Rhythmic diffuse delta frequency activity presenting as an unusual EEG correlate of nonconvulsive status epilepticus: three case studies.

We report three cases of nonconvulsive status epilepticus (NCSE) in which electroencephalograms (EEGs) were dominated by rhythmic or semirhythmic, high-voltage, diffuse, delta activity. These recordings initially contained little or no clear epileptiform activity. Two of these patients had prolonged episodes of NCSE, which were recorded with continuous long-term EEGs. These recordings revealed focal epileptiform discharges as well as persistent generalized epileptiform patterns. Rhythmic or semirhythmic, diffuse, delta activity with little or no clear epileptiform components has only rarely been reported with NCSE. Diffuse delta slowing is commonly seen in many toxic-metabolic encephalopathies, and this activity may occasionally appear rhythmic. EEG and clinical characteristics that may help distinguish these conditions are discussed.