Severe myoclonic epilepsy in infancy (SMEI)

This is a very rare form of childhood epilepsy. Out of 500 children with epilepsy, only one, or at most two, children are likely to have this form of epilepsy.   It is also called Dravet Syndrome.

The epilepsy starts with seizures which may not initially differ from those associated with feverish illnesses (febrile convulsions).

Generally, this syndrome tends to develop during the second year of life. It may not be possible to make this diagnosis until the child is two, three or even four years old..

Symptoms

The seizures begin in the first year of life. They are most often associated with high temperatures and often just involve one side of the body, although both sides of the body may be involved.

The seizures are characterised by jerking rather than stiffness and jerking. They often recur quite frequently in the first year of life. However, at this time it is not easy to differentiate these children from others with febrile convulsions who get better and who do not go on to develop other types of seizure.

During the second year of life of children with SMEI, seizures become more frequent and persistent, are often more obviously partial (involving one part of the body) and no longer occur when a child has a high temperature but at any time of day and night.

In addition to the partial seizures, myoclonic jerks (‘myo’ meaning muscle, and ‘clonus’ meaning jerk) become prominent.

Often the children are photosensitive (have seizures brought on by flashing lights). Seizures may also sometimes be brought on by hot environments or hot showers or baths.

The early development of affected children is usually normal but once the myoclonic seizures and partial seizures start in their second year of life, children may lose skills or their developmental progress may slow down. The child’s speech and language maybe particularly affected..

Diagnosis

A full account of the seizures which have occurred in the past and are occurring at the time the child attends their hospital appointment is very important. A detailed account of the child’s development can be very helpful in making this diagnosis.

The electroencephalogram (EEG) which records the electrical activity in the brain is usually normal early on in this condition. Later, by the time the child is 18 months old, there is evidence of epileptic activity with spike and wave or polyspike discharges, which occur either as single event, or in bursts. These may be generalised involving the whole brain or occurring just from on small area of the brain. Some children show EEG evidence of sensitivity to flashing lights but this does not occur in all. Brain scans are usually normal.

More recently a specific genetic abnormality, called a ‘mutation’ has been found in at least 70 per cent of children with SMEI. This mutation is known as the ‘SCN1A’ mutation. It is likely that other mutations will also be found in children with SMEI. The mutation can be looked for in a simple blood test and this has been very helpful in making or confirming a diagnosis of this epilepsy syndrome.

Treatment

SMEI is one of the epilepsy syndromes which are most resistant to anti-epileptic drugs. Phenobarbital, sodium valproate (Epilim) and lamotrigine (Lamictal) are usually tried first. However, lamotrigine may actually make the myoclonic seizures worse in many children.

Other options include a medication called stiripentol, topiramate (Topamax), clonazepam (Rivotril) and clobazam (Frisium). A combination of sodium valproate with either topiramate or stiripentol may be the most helpful. A short course of a steroid (called prednisolone) and the ketogenic diet may also be helpful.

Because children with SMEI always have learning difficulties, they will also need full educational assessment and support.

Prognosis (outlook)

The seizures continue to be very difficult to control, throughout childhood. Learning difficulties persist. As the condition progresses most children become unsteady on their feet (ataxic).

Children with SMEI will need to be cared for throughout their lives. Usually by the age of 12 or 14 years, the seizures tend to become less frequent.

Support organisation

Contact a Family, 209-211 City Road, London, EC1V 1JN, telephone 0808 808 3555, www.cafamily.org.uk

For further information about epilepsy or anything mentioned in this factsheet, please contact the Epilepsy Helpline freephone 0808 800 5050 or helpline@epilepsy.org.uk.

Epilepsy Action is indebted to Dr Richard Appleton, a Consultant Paediatric Neurologist who specialises in children’s epilepsy, and to Dr Rachel Kneen, Consultant Paediatric Neurologist and Dr Stewart Macleod, Specialist Registrar in paediatric neurology, at Alder Hey at Alder Hey Children’s Hospital, Liverpool, who have kindly prepared this information.

Because this page is written by an epilepsy healthcare professional and not by Epilepsy Action, it falls outside the requirements of the Information Standard. This is why the Information Standard logo is not shown on this page.