Symptomatic epilepsies imitating idiopathic generalized epilepsies.

The diagnosis of idiopathic generalized epilepsies (IGEs) is not generally difficult if one follows the clinical and electroencephalogram (EEG) definitions of each subsyndrome that constitutes IGEs. In contrast, symptomatic epilepsies develop based on organic brain lesions and are easily diagnosed by the presence of developmental delay, neurologic abnormalities, and a characteristic seizure and EEG pattern. However, in clinical practice, it is sometimes difficult to differentiate IGEs from symptomatic epilepsies, especially when the clinical course from the onset of epilepsy is too short to exhibit typical clinical and EEG findings of either epilepsy type, or when patients with symptomatic epilepsies have atypical features that imitate the clinical characteristics of IGEs. The neurodegenerative or metabolic disorders at times start during the clinical course with epileptic seizures and later show typical neurologic abnormalities. The newly recognized metabolic disorder of glucose transporter type 1 deficiency syndrome (Glut-1 DS) may start with myoclonic seizures at an age of less than 1 year and imitate benign myoclonic epilepsy in infancy early in the clinical course. Progressive myoclonus epilepsies (PMEs) that develop at 1-4 years of age at times imitate epilepsy with myoclonic-astatic seizures with respect to the presence of astatic seizures and an epileptic encephalopathic EEG pattern. In addition, young children with focal cortical dysplasia may also have similar clinical and EEG patterns, although the latter may become localized after treatment. Approximately 15% of patients with juvenile myoclonic epilepsy (JME) are resistant to antiepileptic drugs (AEDs) and may require extensive study to make a differential diagnosis from symptomatic epilepsies. PMEs that develop during adolescence may imitate JME early in the clinical course; however, a detailed history and the differentiation between myoclonic seizures and myoclonus would help to distinguish both conditions. The diagnosis of IGEs is very demanding for patients with atypical features with regard to seizure type, EEG findings, and response to appropriate AEDs.