Definition:
Myoclonus refers to a sudden, involuntary jerking of a muscle or group of muscles. In its simplest form, myoclonus consists of 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 occur in normal, healthy persons and cause no difficulties. When more widespread, myoclonus may involve persistent, shock-like contractions in a group of muscles. Myoclonic jerking may develop in people 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 and leads to seizures. 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. It can occur by itself, but most often it is one of several symptoms associated with a wide variety of nervous system disorders.
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Myoclonic jerks may occur alone or in sequence, in a pattern or without pattern. They may occur infrequently or many times each minute. Most often, myoclonus is one of several signs in a wide variety of nervous system disorders such as multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, subacute sclerosing panencephalitis and Creutzfeldt-Jakob disease (CJD), serotonin toxicity, and some forms of epilepsy. Some researchers indicate that jerks persistently may even cause early tremors.
In almost all instances in which myoclonus is caused by central nervous system disease it is preceded by other symptoms; for instance, in CJD it is generally a late-stage clinical feature that appears after the patient has already started to exhibit gross neurological deficits.
Anatomically, myoclonus may originate from lesions of the cortex, subcortex or spinal cord. The presence of myoclonus above the foramen magnum effectively excludes spinal myoclonus, but further localisation relies on further investigation with electromyography (EMG) and electroencephalography (EEG).
Types:
In juvenile myoclonic epilepsy, seizures usually involve the neck, shoulders, and upper arms. These seizures typically occur shortly after waking up. They normally begin between puberty and early adulthood. They can usually be controlled with medication, but it must be taken for life.
In rare cases, myoclonic seizures can be symptomatic of Lennox-Gastaut syndrome, beginning in early childhood and usually involving the face, neck, shoulders, and upper arms. In these cases, the seizures tend to be strong and difficult to control.
Progressive myoclonic epilepsy includes both myoclonic and tonic-clonic seizures. Treatment is not normally successful for any extended period of time.
Classifying the many different forms of myoclonus is difficult because the causes, effects, and responses to therapy vary widely. Listed below are the types most commonly described:
*Action myoclonus is characterized by muscular jerking triggered or intensified by voluntary movement or even the intention to move. It may be made worse by attempts at precise, coordinated movements. 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.
*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, occurring as often as 150 times a minute, 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 diseases characterized by myoclonus, epileptic seizures, and other serious symptoms such as trouble walking or speaking. These rare disorders often get worse over time and sometimes are fatal. Studies have identified at least three forms of PME. Lafora disease is inherited as an autosomal recessive disorder, meaning that the disease occurs only when a child inherits two copies of a defective gene, one from each parent. Lafora disease is characterized by myoclonus, epileptic seizures, and dementia (progressive loss of memory and other intellectual functions). A second group of PME diseases belonging to the class of cerebral storage diseases usually involves myoclonus, visual problems, dementia, and dystonia (sustained muscle contractions that cause twisting movements or abnormal postures). Another group of PME disorders in the class of system degenerations often is accompanied by action myoclonus, seizures, and problems with balance and walking. Many of these PME diseases begin in childhood or adolescence.
*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.
*Spinal myoclonus is myoclonus originating in the spinal cord, including segmental and propriospinal myoclonus. The latter is usually due to a thoracic generator producing truncal flexion jerk. It is often stimulus-induced with a delay due to the slow conducting propriospinal nerve fibers.
*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.
Symptoms:
Myoclonic seizures can be described as “jumps.” They are caused by rapid contraction and relaxation of the muscles. People without epilepsy can suffer small but similar jerks in the form of hiccups or brief twitches. These are perfectly normal.
In someone with epilepsy, myoclonic seizures cause abnormal movements on both sides of the body at the same time. In reflex epilepsies, myoclonic seizures can be brought on by flashing lights or other environmental triggers (see photosensitive epilepsy).
Familiar examples of normal myoclonus include hiccups and hypnic jerks that some people experience while drifting off to sleep. Severe cases of pathologic myoclonus can distort movement and severely limit a person’s ability to sleep, eat, talk, and walk. Myoclonic jerks commonly occur in individuals with epilepsy. The most common types of myoclonus include action, cortical reflex, essential, palatal, progressive myoclonus epilepsy, reticular reflex, sleep, and stimulus-sensitive.
People with myoclonus often describe the symptoms as “jerks,” shakes” or “spasms” that are:
*Sudden
*Brief
*Involuntary
*Shock-like
*Variable in intensity and frequency
*Localized to one part of the body or all over the body
*Sometimes severe enough to interfere with eating, talking or walking
Causes:
Myoclonus may be caused by a variety of underlying problems. Doctors often separate the types of myoclonus based on their causes, which helps determine treatment. Types of myoclonus include the following categories.
Physiological myoclonus
This is the type that occurs in normal, healthy people and rarely needs treatment. Examples include:
*Hiccups
*Sleep starts
*Infant muscle twitching during sleep or after a feeding
Essential myoclonus
Essential myoclonus occurs on its own, typically without other symptoms and without being related to any underlying illness. The cause of essential myoclonus is often unexplained (idiopathic) or, in some cases, hereditary.
Epileptic myoclonus
This type of myoclonus occurs as part of an epileptic disorder. Muscle jerks may be the only symptom or one of many.
Symptomatic (secondary) myoclonus
This is a common form of myoclonus. Muscle jerks occur as a result of an underlying medical problem, such as:
*Head or spinal cord injury or infection
*Stroke
*Brain tumor
*Kidney or liver failure
*Chemical or drug poisoning
*Prolonged oxygen deprivation
*Medication reaction
*Huntington’s disease
*Alzheimer’s disease
*Parkinson’s disease
*Metabolic problems
Treatment:
Discontinuation of drugs suspected of causing myoclonus and treatment of metabolic derangements may resolve some cases of myoclonus. When pharmacological treatment is indicated anticonvulsants are the main line of treatment. Paradoxical reactions to treatment are notable. Drugs which most people respond to may in other individuals worsen their symptoms. Sometimes this leads to the mistake of increasing the dose, rather than decreasing or stopping the drug. Treatment of myoclonus focuses on medications that may help reduce symptoms. Drugs used include sodium valproate, clonazepam and some other anticonvulsants such as piracetam and levetiracetam. Dosages of clonazepam usually are increased gradually until the patient improves or side effects become harmful. Drowsiness and loss of coordination are common side effects. The beneficial effects of clonazepam may diminish over time if the patient develops a tolerance to the drug.
Many of the drugs used for myoclonus, such as barbiturates, phenytoin and primidone, are also used to treat epilepsy. Barbiturates slow down the central nervous system and cause tranquilizing or antiseizure effects. Phenytoin and primidone are effective antiepileptics drugs, although phenytoin can cause liver failure or have other harmful long-term effects in patients with PME. Sodium valproate is an alternative therapy for myoclonus and can be used either alone or in combination with clonazepam. Although clonazepam and/or sodium valproate are effective in the majority of patients with myoclonus, some people have adverse reactions to these drugs.
Some studies have shown that doses of 5-hydroxytryptophan (5-HTP) leads to improvement in patients with some types of action myoclonus and PME. These differences in the effect of 5-HTP on patients with myoclonus have not yet been explained, but they may offer important clues to underlying abnormalities in serotonin receptors.
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.
Prognosis:
Although myoclonus is not a life-threatening condition, it may result in serious, debilitating impairments. Action myoclonus, with its positive and negative myoclonus components, is generally considered the most serious. It varies from person to person as to whether it is life-long.
Research:
The National Institute of Neurological Disorders and Stroke (NINDS) conducts research relating to myoclonus in its laboratories at the National Institutes of Health (NIH) and also supports additional research through grants to major medical institutions across the country. Scientists are seeking to understand the underlying biochemical basis of involuntary movements and to find the most effective treatment for myoclonus and other movement disorders. Researchers may be able to develop drug treatments that target specific biochemical changes involved in myoclonus. By combining several of these drugs, scientists hope to achieve greater control of myoclonic symptoms.
Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose
Resources:
http://www.ninds.nih.gov/disorders/myoclonus/myoclonus.htm
http://www.mayoclinic.com/health/myoclonus/DS00754
http://en.wikipedia.org/wiki/Myoclonus
http://insomnia.ygoy.com/2011/04/28/sleep-myoclonus/
http://www.buzzle.com/articles/palatal-myoclonus.html
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