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General Myoclonus

NORD is very grateful to John N. Caviness, MD, Professor of Neurology, Mayo Clinic College of Medicine, for assistance in the preparation of this report.

Synonyms of General Myoclonus

  • No synonyms found.

Disorder Subdivisions

  • action myoclonus
  • arrhythmic myoclonus
  • cortical myoclonus
  • cortical-subcortical myoclonus
  • dyssynergia cerebellaris myoclonica
  • familial arrhythmic myoclonus
  • hereditary essential myoclonus
  • infantile myoclonic encephalopathy and polymyoclonia
  • intention myoclonus
  • Lance-Adams syndrome
  • myoclonic epilepsy
  • nocturnal myoclonus
  • opsoclonus
  • palatal myoclonus
  • paramyoclonus multiple
  • pathological myoclonus
  • peripheral myoclonus
  • postanoxic intention myoclonus
  • postencephalitic intention myoclonus
  • progressive myoclonic epilepsy
  • respiratory myoclonus
  • rhythmical myoclonus
  • segmental myoclonus
  • stimulus-sensitive myoclonus
  • subcortical/non-segmental myoclonus

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.

Symptoms

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.

Causes

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.

Related Disorders

Symptoms of the following disorders can be similar to those of myoclonus. Comparisons may be useful for a differential diagnosis:

Tourette syndrome is a neurologic movement disorder that is characterized by repetitive motor and vocal tics. The first symptoms are usually rapid eye blinking or facial grimaces. Symptoms may also include facial tics and involuntary movements of the extremities, shoulders, and the voluntary muscles. Inarticulate sounds or sometimes inappropriate words may occur. Tourette syndrome is not a progressive or degenerative disorder; rather, symptoms tend to be variable and follow a chronic waxing and waning course. Symptoms usually begin before the age of 16 years. (For more information on this disorder, choose "Tourette" as your search term in the Rare Disease Database.)

Jumping Frenchmen of Maine is a very rare disorder characterized by an extreme startle response. The symptoms occur as a response to sudden, unexpected noise or movement. The extreme startle reaction includes jumping, raising the arms, hitting, yelling, unintelligible speech, and/or imitation or repetition of another person's body movements (echopraxia). The intensity of the response increases with fatigue and stress. (For more information on this disorder, choose "Jumping Frenchmen of Maine" as your search term in the Rare Disease Database.)

Huntington's disease (Huntington's chorea) is a rare inherited, progressively degenerative neurological disorder characterized by involuntary muscle movements and dementia. Initially there are personality changes and uncontrolled rapid jerky muscle movements. In time, speech and memory become impaired and involuntary muscle movements become more frequent and severe. As Huntington's disease progresses, there is a further loss of cognitive abilities and dementia. The symptoms of this disorder usually begin during adulthood, generally after the age of forty. (For more information on this disorder choose, "Huntington's" as your search term in the Rare Disease Database.)

Torsion dystonia is a rare inherited neurological disorder characterized by involuntary contortions of the muscles in the neck, torso, arms, and legs. Occasionally only one or a few muscles are involved. People with torsion dystonia typically have an awkward, sideways gait. Other symptoms may include foot drag, cramps on the hands and feet, difficulty in grasping objects, and unclear speech. The involuntary movements of dystonia are slow writhing movements. (For more information on this disorder, choose "Torsion Dystonia" as your search term in the Rare Disease Database.)

Benign essential tremor is a rare neurological disorder characterized by a rhythmical tremor that may be pronounced. This disorder typically affects the upper extremities. The tremors may be aggravated by stress, anxiety, fatigue, and/or cold temperatures. Relief from the tremors may be achieved by rest and sedation. The symptoms of benign essential tremor generally stabilize after a period of progression. (For more information on this disorder, choose "Benign Essential Tremor" as your search term in the Rare Disease Database.)

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 www.clinicaltrials.gov. 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
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

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.

General Myoclonus Resources

Organizations:

References

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

JOURNAL ARTICLES
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.

INTERNET
National Institute of Neurological Disorders and Stroke Myoclonus Fact Sheet. January 4, 2012. http://www.ninds.nih.gov/disorders/myoclonus/detail_myoclonus.htm?css=print Accessed on:January 13, 2012.

The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.

Report last updated: 2012/01/20 00:00:00 GMT+0

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