This is a randomized, double-blind, placebo-controlled, parallel-group study. This is a 5-arm, 21-week study comprised of up to a 2-week Screening period, a 15-week Dose-Escalation and Maintenance Phase using 4 doses of E2007 (2 mg, 4 mg, 6 mg, and 8 mg) or placebo, and a 4-week, single-blind placebo Follow-Up Phase. Patients will be randomly assigned to one of the five treatment groups. Those patients assigned to receive either 4 mg, 6 mg, or 8 mg E2007 will be escalated to the appropriate dose according to an escalation schedule. All patients will take four identical-looking tablets on a daily basis for the entire study duration for blinding purposes.