myoclonus

Definition

The word myoclonus ("myo" / muscle, "clonus" / jerk) refers to a brief involuntary twitching of a muscle or group of muscles. It is generally a symptom, not a disease. The twitches may occur alone or in bunches, with or without a pattern. They may occur rarely, or many times each minute. Sometimes myoclonus is precipitated by an external event, or when a person attempts to make a movement.

Two common examples of myoclonus are hiccups and the myoclonic jerk that sometimes wakes you up just as you're drifting off to sleep. These myoclonic jerks can be amusing, irritating, or debilitating, depending on their severity and frequency. If you've only experienced myoclonus in the two aforementioned forms, consider yourself lucky. Recurrent or severe myoclonic jerks can severely impair motor function with their forceful and involuntary muscle contractions. Severely afflicted patients may be unable to stand or walk, reach or grasp objects, feed or dress themselves, speak, or even direct their gaze. The involuntary muscle jerks can interfere with all of these functions.

Causes

Pathological myoclonus is usually caused by damage to the central nervous system. A stray electrical discharge, originating somewhere therein, is transmitted through peripheral nerves to produce sudden muscle contractions. Myoclonus can be caused by almost every known type of brain or spinal cord injury: metabolic, nutritional, degenerative, traumatic, vascular, infectious, hereditary, or toxic.

It can be a defining condition of many neurological diseases, and can be combined with many other symptoms, including (but certainly not limited to) epilepsy, dementia, growth retardation, and visual disturbances. Myoclonus does not cause these additional symptoms, but their presence helps to pin down the underlying cause of the myoclonus.

Diagnosis

In diagnosis of myoclonus, a physician is faced with two challenges: identifying the site of origin of the myoclonus within the nervous system, and establishing the cause. Electrical recording techniques are often used to localize the source.

Treatment

Treatment for myoclonus usually consists of medications that may help reduce symptoms. Many of these drugs, which include barbiturates, clonazepam, phenytoin, primidone, and sodium valproate, are also used to treat epilepsy. There have been reports that propranolol and 5-HTP are sometimes helpful. The complex origins of myoclonus may require the use of multiple drugs for effective treatment. Botulin toxin may be used to temporarily paralyze the offending muscles, as in the case of hemifacial spasms. Surgery is indicated when the myoclonus is caused by pressure on nerves (usually from a tumor).

Prognosis

Although myoclonus is not a life-threatening condition, it may result in serious debilitation and impairment.

Research

Scientists are seeking to understand the biochemical basis of involuntary movements. The National Institute of Neurological Disorders and Stroke (part of the National Institutes of Health is heavily involved in this area of research. Current investigations are focusing on the role of neurotransmitters, most importantly serotonin and gamma-amino butyric acid, in myoclonus.