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Explore This Condition

Many people associate seizures with shaking, twitching, and loss of awareness. These symptoms describe one specific seizure type known as a tonic-clonic seizure. However, seizures come in many types, each with their own symptoms.

As a Level 4 Epilepsy Center, certified by the National Association of Epilepsy Centers, Massachusetts General Hospital provides the highest level of epilepsy care available. Our team provides advanced neurodiagnostic monitoring, along with comprehensive medical, neuropsychological, and psychosocial treatment for even the most complex cases. We also offer full evaluations for epilepsy surgery, including intracranial monitoring and specialized surgical procedures that are not widely available at other institutions.

Seizure Classification

As researchers and clinicians have learned more about seizures, they have updated the terms used to describe them. Today, experts group seizures into three major types, based on where they start in the brain and what symptoms they cause. This modern classification system helps doctors describe seizures more accurately. It also allows patients to better understand their type of seizure and begin the right treatment as early as possible.

Area of Onset: Focal vs Generalized Seizures

Doctors classify seizures into three main types based on where they begin in the brain: focal, generalized, and unknown. These terms describe the type of seizure and where it began in the brain, which can help determine the best treatment.

Focal Seizures

Focal seizures begin in one specific area on one side of the brain. This type of seizure used to be called partial seizures. Focal seizures can be further divided into two subtypes:

  • Focal aware: During a focal aware seizure, the patient is awake and aware of their surroundings.
  • Focal impaired awareness: These seizures cause changes in awareness—such as confusion, unresponsiveness, or staring into space. A person who has an impaired awareness seizure may not realize they had a seizure. This type of seizure used to be called a complex partial seizure.

Generalized Seizures

Generalized seizures begin on both sides of the brain at once. They always affect awareness, often leading to loss of consciousness or unresponsiveness.

Unknown Onset Seizures

Doctors classify a seizure as unknown onset when they can’t determine where it began in the brain. This can happen if no one sees what happened. If doctors later gather enough information, they may reclassify the seizure as focal or generalized.

Seizure Types by Symptom

Modern seizure classification also considers the type of symptoms a person experiences during a seizure. Doctors group seizures into two categories based on whether the symptoms involve movement:

  • Motor seizures involve physical movement, such as jerking, stiffening, or loss of muscle control.
  • Non-motor seizures describe seizures without convulsions or other movement symptoms. They instead may causes changes in awareness, emotions or sensations.
Motor symptoms
  • Atonic: In an atonic seizure, muscles suddenly go limp or weak, which can cause falls.
  • Tonic: Tonic seizures cause the muscles to tighten and become rigid. This can also cause falls since people can't adjust their balance when their body is rigid.
  • Clonic: A clonic seizure causes prolonged shaking, jerking, or twitching movements.
  • Myoclonic: Myoclonic seizures involve brief, sudden jerks or twitches.
  • Tonic-clonic: A tonic-clonic seizure is what most people think of when they picture a seizure. This type of seizure begins with muscle stiffening, often followed by a groan as air is pushed from the lungs. The person may lose consciousness and fall. This is followed by rhythmic jerking movements, which can last several minutes. Eventually, the jerking stops, and the person regains consciousness.
  • Epileptic spasm: These are brief, involuntary muscle contractions that typically last less than 10 seconds. Spasms often occur in clusters, repeating every few seconds over a span of 5 to 10 minutes.

Focal seizures can include tonic, atonic, clonic, myoclonic, and spasm-like symptoms. In some cases, a focal seizure may spread across the brain and evolve into a tonic-clonic seizure.

Non-motor symptoms

Generalized seizures with non-motor symptoms most often appear as absence seizures. During an absence seizure, the person briefly becomes unresponsive and may stare into space. They may also make small, repetitive movements like smacking their lips or rubbing their fingers together.

Focal seizures can also appear as absence seizures, but they tend to involve a wider range of symptoms. During a non-motor focal seizure, a person may experience:

  • Unexpected emotions
  • Sensory changes, such as unusual smells or visual hallucinations
  • Changes in thinking
  • Behavior arrest, where the person suddenly stops moving or speaking

Myoclonic vs clonic seizures

These seizure types can look similar, and you may have a hard time telling them apart. Myoclonic seizures are typically brief, sudden muscle jerks that last just a second or two. Clonic seizures involve longer-lasting, rhythmic jerking movements that are more sustained and repetitive.

Which type of seizure involves a loss of consciousness?

Tonic-clonic seizures, the most widely recognized type of seizure, cause a complete loss of consciousness. Some focal seizures may also also cause changes in awareness or responsiveness.

What to Do If Someone Is Having a Seizure

Learn the right steps to help keep someone safe and comfortable during and after a seizure.

FAQs About Seizure Classification

Which type of seizure affects both sides of the brain?

A seizure that affects both sides of the brain is called a generalized seizure.

What are the three major groups of seizures?

Seizures are classified into three main groups, based on where they start in the brain:

  • Focal seizures begin in one specific area or side of the brain.
  • Generalized seizures affect both sides of the brain.
  • Unknown onset seizures are those where the starting point can’t be determined.
What Is a partial seizure?

"Partial seizure" is an older term to describe what is now called a "focal seizure." They were once called "partial" because they only involved part of the brain. Today, we use “focal” to describe seizures that begin in one area, regardless of severity.

What type of seizure causes the body to go limp?

Seizures that cause a person to go limp are called "atonic seizures."

What type of seizure makes you stare?

Absence seizures are often called "staring spells.” During this type of seizure, a person may briefly stop responding and stare into space. Absence seizures can be focal or generalized, and may include small repetitive movements like lip smacking or finger rubbing.

What is a mild seizure?

There’s no official diagnosis of a “mild seizure,” but people often use the term to describe focal aware seizures. In these seizures, the person maintains awareness of their surroundings and may experience subtle symptoms like unusual sensations, small repetitive movements, or brief hallucinations.

What are the worst types of seizures?

Tonic-clonic seizures are typically the most dramatic in appearance, involving a loss of consciousness and full-body muscle contractions. Seizures that don’t respond to treatment are associated with more serious long-term risks.

What type of seizure has the highest risk of death?

While most seizures are not life-threatening, a rare condition called Sudden Unexpected Death in Epilepsy (SUDEP) can occur in some individuals. It is most commonly associated with tonic-clonic seizures.

What is the rarest seizure disorder?

There are many rare forms of epilepsy. Some of the rarest are Angelman syndrome, Doose syndrome, Dravet syndrome, and Lennox-Gastaut Syndrome.