Episodic low-amplitude events: an under-recognized phenomenon in clinical electroencephalography.

In a series of 20 EEGs from 15 patients, well-defined brief attenuations occurred interspersed among the background activity. These episodic low-amplitude events (ELAEs) typically lasted 0.5-4 s. They were hemispheric or bisynchronous and occurred in patients with coma of various etiologies, including status epilepticus. The episodes of attenuation were brief and no bursts of activity were present, distinguishing this finding from burst-suppression. Prognosis was poor in the patients with coma due to entities other than status epilepticus. In the setting of status epilepticus, the prognosis depended on the etiology. This pattern may be an ictal phenomenon, or a product of waveform simplification. ELAEs are a manifestation of seriously abnormal EEG activity and correlate with a 50% mortality.