Epilepsy with myoclonic absences is a rare form of epilepsy. It happens slightly more commonly in boys than girls, and approximately 25 out of every 100 children (one quarter) will have another family member with epilepsy. The family member may have the same or a different form of epilepsy. The underlying cause of this epilepsy syndrome is unknown. It is likely there will be a genetic cause. Myoclonic absences may be seen in children with brain abnormalities or with some genetic disorders but it may also be seen in children with no obvious cause.
The child loses awareness of their surroundings – this is the ‘absence’. How much their awareness is changed varies from child to child. This is accompanied by severe rhythmical jerking of both upper limbs (possibly one arm more than the other). The jerks usually occur between 2 and 4 times a second. There can often be a stiffening of the upper arms resulting in the arms being raised upwards. Sometimes jerking of the muscles around the chin and mouth, but not the eyes, may also happen.
Each myoclonic absence lasts for between 5 and 10 seconds but sometimes much longer (20-30 seconds). Seizures are more common when the child is tired or has just woken up, either from a daytime nap or a night’s sleep.
Other seizure types such as tonic-clonic, atonic (drop attacks) and typical absence seizures can happen in about 2 out of every 3 children with this syndrome. Almost half of all children with epilepsy with myoclonic absences have some degree of learning disability before the start of their seizures. Of the remainder, a further half will develop learning disabilities and behavioural problems after their seizures start.
A description of the seizure given by the child and any eyewitnesses can help to identify the particular seizure type in this epilepsy syndrome. A video of some of the seizures may also be very helpful. The doctor may try to provoke a seizure by getting the child to hyperventilate (over-breathe) for up to 4 minutes. Although this may feel unpleasant, it is important in order to correctly diagnose this syndrome.
Your child’s hospital doctor will arrange an EEG test, which will usually record or capture an absence, particularly if the child hyperventilates during the EEG. The hospital doctor may also want to order further tests, including a brain scan and a blood test, to look for a number of genetic disorders that might cause this type of epilepsy. Two of these genetic disorders include GLUT1 deficiency and Ring Chromosome 20. They are both very rare disorders.
Treatment is often difficult, as seizures may not respond to epilepsy medicines. Commonly used epilepsy medicines include sodium valproate (Epilim), ethosuximide (Zarontin) and lamotrigine (Lamictal). A combination of lamotrigine and sodium valproate, or ethosuximide and sodium valproate, is often more effective than a single medicine. Another epilepsy medicine, clobazam (Frisium) may also be helpful. Levetiracetam (Keppra) and topiramate (Topamax) may also be helpful in a few children.
The ketogenic diet may also be quite effective, although it will usually have to be given with at least one epilepsy medicine (usually sodium valproate or ethosuximide).
Information about treatments for children can be found on the Medicines for Children website.
There may be research studies that are taking place involving this type of epilepsy syndrome. Your child’s hospital doctor (paediatrician or paediatric neurologist) will be able to discuss this with you.
Epilepsy with myoclonic absences has a variable but often poor outlook. Over half of all children continue to have seizures into adulthood. Children whose seizures don’t respond well to treatment are at particular risk of developing other seizure types. These seizure types often include tonic-clonic seizures and atonic seizures (drop attacks).
There is some evidence that these children are also most at risk of developing learning disabilities and behavioural problems.
What is a syndrome?
A syndrome is a group of signs and symptoms that, added together, suggest a particular medical condition. In epilepsy, examples of these signs and symptoms would be things like the age at which seizures begin, the type of seizures, whether the child is male or female and whether they have physical or learning disabilities, or both. The results of an electroencephalogram (EEG) are also used to help identify epilepsy syndromes.
If you would like to know more about an epilepsy syndrome, please speak to your doctor. If you would like to know more about epilepsy in general, please contact Epilepsy Action.
Epilepsy Action would like to thank Dr Richard Appleton, consultant paediatric neurologist at Alder Hey Children’s Hospital, Liverpool, UK for preparing this information.