Abstracts

Scalp video-EEG (Phase I) studies often do not clearly localize seizure onsets. Depth wire recordings improve accuracy; however, invasive (Phase II) studies carry significant risks including, infection, hemorrhage and stroke. Earlier, non-invasive identification of nonsurgical candidates is warranted. One such population is patients with seizures arising from both left and right hemispheres independently. Various characteristics of this group of patients were examined to determine any noninvasive predictors of independent, bilateral onset seizures (IBOS) in cases that were subsequently confirmed on depth wire studies. All video-EEG monitoring reports from our epilepsy monitoring unit from 11/92 to 12/04 were reviewed. These included phase I and phase II monitored patients. Depth wire reports were examined for evidence of IBOS. Corresponding scalp EEG reports were obtained. Both reports for each patient were examined for the following data points: (1) ictal and interictal activity on scalp EEG recording, (2) MRI results, (3) seizure semiologies and (4) PET scans. Of 2496 total reports, 299 depth wire cases were identified. Twenty-three (7.7%) of these demonstrated IBOS during Phase II and 3 cases were excluded due to lack of Phase I data. Twenty patients were reviewed in detail. During Phase I studies, 6 suggested IBOS with 5 showing interictal epileptiform discharges from both sides. None of 20 MRI reports had evidence of bilateral structural changes. PET scans revealed bilateral hypometabolism in only 2 of 15 cases. Thirteeen (65%) patients had two or more different seizure semiologies. During Phase II exams, there was a characteristic seizure semiology for each side of onset in only 2 patients. However, in 5 cases, the 2 observed semiology types did not correspond with a particular side of onset, and in 7 cases, there was only one seizure type despite varying onset lateralizations. More than 2 semiologies were seen in 6 cases. A surprisingly high number (7.7%) of patients undergoing depth electrode monitoring have IBOS. Certain noninvasive evidence suggests the findings of IBOS in Phase II studies. IBOS on scalp recordings were suggested in less than one-third of these patients but may indicate that depth wires are not indicated in this group. Further cohort studies would be necessary to determine the specificity to support this conclusion. Functional (PET) rather than structural (MRI) imaging appears more sensitive for these cases although this also occurred in a minority of cases (13.3%). Most patients (65%) had at least 2 different seizure semiologies with 6 patients (30%) having 3 or more semiologies and this may be predicitive of IBOS, although the seizure semiologies themselves did not consistently correlate with side of onset, varying widely between patients. Better recognition of patients with IBOS would prevent unnecessary depth electrode placements.