Abstracts

Rationale: For decades, conventional practice of electroencephalography (EEG) in the last 60 years has relied on the standardized International 10-20 system, in which over half of the electrodes are dedicated to midline and parasagittal coverage. The midline parasagittal coverage afforded by the traditional 10-20 EEG system is valuable in detecting focal epileptic abnormalities in the non-urgent evaluation of epilepsy, however the added value of this coverage in the emergent evaluation of adult patients has not been systematically addressed. Methods: We reviewed retrospective EEG data from a cohort of 300 patients at a tertiary care medical center, determined the frequency of seizures localized to the midline parasagittal regions, and reviewed each seizure on a reduced electrode montage limited to the temporal chains of the 10-20 EEG system to determine whether the seizure activity could be seen in the lateral channels. We then compiled previously reported EEG cohorts that reported the prevalence of midline parasagittal seizures to validate our findings. Results: In our cohort of 300 patients, only two EEGs (0.66%) were identified with a midline or parasagittal seizure focus, and both of these were visible in the lateral EEG channels and were associated with clinical symptoms. In a subsequent study of literature evidence from 169,510 EEGs, we found that the prevalence of midline or parasagittal epileptic activity was 0.71%. Conclusions: In critical care settings, where the majority of emergent EEGs are ordered to evaluate for status epilepticus as the cause of altered mental status, extremely focal and confined seizures will be unlikely to account for gross alterations of consciousness without spread to other areas covered by the lateral chains of the 10-20 EEG system. Abnormalities captured exclusively by midline or parasagittal electrodes occur with a very low frequency in adult patients. Therefore, excluding these electrodes in the emergent evaluation of critically ill patients will carry a relatively low risk of missing seizure activity. Funding: Dr. Parvizi is inventor and co-founder of Ceribell Inc, a startup company that develops Rapid Response EEG system that does not include midline or parasagittal electrodes. Dr. Gururangan serves as a consultant for Ceribell Inc. This study was supported by a seed grant from Stanford University Bio-X to Dr. Parvizi and a Stanford University Medical Scholars Fellowship to Dr. Gururangan.