This article emphasizes the clinical and EEG features of epileptic encephalopathy with continuous spike-and-wave during sleep and the occurrence of secondary bilateral synchronies as a mechanism for the generalization of previously focal epileptic discharges. Can it be interpreted as a kindling phenomenon? In addition, the article points out that this syndrome may appear in children, starting first with idiopathic focal epilepsies, and also in children with prenatal cerebral lesions. This article discusses language development and impairment in children and adolescents with the disorder.
Historical note and terminology
Electrical status epilepticus during sleep in children was first reported in 1971 by Patry, Lyagoubi, and Tassinari (125). They described 6 patients with a peculiar EEG pattern characterized by apparently subclinical spike-and-waves occurring almost continuously during NREM sleep with dramatic improvement during awaking and REM sleep. Five of them had epileptic seizures and were mentally retarded. An interesting feature was that 1 child never had presented seizures, had normal motor development, but no acquisition of speech. A few years later, in 1977, Tassinari and colleagues introduced the terms “encephalopathy related to electrical status epilepticus during sleep” and “electrical status epilepticus during slow sleep” for this syndrome (161; 155).
Questions regarding the term of status without detectable simultaneous clinical signs and the finding of electrical status epilepticus during slow sleep in nonepileptic children prompted the use of the term “epilepsy with continuous spike and waves during slow sleep,” which was adopted by the Commission on Classification and Terminology of the International League Against Epilepsy in 1989 (108; 151; 28).
The International League Against Epilepsy Task Force on Classification proposed a group of syndromes named epileptic encephalopathies, which included epilepsy with continuous spike-wave during slow sleep and Landau-Kleffner syndrome, among others (39). Many common features and possible similar physiopathological mechanisms of production between these 2 syndromes have been proposed, leading to questions of whether they are 2 distinct entities or subclasses of a single syndrome (37; 70; 31; 146; 135; 48; 158; 159; 147).
Interestingly, during the last few years, a group of patients with particular evolutive features was recognized: children with benign childhood epilepsy with centrotemporal spikes with initially typical clinical and EEG features who follow an atypical benign childhood epilepsy with centrotemporal spikes (03) or later on develop a status of benign childhood epilepsy with centrotemporal spikes, Landau-Kleffner syndrome, or electrical status epilepticus during slow sleep (03; 49; 48). These peculiar evolutions were reported in new series. Thirty-nine children with continuous spike-and-waves during slow sleep appearing after onset of benign childhood epilepsy with centrotemporal spikes (BECTS) were analyzed in a book (47). Among 30 patients with electrical status epilepticus during sleep, excluding children with Landau-Kleffner syndrome, 11 had previously benign focal epilepsies of childhood (90). It is important to differentiate these atypical evolutions from the cases with BECTS who present atypical features, which are far more frequent (42).
Clearly, there are different pathways to enter into the continuous spike-wave during slow sleep syndrome because the essence of the clinical manifestations is the relation to the presence of electrical status epilepticus during slow sleep.
A survey regarding concepts and terminology in electrical status epilepticus in sleep (ESES) and continuous spikes and waves during sleep (CSWS) among 219 specialists in North America concluded that the professionals caring for children with ESES and CSWS use the terms, concepts, and defining features heterogeneously (51). The most involved epileptologist in this subject stated: “The term continuous spikes and waves during sleep (CSWS) is for us a simplistic and inexact synonym for ESES” (153). These authors proposed the term “Penelope syndrome” as an eponym conveying the encephalopathy mechanism (154).
A group of patients with ESES secondary to a unilateral lesion was reported as having “encephalopathy with hemi-status epilepticus during sleep or hemi-continuous spikes and waves during slow sleep syndrome” (55). In these 21 patients, the EEG abnormality was clearly unilateral.
In June 2012, an international group of clinical and basic science researchers met in London under the auspices of the Waterloo Foundation to discuss and debate these issues in relation to idiopathic focal epilepsies. They represent an updated state-of-the-art thinking on the topics explored. The symposium led to the formation of international working groups under the umbrella of "Luke's Idiopathic Focal Epilepsy Project" to investigate various aspects of the idiopathic focal epilepsies including: semiology and classification, genetics, cognition, sleep, high-frequency oscillations, and parental resources. Proceedings of this symposium were published (123).