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.
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 antihistamines, some antidepressants (such as amitriptyline), bismuth, levodopa (used for Parkinson disease), or opioids (narcotic pain relievers).
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—see Creutzfeldt-Jakob Disease (CJD)), 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.
Diagnosis and Treatment
The diagnosis is based on symptoms. Other tests may be done to identify the cause.
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.
If the cause cannot be corrected, valproate or levetiracetam (anticonvulsants—see Table: Drugs Used to Treat Seizures) or clonazepam (a mild sedative) may help.
Last full review/revision January 2013 by Hector A. Gonzalez-Usigli, MD; Alberto Espay, MD