Original Article EEG Duration: The Long and the Short of It

Current American Clinical Neurophysiology Society guidelines require a minimum of 20 minutes of artifact-free EEG recording; however, the optimum duration for routine EEGs is not established. Our hypothesis was that an EEG recording of 40 minutes’ duration would yield more information than a 20-minute EEG in capturing epileptiform abnormalities and in obtaining sleep. We retrospectively studied 150 consecutive EEGs of 40 minutes ’ duration performed at St Christopher’s Hospital for Children. Although the majority (89%) of interictal EEG abnormalities can be identified within the first 20 minutes of a routine EEG, extending the time of a routine EEG increases the yield significantly by identifying an additional 11 % of abnormal studies (P .0001), precluding the need for further long-term monitoring in these patients. Forty-three percent of interictal epileptiform abnormalities were found during sleep. We recommend that routine EEGs be performed for 40 minutes, whenever possible, to improve yield in a cost-effective manner