Myoclonus refers to a sudden, involuntary (unintended) jerking of a muscle or group of muscles. It is not in itself a disease. In its simplest form, myoclonus consists of a muscle twitch followed by relaxation. There are several forms of myoclonus.
Myoclonic jerks may occur:
- either in sequence, in a pattern of movement or without pattern
- infrequently or many times per minute
- in response to an external event or when a person tries to make a movement.
Examples of myoclonus can include hiccups, the jerks or "sleep starts" that some people experience while drifting off to sleep, or persistent, shock-like contractions in a group of muscles. Myoclonic jerks may occur by themselves or be one of several symptoms associated with nervous system disorders such as epilepsy and multiple sclerosis. Myoclonus may be seen in conjunction with infection, head or spinal cord injury, stroke, brain tumors, kidney or liver failure, lipid storage disease, chemical or drug intoxication, or other disorders.
A doctor will first try to reverse or treat any underlying cause or origin of the myoclonus. Treatment of myoclonus focuses on medications that may help reduce symptoms. The drug of first choice is clonazepam, a type of tranquilizer. Many of the drugs used for myoclonus, such as barbiturates, phenytoin, and primidone, are also used to treat epilepsy. Botulinum toxin injections can reduce excess muscle activity. Hormonal therapy may improve responses to antimyoclonic drugs in some people. Myoclonus may require the use of multiple drugs for effective treatment.
Simple forms of myoclonus occur in healthy persons and cause no difficulties. In some cases, myoclonus begins in one region of the body and spreads to muscles in other areas. More severe cases of myoclonus can distort movement and severely limit a person's ability to eat, talk, or walk. These types of myoclonus may indicate an underlying disorder in the brain or nerves. The beneficial effects of clonazepam may diminish over time if the individual develops a tolerance for the drug.
Scientists at the National Institute of Neurological Disorders and Stroke and elsewhere are seeking to understand the underlying biochemical basis of involuntary movements and to find the most effective treatment for myoclonus and other movement disorders. Researchers may be able to develop drug treatments that target specific biochemical changes involved in myoclonus. The Juvenile Myoclonic Epilepsy Connectome Project aims to define biomarkers--signs that may indicate risk of a disease or be used to monitor its progression--for that disorder. Researchers also are looking to identify genetic mutations that cause myoclonus and other complex movement disorders. Information from the National Library of Medicine’s MedlinePlus Movement Disorders