Increased ictal discharge frequency and neocortex gliosis in lateral temporal lobe epilepsy

Medial temporal lobe epilepsy (TLE) with hippocampal sclerosis has both a scalp EEG initial ictal discharge frequency, which is faster, and also an intracranial EEG onset site that is more restricted to the hippocampus, than lateral TLE without hippocampal sclerosis. This study was performed to determine if lateral TLE patients have either intracranial EEG neocortical initial ictal frequencies or measures of lateral neocortex (LNC) histopathology that differ from patients whose seizures start in medial or multiple temporal lobe areas.

Thirty-six TLE patients undergoing ictal depth and subdural strip electrode recordings were studied to determine the initial ictal discharge site (epileptogenic zone) within the temporal lobe and neocortical ictal frequency. In 25 patients, the number of reactive astrocytes in the neocortex and other measures of pathologic assessment of LNC were assessed.

The initial neocortical ictal frequency was significantly faster when the initial ictal discharge was in the LNC ± medial paleocortex than either when it was in the hippocampus ± medial paleocortex or when it occurred simultaneously over the entire temporal lobe. Intracortical and Chaslin gliosis were both significantly greater when the initial ictal discharge was limited to the LNC than when it was in the hippocampus and/or medial paleocortex.

Temporal lobe seizures originating in neocortex had a faster initial neocortical ictal frequency than seizures arising either medially in the hippocampus or widely over the whole temporal lobe. Epileptogenic zones limited to temporal neocortex were associated with greater intraneocortical and Chaslin gliosis compared with zones confined to medial structures.