It can be caused by a number of different reasons, some benign, unknown reasons, but also are commonly associated with lesions, tumors, and encephalopathies. Association with periventricular white matter disease and cortical atrophy has been documented and they are more likely to show up during acute metabolic derangements such as uremia and hyperglycemia.
Intermittent rhythmic delta activity
Periodic short-interval diffuse discharges
Inter-ictal spiking
Biphasic and polyphasic sleep
Periodic lateralized epileptiform discharges
Generalized periodic epileptiform discharges
Depolarization-induced suppression of inhibition
Cyclic alternating pattern