Chapter 7 - Epileptic Encephalopathies

Abstract

Epileptic encephalopathies (EEs) are epilepsy-related conditions of early-damaged large brain systems in which epilepsy itself causes the associated cognitive symptoms. The cognitive impairment is deemed to originate from the interference of epileptic discharges (both interictal and ictal) with the activity of the widespread corticothalamic network fueling the functions of the associative neocortex. Abundant pathological high-frequency ripples feature in the electrographic picture and probably forecast the cognitive outcome. EEs typically start in infancy or early childhood. They are characterized by an active EEG with abundant interictal signs not related to a single focus, occurring dominantly in, or activated by, slow-wave sleep. The specific combination of symptoms constituting different EEs might have a common pathomechanism resulting from variable etiologic factors. The term “developmental” has been proposed (Scheffer et al., 2017) in naming those encephalopathies with an important developmental component, calling them “developmental epileptic encephalopathies.” We describe here the main features of the early infantile EEs: West syndrome, Lennox–Gastaut syndrome, Landau–Kleffner syndrome, and encephalopathy with electric status epilepticus during SWS. The effect of interictal discharges and pathological high-frequency oscillation activity, especially during sleep, merits further investigation, because interictal epileptic discharge (IEDs) and cognitive impairment have been scrutinized from the viewpoint of transient cognitive impairment during discharges in certain epileptic syndromes (rolandic epilepsy, absence epilepsy), but much less attention has been given to IEDs' impact on long-term cognitive deterioration. Research on the possible link between interictal epileptic activity and long-term cognitive outcome is astonishingly missing.