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Original Investigation |

Long-term Outcomes After Nonlesional Extratemporal Lobe Epilepsy Surgery

Katherine Noe, MD1; Vlastimil Sulc, MD3,7; Lily Wong-Kisiel, MD2,3; Elaine Wirrell, MD, FRCPC2,3; Jamie J. Van Gompel, MD4; Nicholas Wetjen, MD4; Jeffrey Britton, MD3; Elson So, MD3; Gregory D. Cascino, MD3; W. Richard Marsh, MD4; Fredric Meyer, MD4; Daniel Horinek, MD, PhD7; Caterina Giannini, MD5; Robert Watson, MD6; Benjamin H. Brinkmann, PhD3; Matt Stead, MD, PhD2,3; Gregory A. Worrell, MD, PhD3
[+] Author Affiliations
1Department of Neurology, Mayo Clinic, Scottsdale, Arizona
2Divisions of Epilepsy, Clinical Neurophysiology, and Pediatric Neurology, Mayo Clinic, Mayo Systems Electrophysiology Laboratory, Rochester, Minnesota
3Department of Neurology, Mayo Clinic, Mayo Systems Electrophysiology Laboratory, Rochester, Minnesota
4Department of Neurosurgery, Mayo Clinic, Mayo Systems Electrophysiology Laboratory, Rochester, Minnesota
5Department of Pathology, Mayo Clinic, Mayo Systems Electrophysiology Laboratory, Rochester, Minnesota
6Department of Neuroradiology, Mayo Clinic, Mayo Systems Electrophysiology Laboratory, Rochester, Minnesota
7International Clinical Research Center, St Anne’s University Hospital, Brno, Czech Republic
JAMA Neurol. 2013;70(8):1003-1008. doi:10.1001/jamaneurol.2013.209.
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Importance  A focal lesion detected by use of magnetic resonance imaging (MRI) is a favorable prognostic finding for epilepsy surgery. Patients with normal MRI findings and extratemporal lobe epilepsy have less favorable outcomes. Most studies investigating the outcomes of patients with normal MRI findings who underwent (nonlesional) extratemporal epilepsy surgery are confined to a highly select group of patients with limited follow-up.

Objective  To evaluate noninvasive diagnostic test results and their association with excellent surgical outcomes (defined using Engel classes I-IIA of surgical outcomes) in a group of patients with medically resistant nonlesional extratemporal epilepsy.

Design  A retrospective study.

Setting  Mayo Clinic, Rochester, Minnesota.

Participants  From 1997 through 2002, we identified 85 patients with medically resistant extratemporal lobe epilepsy who had normal MRI findings. Based on a standardized presurgical evaluation and review at a multidisciplinary epilepsy surgery conference, some of these patients were selected for intracranial electroencephalographic (EEG) monitoring and epilepsy surgery.

Exposure  Nonlesional extratemporal lobe epilepsy surgery.

Main Outcomes and Measures  The results of noninvasive diagnostic tests and the clinical variables potentially associated with excellent surgical outcome were examined in patients with a minimum follow-up of 1 year (mean follow-up, 9 years).

Results  Based on the noninvasive diagnostic test results, a clear hypothesis for seizure origin was possible for 47 of the 85 patients (55%), and 31 of these 47 patients (66%) proceeded to intracranial EEG monitoring. For 24 of these 31 patients undergoing long-term intracranial EEG (77%), a seizure focus was identified and surgically resected. Of these 24 patients, 9 (38%) had an excellent outcome after resective epilepsy surgery. All patients with an excellent surgical outcome had at least 10 years of follow-up. Univariate analysis showed that localized interictal epileptiform discharges on scalp EEGs were associated with an excellent surgical outcome.

Conclusions and Relevance  Scalp EEG was the most useful test for identifying patients with normal MRI findings and extratemporal lobe epilepsy who were likely to have excellent outcomes after epilepsy surgery. Extending outcome analysis beyond the resective surgery group to the entire group of patients who were evaluated further highlights the challenge that these patients pose. Although 9 of 24 patients undergoing resective surgery (38%) had excellent outcomes, only 9 of 31 patients undergoing intracranial EEG (29%) and only 9 of 85 patient with nonlesional extratemporal lobe epilepsy (11%) had long-term excellent outcomes.

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Figure 1.
Summary of Patient Cohort

Eighty-five consecutive patients with normal magnetic resonance imaging (MRI) findings and medically resistant extratemporal lobe epilepsy were retrospectively identified. The only noninvasive studies associated with excellent surgical outcome were focal interictal epileptiform discharges (IEDs). EEG indicates electroencephalogram; iEEG, intracranial EEG; and SPECT, single-photon emission computed tomography.

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Figure 2.
Kaplan-Meier Survival Curves

Of 24 patients who underwent epilepsy surgery, 10 had a recurrence of seizures within 3 months. Of the remaining 14 patients, 5 had a recurrence of medically resistant seizures over the next 8 years.

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