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Tests and diagnosis
By Mayo Clinic staffDetermining the cause of myoclonus usually is a process of elimination. To rule out potential causes, your doctor may recommend the following types of tests:
Electroencephalography (EEG)
This procedure records the electrical activity of your brain and may help determine from which part of the brain the myoclonus appears to originate. EEGs are painless and take less than an hour. Small electrodes are attached to your scalp with paste or an elastic cap. You may be asked to breathe deeply and steadily for several minutes or to stare at a patterned board. At times a light may be flashed in your eyes.
Electromyography (EMG)
This test measures the electrical discharges produced in muscles and helps establish the pattern of myoclonus. Very fine wire electrodes are inserted into the muscles your doctor wants to study. This may be uncomfortable, but most people are able to complete the test. An instrument records the electrical activity from your muscle at rest and as you contract the muscle, such as by bending your arm. These signals help determine if there's damage to the muscle or to the nerves leading to the muscle. The test takes at least an hour to complete.
Magnetic resonance imaging (MRI)
This scan may be used to check for such things as structural problems or tumors inside your skull, which may be causing your myoclonus symptoms. MRIs use radio waves and a powerful magnet to produce detailed images of internal organs. The scan itself is noisy but painless, although some people experience claustrophobic feelings.
Laboratory tests
Your doctor may want to test your blood or urine for evidence of:
- Metabolic imbalances
- Autoimmune disease
- Diabetes
- Kidney or liver disease
- Drugs or toxins
- Caviness JN. Classification and evaluation of myoclonus. http://www.uptodate.com. Accessed April 27, 2010.
- Jankovic J, et al. Movement disorders: Diagnosis and assessment. In: Bradley WG, et al. Neurology in clinical practice. 5th ed. Philadelphia, Pa.: Butterworth-Heinemann/Elsevier; 2008. http://www.mdconsult.com/book/player/book.do?method=display&type=bookPage&decorator=header&eid=4-u1.0-B978-0-7506-7525-3..50026-1--cesec27&uniq=196879356&isbn=978-0-7506-7525-3&sid=987314823. Accessed April 22, 2010.
- Myoclonus fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/myoclonus/detail_myoclonus.htm. Accessed April 19, 2010.
- Caviness JN. Treatment of myoclonus. http://www.uptodate.com. Accessed April 20, 2010.
- Caviness JM. Classification and evaluation of myoclonus. http://www.uptodate.com. Accessed June 23, 2010.
- Neurological diagnostic tests and procedures. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/misc/diagnostic_tests.htm. Accessed April 22, 2010.
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