Task-specific dystonias: historical review--a new look at the classics.

Although task-specific dystonias (TSD) have been described for almost two centuries, few entities have been characterised so variously as TSD. Over time TSD have been described as pure motor phenomena, "neurasthenic" symptoms, occupational hazards akin to repetitive strain, hysterical symptoms and finally… back to pure motor phenomena. A review of the classic literature can shed light on this subject and show that the same disease can be classified of different ways according to the dominant contemporary concepts over time. In any case, classic authors already defined TSD as motor phenomena of central origin.