Clinical evaluation and diagnosis of severe epilepsy syndromes of early childhood.

The developing brain is particularly susceptible to seizures. Diffuse central nervous system pathology or injury in early infancy, when the brain is most vulnerable, may lead to catastrophic epilepsies such as Ohtahara's epileptic encephalopathy and early myoclonic epileptic encephalopathy. These epileptic encephalopathies are difficult to treat and have poor prognoses. As the brain undergoes programmed synaptogenesis, apoptosis, and myelination, the epilepsy phenotypes and electroencephalography (EEG) findings change, producing age-dependent epileptic encephalopathies. Specifically, as they grow older, 40% to 60% of infants with infantile spasms and a concomitant hypsarrhythmia on EEG will develop Lennox-Gastaut syndrome with tonic and atonic seizures, associated with a synchronous, generalized 1.5- to 2-Hz spike and slow wave discharges on EEG. In the context of age-dependent epileptic encephalopathies, as an epilepsy syndrome is evolving, it is often difficult to accurately diagnose the specific epilepsy syndrome in a young child who presents with seizures. It is the clinical evolution of the seizure types and the EEG that helps the clinician make an accurate diagnosis. As more is known about the underlying pathophysiology for the various epilepsy syndromes, not only the clinical picture and EEG but also a genetic blood test will be used to accurately diagnose a specific epilepsy syndrome. A case in point would be severe myoclonic epilepsy of infancy (classically known as Dravet syndrome) and severe myoclonic epilepsy of infancy-borderland/ borderline, which are associated with specific mutations in the sodium ion channel gene SCN1A.