Subclinical rhythmic electroencephalogram discharge of adults occurring during sleep: a diagnostic challenge.

Subclinical rhythmic electroencephalogram discharge of adults (SREDA) is an electroencephalogram (EEG) pattern of uncertain significance, which occurs without any correlation with epilepsy. It resembles epileptiform activity, and is therefore likely to be misinterpreted as an authentic epileptiform pattern. We describe the occurrence of SREDA during stage II nonrapid eye movement (NREM) sleep and discuss the diagnostic difficulties that may arise when such a pattern is encountered during sleep EEG recordings. SREDA may occur during sleep, leading to difficulties in correct identification of this pattern, as the patient is unconscious and unable to report any symptoms. Although there are rather distinctive EEG features, the lack of changes in electrocardiogram rhythm and the absence of ocular/muscular artifacts suggest a nonepileptic phenomenon. The ultimate diagnosis, and the correct identification of SREDA, may be achieved by a comparison of EEG features between the pattern occurring during sleep and that recorded in the awake state.