Febrile seizures increase hippocampal injury risk

By Ingrid Grasmo, MedWire Reporter

Children with febrile status epilepticus (FSE) are at risk for hippocampal injury and show abnormalities in the development of this brain area, show findings from a prospective multicenter study.

In a commentary accompanying the report in Neurology, Michel Berg (University of Rochester, New York, USA) says the findings from the Consequences of Prolonged Febrile Seizures in Childhood (FEBSTAT) study suggest that both recurrent seizures and underlying hippocampal abnormalities are mechanisms involved in subsequent hippocampal sclerosis and the development of mesial temporal lobe epilepsy, but occur independently rather than synergistically.

In total, 11.5% (n=22) of the 191 children (aged 1 month to 5 years) who presented with FSE lasting a median of 71.7 minutes showed abnormal increased T2 signal in the hippocampus following FSE compared with none in the control group.

Abnormal T2 signal was present in the adjacent temporal lobe, amygdala, or insula in 27% of the 22 children with abnormal hippocampal T2 signal compared with none of the controls.

Shlomor Shinnar (Columbia University, New York, USA) and colleagues also found that developmental abnormalities of the hippocampus were more common among children with FSE (10.5%) than controls (2.1%), with hippocampal malrotation the most commonly occurring abnormality.

However, 67.0% of children did not show visible brain abnormality (either acute or developmental) on magnetic resonance imaging (MRI) within 3 days of FSE, suggesting that current MRI technology may not be adequate for identifying pathologic processes in some individuals.

Electroencephalogram (EEG) may be a useful tool for differentiating children at risk for later epilepsy, since focal EEG slow activity was associated with hippocampal T2 signal abnormalities but not with hippocampal developmental abnormalities.

Overall, extrahippocampal abnormalities did not appear to differ between children with FSE and controls. However, temporal lobe abnormalities were significantly more common in FSE cases.

No risk factors predictive for abnormal hippocampal T2 signal were identified in the study.

The researchers note that the absence of an association between seizure duration and risk for hippocampal injury could be a result of the study being restricted to FSE and seizures occurring for long periods of time.

In addition, the lack of an association with duration and focality could also be a result of including only children with FSE.

"The data from the FEBSTAT study demonstrate that there is MRI evidence of acute hippocampal injury following FSE in a substantial minority of children. This does not imply that the other children have not sustained a more subtle injury. Ongoing follow-up of the FEBSTAT cohort is in progress," say Shinnar and team.

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