Mesial temporal versus lateral temporal interictal epileptiform activity: comparison of chronic and acute...

Intracranial interictal epileptiform activity (EA) was recorded by chronic stereotactic depth electroencephalography (SDEEG) and acute electrocorticography (ECOG) in 22 patients with complex partial seizures of temporal lobe origin. Chronic SDEEG recordings defined two groups of patients with respect to the presence or absence of lateral temporal EA; 13 patients showed independent lateral temporal EA during chronic recordings and 9 patients did not. All patients had EA recorded from mesial temporal structures during SDEEG. The presence of lateral temporal EA was correlated with a higher pre-operative seizure frequency but not with ictal onset zones, structural pathology, age at onset of epilepsy, or duration of epilepsy. Results of acute ECOG recordings performed on the same patients 1-24 months after SDEEG accurately reproduced the mesial versus lateral distribution of EA within patients (P < 0.0003). Though ECOG was less sensitive than SDEEG in demonstrating EA confined to mesial structures, positive findings at ECOG were 100% specific with respect to SDEEG. These results suggest that, at least with respect to mesial temporal versus lateral temporal structures, there is a constancy within patients in the distribution of interictal EA recorded with chronic intracranial electrodes. In addition, acute ECOG provides an accurate representation of individual patients' interictal EA.