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.

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. No aura and minimal to no postictal state should occur. One small study demonstrated that three historical features most likely to be inconsistent with an absence seizure were preserved responsiveness to tactile stimulation, lack of cessation of playing, and initial concern by a teacher or health professional rather than a parent.[36]

childhood onset

Age of onset is pathognomonic. Juvenile myoclonic epilepsy 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.

normal physical examination

Patients with typical absence seizures should have a normal neurological examination.

hyperventilation-induced seizure

The hallmark of typical absence seizures is induction by hyperventilation. The patient should be encouraged to hyperventilate for up to 3 minutes in the office. Telling the patient a word during a seizure can help differentiate a seizure from a non-epileptic event.

Other diagnostic factors

common

simple automatisms

A description by the observer of eyelid blinking, upward eye deviation, or lip smacking is often obtained.

recent decline in school performance

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

uncommon

complex automatisms

Less commonly stereotypical/repetitive hand movements, walking/circling behaviour is obtained. These are more likely to occur with atypical absence seizures.

early onset (before age 4 years)

One in 10 patients with early onset absence seizures may have GLUT1 deficiency.[29][37]

For patients under age 4 years or with intractable absence epilepsy, genetic testing of the SLC2A1 gene for GLUT1 deficiency should be considered.[29][33][34][35]​

Risk factors

strong

family/genetic history of childhood absence epilepsy or juvenile myoclonic epilepsy

Childhood absence epilepsy has a 16% to 45% positive family history.[25] Concordance of 70% to 85% in monozygotic twins, and 33% in first-degree relatives, has been reported.[23][25] One third to one half of juvenile myoclonic epilepsy patients have a family history of epilepsy.

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 medically refractory epilepsy syndrome such as Lennox-Gastaut. A small study identified 3 out of 25 patients with Lennox-Gastaut syndrome to have a history of stroke or central nervous system infection.[19]

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. A small study identified 5 out of 25 patients with Lennox-Gastaut syndrome to have a history of chromosomal abnormality or brain malformation.[19] A study of 14 patients with epilepsy with myoclonic absences identified 7 out of 14 patients with a chromosome abnormality.[30]

developmental delay or intellectual disability

Fifty percent (50%) of patients with epilepsy with myoclonic absences have abnormal cognition at onset of their epilepsy.[8]

female sex

Childhood absence epilepsy and possibly juvenile myoclonic epilepsy have female predominance.[14][17] Studies have shown a female prevalence for generalised epilepsy.[31]

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