Electrophysiological study of myoclonus in pediatric practice.

Myoclonus can be caused from a variety of central nervous system disorders. With regard to its pathophysiology, much work has been done in adult patients, but reports from pediatric clinics are scarce. We describe the clinical and electrophysiological features of four different types of myoclonus in children using back averaging technique. In a patient with cortical reflex myoclonus, myoclonic jerks were induced in the distal right arm by taps on the ipsilateral fingers. Myoclonus was preceded by the cortical spike which was localized posterior to the central sulcus contralateral to the myoclonus, and the cortical spike was time-locked to the myoclonus. In a patient with subcortico-cortical myoclonus, myoclonus occurred as a focal motor seizure. Myoclonic jerks were preceded by generalized cortical waves which were of maximal amplitude over the cortex contralateral to the myoclonus, and cortical waves time-locked to the myoclonus. A patient with spinal myoclonus had rhythmical and segmental myoclonus. Myoclonus was induced in both arms after electrical stimulation at the wrist with a latency which was slightly longer than that of the F wave. In a patient with brainstem myoclonus, muscle activity was bilaterally synchronous and was predominant in the proximal flexors. The pattern of muscle recruitment suggested that the myoclonus signal travelled downward along the spinal cord and upward through the brainstem. The back averaging technique is essential in the differential diagnosis of myoclonus.