What Is Myoclonus?

Overview

A myoclonus is a quick, abrupt, and uncontrollable muscle action like a twitch, jerk, or spasm. It lasts for a brief period of time and is caused by muscles that have been activated wrongly. A single muscle, or a collection of them, may be impacted. Myoclonuses are common and harmless and can occur in healthy individuals at any point in their lives. For example, myoclonus is a condition that causes hiccups, as well as any twitches or "sleep starts" you may experience right before dozing off.

However, myoclonus may be a sign of a more serious condition, such as epilepsy, which is a medical condition that causes seizures. Metabolic disorders or medication reactions are examples of additional causes and connections. A myoclonus, therefore, represents a clinical symptom of a disease rather than a disease in its own right. Therefore, it is crucial to understand myoclonus because it might interfere with daily life and lower one's quality of life. Symptoms can be managed by treating the underlying illness that is producing myoclonus.¹

There are only two possible mechanisms for myoclonus to occur:¹

• Positive myoclonus: This occurs when muscles suddenly contract or flex.
• Negative myoclonus: This occurs due to sudden relaxation of the muscles.

Types of myoclonus 

Myoclonus is difficult to categorise because its origins and treatment outcomes vary greatly. We thought it would be nice to tell you what kinds of myoclonus are most common. However, in the medical community, myoclonus is categorised according to the underlying physiology (cortical, subcortical, etc.).² 

Myoclonus can be categorised as primary or secondary based on its causes. Primary myoclonus appears without a known aetiology, whilst secondary myoclonus results from an underlying condition.

Types of primary myoclonus: 

• Physiological myoclonus (hypnic jerks): Occurs both during sleep and during the transition from one stage of sleep to another. It appears that some types are stimuli-sensitive.
• Essential myoclonus (idiopathic): Occurs on its own and is not influenced by abnormalities in the brain or nerves. It also can appear among members of the same family and may, therefore, be an inherited disorder.
• Epileptic myoclonus: Presence of myoclonus in people living with epilepsy. Myoclonus can occur as the only seizure manifestation, as one component of a seizure, or as one of multiple types of seizures within an epilepsy syndrome.

Potential causes of secondary myoclonus:

• Autoimmune disease
• Kidney and liver disease
• Brain lesions
• Degenerative brain disease
• Genetic disorders
• Infections
• Nerve and spinal cord injuries
• Non-medical drugs
• Prescribed drugs

Understanding the Causes

 Neurological conditions and myoclonus 

1. Epilepsy: a disease in which abnormal electrical signals in your brain impair your ability to function or cause seizures. Myoclonus can happen with or because of seizures (especially myoclonic seizures). As mentioned above, a myoclonic seizure is a type of myoclonus that happens because of an underlying epileptic condition.

2. Multiple Sclerosis: a demyelinating disease that is associated with lots of different symptoms which can be atypical, making it hard to diagnose. However, one known symptom of MS is spinal myoclonic jerks due to focal damage of the neuronal axis.³

3. Parkinson's Disease:  a progressive neurological disorder caused by damage to the brain. Parkinson’s is thought to be the result of abnormal protein clearance, mitochondrial dysfunction, and neuroinflammation.⁴ Parkinson’s disease primarily affects the subcortical region of the brain (which has roles in memory and balance).  Therefore, the symptoms appear focally (at one point) of the body. Patients may initially experience repetitive rhythmic myoclonus (single jerky movements), which will become longer and more spontaneous as their disease progresses.^2[2

4. Alzheimer's Disease: In Alzheimer’s disease, myoclonus may appear in the middle or late stage of the disease. These myoclonuses are usually multifocal, occurring both at rest and during action.

Metabolic and toxic triggers

The following metabolic conditions may cause symptomatic myoclonus:

• Renal (kidney) failure
• Hepatic (liver) failure
• Respiratory failure
• Hyperthyroidism 
• Metabolic alkalosis
• Vitamin E deficiency
• Hypoxia 

Identifying symptoms

Myoclonus can be distinguished from other movement disorders primarily by its quick onset, short duration, and single-event type of muscle activation. Myoclonus can be triggered by external tactile or acoustic stimuli and can happen spontaneously (at rest) or while moving (called “action myoclonus”).

If a patient is experiencing myoclonus, obtaining their medical history is crucial as it enables doctors to detect and pinpoint the underlying causes of their myoclonus. In addition to the typical medical background, it's critical to pinpoint the specific body parts affected by,  and the rhythmicity of, the myoclonus.

Cognitive dysfunction (thinking, problem-solving, and learning difficulties), epilepsy, ataxia (loss of balance and coordination), other movement abnormalities, or neurological symptoms can all indicate symptomatic myoclonus. If a patient’s myoclonus has come on suddenly, a toxic, metabolic, or viral disease is likely to be responsible. However, if a patient’s myoclonus is becoming more severe and frequent, a neurodegenerative disease may be suspected.¹

Diagnosis and evaluation 

Your healthcare professional performs a physical examination, evaluates your medical history and symptoms, and makes a diagnosis of myoclonus. To exclude any other potential causes, you might undergo further testing. Imaging or nerve function tests may be required in some circumstances.¹

Knowing the muscles affected by myoclonus is essential for diagnosis. Electromyography (EMG) and electroencephalography (EEG), two common nerve test instruments, may both be useful in identifying the affected muscles. These (and other tests) are further detailed below:¹

• Electromyography (EMG): electrodes are positioned on a variety of muscles, particularly those that are active during the jerks. When a muscle contracts, such as when your arm bends, a device captures the electrical activity that it produces. These signals aid in identifying the origin and pattern of your myoclonus.
• Electroencephalography (EEG): an EEG captures the electrical activity of the brain. It might provide insight into the location of the myoclonus's genesis in the brain. Small electrodes are initially affixed to the scalp. The next step can involve asking you to breathe slowly and deeply while gazing at flashing lights or listening to noises. These steps could reveal unusual electrical activity..

• Evoked potential: a test that gauges the electrical activity that touch, hearing, sight, and other stimuli cause in the brain, brainstem, and spinal cord.

• Magnetic Resonance Imaging (MRI): an MRI is utilised to find structural issues or lesions inside the spinal cord or brain. An MRI uses magnetic fields and low-intensity radio waves to create precise images of these structures.
• Laboratory tests: Your doctor may suggest you undergo genetic testing to determine the potential causes of your myoclonus. Similarly, blood or urine tests may be needed to screen for metabolic problems, autoimmune diseases, diabetes, kidney disease, or liver disease. They may also perform a drug or toxin check.

Treatment approaches

The best way to treat myoclonus is to resolve the underlying issue. For example, treatment might target a medication, toxin, or other condition that is producing the myoclonus.

The underlying conditions causing myoclonus are frequently incurable or irreversible. In these situations, your treatment programme will likely focus on managing your myoclonuses, especially if they are incapacitating. Whilst there are no medications made expressly to treat myoclonus, some medications for other illnesses may aid with symptom relief. To control the symptoms, more than one medication may be required.^1,2,5 

Medicines that healthcare providers commonly prescribe include:

• Tranquillizers: The most popular medication for treating myoclonus symptoms is clonazepam. Drowsiness and a loss of coordination are side effects.
• Anticonvulsants: Epileptic seizure medication may lessen the symptoms of myoclonus. Levetiracetam, valproic acid, zonisamide, and primidone are the most widely used. Symptoms like nausea are possible adverse effects of valproic acid. Leviteraticatam induces drowsiness and lightheadedness, and primidone may have sedative and nauseous side effects.

Therapies: 

• Botulinum toxin (Botox): Myoclonus of many types may be treated with injections, especially if just one area is affected. This therapy prevents the release of a chemical messenger that causes muscular spasms.
• Surgery: If your myoclonus is being caused by a tumour or a lesion, surgery may be an option. People with myoclonus affecting parts of the face or ear also benefit from surgery.
• Deep brain stimulation (DBS), where electrodes are implanted within certain areas of the brain, has been tried in some people. Electrical signals are generated by the electrodes to stop the erratic impulses that can lead to myoclonus.

Prognosis and outlook 

The underlying cause determines how much myoclonus improves with treatment. A metabolic abnormality or an inflammatory condition are two potential causes for certain forms of myoclonus. In these, discontinuing the problematic medication may be enough to resolve drug-induced myoclonus completely.¹

Summary

Myoclonus is a brief jerky movement in a muscle or group of muscles. It is not a condition that presents frequently amongst the population. Myoclonus can be benign (causing hiccups or jerks before you fall asleep), but can also be indicative of a more concerning disease and have a notable impact on your quality of life. Following diagnosis by a medical professional, myoclonus is normally treated with medication to relieve symptoms or prevent further myoclonus.

FAQs

What is the most common cause of myoclonus?

The most common cause of myoclonus is a disturbance of the brain or spinal cord (CNS - central nervous system).⁵

Can myoclonus be cured?

`Unfortunately, usually not. It is often difficult to treat the underlying conditions causing myoclonus. However,  symptomatic treatment is usually justified if the myoclonus is sufficiently disabling or impacts your quality of life.⁶

Is myoclonus a sign of a serious medical condition? 

Not necessarily. Myoclonus includes hiccups as well as any jerks or "sleep starts" you may experience right before you fall asleep. These types of myoclonus often affect healthy individuals and are not dangerous or indicative of serious disease. However, other types of myoclonus can be brought on by metabolic issues, drug reactions, or neurological conditions like epilepsy.