Myoclonus
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Myoclonus | |
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A person with a myoclonus following a peripheral nerve block | |
Specialty | Neurology |
Myoclonus is a brief, involuntary, irregular (lacking rhythm)
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[
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
Types
The most common types of myoclonus include action, cortical reflex, essential, palatal, those seen in the
Epilepsy forms
- 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 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, or 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.
- Juvenile myoclonic epilepsy (JME) usually consists of jerking and muscle twitches of the upper extremities. This may include the arms, shoulders, elbows, and very rarely, the legs. JME is among the most common types of epilepsy and can affect one of every 14 people with the disease. These seizures typically occur shortly after waking up. Onset for JME can be seen around puberty for most patients. Administration of medications that also treat multiple seizure types is usually the most effective form of treatment.[1]
- Lennox-Gastaut syndrome(LGS), or childhood epileptic encephalopathy, is a rare epileptic disorder accounting for 1–4% of childhood epilepsies. The syndrome has much more severe symptoms ranging from multiple seizures daily, learning disabilities, and abnormal findings in electroencephalograms (EEG). Earlier age of seizure onset is correlated with a higher risk of cognitive impairment.
- Progressive myoclonus epilepsy (PME) is a group of diseases characterized by myoclonus, epileptic seizures, tonic-clonic seizures, and other serious symptoms such as trouble walking or speaking. These rare disorders often get worse over time and can be 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. Treatment is not normally successful for any extended period of time.
- 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.
Diaphragmatic flutter
A very rare form includes the
Only about 50 people in the world have been diagnosed with diaphragmatic flutter.[citation needed]
Other forms
- 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. It is often associated with motor neurons of cranial nerves and anterior horns, and muscle fibers.[3]
- 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; some complain of an occasional "clicking" sound, a noise made as the soft palate muscles contract.
- Middle ear myoclonus occurs in the muscles of the middle ear. These muscles may include the tensor tympani and stapedius muscles. It can involve the muscles surrounding the Eustachian tube, which include the tensor veli palatini, levator veli palatini, and salpingopharyngeus. Those affected describe it as a thumping sound or sensation in the ear.
- 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.[4]
- 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, and include familiar examples of myoclonus such as the hypnic jerk. Some forms appear to be stimulus-sensitive. Some people with sleep myoclonus are rarely troubled by it, or need treatment. If it is a symptom of more complex and disturbing sleep disorders, such as restless legs syndrome, it may require medical treatment. Myoclonus can be associated with patients with Tourette syndrome.
Signs and symptoms
Myoclonic seizure can be described as "jumps" or "jolts" experienced in a single
A myoclonic seizure (myo "muscle", clonic "jerk") is a sudden involuntary contraction of muscle groups. The muscle jerks consist of symmetric, mostly generalized jerks, localized in the arms and in the shoulders and also simultaneously with a head nod; both the arms may fling out together and simultaneously a head nod may occur. Symptoms have some variability amongst subjects. Sometimes the entire body may jerk, just like a startle response. As is the case with all generalised seizures, the patient is not conscious during the event but the seizure is so brief that the person appears to remain fully conscious.
In
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.
Cause
Myoclonus in healthy individuals may indicate nothing other than arbitrary muscle contraction. Myoclonus may also develop in response to infection,
), or other disorders.Benign myoclonic movements are commonly seen during the induction of general anesthesia with intravenous medications such as
Myoclonus can occur by itself, but most often as one of several symptoms associated with a variety of nervous system disorders, including
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
Pathophysiology
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Most myoclonus is caused by a disturbance of the central nervous system. Some are from peripheral nervous system injury. Studies suggest several locations in the brain are involved in myoclonus. One 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 neurotransmitters, 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:
Treatment
Concerning more serious conditions, the complex origins of myoclonus may be treated with multiple drugs, which have a limited effect individually, but greater when combined with others that act on different brain pathways or mechanisms. Treatment is most effective when the underlying cause is known, and can be treated as such. Some drugs being studied in different combinations include
Some studies have shown that doses of
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. Some people have adverse reactions to clonazepam and/or sodium valproate.
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. 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.
In forms of myoclonus where only a single area is affected, and even in a few other various forms,
Surgery is also a viable option for treatment if the symptoms are caused by a tumor or lesion in the brain or spinal cord. Surgery may also correct symptoms in those where myoclonus affects parts of the face or ear. While DBS is still being studied for use with myoclonus,
Prognosis
The effects of myoclonus in an individual can vary depending on the form and the overall health of the individual. In severe cases, particularly those indicating an underlying disorder in the brain or nerves, movement can be extremely distorted and limit ability to normally function, such as in eating, talking, and walking. In these cases, treatment that is usually effective, such as clonazepam and sodium valproate, may instead cause adverse reaction to the drug, including increased tolerance and a greater need for increase in dosage. However, the prognosis for more simple forms of myoclonus in otherwise healthy individuals may be neutral, as the disease may cause few to no difficulties. Other times the disease starts simply, in one region of the body, and then spreads.[11]
Research
Research on myoclonus is supported through the National Institute of Neurological Disorders and Stroke (NINDS). The primary focus of research is on the role of neurotransmitters and receptors involved in the disease. Identifying whether or not abnormalities in these pathways cause myoclonus may help in efforts to develop drug treatments and diagnostic tests. Determining the extent that genetics play in these abnormalities may lead to potential treatments for their reversal, potentially correcting the loss of inhibition while enhancing mechanisms in the body that would compensate for their effects.[12]
Etymology
The word myoclonus uses
See also
- Antidepressant discontinuation syndrome – Flu-like symptoms that happen after discontinuing antidepressant medication
- Benign fasciculation syndrome – Involuntary muscle twitching in the voluntary muscles
- Clonus – Set of involuntary and rhythmic muscular contractions and relaxations
- Exploding head syndrome – Syndrome where people perceive loud imagined noises when falling asleep or waking up
- Fahr's syndrome– Indiana genetic disorder involving calcification of the basal ganglia
- Fasciculation – Spontaneous, involuntary muscle twitch
- Hypnagogia – State of consciousness leading into sleep
- Hypnic jerk – Involuntary twitches
- Periodic limb movement disorder – sleep disorder that involves involuntary limb movement during sleep
- Restless legs syndrome – Long-term disorder that causes a strong urge to move one's legs
References
- ^ Lava, Neil. "What is Juvenile Myonclonic Epilepsy". WebMD Medical Reference. Atlanta, Georgia: WebMD. Treatment of Juvenile Myoclonic Epilepsy. Retrieved 30 April 2015.
- ^ a b c d Patterson, Victoria (9 November 2011). Belly Dancer's Syndrome: Causes, Clinical Presentations, and Treatment Options (PDF) (Senior Research Project). assisted by Powers, EJ. Chesterfield, Missouri: Logan University. Retrieved 1 September 2015.
- PMID 3080851.
- PMID 1998882.
- ^ "Myoclonic Seizures". DooseSyndrome.org. Doose Syndrome Epilepsy Alliance. Archived from the original on 8 October 2018. Retrieved 1 May 2015.
- ^ https://databankws.lareb.nl/Downloads/kwb_2002_3_trama.pdf [bare URL PDF]
- ^ Ramnarine, Mityanand "Anticholinergic Toxicity" emedicine.medscape.com, 09 August 2015
- ^ PMID 12891998.
- S2CID 207477900.
- ^ "Myoclonus Treatments and Drugs." Mayo Clinic.org. Mayo Clinic, n.d. Web. 01 May 2015. <http://www.mayoclinic.org/diseases-conditions/myoclonus/basics/treatment/con-20027364>
- ^ a b "NINDS Myoclonus Information Page." Ninds.nih.gov. National Institute of Neurological Disorders and Stroke, n.d. Web. 01 May 2015. <http://www.ninds.nih.gov/disorders/myoclonus/myoclonus.htm Archived 2016-12-06 at the Wayback Machine>.
- ^ "NINDS Myoclonus Information Page." Ninds.nih.gov. National Institute of Neurological Disorders and Stroke, n.d. [1] Archived 2016-12-06 at the Wayback Machine.
- ^ "Myoclonus". Merriam-Webster.com Dictionary.
- ^ "Myoclonus". Oxford Dictionaries UK English Dictionary. Oxford University Press.[dead link]
- Oxford Dictionaries, Oxford Dictionaries Online, Oxford University Press, archived from the originalon May 16, 2001.
External links
- The first version of this article was adapted from the public domain NINDS Myoclonus Information Page Archived 2008-12-03 at the Wayback Machine.
- "Why do we twitch while falling asleep?" (The Straight Dope)
- Myoclonus Fact Sheet Archived 2016-12-03 at the Wayback Machine, National Institute of Neurological Disorders and Stroke (viewed 5 Apr 2005)