Description

A type of generalized nonmotor seizure characterized by a brief lapse of awareness; classified by the International League Against Epilepsy (ILAE) (1):

• Typical has an 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, with immediate return to normal consciousness with no aura or postictal phase
• Atypical has a less abrupt onset and offset and often associated with loss of muscle tone or subtle myoclonic jerks.
  • Typically occurs at <2.5 Hz, lasts 10 to 45 seconds, with often incomplete impairment of consciousness with continued purposeful activity, albeit done more slowly
  • Brief postictal confusion can sometimes occur.
• Myoclonic has an 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, with impairment of consciousness varying from complete loss of awareness to retained awareness
• Eyelid myoclonia has an 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, with incomplete impairment of consciousness and often with awareness mostly retained

Epidemiology

• Predominant age of onset: between 4 and 10 years, with peak onset between 5 and 7 years
• Predominant gender: female > male (2:1) with male predominance in myoclonic absence seizure

Incidence

• 6 to 8/100,000 person-years in children up to 15 years of age
• Prevalence: 5 to 50/10,000

Etiology and Pathophysiology

• 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 cortico-thalamo-cortical system 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.

Genetics

• 75% concordance occurs in monozygotic twins; 84% share EEG features (2).
• 15–44% of patients with childhood absence epilepsy (CAE) have a family history of epilepsy.
• Mutations of GABA-A/B receptors—involved in spike wave discharges
• Mutations in calcium channels (CACNA1 A, CACNA1 H, CACNA1 I, CACNG3)—thalamocortical dysrhythmia
• Mutations of SLC21A, which encodes GLUT1—associated with a worse prognosis

Risk Factors

• Lack of medication compliance
• Lack of sleep
• Alcohol use
• Medications that lower seizure threshold
• Hyperventilation

Commonly Associated Conditions

Difficulties in visual attention and visuospatial skills, verbal learning and memory, fine motor skills, executive functions, reduced language abilities, ADHD, anxiety, depression, social isolation, and low esteem