Spindles-inducing mechanism modulates sleep activation of interictal epileptiform discharges in the Landau-Kleffner syndrome

Purpose: Landau-Kleffner syndrome (LKS) is characterized by a marked increa se of interictal epileptiform discharges (IEDs) during sleep. During nonrap id eye movement (NREM) sleep, neuronal membrane potential oscillations lead to the appearance of spindles and delta waves in the surface EEG and might develop into paroxysmal synchronization. Spectral analysis allows the quan titative description of the dynamics of delta (slow-wave activity, SWA, 0.5 -4.5 Hz) and sigma activity (SA, 12.0-16.0 Hz) and can be used to assess th e relation between SA, SWA, and IEDs during sleep. Methods: We performed six overnight continuous EEG-polysomnographic studies in three patients with LKS. The temporal series of SWA and SA were obtaine d from a spike-free derivation lead. The IEDs count was performed on the mo st active lead. Relations between sigma and SWA and time series of IEDs wer e tested by means of correlation techniques after data normalization. Results: Our results revealed a significantly higher correlation between IE Ds and SA with respect to SWA in all the subjects, in total sleep time. The same analysis limited to NREM sleep highlights the better correlation betw een SA and IEDs. Conclusions: Our data suggest that neural mechanisms involved in the genera tion of sleep spindles facilitate IEDs production in LKS.