Absence seizures

Absence seizures are characterized by abrupt cessation of activity and responsiveness with minimal, if any, associated movements.

A typical absence seizure comprises behavioral arrest or staring, lasting 5 to 10 seconds, interrupting otherwise normal activity. It may be hyperventilation-induced.

Atypical absence seizures have a less distinct beginning and end, and are not usually precipitated by hyperventilation.

Electroencephalogram (EEG) is the definitive test. Determining the exact nature of the seizure is key to the appropriate treatment and prognosis.

Most typical absence seizures are medically responsive, and childhood absence epilepsy (CAE) tends to remit by adulthood. Typical absence seizures in CAE, juvenile absence epilepsy (JAE), and juvenile myoclonic epilepsy (JME) are usually treated with ethosuximide or valproic acid as first-line therapy, with choice of treatment depending on whether other seizure types are present.

Atypical absence seizures tend to be medically refractory and associated with intellectual disability. Treatment for atypical absence seizures is guided by the associated syndrome.

Absence seizures are subdivided into typical, atypical, myoclonic absence, and eyelid myoclonia with or without absences.[1]Beniczky S, Trinka E, Wirrell E, et al. Updated classification of epileptic seizures: position paper of the International League Against Epilepsy. Epilepsia. 2025 Jun;66(6):1804-23. https://pmc.ncbi.nlm.nih.gov/articles/PMC12169392 http://www.ncbi.nlm.nih.gov/pubmed/40264351?tool=bestpractice.com

Typical absence seizures are approximately 5 to 10 seconds in duration, and have minimal, if any, postictal confusion. They are usually precipitated by hyperventilation and sometimes by photic stimulation. They have a classic ictal EEG pattern of regular symmetric 3 Hz generalized spike-and-wave. Interictal findings depend on the epilepsy syndrome present. Epilepsy syndromes with typical absence seizures include childhood absence epilepsy (CAE; characterized by brief absence seizures, usually without convulsions), juvenile absence epilepsy (JAE; characterized by absence seizures often with generalized tonic-clonic and, less commonly, myoclonic seizures), and juvenile myoclonic epilepsy (JME; generalized syndrome characterized by myoclonic jerks, generalized tonic-clonic seizures, and, less commonly, absence seizures; strongly associated with photosensitivity).

Atypical absence seizures have a less distinct beginning and end, are not usually precipitated by hyperventilation or photic stimulation, and are more often associated with subtle motor or tone changes. The ictal EEG pattern is generalized slow (<2.5 Hz) spike-and-wave discharges with a diffusely slow background.[2]Wylie E, ed. The treatment of epilepsy: principles & practice. Philadelphia, PA: Lippincott Williams & Wilkins; 2006:305-32, 391-440. The classic epilepsy syndrome with atypical absence seizures is Lennox-Gastaut syndrome, which is characterized by multiple typical seizure types (including severe tonic seizures, myoclonic-atonic seizures, and atypical absence seizures), intellectual disability, and a slow spike-and-wave interictal pattern on EEG.