What Is A Myoclonic Seizure?

The word “seizure” may bring about a mental image of someone convulsing on the ground. In reality, there are different types of seizures that vary in intensity and presentation. Myoclonic seizures are one of the most common types and are not severe. 

Myoclonic seizures are a type of seizure where a person retains complete awareness and consciousness. It manifests as a jerk-like movement of the extremities, like the arms and legs. The seizure occurs in a split second, so it’s even possible a person isn’t aware when it happens.

However, keeping track of myoclonic seizures is of utmost importance as it may be an indicator of an underlying condition. Read on to find out more information about the possible causes of myoclonic seizures, as well as the treatments and methods of dealing with this condition. 

Overview 

A myoclonic seizure is a type of generalised seizure. A seizure is a period of abnormal brain activity, characterised by rapid and uncontrolled firing of electric impulses in the brain. If a person suffers from recurrent seizures, their condition is termed epilepsy. Seizures may or may not impair consciousness and are accompanied by muscle spasms or jerk-like movements.

Myoclonic seizures present as brief, jerk-like motions of a muscle or a group of muscles. The origin of the term comes from the prefix “myo”, referring to something related to the muscles, and “clonus”, which means alternating contraction and relaxation of muscles. These seizures do not cause any loss of consciousness. In other words, a person is fully aware and conscious when they experience a myoclonic seizure. 

The spasm may last for a fraction of a second, not intervening with your daily life. However, myoclonic seizures may also occur as continuous and rapid bouts of muscle contractions, impacting your quality of life. 

Myoclonic seizures can be a symptom of a pre-existing condition, like a neurodegenerative disorder, a tumour, or a genetic condition. Proper testing and investigation by medical professionals are necessary to arrive at a proper diagnosis. If you experience multiple incidences of a myoclonic seizure instead of it being an isolated occurrence, you may be living with the condition called myoclonic epilepsy.¹

Causes of myoclonic seizures

Myoclonic seizures are usually signs of a pre-existing condition. The following conditions may present with myoclonic seizures:

Infantile spasms

This type of myoclonic epilepsy presents in infants (between the age of 3-12 months) and typically lasts for several years. In this condition, a seizure is characterised by a sudden jerk-like spasm, followed by stiffness of the extremities. 

Myoclonic seizures can be recognised in an infant or child as the flailing of their arms outward, their knees pulling up, and their body bending forward. This may be an isolated seizure or occur in succession (called a cluster). These usually occur when the child wakes up or is about to sleep. If you suspect that your child may be suffering from this condition, consult a general practitioner as soon as possible as these spasms can cause lasting effects on development and lead to neurological abnormalities.²

Lennox-Gastaut syndrome

Lennox-Gastaut syndrome is a severe form of epilepsy that usually starts in childhood, at around 4 years of age. The child may suffer from multiple types of seizures, including myoclonic seizures. This syndrome can be caused by a variety of conditions, including infections in the central nervous system, brain injuries, neurodegenerative disorders and metabolic disorders.³

Progressive myoclonic epilepsies

Progressive myoclonic epilepsies are a group of more than 10 rare and chronic conditions that are termed as progressive because a person’s condition worsens throughout life. The quality of life of an affected individual declines as their cognitive and motor function gets worse.

Other causes of myoclonic seizures include:

• Brain tumours 
• Cerebral hypoxia
• Neurodegenerative diseases (like Alzheimer’s disease or dementia)
• A part of withdrawal symptoms from alcohol or other drugs  
• Metal poisoning

Signs and Symptoms 

Myoclonic seizures are often missed as they can look like a normal twitch or a tic. As there isn’t a loss of consciousness, the person may continue with whatever they were doing as normal. The main factor to watch out for is a sudden change in muscle tone, with the associated muscle feeling tense as if they have been stimulated by an electric shock. 

Myoclonic seizures can be hard to differentiate from myoclonus. This is a different condition but sudden muscle jerks also appear as a common symptoms. However, these sudden spasms occur while a person is asleep. Myoclonic seizures occur in bouts and are of higher intensity. These happen most frequently after waking up or right before falling asleep. 

Myoclonic seizures can last for less than a second, with the person being almost completely unaware of it, or they can continuously reoccur during a short period of time. The latter may necessitate treatment depending on the extent of the spasms and how much they impair your life. 

Diagnosis and testing

Myoclonic seizures can be identified by a general practitioner based on the symptoms described above, especially in children and the elderly. As seizures are commonly a symptom of an underlying condition, a medical professional will conduct diagnostic tests to gain more insight to investigate the cause.

An electroencephalogram (EEG) is the main method used to diagnose myoclonic seizures. This test measures the electrical impulses in the brain, and any abnormal patterns are an indicator of seizures. 

Other diagnostic tests may be carried out to find out underlying causes:

• Blood tests look for abnormal levels of blood cells, or markers in the plasma, that can be indicative of a tumour. Blood analysis also detects abnormal electrolyte levels and the presence of certain trace metals 
• A CT scan and an MRI can be used to analyse the brain for scar tissue or any other abnormalities, like tumours or structural defects
• Spinal tap, which is a procedure where a sample of cerebrospinal fluid is taken to analyse for any abnormalities, can be used to rule out conditions like meningitis and encephalitis
• Genetic testing may be carried out to rule out certain inherited conditions that can cause seizures

Treatment of myoclonic seizures

Medication is commonly used for the treatment of myoclonic seizures. These are mostly used to control the muscle jerks, and not treat the underlying cause which may be complex. Different therapeutics may be explored for different individuals as a wide variety of diagnoses can lead to myoclonic seizures. Some common treatments include:⁴

• Valproic acid 
• Clonazepam
• Zonisamide 
• Topiramate 

It has been observed that certain diets, like a ketogenic diet (diet with low or no carbohydrate intake), help to alleviate the frequency of seizures. There are also certain implantable devices that can alter the electrical firing within the brain to prevent seizures.

FAQs 

How can I prevent myoclonic seizures?  

Myoclonic seizures can be avoided by recognising one’s triggers (bright lights, overstimulation or certain situations, like driving) and avoiding these triggers. If myoclonic seizures are due to an underlying condition, treatment of said condition can help to reduce the seizures.

How common are myoclonic seizures? 

Myoclonic epilepsy is one of the more common epilepsy types. Juvenile myoclonic epilepsy accounts for up to 10% of all epilepsy cases in children. 

Who is at risk of myoclonic seizures? 

People with a genetic history of neurodegenerative conditions and people who are more likely to develop brain tumours, deformities and other conditions that may cause scar tissue in the brain are at a higher risk of myoclonic seizures.

When should I see a doctor?

Visit your general practitioner as soon as possible if you notice that you, or your child, experience sudden jerk-like movements and stiffness of the extremities, as these can be signs of a myoclonic seizure that can be caused by an underlying condition.  

Summary

Myoclonic seizures are experienced without a loss of consciousness and present in the form of uncontrolled, jerk-like motions of the extremities. The condition may present itself in a fraction of a second, or recur in bouts. If myoclonic seizures repeat over a long period of time, this is categorised as myoclonic epilepsy. Myoclonic seizures are a symptom of a wide variety of conditions. The main mode of diagnosis is an electroencephalogram (EEG). Other procedures, like blood tests and spinal tap, may be carried out to find the underlying condition behind the seizures. Myoclonic seizures occur most frequently among children and the elderly. The condition can be managed with medication, diet changes, or implants that electrically stimulate certain regions of the brain. If you feel that you or someone that you know may be suffering from myoclonic seizures, contact a general practitioner as soon as possible as it may be an indicator of a more serious underlying condition.