Typical absence seizure: behavioural 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.
EEG is the definitive test. Determining the exact nature of their seizures is the 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, valproate, or lamotrigine as first-line therapies.
Atypical absence seizures tend to be medically refractory and associated with mental retardation. Atypical absence seizures in Lennox-Gastaut syndrome and epilepsy with myoclonic absences are treated with valproate 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".  Epilepsy is a disease of the brain defined by any of the following conditions:  (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 aetiology (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 characterised 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; characterised by brief absence seizures, usually without convulsions), juvenile absence epilepsy (JAE; characterised by absence seizures with tonic-clonic and, less commonly, myoclonic seizures), and juvenile myoclonic epilepsy (JME; generalised syndrome characterised by myoclonic jerks, generalised 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 generalised slow (<2.5 Hz) spike-and-wave with a diffusely slow background.  The classic epilepsy syndrome with atypical absence seizures is Lennox-Gastaut syndrome, characterised by multiple seizure types (severe tonic seizures, myoclonic-atonic seizures, and absence seizures), mental retardation, and slow spike-and-wave on EEG. Absence seizures with special features include myoclonic absence and eyelid myoclonia, characteristic of Jeavons syndrome.
Assistant Professor of Neurology
Washington University Medical School
JLZW declares that she has no competing interests.
Dr Judith L. Z. Weisenberg would like to gratefully acknowledge Dr Michael Wong, a previous contributor to this monograph. MW declares that he has no competing interests.
Consultant Paediatric Neurologist
Royal Victoria Infirmary
NHS Foundation Trust
AD and two epilepsy nurses from her department have been reimbursed by UCB Pharma, the manufacturer of levetiracetum, for attending several conferences. One of the epilepsy nurses received a one-off sponsorship payment from UCB Pharma to cover the initial set-up costs of the adolescent epilepsy support group. One epilepsy nurse has been reimbursed by Cyberonics, the manufacturer of vagal nerve stimulators, for attending one or more conferences.
Division of Pediatric Neurology
Columbia University College of Physicians and Surgeons
CA declares that he has no competing interests.
Pediatrics and Neurology
Baylor College of Medicine
Comprehensive Epilepsy Program
Texas Children's Hospital
AAW declares that he has no competing interests.
Head of Neurosciences Unit
The Prince of Wales’s Chair of Childhood Epilepsy
National Centre for Young People with Epilepsy
HC has received research funds from HAS, Epilepsy Research UK, SHS, and the Milk Development Council. She has received funding for an epilepsy training fellowship from UCB and Eisai. She has also received travel funding from Eisai, UCB, and GlaxoSmithKline.
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