Hemodynamic and metabolic aspects of photosensitive epilepsy revealed by functional magnetic resonance imaging and magnetic resonance spectroscopy.
OBJECTIVE
To study in humans the hemodynamic and metabolic consequences of both photic stimulation-triggered and spontaneous generalized epileptiform discharges.


METHODS
Simultaneous EEG, functional magnetic resonance imaging (fMRI) and MR spectroscopy were performed in a 1.5-T scanner in 16 patients with generalized epilepsy, including nine with photosensitive epilepsy, and 12 normal subjects.


RESULTS
With a flash stimulation duration of 2 s, prominent visual cortex activation was seen in all normals and patients. There were no fMRI-registered hemodynamic abnormalities found in relation to the brief photoparoxysmal spike-wave activity evoked in the photosensitive patients. However, irrespective of the presence of a spike-wave response to the photic stimulation, the photosensitive patients showed four unique findings compared with normals: (a) slightly, but significantly, increased lactate levels in the occipital cortex in the resting state, (b) an increased area of visual cortical activation with photic stimulation, (c) simultaneous with the occipital cortex stimulus-induced increased fMRI signal there were noncontiguous areas of signal attenuation most prominent in perirolandic regions, and (d) a marked decrement (undershoot) of fMRI signal intensity immediately after the photic stimulation in the occipital cortex and in the region of the posterior cingulate gyrus.


CONCLUSIONS
These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients.
Neurology Department, Massachusetts General Hospital, Boston 02214, USA.
R A
RA
Hill
K H
KH
Chiappa
F
F
Huang-Hellinger
B G
BG
Jenkins
D000293:Adolescent; D000328:Adult; D002540:Cerebral Cortex / Q000098:blood supply* / Q000378:metabolism* / Q000503:physiopathology; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology; D004829:Epilepsy, Generalized / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007773:Lactates / Q000378:metabolism; D008027:Light / Q000009:adverse effects*; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D014793:Visual Cortex / Q000098:blood supply / Q000378:metabolism / Q000503:physiopathology
D007773:Lactates