Abstracts

Rationale: Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) has come into the spotlight in Japan because of it's specific clinical manifestations, MRI findings and poor prognosis. The clinical characteristics are prolonged seizures with febrile illness and transient recovery for a few days, followed by clustering seizures. The specific MRI finding is called "bright tree appearance", which represents high intense signal in widespread subcortical white matters on diffusion-weighted images (DWI). Some patients present with monophasic seizures and bright tree appearance from the onset. The aim of this study is to reveal incidence of post-encephalopathic epilepsy, types of seizures and prognosis in patients with acute encephalopathy with reduced subcortical diffusion (AED). Methods: We identified 262 children with acute encephalopathy between 2005 and 2012 from the database of Tokai Pediatric Neurology Society. Acute encephalopathy was defined as acute onset of impaired consciousness lasting for more than 24 hours with or without other neurologic symptoms triggered by infectious diseases. Inborn error of metabolism and bacterial meningitis were excluded from the study. Fifty of 262 patients were diagnosed with AED. We defined AED as an acute encephalopathy with 1) seizures during the acute period of encephalopathy, and 2) widespread reduced diffusion in the subcortical white matters on DWI in the acute period. We compared age at onset, clinical characteristics, MRI findings, treatments and neurological outcome between patients with post-encephalopathic epilepsy and patients without epilepsy. We reviewed ictal video-EEG recordings and classified seizure types of post-encephalopathic epilepsy. Results: In 50 patients with AED, 11 patients had post-encephalopathic epilepsy. The period between the onset of encephalopathy and onset of epilepsy was from 2 to 39 months (mean:10 months). Seizure types on clinical observation were focal seizures in 6 patients, spasms in 4, myoclonic seizures in 3, tonic seizures in 2, clonic seizures in 1, and tonic-clonic seizures in 1. Seven patients had startle seizures induced by sudden unexpected sounds. At the last follow-up period, seizures were not controlled by more than 2 antiepileptic drugs in 6 patients. Seizure frequency was dairy in the all 6 patients with uncontroled seizures. Cognitive impairment was severe in patients with epilepsy. Six of 11 patients with epilepsy had ictal video-EEG recordings and seizures in 3 patients were diagnosed as epileptic spasms. Seizures in other 3 patients were diagnosed as frontal focal seizures and seizures in 2 of them were induced by sudden unexpected sounds. Conclusions: Epileptic spasms and startle seizures were common seizure types in patients who had suffered AED. It suggests that abnormal cortico-subcortical or cortico-cortical networks trigger the post-encephalopathic epilepsy in patients with AED.