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Myoclonic seizures or twitches are brief contractions, or relaxations, of a muscle or muscle group, resulting in a sudden, jumpy movement. Positive myoclonus is characterized by muscular contraction, and negative myoclonus by sudden muscular relaxation. They may be the symptom of disease, especially if recurring, but they may also be nothing to worry about. Many neurological disorders, including epilepsy, are capable of causing such seizures.
Most people have experienced these seizures of some form. Hiccups are a myoclonic seizure of the diaphragm muscle, for example. People also commonly experience one called a "hypnic jerk" shortly before falling asleep, and such instances are no cause for alarm.
Myoclonic seizures are a common symptom of a variety of neurological disorders, including myoclonic epilepsy, Lennox-Gastaut syndrome (LGS), Alzheimer's disease, Creutzfeldt-Jakob disease (CJD), lupus, multiple sclerosis, Parkinson's disease, and subacute sclerosing panencephalitis. In addition, they can be the result of sleep disorders, infection, drug poisoning or side effects, or injury to the head or spinal cord. In rare cases, injury to the peripheral nervous system can also cause them to develop. Brain tumors, stroke, and kidney or liver failure can also produce such seizures. Hypoxia, the prolonged deprivation of oxygen to the brain, is another possible trigger.
There are different types of myoclonic seizures, and some are more severe than others. Action myoclonus, sometimes considered the most severe form, is caused by brain damage, and is characterized by muscular twitching accompanying the intent or attempt to move voluntarily. Stimulus-sensitive myoclonus results in a seizure triggered by noise, light, or sound. Other types have no apparent trigger and can even happen during sleep. Many types of myoclonus, such as palatal myoclonus, which affects the soft palate and facial muscles, are limited to a certain area of the body.
These seizures are not life-threatening, but they can be debilitating to some degree and may be a sign of a more serious condition. They are usually treated with medication, such as the benzodiazepine clonazepam, although these drugs can lose their effectiveness with prolonged use and have side effects, including drowsiness and loss of coordination. Medications for epilepsy, such as barbiturates and anti-epileptics like primidone, can also be effective, and they work by slowing down the central nervous system. Sometimes, certain drug combinations are most useful, since such seizures can have complex causes.