Photic cortical reflex myoclonus.
Three 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.
D000328:Adult; D000368:Aged; D002540:Cerebral Cortex / Q000502:physiology*; D007562:Creutzfeldt-Jakob Syndrome / Q000150:complications; D004569:Electroencephalography; D004576:Electromyography; D004831:Epilepsies, Myoclonic / Q000150:complications; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008027:Light / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D009207:Myoclonus / Q000150:complications / Q000209:etiology* / Q000503:physiopathology; D012018:Reflex