Abstracts

Rationale: Magnetic resonance imaging (MRI) studies have shown increased T2 signal intensity in the hippocampus immediately following febrile status epilepticus(FSE). It is assumed that the increased hippocampal T2 signal represents increased water content in the affected hippocampi and is an early sign of hippocampal damage. It is unknown whether or not this increased signal correlates with focal EEG findings. We have conducted MRI and EEG examinations within 72 hours of FSE as part of a prospective study of the consequences of prolonged febrile seizures in children (FEBSTAT). Methods: T2 weighted coronal oblique images of the hippocampi of infants and children with FSE were read by two neuroradiologists who together provided a consensus reading of all MRI findings, including T2 signal abnormality. Hippocampi were classified into two groups, those with normal T2 signal and those with any increased T2 signal. The side of increased T2 signal was also recorded. EEG examinations in the same children were also read by two experts and a consensus classification recorded abnormalities. Focal abnormalities included focal slowing, focal attenuation and focal spikes and the side of each was recorded. This analysis compares focal EEG findings in children with and without increased T2 signal in the hippocampus. Agreement between MRI and EEG findings was assessed using the Kappa statistic.Results: Among 68 children with consensus readings of baseline MRI and EEG examinations, 8 (12%) had increased T2 signal in a hippocampus and 25 (37%) had a focal EEG (p=0.02). Among the 25 children with focal EEG findings, focal slowing occurred in 23 (92%), focal attenuation in 8 (32%), and focal spikes in 7 (28%). Focal slowing was significantly associated with increased hippocampal T2 signal (75% in children with increased hippocampal T2 vs 28% in those without increased T2, p=0.01). Among children with focal slowing and increased hippocampal T2 signal, the side of both was the same for 67%. Nonetheless, the agreement between focal EEG findings and increased T2 signal was low (Kappa=0.26, 95% CI=0.04-0.47). These preliminary data suggest that, for MRI and EEG done within 72 hours of FSE, an increase in hippocampal T2 signal intensity is associated with focal slowing.Conclusions: Focal EEG, in particular focal slowing, is associated with increased hippocampal T2 signal intensity as possible indicators of acute hippocampal injury after FSE. However, MRI and EEG are not interchangeable and contain different information reflecting both anatomy and physiology. In combination, they may increase the chance to detect early injury and serve as biomarkers predicting the development of subsequent mesial temporal sclerosis and temporal lobe epilepsy. Supported by grant NS 43209 from NINDS