An Overview of Myoclonic Epilepsy

Myoclonic epilepsy involves myoclonic seizures. They are characterized by myoclonic jerks—sudden, unintended muscle contractions. There are several types of myoclonic epilepsy, all of which usually begin during childhood, are typically caused by genetic factors, and may also cause cognitive and developmental problems. Juvenile myoclonic epilepsy (JME) is the most common form of this condition.

The diagnosis of myoclonic seizures is based on the description of the seizures, as well as the associated electroencephalogram (EEG) patterns. These epilepsy types can be treated with prescription anti-seizure medications and with interventional procedures, but they are less likely to be fully controlled than other seizure types.

Myoclonic seizures typically begin in early childhood, and they most commonly occur shortly before falling asleep or upon waking up, although they can occur at other times of the day. If you have myoclonic seizures, it is likely that you'll also experience at least one other type of seizure as well.

While the following are classic symptoms of all types of myoclonic epilepsy, there are additional ones related to specific forms and causes.

Myoclonus, also described as myoclonic jerks, are rapid, involuntary muscle contractions. Some people regularly experience one or two myoclonic jerks when falling asleep without any progression to a seizure.

Myoclonus can also occur due to several diseases of the spine or the nerves. Occasionally, myoclonus can occur as a result of electrolyte or hormonal changes. In some situations, myoclonic jerks may occur only a few times throughout a person’s whole life.

Myoclonic seizures tend to recur for years. They are more common during childhood and young adulthood, and often improving during one's adult years.

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

The muscle movements of myoclonic seizures are characterized by rapid, recurrent stiffness and relaxation. During a myoclonic seizure, you may have decreased voluntary movements of your body and a diminished level of consciousness.

Myoclonic seizures can be preceded by an aura, or a sense that a seizure is going to happen. After a myoclonic seizure, you may feel tired or sleepy, but that is not always the case.

Myoclonic seizures are caused by abnormal electrical activity in the brain, which triggers the myoclonic muscle movements. Often, they are exacerbated by tiredness, alcohol, fevers, infections, photic (light) stimulation, or stress.

JME is the most common type of myoclonic epilepsy, and there are also a number of progressive myoclonic epilepsies, which are rare neurological conditions. Additionally, several epilepsy syndromes produce more than one seizure type, including myoclonic seizures.

Each of the myoclonic epilepsies has a different cause, and many of the genetic factors responsible for myoclonic epilepsies have been identified. 

JME (a.k.a. Janz syndrome) is usually a hereditary condition, though some people with it do not have any identified genetic mutations at all. It has been most strongly associated with a defect in the GABRA1 gene, which codes for the α1 subunit, an important part of the GABA receptor in the brain.

GABA is a naturally produced inhibitory neurotransmitter that regulates brain activity. This defect leads to alterations and a decrease in the number of GABA receptors, which makes the brain too excitable, leading to seizures.

The inheritance of the defect in the GABRA1 gene is believed to be autosomal dominant, which means 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, which provides instructions for making a protein that regulates the activity of neurons in the brain. A few other mutations have been associated with JME, but the links are not as consistent as with the GABRA1 and the EFHC1 genes.

Young children often have absence seizures throughout early childhood, which may go unnoticed. In fact, the myoclonic seizures may also not be recognized for years because of their timing and duration.

Once the seizures begin to occur during the day, they may initially be mistaken for tics or Tourette's syndrome, but eventually they are recognized as seizures due to the rhythmic repetitiveness of the movements. Many people who have JME also experience generalized tonic-clonic seizures (formerly called grand mal seizures).

The frequency of the seizures in JME may improve during adulthood, but seizures do tend to occur throughout life, necessitating lifelong treatment.

A number of epilepsy syndromes cause myoclonic seizures, and they are often categorized as progressive myoclonic epilepsy. Each of these progressive myoclonic epilepsy syndromes produces a collection of signs and symptoms as well as a characteristic progression and prognosis.

They all have several features in common, including multiple seizure types, difficult-to-control seizures, and lifelong learning, developmental, and physical impairment. The myoclonic seizures generally improve during adulthood while other types of seizures, such as generalized tonic-clonic seizures, generally worsen throughout adulthood.

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

Epilepsy, Progressive Myoclonus 1 (EPM1), Unverricht–Lundborg Disease

This is a rare, hereditary developmental condition characterized by severe childhood myoclonic seizures, generalized tonic-clonic seizures, balance problems, and learning difficulties. It is caused by mutations that lengthen the CSTB gene and is most common in the Finnish population. People with this condition can have a normal life expectancy.

Epilepsy, Progressive Myoclonus 2 (EPM2A), Lafora Disease

This is a rare hereditary metabolic condition characterized by myoclonic seizures, generalized tonic-clonic seizures, a strong tendency to have seizures in response to flashing lights. It is usually caused by a mutation in the EPM2A or the NHLRC1 genes, both of which normally help the survival of neurons in the brain. Vision loss and severe learning disabilities can occur, and people with this condition are expected to survive about 10 years after diagnosis.

Mitochondrial Encephalomyopathy

A number of rare hereditary conditions, mitochondrial diseases impair the body’s ability to produce energy. These conditions typically begin with symptoms of low energy and myopathy (muscle disease), but they can also cause encephalopathy, or brain dysfunction.

Symptoms include severe muscle weakness, coordination and balance problems, and several types of seizures—particularly myoclonic seizures.

Diagnosis can often be confirmed with muscle biopsy and metabolic abnormalities in the blood, such as elevated lactic acid. Sometimes, genetic testing may be helpful as well, depending on whether the genetic defect has been identified.

Batten Disease, Neuronal Ceroid Lipofuscinosis

This is a group of inherited diseases characterized by severe balance problems, learning deficits, loss of vision, and multiple types of seizures. It can occur in infants, children, teens, or adults. Children who develop this disease in early childhood don’t normally survive for longer than 10 years after diagnosis, while adults who develop the disease may have a normal life expectancy.

It is believed to be autosomal recessive, which means that a child must inherit the defective gene from both parents in order to develop the condition. This autosomal recessive inheritance pattern also means that parents who carry the disease may not know that they are carriers. This genetic defect causes malfunction of lysosomes, which are structures that eliminate waste materials from the body. This waste material interferes with normal brain functioning, resulting in symptoms.

Several epilepsy syndromes are characterized by patterns of developmental problems and seizures, including myoclonic epilepsy. 

Lennox-Gastaut Syndrome (LGS)

LGS is a neurological disorder characterized by many types of seizures, severe learning disabilities, and substantial physical limitations. The seizures of LGS are notoriously difficult to treat, and many strategies, including the ketogenic diet and epilepsy surgery, are usually considered for LGS.  

Rett Syndrome

Rett syndrome, a rare genetic disorder, is a neurodevelopmental condition that affects young girls. It is characterized by communication and autistic-like behavioral problems, and multiple types of seizures, including myoclonic seizures. Deliberate breath holding often triggers the seizures.

Dravet Syndrome

Dravet syndrome is a severe neurodevelopmental disorder characterized by multiple seizure types, including myoclonic seizures, balance problems, and learning deficits. The seizures are often exacerbated by fevers and infections, but they can occur in the absence of triggers.

The diagnosis of myoclonic seizures begins with a description of the seizures. If you tell your doctor or your child’s doctor that you are having brief repetitive jerking movements, with or without loss of consciousness, you are likely to have several tests directed towards the diagnosis of epilepsy

Other diagnostic considerations besides myoclonic seizures include tics, a movement disorder, a neuromuscular disease, or a neurological condition such as multiple sclerosis.

• Blood tests and lumbar puncture: Epilepsy is not specifically diagnosed based on blood tests or lumbar puncture, but these tests are often done to determine whether you have an infection or an electrolyte disorder which could trigger a seizure and which needs to be treated.
• Brain imaging: A brain magnetic resonance imaging (MRI) or brain computed tomography (CT) scan can identify anatomical abnormalities that are characteristic of epilepsy syndromes. Additionally, traumatic injuries, tumors, infections, and strokes that can cause seizures can be identified and treated.
• 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 because the seizures often occur immediately prior to or after sleep. The EEG in JME may show a characteristic pattern during seizures (ictal EEG) and in between seizures (interictal EEG). The ictal EEG pattern is described as 10 to 16 hertz (Hz) polyspikes, while the interictal EEG is a generalized (throughout the whole brain) 3 to 6 Hz spike and wave pattern. EEG patterns for other types of myoclonic epilepsy are consistent with each syndrome specific EEG pattern. For example, with LGS, there is an interictal slow spike and wave pattern.
• Genetic testing: JMA and several of the progressive epilepsy syndromes characterized by myoclonic seizures are associated with known genetic mutations.

There are several treatment options for myoclonic seizures. The treatment plan is generally quite complex for several reasons.

Myoclonic seizures are often difficult to treat, and the frequent presence of other seizure types that also need to be addressed complicates things even further. Ideally, it is considered better to take one anti-seizure medication at a tolerable dose to limit side effects, but multiple anticonvulsants are sometimes required to reduce seizures.

The most commonly used anticonvulsants for prevention of myoclonic seizures include:

Myoclonic seizures are generally brief in duration, and only rarely progress to convulsive status epilepticus, requiring emergency intervention.

Some other treatments include the ketogenic diet, epilepsy surgery, and anti-seizure devices such as the vagal nerve stimulator. Usually, for difficult-to-treat epilepsy, a combination of treatment strategies is needed.

However short they may be, myoclonic seizures can be frightening. Taking steps to prevent them—and to stay safe, should they occur—can go a long way in helping you and your family feel more in control. It is best to avoid raised sleeping situations, such as bunk beds. Set an alarm for your child (or yourself) to remind them to take their medication and alert them as to when it's time to head to bed, so they can get proper rest.