Secondary Outcome: Proportion of patients remaining seizure-free at week 30 (Visit 4); proportion of patients remaining seizure free at week 58 (Visit 6); the time (in days) to first break-through seizure (from day 1 of treatment); the absolute seizure frequency during the maintenance (over 52 weeks) phase; proportion of seizure-free days during the maintenance phase for subjects who enter the maintenance phase; the frequency of adverse events (from day 1 of treatment); QOLIE-31 results at V6; Portland Neurotoxicity scale at V6; results of cognitive testing (EpiTrack© by UCB).