Myoclonus Information Page
A patient primer from the UF Health Center for Movement Disorders & Neurorestoration
What is myoclonus?
Myoclonus is a term that refers to a specific type of movements, rather than a disease. It can be defined as brief, lightening-like muscle jerking movements that occur suddenly. Myoclonus can happen due to quick bursts of muscle activity, or from sudden and brief pauses in ongoing muscle activity (referred to as negative myoclonus). To patients, these movements can look or feel like quick jerks, shakiness, or tremors. They can occur in a single part of the body, in multiple parts, or everywhere in the body at the same time.
Myoclonus can occur intermittently or can happen frequently, and the movements can be irregular or seemingly rhythmic. In some patients, the movements happen without any specific triggers, while in others they can be triggered by holding a posture or moving, or by external stimulation, such as touching. Myoclonic movements are involuntary, meaning that they cannot be willfully suppressed or controlled. Some types of myoclonus can even occur during sleep.
What are the different types of myoclonus?
Myoclonus can be classified in a number of different ways, but one of the most helpful ways to categorize myoclonus is by where in the brain and spinal cord the signals that trigger the movements originate. Although the movements occur from muscle activity, it is important to remember that myoclonus is not caused by a problem with the muscles themselves, but rather by activity in the central nervous system (brain and spinal cord). In rare cases, myoclonus can arise from abnormal activity in more than one area of the brain in the same patient, or can be due to the activity of nerves outside of the brain and spinal cord (which is referred to as peripheral myoclonus). Determining where the abnormal signals are coming from can be helpful in determining the underlying cause of the movements and which treatments are most likely to help.
What causes myoclonus?
As it is a symptom and not a specific disease, myoclonus can occur in a wide variety of settings, making the cause of the movements sometimes difficult to identify. It most commonly occurs secondary to another identifiable disease process or abnormality. Common examples include medication side effects, abnormalities of metabolism, kidney or liver dysfunction, or infections. Myoclonus can also occur due to specific diseases affecting the nervous system, such as Parkinson’s disease, dementia, epilepsy, structural abnormalities in the spinal cord, or a lack of oxygen to the brain. In some diseases, myoclonus is a primary symptom, such as in myoclonus-dystonia. Involuntary jerking movements that look like myoclonus can also be seen in psychiatric disorders. Some types of myoclonus can happen in healthy people, such as the whole body jerk that occurs when one is startled, the quick jerking movements that some people experience as they are drifting off to sleep, or hiccups.
Who does myoclonus affect?
Myoclonus can occur in anyone, from babies to the elderly. In some cases, it can be hereditary. As it can occur in many diseases, it is difficult to know how many people it affects, or the risk of developing myoclonus in the general population. If it is mild, myoclonus is often not reported by patients or can be overlooked by physicians.
How is myoclonus diagnosed?
In most cases, the diagnosis of myoclonus is clinical, meaning that it is based on the examination of an experienced physician. The physician will need a detailed history of the medications that you are taking and have taken in the past. If myoclonus is diagnosed, additional tests are often required to help to identify the cause (if it is not clear based on patient’s history). Blood tests are almost always needed, and in some cases imaging studies of the brain or electroencephalography (EEG) of the brain are helpful. When necessary, specialized tests can be performed at movement disorders specialty centers to distinguish between myoclonus and other types of abnormal movements, and to help determine where in the brain the triggers for myoclonus are occurring.
How is myoclonus treated?
In cases where myoclonus is secondary to another disease or abnormality, whenever possible the treatment should be focused on correcting the underlying process that is causing it. This might include stopping an offending medication, or correcting a metabolic abnormality such as abnormal blood sugar. In cases where myoclonus is the primary abnormality, or where myoclonus is secondary to a disease that is not easily treated, a variety of medications can be helpful in controlling myoclonus if it is disabling. The choice of medications is guided by the information available about the type of myoclonus that is present and its cause, and where in the nervous system it is originating from.
Where do I find more information on myoclonus?
Please feel free to contact me, Dr. Christopher Hess, at the UF Health Center for Movement Disorders and Neurorestoration (http://mdc.mbi.ufl.edu) for further information. Some other sites for information include:
National Institutes of Health (NIH) NINDS Myoclonus Information Page (http://www.ninds.nih.gov/disorders/myoclonus/myoclonus.htm)
National Institutes of Health (NIH) NINDS Myoclonus Fact Sheet
UpToDate Patient information: Myoclonus (The Basics)