Myoclonus - AbsoluteAstronomy.com

Myoclonus is brief, involuntary twitching of a muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

or a group of muscles. It describes a medical sign

Medical sign

A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....

and, generally, is not a diagnosis of a disease. Brief twitches are perfectly normal. The myoclonic twitches are usually caused by sudden muscle contractions; they also can result from brief lapses of contraction. Contractions are called positive myoclonus; relaxations are called negative myoclonus. The most common time for people to encounter them is while falling asleep (hypnic jerk

Hypnic jerk

A hypnic jerk, hypnagogic jerk, sleep start, or night start, is an involuntary myoclonic twitch which occurs during hypnagogia, just as a person is beginning to fall asleep, often causing them to awaken suddenly. Physically, hypnic jerks resemble the "jump" experienced by a person when...

), but myoclonic jerks are also a sign of a number of neurological disorder

Neurological disorder

A neurological disorder is a disorder of the body's nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord, or in the nerves leading to or from them, can result in symptoms such as paralysis, muscle weakness, poor coordination, loss of sensation, seizures,...

s. Hiccup

Hiccup

A hiccup or hiccough is a myoclonus of the diaphragm that repeats several times per minute. In humans, the abrupt rush of air into the lungs causes the vocal cords to close, creating a "hic" sound....

s are also a kind of myoclonic jerk specifically affecting the diaphragm. Also when a spasm is caused by another person it is known as a "provoked spasm". Shuddering attacks with babies also fall in this category.

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

Multiple sclerosis

Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...

, Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

, Alzheimer's disease

Alzheimer's disease

Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

, subacute sclerosing panencephalitis

Subacute sclerosing panencephalitis

Subacute sclerosing panencephalitis is a rare chronic, progressive encephalitis that affects primarily children and young adults, caused by a persistent infection of immune resistant measles virus . No cure for SSPE exists, but the condition can be managed by medication if treatment is started at...

and Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease

Creutzfeldt–Jakob disease or CJD is a degenerative neurological disorder that is incurable and invariably fatal. CJD is at times called a human form of mad cow disease, given that bovine spongiform encephalopathy is believed to be the cause of variant Creutzfeldt–Jakob disease in humans.CJD...

(CJD), serotonin toxicity

Serotonin syndrome

Serotonin syndrome is a potentially life-threatening adverse drug reaction that may occur following therapeutic drug use, inadvertent interactions between drugs, overdose of particular drugs, or the recreational use of certain drugs...

, and some forms of epilepsy

Epilepsy

Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

. 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

Cerebral cortex

The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

, subcortex or spinal cord

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

. The presence of myoclonus above the foramen magnum effectively excludes spinal myoclonus, but further localisation relies on further investigation with electromyography

Electromyography

Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...

(EMG) and electroencephalography

Electroencephalography

Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...

(EEG).

Symptoms

Myoclonic seizure

Seizure

An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...

s can be described as "jumps." They are caused by rapid contraction and relaxation of the muscles. People without epilepsy

Epilepsy

can suffer small but similar jerks in the form of hiccups or brief twitches. These are perfectly normal.

In someone with epilepsy, myoclonic seizure

Seizure

s 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

Photosensitive epilepsy

Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regular moving patterns.-Symptoms:...

).

Familiar examples of normal myoclonus include hiccup

Hiccup

s and hypnic jerk

Hypnic jerk

s 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

Epilepsy

. The most common types of myoclonus include action, cortical reflex, essential, palatal, progressive myoclonus epilepsy, reticular reflex, sleep, and stimulus-sensitive.

Types

In juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy , also known as Janz syndrome, is a fairly common form of idiopathic generalized epilepsy, representing 5-10% of all epilepsies. This disorder typically first manifests itself between the ages of 12 and 18 with myoclonus occurring early in the morning. Most patients also...

, 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

Lennox-Gastaut syndrome

Lennox–Gastaut syndrome , also known as Lennox syndrome, is a difficult-to-treat form of childhood-onset epilepsy that most often appears between the second and sixth year of life, and is characterized by frequent seizures and different seizure types; it is often accompanied by developmental delay...

, 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 seizure

Tonic-clonic seizure

Tonic–clonic seizures are a type of generalized seizure that affects the entire brain...

s. 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
Soft palate
The soft palate is the soft tissue constituting the back of the roof of the mouth. The soft palate is distinguished from the hard palate at the front of the mouth in that it does not contain bone....

. 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
Lafora disease
Lafora disease, also called Lafora progressive myoclonic epilepsy or MELF , is a fatal autosomal recessive genetic disorder characterized by the presence of inclusion bodies, known as Lafora bodies, within neurons and the cells of the heart, liver, muscle, and skin.Most patients with this 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 disorder
Sleep disorder
A sleep disorder, or somnipathy, is a medical disorder of the sleep patterns of a person or animal. Some sleep disorders are serious enough to interfere with normal physical, mental and emotional functioning...

s, such as restless legs syndrome
Restless legs syndrome
Restless legs syndrome or Willis-Ekbom disease is a neurological disorder characterized by an irresistible urge to move one's body to stop uncomfortable or odd sensations. It most commonly affects the legs, but can affect the arms, torso, and even phantom limbs...

, and may require treatment by a doctor.

Cause

Rarely does myoclonus indicate anything other than arbitrary muscle contraction. Myoclonus may develop in response to infection, head or spinal cord injury

Spinal cord injury

A spinal cord injury refers to any injury to the spinal cord that is caused by trauma instead of disease. Depending on where the spinal cord and nerve roots are damaged, the symptoms can vary widely, from pain to paralysis to incontinence...

, stroke

Stroke

A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

, stress

Stress

- Mechanical :* Stress , the average amount of force exerted per unit area* Compressive stress, the stress applied to materials resulting in their compaction...

, brain tumor

Brain tumor

A brain tumor is an intracranial solid neoplasm, a tumor within the brain or the central spinal canal.Brain tumors include all tumors inside the cranium or in the central spinal canal...

s, kidney or liver failure

Liver failure

Acute liver failure is the appearance of severe complications rapidly after the first signs of liver disease , and indicates that the liver has sustained severe damage . The complications are hepatic encephalopathy and impaired protein synthesis...

, lipid storage disease, chemical or drug poison

Poison

In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....

ing, as a side effect of certain drugs (such as tramadol

Tramadol

Tramadol hydrochloride is a centrally acting synthetic opioid analgesic used in treating moderate pain. The drug has a wide range of applications, including treatment for restless legs syndrome and fibromyalgia...

and quinolones), or other disorders.

Benign myoclonic movements are commonly seen during the induction of general anesthesia with intravenous medications such as etomidate

Etomidate

Etomidate is a short acting intravenous anaesthetic agent used for the induction of general anaesthesia and for sedation for short procedures such as reduction of dislocated joints, tracheal intubation and cardioversion...

and propofol

Propofol

Propofol is a short-acting, intravenously administered hypnotic agent. Its uses include the induction and maintenance of general anesthesia, sedation for mechanically ventilated adults, and procedural sedation. Propofol is also commonly used in veterinary medicine...

. These are postulated to result from decreased inhibitory signaling from cranial neurons. Prolonged oxygen deprivation to the brain, hypoxia

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

, 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

Multiple sclerosis

, Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

, Alzheimer's disease

Alzheimer's disease

, Opsoclonus Myoclonus, Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease

, or lupus

Systemic lupus erythematosus

Systemic lupus erythematosus , often abbreviated to SLE or lupus, is a systemic autoimmune disease that can affect any part of the body. As occurs in other autoimmune diseases, the immune system attacks the body's cells and tissue, resulting in inflammation and tissue damage...

. Myoclonic jerks commonly occur in persons with epilepsy

Epilepsy

, a disorder in which the electrical activity in the brain becomes disordered leading to seizures. It is also found in MERRF (Myoclonic Epilepsy with Ragged Red Fibers), a rare mitochondrial encephalomyopathy.

Jerks of muscle groups, much of the body, or a series in rapid succession which results in the person jerking bolt upright from a more relaxed sitting position is sometimes seen in ambulatory patients being treated with high doses of morphine, hydromorphone and similar drugs, and is possibly a sign of high and/or rapidly increasing serum levels of these drugs. Myoclonic jerks also can be caused by some unrelated drugs such as anticholinergics. Opioids which have other neurotransmitter impacts such as tramadol, pethidine, &c. can also cause jerks, but unlike the above are not completely benign.

Pathophysiology

Although some cases of myoclonus are caused by an injury to the peripheral nerves, most myoclonus is caused by a disturbance of the central nervous system

Central nervous system

The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

. Studies suggest that several locations in the brain are involved in myoclonus. One such location, for example, is in the brainstem close to structures that are responsible for the startle response, an automatic reaction to an unexpected stimulus involving rapid muscle contraction.

The specific mechanisms underlying myoclonus are not yet fully understood. Scientists believe that some types of stimulus-sensitive myoclonus may involve overexcitability of the parts of the brain that control movement. These parts are interconnected in a series of feedback loops called motor pathways. These pathways facilitate and modulate communication between the brain and muscles. Key elements of this communication are chemicals known as neurotransmitter

Neurotransmitter

Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

s, which carry messages from one nerve cell, or neuron, to another. Neurotransmitters are released by neurons and attach themselves to receptors on parts of neighboring cells. Some neurotransmitters may make the receiving cell more sensitive, while others tend to make the receiving cell less sensitive. Laboratory studies suggest that an imbalance between these chemicals may underlie myoclonus.

Some researchers speculate that abnormalities or deficiencies in the receptors for certain neurotransmitters may contribute to some forms of myoclonus. Receptors that appear to be related to myoclonus include those for two important inhibitory neurotransmitters: serotonin, which constricts blood vessels and brings on sleep, and gamma-aminobutyric acid

Gamma-aminobutyric acid

γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system...

(GABA), which helps the brain maintain muscle control. Other receptors with links to myoclonus include those for opiates, drugs that induce sleep, and for glycine, an inhibitory neurotransmitter that is important for the control of motor and sensory functions in the spinal cord. More research is needed to determine how these receptor abnormalities cause or contribute to myoclonus.

Treatment

In Asia, the mineral calcium, in the form of supplements or antacids, has been widely known to dispel the commonly experienced sleep myoclonus, or hypnic jerk

Hypnic jerk

, and also restless leg syndrome.

Concerning more serious afflictions, 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

Piracetam

Piracetam is a nootropic drug. Piracetam's chemical name is 2-oxo-1-pyrrolidine acetamide; it shares the same 2-oxo-pyrrolidone base structure with 2-oxo-pyrrolidine carboxylic acid . Piracetam is a cyclic derivative of GABA. It is one of the group of racetams...

, and primidone. Hormonal therapy also may improve responses to antimyoclonic drugs in some people.

Some studies have shown that doses of 5-hydroxytryptophan

5-Hydroxytryptophan

5-Hydroxytryptophan , also known as oxitriptan , is a naturally occurring amino acid and chemical precursor as well as metabolic intermediate in the biosynthesis of the neurotransmitters serotonin and melatonin from tryptophan....

(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.

Many of the drugs used for myoclonus, such as barbiturate

Barbiturate

Barbiturates are drugs that act as central nervous system depressants, and can therefore produce a wide spectrum of effects, from mild sedation to total anesthesia. They are also effective as anxiolytics, as hypnotics, and as anticonvulsants...

s, phenytoin

Phenytoin

Phenytoin sodium is a commonly used antiepileptic. Phenytoin acts to suppress the abnormal brain activity seen in seizure by reducing electrical conductance among brain cells by stabilizing the inactive state of voltage-gated sodium channels...

and primidone

Primidone

Primidone is an anticonvulsant of the pyrimidinedione class, the active metabolites of which, phenobarbital and phenylethylmalonamide , are also anticonvulsants...

, are also used to treat epilepsy

Epilepsy

. Barbiturates slow down the central nervous system

Central nervous system

and cause tranquilizing or antiseizure effects. Phenytoin and primidone are effective antiepileptics drugs

Anticonvulsant

The anticonvulsants are a diverse group of pharmaceuticals used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of bipolar disorder, since many seem to act as mood stabilizers, and in the treatment of neuropathic pain. The goal of an...

, although phenytoin can cause liver failure

Liver failure

or have other harmful long-term effects in patients with PME. Sodium valproate

Sodium valproate

Sodium valproate or valproate sodium is the sodium salt of valproic acid and is an anticonvulsant used in the treatment of epilepsy, anorexia nervosa, panic attack, anxiety disorder, posttraumatic stress disorder, migraine and bipolar disorder, as well as other psychiatric conditions requiring...

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.

When patients are taking multiple medications, the 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

Sodium valproate

, clonazepam

Clonazepam

Clonazepamis a benzodiazepine drug having anxiolytic, anticonvulsant, muscle relaxant, and hypnotic properties. It is marketed by Roche under the trade name Klonopin in the United States and Rivotril in Australia, Brazil, Canada and Europe...

, the anticonvulsant

Anticonvulsant

levetiracetam, and piracetam

Piracetam

. 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.

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.

External links

The first version of this article was adapted from the public domain NINDS Myoclonus Information Page. Please amend and adapt as needed.
What is a myoclonic jerk? at faqs.org
Falling-Asleep Twitches at discovery.com
"Why do we twitch while falling asleep?" (The Straight Dope)
Epilepsy Foundation
Myoclonus Fact Sheet, National Institute of Neurological Disorders and Stroke (viewed 5 Apr 2005)

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Symptoms

Types

Cause

Pathophysiology

Treatment

Prognosis

See also

External links