The presence of spontaneous limbic seizures using chronic video monitoring with concurrent hippocampal and cortical EEGs, in adult rats (starting at 3 months of age) that had sustained experimental febrile seizures (FS) on postnatal day 10 was compared to hyperthermic control rats whose FS had been controlled, in a study at University of California, Irvine, CA, and University of Pennsylvania, Philadelphia. EEGs were normal in hyperthermic control rats, and none developed spontaneous seizures. In rats subjected to prolonged early-life FS, spontaneous electroclinical seizures were recorded in 6 of 17 (35.2%). The seizures, sudden freezing and typical limb automatisms, were associated with polyspike/sharp waves with increasing amplitude and slowing on EEG. Interictal epileptiform discharges were recorded in 15 (88.2%) of the experimental seizure rats and in none of the controls. A diminished amplitude of cortical EEG preceding the hippocampal seizure suggests involvement of normal cortical neurons. This represents a model for studying the relation between FS and human temporal lobe epilepsy. [1]

COMMENT. These laboratory studies support the theory that prolonged infantile FS may predispose to later- onset temporal lobe epilepsy (TLE) [2]. The duration of the FS has been shown to correlate with prognosis and the later development of epilepsy and epileptiform EEGs [3]. Epilepsy developed in 30% of patients with prolonged FS (>20 min) and in only 5% of those with short FS (<20 min). The incidence of EEG abnormalities at followup in patients with long and short FS was 36% and 10%, respectively. In a more recent study, the mean duration of the FS was 100+/-133 min in patients who later developed TLE and 9+/-19 min in those without TLE at prolonged follow-up (mean 32 years) [4]. The prevention of febrile seizures, especially the complex type, requires more effective therapeutic intervention.