Abstracts

Seizures persist in 30-54% of patients after anterior temporal lobectomy performed for the treatment of intractable temporal lobe epilepsy. Predictors and mechanisms of early versus late postoperative seizure outcome remain unclear. We reviewed the records of 371 adult patients operated on between 1990 and 2001 at the Cleveland Clinic Foundation. The primary outcome variable was any seizure recurrence. Multiphase hazard model analysis was used to construct a time-to-event curve. Plots of the predicted probability of any seizure recurrence by significant risk factors were produced. Multivariate logistic regression was used in additional analyses to calculate adjusted odds ratios. Mean duration of follow-up was 5.5 years. Seizures recurred in 140 patients (38%). The rate of seizure freedom was 78% (95% CI=75-81%) at 1 year, and 53% (95%CI= 47-58%) at 10 years. Seizure freedom at two years was lowered by frequent preoperative seizures (67% versus 79%, [p-value = 0.015], generalized-tonic-clonic seizures (74% versus 86%, [p-value = 0.029] ), bilateral MRI abnormalities (58% versus 78%, [p-value = 0.004]), the use of invasive EEG monitoring (66% versus 77%, [p-value = 0.005]), and epileptiform discharges on EEG 6 months postoperatively (54% versus 78%, [p-value = 0.001]). Late seizure freedom (at 8 years) was lower when surgical pathology was restricted to gliosis (44% versus 64%, [p-value = 0.009]), and higher when intraoperative electrocorticography was used [p-value = 0.021]. Epileptiform EEG at 6 postoperative months predicted breakthrough seizures upon discontinuation of anticonvulsants [O.R=4.29(95%CI=1.21-15.13)]. Factors identified by 6 postoperative months predict early and late seizure recurrence after temporal lobectomy. The presence of different predictors of early versus late recurrent seizures suggests different mechanisms of recurrent disease at various postoperative intervals.