What is absence seizure (epilepsy)?

Absence Seizures: A Comprehensive Overview

Absence seizures are brief (seconds) generalized seizures characterized by sudden onset and termination, with impairment of consciousness and generalized 3-4Hz spike/polyspike and slow wave discharges on EEG. 1 These seizures differ fundamentally from other seizure types and have unique pharmacological responses.

Clinical Presentation

Essential Components

• Duration: Typically brief, lasting seconds
• Consciousness: Impairment ranges from mild to severe
• EEG Pattern: Generalized 3-4Hz spike/polyspike and slow wave discharges

Clinical Manifestations

• Behavioral signs:

  • Brief staring spells
  • Sudden cessation of activity
  • Unresponsiveness to verbal stimuli
  • Automatic resumption of activities after seizure ends

• Associated features (may be present):

  • Motor manifestations (most commonly facial myoclonia)
  • Automatisms (lip smacking, fumbling with clothes)
  • Autonomic disturbances
  • Clonic, tonic, or atonic components

Diagnostic Criteria

Absence seizures can be diagnosed based on:

1. Clinical presentation: Brief episodes of impaired consciousness
2. EEG findings: Characteristic 3-4Hz spike-wave discharges
3. Provocation: Hyperventilation triggers seizures in approximately 90% of untreated patients 1
4. Response to medication: Positive response to specific anti-absence medications

Classification

Absence seizures can be categorized as:

1. Typical absence seizures: Classic presentation with 3Hz spike-wave discharges
2. Atypical absence seizures: Associated with symptomatic or cryptogenic generalized epilepsies, with more prominent tonic/myoclonic components 2
3. Absence status epilepticus: Prolonged absence seizures occurring in about 30% of patients 1

Epidemiology

• Absence seizures usually begin in childhood or adolescence
• They occur in approximately 10-15% of adults with epilepsy 1
• Active epilepsy affects 1.2% of the US population (3.4 million people) 3
• Approximately 0.6% of children under 17 years old suffer from epilepsy 4

Pathophysiology

Absence seizures involve abnormal electrical activity in thalamocortical circuits. Ethosuximide, a common treatment, suppresses the paroxysmal three cycle per second spike and wave activity by:

• Depression of the motor cortex
• Elevation of the threshold of the central nervous system to convulsive stimuli 5

Differential Diagnosis

Important conditions to distinguish from absence seizures:

1. Complex partial seizures: Typically longer duration, with post-ictal confusion
2. Syncope: Loss of consciousness due to cardiovascular causes
3. Daydreaming: No EEG changes, responsive to strong stimuli
4. TIA/stroke: Focal neurological signs predominate; TIA of the vertebrobasilar system can cause LOC but always with focal signs 3

Treatment Options

First-line medications for absence seizures include:

1. Ethosuximide:

   • Specifically indicated for absence seizures 5
   • Controls about 70% of absences
   • Not suitable as monotherapy if other generalized seizures coexist 1

2. Valproic acid:

   • Indicated for simple and complex absence seizures 6
   • Controls absences in 75% of patients
   • Also effective for generalized tonic-clonic seizures (70%) and myoclonic jerks (75%)
   • May be undesirable for women of childbearing age due to teratogenicity 1

3. Lamotrigine:

   • May control absences in 50-60% of patients
   • May worsen myoclonic jerks
   • Skin rashes are common 1

For resistant cases, combination therapy may be needed. Low doses of lamotrigine added to valproic acid can have dramatic beneficial effects 1.

Complications and Associated Risks

• Attention deficits: Absence epilepsy is associated with attention impairments 7
• Accidental injuries: Higher risk during activities requiring sustained attention 7
• Academic difficulties: Due to brief lapses in consciousness during school

Prognosis

The prognosis varies depending on the epilepsy syndrome:

• Many patients with childhood absence epilepsy outgrow their seizures
• Others may have lifelong seizures or develop other seizure types
• Absences that persist into adulthood are often more refractory to treatment 8

Key Points for Management

• Accurate diagnosis is crucial, requiring both clinical observation and EEG confirmation
• Syndromic diagnosis impacts treatment strategies and prognosis 1
• First-line medications should be chosen based on seizure type and patient characteristics
• Regular monitoring for medication side effects is essential
• Patient and family education about seizure recognition and safety is important

Absence seizures require prompt diagnosis and appropriate treatment to minimize impact on quality of life and reduce the risk of complications.