Cyclic electrographic seizures in critically ill patients

Prolonged electroencephalographic monitoring has facilitated the detection of nonconvulsive seizures. Compressed displays of EEG frequency spectra (such as compressed spectral array, CSA) can facilitate interpretation of continuous EEG by allowing the reader to observe on a single screen patterns evolving over many minutes or hours.

Patients were identified retrospectively over a 4-year period as displaying a cycling pattern of seizures on CSA.

We describe a pattern of seizures recurring in a cyclic fashion in a series of 13 critically ill patients of all ages. Several patients had a gradual buildup of EEG power prior to each seizure.

We believe that while not rare, this pattern is difficult to recognize on standard EEG recording but it is readily apparent on CSA. The underlying pathophysiology of cyclic seizures is not known, but we speculate that cyclic seizures represent a form of status epilepticus in which the usual seizure terminating factors are present and transiently effective, but are inadequate to prevent resumption of the seizure activity. Studying these patients may provide insight into the pathophysiology of seizure initiation and cessation.