Abstracts

Rationale: TAE occurs in more than half of patients with GBM. Potential risk factors include temporal location, hemorrhage and incomplete resection. The diagnostic and potentially predictive role of EEG has not been defined in this population, including which tumor characteristics may be associated with epileptiform abnormalities. Methods: We performed an IRB-approved retrospective study of all newly diagnosed GBM patients who had obtained a scalp EEG at the University of Rochester between 1/1/05 and 5/13/11. EEGs were classified as epileptiform or non-epileptiform, based on the presence of discharges and paroxysmal rhythmic slowing. Records were reviewed to describe: EEG indication, tumor location, hemorrhage, resection status, and diagnosis of TAE. Characteristics of patients with epileptiform abnormalities were compared to those without. Results: 60 patients with newly diagnosed GBM and EEG were identified, 48 were diagnosed with TAE. 21/48 patients with TAE demonstrated epileptiform abnormalities on EEG. 8/21had a mixture of electrographic seizure patterns including: 7 with PLEDs, 4 with status epilepticus, and 6 had paroxysmal rhythmic slowing. 52% of EEGs with epileptiform abnormalities were seen in temporal tumors. In patients who achieved a complete resection, 12/17 had persistent epileptiform abnormalities; only 2/10 of biopsy patients had epileptiform features. Within this group, 84 EEGs were performed as indicated for new symptoms. Indications were available for all EEGs requested and only 27% of EEGs performed for AMS and 14% for resolved convulsions demonstrated epileptiform abnormalities, while 71% of studies performed for convulsions with prolonged AMS were epileptiform. Conclusions: Electrographic ictal patterns (i.e. SE, PLEDs) are frequent findings in patients with GBM. Epileptiform patterns on EEG were associated with temporal tumor location. Greater extent of resection was associated with more epileptiform abnormalities suggesting that tumor location (cortical vs. deep) may be a more important predictor than the surgery itself.