Epilepsy is a disorder of the brain characterized by repeated seizures. A seizure is usually defined as a sudden alteration of behavior due to a temporary change in the electrical functioning of the brain. Normally, the brain continuously generates tiny electrical impulses in an
Epilepsy is a disorder of the brain characterized by repeated seizures. A seizure is usually defined as a sudden alteration of behavior due to a temporary change in the electrical functioning of the brain. Normally, the brain continuously generates tiny electrical impulses in an orderly pattern. These impulses travel along the network of nerve cells, called neurons, in the brain and throughout the whole body via chemical messengers called neurotransmitters. In epilepsy, however, the brain's electrical rhythms have a tendency to become imbalanced, resulting in recurrent seizures. In patients with seizures, the normal electrical pattern is disrupted by sudden and synchronized bursts of electrical energy which may briefly affect their consciousness, movements, or sensations. Epilepsy is usually diagnosed after a person has had at least two seizures that were not caused by some known medical condition like alcohol withdrawal or extremely low blood sugar.
If seizures arise from a specific area of the brain, then the initial symptoms of the seizure often reflect the functions of that area. The right half of the brain controls the left side of the body, and the left half of the brain controls the right side of the body. So for example, if a seizure starts from the right side of the brain, in the area that controls movement in the thumb, then the seizure may begin with jerking of the left thumb or hand.
Types of Seizures
There are so many kinds of seizures that epilepsy specialists are still updating their thinking about how to classify them. Usually, they classify seizures into two types, primary generalized seizures and partial seizures. The difference between these types is in how they begin.
Primary generalized seizures begin with a widespread electrical discharge that involves both sides of the brain at once. Hereditary factors are important in many of these seizures. Epilepsy in which the seizures begin from both sides of the brain at the same time is called primary generalized epilepsy. Primary generalized epilepsy is more likely to involve genetic factors than partial epilepsy, in which the seizures arise from a limited area of the brain.
Partial seizures begin with an electrical discharge in one limited area of the brain. Some are related to head injury, brain infection, stroke, or tumor, but in most cases the cause is unknown. One question that is used to further classify partial seizures is whether consciousness (the ability to respond and remember) is "impaired" or "preserved." The difference may seem obvious, but there are actually many degrees of impairment or preservation of consciousness.
The following factors may increase the risk of seizures in people predisposed to seizures:
- Sleep deprivation or fatigue
- Insufficient food intake
- Alcohol use or drug abuse
- Failure to take prescribed anticonvulsant medications
About half of the people who have one seizure without a clear cause will have another one, usually within six months. You are twice as likely to have another seizure if you have a known brain injury or other type of brain abnormality. If you do have two seizures, there is about an 80 percent chance that you will have more. If your first seizure occurred at the time of an injury or infection in the brain, you are more likely to develop epilepsy than if you did not have a seizure in that situation.
Prevalence and Incidence
About 2.5 million people in the United States have epilepsy, and as many as 9 percent of the entire population may experience a seizure at some point in their lives. Epileptic seizures may be tied to a brain injury or genetics, but most of the time the cause is unknown. New cases of epilepsy are diagnosed most commonly in the first year of life. The rate of new cases in children gradually declines until about age 10, and then stabilizes. After age 55 or 60, the rate starts to increase, as people develop strokes, brain tumors, or Alzheimer's disease, all of which may cause epilepsy.
About 2.7 million Americans have been treated for epilepsy in the past five years. More men than women have epilepsy. New cases of epilepsy are most common among children, especially during the first year of life. Up to 5 percent of the world’s population may have a single seizure at some time in their lives. It is likely that around 50 million people in the world have epilepsy at any one time. Children and adolescents are more likely to have epilepsy of unknown or genetic origin. Brain injury or infection can cause epilepsy at any age. Recent studies show that up to 70 percent of children and adults with newly diagnosed epilepsy can be successfully treated. About 10 percent of children with epilepsy have seizures that do not respond to treatment. The proportion of adults is higher, up to 15 percent.
The reasons why epilepsy begins are different for people of different ages. But what is known is that the cause is undetermined for about half of all individuals with epilepsy, irregardless of age. Children may be born with a defect in the structure of their brain, or they may suffer a head injury or infection that causes their epilepsy. Severe head injury is the most common known cause in young adults. In middle age, strokes, tumors, and injuries are more frequent. In people age 65 and older, stroke is the most common known cause, followed by degenerative conditio