Classification of Seizures

There are two main groups of seizures: (1) primary generalized seizures and (2) partial seizures. Primary generalized seizures begin with a widespread, excessive electrical discharge involving both sides of the brain at once. Partial seizures begin with an abnormal electrical discharge in one area of the brain.

It is important to know whether someone suffers from primary generalized seizures or partial seizures, because different medications are used to treat them. A description of what happened before, during, and after the seizure, as well as recordings of the brain waves (an electroencephalogram, or EEG), helps the doctor to determine the type of seizure. In primary generalized epilepsy, the EEG shows a widespread increase in electrical activity. In partial seizures, the brain waves show a more restricted, or local, increase of electrical activity. However, the EEG may be normal in people with epilepsy, and the test occasionally shows "epilepsy waves'' in people who have never had a seizure.

Hereditary factors are more important in primary generalized seizures than in partial seizures. In some cases, it can be difficult to tell the difference between primary generalized seizures and partial seizures, since many of their features overlap. For example, a tonic-clonic, or grand mal, seizure may begin as a primary generalized seizure or as a partial seizure, and a "staring spell" can be an absence seizure (a type of primary generalized seizure) or a complex partial seizure.

PRIMARY GENERALIZED SEIZURES The main types of primary generalized seizures are absence seizures, atypical absence seizures, myoclonic seizures, atonic seizures, clonic seizures, tonic seizures, and tonic-clonic seizures.

ABSENCE, OR PETIT MAL, SEIZURES Absence (petit mal) seizures are brief episodes of staring with a lessening of awareness and responsiveness. The episode usually lasts less than 10 seconds but may last as long as 20 seconds. The seizure begins and ends suddenly. There is no warning before the seizure, and immediately afterward the person is alert and attentive and usually unaware that a seizure has taken place. In the majority of cases, these spells occur in children, beginning when they are between 4 and 14 years of age.

In approximately 75 percent of children, absence seizures stop occurring at about age 18. Absence seizures are often provoked by rapid breathing (hyperventilation). For some reason, however, absence seizures are uncommon during exercise with rapid breathing. Children with absence seizures have normal development and intelligence.

Simple absence seizures just involve staring. Complex absence seizures, which are more common, also involve some change in muscle activity, especially if the seizure lasts more than 10 seconds. The most common movements are eye blinks, but others include slight tasting movements of the mouth, automatic hand movements such as rubbing the fingers together, and contraction or relaxation of the muscles.

The EEG is extremely helpful in diagnosing absence seizures. In the majority of cases, a characteristic finding is three-per-second spike-and-wave discharges, especially during hyperventilation.

ATYPICAL ABSENCE SEIZURES The staring spells of atypical absence seizures also occur most frequently in children, and usually begin before 6 years of age. In contrast with absence seizures, atypical absence seizures often begin and end gradually (over seconds), often last more than 10 seconds (the usual duration is 5 to 30 seconds), and are not provoked by rapid breathing. The child stares but often has only a partial reduction in responsiveness. Eye blinking or slight jerking movements of the lips may occur. Children who have these seizures are more likely to have lower-than-average intelligence. In some children, especially those with intellectual deficits, atypical absence seizures may be difficult to distinguish from the child's usual behavior

Most children with these seizures have an abnormal EEG, which reveals slow spike-and-wave discharges, even when they are not having a seizure. The EEG abnormality is not provoked by hyperventilation.

MYOCLONIC SEIZURES Myoclonic seizures occur as brief, shocklike jerks of a muscle or group of muscles. Myoclonus, or involuntary muscle contractions, may occur in people who do not have epilepsy. For example, as many people fall asleep, their body suddenly jerks, which is referred to as sleep jerks, sleep starts, or benign nocturnal myoclonus. Among the abnormal forms of myoclonus are both epileptic and nonepileptic types.

Epileptic myoclonus usually causes abnormal movements on both sides of the body at the same time. The neck, shoulders, upper arms, body, and upper legs are usually involved. Myoclonic seizures occur in a variety of epilepsy syndromes, and the prognosis for control of these seizures varies among the different syndromes.

Myoclonic seizures in patients with Lennox-Gastaut syndrome often occur along with atonic (characterized by lack of muscle tone) and other seizure types. During these attacks, the person may fall. In addition to the areas of the body mentioned above, these seizures may involve the muscles of the face. As with other seizures in patients with Lennox-Gastaut syndrome, myoclonic seizures are often difficult to control with medication.

Myoclonic seizures in patients with juvenile myoclonic epilepsy syndrome most often involve the neck, shoulders, and upper arms. The seizures most commonly occur in the early morning hours, shortly after awakening. The attacks are usually well controlled with medication, which almost always needs to be continued throughout the person's life.

Progressive myoclonic epilepsy refers to a group of disorders associated with neurological deterioration. These disorders are rare in comparison with other types of myoclonic seizures.

ATONIC SEIZURES The brief spells of atonic seizures, lasting less than 15 seconds, are associated with a sudden loss of muscle strength, causing the eyelids to droop, the head to nod, or an object to be dropped, or causing a fall to the ground. Atonic seizures usually begin in childhood. Because of possible sudden falling, injury is common.

CLONIC SEIZURES Generalized convulsive seizures may involve jerking (clonic) movements on both sides of the body without a stiffening (tonic) component. These clonic seizures, in contrast with the more common tonic-clonic seizures, are not followed by a prolonged period of confusion or tiredness after the seizure has ended.

TONIC SEIZURES Tonic seizures, usually lasting less than 20 seconds, are associated with sudden stiffening movements of the body, arms, or legs, and involve both sides of the body. They are more common during sleep. Tonic seizures are most common in children who have lower-than-average scores on intelligence tests, but they can occur in any child or adult.

TONIC-CLONIC (GRAND MAL) SEIZURES Tonic-clonic (grand mal) seizures are convulsive seizures. The person briefly stiffens and loses consciousness, falls, and often utters a cry. It is not a cry from pain, but is caused by air being forced through the contracting vocal cords. The stiffening is followed by jerking of the arms and legs. The seizures usually last 1 to 3 minutes. There may be excessive saliva production, sometimes incorrectly described as "foaming'' at the mouth. Biting of the tongue or cheek may cause bleeding. Loss of urine or, rarely, a bowel movement may occur. After the convulsion the person may be tired and confused for a period of minutes to hours and often goes to sleep, but he or she may be agitated or depressed. The time immediately after the seizure is called the postictal period.

When a tonic-clonic seizure s more than 30 minutes or three or more seizures occur without the person returning to a normal state in between, a dangerous condition called convulsive status epilepticus has developed. If a tonic-clonic lasts longer than 5 minutes, medical help should be obtained immediately.

Some tonic-clonic seizures are preceded by a series of jerking movements. These seizures are referred to as clonic-tonic-clonic seizures and are common among people with juvenile myoclonic epilepsy.

PARTIAL SEIZURES Partial seizures begin with an abnormal burst of electrical activity in a restricted area of brain tissue. Most partial seizures come from the temporal or frontal lobes. Less commonly, partial seizures begin in the visual (occipital lobe) or sensory (parietal lobe) areas of the brain. Head injury, brain infections, stroke, and brain tumors are common causes of partial seizures. In some cases, hereditary factors are also important. In the majority of cases, no cause can be identified.

Partial seizures are divided into two main types, depending on whether consciousness is fully preserved. During simple partial seizures the person is alert, able to respond to questions or commands, and can remember what occurred during the seizure. During complex partial seizures, the ability to pay attention or to respond to questions or commands is impaired. Often, there is no memory of what happened during all or part of the seizure. It is extremely important to know whether a person suffers from simple or complex partial seizures, because the ability to drive, operate dangerous equipment, swim alone, and perform other activities usually has to be restricted in people with uncontrolled complex partial seizures.

SIMPLE PARTIAL SEIZURES Simple partial seizures can cause many different symptoms. In some cases, the symptoms are not recognized as a seizure, because many symptoms of partial seizures can also be caused by other factors. For example, abdominal discomfort is likely to be the result of a gastrointestinal disorder, but it also can be a symptom of a partial seizure coming from the temporal lobe. Tingling in the little finger that spreads to the forearm may come from a seizure, migraine, or nerve disorder.

CONDITIONS CONFUSED WITH EPILEPSY

Many medical, neurological, and psychiatric disorders can mimic epilepsy. Before recommending treatment, the doctor wants to be sure that the diagnosis is correct. Among the disorders with some symptoms that are similar to epilepsy are fainting, hypoglycemia, narcolepsy, panic attacks, and psychogenic (nonepileptic) seizures.

For more information about the New York University-Mount Sinai Comprehensive Epilepsy Center click here.

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