U.S. DEPARTMENT OF HEALTH

AND HUMAN SERVICES

Public Health Service

National Institutes of Health

Myoclonus

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Myoclonus

What is myoclonus?

Myoclonus describes a clinical sign and is not itself a disease. It refers to sudden, 

involuntary twitching or jerking of a muscle 

or group of muscles. Myoclonic twitches or 

jerks usually are caused by sudden muscle 

contractions, called positive myoclonus, or by 

muscle relaxation, called negative myoclonus. 

Myoclonic jerks may occur alone or in sequence, 

in a pattern or without pattern. They may 

occur infrequently or many times each minute. 

Myoclonus sometimes occurs in response to 

an external event or when a person attempts 

to make a movement. The twitching cannot 

be controlled by the person experiencing it.

In its simplest form, myoclonus consists of a 

muscle twitch followed by relaxation. A hiccup 

is an example of this type of myoclonus. Other 

familiar examples of myoclonus are the jerks 

or “sleep starts” that some people experience 

while drifting off to sleep. These simple forms 

of myoclonus occur in healthy people and 

cause no difficulties. 

When it is more widespread, myoclonus may 

involve persistent, shock-like contractions in 

a group of muscles. In some cases, myoclonus 

begins in one region of the body and spreads 

to muscles in other areas. More severe cases 

of myoclonus can affect movement and 

severely limit a person’s ability to eat, talk, or 
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walk. These types of myoclonus may indicate 

an underlying disorder in the brain or nerves.

What are the causes of myoclonus?

T here are several different causes of myoclonus. For example, myoclonus may 

be seen in conjunction with infection, head 

or spinal cord injury, stroke, brain tumors, 

kidney or liver failure, lipid storage disease, 

chemical or drug intoxication, or other disorders. Prolonged oxygen deprivation to the 

brain, called hypoxia, may result in posthypoxic myoclonus. Myoclonus can occur by 

itself or as one of several symptoms associated with a wide variety of nervous system 

disorders. For example, myoclonic jerks may 

develop in individuals with multiple sclerosis and neurodegenerative diseases such as 

Parkinson’s disease, Alzheimer’s disease, or 

Creutzfeldt-Jakob disease. Myoclonic jerks 

also may occur in persons with epilepsy.

What are the types of myoclonus?

Classifying the many different forms of myoclonus is difficult because the causes 

and responses to therapy vary widely. Some 

of the commonly described types are:

•	 Action myoclonus is triggered or intensified 

by voluntary movement or even the intention 

to move. It may be made worse by attempts 

at precise, coordinated movements. Action 

myoclonus can be the most disabling form 

of myoclonus and can affect the arms, legs, 

and face. This type of myoclonus may be 

caused by brain damage that results from a 

lack of oxygen and blood flow to the brain.
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•	 Cortical reflex myoclonus originates in the 

cerebral cortex—the outer layer of the brain 

that is responsible for much of the information processing that takes place in the brain. 

In this type of myoclonus, jerks usually 

involve only a few muscles in one part of 

the body, but jerks involving many muscles 

also may occur. Cortical reflex myoclonus 

can be intensified when a person attempts 

to move in a certain way (action myoclonus) 

or perceive a particular sensation.

•	 Essential myoclonus occurs in the absence 

of apparent abnormalities in the brain or 

nerves. Its involuntary twitches or spasms 

can occur in people with no family history, 

but it also can appear among members of 

the same family—indicating that it sometimes may be an inherited disorder. Essential 

myoclonus tends to be stable without increasing in severity over time. In some families, 

there is an association of essential myoclonus with essential tremor, or a form of 

dystonia (myoclonus-dystonia). Dystonia 

is a movement disorder in which sustained 

muscle contractions cause twisting and 

repetitive movements or abnormal postures. 

•	 Palatal myoclonus, also called palatal tremor, 

is a regular, rhythmic contraction of one or 

both sides of the rear of the roof of the mouth, 

called the soft palate. The contractions are 

very rapid and may persist during sleep. The 

condition usually appears in adults and can 

last indefinitely. People with palatal myoclonus may note a “clicking” sound in the ear 

when the muscles in the soft palate contract.

•	 Progressive myoclonus epilepsy (PME) is a 

group of disorders characterized by myoclonus, 

seizures, and other neurologic symptoms 
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such as trouble walking or speaking. These 

rare disorders often get worse over time 

and sometimes are fatal. Studies have identified many forms of PME. One example 

is Lafora body disease, which occurs only 

when a child inherits two copies of a defective gene, one from each parent. Lafora 

body disease is characterized by myoclonus, 

seizures, and dementia (progressive loss of 

memory and other intellectual functions).

•	 Reticular reflex myoclonus originates in the 

brain stem, the part of the brain that connects to the spinal cord and controls vital 

functions such as breathing and heartbeat. 

Myoclonic jerks usually affect the whole body, 

with muscles on both sides of the body affected simultaneously. In some people, myoclonic 

jerks occur in only a part of the body, such 

as the legs, with all the muscles in that part 

being involved in each jerk. Reticular reflex 

myoclonus can be triggered by either a 

voluntary movement or an external stimulus.

•	 Stimulus-sensitive myoclonus is triggered 

by a variety of external events, including 

noise, movement, and light. Surprise may 

increase the sensitivity of the individual.

•	 Sleep myoclonus occurs during sleep and 

sleep transitions, often as one is dropping off to sleep. Some forms appear to 

be stimulus-sensitive. Some persons with 

sleep myoclonus are rarely troubled by, or 

need treatment for, the condition. However, 

myoclonus may be a symptom in more 

complex and disturbing sleep disorders, 

and may require treatment by a doctor.
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What do scientists know about myoclonus?

Most myoclonus is caused by a disturbance of the brain and spinal cord (the central 

nervous system); although rare cases of myoclonus are caused by an injury to the peripheral 

nerves (the nerves outside the central nervous 

system that connect to sensory and other 

organs, muscles, and blood vessels and relay 

information from/to the CNS). Studies suggest 

that several locations in the brain are involved 

in myoclonus. One such location, for example, 

is in the brain stem close to structures that 

are responsible for the startle response, an 

automatic reaction to an unexpected stimulus 

involving rapid muscle contraction.

The specific mechanisms underlying myoclonus are not yet fully understood. Scientists 

believe that some types of stimulus-sensitive 

myoclonus may involve overexcitability of 

the parts of the brain that control movement. 

Laboratory studies suggest that an imbalance 

between chemicals called neurotransmitters 

may underlie myoclonus. Neurotransmitters 

carry messages between nerve cells. They 

are released by one nerve cell and attach to 

a protein called a receptor on neighboring 

(receiving) cells. This attachment signals the 

receiving cell to act in a certain way.

There is some evidence that abnormalities or 

deficiencies in the receptors for certain neurotransmitters may contribute to some forms of 

myoclonus. Receptors that appear to be related 

to myoclonus include those for two important 

inhibitory neurotransmitters: serotonin and 

gamma-aminobutyric acid (GABA). Other 

receptors with links to myoclonus include 

those for opiates and glycine, the latter an 

inhibitory neurotransmitter important for the 
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control of motor and sensory functions in the 

spinal cord. More research is needed to determine how these receptor abnormalities cause 

or contribute to myoclonus.

How is myoclonus treated?

Treatment of myoclonus focuses on medications that may help reduce symptoms. 

Clonazepam is commonly used to treat 

myoclonus. Dosages of clonazepam usually 

are increased gradually until the individual 

improves or side effects become bothersome. 

Drowsiness and loss of coordination are 

common side effects. The beneficial effects 

of clonazepam may diminish over time if the 

individual develops a tolerance for the drug.

Many of the other drugs used for myoclonus, 

such as barbiturates, phenytoin, levetiracetam, valproate, and primidone, also are 

used to treat epilepsy. Each has side effects 

that may impact which medication a doctor 

selects for an individual patient.

Some studies have shown that doses of 

5-hydroxytryptophan (5-HTP), a building 

block of serotonin, leads to improvement in 

individuals with some types of action myoclonus 

and PME. However, other studies indicate 

that 5-HTP therapy is not effective in all people 

with myoclonus, and, in fact, may worsen the 

condition in some individuals. These differences in the effect of 5-HTP on people with 

myoclonus have not yet been explained, but 

they may offer important clues to underlying 

abnormalities in serotonin receptors.

The complex origins of myoclonus may require 

the use of multiple medications for effective 

treatment. Although some medications have 
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a limited effect when used individually, they 

may have a greater effect when used with 

others that act on different pathways or mechanisms in the brain. By combining several 

drugs, physicians can often achieve greater 

control of myoclonic symptoms. Hormonal 

therapy also may improve responses to antimyoclonic drugs in some people.

What research is being done?

Within the Federal government, the National Institute of Neurological 

Disorders and Stroke (NINDS), a component of the National Institutes of Health, 

has primary responsibility for sponsoring 

research on neurological disorders. As part 

of its mission, the NINDS supports research 

on myoclonus at its laboratories in Bethesda, 

Maryland, and through grants to major 

research institutions across the country.

Scientists are seeking to understand the underlying biochemical basis of involuntary movements and to find the most effective treatment 

for myoclonus and other movement disorders.

NINDS investigators are evaluating the role of 

neurotransmitters and receptors in myoclonus. 

If abnormalities in neurotransmitters or 

receptors are found to play a role in causing 

myoclonus, future research can focus on 

determining the extent to which genetic 

alterations are involved and on identifying 

the nature of those alterations. Scientists 

also may be able to develop drug treatments 

that target specific changes in the receptors 

to reverse abnormalities, such as the loss 

of inhibition, and to enhance mechanisms 

that compensate for these abnormalities. 

Identifying receptor abnormalities also may 
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help researchers develop diagnostic tests for 

myoclonus. NINDS-supported scientists are 

studying various aspects of PME, including 

the basic mechanisms and genes involved in 

this group of diseases.

Where can I get more information?

T he National Institute of Neurological Disorders and Stroke conducts and 

support a wide range of research on neurological disorders, including myoclonus. For 

information on other neurological disorders 

or research programs funded by the NINDS, 

contact in the Institute’s Brain Resources 

and Information Network (BRAIN) at:

BRAIN

P.O. Box 5801

Bethesda, MD 20824

301-496-5751

800-352-9424

www.ninds.nih.gov

Interested individuals may wish to contact 

the following organizations for additional 

information:

Opsoclonus Myoclonus Support Network, Inc.

2116 Casa Linda Drive

West Covina, CA 91791

626-315-8125 

sangreenca@yahoo.com

National Organization for 

Rare Disorders (NORD)

55 Kenosia Avenue

Danbury, CT 06813-1968

203-744-0100

800-999-6673 (voicemail only)

www.rarediseases.org

Prepared by:

Office of Communications and Public Liaison

National Institute of Neurological 

Disorders and Stroke

National Institutes of Health

Department of Health and Human Services

Bethesda, Maryland 20892-2540

NIH Publication No. 12-4793 July 2012

NIH . . . Turning Discovery into Health