Myoclonus is a sudden muscle spasm. The movement is involuntary and can’t be stopped or controlled. It may involve one muscle or a group of muscles. The movements may occur in a pattern or randomly.
Myoclonus is usually a symptom of an underlying disorder rather than a condition itself.
Hiccups are a mild type of myoclonus, a muscle twitch followed by relaxation. These types of myoclonus are rarely harmful. However, some forms of myoclonus can cause recurring, shock-like spasms that can interfere with a person’s ability to eat, talk, and walk.
Myoclonus may develop on its own or as a result of:
- trauma to the spinal cord or head
- tumors on the brain or spinal cord
- kidney failure
- liver failure
- lipid storage disease
- adverse effects of drugs or chemicals
- hypoxia (a condition in which the body, including the brain, is deprived of oxygen)
- autoimmune inflammatory conditions, such as multiple sclerosis and the malabsorption syndrome celiac disease
- metabolic disorders
Myoclonus also is a symptom of numerous neurological disorders such as:
- Parkinson's disease
- Lewy body dementia
- Alzheimer's disease
- Creutzfeldt-Jakob disease
- paraneoplastic syndromes (conditions that affect some cancer patients)
- corticobasal degeneration
- frontotemporal dementia
- multiple system atrophy
There are many types of myoclonus. The condition is typically described according to the underlying causes or where the symptoms originate. The following are some of the most common types:
- Action myoclonus is the most severe form. It may affect the arms, legs, face, and voice. The muscular jerking is made worse by attempts at controlled, voluntary movement. It’s often caused by a lack of oxygen or blood flow to the brain.
- Cortical reflex myoclonus originates in the outer layer of the brain tissue. It’s thought to be a form of epilepsy. Spasms may affect a few muscles in one part of the body or many muscles all over. It can be worsened by attempts to move in a certain way.
- Essential myoclonus occurs without an underlying condition and with unknown cause. It usually remains stable without getting worse over time.
- Palatal myoclonus affects the soft palate, which is the rear of the roof of the mouth. It causes regular, rhythmic contractions on one or both sides of the palate. It may also affect the face, tongue, throat, and diaphragm. Spasms are rapid, with up to 150 in a minute. Some people hear a clicking sound in the ear as the muscles contract.
- Physiological myoclonus occurs in healthy individuals. It usually doesn’t need treatment. This type includes hiccups, sleep starts, spasms related to anxiety or exercise, and infant muscle twitching while asleep.
- Progressive myoclonus epilepsy (PME) is a group of diseases that can worsen with time and might become fatal. They often begin in children or adolescents. They cause myoclonus, epileptic seizures, and severe symptoms that can make speech and movement difficult. There are many forms of PME:
- Lafora body disease is inherited. It causes myoclonus, epileptic seizures, and dementia.
- Cerebral storage diseases usually cause myoclonus, visual problems, and dementia. They can also cause dystonia, continued muscle contractions that cause twisting movements and irregular posture.
- System degenerations cause action myoclonus, seizures, and irregular balance and walking.
- Reticular reflex myoclonus is a form of epilepsy that starts in the brain stem. Spasms usually affect the whole body, causing reactions with muscles on both sides. In some, intense jerks may affect all of the muscles in only one part of the body. A voluntary movement or an external stimulus can trigger spasms.
- Stimulus-sensitive myoclonus is set off by a variety of external events such as noise, movement, and light. Surprise may intensify the sensitivity of an affected person.
- Sleep myoclonus occurs as a person is falling asleep. Treatment may not be needed. However, it may indicate a more significant sleep disorder such as restless leg syndrome.
- Symptomatic (secondary) myoclonus is a common form. It’s associated with an underlying medical condition or traumatic event.
Myoclonus attacks males and females at equal rates. Having a family history of myoclonus is the only common risk factor that’s been identified, but the genetic link hasn’t been clearly established and understood.
Symptoms of myoclonus can range from mild to severe. Spasms may occur rarely or often. One region of the body or all muscle groups can be affected. The nature of the symptoms will depend on the underlying condition.
Typically, signs of myoclonus include jerks or spasms that are:
- brief in duration
- similar to shock-like jerks
- irregular in intensity and frequency
- localized to one part of the body
- spread throughout the entire body
- interfering with normal eating, speech, or movement
Several tests can help identify and diagnose the cause of myoclonus. After an initial physical examination, a doctor also may request any of the following tests:
- electroencephalography (EEG) to record the electrical activity of the brain
- MRI or CT scan to determine whether structural problems or tumors are present
- electromyogram (EMG) to measure the electrical impulses in muscles to determine the pattern of myoclonus
- laboratory tests to look for the presence of conditions that may be contributing to myoclonus, such as:
- diabetes mellitus
- metabolic disorders
- autoimmune disease
- kidney or liver disease
- drugs or toxins
If myoclonus is caused by an underlying condition, a doctor will attempt to treat that condition first. If the disorder can’t be cured, treatment is designed to reduce the severity and frequency of symptoms.
A doctor may prescribe a sedative (tranquilizer) or anticonvulsant medication to help reduce spasms.
A doctor may recommend surgery if myoclonus is related to an operable tumor or lesion in the brain or spinal cord. Surgery also may be helpful for certain cases of myoclonus that target the face or ears.
Injections of onabotulinumtoxinA (Botox) may be effective in treating cases of myoclonus that affect a specific area. It can work to block the release of the chemical messenger that causes the muscle spasms.
For some people, hormone therapy with adrenocorticotropic hormone (ACTH), may be effective in improving responses to some medications.
While it’s not always possible to prevent myoclonus, you can take precautions to reduce your risk of being vulnerable to known causes. You may reduce your risk of myoclonus if you:
- Protect yourself against brain injury by wearing a helmet or headgear during activities such as riding a bicycle or motorcycle.
- Contact your doctor if you experience twitching after starting a new medication so that changes can be made.
While medications can be helpful in easing severe symptoms of myoclonus, side effects such as sleepiness, dizziness, fatigue, and unsteadiness may occur. In addition, the benefits of some drugs may decrease when taken for long periods of time.