Normal interictal EEG Lack of observable abnormal electroencephalographic (EEG) patterns in an individual with a history of seizures. About half of individuals with epilepsy show interictal epileptiform discharges upon the first investigation. The yield can be increased by repeated studies, sleep studies, or by ambulatory EEG recordings over 24 hours. Normal interictal EEG is a sign that can be useful in the differential diagnosis. HP:0002372 UMLS:C1843146 Interictal EEG abnormality