Cyclic seizures in critically ill patients: Clinical correlates, DC recordings and outcomes.

OBJECTIVE:To describe EEG and clinical correlates, DC recordings and prognostic significance of cyclic seizures (CS). METHODS:We reviewed our prospective continuous EEG database to identify patients with CS, controls with non-cyclic status epilepticus (SE) and controls without seizure matched for age and etiology. EEG was reviewed with DC settings. RESULTS:39/260 (15%) patients with electrographic seizures presented with CS. These patients were older (62 vs. 54years; p=0.04) and more often had acute or progressive brain injury (77% vs. 52%; p=0.03) than patients with non-cyclic SE and had a lower level of consciousness, were more severely ill, than matched controls. CS almost always had focal onset, often from posterior regions. Patients with CS trended towards worse prognosis. When available (12 patients), DC recordings showed an infraslow cyclic oscillation of EEG baseline synchronized to the seizures in all cases. CONCLUSIONS:CS occur mostly in older patients with acute or progressive brain injury, are more likely to be associated with poor outcome than patients with other forms of nonconvulsive SE, and are accompanied by synchronous oscillations of the EEG baseline on DC recordings. SIGNIFICANCE:CS are a common form of non-convulsive status epilepticus in critically ill patients and provide further insights into the relationship between infraslow activity and seizures; further study on this relationship may shed light on the mechanisms of seizure initiation and termination.