Relationship of sigma activity to sleep interictal epileptic discharges: a study in children affected by benign epilepsy with occipital paroxysms

Introduction: By applying spectral analysis techniques we recently showed that Interictal Epileptic Discharges (IEDs) are modulated by sleep spindle synchronization mechanisms (sigma activity, SA, 12.0–16.0 Hz). This finding applies to both benign epilepsy of childhood with rolandic spikes (BECRS), to symptomatic epilepsy of childhood strongly activated by sleep and to the Landau–Kleffner syndrome. These results are quite different from those found in adult partial epileptic patients where slow wave activity (SWA, 0.5–4.5 Hz) plays the main role in the modulation of IEDs during sleep. This finding could suggest that the activation of IEDs by spindle activities could be an age-related feature of epilepsy. In order to verify this hypothesis we studied a group of epileptic children performing a polysomnographic study on five patients with BEOP strongly activated by sleep. Methods: We performed overnight continuous EEG-polysomnographic studies in five patients (mean age 6.0±2.5). The IEDs count was performed on the most active occipital lead. The temporal series of SWA and SA values, derived from spectral analysis, were obtained from a spike-free central, controlateral lead. Relationships between SA, SWA and time series of IEDs were tested by means of correlation techniques after data normalization. Results: Our results revealed a significantly higher correlation between IEDs and SA with respect to SWA in all subjects, in total sleep time. When the analysis was limited only to NREM sleep the correlation between sigma and IEDs was even more impressive. Conclusions: Data suggest that also in BEOP the spindle generating mechanism modulates the IEDs during sleep. This mechanism seems to be an age-dependent phenomenon with no relation whatsoever either with the type of epilepsy or with the brain region.