Unusual variants of subclinical rhythmic electrographic discharge of adults (SREDA)

Since 1981, when we first described a group of patients with subclinical rhythmic electrographic discharge of adults (SREDA), we have seen 108 patients with SREDA. Nineteen of these patients had unusual or atypical features of SREDA. The typical pattern consists of a non-evolving theta rhythm occurring in a widespread manner but maximal over the parietal and posterior temporal regions and lasting for a few seconds to a minute without clinical manifestations or symptoms. The unusual variants consist of predominantly delta frequencies, notched waveforms, a frontal or more focal distribution, a more prolonged duration, and presence during sleep. There was no significant difference in the patient group that had the atypical pattern compared with those with the typical pattern. Although the mechanism of the SREDA is unclear, it appears to represent a benign EEG phenomenon that has little diagnostic significance and should be distinguished from seizure discharges.