Seizure Disorder, Absence
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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
- Myoclonic absence:
Specific diagnoses according to ILAE (2010):
- 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.
- 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.
- 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.
6 to 8/100,000 per year
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.
- 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.