Lennox–Gastaut Syndrome

Lennox–Gastaut syndrome (LGS) is a developmental and epileptic encephalopathy characterised by multiple drug-resistant seizure types, a distinctive EEG pattern and cognitive or behavioural impairment. It usually begins in childhood and can arise from many different structural, genetic, metabolic or unknown causes.

LGS is not defined by one gene or one seizure type. The diagnosis is electroclinical: clinicians combine the seizure pattern, EEG and developmental course.

Where LGS fits in the ILAE classification

The International League Against Epilepsy includes LGS among developmental and epileptic encephalopathies with onset in childhood.

The syndrome is important to recognise because it changes diagnostic investigation, medication selection, prognosis and consideration of non-drug treatments such as ketogenic dietary therapy, vagus nerve stimulation and epilepsy surgery in selected people.

Age at onset

LGS most often emerges between early childhood and the early school years. Some children have a previous infantile epilepsy syndrome, including infantile epileptic spasms syndrome, before evolving into LGS.

Others develop LGS after structural brain injury, malformation, genetic disease or another identifiable neurological disorder.

The defining seizure pattern

Multiple seizure types are typical. Tonic seizures are especially important diagnostically and often occur during sleep.

Other common seizure types include atypical absence seizures, atonic seizures, focal seizures and bilateral convulsive seizures. Myoclonic seizures can occur but are not mandatory.

Drop attacks are a clinical description, not a single seizure type

Sudden falls can result from tonic seizures, atonic seizures or other seizure mechanisms. Witness description alone may not identify which mechanism caused a fall.

Video-EEG can therefore be particularly useful when clinicians need to determine the seizure type responsible for recurrent drop attacks.

EEG: slow spike-and-wave

The characteristic interictal EEG includes generalised slow spike-and-wave activity, classically at less than 2.5 Hz.

This pattern is usually most evident in childhood and can change with age. A routine awake EEG may not capture the full syndrome.

EEG during sleep: generalised paroxysmal fast activity

Generalised paroxysmal fast activity during sleep is another important EEG feature. For this reason, sleep EEG is important when LGS is suspected.

The ILAE childhood syndrome paper specifically notes that sleep recording is required to identify mandatory EEG patterns in syndromes such as LGS.

Development and cognition

Cognitive impairment is common, but it may pre-date the onset of LGS when the underlying brain disorder has already affected development.

In other children, development plateaus or regresses as the epilepsy becomes more active. This is why LGS is described as both developmental and epileptic encephalopathy: the underlying cause and the epileptic activity can both contribute.

Behaviour and communication

Behavioural difficulties, sleep problems, autistic features, attention difficulties and communication impairment are common. The degree varies substantially between individuals.

Support therefore often needs to extend beyond seizure counting to education, communication, behaviour, mobility and family wellbeing.

What causes LGS?

LGS is a syndrome, not a single disease. Causes include cortical malformations, hypoxic-ischaemic brain injury, tuberous sclerosis complex, genetic developmental disorders, infections, metabolic disease and other structural abnormalities.

In some people, no specific cause is identified even after extensive investigation.

MRI and genetic testing

MRI is important because identifying a focal or hemispheric structural cause can affect treatment options, including surgical assessment.

Genetic testing is increasingly used, particularly when MRI is non-lesional, developmental impairment is unexplained or other features suggest a genetic disorder.

Treatment goals

Complete seizure freedom is difficult to achieve in many people with LGS. Treatment therefore often has several goals at once: reduce the most dangerous seizure types, reduce status epilepticus, protect against injury, improve alertness where possible and minimise treatment burden.

A reduction in drop attacks can be clinically meaningful even when other seizure types continue.

Antiseizure medicines

Medicines commonly used internationally include valproate, lamotrigine, rufinamide, clobazam, topiramate and cannabidiol, among others. Regulatory approval and availability vary between countries.

Because LGS usually involves several seizure types, treatment is individualised and combination therapy is common.

Medication adverse effects matter

Sedation, slowed cognition, behavioural change, appetite effects and gait instability can substantially affect quality of life. In a person already vulnerable to falls and learning difficulties, medication burden can be as important as seizure count.

Regular review should therefore ask whether each medicine is still providing enough benefit to justify its adverse effects.

Ketogenic dietary therapy

Ketogenic dietary therapies can reduce seizures in some people with LGS and are widely recognised as an important non-drug option for drug-resistant epilepsy.

Access is highly unequal worldwide because treatment requires trained dietitians, monitoring and reliable food or formula supply.

Vagus nerve stimulation

VNS can reduce seizure burden in some people with LGS, particularly when resective surgery is not appropriate.

Response usually develops gradually and seizure freedom is uncommon, but reductions in drop attacks or convulsive seizures can still be clinically valuable.

Corpus callosotomy

Corpus callosotomy is a disconnective surgical procedure that can be considered when injurious drop attacks remain severe. It does not remove a seizure focus; instead, it reduces rapid spread between the cerebral hemispheres.

It is generally considered in specialist epilepsy-surgery programmes after detailed multidisciplinary assessment.

Resective surgery can still be relevant

The label “generalised” or the presence of LGS does not automatically rule out epilepsy surgery. If evaluation identifies a dominant structural lesion or hemispheric abnormality driving the epileptic network, resective or disconnective surgery may be considered.

This is why good-quality MRI and specialist review remain important even in a syndrome with widespread EEG abnormalities.

Status epilepticus

People with LGS can experience prolonged seizure states, including non-convulsive status epilepticus with reduced responsiveness or increased seizure activity.

Families and carers may need an individual emergency plan describing usual recovery, rescue medication and when urgent medical care is required.

Injury prevention

Frequent tonic or atonic falls can cause facial and head injuries. Helmets may be considered for some people, but they do not remove all injury risk.

Home, school and care environments may need adaptations based on the person’s specific seizure pattern.

Adolescence and adulthood

LGS often continues into adulthood, although seizure types and EEG features can evolve. Tonic seizures and drug-resistant epilepsy frequently persist.

Adult services need to recognise the childhood syndrome history because the classic childhood EEG pattern may become less obvious later.

Worldwide diagnosis

Diagnosis is easier where prolonged video-EEG, sleep EEG, MRI and genetic testing are available. In resource-limited settings, these investigations may be difficult to obtain.

The ILAE syndrome framework is designed to support diagnosis from the strongest available clinical and EEG evidence while making clear when missing investigations reduce certainty.

The central point

Lennox–Gastaut syndrome is not simply “severe childhood epilepsy”. It is a defined developmental and epileptic encephalopathy with characteristic tonic seizures, slow spike-and-wave and sleep-related fast activity, usually accompanied by cognitive or behavioural impairment.

Sources

Medical note: treatment in LGS is individualised and often involves several therapies. Medication availability and licensing differ internationally.

Evidence checked: September 2026.