Focal epilepsies in adult patients attending two epilepsy centers: classification of drug-resistance, assessment of risk factors, and usefulness of "new" antiepileptic drugs

Purpose: To classify the grade of antiepileptic drug (AED) resistance in a cohort of patients with focal epilepsies, to recognize the risk factors for AED resistance, and to estimate the helpfulness of "new-generation" AEDs.

Methods: We included 1,155 adults with focal epilepsies who were observed consecutively after 1990 and followed regularly at two epilepsy centers. We systematically collected the clinical, diagnostic, and therapeutic data using a custom-written database. We classified the patients as seizure-free or AED resistant according to the International League Against Epilepsy (ILAE) criteria, and we evaluated the risk factors associated with AED resistance using logistic regression analysis. We further grouped AED-resistant patients in different grades (I, II, and III) according to the number of AEDs already tried as proposed by Perucca.

Key findings: AED resistance occurred in 57.8% of the 729 patients with symptomatic focal epilepsies and was positively associated with electroencephalography (EEG) abnormalities, seizure type, and the presence of mesial temporal sclerosis. Among 426 patients without detectable causes, the percentage of AED resistance was significantly lower (39.2%) and correlated with EEG abnormalities and psychiatric symptoms. Among AED-resistant patients, the majority (64.6%) had tried three or more AEDs, which fit the more severe grade III proposed by Perucca. Among seizure-free patients, more than one-half (57%) needed to try two or more AEDs before reaching seizure control (14.9% needed three or more AEDs). Furthermore, among seizure-free patients who could be previously classified as resistant to two or more AEDs, 52.2% reached seizure freedom while receiving treatment with "new generation" AEDs.

Significance: The ILAE classification of AED resistance, as well the graded classification proposed by Perucca, was easily exploitable in our patients, although these classifications systems appear to have a limited value in predicting seizure outcome. Actually, a small but not negligible percentage of patients reached seizure freedom after trying several AEDs (including "new" AEDs), suggesting repeated trials may be necessary for seizure control.