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Dyskinesia
Introduction
Dyskinesia or myoclonus refers to a quick, involuntary muscle jerk. For example, hiccups are a form of myoclonus. So are the sudden jerks, or "sleep starts," you may experience just before falling asleep. These forms of myoclonus occur in healthy people and rarely present a problem.
But in some cases, more severe forms of myoclonus can be triggered by an underlying problem, such as a head or spinal cord injury, a stroke, a nervous system or metabolic disorder, lack of oxygen to your brain, an infection, ingestion of a toxin, a reaction to a medication or other medical problems.
If the underlying problem that's causing myoclonus- a medication, for example - can be eliminated, the myoclonus usually resolves, too. But some disorders that cause myoclonus, such as epilepsy or Alzheimer's disease, aren't reversible and treatment of associated myoclonus may not eliminate it completely.
In a few cases, the cause of myoclonus may not be found. If the cause of myoclonus is chronic or unexplained, then the goal becomes to ease the effects of myoclonus on your quality of life.
Signs and symptoms
The way myoclonus presents itself can range from mild to severe. The frequency and intensity of myoclonus may vary from simple, temporary twitches to severe, persistent jerks that distort movement and impair your ability to walk, talk and eat.
Myoclonus may affect one or more areas of your body:
- Focal myoclonus affects only one part of your body, such as your arm or spine. Focal seizures are the most common cause.
- Segmental myoclonus affects neighboring parts of your body. An example is palatal myoclonus, which affects the roof of your mouth near your throat (soft palate) and sometimes other nearby muscles, such as those in your face, tongue, throat or diaphragm.
- Multifocal myoclonus affects two or more areas of your body that aren't next to each other. This is commonly seen in metabolic disorders and cognitive problems.
- Generalized myoclonus affects one or more major muscle groups simultaneously. A hyperactive startle reaction is an example.
Some forms of myoclonus are spontaneous, but others may be triggered by external stimuli, such as light, sound, weakness or fatigue. The most disabling form of myoclonus (action myoclonus) is triggered by the initiation of voluntary movement. For example, you may begin to take a step or reach for an item, but this action stimulates jerks that disrupt your movement.
Other neurological conditions may mimic the muscle contractions of myoclonus. But these are more accurately referred to as:
- Tics. These repetitive movements are usually preceded by an urge to perform the movement, and you may be able to temporarily suppress the movement.
- Chorea. These are involuntary, complex, "dance-like" body movements.
- Dystonia. This refers to prolonged, twisting, involuntary movements.
- Tremor. This is usually a rapid, rhythmic movement similar in appearance to shaking.
- Periodic leg movements of sleep. These are characterized by jerking leg movements during sleep and are often associated with restless legs syndrome.
Causes
Understanding myoclonus can be confusing because myoclonus has many possible causes, may affect any part of the body, and may have different patterns and rhythms, even in the same person.
The underlying mechanism of myoclonus appears to be, in most cases, a malfunction in your central nervous system. This may occur in a brain area such as your cortex - the outer layer of your brain that's heavily involved in information processing, including skilled and voluntary movement - or in your brainstem, an area located at the base of your brain that helps control involuntary muscle contractions. Researchers believe that an imbalance in brain chemicals (neurotransmitters) may lead to miscommunication between nerve cells, especially those involved in movement control.
Doctors often separate the types of myoclonus based on their causes. These include the following categories:
Physiological myoclonus
This type occurs in normal, healthy people. Examples include sleep starts - muscle jerks some people experience just before drifting off to sleep - and hiccups, involuntary contractions of your diaphragm. Some infants experience muscle twitching after a feeding or during sleep, but this is benign and doesn't usually require treatment.
Essential myoclonus
Essential myoclonus occurs on its own, without being related to any underlying illness. The muscle jerks are the most prominent or the only finding during evaluation. Essential myoclonus is fairly stable, meaning it doesn't usually get worse. The cause may be unexplained (idiopathic) or, in some cases, hereditary.
Idiopathic essential myoclonus may vary substantially in how it affects your body and in what triggers it. Hereditary essential myoclonus usually affects your upper body and is aggravated by voluntary movement, but it's generally mild. It tends to develop before age 20.
Epileptic myoclonus
This type of myoclonus occurs as part of a chronic seizure disorder (epilepsy). Myoclonic jerks may be one component of a seizure or the only component. In addition, a myoclonic seizure may be one of multiple seizure types occurring within a particular kind of epilepsy.
A specific type of epileptic myoclonus, called progressive myoclonus epilepsy, includes a rare group of diseases characterized by myoclonus, epileptic seizures and progressive deterioration of nerve cells (neurodegeneration). These disorders tend to get worse over time.
Symptomatic myoclonus
Also referred to as secondary myoclonus, this is by far the most common form of myoclonus. It occurs as a result of an underlying medical problem. Examples of problems that may cause myoclonic jerking are:
- Diseases of the brain or nervous system, such as Creutzfeldt-Jakob disease, Alzheimer's, dementia with Lewy bodies, Parkinson's disease, Huntington's disease, Wilson's disease and multiple sclerosis, among others
- Infections, such as HIV, malaria, syphilis, and various bacterial infections
- Metabolic disorders, such as hyperthyroidism, liver failure, kidney failure, hypoglycemia and vitamin E deficiency
- Chemical or drug reaction, such as from a toxic substance or as a side effect of a medication
- Damage to the brain or nervous system from a stroke, trauma, tumor or infection
- Disorders that affect your ability to digest nutrients (malabsorption disorders), such as celiac disease or Whipple's disease
Palatal myoclonus is another form of myoclonus that may occur on its own (essential palatal myoclonus) or secondary to brain nerve cell damage (palatal symptomatic myoclonus). Palatal myoclonus is characterized by rhythmic contractions of the muscles in the roof of your mouth. These contractions may cause a clicking noise in your ear. They may also be accompanied by contractions in your face, tongue, throat or diaphragm muscles.
Treatment
Treatment of myoclonus is most effective when a reversible underlying cause can be found, such as a medication or toxin that can be discontinued or "flushed out" of your body, a metabolic abnormality that can be corrected or a spinal lesion that can be removed. In such cases, associated involuntary muscle contractions may disappear quickly.
Treating other forms of myoclonus can be more challenging, but options are available.
Medications
There are no drugs specifically designed to treat myoclonus, but doctors have borrowed from other disease treatment arsenals to relieve myoclonic signs and symptoms. Which drugs might help usually depends on the form of myoclonus and where in the nervous system it originates. A drug that may help one form of myoclonus may not help another.
You may need to try different drugs, sometimes individually but often in combination, before experiencing the most effective results. Some of the drugs have side effects that may limit their use and some require that you taper off slowly to avoid withdrawal effects, should you need to discontinue it.
Medications that doctors commonly prescribe for myoclonus include:
- Clonazepam (Klonopin), a type of tranquilizer. Drowsiness is the most common side effect.
- Divalproex sodium (Depakote), an anticonvulsant. An effective medication, divalproex sodium rarely can cause liver failure or inflammation of the pancreas (pancreatitis). Other side effects include digestive upset, hair loss and tremor.
- Primidone (Mysoline), an anticonvulsant. Its main side effect is dizziness, but it also can cause irritability, worsen behavioral problems and affect memory.
- Levetiracetam, a newer anticonvulsant. It's often used as an add-on therapy but may be used alone. It has few side effects - dizziness, drowsiness, weakness - and is generally well tolerated.
- Other anticonvulsants, such as lamotrigine, ethosuximide and zonisamide. These may be combined with divalproex sodium to treat epileptic myoclonus.
- Medications to suppress the immune system (immunosuppressants). These may be used to treat opsoclonus-myoclonus in children. They may include adrenocorticotropic hormone (ACTH), azathioprine (Imuran), corticosteroids or immunoglobulin therapy (IVIg).
Surgery may be an option to remove a lesion on the spine that's causing myoclonus. Occasionally, palatal myoclonus is treated with surgical techniques to alleviate the clicking sound in the ear. In opsoclonus-myoclonus, doctors may use surgery to remove abnormal tissue growth.
Other therapies
Botulinum toxin type A (Botox) injections may be helpful in treating various forms of myoclonus, particularly focal myoclonus that affects a single area, and spinal myoclonus. Botulinum toxins help to ease symptoms by blocking the release of a chemical messenger that triggers muscle contractions.
Information obtained from National Institute of Health