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Seizure Disorder, Absence

Seizure Disorder, Absence is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

An absence seizure is a generalized epileptic seizure characterized by a brief lapse of awareness.


Absence Seizure Types

Absence seizure types according to the International League Again Epilepsy (ILAE) 2010 classification include (1):

  • Typical absence
    • Formerly called petit mal seizures
    • Abrupt-onset behavioral arrest, loss of awareness, and blank staring, sometimes with mild upward eye deviation, repetitive blinking
    • May include automatisms, tonic or atonic features, eyelid or facial clonus, autonomic features
    • Lasts 5 to 30 seconds
    • Immediate return to normal consciousness
    • Associated with genetic generalized epilepsies, namely, childhood absence epilepsy (CAE), juvenile absence epilepsy (JAE), and juvenile myoclonic epilepsy
  • Atypical absence
    • Onset and offset less abrupt than typical absence seizures
    • Lasts 10 to 45 seconds
    • Impairment of consciousness often incomplete with continued purposeful activity
    • Postictal confusion sometimes occur.
    • Associated clinical features more pronounced and frequent than in typical absence; atonia is most common.
    • Associated with syndromic epilepsies, such as Lennox-Gastaut and nonsyndromic epilepsies in patients with developmental delay
  • Absence with special features
    • Myoclonic absence:
      • Rhythmic clonic jerking at 2 to 4 Hz which lasts 5 to 10 seconds
      • Unlike myoclonic seizures with no impairment of consciousness, brief lapses of awareness are characteristic of myoclonic absence.
    • Eyelid myoclonia:
      • Rhythmic clonic jerking of the eyelids at 5 to 6 Hz which lasts 3 to 5 seconds
      • Eyelid myoclonia with absence associated with an impairment of consciousness
Epilepsy Diagnoses

Specific diagnoses according to ILAE (2010):

  • CAE
    • Also known as pyknolepsy
    • Typical absence seizures are the only seizure type in 90% of children.
    • 10% develop additional generalized tonic–clonic seizures.
    • Seizures last ~10 seconds and often occur hundreds of times per day.
    • Normal neurologic state and development
    • Spontaneous remission occurs in 65–70% of patients during adolescence.
  • JAE
    • Typical absence seizures are the main seizure type.
    • Seizures last longer than in CAE and occur usually less than once a day.
    • Generalized tonic–clonic seizures occur in most patients, often in the first 1 to 2 hours after awakening.
    • Seizures often persist into adulthood.

Epidemiology

  • Predominant age
    • CAE: onset ages 4 to 10 years, with peak at ages 5 to 8 years
    • JAE: onset ages 9 to 16 years, with peak at ages 10 to 12 years
  • Predominant gender
    • Female > male (3:2 to 2:1)
    • Epilepsy with myoclonus has male predominance.

Incidence
6 to 8/100,000 per year

Prevalence
5 to 50/100,000

Etiology and Pathophysiology

  • Corticoreticular theory implicates abnormal activity in thalamocortical circuits.
  • Thalamic reticular nucleus is responsible for both normal sleep spindles and pathologic slow-wave discharges; contains inhibitory γ-aminobutyric acid-ergic (GABAergic) neurons
  • These neurons affect low-threshold calcium currents.
  • These circuits can fire in oscillatory/rhythmic fashion:
    • Normally, activation of GABAA receptors causes 10-Hz oscillations in sleep spindle frequency.
    • If GABAB receptors are strongly activated, oscillation frequency will be 3 to 4 Hz, similar to spike-and-wave typical absence seizure frequency.

Genetics
  • 70–85% concordance occurs in monozygotic twins; 82% share EEG features.
  • 33% concordance among first-degree relatives
  • 15–45% have a family history of epilepsy.
  • Complex multifactorial inheritance
  • For childhood absence, genes/loci implicated include 6q, 8q24, and 5q14.
  • Mutations of GABAA receptor and voltage-gated Ca2+ channel are implicated.

Commonly Associated Conditions

  • 3–8% of CAE cases evolve into juvenile myoclonic epilepsy.
  • Associated with difficulties in visual attention and visuospatial skills, verbal learning and memory, and reduced language abilities
  • Children with CAE have elevated rates of behavioral and psychiatric comorbidities including attentional deficits, anxiety, depression, isolation, and low self-esteem.
  • A large study in 2010 detected overall normal cognition, but 35% of subjects had pretreatment attentional deficits that did not resolve with seizure control.

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Citation

Stephens, Mark B., et al., editors. "Seizure Disorder, Absence." 5-Minute Clinical Consult, 27th ed., Wolters Kluwer, 2019. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116854/all/Seizure_Disorder__Absence.
Seizure Disorder, Absence. In: Stephens MB, Golding J, Baldor RA, et al, eds. 5-Minute Clinical Consult. 27th ed. Wolters Kluwer; 2019. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116854/all/Seizure_Disorder__Absence. Accessed April 18, 2019.
Seizure Disorder, Absence. (2019). In Stephens, M. B., Golding, J., Baldor, R. A., & Domino, F. J. (Eds.), 5-Minute Clinical Consult. Available from https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116854/all/Seizure_Disorder__Absence
Seizure Disorder, Absence [Internet]. In: Stephens MB, Golding J, Baldor RA, Domino FJ, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2019. [cited 2019 April 18]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116854/all/Seizure_Disorder__Absence.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Seizure Disorder, Absence ID - 116854 ED - Stephens,Mark B, ED - Golding,Jeremy, ED - Baldor,Robert A, ED - Domino,Frank J, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116854/all/Seizure_Disorder__Absence PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -