Hemodynamic and Metabolic Aspects of Photosensitive Epilepsy Revealed by Functional Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy

Abstract

Summary: Purpose: To study in humans the hemodynamic and metabolic consequences of both photic stimulationtriggered 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 gyms.Conclusions: These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients. Key Words: Functional MRI-MR spectroscopyGeneralized epilepsy-Photosensitive-EEG.Most studies of the pathophysiology of the generalized epilepsies in humans have used positron emission tomography (PET) and fluorodeoxyglucose (FDG). In the interictal periods, these investigations showed a normal cerebral metabolic rate for glucose (CMRGlc) (1-3), and during ictal episodes of various types showed both increased and decreased CMRGlc and cerebral blood flow (CBF) (1-7). Thus these data suggest that further investigations in the human generalized epilepsies might advance the understanding of their pathophysiologies.Functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy (MRS) are noninvasive and require no isotopes or contrast agents. fMRI has a spatial resolution of a few millimeters or less and a

MRI, 1H-MRS, and functional MRI during and after prolonged nonconvulsive seizure activity

“…Metabolic changes assessed by 1 H-MRS have been observed in adjacent temporal neocortex and in extratemporal epileptic areas. 10,[12][13][14]26,27 Our results confirm the high sensitivity of 1 H-MRS to detect epileptic activity in extratemporal cortex. Nevertheless, the main limitation of single voxel 1 H-MRS used in this study is related to the choice of the voxel placement, which may be difficult in the absence of a lesion detected either by structural or functional MRI.…”

“…10 In the neocortex involving epileptic activity, metabolite alterations including elevated glutamine/glutamate signal (glx) and lactate have been observed as well. [12][13][14] Few studies have used the outlined techniques in combination to identify the epileptic focus in patient with the initial diagnosis of nonlesional extratemporal epilepsy. In fact, this patient group is the most difficult to treat surgically if this line of treatment needs to be pursued because of pharmacoresistance.…”

Photosensitive Epilepsy Studied by Functional Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy

“…patients and was never seen in either the normal controls or in PGE patients who did not have a PPR (7). The EEG recordings showed no unusual eye-movement activity during these periods in any patient.…”

“…In one PGE+PPR patient studied more than once, several weeks apart, this result was reproducible. Maps of this effect revealed that the areas demonstrating the undershoot were distant from and noncontiguous with V, (as well as in V , ) and were widely but unevenly and focally distributed (see Hill et al, 1999). The most prominent area demonstrating this finding in all patients was the posterior cingulate.…”

Influence of EEG electrodes on the BOLD fMRI signal

“…The measurement of EEG during fMRI is a new tool in epilepsy research Hill et al, 1999;Huang-Hellinger et al, 1995;Ives et al, 1993;Krakow et al, 1999;Schomer et al, 2000;Seeck et al, 1998;Symms et al, 1999;Warach et al, 1996]. As this technique becomes increasingly popular, the need for evaluating possible image artifacts on the fMRI BOLD signal arises [Krakow et al, 2000].…”