cords due to an insufficiently innervated cricothyroid muscle. In healthy subjects a continuous muscle activity of the cricothyroid muscle can be noted even in a resting position. During phonation the density and amplitude of this activity increases, showing a spindle-shaped pattern. In our strumectomised patients the resting activity of the impaired side was either greatly diminished when compared with the healthy side, or showed signs of denervation including the recording of fibrillations and positive sharp waves. The activity during phonation was reduced or completely missing. Electrical stimulation of the superior laryngeal nerve produced a delayed indirect muscle response. In those patients with traumatic lesions, the resting activity was reduced while a regular activity increase during phonation was completely missing. However, no signs of denervation were found in these patients. Our findings show evidence of neurogenic damage during thyroid surgery and an impairment of structures of the muscle itself following traumatic lesions.