Prognostic significance of interictal epileptiform discharges in newly diagnosed seizure disorders

EEGs performed for new-onset seizures show epileptiform discharge in approximately 18% to 56% of children and 12% to 50% of adults. An EEG after sleep deprivation improves detection of epileptiform abnormalities, showing discharge in 13% to 35% of patients whose standard EEG findings were normal. Some studies have also shown a higher yield with EEG performed within 24 hours after the seizure. The EEG is a useful diagnostic study in this clinical setting for a number of reasons. First, specific EEG abnormalities help characterize the seizure type and epilepsy syndrome, which allows more informed decisions regarding therapy and more accurate prediction of seizure control and ultimate remission. Second, in certain cases, the EEG may detect more subtle seizures, including absence, myoclonic, or partial seizures. Third, specific EEG patterns may alert the clinician to the presence of a focal cerebral lesion. Fourth, most studies have shown that an epileptiform discharge is predictive of seizure recurrence, particularly in patients with idiopathic epilepsy. In the presence of epileptiform discharge, the recurrence risk is approximately double what would be predicted after a normal EEG. The predictive value of nonepileptiform abnormalities is not clearly established.