Neurophysiological mechanisms of paroxysmal motor manifestation, induced by visual stimulation, in photosensitive epilepsies | [Meccanismi neurofisiologici delle manifestazioni motorie nelle epilessie fotosensibili]

Myoclonus is the most common motor clinical manifestation of photosensitivity. We investigated, by means of computerized video-polygraphic techniques, the neurophysiological characteristics of photic-induced myoclonia in four patients with progressive myoclonus epilepsies and marked photosensitivity. In all four patients, intermittent photic stimulation induced either focal or massive myoclonic jerks. Myoclonic jerks at the limbs were associated with a contralateral cortical potential, whose peak preceded the onset of the myoclonic potential by a latency compatible with a conduction along direct cortico-spinal pathways. Propagation of photic- induced myoclonia in different cranial and limb muscles followed a rostro- caudal pattern. Our findings indicate a cortical origin of photic-induced myoclonia in PME, with neurophysiological features similar to those described in photic cortical reflex myoclonus.