Myoclonus

Definition

Myoclonus is a brief, rapid, shock-like jerking movement.

Description

Myoclonus can be a symptom of a separate disorder, or can be the only or primary neurological finding, in which case it is termed "essential myoclonus." Myoclonus may occur in epilepsy , or following many different types of brain injury, such as lack of oxygen, stroke , trauma, or poisoning. Myoclonus can occur in one or more limbs, or may be generalized, involving much of the body.

Demographics

Because myoclonus is so often part of another disorder, the prevalence of myoclonus is not known with certainty. One study indicates that the prevalence of all types of myoclonus may be approximately 10 per 100,000 population.

Causes and symptoms

Myoclonus can be a symptom of a very wide variety of disorders. A partial list includes:

• epilepsy (several types)
• Tay-Sachs disease and other storage diseases
• spinocerebellar degenerative diseases
• Hallervorden-Spatz syndrome
• Huntington's disease
• multiple system atrophy
• corticobasal degeneration
• Creutzfeldt-Jakob disease
• brain infections, including HIV
• focal brain damage, including from stroke or tumor
• heat stroke
• electrical shock
• hypoxia (oxygen deprivation)
• toxins and drugs

Myoclonus also occurs normally, as a person falls asleep or while sleeping. This type of myoclonus is not associated with disease.

Diagnosis

The diagnosis of myoclonus is not difficult, and depends on careful patient description of the symptoms. Much more effort is devoted to determining the underlying cause. Blood tests, neuroimaging studies, genetic tests, electroencephalography (EEG) and other types of studies may be performed in order to determine the underlying disorder.

Treatment team

Myoclonus is treated by a neurologist .

Treatment

If an underlying disorder can be identified, this is treated with the expectation that successful treatment may diminish the myoclonus. In many cases this is not possible, however. Alternatively, the underlying disorder may be discovered, but may be impossible to treat. Such is the case with hypoxic myoclonus, or damage done by a stroke or trauma.

Several medications can be used to reduce the severity or frequency of the myoclonus. Valproic acid and clonazepam are the two most widely used drugs. Anticholinergic drugs, such as benztropine or trihexyphenidyl, may be useful. Anticonvulsants may be helpful, as may benzodiazepines , depending on the type of myoclonus. Deep brain stimulation has been reported to help at least one patient. Botulinum toxin injection may be useful in focal myoclonus.

Recovery and rehabilitation

Treatment of myoclonus is rarely entirely successful. The patient is likely to have some residual myoclonus even with the most successful treatments. Nonetheless, treatment may reduce frequency and severity, allowing more normal function.

Prognosis

Myoclonus is not a life-threatening disorder, but may continue to have a significant impact on quality of life and activities of daily living.

Resources

WEBSITES

Myoclonus Research Foundation. <http://www.myoclonus.com/index.htm>.

WE MOVE. <http://www.wemove.org>.

Richard Robinson

myoclonus (my-oh-kloh-nŭs) n. a sudden spasm of the muscles. Myoclonus is a major feature of some progressive neurological illnesses with extensive degeneration of brain cells. nocturnal m. spasm of the muscles on falling asleep, which occurs in normal individuals.
—myoclonic (my-oh-klon-ik) adj.