Abstracts

Rationale: Patients with acute encephalopathy often present with prolonged seizures as the initial symptoms. Differential diagnosis of prolonged febrile seizure (PFS) and acute encephalopathy (AE) in children during early phase is important because treatment with corticosteroid or gammaglobulin should be considered in some patients with encephalopathy. Recently it is recognized that diffusion-weighted magnetic resonance imaging (DWI) is a sensitive method in detecting cerebral lesions in various neurological disorders. However, it is reported that DWI does not show any abnormalities in children with some types of AE during early phase, such as “AE with biphasic seizures and late reduced diffusion (AESD)”. In this study we determined the usefulness of EEG and MRI for differentiation of PFS and AE in early stage. Methods: We prospectively enrolled children with PFS and AE who were admitted to Nagoya University Hospital or its affiliated hospitals over six months. We also retrospectively reviewed medical records of patients with AESD. The diagnosis of PFS and AE was based on clinical characteristics. Diagnosis of AE was made when patients had continuous disturbance of consciousness lasting for 24 hours or longer in children with infectious symptoms. Encephalopathy caused by inborn error of metabolism, bacterial meningitis and herpes simplex encephalitis were excluded. PFS patients had favorable neurological conditions after secession of prolonged (lasting at least 30 minutes) seizures. Interictal EEG and MRI including DWI were performed within four days after the onset of illness. Results: We studied nine patients with PFS and thirteen patients with AE. Median age of patients with PFS was 23 months (range, 9-47 months) and that with AE was 53 months (range, 10-108 months). Eight patients with AE had seizures at the onset of encephalopathy and six of them had prolonged seizures lasting at least 30 minutes. Six patients were diagnosed with AESD. MRI findings were categorized as follows: (1) normal, (2) late reduced diffusion in the subcortical white matters, (3) deep white matter abnormalities at the onset, and (4) hippocampal DWI abnormalities. We also classified EEG findings into four groups as follows: (1) normal, (2) attenuation of background activities, (3) focal abnormalities (paroxysmal activities or slow waves), and (4) widespread slow waves. All AE patients had abnormal EEG findings, which are mainly consisted of widespread slow waves. On the other hand only three patients with PFS had abnormal EEG and one of them showed unilateral hippocampal DWI abnormalities. Four patients with PFS or AE showed hippocampal DWI abnormalities and prolonged seizures were observed at the onset in all these patients. Conclusions: Even in patients with AE without MRI abnormalities at the onset EEG showed widespread abnormalities. Combined evaluation of serial EEG and MRI is useful in early differentiation of PFS and AE in childhood.