Abstracts

To determine the prognostic significance of spikes on postoperative EEGs after Gamma Knife radiosurgery (GKS) for mesial temporal lobe epilepsy (MTLE) in a multicenter, prospective pilot study., GKS, randomized to 20 Gy or 24 Gy comprising 5.0-7.5mL at the 50% isodose volume, was performed on mesial structures of patients with unilateral MTLE. Routine scalp EEGs were performed at presurgical baseline and at 24 months postoperatively and scored for the presence of clinically-significant interictal epileptiform discharges (IEDs) or focal slowing (FS) ipsilateral to GKS., Preoperative IEDs were present in 63% of a sample of 27 patients. IEDs remitted in 12 patients and appeared anew in 2, leaving postoperative incidence of 26% (P value = 0.002). Neither seizure remission nor dose were associated with postoperative IEDs. FS was present preoperatively in 30% and postoperatively in 26% (P value = 0.285) and had no associations with seizure remission or dose., Although IEDs remitted in the majority of patients, the presence of IEDs or FS bore no relationship to seizure remission. The dissociation of IED from seizure outcome after GKS, in a setting lacking the confound of skull breach, further supports the concept that different mesial networks are responsible for the generation of IEDs versus seizures., (Supported by NIH R01 NS039280; Elekta AB (Stockholm, Sweden).)