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ISRN Neurology
Volume 2012 (2012), Article ID 942849, 9 pages
http://dx.doi.org/10.5402/2012/942849
Clinical Study

Scalp and Intracranial EEG in Medically Intractable Extratemporal Epilepsy with Normal MRI

1Mayo Systems Electrophysiology Laboratory, Division of Electroencephalography and Epilepsy, Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA
2Department of Neurology, Mayo Clinic, Scottsdale, AZ 85259, USA
3Department of Neurosurgery, Mayo Clinic, Rochester, MN 55905, USA
4Department of Pathology, Mayo Clinic, Rochester, MN 55905, USA
5Department of Neuroradiology, Mayo Clinic, Rochester, MN 55905, USA

Received 21 February 2012; Accepted 18 April 2012

Academic Editors: A. Conti and W. D. Dietrich

Copyright © 2012 Tarek Zakaria et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose. To investigate EEG and SPECT in the surgical outcome of patients with normal MRI (nonlesional) and extratemporal lobe epilepsy. Methods. We retrospectively identified 41 consecutive patients with nonlesional extratemporal epilepsy who underwent epilepsy surgery between 1997 and 2007. The history, noninvasive diagnostic studies (scalp EEG, MRI, and SPECT) and intracranial EEG (iEEG) monitoring was reviewed. Scalp and iEEG ictal onset patterns were defined. The association of preoperative studies and postoperative seizure freedom was analyzed using Kaplan-Meier analysis, log-rank test, and Cox proportional hazard. Results. Thirty-six of 41 patients had adequate information with a minimum of 1-year followup. Favorable surgical outcome was identified in 49% of patients at 1 year, and 35% at 4-year. On scalp EEG, an ictal onset pattern consisting of focal beta-frequency discharge (>13–125 Hz) was associated with favorable surgical outcome ( ๐‘ƒ = 0 . 0 2 ). Similarly, a focal fast-frequency oscillation (>13–125 Hz) on iEEG at ictal onset was associated with favorable outcome ( ๐‘ƒ = 0 . 0 3 ). Discussion. A focal fast-frequency discharge at ictal onset identifies nonlesional MRI, extratemporal epilepsy patients likely to have a favorable outcome after resective epilepsy surgery.