Myoclonus describes sudden and uncontrollable jerks of a muscle or a group of muscles. The word, "myoclonus", comes from "myo" meaning muscle and "clonus" meaning twitch. It can happen at rest (negative myoclonus) or with movement (positive myoclonus). Myoclonus can occur infrequently or every few seconds and can range in severity from a minor irritation to a disabling symptom that can make walking or other activities very difficult.
Some myoclonic jerks are quite normal - hiccoughs (hippcups) and the twitches as you fall asleep are both examples of myoclonus. However, myoclonus is often associated with neurological or biochemical conditions including multiple sclerosis, Parkinson's disease, stroke, spinal cord injury, kidney or liver failure and lipid storage disease. Other forms occur in the absence of any other disease. Myoclonus in one or both legs during the night is known as Noctural Myoclonus or Restless Leg Syndrome (RLS) and can also occur in the absence of any other disease. Myoclonic jerks are often seen during epileptic siezures.
Although it can be caused by damage to peripheral nerves, most forms of myoclonus are caused by problems in the central nervous system. The precise mechanisms unlying it are not fully understood and it is possible that the different forms may have different causes. Some people speculate that it results from a chemical imbalance in neurotransmitters causing nerves to become over-excitable. Another theory is that nerve signals from the brain, that would normally suppress these primitive reflexes, may be prevented from getting through by nerve damage.
Clonazepam, Piracetam, Sodium valproate, Phenytoin and Primidone and several other tranquilising or anti-epilepsy drugs are often used to treat myoclonus.
NINDS: Myoclonus Fact Sheet
What is myoclonus?
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