Abstracts

RATIONALE: Depth electrode recordings in "difficult" patients with mesial temporal lobe epilepsy (MTLE) often demonstrate interictal epileptiform potentials (IEP) on the side contralateral to the subsequentially resected sclerotic hippocampus. However, it is unclear, whether these findings reduce the chances of postoperative seizure control. METHODS: We investigated retrospectively contralateral depth IEPs in 58 patients who underwent resective surgery because of mesial temporal lobe epilepsy between 1993 and 1998. In all resected specimens, postoperative histopathological analyses demonstrated signs of hippocampal sclerosis. We measured amplitude, duration and frequency of contralateral depth IEPs and related these measurements to the surgical outcome and history of the patients. RESULTS: 96,4% (27/28) of patients with contralateral spikes less frequent than 1/min became seizure free, while 50% (15/30, p<0,0007) of those with more frequent contralateral spikes experienced seizure recurrence. In the latter group, we found a significantly greater incidence of diffuse brain damage, febrile convulsions, or early seizure onset than in the group with low contralateral spike frequency (46,4 vs 90%; p < 0,0005). Moreover, only in those patients with high contralateral spike frequency, epilepsy duration correlated negatively with both contralateral IEP measures and contralateral hippocampal volum and differentiated between those who became seizure free on those who did not. CONCLUSIONS: We suggest that in patients with either early and/or bilaterally injurious adverse events, the epileptogenic process may progress thus leading to contralateral neuronal loss associated with more frequent but smaller and shorter contralateral IEPs. Especially in these patients, early epilepsy surgery seems paramount with regard to seizure control.