Myoclonus may occur normally, but it may result from a disorder, such as liver failure, a head injury, low blood sugar, or Parkinson disease or from certain drugs.
Muscles may jerk quickly or slowly, and jerking may be rhythmic or not.
Doctors diagnose myoclonus based on symptoms and do blood tests and/or magnetic resonance imaging to identify the cause.
The cause of myoclonus is corrected if possible, but if the cause cannot be corrected, certain antiseizure drugs or clonazepam (a mild sedative) may lessen symptoms.
(See also Overview of Movement Disorders.)
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.
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:
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 a 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.
The diagnosis of myoclonus is based on symptoms.
Testing is usually done to identify the cause:
Blood tests are usually done to check kidney and liver function and 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 or Creutzfeldt-Jacob disease.
Electroencephalography may be done to check for myoclonus in people with a seizure disorder.
The cause of myoclonus 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.
If the cause cannot be corrected, certain antiseizure drugs (such as valproate and levetiracetam) 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.