IEDs must be carefully distinguished from benign variants or normal brain waves to avoid overinterpretation of benign variants and artifacts (as discussed above) that may be mistaken for epileptiform activity. Patients with epilepsy may show generalized or focal slowing of the background, but the most useful diagnostic finding supportive of a diagnosis of epilepsy is the activation of IEDs, which may be either focal or generalized in distribution. While the background EEG is usually normal in patients with epilepsy (5), abnormal interictal EEG manifestations may include nonepileptiform abnormalities and interictal epileptiform discharges. The main purpose in obtaining EEG (other than evaluation of focal or generalized cerebral function) is to evaluate patients with known seizures to permit an accurate diagnosis of the seizure type and epilepsy syndrome so that therapy may be appropriately directed or to diagnose unknown paroxysmal spells that may represent seizures. Routine Interictal EEG in Epilepsy and Spells
