What is myoclonus?

Myoclonus is a symptom of a disease in which a muscle or group of muscles suddenly starts twitching or jerking. Some common examples of myoclonus are:

  • Hiccups
  • A sudden violent jerking or twitching motion when one is startled; or,
  • The twitching of an arm or leg as you begin to fall asleep

These types of muscle contractions (tightening) are normal. However, when muscle jerks or twitches happen frequently or affect more than one area of the body, they may cause problems with ordinary activities, such as walking, talking, or eating.

There are two basic types of myoclonus:

  • Positive myoclonus is the contraction of muscles.
  • Negative myoclonus is the sudden involuntary (uncontrolled) relaxation of a muscle or group of muscles. If a person is walking or standing, the sudden loss of muscle tone can cause him or her to fall.

Myoclonus may be categorized according to the part of the brain or central nervous system that is involved, or according to its cause.

Symptoms and Causes

What causes myoclonus?

Exactly why myoclonus occurs is not fully understood. In general, a myoclonic episode occurs when an abnormal electrical impulse is sent to a muscle or groups of muscles. The impulse usually comes from a location in the central nervous system, such as the brain’s cortex, the brainstem, or nerves. In some cases, the cause is damage to a peripheral nerve or nerves (those outside the central nervous system).

There are many underlying disorders or conditions that are associated with myoclonus, including:

  • Epilepsy
  • Head or spinal cord injuries
  • Brain tumors
  • Kidney or liver failure
  • Chemical or drug poisoning
  • A long period of time without oxygen (hypoxia)
  • Nervous system disorders
  • Genetic disorders

What are the types of myoclonus?

The different types of myoclonus are:

  1. Essential myoclonus is not caused by any underlying medical condition. This type of myoclonus remains stable (unchanging) over time.
  2. Opsoclonus myoclonus (Dancing Eyes-Dancing Feet Syndrome): a rare neurological condition whose symptoms include sudden, brief muscle spasms and rapid, irregular eye movements called opsoclonus. It may occur in children who have tumors, or as a result of a viral infection. Patients may also have trouble speaking. Other symptoms include poor muscle tone, irritability, or lethargy (feeling tired).
  3. Action myoclonus: This type can come on when the person moves or even tries to move. Action myoclonus is the most disabling type, because the muscle spasms can affect the arms, legs, face, and voice.
  4. Stimulus sensitive myoclonus: This type is triggered by outside stimuli, such as noise, lights, or movement.

Diagnosis and Tests

How is myoclonus diagnosed?

The pediatrician will ask about the child’s medical history and general health. You should provide detailed information about your family’s medical history and about any medications or toxins (poisons) your child might have been exposed to. You should also try to observe whether the movements occur while the child is resting or moving, and whether they appear to be caused by light, sounds, touch, or other factors.

The doctor may order certain tests to learn what is causing the myoclonus. These may include:

  • Electroencephalogram, or EEG (a record of brain activity)
  • Electromyography (measures muscle activity and the electrical impulses associated with myoclonus)
  • Imaging tests, including MRI, CT scan, or PET scan, to look for abnormalities, such as a tumor or a lesion
  • Blood tests to see whether there are any medical conditions that could be causing the twitching

Management and Treatment

How is myoclonus treated?

The treatment depends on what is causing the disorder. The aim is to reduce symptoms with medications.

  • Medications: Anti-convulsant drugs, sedatives, or tranquilizers may help to reduce the frequency and/or intensity of myoclonic episodes in children with epilepsy. Sometimes more than one medication is needed to control myoclonus. Anti-convulsant drugs usually are prescribed for patients with juvenile myoclonus epilepsy.
    Clonazepam (Klonopin), a tranquilizer, is effective for some forms of myoclonus. Valproic acid (Depakene) is the drug of choice for young men with this condition, while lamotrigine (Lamictal) is recommended for young women, because it causes fewer side effects such as weight gain and polycystic ovary disease. Other effective anticonvulsant medications include levetiracetam (Keppra), topiramate (Topamax), and zonisamide (Zonegran).
    Barbiturates are sedatives that decrease the activity of the central nervous system and can reduce seizures.
  • Surgery: Tumors that cause myoclonic activity in children with opsoclonus-myoclonus may have to be removed through surgery or treated with chemotherapy and radiation. Oral corticosteroids such as prednisone or adrenocorticotropic hormone (ACTH) may be prescribed.
  • Behavioral changes: A lack of sleep can increase seizure activity in some children with epilepsy, so it is important for them to get enough sleep. People whose seizures are caused by light (photosensitivity seizures) should avoid exposure to flickering lights. Some recommendations include sitting farther away from video monitors and making sure there is enough back lighting.

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