Seizure Disorder, Absence
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- 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:
- 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)
- 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
- 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
- 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
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