Myoclonus is a brief and rapid twitching of a muscle or muscle groups. The twitching happens suddenly. It cannot be stopped or controlled.
There are different types of myoclonus. Some occur normally, like the hiccups or a movement while falling asleep. Other types are abnormal. The condition can be classified according to:
- Underlying cause
- Pattern of movement
- Origin within the body
The movements are caused by an abnormal electrical discharge in the nervous system. The electrical discharge may begin in the:
- Spinal cord
- Nerves in the body
The message travels along the nerves to the muscle. The nerve stimulates a muscle or group of muscles to suddenly contract.
The Nervous System Pathways
What triggers the abnormal electrical discharge depends on the cause. Myoclonus is often a symptom of a nervous system or metabolic condition. Possible causes include:
- A lack of oxygen or nutrients
- Certain medications or toxins
Nervous system disorders, such as:
- Head or spinal cord trauma or injury
- Tumors of the brain or spinal cord
- Multiple sclerosis
- Parkinson's disease
- Alzheimer's disease
- Creutzfeldt-Jakob disease and other prion diseases
- Huntington's disease
- Paraneoplastic syndromes—disorders that happen in people with certain types of cancer
- Metabolic disorders, such as:
A family history of myoclonus is the only common risk factor that has been identified.
Myoclonic symptoms vary from mild to severe. This depends on the cause of the problem. It may begin in childhood or adulthood. The sudden jerking or twitching may occur once in a while or often. It may be limited to one region of the body or affect all muscle groups.
Light, sound, touch, or movement may be triggers. Or, it may happen for no known reason. Movements can occur at rest or during other movements. There may be one or a series of twitches. Sometimes, the jerking occurs in a pattern. Other times, there is no pattern. Myoclonus can become so severe that it interferes with eating, speaking, or walking.
Your doctor will ask about your symptoms and medical history. A physical exam will be done. Your doctor will try to determine the following:
- The localization of the myoclonus in the nervous system
- If an underlying condition is responsible for the symptoms
You may have your brain and muscle activity measured and recorded. This can be done with:
Pictures may be taken of your brain and spinal cord. This can be done with:
Your bodily fluids may be tested. This can be done with blood tests.
Treatment will begin by attempting to cure any underlying causes, such as tumors or electrolyte imbalances. If these treatments do not work, then treatment aims to reduce how severe the movements are. In some case, multiple drugs are needed to reduce twitching. Some have serious side effects.
- Divalproate sodium
- 5-hydroxytryptophan (5-HTP)
- Adrenocorticotropic hormone (ACTH)
Taking these steps may help to reduce your chance of myoclonus:
- Take care to prevent brain injury. For example, wear a helmet when riding a bicycle or motorcycle.
- If twitching begins after starting a new medication, tell your doctor. Your doctor may be able to lower the dose or prescribe a different medication.
National Institute of Neurological Disorders and Stroke
Canadian Association of Neuroscience Nurses
Dalmau J, Rosenfeld MR. Paraneoplastic syndromes of the CNS. Lancet Neurology. 2008;7:327-340.
Myoclonus and its disorders. Neurologic Clinics. August 2001.
Last reviewed July 2013 by Rimas Lukas, MD; Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.