Electrophysiological study of myoclonic seizures in children

To investigate the neurophysiological mechanisms underlying myoclonic seizures in childhood, we measured the latency between the onset of electromyogram (EMG) potentials and that of corresponding spikes obtained by the back-averaging method. The subjects were nine patients, with various epileptic syndromes, ranging in age from 2 months to 15 years, 11 months. The numbers of seizure events obtained by averaging ranged from five to 51 with a mean of 25. The latencies between averaged spike-and-wave complexes and deltoid EMG potentials ranged from 21 to 80, with a mean of 38 ms. Comparing these results with reported age-matched physiological conduction times, these latencies appeared to be slightly prolonged in all of our patients. Our results support the hypothesis that myoclonic seizures are produced through either a cortical or a subcortical generator, via a polysynaptic mechanism acting on muscles, rather than a monosynaptic corticospinal pathway.