Absence seizures are a type of generalized seizure, but we'll discuss them separately because the syndrome of absence epilepsy has characteristic findings. Typical absence seizures are defined clinically by abrupt and brief cessation of awareness and activity, often with eye fluttering or blinking, with rapid return to normal after the seizure ends. Atypical absence seizures may come with other features such as motor activity or more prolonged postictal states.

What are Absence Seizures?

Absence seizures, also known as petit mal seizures, are a type of generalized seizure. They are characterized by a sudden, brief loss of awareness or consciousness, typically with minimal or no motor activity. These seizures are particularly common in childhood and are one of the most common seizure types in epilepsy, especially in absence epilepsy syndromes.

Absence seizures are usually very brief, lasting just a few seconds, but can occur frequently, sometimes hundreds of times a day, particularly in younger children.

Key Clinical Features of Absence Seizures

  • Sudden Loss of Awareness: The primary characteristic of an absence seizure is the abrupt interruption of awareness. The person may suddenly stop whatever they are doing and stare blankly into space. During the seizure, they do not respond to external stimuli such as calling their name or touch.
  • Minimal or No Motor Activity: In many cases, there is no observable motor activity. However, some individuals may display eye fluttering, blinking, or slight facial twitching. These movements are subtle and are often not noticeable unless the observer is aware of the seizure.
  • Duration: Absence seizures are typically short, often lasting between 10 and 20 seconds. The person will return to their normal state of awareness immediately after the seizure ends.
  • No Postictal Confusion: Unlike many other types of seizures, absence seizures do not have a postictal state—meaning there is no prolonged confusion or disorientation following the seizure. After the seizure ends, the person may resume their previous activities without any noticeable lingering effects.
  • Abrupt Onset and Termination: The seizure begins suddenly, without any warning signs. Similarly, it ends abruptly, with the person regaining awareness almost immediately. This is in contrast to seizures like tonic-clonic seizures, which often have gradual onset and resolution.

Types of Absence Seizures

Typical Absence Seizures

These are the most common form of absence seizures, typically seen in childhood.

  • Characteristics: Sudden and brief cessation of awareness, minimal to no motor activity, sometimes with subtle signs like eye fluttering, no postictal confusion, typically 3 Hz generalized spike-and-wave discharges on EEG, no postictal confusion or lethargy, and a rapid return to normal behavior after the seizure ends.

Atypical Absence Seizures

These seizures are less common and may present with additional features or more complex symptoms.

  • Characteristics: May involve more pronounced motor activity such as movements of the hands, arms, or facial muscles, longer duration (more than 20 seconds), postictal confusion or drowsiness, EEG patterns may vary, showing polyspike-and-wave discharges instead of the typical 3 Hz spike-and-wave, and often associated with more complex epilepsy syndromes such as Lennox-Gastaut syndrome or West syndrome.

EEG Characteristics of Absence Seizures

  • 3 Hz Spike-and-Wave Discharges: The hallmark EEG finding for typical absence seizures is a 3 Hz generalized spike-and-wave pattern. This pattern consists of a sharp spike followed by a slow wave, occurring at a frequency of approximately 3 cycles per second. This pattern is seen across the entire brain and represents the abnormal electrical discharges during the seizure.
  • Polyspike-and-Wave Discharges: In atypical absence seizures, the EEG may show polyspikes (multiple spikes followed by a wave), indicating more complex and irregular brain activity compared to typical absence seizures.
  • Sudden Onset and Termination: The spike-and-wave discharges on EEG typically appear suddenly and stop abruptly, just as the seizure begins and ends.
  • No Postictal Slowing: Unlike tonic-clonic seizures or focal seizures, absence seizures do not show postictal slowing on EEG. There is no prolonged period of abnormal brain activity or confusion following the seizure. The EEG returns to baseline immediately after the seizure ends.
  • Rapid Transition: Absence seizures have a rapid onset and offset. On EEG, this means there is no gradual increase or decrease in abnormal brain activity before or after the seizure. The transition is sharp, with the brain activity either spiking or returning to baseline almost instantly.

Differentiation from Other Seizure Types

  • Absence Seizures vs. Focal Seizures: Focal seizures involve localized brain activity, often affecting a specific part of the body (such as an arm or leg). In contrast, absence seizures involve generalized brain activity, leading to a complete loss of awareness.
  • Absence Seizures vs. Tonic-Clonic Seizures: Tonic-clonic seizures (grand mal seizures) are much more dramatic and last longer, with a tonic phase (muscle stiffening) followed by a clonic phase (rhythmic jerking). These seizures often last 1-2 minutes and are followed by postictal confusion and lethargy. Absence seizures, by contrast, are brief, with no postictal state and minimal or no motor activity.
  • Absence Seizures vs. Psychogenic Non-Epileptic Seizures (PNES): PNES are seizure-like episodes caused by psychological factors, not abnormal brain activity. While both PNES and absence seizures may involve staring or brief loss of awareness, PNES often have a more gradual onset, longer duration, and can include more complex motor movements (e.g., shaking or thrashing).

Management of Absence Seizures

  • First-line Medications: Valproate (Depakote) is often the first-line treatment for absence seizures and is effective in many patients. Ethosuximide (Zarontin) is another medication specifically approved for treating absence seizures and is often preferred for typical absence seizures.
  • Other Medications: If absence seizures do not respond to valproate or ethosuximide, other medications such as lamotrigine, levetiracetam, or topiramate may be considered.
  • Avoiding Triggers: Sleep deprivation, stress, and flashing lights are common triggers for absence seizures. Avoiding these triggers can help reduce the frequency of seizures.
  • Long-Term Management: Treatment often requires ongoing adjustments in medication dosages. Continuous EEG monitoring and follow-up with a neurologist are crucial to ensure that seizures remain under control.

Prognosis

The prognosis for absence seizures is generally good. Many children outgrow absence seizures as they reach adolescence, and some may have full remission of seizures over time. However, in some individuals, absence seizures may persist into adulthood or evolve into other types of epilepsy. Educational and social support are important for managing the impact of seizures on daily activities.