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Myoclonus is brief, involuntary twitching of a [[muscle]] or a group of muscles. It describes a [[medical sign]] (as opposed to [[symptom]]) and, generally, is not a diagnosis of a disease. The myoclonic twitches or jerks 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 [[sleep|asleep]] ([[hypnic jerk]]), but myoclonic jerks are also a sign of a number of [[neurological disorder]]s. [[Hiccup]]s are also a kind of myoclonic jerk specifically affecting the [[diaphragm (anatomy)|diaphragm]]. | Myoclonus is brief, involuntary twitching of a [[muscle]] or a group of muscles. It describes a [[medical sign]] (as opposed to [[symptom]]) and, generally, is not a diagnosis of a disease. The myoclonic twitches or jerks 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 [[sleep|asleep]] ([[hypnic jerk]]), but myoclonic jerks are also a sign of a number of [[neurological disorder]]s. [[Hiccup]]s are also a kind of myoclonic jerk specifically affecting the [[diaphragm (anatomy)|diaphragm]]. | ||
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]] and some forms of [[epilepsy]]. | 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]] and some forms of [[epilepsy]]. | ||
In almost all instances in which myoclonus is caused by CNS 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. | In almost all instances in which myoclonus is caused by CNS 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. | ||
Revision as of 13:07, 6 May 2013
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2] Associate Editor(s)-in-Chief: Saumya Easaw, M.B.B.S.[3]
Overview
Myoclonus is brief, involuntary twitching of a muscle or a group of muscles. It describes a medical sign (as opposed to symptom) and, generally, is not a diagnosis of a disease. The myoclonic twitches or jerks 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), but myoclonic jerks are also a sign of a number of neurological disorders. Hiccups are also a kind of myoclonic jerk specifically affecting the diaphragm.
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 and some forms of epilepsy.
In almost all instances in which myoclonus is caused by CNS 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 magnumeffectively excludes spinal myoclonus, but further localisation relies on further investigation with electromyography (EMG) and electroencephalography (EEG).
Causes
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. Benign myoclonic movements are commonly seen during the induction of general anesthesia with intravenous medications such as etomidate and propofol. These are postulated to result from decreased inhibitory signaling from cranial neurons. Prolonged oxygen deprivation to the brain, called 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 or Lupus. Myoclonic jerks commonly occur in persons with epilepsy, a disorder in which the electrical activity in the brain becomes disordered leading to seizures.