[Dystonia.].

Dystonia is defined as a syndrome of sustained involuntary muscle contractions, frequently causing twisting, repetitive movements and abnormal postures. Categorisation of the dystonia syndromes is variable and depends on etiology, age at onset, distribution of symptoms or genetic causes, reflecting the variability of the clinical spectrum of these diseases and the many underlying causes. The prevalence of the dystonias is largely unknown, as few epidemiological studies have been carried out and many of these have been service based rather than community based. This article reviews the phenomenology, pathophysiology, various etiologies and treatment of the dystonias.