Lennox Gastaut Syndrome (LGS)


  • Lennox Gastaut Syndrome (LGS) is characterised by epileptic seizures, a characteristic electroencephalogram (EEG), psychomotor delay and behaviour disorders. The syndrome is an example of an epileptic encephalopathy.
  • LGS occurs more frequently in males and onset is usually before the age of eight with a peak between three and five. Late cases can occur in adolescence and early adulthood.
  • Seizures typically include prominent tonic seizures in sleep, atypical absences and drop attacks (tonic and atonic seizures). Other seizures such as generalised tonic clonic and focal seizures are less frequent.
  • Psychomotor delay and behavioural disturbance in the school-aged child can be heralding signs.
  • The interictal EEG can have irregular slow spike wave. Generalised paroxysmal fast activity is seen on EEG. Decrements can be seen during tonic seizures.
  • Prognosis is poor and remission with preserved mentation occurs in very few.
  • The treatment has been difficult and disappointing. Epilim, clobazam, lamotrigine, levetiracetam, topiramate, and rufinamide are reported to reduce the frequency of seizures. Ketogenic diet is also an option. Surgical options of corpus callosotomy and vagal nerve stimulator are indicated when frequent injuries with seizures occur.
  • Neurology review is recommended.

According to the NICE Guideline: The Epilepsies:

  • The seizure type(s) and epilepsy syndrome, aetiology, and co-morbidity, should be determined.
  • If there is diagnostic uncertainty, individuals should be referred to tertiary services soon (within 4 weeks) for further assessment.


Age at onset

  • ~1 to 8 years – peaks 3 to 5 years and can persist into adulthood.


  • Males slightly predominate.


  • Most cases of Lennox Gastaut Syndrome are sporadic.
  • Researchers have not identified any genes specific for this syndrome, although the disorder has a genetic component.

About 2/3's of cases are related to an existing neurological problem such as a brain injury that occurs before or during birth, malformations, or a genetic disorder such as tuberous sclerosis. Many children with Lennox Gastaut Syndrome have a history of epileptic spasms.

Signs | Symptoms

Seizure semiology

 - Tonic seizures occur in most affected children and most frequently when falling asleep. They are usually brief, lasting seconds. They may be axial, with flexor movements of the head and neck. They may involve elevation and adduction of the proximal upper limbs, stiffening of posterior neck muscles, elevation of the shoulders, opening of the mouth, upward deviation of the eyes and brief apnoea. They may lead to sudden falls if the patient is upright.

 - Atypical absence seizures are also common.  Both the onset and the termination are gradual which is very different to typical childhood absence seizures. Atypical absences are often followed by some post-ictal cognitive impairment. Associated manifestations are more common than in typical childhood absence seizures including eyelid and perioral myoclonus, progressive flexion due to loss of postural tone, and localised phenomena such as head-nodding and neck stiffening.

 - Atonic seizures are characterised by sudden intense loss of postural tone of the head or whole body.

 - Other types of seizures are also possible including generalised tonic clonic seizures, focal seizures - but are less frequent. Myoclonic seizures are rare.

 - Most patients with LGS have 1 or more episodes of status epilepticus which can take a number of forms including:

  • A prolonged absence status epilepticus that can last for days or weeks and looks like an insidious confused state. This can be very difficult to recognise in children with mental retardation.
  • Pure tonic status epilepticus which is more often seen in older patients and can be life threatening due to the inherent risk of prolonged apnoea.

Neurological and mental state

The Lennox-Gastaut syndrome is an age-specific disorder that may result from diffuse encephalopathies. It usually begins with episodes of sudden falls. 

Behavioural disturbance in the school-aged child is also typical. Language is frequently affected, with both slowness in ideation and expression, in addition to difficulties of motor dysfunction. In most children there is slowing or even complete arrest of psychomotor development.

Severe behavioural disorders (for example hyperactivity, aggressiveness, and autistic tendencies) and personality disorders are nearly always present. There is also a tendency for psychosis to develop with time.

Differential diagnosis

  • Other epileptic encephalopathies such as Epilepsy with Continuous Spikes and Waves during Slow Wave Sleep otherwise known as ESES. This begins between 3 and 6 years of age with atonic seizures and atypical absences. This syndrome typically has no tonic seizures.
  • Myoclonic Astatic Epilepsy (Doose syndrome) – the presence of myoclonic astatic seizures in Doose syndrome helps distinguish, although some forms of severe MAE (Doose) can closely resemble LGS.
  • Infantile ceroid lipofuscinosis and other neurodegenerative disorders should be considered in the differential diagnosis.
  • Atypical childhood epilepsy with centrotemporal spikes.



  • Background is commonly slow with paroxysms of <2.5 Hz slow spike wave.  Paroxysmal fast activity (≥ 10 Hz) is seen in slow sleep. The latter 2 features are mandatory requirements (slow spike/wave and paroxysmal fast activity).
  • Ictal EEG is variable according to seizure type. Tonic seizures are often associated with paroxysms of generalised fast activity (~20 Hz); atypical absences with <2.5 Hz slow spike and wave. Flattening of the EEG is also seen during tonic seizures.  

Neuro Imaging

  • Needs careful consideration in an obtunded patient with LGS, particularly if head injury has occurred during the tonic seizures and drop attacks (looking for subdural haemorrhages).
  • Findings depend on aetiology. Structural abnormalities are common.


The long-term prognosis is poor. Although the epilepsy often improves, complete seizure freedom is rare and conversely the mental and psychiatric disorders tend to worsen with time.


    • The optimum treatment for Lennox-Gastaut syndrome remains uncertain and no study to date has shown any one drug to be highly efficacious.
    • Sodium valproate, lamotrigine, levetiracetam, clobazam and topiramate may be helpful to treat drop attacks and atypical absences. Sodium valproate and lamotrigine are synergistic in action.
    • Newer drugs are currently being trialled such as rufinamide.
    • The ketogenic diet has been effective in some patients.
    • Early referral to a paediatric neurologist is recommended.
    • When there are drug resistant frequent drop attacks causing significant injuries then surgical options such as corpus callosotomy and/or vagal nerve stimulator may be indicated.
    • Clinicians will need to continue to consider each patient individually, taking into account the potential benefit of each therapy weighed against the risk of adverse effects.

    Discussion with family


    Epilepsy Action (UK) have information for Parents on Lennox-Gastaut syndrome


    • Panayiotopoulos CP. The epilepsies: Seizures, syndromes and management: Based on the ILAE classifications and practice parameter guidelines. Chipping Norton, Oxfordshire: Bladen Medical Publishing; 2005.
    • Roger J, Bureau M, Dravet C, Genton P, Tassinari CA, Wolf P, editors. Epileptic syndromes in infancy, childhood and adolescence (4th ed).  Montrouge, France: John Libbey Eurotext Ltd ; 2005.