Epilepsy Information

(Abst. 2.073)

EEG characteristics of low-grade and high-grade gliomas of the central nervous system

Authors: Igor Ugorec, Jeffrey Politsky, S. Thompson and M. Gruber

Primary glial-based brain tumors typically present as isolated mass lesions in one cortical region. Presenting symptoms are usually headache or seizures. Non-epileptiform electrographic findings are often described as regional or focal slowing, mainly delta activity (0.5-4.0 Hz), along with attenuation of background characteristics. Epileptiform abnormalities include spikes or sharp waves, periodic lateralized epileptiform discharges (PLEDs), and seizure activity. Most of these findings, however, while indicative of focal pathology, are not specific of etiology. Nonetheless, not only are the epileptogenic and neuropathologic mechanisms underlying brain tumors distinct from other focal cerebral disturbances, evidence exists that differences exist among tumor subtypes as well. Thus, in an effort to distinguish electrographic characteristics in brain tumor patients, we analyzed EEG findings in patients with primary glial based brain tumors, segregating tumor type and tumor location.


We reviewed the EEG findings of 65 consecutive patients diagnosed with a primary brain tumor who underwent EEG evaluation as part of their evaluation. All EEG studies were performed using the 10-20 International system of EEG placement using either an XLTEK or a Biologic EEG machine. Virtually all EEGs were performed on inpatients either in the EEG lab or in the Intensive Care Unit. Epileptiform EEG abnormalities were characterized as spikes, sharp waves, PLEDs, or electrographic seizure activity. Non-epileptiform abnormalities were classified as delta slowing (polymorphic or focal), theta slowing, intermittent rhythmic delta activity (IRDA), mixed frequency slowing, background attenuation, or excess fast frequency activity.

Overall, there was a slightly greater number of patients diagnosed with high grade neoplasms compared with tumors of low biologic activity. Low grade tumors were more likely to be associated with minimal regional slowing or be associated with focal electro-clinical seizure activity. High grade tumors were more likely to be associated with high amplitude focal slowing, diffuse slowing, background attenuation, IRDA, PLEDs, and electrical seizures without clinical correlation. Tumors located in frontal and temporal regions showed more evident EEG disturbances than tumors elsewhere.

This study aimed to distinguish EEG findings amongst brain tumor patients. Careful analysis of EEG findings show that tumors can be distinguished by location based on regional EEG abnormalities and by level of biologic activity, based on amplitude and type of EEG disturbance. EEG also predicts underlying epileptic potential, both in de novo presentation, and in patients with possible tumor recurrence. EEG, however, does not specify exact tumor type or grade. EEG remains an invaluable tool in assessment of brain tumor patients.