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.
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, valproate, 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 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), intellectual disability, and slow spike-and-wave on EEG.
Absence seizures with special features include myoclonic absence and eyelid myoclonia, characteristic of Jeavons syndrome.
History and exam
Key diagnostic factors
- family history of childhood seizures
- staring episode, lasting 5 to 10 seconds; several times per day with no aura/postictal state
- childhood onset
- normal physical examination
- hyperventilation-induced seizure
Other diagnostic factors
- simple automatisms
- recent decline in school performance
- complex automatisms
- early onset (before age 4 years)
- family/genetic history of childhood absence epilepsy or juvenile myoclonic epilepsy
- acquired brain injury: for example, hypoxia-ischaemia, trauma, infection
- other congenital inborn errors of metabolism, structural defects, chromosomal abnormalities
- developmental delay or intellectual disability
- female sex
1st investigations to order
Investigations to consider
- MRI brain
- testing for metabolic disorders (e.g., serum amino acids, urine organic acids, lactate pyruvate or specific enzymatic tests)
- cerebrospinal fluid and serum glucose
- gene testing
typical absence seizures without a history of generalised tonic-clonic seizures (childhood absence epilepsy)
typical absence seizures with a history of generalised tonic-clonic seizures (CAE, JAE, JME)
atypical absence seizures
refractory to treatment
- Attention deficit hyperactivity disorder (ADHD)
- Complex partial epilepsy of frontal or temporal lobe origin
- Epilepsies in children, young people and adults
- Antiseizure medication withdrawal in seizure-free patients: practice advisory update summary
Absence seizures in childrenMore Patient leaflets
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