What Causes Epilepsy?

Anything that disturbs the normal pattern of activity in the brain can trigger epilepsy.

The cause can be illness, brain damage, or abnormal development of the brain. No cause can be determined for about three-quarters of the cases of epilepsy.

Because epilepsy has so many causes and can be linked to a number of other conditions, it is sometimes very difficult to determine the cause of a particular case. They include:

• Brain chemistry

• Hereditary causes

• Other disorders

• Head injury

• Prenatal injuries

• Environmental causes

Brain Chemistry

Epilepsy may develop because of an imbalance in those chemicals in the brain that help the nerve cells in the brain transmit electrical impulses. These chemicals are called neurotransmitters.

Researchers think that some people who have epilepsy have too much of a neurotransmitter that increases impulse transmission (an excitatory neurotransmitter) and others have too little of neurotransmitters that reduce transmission (an inhibitory neurotransmitter).

Gamma-aminobutyric acid (GABA) is a neurotransmitter that slows electrical transmission between the nerve cells. Low levels of GABA in the body have been linked to epilepsy and an increased risk for seizure. A number of the drugs used to treat epilepsy stimulate production of GABA.

Epilepsy may also be caused by changes in brain cells called glia. Glia regulate concentrations of chemicals in the brain that can change the way neurons signal.

The tendency to abnormal brain chemistry can sometimes be inherited and can sometimes be caused by an injury or a disease.

Hereditary Causes

Many types of epilepsy tend to run in families, and some have been traced to an abnormality in a specific gene. These genetic abnormalities can cause subtle changes in the way the body processes calcium, potassium, sodium, and other body chemicals.

People who have progressive myoclonus epilepsy are missing a gene that helps break down protein. Those with a severe form of epilepsy called LaFora's disease are missing a gene that helps break down carbohydrates.

Hereditary factors are not always a direct cause of epilepsy but may influence the disease indirectly. Genes can affect the way people process drugs or can cause areas of malformed neurons in the brain.

Other Disorders

Epilepsy can be triggered by brain damage caused by other disorders.

Epilepsy can sometimes be stopped by treating these underlying disorders. In other cases, epileptic seizures will continue after the underlying cause is treated.

Whether the seizures can be stopped depends on the type of disorder, the part of the brain that is affected, and how much damage has been done. Disorders that may trigger epilepsy include:

• Brain tumors, alcoholism, and Alzheimer's disease can cause epilepsy because they alter the normal workings of the brain.

• Stroke, heart attacks, and other conditions that affect the blood supply to the brain (cerebrovascular diseases) can cause epilepsy by depriving the brain of oxygen. About a third of all new cases of epilepsy that develop in older people are caused by cerebrovascular diseases.

• Infectious diseases such as meningitis, viral encephalitis, and AIDS, can cause epilepsy.

• Cerebral palsy, autism, and a number of other developmental and metabolic disorders can cause epilepsy.

Head Injury

Head injuries can cause seizures. If the head injury is severe, the seizures may not begin until years later. If the injury is mild, the risk is slight.

Prenatal Injuries

In a fetus, the developing brain is susceptible to prenatal injuries that may occur if the pregnant mother has an infection, doesn't eat properly, smokes or abuses drugs or alcohol. These conditions may cause cerebral palsy.

About 20% of seizures in children are caused by cerebral palsy or other nervous system diseases. Sometimes epilepsy is linked to areas in the brain where neurons may not have formed properly during prenatal development.

Environmental Causes

Epilepsy can be caused by:

• Environmental and occupational exposure to lead, carbon monoxide, and certain chemicals

• Use of street drugs and alcohol

• Lack of sleep, stress, or hormonal changes

• Withdrawal from certain antidepressant and anti-anxiety drugs