Chapter 6 - Idiopathic Polyfocal Hyperexcitability Conditions (HIEC) of Childhood and Their Transition to Electrical Status Epilepticus in Sleep

Abstract

Childhood idiopathic regional (polyfocal) hyperexcitability conditions (HIECs) are held to be developmental abnormalities of genetic origin without gross structural lesions. The exact genetic background has remained unclear. These conditions start in early childhood—with some age variance—when the brain is in a plastic state. Intensive spiking during non–rapid eye movement (NREM) sleep is a typical feature. Some of the patients undergo a further increase and exaggeration of spiking during night sleep, progressing to an electrical status epilepticus leading to a serious cognitive decline. The NREM sleep activation of inrerictal epileptiform discharges (IEDs) in HIEC patients is a well-known feature. The continuous transformation of IEDs to electrical status epilepticus in sleep (ESES) occurs with variable activation, localization, synchronization, and amount, but with no basic change in the original (before ESES) IED discharge morphology. Therefore, ESES and Landau–Kleffner syndrome (LKS) are clear examples of cognitive decline caused by sleep IED activation (diffuse in ESES and regional in LKS), similar to medial temporal lobe epilepsy, in which sleep spiking interferes with memory consolidation. Although the cognitive consequences reflect an important quality change in the outcome of these children, the interictal discharges do not change, just their activation during NREM sleep.