Absence seizures

Typical absence seizure: behavioral arrest or staring, lasting 5 to 10 seconds, interrupting otherwise normal activity. Can be hyperventilation-induced.

Atypical absence seizures: less distinct beginning and end, 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 treated with ethosuximide, valproic acid, or lamotrigine as first-line therapies.

Atypical absence seizures tend to be medically refractory and associated with intellectual disability. Atypical absence seizures in Lennox-Gastaut syndrome and epilepsy with myoclonic absences are treated with valproic acid or lamotrigine as first-line therapies.

An epileptic seizure is defined as "a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain."[1]Fisher RS, Acevedo C, Arzimanoglou A, et al. ILAE official report: a practical clinical definition of epilepsy. Epilepsia. 2014 Apr;55(4):475-82 https://onlinelibrary.wiley.com/doi/full/10.1111/epi.12550 http://www.ncbi.nlm.nih.gov/pubmed/24730690?tool=bestpractice.com Epilepsy is a disease of the brain defined by any of the following conditions:[1]Fisher RS, Acevedo C, Arzimanoglou A, et al. ILAE official report: a practical clinical definition of epilepsy. Epilepsia. 2014 Apr;55(4):475-82 https://onlinelibrary.wiley.com/doi/full/10.1111/epi.12550 http://www.ncbi.nlm.nih.gov/pubmed/24730690?tool=bestpractice.com (1) at least two unprovoked (or reflex) seizures occurring >24 hours apart; (2) one unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence risk (at least 60%) after two unprovoked seizures, occurring over the next 10 years; (3) diagnosis of an epilepsy syndrome. Epilepsy is further classified by etiology (genetic, structural/metabolic, or unknown cause) and by epilepsy syndromes, which are defined by the conglomeration of seizure types, EEG patterns, age of onset, as well as a variety of other signs and symptoms. Classification of specific epilepsy syndromes allows for prediction of prognosis and appropriate therapy.

Absence seizures are a specific type of seizure characterized by abrupt cessation of activity and responsiveness with minimal, if any, associated movements. Absence seizures are further subdivided into typical, atypical, and absence with special features.

Typical absence seizures are approximately 5 to 10 seconds in duration, have minimal, if any, postictal confusion, and are usually precipitated by hyperventilation and sometimes by photic stimulation. They have a classic ictal EEG pattern of bilateral symmetric 3 Hz spike-and-wave with normal interictal background. 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 with 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; strong association with photosensitivity).

Atypical absence seizures have a less distinct beginning and end and are not usually precipitated by hyperventilation or photic stimulation, and the EEG shows generalized slow (<2.5 Hz) spike-and-wave 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, characterized by multiple seizure types (severe tonic seizures, myoclonic-atonic seizures, and absence seizures), intellectual disability, and slow spike-and-wave on EEG.

Absence seizures with special features include myoclonic absence and eyelid myoclonia, characteristic of Jeavons syndrome.