Lennox-Gastaut syndrome (LGS) is a severe and rare form of epilepsy that usually starts in early childhood and often continues into adulthood. It causes different types of seizures, cognitive (learning or thinking) difficulties, and unusual brain activity seen on an electroencephalogram (EEG). About 70 percent of LGS cases are linked to brain malformations, injuries, or infections.

Approximately 3 percent to 4 percent of children with epilepsy develop LGS. It most commonly begins between ages 2 and 5 and affects males more frequently than females. While some people with LGS can live independently, most need ongoing help because of the condition’s serious effects on thinking, memory, and behavior.

LGS is part of a group of disorders called epileptic encephalopathies, which cause worsening developmental delays, trouble with thinking and learning, and behavioral issues over time. It is very hard to treat because it does not respond well to many antiepileptic drugs (AEDs). Early diagnosis and aggressive intervention aimed at both seizure control and neurodevelopmental support are crucial.

Complete recovery from LGS is rare, and there is currently no cure. The death rate for individuals with LGS is 14 times higher than in the general population, largely due to seizure-related complications such as status epilepticus, sudden unexpected death in epilepsy (SUDEP), and complications related to intellectual and physical disabilities.

Lennox-Gastaut Syndrome Symptoms and Seizures

People with LGS experience multiple types of epileptic seizures, including the types described here. However, it’s important to note that intellectual disabilities may appear earlier than these seizures do.

Lennox-Gastaut Syndrome Behavioral Problems and Developmental Issues

Most children with LGS have cognitive and developmental impairments, including intellectual disabilities or learning problems even before seizures begin. These issues may worsen over time, particularly if seizures are frequent or severe. In a study that followed children with LGS for 17 years, up to 99 percent of participants had mental disabilities. Many had delayed development of motor skills, such as sitting and crawling. Behavioral problems, such as hyperactivity and aggression, occurred in half the participants.

Most children with LGS will continue to have seizures as adults. Due to the developmental and behavioral challenges, many people with LGS need help with daily activities throughout their lives.

Tonic Seizures

The majority of individuals with LGS experience tonic seizures. Tonic seizures typically cause muscles to uncontrollably stiffen. They usually last around 20 seconds and happen mostly during sleep. If they occur while a person is awake, they might suddenly fall and feel tired or confused afterward.

Atonic Seizures

Individuals with LGS may experience atonic seizures, also known as drop attacks. During an atonic seizure, a person loses muscle tone (control), causing their body to go limp and fall to the ground. A helmet or other head protection may be needed to protect from injury.

Atypical Absence Seizures

People with LGS may also have atypical absence seizures. They are characterized by brief staring spells, often accompanied by subtle motor features such as eye blinking or head nodding. They can be difficult to distinguish from inattention or daydreaming. The person typically does not remember the seizure afterward.

Focal Seizures

Focal seizures, which typically affect just one side of the brain, are another common seizure in people with LGS. These seizures can cause unusual sensations, movements, or changes in awareness, depending on which part of the brain is affected.

Myoclonic Seizures

Myoclonic seizures are less common than other kinds of seizures but sometimes seen with LGS. These seizures cause brief, shocklike jerks in a muscle or a group of muscles, which may happen in clusters or as single, sudden movements.

Tonic-Clonic Seizures

Tonic-clonic seizures combine two phases: a tonic phase, where the muscles stiffen, and a clonic phase, which involves rhythmic jerking movements. During these seizures, a person typically loses consciousness and may also experience confusion or fatigue (tiredness) afterward.

Infantile Spasms

Some children with LGS may start with infantile spasms (also called West syndrome). These spasms involve sudden, involuntary movements, such as jerking the head, neck, and torso or extending the legs and arms uncontrollably. They often occur in clusters and may be an early sign of developmental issues.

More than two-thirds of people with LGS experience status epilepticus.

Status Epilepticus

Status epilepticus is a critical complication of LGS, defined as seizures that last longer than five minutes or happen so close together that the person doesn’t recover in between. This condition is life-threatening and requires emergency medical care. There are two types: convulsive, which causes jerking and stiffness, and nonconvulsive, which affects awareness without noticeable movements. Both types can worsen mental decline over time. More than two-thirds of people with LGS experience status epilepticus.

Status epilepticus requires immediate medical intervention due to the risk of brain damage, injury, and other serious consequences. The frequency of status epilepticus in LGS significantly contributes to lower quality of life and mortality.

Dangers Associated With Seizures

Among the most disabling seizures for people with LGS are drop attacks, which can result in recurrent injuries and debilitation. Uncontrolled seizures also increase the risk of SUDEP.

The best way to prevent injury or death due to status epilepticus or SUDEP is to control seizures as much as possible. Your doctor can find the best treatment plan with medication, dietary treatments, or alternative treatments.

Diagnosing Lennox-Gastaut Syndrome

To be diagnosed with LGS, a person must have the following symptoms:

• Multiple seizure types
• Abnormal EEG with a specific brain wave pattern
• Mental or behavioral challenges

A team of different doctors makes a diagnosis after doing a full checkup, looking at medical history, and testing the brain and nerves. An EEG is often done to analyze the brain’s electrical activity and seizures. Doctors might order an MRI to take detailed pictures of the brain and find the cause of the seizures.

It can take several years to correctly diagnose LGS because the disease has significant overlap with other types of epilepsy, and it may not show its unique features when seizures begin.​

Learn more about how severe forms of epilepsy are diagnosed in children.

Causes of Lennox-Gastaut Syndrome

An estimated 70 percent to 80 percent of people experience symptomatic LGS — when the disease has an identifiable cause. Here are some of the causes of LGS.

Brain Injury or Developmental Problems

When part of the brain has developed abnormally (also called brain malformation) or is injured, it’s more likely to cause seizures.

In 70 percent to 80 percent of people with LGS, the disease has an identifiable cause.

Genetic Disorders

In most LGS cases, there is no family history of the disorder. A family history of epilepsy has been observed in anywhere from 3 percent to 30 percent of people with LGS.

Other Causes

LGS can also develop from other epilepsy syndromes, such as infantile spasms or Ohtahara syndrome. When the cause is unknown, LGS is classified as cryptogenic. In 25 percent of people with LGS, no cause can be found.

Talk With Your Doctor

Lennox-Gastaut syndrome is a serious and lifelong form of epilepsy that affects thinking, behavior, and daily living. Because it involves multiple seizure types and developmental challenges, staying informed can help individuals and families better navigate its effects. If you have questions about LGS or how it might affect you or your loved one, talk to a doctor who can provide information specific to your situation.

Talk With Others Who Understand

MyEpilepsyTeam is the social network for people with Lennox-Gastaut Syndrome and their loved ones. On MyEpilepsyTeam, more than 124,000 members come together to ask questions, give advice, and share their stories with others who understand life with epilepsy.

Are you living with Lennox-Gastaut syndrome or caring for a family member who has LGS? Do you have questions or suggestions about managing symptoms? Share your experience in the comments below, or start a conversation by posting on your Activities page.