Abstracts

RATIONALE: The mechanism of temporal spike generation in patients with temporal lobe epilepsy (TLE) is not fully understood. We attempted to determine the significance of the pre-and post-operative interictal epileptiform activity (IEA) and its relation with surgical outcome in patients with medically refractory TLE who underwent selective amygdalo-hippocampectomy (SAH).
METHODS: We retrospectively reviewed the records and EEGs of TLE patients from the Montreal Neurological Hospital and Institute database with medically refractory epilepsy who had transcortical SAH. Inclusion criteria were: 1) patients with non-lesional TLE; 2) at least one pre-operative routine EEG showing IEA; 3) at least two post-operative EEGs; and 4) a minimum of one year follow up. Patients who had insufficient data, a foreign-body, congenital or vascular lesion, or multiple or palliative surgeries were excluded. Patients were classified as being seizure-free (Engel[scquote]s class Ia) or having persistent seizures (classes Ib - IV).
RESULTS: Among 170 patients who underwent SAH between 1985 and 2001, we identified 55 (25 men; mean age [plusminus] SD at seizure onset, 13.2 [plusminus] 8.7; at surgery, 35 [plusminus] 12; at last evaluation, 41.9 [plusminus] 11.7) who fullfilled the inclusion criteria. Etiological factors were described in 29 patients: febrile convulsions, 18; and head trauma, meningitis, family history of epilepsy, pre- or perinatal, four each. Forty-two patients had unilateral and six bilateral hippocampal atrophy (HA), six had a normal MRI and in one patient MRI was not available. The number [plusminus] SD of pre-operative EEGs were 6.5 [plusminus] 4.0 and of post-operative EEGs, 2.8 [plusminus] 1.4. Mean follow-up was 4.3 years (range, 1 to 11.5). Twenty-four patients had IEA in at least one post-operative EEG. Twenty-two of them had persistent seizures after SAH compared to two seizure-free patients (Chi-square test, yates corrected, p = 0.013). There were no significant difference between the post-operative spiking and non-spiking groups with respect to the following variables: age at onset of seizures and at surgery, duration of follow-up, number of pre- and post-operative EEGs, etiological factors and proportion of patients with HA.
CONCLUSIONS: In nonlesional TLE patients who underwent SAH a large fraction of them have persistant post-operative IEA. This activity is probably not the result of mesial TL epileptogenesis and when these spikes are present it is very likely that patients will continue to have seizures. Therefore, neocortical epileptogenesis must play an important role in TLE.