Landau-Kleffner syndrome: sleep EEG characteristics at onset
Landau-Kleffner syndrome (LKS) and benign epilepsy with centro-temporal spikes (BECTS) are two forms of non-lesional age-related focal epilepsies. LKS is a severe disease, affecting language abilities, attention and behavior, and evolving to acquired global aphasia. As LKS is usually readily responsive to an adequate pharmacological management, an early diagnosis of children at risk for this syndrome is essential. BECTS is characterized by the absence of neurological or neuropsychological deficits throughout the course of epilepsy. However, children initially presenting some clinical and EEG features suggesting BECTS may develop severe cognitive impairments during the course of epilepsy. These cases raise the question of whether LKS and BECTS delineate fundamentally different conditions, or represent subclasses of a broad continuum. We compared sleep EEG characteristics of 7 children with typical LKS to those of 6 children with classical BECTS. Morphology, topography, organization, and abundance of interictal abnormalities during sleep differentiated these two syndromes from epilepsy onset, before the occurrence of aphasic deficits in LKS. The specific sleep EEG patterns possibly predictive of LKS were (1) unilateral slow wave foci, (2) bilateral independent spike-and-wave discharges, and (3) major activation of spike-and-wave discharges during sleep, exceeding 40% (40-90%) of the first sleep cycle and 30% (30-80%) of the following cycles. These data support the hypothesis that during LKS evolution, language networks involved in the spread of abundant idiopathic interictal abnormalities (and mainly slow waves) may be progressively inhibited and become unable to carry out their normal physiological role.