Lennox-Gastaut syndrome is a progressive epilepsy syndrome that causes tonic and atypical absence seizures and mental retardation. 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?
About 70% of cases of Lennox-Gastaut syndrome are symptomatic and the rest are cryptogenic, with no obvious underlying cause. Between 3% and 27% 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 a number of factors, including:
- brain injury due to problems before, 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?
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. Approximately one-third of children with Lennox-Gastaut syndrome have a history of infantile spasms.
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 anti-epileptic drugs.
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; other seizure types, both generalized and partial, may also be seen
- diffuse slow spikes and waves on the EEG
- mental retardation, which may not develop until later in the course of the syndrome
Tonic seizures occur in between 74% and 90% 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, his neck muscles stiffen, his mouth opens, his eyes roll upward, and he briefly holds his breath.
- With global tonic seizures, the child’s whole body is involved and he 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; they start gradually and the child is usually confused for a short time afterwards. The child may not lose consciousness completely. He may also have some twitching around the eyes or mouth, or his neck may stiffen. His 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 mental retardation. Tonic status epilepticus is more common in adolescents and adults.
Most children with Lennox-Gastaut syndrome have mental retardation, although it may not develop until later. Severe mental retardation 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 mental 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, although 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 between 50,000 and 100,000 will develop Lennox-Gastaut syndrome. It seems to be slightly more common in boys than in girls.
How do you know that a child has 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 and frustrating to treat. There is no one anti-epileptic drug that is always effective for the syndrome, and many anti-epileptic drugs 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 be able to 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 mental 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% of the study participants were in regular school classes or jobs.
Factors that are associated with poor seizure control and severe mental retardation include:
- symptomatic syndrome
- early onset of seizures
- frequent seizures
- repeated episodes of status epilepticus