Abstracts

Subtraction Ictal SPECT Co-registered to MRI (SISCOM) has proven valuable in localizing the epileptogenic focus in extratemporal epilepsy surgery candidates. However, little is known about the factors tht predict a positive study in these patients. We assessed the effect of various factors on SISCOM result in extratemporal epilespy surgery candidates. Pateints in this study had extratemporal seizure semiology by history and video recording. Exclusion criteria were the presence of exclusively temporal interictal epileptiform discharges or potentially epileptogenic MRI lesion in the temporal lobe. The following factors were evaluated: age at first unprovoked seizure, age at SISCOM study, MRI lesion presence and location, dominant interictal EEG focus, generalized interictal discharges, lateralizing seizure semiology, clinical secondary generalization, lateralizing ictal EEG onset, ictal EEG spread to contralateral hemisphere or generalization, location of ictal EEG focus, duration of injected seizure, SPECT injection latency, time from injection to seizure offset, and ratio of injection latency and seizure duration. Two hundred and four SISCOM studies performed from 1997 to 2003 met the study criteria. Median age at SISCOM was 20.5 years (range 1-62 years). Median seizure duration was 56 seconds (range 5-4140 seconds). Median injection latency was 24 seconds (range 2-840 seconds). The median ratio between injection latency and total seizure duration was 0.5 (i.e. half-way into the seizure). SISCOM was localizing in 74%. 89% of the studies were concordant with localization by scalp EEG. Factors which contributed significantly to a non-localizing study were clinical secondary generalization (p[lt]0.01) and generalized discharges on inctal EEG (p[lt]0.05). Generalized seizure activity, either clinical secondary generalization or ictal generalized EEG activity, is the single most important factor influencing the yield of SISCOM studies in extratemporal epilepsy surgery candidates. Strategies to enhance the yield of SISCOM in these patients must emphasize prompt injection of the radioligand prior to seizure generalization, or the avoidance of secondary generalization of seizures. (Supported by Mayo Foundation for Clinical Education and Research)