What is Lennox-Gastaut Syndrome?

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What is LGS?

Lennox-Gastaut syndrome (LGS) is a neurodevelopmental brain disorder that frequently evolves from early-life-onset epilepsy. The abnormal brain waves seen in LGS are a sign that typical brain development has been disrupted and learning and developing in a typical way will be difficult.

Epilepsy is a brain disorder characterized by seizures.

In LGS, seizures usually begin in the pre-school years, and LGS usually emerges between 3-5 years of age. LGS can, however, start later in childhood.   

LGS is a Developmental and Epileptic Encephalopathy (DEE). This means two things: 

  • Persons with LGS have developmental and behavioral problems as well as epilepsy.
  • These problems are often worsened by seizures and seizure activity.

Persons with LGS have more than one seizure type and seizures are nearly always treatment-resistant. 

A diagnosis of LGS and the abnormal brain waves associated with it can be supported by an electroencephalogram (EEG).  

LGS can be due to a wide range of causes.

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.  

Anything that affects the brain at a critical time in its development can result in learning problems and seizures. In some cases, the exact cause of seizures that lead to LGS is unknown. Why some children develop the abnormal brain waves associated with LGS and some don’t is not well understood.

Severity differs to some degree between patients. However, LGS is considered very severe.  

Many with LGS survive into late adulthood. However, there is an increased risk of early death known as Sudden Unexpected Death in Epilepsy (SUDEP). This is due to seizure complications. In addition, those with severe neurological disabilities may have limited mobility and have difficulty swallowing. This increases the risk of infection, such as aspiration pneumonia.  The limited mobility can also result in falls and injuries with seizures.

The 4 Core features of  LGS

There are four key features of a diagnosis of LGS:


Seizures that begin in early 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.

More About the Signs and Symptoms of LGS

Age of Onset

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. 

Seizure Types Seen in LGS

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. 

Intellectual Disability

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.

Motor and Mobility Difficulties

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

Sleep problems are common in those with LGS. These include trouble falling asleep, staying asleep, waking up, frequent nighttime seizures, and other issues. 

Risk of Death

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. Persistent abnormal brain waves seen on the EEG suggest that brain damage is occurring or has already occurred. 

  • Slow spike-and-wave (SSW) is a pattern seen on the EEG in those with LGS and is a sign that the underlying brain region is not functioning correctly. SSW is usually generalized, meaning it occurs on both sides of the brain and usually occurs at a frequency of <3 per second (<3 Hz). The hallmark of the LGS EEG is the presence of SSW when the person with LGS is awake and not having a seizure. Those with LGS often no longer show the SSW on EEG in adulthood.
  • Generalized paroxysmal fast activity (GPFA) is a pattern seen on the EEG in those with LGS and is usually a sign that a tonic seizure is occurring. It 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. 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

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 Reviewed: April 2021 

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. 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.