Abstracts

Rationale: Routine EEG s are commonly requested in patients suspected of having epileptic seizures. Current American EEG Society guidelines require a minimum of 20 minutes of artifact free EEG recording for a routine EEG. Several studies suggest that in extended ambulatory and video EEG monitoring, the greatest yield of interictal epileptiform abnormalities is obtained within 24 hours. However, no such ideal length of time has been established for routine EEG s. Another factor which makes extended EEGs more useful is the likelihood of capturing epileptiform activity during sleep. Our aim was to determine whether a 40 minute EEG yields more information than a 20 minute routine EEG in capturing epileptiform abnormalities and in obtaining sleepMethods: A retrospective chart review was performed. The routine EEG database from St. Christopher s Hospital for Children from March 2013 to April 2013 was reviewed. The following data was obtained from all routine 40 minute EEGs: age of the patient, if the EEG was normal or abnormal within the first 20 minutes, if the EEG was normal or abnormal in the second 20 minutes, if sleep was captured during the study, time to sleep onset, and if abnormalities were seen during sleep. Abnormalities were defined as epileptiform sharp or spike wave activity or any areas of abnormal slowingResults: Total number of routine EEGs reviewed was 150. Thirty-seven out of 150, or 25%, were found to have abnormalities within the 40 minute study. Of the abnormal EEGs, 33/37 or 89% were found to be abnormal within the first 20 minutes, and sleep was captured in 12/33 or 36%. Four out of 37, or 11% were found to be abnormal within the 21-40 minute time period alone with 3 of 4 showing generalized spike wave epileptiform activity exclusively during sleep. Sixty-six out of 150, or 44%, fell asleep during the study, 61% within the first 20 minutes and 39% during the second 20 minutes. The mean time to sleep was 18.4 minutes. 40% of abnormal EEGs captured sleep. Conclusions: While the majority of inter-ictal EEG abnormalities can be identified within the first 20 minutes of a routine EEG, extending the time of a routine EEG will increase the yield by identifying an additional 11 % of abnormal studies, precluding the need for further long term monitoring in these patients. Capturing sleep during routine EEG also increases the yield as in this study, 40 % of abnormal EEGs captured sleep and 75% of abnormalities captured only during the latter part of the recording were seen in sleep. The results of our study may be useful in determining the appropriate EEG duration for patients.