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