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Friedreich in 1881 first described a condition characterised by frequent - 10 to 50 times a minute - myoclonic muscular contractions of onset during adult life. Whole muscles or groups of muscle are affected, contracting symmetrically although not necessarily simultaneously.
The contractions disappear during sleep, are inhibited by voluntary contraction, and are increased by tension and anxiety.
On examination, sensation is unimpaired and reflexes may be brisk.
There is an hereditary element to the condition.