Myoclonus: Definition, Types, Causes, Symptoms, Diagnosis and Treatment

It is a term used to describe a wide range of brief, involuntary muscle jerks or “contractions.”

These contractions originate within the central nervous system .

Myoclonic contractions occur unexpectedly and range from minor disorders (such as hiccups) to severe, jarring movements that affect a child’s quality of life (including problems eating, speaking, or walking).

The myoclonic movements can not be controlled and can occur at any time, often occur at night when the body begins to relax at the beginning of the dream.

Actions can move from one location on the body to another and can vary in frequency, from multiple spasms per minute to a few spasms per hour.

Jerking can occur in many muscles throughout the body and is caused by muscle contractions or lapses in muscle contraction, which are called positive and negative myoclonus, respectively.

The symptoms associated with myoclonus vary greatly between different people.

At one end of the scale, myoclonus is a fairly harmless condition that most people commonly experience.

For example, the “jerk” experienced in the early stages of sleep is a type of myoclonus, as is hiccups.

At the other end of the scale, myoclonus is associated with more severe muscle contractions that are generally caused by one of several neurological disorders.

In other cases, myoclonus is not considered a symptom associated with a disease, but it is considered a disorder in itself, however, this is quite rare.

Causes of myoclonus

Myoclonus is believed to originate from several locations in the central nervous system, such as:

  • The cerebral cortex which is the part of the brain responsible for initiating voluntary movement.
  • The cerebellum, this is the part of the brain responsible for adjusting voluntary movement.
  • The brain stem, which has a role in movement.
  • The spinal cord that is responsible for transmitting signals from the brain to the rest of the body.

Myoclonus is often a symptom associated with the following neurological events and conditions:

  • Spinal cord injury.
  • Epilepsy .
  • Multiple sclerosis.
  • Alzheimer disease.
  • Parkinson’s disease.
  • Lipid storage disease.
  • Tumor cerebral.
  • Chemical or drug poisoning.
  • Complex region pain syndrome.
  • After prolonged oxygen deprivation to the brain (a condition called hypoxia or anoxia).
  • Mitochondrial encephalopathy.
  • Heart attack.
  • Renal insufficiency.
  • Liver failure.

Types and symptoms

The characteristics of myoclonus vary among people with the condition. The different characteristics of the condition that are exhibited may include the following:

  • Simple or repetitive muscle contractions. Involving any part of the muscle contractions mild to large.
  • Contractions that involve only muscles or are extended to also involve muscles and joints.
  • Rare or frequent muscle contractions.
  • Muscle contractions experienced as isolated events or frequent patterns.
  • Muscle contractions that occur after an intentional action or during rest.
  • Muscle contractions that occur in response to a known (predictable) stimulus or that occur randomly.
  • Regular or irregular muscle contractions.

From this very varied expression of myoclonic symptoms, it is evident that it is a very difficult condition to classify.

The first step that the neurologist or physical therapist will take to classify the condition is to determine the pattern of the affected muscles. And this classification can be:

  • Focal myoclonus: in this type of myoclonus, only a very small area or the muscles that are close to each other are affected.
  • Segmental myoclonus: Only one or two muscles that are not close to each other are affected here (for example, the wrist muscles and the thigh muscles).
  • Multifocal myoclonus: in this case two or more local areas of muscles are affected.
  • Generalized myoclonus: this is a generalized muscle contraction.

Myoclonus is then separated into one of the following categories based on the cause:

Physiological myoclonus

It is the most common type of myoclonus that often occurs in otherwise healthy people.

An example of physiologic myoclonus is hiccups caused by myoclonus of the diaphragm. Sleep jerks are also an example of physiological myoclonus.

Essential myoclonus

This is often described as a condition in its own right, as in many cases it does not appear to be associated with any other neurological cause.

Essential myoclonus can be inherited and does not seem to get worse over time.

Progressive myoclonic epilepsy

It describes a large and varied group of progressive disorders involving myoclonus as the main complaint of epilepsy.

The group is subdivided according to the presentation of other conditions, such as dementia or dystonia, and is often accompanied by neurological disorders in vision, balance, or speech.

Most people with progressive myoclonic epilepsy will have developed the disease in childhood or during adolescence.

Symptomatic myoclonus

In this classification myoclonus is exhibited as part of the great and diverse range of brain diseases.

Myoclonus can be classified according to its specific characteristics and / or associated neurology:

  • Action-induced myoclonus is disabling myoclonus, often expressed in more than one location and worsened by voluntary movement; especially fine and coordinated movements.
  • Juvenile myoclonic epilepsy is a progressive myoclonic epilepsy that is a common cause of myoclonic and tonic-clonic seizures (body rigidity followed by jerks) in epilepsy. Some people with juvenile myoclonic epilepsy will experience myoclonic seizures as their only type of seizure.
  • Reticular reflex myoclonus is a subtype of progressive myoclonic epilepsy. It is a generalized epilepsy that originates in the brain stem. Myoclonus is triggered by voluntary or involuntary muscle reflexes.
  • Stimulus-sensitive myoclonus describes myoclonus that is specifically triggered by external events. These events can surprise the individual, such as a sudden and loud noise or movement.
  • Nocturnal myoclonus or sleep myoclonus is a very common phenomenon that occurs in the early stages of sleep, also known as “sleep jerks.”
  • Standing myoclonus is the myoclonus that is exhibited when the person is standing, decreasing significantly when walking, sitting or lying down.

The following are more specific subtypes of myoclonus that are named according to the disease causing the condition to develop or named after the part of the body affected by muscle contractions.

  • Myoclonus of the diaphragm (hiccups).
  • Celiac-Related Myoclonus: Some people with celiac disease have myoclonic movements.
  • Posanoxic myoclonus: the myoclonus experienced after prolonged oxygen deprivation in the brain.
  • Palatal myoclonus : a condition in which rapid contractions of the soft palate (roof of the mouth) persist, sometimes even during sleep. Often other local muscle groups will also be affected, such as the face and throat.
  • Myoclonus-dystonia: it is the combination of myoclonic jerks and dystonia. In most cases, myoclonus is the most disabling feature in the condition.
  • Cortical reflex myoclonus: It is involved in epileptic patients and is characterized by muscle jerks that occur in multiple muscle groups. It is sometimes difficult to distinguish between this form of myoclonus and a multifocal seizure.

Spasmodic tremor has many possible causes and is characterized by continuous bursts of muscle activity on the surface of the skin.
Axterixis describes wrist tremor associated with lapses of muscle contraction, known as negative myoclonus.

Researchers have further suggested that tremors such as spasmodic tremor and tremor of the wrist (axterixis) are types of myoclonus, however many still believe that these are completely separate symptoms.

Diagnosis of myoclonus

Because myoclonus is an extremely diverse disorder, there is no single clinical evaluation that can be used to diagnose the disease.

Although it is possible, it is not common for myoclonus to exist as a neurological diagnosis on its own. More often, myoclonus will be associated with a neurological condition, and therefore the diagnosis will be greatly reduced.

For example, a person with myoclonus who is diagnosed with epilepsy can be confidently diagnosed as having a type of progressive myoclonic epilepsy.

When myoclonus is part of a broader neurological syndrome, muscle contractions are usually milder than if the myoclonus presents as a disorder in its own right.

However, all persons will exhibit various presentations of the condition; One person may have more regular and mild muscle contractions, while another person will have irregular but strong muscle contractions.

Once myoclonus has been classified, there are certain diagnoses that can be confused.

For example, generalized myoclonus that appears to be rhythmic can easily be mistaken for tremor; two conditions that can accompany a neurodegenerative condition but are treated very differently.

An important indicator of myoclonus is non-periodic muscle movements, whereas the tremor is perfectly rhythmic.

Any myoclonus that is disrupting a person’s normal life or causing discomfort should be investigated by a doctor, as it may be a symptom of a major health problem.

For example, what may appear to be jerky sleep may actually be a symptom of complex sleep disorders that need to be managed accordingly, such as restless leg syndrome.

Muscle activity

Surface electromyography will confirm myoclonus. Surface electromyography is a technique that allows the activity of a muscle to be measured by placing electrodes on the surface of the skin.

When the muscles contract, the electrodes capture the intensity of the contraction and this can be displayed graphically on what is specifically called an electromyograph.

Myoclonic contractions will show bursts of asymmetric muscle activity. The duration of contractions is specific to the type of myoclonus exhibited.


Experienced neurologists will generally only need to observe the muscle contractions of an outstretched arm to increase the suspicion of myoclonus.

Genetic testing

There is no specific genetic mutation that has been identified as a predisposing factor for myoclonus.

Treatment of myoclonus

In cases where myoclonus is secondary to another disease or abnormality, whenever possible, treatment should focus on correcting the underlying process that is causing it.

This could include stopping a harmful medicine or correcting a metabolic abnormality, such as an abnormal blood sugar level.

In cases where myoclonus is the primary abnormality, or when the myoclonus is secondary to a disease that is not easily treated, a variety of medications may be helpful to control the myoclonus if it is disabling.

The choice of medications is guided by the information available about the type of myoclonus that is present and its cause, and where it originates from in the nervous system.

Treatments for myoclonus often cause side effects, some of which are intolerable, so drug treatment (medications) of the condition is only recommended if the condition causes lifestyle disturbances or discomfort.

The management of myoclonus is closely related to the management of epilepsy.

Clonazepam is the first-line treatment for myoclonus, other commonly used treatments are levetiractam, phenytoin, valproic acid, primidone, or a suitable combination of the latter.

Some antiepileptic drugs will be better suited to some types of myoclonus, for example, it is suggested that levetiracetam is the most effective drug in multifocal cases.

As with any antiepileptic medication regimen, different people will respond differently to different doses and combinations of the medication, and the optimal therapeutic regimen will need to be evaluated to suit individual cases.