30 Pathophysiology of Absence Seizures

Introduction and Definitions Absence epilepsy is a relatively common subtype of idiopathic generalized epilepsy. Affecting approximately 10% of all children with epileptic disorders, absence epilepsy is characterized by seizures lasting 3–10 s. Typical absence seizures consist of brief episodes of staring and unresponsiveness and are, at times, accompanied by subtle myoclonic jerks or eyelid fluttering. No obvious deficits are present after the conclusion of each seizure, though in severe forms of untreated disease, hundreds of seizures per day can occur (Blumenfeld 2005). Onset of absence seizures (also known as petit mal seizures) is typically between the ages of 5 and 7 years, and most children outgrow the seizures in adolescence. Treatment with medications such as ethosuximide, sodium valproate, or lamotrigine control seizures about 80% of the time (Shorvon 2005). Seizures may be triggered by hyperventilation, photic stimulation, sleep deprivation, or medication withdrawal. Electroencephalogram (EEG) recordings during absence seizures reveal large amplitude, bilateral, 3–4 Hz spike-and-wave discharges (SWD) with a frontal predominance (> Fig. 30-1).