Lennox-Gastaut Syndrome (LGS)

Lennox-Gastaut syndrome (LGS) is a rare type of severe childhood epilepsy characterized by a triad of signs, including multiple seizure types, cognitive impairment/developmental delay, and a specific brain wave pattern as seen on electroencephalograms (EEGs).1 

While multiple seizure types and the hallmark slow spike-and-wave pattern on EEG are required for LGS diagnosis, evidence of cognitive impairment or developmental delay, although initially present in approximately 70% of children with LGS, is not necessary for an official diagnosis.2

Multiple Seizure Types

The most common types of seizures experienced by children with LGS include tonic, atonic, atypical absence, myoclonic, generalized tonic-clonic, and non-convulsive status epilepticus seizures.2 Each seizure type has its own characteristic symptoms.

Tonic Seizures

Tonic seizures occur in 17% to 95% of individuals with LGS.3 They most frequently manifest during non-rapid eye movement (non-REM) sleep, but they can occur during wakefulness and potentially lead to falling and injury.3,4 

Tonic seizures involve axial, global, or axio-rhizomelic stiffening of the torso and/or extremities.3-5 These seizures usually impact both sides of the body; however, they can be asymmetric.3-5 Other signs indicative of tonic seizures include an upward eye gaze, dilated pupils, and altered breathing patterns.5  

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Atonic Seizures

Atonic seizures, also known as drop attacks, involve a sudden, brief loss of muscle tone and consciousness. If this type of seizure occurs when the individual with LGS is standing, the sudden loss of muscle tone makes the person go completely limp and abruptly fall to the ground, potentially causing serious injury. Atonic seizures may be limited to the head drooping onto the chest.3-5 

Read more about LGS risk factors

Atypical Absence Seizures

Atypical absence seizures range in frequency between 17% and 100% of individuals with LGS. Seizure onset can occur gradually with an incomplete loss of consciousness.3 

Atypical absence seizures are characterized by staring episodes in which the person with LGS has a loss of awareness. Associated eyelid myoclonias may be observed during atypical absence seizures.3-5

Myoclonic Seizures

Myoclonic seizures involve sudden, rapid muscle jerks or spasms that occur involuntarily, appearing almost shock-like in nature. These muscle jerks may affect a specific part of the body or the entire body. These involuntary muscle jerks vary in intensity and frequency. If severe, they may limit their ability to eat, speak, or walk.3-5

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Generalized Tonic-Clonic Seizures

Generalized tonic-clonic seizures occur in individuals with LGS at around a 15% frequency.3 These patients demonstrate a combination of symptoms that occur in both tonic and myoclonic seizures, including muscle tensing and rhythmic muscle jerking. Consciousness is lost in the initial tonic phase, and an individual often falls to the ground, where the rhythmic jerking of the clonic phase may last an additional one to 3 minutes.5

Status Epilepticus

According to the Neurocritical Care Society’s revised definition, status epilepticus is a seizure that lasts longer than 5 minutes or multiple seizures that occur within a 5-minute period without allowing sufficient recovery time in between seizures. Because of this, status epilepticus is considered a medical emergency, requiring immediate assessment and treatment to prevent significant morbidity or mortality. 6,7

There are varying subtypes of status epilepticus, such as nonconvulsive, absence, and tonic status epilepticus.3 According to the LGS Foundation, the most common subtype that occurs in LGS is nonconvulsive status epilepticus.2 Around half of patients with LGS experience nonconvulsive status epilepticus at some point.1

Individuals experiencing status epilepticus can present with staring episodes, dizziness, apathy, stupor, and lack of responsiveness. This seizure type may increase cognitive impairments and worsen developmental delays.1

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Cognitive Impairments/Developmental Delays

Approximately 70% to 80% of children who develop LGS demonstrate cognitive impairments or developmental delays prior to seizure onset and initial LGS diagnosis.2,8 Once seizures manifest, cognitive impairments and developmental delays are almost always present and progressively worsen.2,8 Nearly 5 years after LGS onset, approximately 75% to 95% of children exhibit cognitive impairments and/or developmental delays.9

Neurological examination reveals abnormalities in mental status and higher cognitive functional deficits indicative of intellectual disabilities.3 Intelligence quotient (IQ) scores significantly decrease over time in children with LGS. Reaction times and information processing are also significantly impacted by LGS.9

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Behavioral Disorders

Behavioral problems often accompany progressive intellectual impairment in children with LGS.9 Behavioral issues such as hyperactivity, aggression, agitation, and autism are commonly seen in children with LGS.8

Slow Spike-and-Wave Brain Pattern

The slow spike-and wave pattern is one of the three criteria for LGS diagnosis and a characteristic feature visible on EEG. In patients with LGS, interictal findings on EEG show abnormal basic rhythms interrupted by these diffuse slow spike-and-wave complexes.10

Slow spike-and-wave brain patterns are characterized by irregular bursts of spikes or sharp waves followed by slow waves lasting between 35 and 400 milliseconds at amplitudes between 200 and 800µV that may be either symmetric or asymmetric. Frequencies of the slow spike-and wave complexes are typically less than 3 Hertz (Hz), usually between 1.5 and 2.5 Hz.10 

Neuroimaging in the presence of specific EEG findings can play a critical role in the diagnosis of LGS. Brain scans can reveal frontal lobe lesions, hypoxic-ischemic injury, tuberous sclerosis complex, cortical dysplasia, and other structural malformations contributing to LGS development.10

Read more about LGS testing


  1. Amrutkar C, Riel-Romero RM. Lennox Gastaut syndrome. In: StatPearls. StatPearls Publishing; 2022. Accessed February 14, 2023. 
  2. What is LGS? LGS Foundation. Accessed February 14, 2023.
  3. Cherian KA. Lennox-Gastaut syndrome: practice essentials. Medscape. Updated August 6, 2020. Accessed February 14, 2023. 
  4. Lennox-Gastaut syndrome. Cedars-Sinai. Accessed February 14, 2023.
  5. Lennox-Gastaut syndrome. National Institute of Neurological Disorders and Stroke. Accessed February 14, 2023.
  6. Wylie T, Sandhu DS, Murr N. Status epilepticus. In: StatPearls. StatPearls Publishing; 2022. Accessed February 14, 2023.
  7. Status epilepticus. Johns Hopkins Medicine. Accessed February 14, 2023. 
  8. Lennox-Gastaut syndrome (LGS). Epilepsy Foundation. Accessed February 14, 2023.
  9. Gallop K, Wild D, Nixon A, Verdian L, Cramer JA. Impact of Lennox-Gastaut syndrome (LGS) on health-related quality of life (HRQL) of patients and caregivers: literature review. Seizure. 2009;18(8):554-558. doi:10.1016/j.seizure.2009.06.005
  10. 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

Reviewed by Debjyoti Talukdar, MD, on 3/1/2023.