Lennox-Gastaut syndrome is a progressive epilepsy syndrome that causes tonic and atypical absence seizures and intellectual disability. It is difficult to treat, although some newer treatments are being investigated. Although the long-term outlook for this syndrome is generally poor, some children are able to attend normal classes in school and eventually hold jobs as adults.
What are other terms for Lennox-Gastaut syndrome?
Lennox-Gastaut syndrome is also known as childhood epileptic encephalopathy with diffuse slow spikes and waves.
What causes Lennox-Gastaut syndrome?
Lennox-Gastaut syndrome may develop in a child with no previous problems, a child with an existing neurological problem or a child with another form of epilepsy. About one-third of children with Lennox-Gastaut syndrome have a history of infantile spasms.
About 70 per cent of cases of Lennox-Gastaut syndrome are symptomatic and the rest are cryptogenic, with no obvious underlying cause. Up to 27 per cent of children with Lennox-Gastaut syndrome have a family history of epilepsy. Children with cryptogenic Lennox-Gastaut syndrome are more likely to have a family history of epilepsy than children with the symptomatic form of the syndrome. However, there is no direct evidence that the syndrome is inherited.
Symptomatic Lennox-Gastaut syndrome can be caused by:
- brain injury due to problems at or around birth
- brain malformations such as tuberous sclerosis or cortical dysplasia
- central nervous system (CNS) infection
- degenerative or metabolic disorders of the nervous system.
The frontal lobes seem to play an important role in Lennox-Gastaut syndrome. The syndrome usually appears at about the same time as the frontal lobes mature.
What are the features of Lennox-Gastaut syndrome?
The first seizure usually happens when the child is between one and eight years old. Cryptogenic Lennox-Gastaut syndrome usually appears later than the symptomatic form. In a few cases, Lennox-Gastaut syndrome has also been seen in older children with idiopathic generalized epilepsy who developed status epilepticus after discontinuing medications.
The three classic features of Lennox-Gastaut syndrome are:
- frequent generalized seizures of different types, usually atypical absence (staring), myoclonic, tonic and atonic (drop) seizures
- diffuse slow spikes and waves on the EEG
- intellectual disabilities, which may not develop until later in the course of the syndrome.
Tonic seizures occur in between 74 per cent and 90 per cent of children with Lennox-Gastaut syndrome. They may involve just a few muscles or the child’s whole body.
- With axial tonic seizures, the child’s head and body bend inward.
- With axial rhizomelic tonic seizures, the child’s upper arms and shoulders rise, their neck muscles stiffen, their mouth opens, their eyes roll upward and they briefly hold their breath.
- With global tonic seizures, the child’s whole body is involved and they can fall suddenly.
The seizures usually happen when the child is falling asleep, but they can happen at any time of day. They may be triggered by noise, contact or movement.
About two-thirds of children with Lennox-Gastaut syndrome have atypical absence seizures. These are usually longer than typical absence seizures, starting gradually and usually leaving the child confused for a short time afterwards. The child may not lose consciousness completely. They may also have some twitching around the eyes or mouth or their neck may stiffen. Their head and body may droop due to a loss of muscle tone.
Most people with Lennox-Gastaut syndrome will have at least one episode of non-convulsive status epilepticus. Absence status epilepticus is more common in children, and may be difficult to recognize in children with severe developmental disability. Tonic status epilepticus is more common in adolescents and adults.
Most children with Lennox-Gastaut syndrome have intellectual disability, although it may not develop until later. Developmental disability is more likely if the seizures begin before age three, the child has frequent seizures or repeated status epilepticus, the syndrome is symptomatic, or the child had infantile spasms.
In young children with Lennox-Gastaut syndrome, psychomotor development (in which skills that involve both thought and movement are learned) slows down or stops. If the syndrome develops later, the cognitive impairment may not be as severe. Motor development is usually affected less than cognitive development.
About half of all children with this syndrome, particularly older children, have behavioural problems. These may include hyperactivity, emotional instability, aggressive or destructive behaviour autism or hypersexuality.
Children with Lennox-Gastaut syndrome may also have associated neurological problems, including cerebral palsy, blindness or hearing loss.
How many other children have Lennox-Gastaut syndrome?
Lennox-Gastaut syndrome is rare, but it is seen quite often in paediatric epilepsy clinics. Different studies have found different rates of Lennox-Gastaut syndrome in various populations. It is estimated that one child in 50,000 to 100,000 will develop Lennox-Gastaut syndrome. It seems to be slightly more common in boys than in girls.
What are the features of Lennox-Gastaut syndrome?
Lennox-Gastaut syndrome has features in common with several other conditions, including epilepsy with myoclonic-astatic seizures, continuous spike waves in slow sleep, infantile spasms and Angelman’s syndrome. To rule these out and make a diagnosis of Lennox-Gastaut syndrome, the doctor will need to assess the seizures carefully and perform EEG.
How is Lennox-Gastaut syndrome treated?
Lennox-Gastaut syndrome is difficult to treat. There is no one anti-epileptic medication that is always effective for the syndrome, and many medications have side effects, lose their effect over time or make certain seizure types worse. However, all children are different, and your child’s doctor may find a medication or combination of medications that works for your child.
The ketogenic diet is often able to reduce seizures in children with Lennox-Gastaut syndrome.
Vagus nerve stimulation (VNS) may reduce seizures in some children.
A surgical procedure called corpus callosotomy may reduce or eliminate tonic or atonic seizures.
What is the outlook for a child with Lennox-Gastaut syndrome?
Lennox-Gastaut syndrome has a poor long-term outlook. Complete seizure control is rare, and most children have cognitive and behavioural problems. The child’s IQ usually deteriorates over time. Few adults with this syndrome are able to live independently. At the end of one study that observed children with this syndrome for more than 12 years, 21 per cent of the study participants were in regular school classes or jobs.
Factors that are associated with poor seizure control and developmental disability include:
- symptomatic syndrome
- early onset of seizures
- frequent seizures
- repeated episodes of status epilepticus.