Myoclonus is a muscle twitch or sudden, involuntary jerking of a muscle or group of muscles. Myoclonic twitches or jerks usually are caused by sudden muscle contractions, called positive myoclonus, or by muscle relaxation, called negative myoclonus.
Myoclonic jerks may occur alone or in sequence, in a pattern or without pattern. They may occur infrequently or many times each minute. Myoclonus sometimes occurs in response to an external event or when a person attempts to make a movement. The twitching cannot be controlled by the person experiencing it.
In some cases, myoclonus begins in one region of the body and spreads to muscles in other areas. More severe cases of myoclonus can affect movement and limit a person's ability to move or walk. These types of myoclonus may indicate an underlying disorder in the brain or nerves.
Myoclonic jerking often is a symptom of a nervous disorder, such as 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, leading to seizures.
In addition to being caused by epileptic seizures, myoclonus also can be triggered by:
- Head or spinal cord injury
- Brain tumors
- Kidney or liver failure
- Lipid storage disease
- Sleep disturbances
- Chemical or drug poisoning
- Prolonged oxygen deprivation to the brain
Source: National Institute of Neurological Disorders and Stroke