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More on Myoclonus
More on Myoclonus
More on Myoclonus
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More on Myoclonus
Myoclonus refers to a symptom — sudden, involuntary jerking of a muscle or group of muscles — and generally is not a diagnosis of a disease. Myoclonic jerks may occur alone or in sequence, in a pattern or without pattern. They may occur infrequently or many times each minute. Myoclonus sometimes occurs in response to an external event or when a person attempts to make a movement. The twitching cannot be controlled by the person experiencing it.
Actually, most normal, healthy people have experienced myoclonus in its simplest form, a muscle twitch followed by relaxation. A hiccup is an example of this type of myoclonus. Other familiar examples of myoclonus are the jerks or "sleep starts" that some people experience while drifting off to sleep. These simple forms of myoclonus cause no difficulties.
However, when more widespread, myoclonus may involve persistent, shock-like contractions in a group of muscles. In some cases, myoclonus begins in one region of the body and spreads to muscles in other areas. More severe cases of myoclonus can distort movement and severely limit a person's ability to eat, talk, or walk. These types of myoclonus may indicate an underlying disorder in the brain or nerves.
Myoclonus may develop in response to infection, head or spinal cord injury, stroke, brain tumors, kidney or liver failure, lipid storage disease, chemical or drug poisoning, or other disorders. Prolonged oxygen deprivation to the brain ("hypoxia") may result in posthypoxic myoclonus. Myoclonus can occur by itself, but most often it is one of several symptoms associated with a wide variety of nervous system disorders. For example, myoclonic jerking may develop in patients with multiple sclerosis, Parkinson's disease, Alzheimer's disease, or Creutzfeldt-Jakob disease. Myoclonic jerks commonly occur in persons with epilepsy, a disorder in which the electrical activity in the brain becomes disordered leading to seizures.
Types of myoclonus
Classifying the many different forms of myoclonus is difficult because the causes, effects, and responses to therapy vary widely. Listed below are the most common types:
- Action myoclonus is the most disabling form of myoclonus and can affect the arms, legs, face, and even the voice. This type of myoclonus often is caused by brain damage that results from a lack of oxygen and blood flow to the brain when breathing or heartbeat is temporarily stopped. Triggered or intensified by voluntary movement or even the intention to move, it may be made worse by attempts at precise, coordinated movements.
- Cortical reflex myoclonus is thought to be a type of epilepsy that originates in the cerebral cortex - the outer layer, or "gray matter," of the brain, responsible for much of the information processing that takes place in the brain. In this type of myoclonus, jerks usually involve only a few muscles in one part of the body, but jerks involving many muscles also may occur. Cortical reflex myoclonus can be intensified when patients attempt to move in a certain way or perceive a particular sensation.
- Essential myoclonus occurs in the absence of epilepsy or other apparent abnormalities in the brain or nerves. It can occur randomly in people with no family history, but it also can appear among members of the same family, indicating that it sometimes may be an inherited disorder. Essential myoclonus tends to be stable without increasing in severity over time. Some scientists speculate that some forms of essential myoclonus may be a type of epilepsy with no known cause.
- Palatal myoclonus is a regular, rhythmic contraction of
one or both sides of the rear of the roof of the mouth, called the soft palate. These contractions may be accompanied by myoclonus in other muscles, including those in the face, tongue, throat, and diaphragm. The contractions are very rapid and may persist during sleep. The condition usually appears in adults and can last indefinitely. People with palatal myoclonus usually regard it as a minor problem, although some occasionally complain of a "clicking" sound in the ear, a noise made as the muscles in the soft palate contract.
- Progressive myoclonus epilepsy (PME) is a group of rare diseases characterized by myoclonus, epileptic seizures, and other serious symptoms such as trouble walking or speaking. Many of these PME diseases begin in childhood or adolescence. These disorders often get worse over time and sometimes are fatal. Studies have identified at least three forms of PME.
- Lafora body disease occurs when a child inherits one copy of a defective gene from each parent. Lafora body disease is characterized by myoclonus, epileptic seizures, and dementia (progressive loss of memory and other intellectual functions).
- Cerebral storage diseases usually involve myoclonus, visual problems, dementia, and dystonia (sustained muscle contractions that cause twisting movements or abnormal postures).
- System degeneration often is accompanied by action myoclonus, seizures, and problems with balance and walking.
- Reticular reflex myoclonus is thought to be a type of generalized epilepsy that originates in the brainstem, the part of the brain that connects to the spinal cord and controls vital functions such as breathing and heartbeat. Myoclonic jerks usually affect the whole body, with muscles on both sides of the body affected simultaneously. In some people, myoclonic jerks occur in only a part of the body, such as the legs, with all the muscles in that part being involved in each jerk. Reticular reflex myoclonus can be triggered by either a voluntary movement or an external stimulus.
- Stimulus-sensitive myoclonus is triggered by a variety of external events, including noise, movement, and light. Surprise may increase the sensitivity of the patient.
- Sleep myoclonus occurs during the initial phases of sleep, especially at the moment of dropping off to sleep. Some forms appear to be stimulus-sensitive. Some persons with sleep myoclonus are rarely troubled by, or need treatment for, the condition. However, myoclonus may be a symptom in more complex and disturbing sleep disorders, such as restless legs syndrome, and may require treatment by a doctor.
Treatment of myoclonus focuses on medications that may help reduce twitching. The drug of choice, especially in action myoclonus, is clonazepam, a type of tranquilizer. Many of the drugs used for myoclonus, such as barbiturates, phenytoin, and primidone, are also used to treat epilepsy. The complex origins of myoclonus may require the use of multiple drugs for effective treatment. Although some drugs have a limited effect when used individually, they may have a greater effect when used with drugs that act on different pathways or mechanisms in the brain. By combining several of these drugs, scientists hope to achieve greater control of myoclonic symptoms. Some drugs currently being studied in different combinations include clonazepam, sodium valproate, piracetam, and primidone. Hormonal therapy also may improve responses to antimyoclonic drugs in some people.