Abstracts

Rationale: This study investigated the diagnostic utility and yield of routine electroencephalogram (EEG) study to help clarify the diagnosis of seizure or epilepsy in patients referred by epileptologists in our hospital with a diagnosis of seizure or epilepsy. Our aim was to determine the diagnostic utility and yield of routine EEG in a subgroup of patients referred for study by epileptologists, carrying a diagnosis of epilepsy or seizure. Methods: All studies performed in the EEG laboratory of adult and pediatric patients referred by epileptologists from the Comprehensive Epilepsy Center of our hospital, carrying a requisition diagnosis of epilepsy or seizure over a two year period (July 2011 - June 2013) were reviewed by board certified electroencephalographers and clinical neurophysiology fellows in training. EEG duration ranged from 20-70 minutes. Anticonvulsant (AED) use was determined from the EEG requisition form or direct questioning of the patient at the time of the study. Studies were reviewed for the presence of epileptiform abnormalities (sharp waves or spike wave discharges), diffuse or focal slowing, and other non-diangostic abnormalities such as excess fast beta activity. Results: Over a 2 year period (July 2011-June 2013), a total of 118 adult patients had 123 EEGs and 117 pediatric patients had 150 EEGs. In adult patients, 73 (59.3%) of EEGs were abnormal, with focal slowing (65.6%) and focal epileptiform discharges (53.4%) the most common abnormalities. Of the 73 abnormal EEGs, 70 (95.9%) were suggestive of a seizure disorder or a focal cerebral abnormality (i.e. focal slowing, focal epileptiform discharges, or generalized epilpetiform discharges). For adult patients on AEDs, 57 of 93 (61.3%) EEGs were abnormal; in patients off AEDs, 16 of 30 (53.3%) were abnormal. In pediatric patients, 98 (65.3%) of EEGs were abnormal, with focal epileptiform discharges (52.0%) and focal slowing (35.7%) the most common abnormalities. Of these 98 abnormal EEGs, 86 (87.8%) were suggestive of a seizure disorder or a focal cerebral abnormality (i.e. focal slowing, focal epileptiform discharges, generalized epilpetiform discharges, or seizures). For pediatric patients on AEDs, 76 of 106 (71.7%) EEGs were abnormal; in patients off AEDs, 22 of 44 (50.0%) were abnormal. EEGs were repeated in 2 adult patients and 18 pediatric patients; they were changed in 50% of pediatric patients and 0% of adult patients. Conclusions: The published yields for routine EEG are low (20-55%), and factors that improve this yield are not well studied. In our experience, selecting patients from an appropriate population can optimize the yield, as demonstrated in our study, especially in the pediatric patients.