What is Lennox-Gastaut Syndrome?

LGS is tough. So are we! As you read about LGS, please remember that you are not alone.

What is LGS?

Lennox-Gastaut Syndrome (LGS) is a severe epilepsy syndrome that develops in young children and often leads to lifelong disability. 

Nobody is born with LGS. It develops over time.

LGS is a rare disease (less than one person in every 2,000).


  • Seizures usually begin in the pre-school years.
  • More than one seizure type is always present.
  • Tonic seizures are present in nearly all with LGS at some point.
  • Seizures are nearly always treatment-resistant.
  • Many LGS Associated Disorders exist, including issues with sleep, behavior, movement, feeding, toileting, communication, and many others.
  • Slow spike and wave (SSW) and Generalized Paroxysmal Fast Activity (GPFA) are seen on the EEG. These are the hallmarks of LGS.
  • SSW and GPFA usually emerge between ages 3-5 years but can begin later in childhood.
  • SSW and GPFA, which occur between seizures, worsen seizures, development, and behavior problems.

Watch: LGS: What we know, what we are learning.

Elaine Wirrell, MD, Director of Pediatric Epilepsy at Mayo Clinic, gives an overview of how diagnostic and treatment options for Lennox-Gastaut Syndrome have changed over the years and the importance of understanding the cause of your loved one’s LGS.

Other things to know about LGS:

  • Diagnosis of LGS, and the abnormal brain waves associated with it, requires an electroencephalogram (EEG). 
  • Seizures that evolve into LGS can be due to a wide range of causes.
  • While we know much about what causes early-life seizures, we do not know how seizures evolve into LGS.
  • LGS may develop in children without a history of epilepsy, although this is rare. The majority of the time, LGS evolves from another type of epilepsy.
  • Severity differs to some degree between patients. However, LGS is considered very severe.
  • Many with LGS survive into late adulthood, and most require lifelong care.
  • Those with LGS have an increased risk of:
  • LGS is a rare disease and one of the Developmental and Epileptic Encephalopathies (DEEs). 

The 4 Core features of  LGS

There are four key features of a diagnosis of LGS:


Seizures begin in early childhood.

  • Most with LGS have seizures that begin in the first three years of life. However, seizure onset in LGS can occur at any time in childhood.

More than one seizure type (tonic seizures occur in nearly all with LGS). Seizures regularly continue despite treatment.


Abnormal brain waves on the electroencephalogram (EEG) test. These include:

  • Slow spike-and-wave (SSW)
  • Generalized paroxysmal fast activity (GPFA)

Developmental delay and/or intellectual disability.

  • Not all who are diagnosed with LGS have a developmental delay at the time of diagnosis. However, nearly all with LGS will have developmental delay within five years of seizure onset.

Hear about LGS from families living with it. This video was filmed at our Family and Professional Conference in 2019. LGS is tough. So are we!

More About the Signs and Symptoms of LGS

Age of Onset Seizure Types Seen Etc

LGS usually develops in the preschool years. In about one in four cases, it nearly always evolves from another type of epilepsy. In these cases, it usually evolves from epilepsy that starts very early in life. LGS very commonly evolves from infantile spasms or West syndrome. It usually takes time for all features of LGS to appear. Therefore, it can be challenging to accurately diagnose the disease early in childhood.
Persons with LGS have several types of seizures. These can include:
  • Tonic seizure. This is the most common type in LGS. They consist of neck, and sometimes arm and leg, stiffening. They often involve eye-opening and upward eye-rolling. They often occur in sleep. They can be subtle and easily missed. An overnight-video laboratory test can reliably detect them. If they occur during the day, while a child is upright, they can result in a fall.
  • Atypical absence seizure. This type consists of brief blank-outs where a child is less aware. Atonic seizure. In an atonic seizure, a child abruptly loses body tone and slumps. If these occur while sitting, they can look like a quick head nod. If they occur while upright, they can lead to abrupt falls and injury.
  • Myoclonic seizure. These consist of isolated, brief body jerks.
  • Focal impaired awareness seizure. These typically begin with staring and altered awareness. This lasts up to several minutes and is followed by a period of confusion. These seizures can progress into generalized tonic-clonic seizures.
  • Generalized tonic-clonic seizure. These consist of generalized stiffening and rhythmic shaking. Seizures often change in children with LGS as they grow and develop.
LGS is a lifelong neurodevelopmental disorder and seizures are the main feature, are frequent, and are debilitating. Therapies may help. However, they do not completely stop seizures. Persons with LGS have varying degrees of intellectual disability and behavioral issues. Some struggle with aggression. Some meet autism spectrum disorder criteria.
Persons with LGS nearly always have intellectual disabilities. It may be mild in earlier childhood. However, those with LGS often gain developmental skills more slowly. They may have moderate to severe intellectual disability by adolescence. Behavioral differences are also common. They become more of a problem with age. Behavioral issues include:
  • Aggression
  • Autism spectrum disorder
  • Inattention
  • Hyperactivity
Developmental delay and/or intellectual disability occur in most with LGS. Delays in development are not always present at the start of LGS and are not required for the diagnosis to be made.
Most children with LGS also have motor difficulties. These include:
  • Problems with balance and coordination. This is a common motor difficulty.
  • Problems with feeding and swallowing. A small number require a feeding tube.
Limited mobility and frequent seizures can also mean a higher risk of infections such as pneumonia.
Sleep problems are common in those with LGS. These include trouble falling asleep, staying asleep, waking up, frequent nighttime seizures, and other issues.
Children with LGS are at higher risk of death. This is for several reasons:
  • Sudden Unexpected Death in Epilepsy (SUDEP). This is a major concern in LGS. The exact cause of SUDEP is not well understood. However, it may be related to post-seizure heart and breathing issues. Those with frequent convulsive seizures are at the highest risk.
  • Infection. Lower mobility can lead to infection. Pneumonia is an example.
  • Accidental injury. Seizures, particularly atonic or tonic seizures, may cause falling and injury.

Can you tell me more about the LGS EEG?

The EEG in LGS is important for diagnosis, and it also tells us where the brain is not functioning correctly. The persistent abnormal brain waves seen on the EEG in LGS (SSW and GPFA)  suggest that brain damage is occurring or has already occurred. 

  • Slow spike-and-wave (SSW):
      • SSW is a pattern seen on the EEG in those with LGS and is a sign that the underlying brain regions are not functioning correctly.
      • SSW is usually generalized, meaning it occurs on both sides of the brain and usually occurs at a frequency of less than 3 per second (<3 Hz).
      • SSW, when the person is awake and not having a seizure, is the hallmark of the LGS EEG.
      • Those with LGS often no longer show the SSW on EEG in adulthood.

  • Generalized paroxysmal fast activity (GPFA):
      • GPFA is a pattern seen on the EEG in those with LGS and is usually a sign that a tonic seizure is occurring.
      • GPFA is associated with mental deterioration.
      • GPFA is usually generalized, meaning it occurs on both sides of the brain.
      • GPFA is a burst of rhythmic discharges that occur at a frequency of 10-20 per second (10-20 Hz).
      • GPFA is often stronger in the frontal lobe and occurs mainly during non-REM sleep. 

​Watch: Understanding the LGS EEG

2019 LGS Foundation Family Conference in Seattle, Washington, Brenda Porter, MD – UNDERSTANDING THE LGS EEG

Is there a cure for LGS?

  • There is no cure for LGS.
  • Seizures may go into remission but may also recur.
  • It is important to try to achieve the best possible seizure control in LGS.
  • Seizure management options include anti-seizure medications, specialized diets, brain surgery (e.g., corpus callosotomy, deep brain stimulation), and neurostimulation.
  • There are currently no therapies that target the EEG features of LGS (e.g., a disease-modifying therapy).

What is likely to happen in the future for those with LGS?

  • The prognosis for LGS is poor, and the progression of LGS is almost always associated with developmental slowing and/or regression.
  • Despite the best treatments, more than 85% of children with LGS will continue to have seizures into adulthood. The LGS Foundation is working hard to change this.
  • Because of the abnormal brain waves in those with LGS, more than 90% have significant intellectual disabilities. The LGS Foundation is also working hard to change this. It is believed that seizure control is key to improving developmental outcomes in LGS. 
  • A few with LGS live a generally normal life, but more than 50% with LGS suffer many LGS Associated Disorders (LAD), including communication issues, balance issues, behavioral issues, sleep disturbances, rage attacks, aggression, autistic features, and other issues.
  • Those with LGS can live into their 50s or 60s but are also more likely to die prematurely due to the underlying brain disorder, seizures, injuries, accidents, aspiration pneumonia, or Sudden Unexpected Death in Epilepsy (SUDEP).
  • The LGS Foundation is fighting every day to save and improve the lives of those living with LGS. 

Watch: LGS 101: Why the Diagnosis Matters

2019 LGS Foundation Family Conference in Seattle, Washington, Michael Chez, MD – LGS 101:WHY THE DIAGNOSIS MATTERS

Related Disorders

These disorders can sometimes be mistaken for LGS:

Infantile Spasms / West Syndrome

  • Infantile Spasms often progress to LGS over time. It can be hard to tell when LGS begins.  The hallmarks of LGS are more than one type of seizure, slow spike and wave, and generalized paroxysmal fast activity (GPFA) on the EEG.

Myoclonic-Atonic Epilepsy / Doose syndrome

  • In this disorder, seizures are preceded by normal development. Persons with Doose syndrome typically have a unique seizure type called a myoclonic-atonic seizure, with a brief jerk or vocalization that precedes the fall. It is often outgrown in early childhood.

Dravet Syndrome

  • Dravet syndrome typically presents with recurrent prolonged seizures in the first year of life. It has its own brain and seizure pattern.

Other Developmental and Epileptic Encephalopathies (DEEs)

  • Like LGS, other DEEs include multiple types of seizures. Many DEEs evolve into LGS as well.

Frontal Lobe Epilepsy

  • This has its own brain and seizure pattern. The seizures often have asymmetrical features.

While there is no cure for LGS, there is a hopeful path forward. On this site, you will find useful information and resources – and, most importantly, a community of support.

LGS Fact Sheet


For more information, download our 2021 LGS Fact Sheet.


Thank you to the Child Neurology Foundation for allowing us to adapt this article for this site.

Authors: Shaun Ajinkya, MD; Elaine Wirrell, MD,  Mayo Clinic – Rochester, Minnesota 

The information here is not intended to provide diagnosis, treatment, or medical advice and should not be considered a substitute for advice from a healthcare professional. The content provided is for informational purposes only. LGSF is not responsible for actions taken based on the information included on this webpage. Please consult with a physician or other healthcare professional regarding any medical or health related diagnosis or treatment options.

The information here is not intended to provide diagnosis, treatment, or medical advice and should not be considered a substitute for advice from a healthcare professional. The content provided is for informational purposes only. LGSF is not responsible for actions taken based on the information included on this webpage. Please consult with a physician or other healthcare professional regarding any medical or health related diagnosis or treatment options.

Updated 8/27/22