Sinal myoclonus.

A 5-year-old boy is reported with spinal myoclonus caused by cervical astrocytoma due to neurofibromatosis. The essential clinical and electromyographical signs of spinal myoclonus are the following: (1) Continuous rhythmical appearance in muscles innervated by the affected segments of the spinal cord. (2) Synchronous myoclonus in muscles innervated by the same spinal segments of one body side, asynchronous myoclonus in muscles of different segments as well as in contralateral muscles of the same segments. (3) Usually stable frequency, which may increase to a manifold under the influence of different stimuli. (4) Accentuation of the myoclonus under mental distress, disappearance during deeper sleep. The pathophysiological basis of spinal myoclonus might be a disinhibition in the area of the spinal formatio reticularis. Supraspinal stimuli can influence the myoclonus.