Types of Seizures

Absence seizures are generalized onset seizures, which means they start in both sides of the brain. During an absence seizure, people blink and stare for a few seconds. They do not speak, listen, nor are they able to notice anything. Fluttering of the eyelids is sometimes seen in absence seizures. Once the seizure is over, the patient usually has no memory of the incident. There are two different types of absence seizures: typical and atypical.

Atonic seizures, also known as drop seizures, are characterized by a sudden loss of muscle strength. As its name implies, atonic seizures are different from tonic seizures, where patients experience muscle stiffening. Episodes are usually very brief, often lasting less than two seconds. Disturbances in electrical activity in the brain leading to an atonic seizure can originate from both sides of the brain (generalized onset), or from one side of the brain (focal onset).

Clonic seizures are characterized by rhythmic jerking movements caused by muscles repeatedly stiffening and relaxing. These motor symptoms can affect the whole body or individual parts of the body such as the arms or legs. Episodes may last just a few seconds or up to one minute.  This type of seizure can start on just one side of the brain (focal onset) or on both sides of the brain simultaneously (generalized onset).

Focal impaired-awareness seizures are partial seizures that start in one area of the brain. They usually last one to two minutes and may start as a simple partial seizure. When the simple partial seizure develops into a focal impaired-awareness seizure, the person loses awareness and stares blankly. A focal-impaired awareness seizure can spread to both sides of the brain and become a generalized focal to bilateral tonic-clonic seizure.

A myoclonic seizure is characterized by a sudden brief muscle jerk that usually lasts for one or two seconds. Individuals experiencing myoclonic seizures might have just a single seizure or many that might occur within a short period of time. During a myoclonic seizure, the person is conscious and aware of what is happening. A prolonged period of frequent myoclonic seizures with little time between them is known as myoclonic status epilepticus.

Partial seizures can be simple, in which patients remain conscious, or complex, in which consciousness is impaired or lost. A simple partial seizure may trigger a complex partial seizure also known as focal impaired-awareness seizure, or a generalized seizure. A partial seizure affects only a specific area of the brain, while a generalized seizure, also called a tonic-clonic seizure, is characterized by convulsions and loss of consciousness.

Tonic-clonic seizures are characterized by convulsions and loss of consciousness. These seizures have two phases: tonic (stiffening) and clonic (rhythmical jerking). When the seizure begins, all the muscles stiffen and the person loses consciousness. During the clonic phase, the arms and legs begin to jerk rapidly and rhythmically as the person convulses. A tonic-clonic seizure typically lasts for one to three minutes.

Tonic seizures cause “increased muscle tone,” or the sudden stiffening of muscles. During a tonic seizure, different muscle groups may stiffen and the patient generally loses consciousness. This type of seizure is typically not associated with convulsions or jerking movements. Tonic seizures are generally short, lasting no longer than a minute and typically less than 20 seconds.