Introduction

Epilepsy is a neurological disorder characterized by unprovoked, recurring seizures that disrupt the nervous system and can cause mental and physical dysfunction. In the U.S., about 2.5 million people are affected by epilepsy and seizures. About 10% of the American population will experience at least one seizure during their lifetime.

Criteria for Classifying Epilepsies and Seizures

Epilepsy is not a single disorder but rather a wide spectrum of problems. What all types of epilepsy share are recurrent, unprovoked seizures caused by an uncontrolled electrical discharge from nerve cells in the cerebral cortex. This part of the brain controls higher mental functions, general movement, and the functions of the internal organs in the abdominal cavity, perception, and behavioral reactions.

Seizures are a symptom of epilepsy. Epilepsy types are generally put into two categories, which are based on the specific biologic mechanisms involved in the seizure and the anatomical location of the seizure. The two types are:

• Partial (also called focal or localized) seizures. These seizures are more common than generalized seizures and occur in one or more specific locations in the brain. In some cases, partial seizures can spread to wide regions of the brain. They are likely to develop from specific injuries, but in most cases the exact origins are unknown.
• Generalized seizures. These seizures typically occur in both sides of the brain. Many forms of these seizures are genetically based. There is usually normal neurologic function.

Doctors are finding, however, that these categories do not actually reflect what is now known about the brain's anatomy. For example, the words "partial" and "generalized" suggest that seizures either involve only part of the brain or are widespread. However, a number of events in the brain occur with either type, muddying these distinctions. Researchers are now in the process of making clearer definitions and terms that reflect what actually is happening in the brain.

New classification systems better define specific epilepsies. Some professional groups now suggest that epilepsies be classified in the following five ways:

• Type of seizure (partial or generalized)
• Description of the seizure onset and evolution
• Specific syndromes that are associated with one or more seizure types (however, not all seizures will be part of a syndrome)
• Specific causes of the seizures, if known
• Degree of impairment

Partial Seizures (also called Focal Seizures)

These seizures are subcategorized as "simple" or "complex partial."