Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Epilepsy

What Is It?

Epilepsy is a condition of the nervous system that causes repeated, sudden, brief changes in the normal electrical activity of the brain. During one of these epileptic episodes, commonly called a seizure or convulsion, brain cells fire uncontrollably at up to four times their normal rate, temporarily affecting the way a person behaves, moves, thinks or feels.

There are two main types of seizures:

• A primary generalized seizure involves the entire brain.

• A partial seizure begins in one brain area, called a focus, and affects only part of the brain.

Many conditions can affect the brain and trigger epilepsy, including:

• Brain injury, either before or after birth

• Brain tumors

• Infections, especially meningitis and encephalitis

• Genetic conditions, including tuberous sclerosis

• Abnormal blood vessels in the brain

• Lead poisoning

However, in about 70% of people with epilepsy, the specific cause is unknown.

Approximately 2.7 million Americans have active epilepsy. Each year, about 200,000 people are diagnosed with epilepsy in the United States, and up to 25% of these are children under the age of 15. Epilepsy is most common under the age of 2 and over the age of 65.