What Are Myoclonic Seizures?

Myoclonic seizures are a type of seizure that involves brief jerking or twitching muscle motions. The sudden unintended muscle motions, also known as myoclonic jerks, typically last one or two seconds. These seizures are common in people with myoclonic epilepsy.

This type of seizure is usually caused by genetic factors. The seizures usually begin in childhood, with the most common form known as juvenile myoclonic epilepsy (JME).

This article explains myoclonic seizures and myoclonic epilepsy. It also details the fairly complex reasons for the condition and how it is diagnosed and treated.

Symptoms

Myoclonic seizures typically begin in early childhood. These brief jerking motions often occur right before falling asleep or waking up. They can occur at other times of the day.

If you have myoclonic seizures, you'll also likely have at least one other type of seizure disorder. The classic symptoms of epileptic seizures include:

• Muscle jerks and contractions
• Loss of consciousness
• Weakness, usually in a specific body part
• A feeling of anxiety right before a seizure
• Staring into space

However, each type of myoclonic seizure will have specific symptoms that arise. The way in which these symptoms present will depend on the different types and causes of myoclonic seizures.

Myoclonic Jerks

Myoclonus is the term used to describe the rapid muscle jerks associated with a myoclonic seizure. In some cases, people may experience this type of muscle activity even though they are not diagnosed with one of the common types of myoclonic seizures.

Some people may feel this type of muscle motion as they are falling asleep. This may happen often, even though the muscle motion does not progress into a seizure.

In other cases, myoclonus can be due to a spinal or nerve disease. Changes in hormones, or in the balance of minerals in the body known as electrolytes, also may cause it.

In some situations, myoclonic jerks may occur only a few times throughout a person’s whole life.

Myoclonic Seizures 

Myoclonic seizures tend to happen more than once over a period of years. Because they are more common in youth, it is not unusual to see the condition improve during one's adult years.

A myoclonic seizure typically lasts for a few seconds. It looks like a sudden, repetitive jerking in an arm, a leg, or the face. Sometimes, myoclonic seizures can involve both sides of the body. They may affect more than one body part, such as an arm and a leg.

During a myoclonic seizure, the muscles become stiff and then relax in a rapid pattern of motions. You may have less voluntary control over your body and an altered state of consciousness.

An aura, or a sense that a seizure is going to happen, may come before a myoclonic seizure. You may feel tired or sleepy after it happens, but that is not always the case.

Types and Causes

Myoclonic seizures are caused by abnormal electrical activity in the brain. This is what leads to myoclonic muscle motion. Other factors can influence this activity. They include:

• Tiredness
• Alcohol
• Fever
• Infection
• Photic (light) stimulation
• Stress

Young children often have absence seizures throughout early childhood. This type of seizure (sometimes called a petit mal seizure) may go unnoticed because they have no obvious muscle motion.

Myoclonic seizures may be overlooked in the same way. Once the seizures begin to occur during the day, they may be mistaken for tics or Tourette's syndrome. This is a disorder that also usually has vocal sounds as a symptom too.

Eventually, the rhythm and repetition of the motion make clear that they are seizures.

JME and other types of progressive myoclonic epilepsies are rare neurological (brain and nervous system) conditions. Each of the myoclonic epilepsies has a different cause. Many of the genetic factors responsible for these conditions have been identified.

Juvenile Myoclonic Epilepsy

Many people who have JME also have the more classic symptoms of tonic-clonic (grand mal) seizures, in addition to the myoclonic type. The seizures tend to occur throughout life, though they may improve in adulthood. This means that a person with JME will need to be treated for a lifetime.

JME is most strongly linked to a defect in the GABRA1 gene. This gene codes for what is called the α1 subunit, an important part of the GABA receptor in the brain.

GABA is a neurotransmitter, a chemical that is naturally produced. It regulates brain activity. This defect leads to changes in the brain's GABA receptors. It also lowers the number of them. The brain becomes more excitable because of this, which leads to seizures.

Researchers believe there is a known pathway for how the GABRA1 gene defect is inherited. It is autosomal dominant, meaning that a child who inherits the defect from one parent is likely to develop JME.

JME can also be caused by mutations in the EFHC1 gene. This gene gives instructions for making a protein that regulates the activity of neurons in the brain. A few other gene mutations, such as CHD2, may be linked to JME, but the evidence is not as strong as it is with GABRA1 and EFHC1 genes.

Progressive Myoclonic Epilepsy

There are a number of epilepsy syndromes that cause myoclonic seizures. Together, they are often known as progressive myoclonic epilepsy.

Each of these syndromes has its own signs and symptoms. They also have their own signs of progression and prognosis (outcomes).

They do, however, have several features in common. These include:

• Multiple seizure types
• Seizures that are difficult to control
• Lifelong learning and developmental issues
• Physical impairments

The epilepsy syndromes that fall under the category of progressive myoclonic epilepsies include:

Progressive Myoclonus 1 (EPM1)

This genetic condition, also called Unverricht–Lundborg disease, is rare. It is known for its severe childhood myoclonic seizures. But it also comes with generalized tonic-clonic seizures, balance problems, and learning difficulties.

It is linked to mutations of the CSTB gene that cause it to lengthen. People with this condition can have a normal life expectancy.

Progressive Myoclonus 2 (EPM2A)

This condition, also known as Lafora disease, is a rare and inherited metabolic disorder. It is known for both myoclonic and tonic-clonic seizures. People who have this type of epilepsy also tend to have seizures in response to flashing lights.

Lafora disease is usually caused by a mutation in the EPM2A or the NHLRC1 genes. These genes normally help the neurons in the brain to survive.

Vision loss and severe learning disabilities can occur with Lafora disease. People with this condition are expected to survive about 10 years after diagnosis.

Mitochondrial Encephalomyopathy

Mitochondrial diseases impair the body’s ability to produce energy. These rare, inherited conditions begin with symptoms of low energy and myopathy or muscle disease. They can also cause brain dysfunction, also known as encephalopathy.

Symptoms include severe muscle weakness and coordination and balance problems. The disease causes several types of seizures, especially myoclonic seizures.

The disorder can be diagnosed when blood tests show abnormalities, such as high lactic acid levels. A biopsy, or sample of muscle tissue, may show evidence of the disorder when examined under a microscope. Sometimes, genetic testing may be helpful.

Batten Disease

Batten disease refers to a group of inherited diseases. The name originally referred to its juvenile forms, but it is now used to describe all forms of what is known as neuronal ceroid lipofuscinosis (NCL). It can occur in infants, children, teens, or adults.

NCL is known by the symptoms of:

• Severe balance problems
• Learning deficits
• Loss of vision
• Multiple types of seizures
  

Children who develop this disease in early childhood don’t normally survive for longer than 10 years after diagnosis. Adults who develop the disease may have a normal life expectancy.

For a child to develop this disorder, it's believed that they need to inherit the defective gene from both parents. The hereditary pattern also means that parents may not know that they can carry the disease.

This genetic defect causes a malfunction of lysosomes. These are structures that eliminate waste materials from the body. This, in turn, disrupts normal brain function and results in symptoms.

Epilepsy Syndromes

Several epilepsy syndromes are known for their developmental problems and seizure patterns, including myoclonic epilepsy. 

Lennox-Gastaut Syndrome

Lennox-Gastaut Syndrome (LGS) is a neurological disorder. Symptoms include many types of seizures, severe learning disabilities, and serious physical limitations. LGS seizures are hard to treat and often resistant to drug therapies.

The ketogenic diet and epilepsy surgery are among the options often considered for LGS.  

Rett Syndrome

Rett Syndrome, a rare genetic disorder, is a developmental condition that affects people assigned female at birth. It is known for causing communication and behavioral problems similar to those seen in autism.

Myoclonic and other types of seizures are associated with the disorder. Deliberate breath-holding often may bring on seizures.

Dravet Syndrome

Dravet Syndrome is a severe disorder that causes multiple seizure types, including myoclonic seizures. It begins in early childhood, with seizures often following a history of fever.

The child's development is often normal during the first year of life. However, learning deficits and cognitive problems follow. Balance and mobility problems also are common.

A high fatality rate is linked to people diagnosed with this disorder. It has been associated with SCN1A genetic mutations in 70% to 80% of cases.

Myoclonic Seizure Diagnosis

The diagnosis of myoclonic seizures begins with a description of the seizures. In most cases, you're likely to tell a healthcare provider that you or your child have repetitive muscle jerks. They may come with or without loss of consciousness.

The provider may want to do several tests to help with a diagnosis of epilepsy. They often include a look at brain wave patterns found on electroencephalogram (EEG) tests.

Besides myoclonic seizures, your provider may test for other symptoms and conditions. They may include tics, a movement disorder, or a disease such as multiple sclerosis that may be at work.

Many of these seizure disorders are hereditary. For this reason, it's likely that blood tests and genetic tests will be needed to help arrive at the right diagnosis.

Blood Tests and Lumbar Puncture

Epilepsy is not diagnosed on the basis of blood tests or lumbar puncture, also called a spinal tap. However, these tests may be done to see if you have an infection or an electrolyte disorder that may cause seizures. Treatment would then focus on the underlying condition.

Brain Imaging

A magnetic resonance imaging (MRI) or brain computed tomography (CT) scan can identify any structural abnormalities in the brain. Some of these abnormalities are common in epilepsy syndromes.

Brain imaging also may reveal evidence of tumors, infections, injuries, or strokes. Any of these causes can lead to seizures. They can be treated once they are identified.

EEG and Sleep-deprived EEG

An EEG is a brain wave test that detects seizure activity in the brain. Myoclonus is considered a seizure when it is accompanied by EEG changes. A sleep-deprived EEG is particularly helpful for myoclonic seizures. This is because the seizures often occur right before or after sleep, and sleep patterns are known to affect seizure activity.

With JME, the test may show a specific pattern during seizures called ictal EEG. Another pattern, called interictal EEG, will appear between seizures.

There are specific EEG patterns for other types of myoclonic epilepsy and the related syndromes. For example, LGS has an interictal slow spike and wave pattern.

Genetic Testing

JME and some of the progressive epilepsy syndromes that lead to myoclonic seizures are linked to known genetic mutations. Genetic testing can help in planning treatment. Identifying these syndromes can help families understand the prognosis and may also help with family planning.

Myoclonic Seizure Treatment

There are several treatment options for myoclonic seizures. However, the treatment plan is often quite complex for several reasons.

Myoclonic seizures are often hard to treat. It's common for other seizure types to be present, making things even more complicated. While these types of epilepsy can be treated with drugs and other interventions, they are less likely to be fully controlled than other seizure types.

Ideally, just one anti-seizure medication would be used at a tolerable dose to limit side effects. In these cases, though, more than one drug may be needed to reduce seizures.

When myoclonic seizures happen, they are usually brief. It is rare for them to progress to convulsive status epilepticus. This is a severe seizure that won't stop and requires emergency intervention.

For difficult-to-treat epilepsy, a combination of treatment strategies is usually needed. Options may include the ketogenic diet, epilepsy surgery, and anti-seizure devices such as the vagal nerve stimulator.

Summary

Myoclonic seizures are a type of mild seizure that can occur on their own or as a part of a larger pattern of symptoms that are quite serious.

The motions are small, brief, and jerky when compared with body-wide seizures. In some cases, children with myoclonic seizures will outgrow them. For others, including those with juvenile myoclonic epilepsy, will need to be treated for JME all their lives.

Myoclonic seizures are often seen in far more serious and oft-fatal epilepsy syndromes. These conditions, such as Lennox-Gastaut Syndrome or Batten disease, are in many cases linked to a known genetic mutation.

Diagnosis and treatment of these typically rare disorders can be complicated. Your healthcare provider may develop a treatment plan with more than one strategy, including drugs, diet changes, and medical devices to control seizure activity.