What is Juvenile Myoclonic Epilepsy?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 10 October 2018
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Juvenile myoclonic epilepsy (JME), also known as Janz Syndrome, is a form of epilepsy which usually has an onset in adolescence, with the typical age of onset being between 12 and 18, although children as young as six and adults as old as 36 can develop juvenile myoclonic epilepsy. JME is characterized by myoclonic seizures in which the shoulders and arms jerk for several minutes. This condition can usually be managed with anticonvulsant drugs which reduce the incidence and severity of seizures.

In juvenile myoclonic epilepsy, the patient experiences myoclonic seizures in the first few hours after waking. This type of seizure involves small jerks of the shoulders and arms, and sometimes the legs. Patients do not lose consciousness during myoclonic seizures, and they do not usually fall, although they may drop objects which they are carrying. The duration of the seizure is typically brief.

Many patients with juvenile myoclonic epilepsy also develop tonic-clonic seizures, also known as grand mal or convulsive seizures. This type of seizure involves a tonic stage, in which the patient becomes unconscious and the whole body tenses, and a clonic stage, in which the body rapidly jerks or twitches. These distinctive seizures are what many people think of when they hear the word “seizure.” Juvenile myoclonic epilepsy can also be accompanied with absence seizures, in which the patient is momentarily unresponsive to stimuli, staring off into the distance.


Identifying juvenile myoclonic epilepsy can be difficult if the patient only experiences myoclonic seizures and absence seizures. Myoclonic jerks are very common, and not necessarily harmful, and absence seizures can be dismissed as simple daydreaming or inattention. In patients who develop tonic-clonic seizures, the condition is usually easier to spot. Diagnostic testing for JME can include an EEG, MRI, or CT scan of the brain to look for unusual brain activity.

The cause of juvenile myoclonic epilepsy is not known. There appears to be a genetic component, with children in families with a history of epilepsy being at higher risk for developing this condition. Certain stimuli may also trigger the onset of seizures in children. The appearance of seizures or seizure-like activity in children is definitely a cause for concern, and parents should take their children to see a neurologist or pediatrician if they experience seizures. Routine testing can determine whether or not the child has epilepsy, and a treatment plan can be developed to manage the condition.



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