Summary

Childhood Absence Epilepsy (CAE) is a common idiopathic generalized epilepsy syndrome characterized by frequent, brief (typically 4-20 seconds) episodes of impaired consciousness with sudden onset and offset. The child appears to "zone out" or stare blankly, often mistaken for daydreaming or inattention. EEG shows the pathognomonic 3Hz generalized spike-and-wave discharge. Most children have an excellent prognosis with 80-90% achieving remission by adolescence. Ethosuximide is first-line treatment for typical absence seizures without generalized tonic-clonic seizures.

Key Facts

• Definition: Brief (less than 20 seconds) episodes of impaired awareness with abrupt onset and offset
• Prevalence: 10-15% of childhood epilepsies; incidence 6-8 per 100,000 children
• Peak age: 4-10 years (peak 5-7 years)
• Sex ratio: Girls greater than Boys (approximately 60:40)
• EEG finding: 3Hz generalized spike-and-wave (pathognomonic)
• First-line treatment: Ethosuximide (if no GTC risk) or Valproate
• Prognosis: 80-90% remission by adolescence

Clinical Pearls

The "Light Switch": Absence seizures start and stop abruptly. There is NO post-ictal confusion. The child returns to normal activity immediately, unlike focal impaired awareness seizures.

Hyperventilation Trigger: Always ask the child to hyperventilate for 3 minutes during clinic assessment. This reliably provokes absence seizures and is a simple bedside diagnostic tool.

Carbamazepine Warning: Carbamazepine, phenytoin, and gabapentin can WORSEN absence seizures. Sodium channel blockers are contraindicated in generalized epilepsies.

Why This Matters Clinically

Absence seizures significantly impact learning and school performance due to their high frequency (10-100+ per day). Children may be mislabeled as inattentive or having ADHD. Early recognition and treatment restores normal attention and prevents educational disadvantage. The condition is highly treatable with excellent long-term outcomes.

Structured Approach

General:

• Developmental assessment (should be normal in CAE)
• School performance history
• Growth parameters

Neurological Examination:

• Typically NORMAL in CAE
• Higher functions: intact between seizures
• Cranial nerves: normal
• Motor/sensory: normal
• Cerebellar: normal

Hyperventilation Test:

• Ask child to blow on a pinwheel or count breaths for 3 minutes
• Observe for typical absence: staring, unresponsive, abrupt onset/offset
• Highly sensitive bedside provocation test

Special Tests

Natural History

• Untreated: Seizures continue and significantly impair school performance
• Treated: Majority achieve seizure freedom with medication

Outcomes with Treatment

Prognostic Factors

Good Prognosis:

• Typical CAE presentation (age 4-10)
• Normal development and neurological examination
• Good response to first-line AED
• Normal EEG after treatment
• Absence of GTC seizures

Poor Prognosis:

• Late onset (greater than 8 years)
• Presence of GTC seizures
• Atypical absence features
• Abnormal EEG background
• Poor response to treatment
• Photosensitivity

Key Guidelines

1. NICE NG217 (2022) — Epilepsies in children, young people and adults. Recommends ethosuximide or valproate as first-line; avoid sodium channel blockers. NICE NG217
2. ILAE Classification (2017) — International League Against Epilepsy classification of epilepsies. Defines CAE syndrome criteria. ILAE
3. SIGN 143 (2015) — Diagnosis and management of epilepsy in adults and children. SIGN

Landmark Trials

CAT Study (Glauser et al., 2010, 2013) — Childhood Absence Epilepsy Treatment Study

• 453 children with newly diagnosed CAE
• Randomised to ethosuximide, valproate, or lamotrigine
• Key finding: Ethosuximide and valproate both 53% seizure-freedom at 12 months; lamotrigine inferior (29%)
• Key finding: Ethosuximide had fewer attentional side effects than valproate
• Clinical Impact: Ethosuximide recommended as first-line if no GTC risk

Evidence Strength

What is happening during an absence seizure?

When your child has an absence seizure, a small "short-circuit" happens in the brain that makes them "switch off" for about 10-20 seconds. They will stare blankly and will not be able to hear or see you during this time. It is NOT daydreaming – they are genuinely unconscious, but their body stays upright because it only affects their awareness, not their muscles.

Is my child ignoring me?

No. When they do not respond to their name or seem to be staring into space, it is because the seizure is happening. Once the seizure ends (usually within 20 seconds), they will immediately snap back to normal as if nothing happened. They will not remember the seizure and may not even know it occurred.

How is it treated?

1. Medication: Most children take a daily medicine called ethosuximide (or sometimes sodium valproate). This is very effective – about 8 out of 10 children become seizure-free.
2. Regular follow-up: We will see your child regularly and may do EEGs (brain wave tests) to monitor progress.
3. School: We will write to the school to explain the condition so teachers understand. It is important they know your child is not misbehaving.

What to expect

• Most children with this condition grow out of it by their teenage years
• Once seizure-free for 2 years, we may try slowly stopping the medication
• There is about an 80-90% chance your child will not need medication as an adult

When to seek help

Contact your doctor or go to hospital if:

• Seizures are lasting longer than usual (more than 30 seconds)
• Your child seems confused or unwell after seizures
• Your child has a convulsion (stiffening, shaking, falling)
• Seizures are becoming more frequent despite medication
• Your child develops a rash or feels unwell on their medication

The "Paediatric Epilepsy" Station

1. The History (The "Gold" is here)

• Description: Staring? Eyelid fluttering? Automatisms?
• Interruptible?: "If you touch them/call a name, do they stop?" (Yes = Daydreaming. No = Seizure).
• Duration: "How long?" (Seconds = Absence. Minutes = Focal).
• Recovery: "Are they confused after?" (Yes = Focal. No = Absence).

2. The Hyperventilation Test (HV)

• Technique:
  • "I want you to blow on this windmill/tissue."
  • "Keep going! Big breaths! Like blowing out 100 candles!"
  • Guide them for 3 full minutes.
• Positive Test:
  • Child abruptly stops blowing.
  • Stares blankly.
  • Eyelids flutter (3Hz).
  • Unresponsive to name.
  • Ends abruptly and child smiles/continues.
• Utility: Diagnostic in >90% of untreated CAE. If negative, diagnose is unlikely (or child is on meds).

3. Video EEG Interpretation

• Background: Normal (distinguishes from Lennox-Gastaut).
• Ictal:
  • High voltage (huge spikes).
  • 3Hz (3 spikes per second).
  • Spike-and-Wave morphology.
  • Generalized (Every channel involved instantly).
  • Abrupt onset/offset.

Viva Questions:

• Q: Why is Ethosuximide preferred over Valproate?
  • A: Similar efficacy, but Ethosuximide has fewer cognitive/attentional side effects and no teratogenicity.
• Q: What drugs worsen Absences?
  • A: Sodium Channel Blockers (Carbamazepine, Phenytoin, Lamotrigine can sometimes, Gabapentin). "Narrow spectrum" agents.
• Q: Differentiate Absence from Focal Impaired Awareness Seizures.
  • A: Focal: Aura (sometimes), longer (greater than 30s), automatisms common, POST-ICTAL CONFUSION (Key). Absence: No aura, brief (less than 20s), immediate recovery.