Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Absence Seizures (Petit Mal Seizures)

What Is It?

The brain's nerve cells (neurons) communicate with one another by firing tiny electric signals. When someone has a seizure (also known as a convulsion), the firing pattern of the brain's electric signals suddenly becomes unusually intense and changes from normal. The seizure can affect only a small area of the brain or it can involve the whole brain. If the whole brain is involved, the electrical disturbance is called a generalized seizure. The two most common forms of generalized seizures are tonic-clonic seizures (often called grand mal seizures) and absence seizures (also called petit mal seizures). Although both forms of generalized seizures cause the patient to lose consciousness temporarily, only the grand mal form causes an obvious convulsion, in which the person stiffens and falls to the ground, with clenched teeth and rhythmic muscle movements that may last two minutes or longer.

An absence seizure causes a loss of consciousness that is usually very brief -- 30 seconds or less -- and barely noticeable, if at all. The person simply stops moving or speaking, stares straight ahead blankly, and does not respond to questions. The seizure is so short and hard to even notice that a person can have 50 or 100 absence seizures a day, without them being detected. When the seizure ends, the person goes back to his or her normal activities without realizing that anything has happened; he or she also does not have any memory of the seizure.

Epilepsy is a problem with the brain that causes a seizure to occur at different times again and again. Therefore, a child with repeated absence seizures is said to have childhood absence epilepsy or petit mal epilepsy. Although absence epilepsy can begin at any time during childhood, it is most common in children between the ages of 5 and 15 years. Girls have absence epilepsy more often than boys, and in most cases the reason for the seizures is unknown. Although research suggests that genetic (inherited) factors may play some role in the development of absence epilepsy, there is no practical way to use this information to diagnose the disorder or to screen for it.