Absolute spike frequency predicts surgical outcome in TLE with unilateral hippocampal atrophy.

OBJECTIVE: To assess the prognostic implications of both the absolute spike frequency over the affected temporal lobe and the relative spike distribution between the two temporal lobes (i.e., uni- vs bitemporal spike distribution) for postoperative seizure control in a series of consecutive patients with medically refractory mesial temporal lobe epilepsy (MTLE) and MRI evidence of unilateral hippocampal atrophy (HA).
METHODS: In this study we included 55 patients (26 women; 29 men) with medically refractory MTLE and unilateral HA on high resolution MRI who underwent a comprehensive noninvasive presurgical evaluation including prolonged video-EEG monitoring. Patients were classified both according to absolute interictal spike frequency and to relative spike distribution between the two temporal lobes as follows: first, we distinguished between patients with frequent spikes (>/=60 spikes/hour over the affected temporal lobe) and patients with nonfrequent spikes (<60 spikes/hour over the affected temporal lobe). Second, we categorized patients in a unitemporal group (>/=90% of spikes over the affected temporal lobe) and a bitemporal group (<90% of spikes over the affected temporal lobe). In all patients first-time epilepsy surgery was performed with a minimum postoperative follow-up of 1 year.
RESULTS: One year following surgery we found that only 4 of 14 patients (28.6%) in the frequent spikes group remained completely seizure free since surgery compared to 33 of 41 patients (80.5%) in the nonfrequent spikes group (p = 0.001). Relative spike distribution did not show any significant implication for postoperative outcome.
CONCLUSIONS: This study identified absolute preoperative spike frequency as a strong predictor for surgical outcome, while relative spike distribution had no significant influence on postoperative seizure control.