Clinical Signs of Absence Seizures
Absence seizures are characterized by brief episodes of impaired awareness lasting seconds, during which the patient remains upright and does not fall, with minimal to no post-event confusion. 1
Core Clinical Features
Consciousness and Awareness
- Altered consciousness rather than complete loss, with impairment of awareness and responsiveness while the patient remains standing throughout the episode 1
- The impairment of consciousness can range from severe to mild or even inconspicuous, depending on the specific syndrome 2
- Episodes are brief, typically lasting only seconds, with sudden onset and sudden termination 2
Motor Manifestations
- Patients do not fall during absence seizures, which is a key distinguishing feature from other seizure types 1
- Motor symptoms may include clonic, tonic, or atonic components, either alone or in combination 2
- Myoclonic movements, particularly of facial muscles, are the most common motor manifestation 2
- Automatisms (repetitive, purposeless movements) may occur during the episode 2
Autonomic Features
- No pallor or sweating, which distinguishes absence seizures from syncope 1
- Autonomic disturbances may be present but are not the predominant feature 2
Key Distinguishing Characteristics
What Absence Seizures Are NOT
- No loss of consciousness leading to falls—patients remain standing throughout 1
- Absence of typical syncopal triggers such as orthostatic stress or emotional stimuli 1
- Post-event confusion is minimal or absent, in stark contrast to the prolonged postictal confusion (>20-30 seconds) typical of generalized tonic-clonic seizures 3, 1
Triggers and Precipitation
- Easily precipitated by hyperventilation in approximately 90% of untreated patients 2
- May be triggered by photic stimulation, pattern stimuli, video games, or mental/emotional factors 2
- Usually occur spontaneously but can have identifiable triggers 2
EEG Characteristics
- Generalized 3-4 Hz spike-and-wave discharges are the hallmark EEG finding 2
- The ictal EEG discharge may be brief (2-5 seconds) or longer (15-30 seconds), continuous or fragmented 2
- EEG findings show bilateral, synchronous discharges consistent with generalized onset seizures 4
Age and Demographics
- Most commonly start in childhood or adolescence, with the most affected ages being 4-9 years 5
- Both genders are equally affected 5
- Can occur in approximately 10-15% of adults with epilepsy, often combined with other generalized seizure types 2
Common Clinical Pitfalls
- Absence seizures are often misinterpreted as daydreaming or inattention, particularly in school-aged children 5
- Brief tonic-clonic activity may accompany syncope and should not be confused with true seizure activity 3
- The brevity of episodes and lack of dramatic motor manifestations can lead to underrecognition 2