The study of laryngeal muscle activity in normal human subjects and in patients with laryngeal dystonia using multiple fine-wire electromyography.
The normal human larynx performs numerous complex tasks with nearly complete reliability. These tasks require precise timing of movements that are effected by the laryngeal muscles. The most specific method to examine these muscles is by electromyography. Although many studies on laryngeal electromyography have been reported using multichannel recordings, none has provided a detailed analysis of each laryngeal muscle's role during a variety of common tasks and the spectrum of normative values. Simultaneous eight-channel, fine-wire electromyographic recordings were made in 11 human subjects. The timing patterns of the laryngeal muscles during the coordinated efforts for phonation and other common glottic functions were examined. In addition, normative values for latencies and amplitudes of response were determined. During simple phonation, a "set pattern" for the thyroarytenoid, lateral cricoarytenoid , and interarytenoid muscles was found. The thyroarytenoid and lateral cricoarytenoid muscles demonstrated a burst at onset preceding phonation and then decreased activity, whereas the interarytenoid sustained glottic position during phonation. The coordination of the laryngeal muscles was similarly determined for connected speech, respiration, Valsalva maneuver, cough, throat-clear task, and swallow. These patterns of response, the latencies for activities, and the amplitudes of response in normal subjects provided the basis to examine the abnormal laryngeal function in a group of 59 patients with four clinical varieties of laryngeal dystonia (adductor, tremor, abductor, and mixed). The findings include abnormal patterns of response, increased latencies, and increased amplitudes of recruitment in many tasks including nonphonatory tasks. Although specific distinctions were noted in each group, the responses were remarkably similar, indicating that all clinical varieties of laryngeal dystonia should be classified as mixed dystonia with a clinical preponderance for one or more types of behavior.