Landau-Kleffner syndrome, or acquired epileptic aphasia, was first reported in 1957 and is now recognized as an epileptic encephalopathy. Many authors state that there is a spectrum, including this syndrome and the syndrome of continuous spikes-and-waves during slow sleep, and data supporting this concept are presented. An interesting pathogenetic interpretation regarding seizures and language dysfunction in Landau-Kleffner syndrome is discussed in this update. Following this line, it was interpreted that activation of spike-wave discharges during NREM sleep might alter the blood-brain barrier and provoke an autoimmune reaction. Data for 39 children with benign focal epilepsies evolving into syndromes associated with continuous spikes-and-waves during slow sleep, 5 of them with typical features of Landau-Kleffner syndrome, are presented. A long-term follow-up of 29 patients with Landau-Kleffner syndrome showed that before the onset of aphasia, developmental language and behavioral disturbances were present in 19 and 14 patients, respectively.
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• Verbal auditory agnosia is present in all patients with Landau-Kleffner syndrome.
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• The spike-wave index in sleep EEG may be lower than 85%.
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• The prevalence of Landau-Kleffner syndrome was estimated to range from 44.2 to 59.6 among a population of 18 million children (67).
Historical note and terminology
In 1957 Landau and Kleffner described 6 children with a "syndrome of acquired aphasia with convulsive disorder” (72). The language disorder was later recognized as being different from typical childhood aphasia, which is usually expressive. Instead, the aphasia of the Landau-Kleffner syndrome is an auditory verbal agnosia (111). The language disorder was initially considered to be a seizure manifestation because epileptiform activity from 1 or both temporal lobes is generally present on EEG recordings. Seizures are not a constant feature, and when present, they may precede or follow the onset of the language disorder.
Mantovani and Landau followed the 6 original cases plus 4 others and found that the outcome was variable; 5 of the children had recovered good language function as adults (83). Their hypothesis that outcome correlated with seizure frequency was not substantiated by subsequent reports (25; 62).
The 1989 International League Against Epilepsy placed this syndrome under the classification of "epilepsies and syndromes undetermined as to whether they are focal or generalized" (01). In the same category, the syndrome of continuous spikes and waves during slow sleep was included as a definite entity. However, many common features between these 2 syndromes have been recognized, and there are questions as to whether they are 2 distinct entities or subclasses of a single syndrome (28; 59; 22; 126; 117; 134; 135; 127). Furthermore, the mechanism of bilateral secondary synchronies after an initial functional spike focus seems to be the basis of language impairment and represents both for Landau-Kleffner syndrome and continuous spikes and waves during slow sleep syndrome--an explanation for the inclusion of these syndromes among the epileptic encephalopathies as proposed by ILAE´s Task Force on Classification (47; 39). In a retrospective review of 102 patients with electrical status epilepticus during sleep (ESES), 18 of the patients could be diagnosed with Landau-Kleffner syndrome. The authors concluded that Landau-Kleffner syndrome and the syndrome of continuous spikes and waves during slow sleep could be classified in a dichotomous manner rather than be seen as 2 points along a continuum (146). In a survey on concepts and terminology on electrical status epilepticus during sleep and continuous spikes and waves during slow sleep syndrome (CSWSS) among 137 members of the American Child Neurology Society and the American Epilepsy Society, it was concluded that the professionals use the terms, concepts, and defining features heterogeneously (Sánchez Fenández et al 2012). We know that this EEG pattern is frequent in children with Landau Kleffner syndrome.
In November 2007, an international symposium celebrating the 50th anniversary of the seminal study by Landau and Kleffner was held in Belgium. The symposium focused on the developments during the last 15 years in the fields of neurophysiology, neuropsychology, functional neuroimaging, pathophysiology, and treatment of Landau-Kleffner syndrome (144).
Existing and future diagnostic issues and dilemmas were discussed, emphasizing the potential relevance of Landau-Kleffner syndrome to understanding other disorders (131).
The term epilepsy-aphasia spectrum has been coined encompassing Landau-Kleffner syndrome, atypical benign partial epilepsy, and intermediate epilepsy-aphasia disorders (137).
In 2016, a thorough internationally based review on idiopathic focal epilepsies and their associations with Landau-Kleffner syndrome and continuous spike wave slow-wave sleep (CSWS) or electrical status epilepticus in sleep (ESES) syndromes was published (100).