Photic cortical reflex myoclonus

AbstractThree patients with flash‐evoked myoclonus were studied electrophysiologically. Myoclonic jerks were elicited at a fixed latency after the application of photic stimuli and were always preceded at a fixed time interval by extremely enhanced cortical evoked potentials. The enhanced electroencephalographic (EEG) responses to flash were widely distributed over the scalp and were maximal at the central region; the occipital response preceded the frontocentral response by 3.4 to 5.1 msec. The interval from the frontocentral EEG response to the flash‐evoked myoclonus was similar to that from the giant somatosensory evoked potential to the electrically evoked myoclonus. Investigation of recovery of evoked cortical responses and of myoclonic jerks showed a period of extremely enhanced excitability of both central and peripheral phenomena following stimulus. All of these findings suggest a cortical reflex mechanism. The role of the occipital cortex in the pathogenesis of photic cortical reflex myoclonus remains to be elucidated.