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

Authors

  • Keith H. Chiappa,

    Corresponding author
    1. The Clinical Neurophysiology Laboratory, Neurology Department
      Address correspondence and reprint requests to Dr. K. H. Chiappa at EEG Laboratory, Massachusetts General Hospital, Boston, MA 02214, U.S.A. E-mail: chiappa@helix.mgh.harvard.edu
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  • Rosamund A. Hill,

    1. The Clinical Neurophysiology Laboratory, Neurology Department
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  • Frank Huang-Hellinger,

    1. The NMR Center, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, U.S.A.
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  • Bruce G. Jenkins

    1. The NMR Center, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, U.S.A.
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  • Dr. Hill is currently at the Clinical Neurophysiology Laboratory, Auckland Public Hospital, Auckland, New Zealand.

Address correspondence and reprint requests to Dr. K. H. Chiappa at EEG Laboratory, Massachusetts General Hospital, Boston, MA 02214, U.S.A. E-mail: chiappa@helix.mgh.harvard.edu

Summary:

Purpose: To study metabolic and hemodynamic correlates of photic stimulation-triggered discharges.

Methods: Simultaneous EEG, functional MRI (fMRI) and magnetic resonance spectroscopy (MRS) were performed in nine patients with photosensitive epilepsy and in 12 normal subjects.

Results: Prominent visual cortex activation was seen in all normal subjects and patients, and no fMRI-registered hemodynamic abnormalities were correlated with 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 findings not seen in the normal subjects: (a) slightly, but significantly, elevated 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.

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