Abstracts

Rationale: There is an association between temporal lobe epilepsy due to mesial temporal sclerosis (MTS) and a childhood history of convulsive status epilepticus (CSE), in particular prolonged febrile seizures (PFS). Imaging done within 72 hours of PFS has shown increased hippocampal volumes and T2 signal, and follow-up imaging at 4 months has shown an increase in hippocampal asymmetry. These changes have been interpreted as suggestive of hippocampal injury caused by the PFS. As part of an ongoing longitudinal prospective study of childhood CSE we have conducted serial hippocampal volume measurements to characterise the time course of any changes. Methods: Children are being enrolled from London hospitals following an episode of CSE and their clinical and demographic data collected. Enrolled patients underwent MRI investigations in a Seimens Avanto 1.5T scanner at 1 month (mean 29 days, range 5-83) and 6 months (mean 180 days, range 124-280) after their episode of CSE. The investigations included a T1 weighted three-dimensional fast low angle shot (3D FLASH) which was used to derive the hippocampal volumes. Hippocampal volumes were measured by manually tracing consecutive coronal slices with simultaneous reference to a 3 dimensional visualisation in 3 orthogonal planes using a T1 weighted FLASH sequence dataset. The mean of right and left hippocamapal volumes was calculated and used for this analysis. Data was analysed in SPSS 16.0 (Chicago, Illinois) for Windows. Univariate ANalysis Of VAriance (ANOVA) was used to compare hippocampal volumes in patients with PFS and other forms of CSE. Results: To date 53 patients have been enrolled. Mean age was 3.29 years (range 0.21 - 15.5). 25 had a PFS and 28 had CSE due to other aetiologies. 26 patients have received repeat scans at 4 months (13 PFS, 13 other CSE). The two groups did not differ significantly in age, sex or seizure duration. Univariate ANOVA showed a significant effect of age on hippocampal volume (p = 0.002). After adjusting for this, at 1 month patients with PFS had on average a 278mm3 (p = 0.018, 95%CI: 50-506mm3) larger mean hippocampal volume than patients with other CSE. This difference was maintained at 4 months with patients with PFS having on average 411mm3 (p = 0.007, 95%CI: 122 - 700mm3) larger hippocampi. Conclusions: Psychological testing of these patients has shown that children with PFS perform better on tests of developmental ability than children with other forms of CSE. Taken together with these findings this suggests that both functional and structural outcome post-CSE is relatively better in patients with PFS than in those with CSE from other aetiologies. This supports the view that PFS is a relatively benign condition in the majority and that aetiology of CSE is the primary determinant of outcome. Further follow-up at 1 year is ongoing, as is the recruitment of control subjects to determine if there is any impairment in patients with PFS and if there are any signs of developing MTS.