Myoclonus

Definition

Myoclonus is a brief and rapid twitching of a muscle or muscle groups. The twitching happens suddenly. It cannot be stopped or controlled.There are different types of myoclonus. Some occur normally, like the hiccups or a movement while falling asleep. Other types are abnormal. The condition can be classified according to:
  • Underlying cause
  • Pattern of movement
  • Origin within the body

Causes

The movements are caused by an abnormal electrical discharge in the nervous system. The electrical discharge may begin in the:
  • Brain
  • Spinal cord
  • Nerves in the body
The message travels along the nerves to the muscle. The nerve stimulates a muscle or group of muscles to suddenly contract.
The Nervous System Pathways
CNS and PNS
Copyright © Nucleus Medical Media, Inc.
What triggers the abnormal electrical discharge depends on the cause. Myoclonus is often a symptom of a nervous system or metabolic condition. Possible causes include:

Risk Factors

A family history of myoclonus is the only common risk factor that has been identified.

Symptoms

Myoclonic symptoms vary from mild to severe. This depends on the cause of the problem. It may begin in childhood or adulthood. The sudden jerking or twitching may occur once in a while or often. It may be limited to one region of the body or affect all muscle groups.Light, sound, touch, or movement may be triggers. Or, it may happen for no known reason. Movements can occur at rest or during other movements. There may be one or a series of twitches. Sometimes, the jerking occurs in a pattern. Other times, there is no pattern. Myoclonus can become so severe that it interferes with eating, speaking, or walking.

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Diagnosis

Your doctor will ask about your symptoms and medical history. A physical exam will be done. Your doctor will try to determine the following:
  • The localization of the myoclonus in the nervous system
  • If an underlying condition is responsible for the symptoms
You may have your brain and muscle activity measured and recorded. This can be done with:Pictures may be taken of your brain and spinal cord. This can be done with:Your bodily fluids may be tested. This can be done with blood tests.

Treatment

Treatment will begin by attempting to cure any underlying causes, such as tumors or electrolyte imbalances. If these treatments do not work, then treatment aims to reduce how severe the movements are. In some case, multiple drugs are needed to reduce twitching. Some have serious side effects.
  • Sedatives:
    • Lorazepam
    • Diazepam
    • Clonazepam
    • Piracetam
    • Tetrabenazine
  • Anticonvulsants:
    • Clonazepam
    • Divalproate sodium
    • Gabapentin
    • Topiramate
    • Primidone
    • Carbamazepine
  • 5-hydroxytryptophan (5-HTP)
  • Adrenocorticotropic hormone (ACTH)

Prevention

Taking these steps may help to reduce your chance of myoclonus:
  • Take care to prevent brain injury . For example, wear a helmet when riding a bicycle or motorcycle.
  • If twitching begins after starting a new medication, tell your doctor. Your doctor may be able to lower the dose or prescribe a different medication.

RESOURCES

National Institute of Neurological Disorders and Stroke
http://www.ninds.nih.gov

WE MOVE
http://www.wemove.org

CANADIAN RESOURCES

Canadian Association of Neuroscience Nurses
http://cann.ca

Health Canada
http://www.hc-sc.gc.ca

References

Dalmau J, Rosenfeld MR. Paraneoplastic syndromes of the CNS. Lancet Neurology. 2008;7:327-340.

Myoclonus and its disorders. Neurologic Clinics . August 2001.

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