Juvenile myoclonic epilepsy (JME) is a fairly common epilepsy syndrome that usually begins when a child is between 12 and 18 years old. The child will have one or several myoclonic jerks, usually shortly after waking up. About three years after the myoclonic jerks begin, most children with juvenile myoclonic epilepsy start having generalized tonic-clonic seizures as well. Sometimes, patients will seek medical attention only after they present with tonic-clonic seizures.
What are other terms for juvenile myoclonic epilepsy?
Other terms for juvenile myoclonic epilepsy include:
- adolescent myoclonic epilepsy
- Janz syndrome
- JME
- juvenile myoclonic epilepsy of Janz
What are the features of juvenile myoclonic epilepsy?
Children with JME usually begin having seizures when they are between eight and 24 years old. Most start having seizures between the ages of 12 and 18.
The child has myoclonic jerks with sudden, brief muscle contractions on one or both sides of the body. The jerks mainly affect the shoulders and arms; if the child is holding an object, it may be thrown across the room. Occasionally, the jerks may affect the legs or even the entire body, in which case the child may fall down. The child remains aware during the seizures.
The jerks usually happen soon after the child wakes up in the morning or after a nap. They can interfere with normal activities like eating breakfast, brushing teeth or putting on makeup. The child and their parents may assume that the jerks are normal or that they are caused by nervousness or clumsiness. For this reason, it can be easy to overlook the seizures until they present with generalized tonic-clonic seizures.
The seizures can also be triggered by early awakening, lack of sleep, alcohol, drugs, fasting (not eating for long periods of time), menstruation or (in about one third of cases) flashing or flickering lights. They may also happen when the child is tired or relaxed.
In some cases, the seizures do not cause visible movements. The child only feels an electric shock-like feeling inside their body.
Once a child has had JME for several years, they will usually start to have generalized tonic-clonic seizures. These seizures usually begin with a series of myoclonic jerks, which become more and more severe and spread through the body. The child then has a tonic-clonic seizure. Some adolescents and adults may be able to tell from the myoclonic jerks that they are about to have a tonic-clonic seizure, and they can lie down in a safe place to avoid injury.
Between 15% and 30% of children with JME also have absence seizures, which usually begin when the child is aged 11 to 12.
Children with JME usually have average intelligence . However, some researchers have reported that children with juvenile myoclonic epilepsy may have an immature personality, poor social adjustment or difficulty with tests that need mental flexibility and abstract reasoning. Adolescents with this syndrome may also fail to follow their course of treatment properly.
What causes juvenile myoclonic epilepsy?
Juvenile myoclonic epilepsy is a generalized epilepsy syndrome with a strong but complex underlying genetic component. One-third to one-half of affected children have a family history of seizures or epilepsy, not necessarily from parents or siblings. In some cases, children had febrile seizures or childhood absence epilepsy before they developed JME.
The genetic basis of JME is not completely clear. More than one gene appears to be involved, and the disorder has been linked to different genes in different families.
In rare cases, children with juvenile myoclonic epilepsy also have small structural brain abnormalities, but these do not seem to affect the response to treatment or the outlook. One MRI study found that people with JME and other generalized epilepsies with an unidentified cause had subtle differences in grey matter volume, grey matter distribution and brain metabolism.
How many other children have juvenile myoclonic epilepsy?
Because children and their parents may not realize that myoclonic jerks in the morning are abnormal and may not tell their health-care provider about them, it is not certain how many children have juvenile myoclonic epilepsy. Health-care providers are becoming more aware of this syndrome. It is estimated that about 10% of cases of epilepsy, and perhaps more, are JME.
How do you know that a child has juvenile myoclonic epilepsy?
A description of the seizures is very important for your child’s health-care provider to make a diagnosis of JME. Your child’s health-care provider will need to know what the jerks look like and if your child drops or throws things in the morning after they wake up. They will also ask if any family members have or had seizures.
Syndromes associated with myoclonic jerks that differ from JME include progressive myoclonic epilepsies, such as Unverricht-Lundborg disease and Lafora’s disease. They Your child’s health-care provider may consider them as a possible cause if there are other associated brain conditions. These conditions also cause progressive neurological deterioration with movement problems and dementia. By contrast, if a child has JME, their physical and neurological examinations are usually normal.
The child will usually have a specific EEG pattern between seizures. The health-care provider may want to obtain an EEG after the child has been sleep-deprived for some time to see any changes in the EEG while the child is sleeping or tired.
If the diagnosis of JME is clear, your child’s health-care provider will not necessarily need to obtain an MRI.
How is juvenile myoclonic epilepsy treated?
JME is treated with anti-seizure medications in combination with proper sleep routine, in order to keep seizures under control.
The anti-seizure medication valproate is an effective treatment in almost 90 per cent of people with JME, however it is avoided in girls who have attained puberty. Options for post-pubertal girls and boys in whom it is not effective or if it causes side effects, include levetiracetam, lamotrigine and topiramate.
Because factors such as tiredness, irregular sleep patterns, alcohol and missing doses of medication can all trigger seizures, it is important for teens with JME to adopt regular lifestyle habits and follow their course of treatment carefully. Teens should sleep for eight to 10 hours per night and avoid staying up late or waking up early. They should avoid alcohol and large amounts of caffeine, found in coffee, tea, cola and energy drinks. If the child or teen is expecting a change in their sleep cycle, for instance if they are flying to a different time zone, they should talk with their health-care provider about techniques to prevent sleep deprivation.
JME often starts at an age when the child or teen is starting to stay up late to study, go to parties or drink alcohol. They may feel that the syndrome and the lifestyle changes that are needed can interfere with their social life. Juvenile myoclonic epilepsy is sometimes linked with lack of compliance with treatment, such as forgetting to take or not taking their anti-epileptic medication. For all these reasons, some health-care providers recommend counselling to help children and teens manage the condition.
Because JME can affect learning and social development, your child’s doctor may recommend a neuropsychological evaluation.
What is the outlook for a child with juvenile myoclonic epilepsy?
It is rare for seizures in JME to go away. Anti-seizure medications control seizures for most people with this syndrome, but the relapse rate if the medication is stopped is up to 90%. For this reason, withdrawing medication is not recommended, even if the child has been free of seizures for a long time. The child may need to take medication for the rest of their life.
It is possible that early treatment of the seizures may lead to better seizure control. Children with mostly myoclonic seizures and only a few tonic-clonic seizures have the best chance of achieving complete seizure control.