Abstracts

Patients with intractable extratemporal epilepsy and a normal magnetic resonance imaging (MRI) study make up a disproportionate number of non-excellent (Engel Class III-IV) epilepsy surgery outcomes. This study utilizes a standardized pre-surgical evaluation (seizure semiology, MRI, interictal and ictal scalp EEG, and SPECT) to identify favorable epilepsy surgery candidates. The Mayo Clinic electronic record system was used to retrospectively identify adult and pediatric patients (1997-2003) with normal MRI and extratemporal partial epilepsy who underwent a standardized pre-surgical evaluation that included: 1.) History and examination. 2.) Seizure protocol MRI. 3.) 31-channel interictal and ictal scalp EEG. 4.) Subtraction interictal and ictal SPECT co-registered to MRI (SISCOM).
Patients with any abnormality on MRI, or a clinical history or EEG suggesting possible temporal lobe epilepsy or generalized epilepsy were excluded from the study. A pre-surgical evaluation (PSE) score was devised from the non-invasive evaluation with one point given for each concordant finding: 1.) Lateralized interictal EEG discharges 2.) Dominant lobar interictal EEG discharges 3.)Lateralizing ictal EEG discharge 4.) Localizing (lobar) ictal EEG discharge 5.) Localizing SISCOM. The Engel classification system was used to identify excellent (Class I, and IIA) and non-excellent (Class IIB, IIC, IID, III and IV) outcome from surgery. Eighty-five consecutive patients were identified. Seizure semiology was lateralizing in 51 (60%) of patients. Interictal EEG was lateralized in 31 (36.5%) with a dominant focus in 22 (26%). Ictal EEG was lateralized in 42 (49%) and localized in 37. The SISCOM was localizing in 59 (69%) of patients.
Thirty-one (37%; [31/85]) patients went on to intracranial monitoring and 24 (77%; [24/31]) of these patient had epilepsy surgery. Of the 24 patients undergoing surgery 12 (50% [12/24]) had excellent outcome after a mean follow-up of 2 years.
The probability of excellent surgical outcome was significantly decreased by a PSE score of 0 or 1 (n=5; p[lt]0.001). There was a trend of increased excellent outcome with higher PSE score [60% with PSE score of 2 or 3 (n=10); 86% with PSE score of 4 or 5 (n=7)]. Noninvasive test results are important in stratifying candidates for non-lesional extratemporal epilepsy surgery, even after intracranial electrode recordings are performed. While the overall rate of excellent outcome from surgery was 50%, the PSE score identified a favorable subset with up to 86% excellent outcome. (Supported by Mayo Clinic Foundation.)