History and exam

Key diagnostic factors

common

family history of childhood seizures

Key risk factors include family history of childhood absence epilepsy or juvenile myoclonic epilepsy (JME).[9]

staring episode, lasting 5 to 10 seconds; several times per day with no aura/postictal state

A description of the event consisting of behavioural arrest or staring, typically lasting 5 to 10 seconds and interrupting otherwise normal activity.[29]​ No aura and minimal to no postictal state should occur.[30]​ 

childhood onset

CAE has a typical age of onset between 4 and 10 years.[9]​ Juvenile myoclonic epilepsy has a typical age of onset between 9 and 13 years and is most likely to have delayed diagnosis, as the myoclonus is often ignored and only comes to attention when the patient has a generalised tonic-clonic seizure.[9]

normal physical examination

Patients with typical absence seizures should have a normal neurological examination.[9][30]​​

hyperventilation-induced seizure

The hallmark of typical absence seizures is induction by hyperventilation.[30]​ The patient should be encouraged to hyperventilate for up to 3 minutes in the office. Having the patient perform a motor task such as repetitively patting their legs during hyperventilations, and asking them to recall a word during a suspected absence seizure can help differentiate a seizure from a non-epileptic event.

Other diagnostic factors

common

automatisms

Repetitive movements involving mouth, limbs or eyes may occur during seizure.[30]​ Automatisms may be defined as simple or complex.[31]

recent decline in school performance

With the onset of frequent absence seizures, patients with childhood absence epilepsy (CAE) may have a decline in school performance, particularly if there is a delay in diagnosis.[9]​ This is likely due to missed instruction time, as most children seem to resume typical academic performance subsequently. 

uncommon

early onset (before age 4 years)

One in 10 patients with early onset absence seizures may have GLUT1 deficiency.

For patients under age 4 years or with intractable absence epilepsy, genetic testing of the SLC2A1 gene for GLUT1 deficiency should be considered.[9][26]​​​​​

Risk factors

strong

family/genetic history of absence epilepsy syndrome

Absence epilepsy syndromes (childhood absence epilepsy, juvenile myoclonic epilepsy, juvenile absence epilepsy, epilepsy with myoclonic absence, and epilepsy with eyelid myoclonia) have a strong genetic component. Inheritance is complex, with a polygenic basis with or without an environmental contribution, making pathogenic variants difficult to identify.[9][14][18]

weak

acquired brain injury: for example, hypoxia-ischaemia, trauma, infection

Patients with a history of hypoxia-ischaemia, trauma, or infection are more likely to have atypical absence seizures, and are at increased risk for a drug-resistant epilepsy syndrome such as Lennox-Gastaut syndrome.[5][14]​​​[28]​​​

other congenital inborn errors of metabolism, structural defects, chromosomal abnormalities

Patients with a history of congenital inborn errors of metabolism, structural defects, or chromosomal abnormalities are more likely to have atypical absence seizures and are at increased risk for a medically refractory epilepsy syndrome such as Lennox-Gastaut syndrome.[5][14]

developmental delay or intellectual disability

Developmental delay or intellectual disability may be seen at onset of epilepsy in patients with epilepsy with myoclonic absence, epilepsy with eyelid myoclonia, and (especially) Lennox-Gastaut syndrome, but is not typical of the idiopathic generalised epilepsy syndromes.[9][14]​​

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