What is juvenile myoclonic epilepsy?
Juvenile myoclonic epilepsy is a form of epilepsy that starts in childhood or adolescence. People with juvenile myoclonic epilepsy 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 has juvenile myoclonic epilepsy. Treatment with an epilepsy drug that works for multiple seizure types is usually effective.
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. These 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.
- Tonic-clonic seizures. Myoclonic seizures can sometimes spread to the rest of the brain. When this happens, a generalised tonic-clonic seizure (convulsive seizure) can occur.
- Absence seizures. In absence seizures, which affect the whole brain, a person becomes unresponsive and stares into space for short periods, usually from about 10 to 40 seconds. No twitching or convulsing occurs during absence seizures. These seizures can go unnoticed or are passed off as daydreaming or inattentiveness.
Causes and risk factors
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 juvenile myoclonic epilepsy:
- 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 play 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 juvenile myoclonic epilepsy are also more likely during sleep deprivation or after drinking alcohol.
Sometimes seizures in juvenile myoclonic epilepsy can be triggered by flickering light such as the sun reflecting off ocean waves or strobe lighting at a party. In some people acts of concentration such as decision-making or making 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. The most common test to help make the diagnosis of juvenile myoclonic epilepsy is an electroencephalogram (EEG). A set of adhesive electrodes are attached to the scalp and 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, or it can be triggered by exposure to flashing lights. To confirm the diagnosis an EEG can be done while the person is asleep and just after awakening.
Myoclonic jerks of the legs and arms are common in people without epilepsy. In fact they’re normal as a person falls off to sleep. The key to the diagnosis of juvenile myoclonic epilepsy is the additional presence of either absence seizures or convulsive seizures.