Description

• Absence seizures are a type of generalized nonmotor seizure characterized by a brief lapse of awareness.
• Absence seizure types according to the International League Against Epilepsy (ILAE) 2017 classification include:
  • Typical
    • Abrupt onset and offset of behavioral arrest, loss of awareness, and blank staring, sometimes with eyelid movements, eye opening, or oral automatisms (e.g., lip smacking)
    • Typically occurs at 3 Hz
    • Lasts 5 to 30 seconds
    • Immediate return to normal consciousness with no aura or postictal phase
    • Associated with childhood absence epilepsy (CAE), juvenile absence epilepsy (JAE), and juvenile myoclonic epilepsy (JME)
  • Atypical
    • Onset and offset less abrupt than typical absence seizures and often with loss of muscle tone or subtle myoclonic jerks
    • Typically occurs at <2.5 Hz
    • Lasts 10 to 45 seconds
    • Impairment of consciousness often incomplete with continued purposeful activity, albeit done more slowly
    • Brief postictal confusion can sometimes occur.
    • Associated with Lennox-Gastaut syndrome and Dravet syndrome
  • Myoclonic
    • Abrupt onset and offset of staring and loss of awareness with continuous rhythmic jerks of shoulders, arms, legs, head, or perioral muscles
    • Typically occurs at 2.5 to 4.5 Hz
    • Lasts 10 to 60 seconds
    • Impairment of consciousness varies from complete loss of awareness to retained awareness.
    • Associated with epilepsy with myoclonic absences, learning disability, and behavioral problems
  • Eyelid myoclonia
    • Abrupt onset and offset of repetitive, rhythmic jerks of the eyelids with simultaneous upward deviation of the eyeballs and extension of the head
    • Typically occurs at 4 to 6 Hz
    • Lasts <6 seconds
    • Impairment of consciousness often incomplete with awareness mostly retained
    • Associated with epilepsy with eyelid myoclonus

Epidemiology

• Incidence: 6 to 8/100,000 per year
• Prevalence: 5 to 50/100,000
• Predominant age of onset: 1 to 8 years
• Predominant gender: female > male (2:1) with male predominance in myoclonic absence seizure

Etiology and Pathophysiology

• Etiology is mainly genetic with complex, multifactorial inheritance; however, may be secondary to a variety of congenital or acquired brain disorders such as hypoxia–ischemia, trauma, CNS infection, cortical malformations, or inborn errors of metabolism
• Absences are triggered in the thalamus when γ-aminobutyric acid (GABA)-mediated activity induces prolonged hyperpolarization and activates T-type (“low-threshold”) calcium channels, resulting in sustained-burst firing of these neurons causing absence seizures.

• 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.
• Mutations of GABA-A/B receptors, calcium or chloride channels
• Mutations of SLC21A, which encodes GLUT1

ALERT
Onset of absence seizures <4 years, consider GLUT1 deficiency syndrome

Commonly Associated Conditions

• Difficulties in visual attention and visuospatial skills, verbal learning and memory, fine motor skills, executive functions, and reduced language abilities
• Elevated rates of behavioral and psychiatric comorbidities including ADHD, anxiety, depression, social isolation, and low self-esteem