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What Is Juvenile Myoclonic Epilepsy?

Juvenile myoclonic epilepsy, or JME, is a form of epilepsy that starts in childhood or adolescence. People with disorder experience muscle twitching or jerking. They may also have other seizure types, including full-blown convulsive seizures or absence seizures (staring spells).

Juvenile myoclonic epilepsy is among the most common forms of epilepsy. One of every 14 people with epilepsy have juvenile myoclonic epilepsy. Treatment with an epilepsy drug that works for multiple seizure types is usually effective.

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Symptoms of Juvenile Myoclonic Epilepsy

Juvenile myoclonic epilepsy usually starts around puberty, in late childhood, or adolescence. Three different seizure types can occur in juvenile myoclonic epilepsy:

  • Myoclonic seizures are the defining symptoms of juvenile myoclonic epilepsy. Myoclonic seizures cause sudden, quick, small jerks of the arms, shoulder, or (less often) the legs. The myoclonic seizures usually occur in the early morning just after waking up. 
  • Myoclonic seizures can sometimes spread to the rest of the brain. When this happens, a generalized tonic-clonic seizure (convulsive seizure) can occur. 
  • Absence seizures affect the whole brain, as well. In absence seizures, a person becomes unresponsive and stares into space for short periods. No twitching or convulsing occur during absence seizures. These seizures can go unnoticed, or be passed off as daydreaming or inattentiveness.

Causes And Risk Factors of Juvenile Myoclonic Epilepsy

Like other forms of epilepsy, the cause is unknown in most cases of juvenile myoclonic epilepsy. There are several factors that increase the likelihood of developing the condition:

  • About one in eight children with childhood absence epilepsy will later develop juvenile myoclonic epilepsy. 
  • People with family members affected by epilepsy are more likely to develop juvenile myoclonic epilepsy. 
  • Genetics often plays a role in juvenile myoclonic epilepsy. Multiple genes have been identified that increase the risk.

Although the underlying cause of juvenile myoclonic epilepsy is unknown, certain factors can make seizures more likely in people with the condition. Like other forms of epilepsy, seizures in JME are also more likely during sleep deprivation or after drinking alcohol.

Sometimes seizures in juvenile myoclonic epilepsy can be triggered by flickering light, like the sun reflecting off ocean waves, or strobe lighting at a party. In some people, acts of concentration like decision making or calculations can trigger seizures.

Diagnosis of Juvenile Myoclonic Epilepsy

Doctors diagnose juvenile myoclonic epilepsy based on the presence of myoclonic jerks together with other seizure types. Different tests can help make the diagnosis of juvenile myoclonic epilepsy:

  • Electroencephalogram (EEG): by attaching a set of adhesive electrodes to the scalp, a technician records brain waves during this painless test. A neurologist interprets the EEG. In juvenile myoclonic epilepsy, a pattern of spikes and waves is often present, especially in response to flashing lights. To confirm the diagnosis, an EEG can be done while asleep and just after awakening. 
  • Magnetic resonance imaging (MRI): this high-resolution scan of the brain is normal in children with juvenile myoclonic epilepsy.
  • Computed tomography (CT): this brain scan creates lower quality images than an MRI, but is faster and more widely available. CT brain scans are also normal in people with juvenile myoclonic epilepsy.

Myoclonic jerks of the legs and arms are common in people without epilepsy. In fact, they're normal as a person falls to sleep. The key to the diagnosis of juvenile myoclonic epilepsy is the additional presence of either absence seizures or convulsive seizures.

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