[Suppression of myoclonus associated with intermittent photic stimulation (IPS) in a case of Creutzfeldt-Jacob disease: with special reference to the specificity of IPS frequency].
The present study deals with electrophysiological findings 3 months after the patient fell into an apallic state during the course of Creutzfeldt-Jacob disease (CJD), when periodic limb myoclonus synchronizing with periodic synchronous discharge (PSD) began to diminish. The findings were as follows: On 2 Hz intermittent photic stimulation (IPS), myoclonus and the diffuse bisynchronous high amplitude sharp wave showed dissociation; the myoclonus was completely suppressed, while the high amplitude sharp wave was elicited. On 3 Hz IPS, myoclonus was incompletely suppressed, corresponding to every other high amplitude sharp waves which were induced synchronous to IPS. On 1 Hz IPS, the high amplitude sharp waves were scarcely induced while neither PSD nor the myoclonus were suppressed. The frequency of the PSD was about 1.2 Hz. Based on these findings, we propose that in addition to the cortical refractory period after PSD or the giant response to photic stimulation, there must be another refractory period in the distal impulse pathway longer than the cortical one. Although the exact electrophysiological mechanism involved in the present findings remains unknown, the possible mechanism responsible for the suppression of myoclonus by IPS and the specificity of IPS frequency in the suppression could be due to competitive suppression of the impulse between periodic myoclonus and the cortical reflex myoclonus through the interaction of the two independent refractory periods in the transmission pathway of the impulse.
Kitamura
K
K
Central Clinical Laboratory, Kanazawa University Hospital.
Maeda
Y
Y
Mukai
H
H
Futamata
H
H
Hashimoto
T
T
D000368:Aged; D002540:Cerebral Cortex / Q000503:physiopathology; D007562:Creutzfeldt-Jakob Syndrome / Q000503:physiopathology*; D004569:Electroencephalography; D004594:Electrophysiology; D005260:Female; D006801:Humans; D009207:Myoclonus / Q000503:physiopathology*; D010507:Periodicity; D010775:Photic Stimulation; D012018:Reflex; D012032:Refractory Period, Electrophysiological