General Myoclonus

National Organization for Rare Disorders, Inc.

Skip to the navigation


It is possible that the main title of the report General Myoclonus is not the name you expected.

Disorder Subdivisions

  • None

General Discussion

Myoclonus is the term used to describe the sudden, involuntary jerking of a muscle or group of muscles caused by muscle contractions (positive myoclonus) or muscle relaxation (negative myoclonus). The twitching or jerking of muscles cannot be controlled by the person experiencing it. Myoclonic jerks may occur infrequently or many times a minute. They sometimes occur in response to an external event or when a person attempts to make a movement. By itself, myoclonus may be seen as a symptom rather than a disease. To some degree, it may occur occasionally to otherwise healthy people. (For instance, hiccups may be considered a type of myoclonus.) In severe cases, it can interfere with movement control and balance, and limit various everyday activities such as eating or talking.


There are different forms of myoclonus and they are classified in different ways. One way of classifying the different forms is by their cause. Some of the types of myoclonus are:

Physiologic myoclonus

This occurs in neurologically normal people. The occurrence of myoclonus during sleep and sleep transitions is the most common example.

Essential myoclonus

In this type, the myoclonic jerks or twitches are usually the most prominent or only clinical finding. This type of myoclonus usually progresses slowly or not at all. There are hereditary (autosomal dominant) and non-inherited, random (sporadic) forms.

Progressive myoclonus epilepsy (PME)

This is a group of diseases characterized by myoclonus, epilepsy, and other symptoms such as trouble walking or speaking. These disorders tend to get worse over time (progressive).

Sleep myoclonus

This typically occurs just at the moment of dropping off to sleep. In some cases, the affected individual does not find it particularly troublesome. In other cases, it may interfere with the sleep process. Myoclonus may be a symptom in certain sleep disorders such as restless legs syndrome.

Symptomatic (secondary) myoclonus

This is the most common category and usually is found in the setting of an identifiable underlying disorder. Myoclonus may not be the most prominent clinical symptom. Common co-existing problems include ataxia, dementia, and Parkinsonism. Myoclonus may also be a symptom associated with infections, non-neurologic medical illnesses, toxic-metabolic states, and storage diseases.


Myoclonus is caused by an abrupt and brief discharge of motor neurons to affected muscles. In most cases, this results from a disturbance in the central nervous system, although it is believed that in rare cases may be caused by an injury to the nerves outside the central nervous system (peripheral nerves). Several different locations within the brain are thought to be involved in myoclonus. As a result, various types of testing is usually required to define the cause of myoclonus.

The locations that cause myoclonus are reflected in the physiological classification of myoclonus:

- Cortical (Focal or multifocal source)

- Cortical-Subcortical (e.g. Myoclonic Epilepsy)

- Subcortical/Nonsegmental

- Segmental

- Peripheral

Chemicals that carry messages from one nerve cell to another (neurotransmitters) may play a role. In some cases, myoclonus may be present because of an imbalance in these chemicals. However, the specific causes are not well understood at this time.

Affected Populations

Myoclonus affects males and females in equal numbers. Some forms of myoclonus are common and some forms are rare. In general, the incidence of myoclonus is 1.3 cases per 100,000 person-years, and the prevalence is 8.6 cases per 100,000 populations.

Standard Therapies

If the cause for the underlying disorder cannot be cured, then the standard treatment for myoclonus is medications that may help reduce symptoms. The first line of therapy depends on where the myoclonus originates within the nervous system (i.e. physiological classification).. This would include levetiracetam and clonazepam, a type of tranquilizer, and other drugs known as benzodiazepine derivatives. The beneficial effects of certain drugs, including clonazepam, may diminish over time.

Many of the drugs used for myoclonus, such as barbiturates, phenytoin, and primidone, are also used to treat epilepsy. Certain of these drugs may have side effects such as sleepiness, unsteady gait (ataxia), or lethargy, and patients and their families should be aware of these beforehand.

Genetic counseling will be of benefit for patients with the inherited forms of myoclonus and their families.

Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:

Toll-free: (800) 411-1222

TTY: (866) 411-1010


For information about clinical trials sponsored by private sources, contact:

Some studies have shown that doses of 5-hydroxytryptophan (5-HTP), a building block of serotonin, leads to improvement in patients with some types of myoclonus. However, other studies indicate that this therapy is not effective in all people with myoclonus and may even cause the jerks and twitches to worsen in some affected individuals.

Because myoclonus is complex in nature it may require a combination of drugs for effective treatment. Some drugs currently being studied in different combinations include levetiracetam, clonazepam, sodium valproate, and primidone. In some people, treatment may also include hormonal therapy.



Caviness J. Myoclonus in NORD Guide to Rare Disorders. Lippincott, Williams & Wilkins. 2003. 627-28.


Camfield P, Camfield C. Long-term prognosis for symptomatic (secondarily) generalized epilepsies: a population-based study. Epilepsia. 2007; April 18 (epub ahead of print).

Abraham A, Elena C, Melamed E, Djaldetti R. Successful treatment of truncal myoclonus. Mov Disord. 2007; 5;22(7):1055-6.

Walters AS. Clinical identification of the simple sleep-related movement disorders. Chest. 2007; 131:1260-66.

Caviness JN, Brown P. Myoclonus: Current Concepts and Recent Advances. Lancet Neurology 2004;3:598-607.


National Institute of Neurological Disorders and Stroke Myoclonus Fact Sheet. January 4, 2012. Accessed on:January 13, 2012.


National Sleep Foundation

1010 N. Glebe Road

Suite 310

Arlington, VA 22201

Tel: (703)243-1697



Epilepsy Foundation

8301 Professional Place

Landover, MD 20785-7223

Tel: (866)330-2718

Fax: (877)687-4878

Tel: (800)332-1000

TDD: (800)332-2070



Opsoclonus-Myoclonus Support Network, Inc.

2116 Casa Linda Dr.

West Covina, CA 91791


Tel: (626)315-8125

Email: sandragreenberg@

NIH/National Institute of Neurological Disorders and Stroke

P.O. Box 5801

Bethesda, MD 20824

Tel: (301)496-5751

Fax: (301)402-2186

Tel: (800)352-9424

TDD: (301)468-5981


National Pediatric Myoclonus Center

P.O. Box 19643

Springfield, IL 62794-9643


Tel: (217)545-7635

Fax: (217)545-1903



Epilepsy Canada

2900 John St., Suite 402


Ontario, L3R 5G3


Fax: 9055139461

Tel: 8777340873


Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223


Madisons Foundation

PO Box 241956

Los Angeles, CA 90024

Tel: (310)264-0826

Fax: (310)264-4766



Movement Disorder Society

555 E. Wells Street

Suite 1100

Milwaukee, WI 53202-3823

Tel: (414)276-2145

Fax: (414)276-3349



For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see