Lennox-Gastaut Syndrome (LGS)

Lennox-Gastaut syndrome (LGS) is a rare neurological condition characterized by severe, recurrent seizures that manifest in early childhood. LGS accounts for fewer than 5% of all cases of childhood epilepsy.1 LGS is a syndrome consisting of multiple signs and symptoms, and may develop as a consequence of multiple etiological factors.2

Diagnosing LGS can be very challenging, as it lacks a specific biomarker or underlying genetic cause. Therefore, serological and genetic testing cannot be used as a means of confirming the diagnosis.2 Instead, LGS is diagnosed on the basis of characteristic findings on electroencephalography (EEG), the occurrence of multiple seizure types, and cognitive impairment or developmental delay, which is often severe.1 

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Screening Tool for LGS

Clinicians who have treated children with LGS used a consensus process to develop a tool specifically intended for LGS screening. The Refractory Epilepsy Screening Tool for LGS (REST-LGS) is used to assess individuals with drug-resistant epilepsy, with the aim of reducing delay in diagnosing LGS.2 


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Electroencephalography for LGS

EEG testing is essential for confirming a diagnosis of LGS. It is used to differentiate among multiple seizure types and to identify the hallmark brain wave patterns seen in patients with LGS.3

Characteristic Brain Wave Patterns 

One of the criteria for a diagnosis of LGS is the presence of a specific interictal brain wave pattern — the diffuse slow spike-and-wave pattern — which is observed between seizure episodes while the patient is awake.3 

This hallmark characteristic EEG finding in patients with LGS consists of bursts of irregular and generalized spikes or sharp waves followed by slow sinusoidal waves that last for 35 to 400 ms and have an amplitude of 200 to 800 µV. The slow spike waves can be either symmetrical or asymmetrical, and their frequency is generally between 1.5 and 2.5 Hz.3,4 

During non-rapid eye movement (REM) sleep, the discharges become more generalized; during REM sleep, the spike waves decrease.3

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Multiple Seizure Types

Another criterion for a diagnosis of LGS is the presence of multiple types of seizures. Each seizure type manifests with different symptoms and characteristics, and EEG testing during epileptic episodes can reveal specific brain wave patterns characteristic of various seizure types.3

Routine 20-minute EEG testing is not recommended for patients with suspected LGS. Instead, the patient should undergo prolonged video/EEG telemetry, which captures brain wave patterns during both wakefulness and sleep and can be used to identify various types of seizures, some of which occur more frequently at night.3 

Additionally, the video recordings can be used to educate the family of a child with LGS, so that they can distinguish between seizures (especially atypical absence seizures, which are difficult to recognize) and nonepileptic behavioral events.3

Read more about LGS signs and symptoms

Neuroimaging Studies for LGS

In the management of a patient with LGS, magnetic resonance imaging (MRI) studies of the brain are preferred to computed tomography (CT). MRI of the brain can detect abnormalities contributing to the development of LGS, including tuberous sclerosis complexes, cortical dysplasia, structural malformations of the brain, hypoxic/ischemic brain injuries, and lesions of the frontal lobes.5

There are specific situations in which clinicians still may choose CT as the preferred imaging technique. For example, when a patient with LGS presents with head trauma after a seizure, CT can be used to assess for an intracranial injury or hematoma.5

Positron emission tomography (PET) or single-photon emission computed tomography (SPECT) can be used to evaluate patients with severe, refractory LGS to determine if they are eligible for epilepsy surgery.5,6 PET or SPECT can identify if there is a localized region of the brain causing seizures that can be surgical resected without causing functional harm.6

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Cognitive/Developmental Testing for LGS

LGS is classified as a type of epileptic encephalopathy, indicating that recurrent seizure activity contributes to progressively worsening cognitive and developmental impairment.7 

Types of cognitive and developmental impairment are determined by psychiatric testing, careful interviews, and performance observations of a child with suspected LGS. The tools used to assess cognitive function in children with epileptic conditions, such as LGS, not only provide a global assessment of cognitive performance but also gauge specific cognitive functions, such as memory, attention, and executive function.8

Cognitive tests may include the Bayley Scales of Infant and Toddler Development III, the Stanford-Binet Intelligence Scale, the Wechsler Preschool and Primary Scale of Intelligence III, the Wechsler Intelligence Scale for Children, the Kaufman Assessment Battery for Children II, the ADHD Diagnostic System to diagnose attention-deficit/hyperactivity disorder, and basic tests of memory and learning.8  

Tests of cognitive function are important when epileptic encephalopathies such as LGS are suspected. Approximately 70% of children with LGS have pre-existing cognitive impairment at the time of seizure onset. Over 50% of children with LGS exhibit behavioral issues, such as aggression, features of the autistic spectrum, hyperactivity, and rage attacks. However, cognitive impairment and developmental delays are progressive and not always present at time of diagnosis, so this feature is not a requirement for diagnosis.9

Read more about LGS comorbidities


  1. Lennox-Gastaut syndrome. MedlinePlus. Accessed February 17, 2023.
  2. Wolf SM. Epilepsy essentials: screening for Lennox-Gastaut syndrome. Practical Neurology. June 2022. Accessed February 17, 2023. 
  3. Cherian KA. Lennox-Gastaut syndrome workup: electroencephalography. Medscape. Updated August 6, 2020. Accessed February 17, 2023.
  4. Ramanathan RS, Ahluwalia T, Sharma A. Lennox-Gastaut syndrome: an overview. J Pediatr Neurosci. 2010;5(1):86-88. doi:10.4103/1817-1745.66666
  5. Cherian KA. Lennox-Gastaut syndrome workup: neuroimaging studies. Medscape. Updated August 6, 2020. Accessed February 17, 2023.
  6. Douglass LM, Salpekar J. Surgical options for patients with Lennox-Gastaut syndrome. Epilepsia. 2014;55(s4):21-28. doi:10.1111/epi.12742
  7. Ajinkya S, Wirrell E. Lennox-Gastaut syndrome. Child Neurology Foundation. April 2021. Accessed February 17, 2023.
  8. Kim EH, Ko TS. Cognitive impairment in childhood onset epilepsy: up-to-date information about its causes. Korean J Pediatr. 2016;59(4):155-164. doi:10.3345/kjp.2016.59.4.155 
  9. Lennox Gastaut syndrome. LGS Foundation. Accessed February 17, 2023.

Reviewed by Kyle Habet, MD, on 2/27/2023.