A long-standing hypothesis holds that prolonged febrile (fever induced) seizures (PFS), the most common form of childhood convulsive status epilepticus (CSE), cause mesial temporal sclerosis (MTS). CSE is a single seizure, or two or more seizures between which consciousness is not regained, lasting for more than 30 minutes. In MTS there is a loss of neurons and scarring of a key brain structure called the hippocampus. Whether prolonged convulsions lead to long-term damage to hippocampus or MTS is uncertain. A team of investigators from the United Kingdom and United States looking into this question has found that a subgroup, and not all, children who experience CSE have impaired hippocampal growth years after the prolonged seizure.
In research reported today at the American Epilepsy Society 67th Annual Meeting, the investigators used three-dimensional, MRI imaging to measure hippocampal volume in 144 children. The cohort included 70 healthy controls and four patient groups based on how the episodes were classified: prolonged febrile seizure, acute symptomatic (CSE at time of causative event such as meningitis, head injury), remote symptomatic (CSE months to years after causative event), and idiopathic/ unclassified. The volumetric images were taken at a mean follow up of 8.5 years (range 6.3-10 yrs.) after the convulsive episode.
The investigators compared the volume of the left and right hippocampus and calculated their asymmetry. They then compared these measures across all groups.
There was no significant corrected volumetric difference among the groups, except for the subgroup of children with remote symptomatic CSE whose mean corrected volume was found to be lower than that of healthy controls. Asymmetry of the hippocampal structure also was significantly greater in the remote symptomatic subgroup compared to all of the other groups in the study. No significant differences in either asymmetry or corrected volume were found between the other CSE groups and healthy controls.
"On group analysis, hippocampal growth in children who had prolonged febrile seizures, acute symptomatic, and idiopathic or unclassified CSE was not impaired at a mean follow-up of eight-and-a-half years post convulsive status epilepticus," says lead author Suresh Pujar, M.D., of the Institute of Child Health, University College of London. "But children with remote symptomatic convulsive status epilepticus have a significant reduction in hippocampal volume and increased asymmetry compared to all the other groups in our study."
According to the investigators, the results of the study suggest that prolonged seizures, whether febrile or afebrile, may not have a long lasting effect on hippocampal growth in children who were neurologically normal prior to convulsive status epilepticus. If it does occur it is uncommon.
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