Electromyographic findings in focal laryngeal dystonia (spastic dysphonia)

Spastic dysphonia is a clinical speech disorder characterized by spasms of the laryngeal muscles during phonation, producing a broken pattern of speech sometimes termed laryngeal stuttering. Fourteen patients with the diagnosis of spastic dysphonia based on voice quality were referred for evaluation; detailed clinical and electrophysiologic evaluations were performed. Laryngeal electromyographic (EMG) testing failed to demonstrate any spontaneous activity in the 14 patients tested. Seven patients (50%) had normal number and amplitude of motor unit potentials. Four of these had disparate amplitudes when compared with the other side, and two had complex motor unit potentials. The other seven patients (50%) had abnormal findings, including three patients with abnormally increased amplitude. Two patients had asynchronous activity characteristic of a tremor disorder. One patient had synchronous bursts of activity also affecting the diaphragm, later diagnosed as pyramidal and extrapyramidal disease. One patient had bursts of activity, and later presented with diffuse myoclonus. Laryngeal EMG therefore seemed to be a more precise way of evaluating patients presenting with a tremulous voice pattern termed spastic dysphonia. Clinical observation and EMG data demonstrated that spastic dysphonia is not a "spastic" disease. We identified patients with tremor (2), pyramidal and extrapyramidal disease (1), and myoclonic disorders (1). The remainder of the patients had clinical and EMG findings consistent with dystonia, a neurologic disorder characterized by abnormal, often action-induced, involuntary movements or uncontrolled spasms. We classify these patients as having "focal laryngeal dystonia" when the disorder occurs in isolation. It may also present as a component of a generalized dystonic syndrome.