Abstracts

Rationale: To gain information on the predictive and prognostic value of MEG or magnetic source imaging (MSI), FDG-PET, and ictal SPECT as compared to intracranial electroencephalography (ICEEG) localization in epilepsy surgery.Methods: This work was part of a cohort study of epilepsy surgery candidates that were not sufficiently localized with non-invasive studies (EEG and MRI). Of 160 patients enrolled since April 2001, 77 completed ICEEG seizure monitoring. Five patients did not have seizures and were excluded from analysis. Sixty one percent of the cases were localized to extra- or lateral temporal regions. Sensitivity, specificity, and predictive values relative to ICEEG were computed for each modality and compared across the same subjects for each pair and those with all three tests. Results: Depending on patient subgroups (defined by modality comparisons), sensitivity and specificity ranged from 58-64% and 79-88% (MSI), 22-40% and 53-63% (FDG-PET), 39-48% and 44-50% (ictal SPECT). Gains in diagnostic yield were seen only from combination of MSI with either FDG-PET or ictal SPECT. MSI concordance with ICEEG was significantly greater than PET (McNemar’s (S)=5.8275, P=0.016). Large agreement was seen between PET and ictal SPECT (kappa=0.452, P=0.0107). No other comparisons–either concordance with ICEEG or agreement between modalities–were significant.Conclusions: MSI has the highest yield for predicting localization of ICEEG recordings, and that diagnostic gain is likely to be achieved with addition of either PET or ictal SPECT, not both. However, ICEEG false negatives must be accounted for in determining true clinical utility of all epilepsy imaging tests.