Continuous electrocorticogram epileptiform discharges due to brain gliosis

Cortical dysplasia is known to produce continuous epileptiform discharges (CEDs) on electrocorticogram (EcoG) and EEG recordings. The authors studied the incidence of CEDs on ECoGs and correlated this data with pathologic findings. Thirty ECoGs were reviewed that were performed on patients with parietal or occipital lobe epilepsy operated on since 1960. CED was classified as: (1) continuous or semicontinuous rhythmic spikes or sharp waves at frequencies ranging from 2 to 8 Hz, and (2) repetitive bursts of rhythmic polyspike activity lasting 2 to 10 s. All nontumoral pathologic specimens were reviewed. Epileptiform activity was classified using the following criteria: focal (one gyrus), regional (two gyri), lobar (three gyri), bilobar, or multilobar. Pathologic examination showed gliosis in eight specimens, focal cortical dysplasia in five specimens, tumoral lesions in eight specimens, and other pathology in nine specimens. CED was found in 11 ECoGs. In seven pathology specimens, significant gliosis was shown, and in the remaining four specimens, a dysplastic lesion was diagnosed. Epileptiform activity was widespread (lobar, bilobar, or multilobar) when gliosis or focal cortical dysplasia was present. Absence of epileptiform activity or a focal/regional distribution was found in tumors and other lesions. These data suggest that extensive gliotic lesions are highly epileptogenic and produce CEDs, which are morphologically undistinguishable from those produced by focal cortical dysplasia.