Cyclic alternating pattern (CAP) and epilepsy during sleep: how a physiological rhythm modulates a pathological event

Objectives: Epileptic susceptibility is triggered by the sleeping condition . However, both ictal and interictal events are not equally affected by the different sleep states. Besides the well-known dichotomy between non-REM s leep (high activation) and REM sleep (low activation), epileptic phenomena are deeply sensitive to the ongoing level of arousal. Methods: During non-REM sleep the arousal level can be either unstable, as expressed by the repetitive sequences of the cyclic alternating pattern (CA P), or stable, as reflected by non-CAP. Phase A (arousal complex) and phase B (post-arousal rebound response) are the two basic components of the CAP cycle, which presents a 20-40 s periodicity. Three subtypes of A phases can be recognized: the A1 subtypes, which are thoroughly composed of K-complex es and delta bursts, and subtypes A2 and A3 dominated by moderate (A2) or p rominent (A3) EEG desynchrony. Results: As a manifestation of unstable sleep, CAP offers a favorable backg round for the occurrence of nocturnal motor seizures that in most cases ari se in concomitance with a phase A. In primary generalized epilepsy (PGE) an d in lesional epilepsies with fronto-temporal focus, activation of interict al discharges is high during CAP reaching the climax during phase A and the strongest inhibition during phase B. A lack of modulation is observed inst ead in epilepsy with benign rolandic spikes. In PGE, the interictal bursts are mostly associated with the highly synchronized phase A1 subtypes. Conclusions: The analysis of sleep microstructure based on CAP parameters o ffers a sensitive framework for exploring the linkage between dynamic EEG e vents and epileptic phenomena. (C) 2000 Elsevier Science Ireland Ltd. All r ights reserved.