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Myoclonus ˌmī-ˈäk-lə-nəs

By Hector A. Gonzalez-Usigli, MD, Professor of Neurology, HE UMAE Centro Médico Nacional de Occidente; Movement Disorders Clinic, Neurology at IMSS
Alberto Espay, MD, Associate Professor and Clinical Research Director of the James J. and Joan A. Gardner Center for Parkinson's Disease and Movement Disorders, University of Cincinnati

Myoclonus refers to quick, lightning-like jerks (contractions) of a muscle or a group of muscles.

Myoclonus may involve only one hand, a group of muscles in the upper arm or leg, or a group of facial muscles. Or it may involve many muscles at the same time.

Causes of Myoclonus

Myoclonus may occur normally, often when a person is falling asleep. For example, as people start to doze off, they may jerk awake (as if startled), or muscles in part of the body may twitch.

However, in some cases myoclonus may result from a disorder, such as the following:

Myoclonus can occur after a person takes high doses of certain drugs such as the following:

  • Antihistamines

  • Some antidepressants (such as amitriptyline)

  • Bismuth

  • Levodopa (used for Parkinson disease)

  • Opioids (narcotic pain relievers)

Symptoms of Myoclonus

Myoclonus can be mild or severe. Muscles may jerk quickly or slowly, rhythmically or not. Myoclonus may occur once in a while or frequently. It may occur spontaneously or be triggered by a stimulus, such as a sudden noise, light, or a movement. For example, reaching for an object or taking step may trigger jerks that disrupt the movement. In Creutzfeldt-Jacob disease (a rare degenerative brain disorder), myoclonus becomes more obvious when people are suddenly startled.

If myoclonus is due to a metabolic disorder, it may persist and affect muscles throughout the body, sometimes leading to seizures.

Did You Know...

  • Some types of myoclonus—such as the quick twitches of muscles as a person falls asleep—are normal.

Diagnosis of Myoclonus

  • A doctor's evaluation

  • Blood tests and sometimes other tests to identify the cause

The diagnosis is based on symptoms.

Testing is usually done to identify the cause:

  • Blood tests are usually done to measure the level of sugar, calcium, magnesium, or sodium in the blood. Abnormal levels of these substances may indicate that the cause is a metabolic disorder.

  • Magnetic resonance imaging may be done to check for abnormalities in the brain, such as those caused by Alzheimer disease.

  • Electroencephalography may be done to check for myoclonus in people with a seizure disorder.

Treatment of Myoclonus

  • Correction of the cause if possible

  • Drugs to lessen symptoms

The cause is corrected if possible. For example, drugs that can cause myoclonus are stopped. A high or low blood sugar level is corrected, and kidney failure is treated with hemodialysis. Anticonvulsants (such as valproate and levetiracetam) are used to control myoclonus in people with a seizure disorder.

If the cause cannot be corrected, anticonvulsants or clonazepam (a mild sedative) may lessen symptoms.

5-Hydroxytryptophan (5-HTP) may help people with certain types of myoclonus that do not respond to other treatments.

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