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Absence Seizures

Absence seizures (say: ab-SAHNs) are a type of generalized seizure. They involve short periods of unresponsiveness, often many times a day. They usually begin in childhood, although they can occasionally begin in adulthood; they are very rare in infants. There are several different types of absence seizures. The major divisions are typical or atypical.

Once parents or teachers have become aware of them, absence seizures are usually quite easy to diagnose, although if they have certain less typical features they may be confused with complex partial seizures. A diagnosis of absence seizures is made when parents or teachers report that the child is having staring spells and the doctor sees a typical pattern on the child’s EEG. Typical absence seizures can often be triggered in the doctor’s office by asking the child to hyperventilate (breathe fast and deeply).

Children with absence seizures may also have other seizure types; for instance, one study found that 37% of people with absence seizures also had tonic-clonic seizures.

What are other terms for absence seizures?

Other terms for absence seizures that you may come across include:

  • petit mal
  • epileptic absence
  • pyknolepsy

How can you tell if your child has absence seizures?

Absence Seizures
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Typical absence seizures

A child having a typical absence seizure stops what she is doing and stares blankly. Her eyes may roll upwards. She will not react if someone speaks to her or touches her arm. The seizure usually lasts for about 10 seconds and the child is alert immediately after the seizure, or is confused for at most two to three seconds. She usually does not know that she has had a seizure. Her EEG will be normal between seizures and will have a typical “spike-and-wave” pattern during seizures.

The seizures may have one or more other features, such as clonic components or automatisms, in addition to the symptoms described above. Children whose seizures have some of these features are less likely to have the syndrome of Childhood Absence Epilepsy.

  • An absence seizure with mild clonic components involves mild, often subtle twitching of the eyelids, the corners of the mouth, and sometimes the arms.
  • In an absence seizure with atonic components, the child’s head or body may slump forward or objects may drop from her hand due to a sudden loss of muscle tone. It is rare for a child to fall during such a seizure.
  • An absence seizure with tonic components may be symmetric (the same on both sides) or asymmetric (stronger on one side). With tonic activity, the muscles stiffen and contract suddenly, so a child that is standing may be pushed backward, or her head or body may turn to one side.
  • An absence seizure with automatisms may look a bit like a complex partial seizure. The child makes purposeful-seeming movements such as raising her eyelids, licking, swallowing, and fiddling or scratching with her hands.
  • In an absence seizure with autonomic symptoms, the child may become pale around the mouth, her pupils may dilate, her face may become flushed, her heart may beat faster, she may get goosebumps, her mouth may water, or she may wet herself.

Atypical absence seizures

Atypical absence seizures are harder to define. The beginning and end of the staring spell are not as clear-cut as in typical absence seizures, and the child is often confused after the seizure. The seizure usually lasts five to 10 seconds and may include mild eyelid twitching, tonic or autonomic symptoms, or automatisms; the child may fall down. Atypical absence seizures are more often seen in children who have other neurological problems such as mental retardation. These children often have other seizure types as well. Their EEG is usually abnormal between seizures as well as during seizures.

How many other children have absence seizures?

Approximately one child in 4300 to 8300 children under 15 years of age has absence epilepsy. The rates are usually higher in girls than in boys. Most children develop absence seizures between six and eight years old. It is uncommon for absence seizures to begin after age 14.

What causes absence seizures?

Typical absence seizures are seen with childhood absence epilepsy, juvenile absence epilepsy, and juvenile myoclonic epilepsy. There is a genetic component to these syndromes, but the details are unclear. These syndromes are all idiopathic; the brain appears normal on imaging (CT or MRI scan), but may have microscopic changes at the cellular level.

We know less about what causes atypical absence seizures. They are often seen in Lennox-Gastaut syndrome, cryptogenic or symptomatic generalized epilepsy, continuous spike waves in slow sleep, and myoclonic-astatic epilepsy. Some children with atypical absence seizures have obvious brain abnormalities while others have microscopic changes.

How are absence seizures treated?

Typical absence seizures can usually be controlled easily with anti-epileptic drugs. Atypical absence seizures are also treated with drugs, but often are not as easily controlled.

What should I do when my child has an absence seizure?

If your child is having an absence seizure:

  • Don’t shout; she cannot hear you.
  • If you are not sure whether she is having a seizure or just daydreaming, touch her gently on the arm.
  • No other intervention is usually needed.

What is the outlook for a child with absence seizures?

The outlook for a child with absence seizures depends on the underlying syndrome.

  • In childhood absence epilepsy, the seizures can be controlled with medication in 80% to 95% of cases. Some researchers believe that earlier treatment improves the prognosis and reduces the chance of relapse. The seizures from childhood absence epilepsy usually stop two to five years after they begin. Usually, once the child has been free of seizures for two to three years, her anti-epileptic medications can be gradually discontinued.

  • Other syndromes with typical absence seizures, such as juvenile absence epilepsy and juvenile myoclonic epilepsy, may continue for the rest of the child’s life, although in 80% to 90% of cases the seizures can be controlled with medication.
  • The prognosis for atypical absence seizures also depends on the underlying disorder. In Lennox-Gastaut syndrome, for instance, it is difficult to control the seizures, and mental disability is common.

Elizabeth J. Donner, MD, FRCPC

2/4/2010




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