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.