The spectrum of cortical myoclonus. From focal reflex jerks to spontaneous motor epilepsy.

The purpose of this paper is to draw attention to the wide range of clinical motor phenomena which may be caused by abnormal sensorimotor cortical discharge. Eleven selected patients with cortical myoclonus are described. In all cases the brief muscle jerks appeared to involve cerebral cortical mechanisms, for there were enlarged cerebral evoked potentials to somatosensory or visual stimuli and (in 5 of the 6 cases investigated in this way) a time-locked cortical event preceded spontaneous or action-induced jerking. In some patients, cortical myoclonus occurred only in response to a variety of afferent inputs (cortical reflex myoclonus). In others, the myoclonus occurred only during movement, when cortical mechanisms were activated voluntarily (cortical action myoclonus), or the cortical discharge occurred spontaneously (spontaneous cortical myoclonus and epilepsia partialis continua), and even spread to cause focal motor epilepsy (Jacksonian seizures). Some patients showed combinations of stimulus sensitive and spontaneous myoclonus, epilepsia partialis continua, focal motor epilepsy and generalized grand mal seizures. Such variations probably represent subtle differences in the site of abnormality in sensorimotor cortical neuronal mechanisms.