What are the signs and symptoms of absence seizures?

Signs and Symptoms of Absence Seizures

Absence seizures are characterized by brief episodes of impaired consciousness where patients remain upright without falling, typically lasting seconds, with sudden onset and termination. 1

Core Clinical Manifestations

Consciousness Alterations

• Impairment of awareness and responsiveness is the hallmark feature, with patients experiencing altered rather than completely lost consciousness 1
• Patients remain standing throughout the episode and do not fall, which is a critical distinguishing feature from other seizure types 1
• The severity of consciousness impairment varies from severe to mild or even inconspicuous, depending on the specific epileptic syndrome 2
• Impairment of expressive speech is typically more severe than receptive speech 3

Motor Manifestations

• Motor and behavioral arrest (sudden cessation of ongoing activity) occurs as a cardinal feature 4
• Eye manifestations are common, with eye opening occurring within 1-2 seconds of seizure onset in childhood absence epilepsy, and eye blinking observed in 41.5% of seizures 3, 4
• Myoclonic jerks, particularly of facial muscles, are the most common motor symptom when present 2
• Clonic, tonic, and atonic components may occur alone or in combination 2

Automatisms

• Automatisms occur in 45% of seizures and are proportional to the severity of consciousness impairment 4
• Oral automatisms (such as chewing or lip smacking) occur earlier than limb automatisms (4.03 vs 6.19 seconds after onset) 4
• Simple automatisms may accompany the impairment of consciousness 2

Autonomic Features

• Autonomic disturbances may be present 2
• Notably absent are pallor and sweating, which helps distinguish absence seizures from syncope 1

Temporal Characteristics

Duration and Pattern

• Seizures are brief, typically lasting seconds (mean duration 9-16 seconds depending on syndrome), with sudden onset and termination 2, 4
• Duration varies by syndrome: juvenile absence epilepsy shows longer seizures (mean 16.3 seconds) compared to childhood absence epilepsy (12.4 seconds) or juvenile myoclonic epilepsy with absences (6.6 seconds) 3
• Seizures are easily precipitated by hyperventilation in approximately 90% of untreated patients 2

Post-Event Features

• Minimal or absent post-event confusion, with brisk recovery of consciousness 1, 2
• This contrasts with the immediate clearheadedness typical of syncope 1

Syndrome-Specific Variations

Childhood Absence Epilepsy

• Demonstrates more severe impairment of consciousness 3
• Automatisms are frequent 3
• Characteristic early eye-opening within 1.8 seconds of EEG discharge onset 3

Juvenile Absence Epilepsy

• Interrupted speech and overbreathing may be restored during the seizure 3
• Automatisms are frequent 3
• Longer seizure duration compared to other syndromes 3

Juvenile Myoclonic Epilepsy with Absences

• Ictal manifestations are frequently mild and difficult to detect 3
• Patients may continue their activity and even perform mathematical calculations 3
• Speech is often not disturbed 3
• Myoclonic jerks during absences are extremely rare, though independent myoclonic jerks occur on awakening 3

Key Distinguishing Features from Other Conditions

• No loss of consciousness leading to falls - patients remain upright throughout 1
• Absence of typical syncopal triggers (orthostatic stress, emotional stimuli) 1
• No pallor or sweating unlike syncope 1
• Different from tonic-clonic seizures which show prolonged movements with onset coinciding with loss of consciousness 5
• Lack of aura (such as funny smell) that may precede other seizure types 5
• No prolonged post-ictal confusion or aching muscles typical of generalized tonic-clonic seizures 5

Additional Clinical Considerations

• Additional semiological features beyond behavioral arrest and non-responsiveness occur in 87% of patients (75% of seizures) 4
• Seizures may be spontaneous or triggered by photic stimulation, pattern stimulation, video games, or mental/emotional factors 2
• The presence of polyspikes on EEG (occurring in 31% of patients) predicts unfavorable therapeutic outcome with 92% positive predictive value 4