Abstracts

Rationale: Retrospective studies highlight an association between hippocampal sclerosis and a childhood history of prolonged febrile seizures (PFS). Our own work has shown that despite the lack of mean hippocampal volume (HV) differences between children following PFS and controls, a larger proportion of children following PFS have hippocampal asymmetry (Pujar et al., AES 2012 abstract; Scott et al., 2002). Given the established segregation of memory roles within the hippocampus, i.e. visual memory is more dependent on the right hippocampus and verbal memory is more dependent on the left hippocampus, we wanted to investigate whether these roles were preserved in children following PFS or whether plasticity interfered with these normal functional divisions post-PFS. Methods: We have recruited children with a history of PFS originally identified by the population-based North London Convulsive Status Epilepticus in childhood surveillance study (NLSTEPSS). Recruited children underwent detailed investigations to determine their outcome 6-10 years following their episode. Memory abilities were assessed using the Children's Memory Scale (CMS) which provides a proxy for both visual delayed and verbal delayed memory scores. To arrive at our discrepancy score we subtracted the verbal from visual memory scores. Hippocampal volumetry was performed on 3D FLASH images using FSL version 4.1.9. The HV was measured for each side and right-left asymmetry was calculated using the asymmetry index (AI= (HV Right- HV Left) / 0.5x (HV Right+ HV Left)). Pearson's correlations were used to investigate relationships between AI and memory in SPSS version 18. Results: Nineteen children (mean age: 9.1 years; range: 7-13 years) have completed MR and neuropsychological investigations a mean of 7.6 years following their episode. Their general memory quotient falls within the normal range (mean: 102.7), and is highly correlated with their FSIQ (r=0.676, p=0.001). One PFS case (patient with highest AI) was excluded from the correlational analysis due to the presence of neurological comorbidities (neurofibromatosis), which may have affected his developmental trajectory. There is a positive relationship between AI and memory discrepancy scores in PFS patients (r=0.492, p=0.038) (Figure) suggesting the presence of normative structural-functional relationships in this group. Children with larger right compared to left hippocampi were shown to do better on visual compared to verbal memory materials and the opposite was true of children with larger left compared to right hippocampi. Conclusions: Despite the higher incidence of hippocampal asymmetry in children following PFS, our findings suggest that experiencing a PFS during childhood does not alter the functional roles undertaken by the hippocampus during development.