The clinical expression of primary dystonia.

Dystonia (from the Greek, "altered muscle tone") refers to sustained and vigorous contractions forcing a body region into an abnormal position that is consistently present. Dystonic postures and movements can variably combine to produce a wide spectrum of clinical presentations. The movement can affect one, two or more body regions, as in focal, segmental or generalised dystonia. Dystonia arising in childhood tends to progress to a generalised form; adult-onset dystonia, instead, is often focal or segmental. Dystonic movements have specific features that can be recognised by clinical observation, such as speed, consistency, predictability, variability and relationship with voluntary movement. Sensory tricks and gestes antagonistes are manoeuvres that specifically alleviate dystonic movements and postures thereby providing diagnostic clues. The diagnosis of primary dystonia requires the observation of a consistent clinical picture.