
7 Based on these recommendations, many routine outpatient EEGs last 20–30 minutes. 6 The International League Against Epilepsy recommends recording for at least 30 minutes. The American Clinical Neurophysiology Society recommends a minimum of 20 minutes of artifact-free recording to evaluate baseline wakefulness, but concedes that longer studies may be needed for activation procedures and sleep. The duration of standard outpatient EEG varies across practices. 1, – 4 Prolonged ambulatory EEGs are also sometimes used to identify interictal epileptiform discharges (IEDs) in patients with normal or nonepileptiform routine EEGs. This yield may be increased by performing serial recordings.

Only 29%–55% of epilepsy patients have epileptiform abnormalities on a single routine outpatient EEG. Routine outpatient EEGs in epilepsy are frequently nondiagnostic. EEG is a cornerstone in diagnosing epilepsy and other paroxysmal events.
