Absence seizures: Symptoms, diagnosis and treatment

What is an absence seizure?

Absence seizures affect fewer than one in 1,000 children under 15, and girls are more likely to be affected than boys.

Absence seizures used to be called petit mal seizures and are caused by abnormal and intense electrical activity in the brain.

Normally, the brain's nerve cells (neurons) communicate with one another by firing tiny electric signals, but with a seizure, these signals become abnormal. Seizures may affect an isolated part of the brain or may involve abnormal activity in the whole brain (called generalised seizures).

Absence seizures are one form of generalised seizure. These last up to 20 seconds.

The person, most often a child aged five to 15, abruptly stops whatever he's doing (talking, walking) and appears to "stare into space." Absence seizures rarely cause a true convulsion in which the person falls down or collapses, and despite briefly losing consciousness, the person recovers fully with no lingering confusion or other ill effects. These "spells" may occur infrequently or several times per hour. In children, absence seizures may interfere with learning and are often misinterpreted as impertinence or inattention. About a quarter of people who have absence seizures will develop another type of generalised seizure called tonic-clonic (formerly called grand mal) seizures. The vast majority of children, however, will outgrow them.

What causes absence seizures?

Scientists are unsure of the underlying reasons for absence seizures in most cases. Some research suggests that genetics may play a role.

What are the symptoms of an absence seizure?

Because absence seizures (also known as petit mal) are usually quite brief, tend to strike during times of inactivity, and closely resemble daydreaming or "being off in one's own world," they may pass unnoticed by others and go undiagnosed for some time.

Absence seizures fall into two categories: typical and atypical.

Typical absence seizures begin abruptly, last up to 20 seconds, and resolve themselves without complication. The person simply stops in his or her tracks (and/or mid-sentence), and enters a staring, trance-like state during which he or she is unresponsive and unaware of his or her surroundings. He or she may make fumbling movements with his or her hands, and there may also be eyelid fluttering, lip smacking, or chewing motions during the seizure. When the seizure passes, the person returns to normal, with no memory of the event and no lingering effects. Generally speaking, typical absence seizures have no discernible cause.

Atypical seizures are similar to typical seizures, except that they tend to begin more slowly, last longer (up to a few minutes) and can include slumping or falling down. The person may also feel confused for a short time after regaining consciousness. While the cause of atypical seizures may be unidentifiable, they are sometimes traced to abnormalities in the brain that were present at birth (congenital) or from trauma or injury, or from complications from liver or kidney disease. This type of seizures may continue into adulthood.