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Myoclonus

Definition

Myoclonus is a brief and rapid twitching of a muscle or muscle groups. The twitching or jerking happens suddenly. Myoclonus cannot be stopped or controlled at will.

There are different types of myoclonus. Some occur normally. Examples of normal myoclonus include hiccups and an occasional movement while falling asleep. Other types are pathological, or abnormal.

Myoclonus is classified according to:

  • Underlying cause
  • Pattern of movement
  • Origin within the body

Causes

Myoclonic jerk-like movements are caused by an abnormal electrical discharge in the nervous system. The electrical discharge may originate in the brain, the spinal cord, or a nerve 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

© 2008 Nucleus Medical Art, Inc.

The exact mechanism triggering the abnormal electrical discharge depends on what is causing the myoclonus. Myoclonus is often a symptom of a nervous system or metabolic condition. Possible causes include:

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. A family history of myoclonus is the only common risk factor that has been identified.

Symptoms

Myoclonic symptoms vary from mild to severe, depending on the cause of the problem. Myoclonus may begin in childhood or adulthood. The unexpected 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 apparent 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.

Diagnosis

Your doctor will ask about your symptoms and medical history, and perform a physical exam. Your doctor will try to determine the following:

  • The origin in the nervous system of the myoclonus
  • If an underlying condition is responsible for the symptoms

Tests may include:

  • Electroencephalogram (EEG)—a test that records the brain's activity by measuring electrical currents through the brain
  • Electromyogram (EMG)—a test that measures and records the electrical activity of the muscles
  • MRI scan—a test that uses magnetic and radio waves to take pictures of the inside of the body
  • CT scan—a type of x-ray that uses a computer to make pictures of the inside of the body
  • Blood tests—may include:
    • Thyroid function
    • Blood chemistry
    • Complete blood cell count
    • Toxicology screen to check for drugs or toxins
    • Blood tests looking for other metabolic causes
  • Single photon emission computed tomography (SPECT)—a test that takes pictures of the inside of the body and displays them on a computer screen

Treatment

Treatment aims to reduce the severity of involuntary movements, which is usually done with medications. The drugs given will depend on the underlying cause, and in some cases, multiple drugs may be needed to decrease the twitching. The drugs may produce serious side effects.

  • Sedatives:
    • Lorazepam (Ativan)
    • Diazepam (Valium)
    • Clonazepam (Klonopin)
    • Piracetam
    • Tetrabenazine
  • Anticonvulsants:
    • Clonazepam (Klonopin)
    • Divalproate sodium (Depakote)
    • Gabapentin (Neurontin)
    • Topiramate (Topamax)
    • Primidone (Myidone, Mysoline)
    • Carbamazepine (Tegretol)
  • Serotonin precursor 5-hydroxytryptophan (5-HTP)
  • Adrenocorticotropic hormone (ACTH)

Prevention

Guidelines for preventing myoclonus depend on the cause. In many cases, myoclonus is not preventable. For example, if you have a family history of myoclonus, there is no known way to stop the disorder from developing.

Some cases that may be prevented include:

  • Brain injury—Take care to prevent accidents or injury. For example, wear a helmet when riding a bicycle or motorcycle.
  • Medication side effects—If twitching begins after starting on a new medication, tell your doctor. Your provider may be able to lower your dose or switch to a different medication.

RESOURCES:

Myoclonus Research Foundation
http://www.myoclonus.com

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

We Move
http://www.wemove.org

CANADIAN RESOURCES:

The Canadian Brain and Nerve Health Coalition
http://www.ccns.org/ccns_information/brain_nerve.html

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

References:

Cecil Textbook of Medicine . 21st ed. WB Saunders Co; 2000.

Harrison's Principles of Internal Medicine . 14th ed. The McGraw-Hill Companies; 2000.

Myoclonus and its disorders. Neurologic Clinics . 2001 Aug.

Primary Care Medicine . 4th ed. Lippincott, Williams, and Wilkins; 2000.

Pulmonary and Critical Care Medicine . Mosby-Year Book Inc; 1998.

Textbook of Clinical Neurology . WB Saunders Co; 1999.



Last reviewed November 2007 by Rimas Lukas, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.


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