Myoclonus
Myoclonus refers to quick, lightning-like jerks (contractions) of a muscle or a group of muscles.
Myoclonus is similar to sudden muscle cramps, but muscle contractions begin and end more rapidly, lasting only moments. Myoclonus may involve only one hand, a group of muscles in the upper arm or leg, or a group of facial muscles. Hiccups are a type of myoclonus that involves only the diaphragm, the muscle that separates the chest from the abdomen. Myoclonus may also involve many muscles at the same time.
Myoclonus may occur normally, often when a person is falling asleep. Or it may result from a disorder such as liver or kidney failure. Myoclonus may also occur after cardiac arrest--when the heart's pumping stops suddenly--or after taking high doses of certain drugs such as levodopa or bismuth. Other causes include certain types of seizure disorders (progressive myoclonic epilepsy), degenerative diseases that occur late in life (such as Alzheimer's disease), prion diseases (such as Creutzfeldt-Jakob disease), and head injuries.
If myoclonus is severe, anticonvulsants, such as clonazepam or valproate (see Section 6, Chapter 85), are sometimes helpful.
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