Focal and/or lateralized polymorphic delta activity. Association with either 'normal' or 'nonfocal' computed tomographic scans.

Focal continuous polymorphic delta activity (PDA) is classically taught to be associated with destructive lesions of cerebral white matter. One hundred patients with focal or lateralized continuous PDA recorded by an electroencephalogram who also had computed tomographic (CT) scans of the head performed at approximately the same time were studied. Thirty-three percent had normal or "nonfocal" abnormalities on their CT scans. Most of these had a history of either seizures (51%) or transient cerebral ischemia/stroke (27%); however, a wide variety of causes were possible. This high percentage of patients with focal continuous PDA without corresponding CT scan lesions supports the concept that the electroencephalogram is a physiologic study that is complementary to anatomic imaging techniques.