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. Hiccups are a type of myoclonus that involves only the diaphragm, the muscle that separates the chest from the abdomen.

Myoclonus may occur normally, often when a person is falling asleep. Or it may result from a disorder, such as the following:

• Liver failure
• Kidney failure
• Cardiac arrest (when the heart's pumping stops suddenly)
• Brain damage due to a virus (viral encephalopathy)
• Metabolic disorders (such a high or low blood sugar level)
• Oxygen deprivation
• Head injuries
• Alzheimer's disease (occasionally)
• Creutzfeldt-Jakob disease
• Juvenile myoclonic epilepsy (which causes seizures)

Myoclonus can occur after a person takes high doses of certain drugs such as antihistamines, some antidepressants (such as amitriptyline), bismuth, levodopa, or opioids (narcotics).

Symptoms

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—hiccups and the quick twitches of muscles as a person falls asleep—are normal.

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 Seizure Disorders: Drugs Used to Treat Seizures.) or clonazepam (a mild sedative) sometimes helps. When given with carbidopa, the dietary supplement 5-hydroxytryptophan (which is produced by the brain) may also help.

Last full review/revision August 2007 by David Eidelberg, MD; Michael Pourfar, MD