Abstracts

Rationale: Brain tumors typically present as isolated mass lesions. Presenting signs and symptoms, which often depend on tumor location and associated characteristics, are usually headache, seizures, or focal deficit. Infiltrative tumors cause neuronal injury through multiple mechanisms, one of which is seizure generation. Approximately 40% of patients with tumors develop seizures, but the exact mechanisms underlying tumor-induced seizures (TIS) are not known. Evidence exists not only that epileptogenic and neuropathologic mechanisms underlying brain tumors are distinct from other cerebral pathologies, but that tumor subtype is also important. The prevalence of TIS, including sub-clinical status epilepticus (SE) is not well documented. To determine the prevalence of SE in brain tumor patients we analyzed EEG data from this patient population. Methods: We reviewed the EEG findings of over 600 patients admitted consecutively with the diagnosis of brain tumor from 01/01/2007 to 12/31/2010. Epileptiform EEG abnormalities were characterized as spikes, sharp waves, PLEDs, or electrographic seizure activity. Non-epileptiform (NE) abnormalities were also classified.Results: Less than 20% of patients underwent either EEG analysis. Epileptiform activity was identified in 37% of patients. Findings were compatible with sub-clinical seizures including sub-clinical SE in 26%. NE abnormalities only were evident in 63% of cases. High grade tumors were more likely to be associated with high amplitude focal slowing, diffuse slowing, intermittent rhythmic delta activity, background attenuation, and PLEDs. All tumor grades were associated with sub-clinical seizures. Tumors located in frontal and temporal regions showed more evident EEG disturbances than tumors elsewhere. Conclusions: Brain tumors are a significant cause of clinical and sub-clinical seizure activity: the prevalence of sub-clinical seizures and status epilepticus in our patient population was over 25%. This implies that seizure activity went undetected in over 100 patients who were never evaluated. Missing the diagnosis of sub-clinical seizures would be expected to have a negative impact on patient outcome, especially in this patient population, making cEEG is an invaluable diagnostic tool in brain tumor patients.