dystonia

n. impairment of muscle tone

Dystonia is a neurological movement disorder in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures. The disorder may be inherited or caused by other factors such as birth-related or other physical trauma, infection or reaction to drugs.
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Dystonia /dys·to·nia/ dyskinetic movements due to disordered tonicity of muscle.dyston´ic dystonia musculo´rum defor´mans a hereditary disorder [more]Dystonia - Community and Resources

Involuntary movements and prolonged muscle contraction, resulting in twisting body motions, tremor, and abnormal posture. These movements may involve the entire body, or only an isolated area. Symptoms may even be "task specific," such as writer’s cramp. Dystonia can be inherited, occur sporadically without any genetic pattern, or be associated with medications or diseases (for example, a specific form of lung cancer). The gene responsible for at least one form of dystonia has recently been identified. Some types of dystonia respond to dopamine, or can be controlled with sedative-type medications, or surgery.

DISTONIA