Abstracts

Although atonic seizures are not uncommon in infants and children, the precise ictal semiology and EEG have not been characterized. This study was performed to demonstrate the clinical and electrophysiological characteristics of atonic seizures in infants and children. Twenty six patients (19 males and 7 females) showed atonic seizures during long-term video-EEG monitoring (VEM). The mean age on VEM was 37 months. Ictal semiology, interictal and ictal EEG, and brain imaging findings were analyzed. The brain MRI findings were normal in 14 (53.8%) and abnormal in 11 patients (42.3%). Thirteen patients (50%) had atonic seizures only, while the other 13 patients (50%) showed other type of seizures in addition. The types of accompanying seizures were myoclonic seizures in 5, atypical absence seizures in 4, partial seizures in 3, tonic spasms in 2, and generalized tonic-clonic seizures in 1 patient. In the patients with atonic seizures only, 12 showed generalized epileptiform discharges as ictal rhythm such as diffuse or bilateral polyspike/spike and wave complexes (9) or diffuse theta or delta bursts (1) sometimes followed by diffuse attenuation of the background activity (2). One patient showed hemispheric polyspike wave bursts. Abnormalities in the interictal EEG were as follows; 1) 15 showed abnormal background activity, 2) interictal epileptiform discharges included generalized spike or spike wave in 9, generalized with multifocal spike in 7, focal or multifocal spike in 7. Fifty percent of the patients with atonic seizures experienced other types of seizures. In some cases, interictal EEG showed focal or multifocal epileptiform discharges. Therefore, VEM can be helpful for accurate diagnosis and classification of atonic seizures.