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

The structures of the brain include: the brainstem, consisting of the spinal cord, the medulla oblongata, the pons and the midbrain; the cerebellum; the cerebrum (one half, or hemisphere shown), and the diencephalon .

Epilepsy affects all age groups. Males have a slightly higher risk than females. The incidence is highest in children with another, but lesser, peak occurring after age 60. According to one estimate, 14% of epilepsy patients are under 15 years old and approximately a quarter are over age 64.

Every year between 25,000 and 40,000 American children have a first seizure that is unrelated to a fever. Epilepsy is decreasing in childhood but increasing in the elderly, probably because of mild strokes and cardiac arrest.

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. At this time, epilepsy types are generally into two categories, which are based on the specific biologic mechanisms involved in the seizure and the anatomical location of the seizure. They 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.

Experts 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.

Improved definitions of terms and new diagnostic technologies, including advanced imaging and genetic testing, have spawned new classification systems that better define specific epilepsies. The evolving methods may help researchers more accurately focus on specific epilepsies and allow doctors to make more appropriate therapeutic decisions. For example, some professional groups now suggest that epilepsies be classified in the following five ways:

Type of seizure (partial or generalized). Currently these categories are undergoing change.
Description of the seizure onset and evolution.
Specific syndromes that are associated with one or more seizure types. (Not all seizures will be part of a syndrome.)
Specific causes of the seizures, if known.
The degree of impairment.

Partial Seizures (also called Focal Seizures)

Partial, or focal, seizure is the more common type of epilepsy, and is generally defined as a disorder of neurons that starts on one side of the brain. The seizures are currently subcategorized as "simple" or "complex partial."

Simple Partial Seizures. A person with a simple partial seizure (sometimes known as Jacksonian epilepsy) does not lose consciousness, but may experience confusion, jerking movements, tingling, or odd mental and emotional events. Such events may include deja vu, mild hallucinations, or extreme responses to smell and taste. After the seizure, the patient usually has temporary weakness in certain muscles.
Complex Partial Seizures. Slightly over half of the seizures in adults are complex partial type. About 80% of these seizures originate in the temporal lobe, the part of the brain located close to the ear. Disturbances there can result in loss of judgment, involuntary or uncontrolled behavior, or even loss of consciousness. About 20% of these patients have seizures that start in the brain's frontal lobes. Prior to the actual seizure, people sometimes experience a warning sign, known as an aura, which can be a visual or auditory hallucination, an odd odor or a feeling of warmth. They may lose consciousness briefly and appear to others as motionless with a vacant stare. Emotions can be exaggerated; some sufferers even appear to be drunk. After a few seconds, a patient may begin to perform repetitive movements, such as chewing or smacking of lips. Episodes usually last no more than two minutes. People can have them infrequently, or as often as every day. A throbbing headache may follow a complex partial seizure.

In some cases, simple or complex partial seizures evolve into what are known as secondarily generalized seizures. The progress may be so rapid that the partial stage is not even noticed.

While the term "partial" implies the seizures affect only small or specific brain locations, in reality, they almost always involve diffuse and even widespread areas. In the future, the term "focal seizures" will most likely replace the term "partial seizures," and its subcategories. Until new classifications are more widely in use, this report will continue to use the term "partial seizures" and its subcategories.

Generalized Seizures

Generalized seizures are caused by nerve cell disturbances that occur in more diffuse areas of the brain than do partial seizures. Therefore, they have a more serious effect on the patient. They are further subcategorized as tonic-clonic (or grand mal) or absence (petit mal) seizures.

Tonic-Clonic (Grand Mal) Seizures. The first stage of a grand mal seizure is called the tonic phase, in which the muscles suddenly contract, causing the patient to fall and lie stiffly for about 10 to 30 seconds. Some people experience a premonition or aura before a grand mal seizure; most, however, lose consciousness without warning. If the throat or larynx is affected, there may be a high-pitched musical sound (stridor) when the patient inhales. Spasms occur for about 30 seconds to a minute, then the seizure enters the second phase, called the clonic phase. The muscles begin to alternate between relaxation and rigidity. After this phase, the patient may lose bowel or urinary control. The seizure usually lasts a total of two to three minutes, after which the patient remains unconscious for a while and then awakens to confusion and extreme fatigue. A severe throbbing headache similar to migraine may also follow the tonic-clonic phases.
Absence (Petit Mal) Seizures. Absence or petit mal seizures are brief losses of consciousness that occur for 3 to 30 seconds. Physical movement and loss of attention may stop for only a moment. Such seizures may pass unnoticed by others. Small children may simply appear to be staring or walking distractedly. Petit mal may be confused with simple or complex partial seizures, or even with attention deficit disorder. [See In-Depth Report #30: Attention deficit hyperactivity disorder.] In petit mal, however, a person may experience attacks as often as 50 to 100 times a day. About 25% of patients with petit mal develop grand mal seizures. An electroencephalogram (EEG) test that shows a specific brain wave pattern can usually identify these patients.

Click the icon to see a depiction of a tonic-clonic seizure.

Other Seizures

Atonic (Akinetic) Seizures. A person who has an atonic (or akinetic) seizure loses muscle tone. Sometimes it may affect only one part of the body so that, for instance, the jaw slackens and the head drops. At other times, the whole body may lose muscle tone, and the person can suddenly fall. A brief atonic episode is known as a drop attack.

Simply Tonic or Clonic Seizures. Seizures can also be simply tonic or clonic. In tonic seizures, the muscles contract and consciousness is altered for about 10 seconds, but the seizures do not progress to the clonic or jerking phase. Clonic seizures, which are very rare, occur primarily in young children, who experience spasms of the muscles but not tonic rigidity.

Myoclonic. Myoclonic seizures are a series of brief jerky contractions of specific muscle groups, such as the face or trunk.

Epilepsy Syndromes

Epilepsy is also grouped according to a set of common characteristics, including:

Patient age.
Type of seizure or seizures.
Whether a cause is known or not (idiopathic).

A few syndromes and inherited epilepsies are listed as follows. They do not represent all epilepsies.

West Syndrome (Infantile Spasms)

West syndrome, also called infantile spasms, is a disorder that involves spasms and developmental delay in children within the first year, usually in infants between four and eight months.

Benign Familial Neonatal Convulsions

Benign familial neonatal convulsions (BFNC) are a rare, inherited form of generalized seizures that occur in infancy.

Juvenile Myoclonic Epilepsy (Impulsive Petit Mal)

Juvenile myoclonic epilepsy, also called impulsive petit mal epilepsy, is characterized by generalized seizures, usually tonic-clonic marked by jerky movements (called myoclonic jerks), and sometimes absence seizures. This accounts for 7% of epilepsies, and usually occurs in individuals age 8 to 20.

Adult Myoclonic Epilepsy

Some research now suggests that adult myoclonic epilepsy may be a previously undescribed and distinct syndrome. It involves the development of generalized epilepsy of unknown causes in middle-aged adults.

Lennox-Gastaut Syndrome

Lennox-Gastaut syndrome is a severe form of epilepsy in young children that causes multiple seizures and some developmental retardation. It usually involves absence, tonic, and partial seizures.

Myoclonic-Astatic Epilepsy

Myoclonic-astatic epilepsy (MAE) is a combination of myoclonic seizures and astasia (a decrease or loss of muscular coordination), often resulting in the inability to sit or stand without aid.

Progressive Myoclonic Epilepsy

Progressive myoclonic epilepsy is an inherited disorder occurring in children between the ages of six and 15. It usually involves tonic-clonic seizures and marked sensitivity to light flashes. Although the disease was previously considered to be progressive throughout life, current therapies have significantly improved its outlook.

Autosomal Dominant Nocturnal Frontal Lobe Epilepsy

Autosomal dominant nocturnal frontal lobe epilepsy is a rare, inherited syndrome that usually occurs during childhood, typically around age 11. However, onset varies widely within families. Seizures can be dystonic (twisting contractions) or tonic (muscle contractions), or involve thrashing. They are brief, frequent, and occur in clusters during the night. The seizures often subside with age.

Landau-Kleffner Syndrome

Landau-Kleffner syndrome is an epileptic condition that results in the inability to communicate either with speech or by writing (aphasia).

Review Date: 12/7/2005
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital