Stereotypies: a critical appraisal and suggestion of a clinically useful definition.

The foundations of the clinical classification of movement disorders rest on the precise definition of the words used to describe the disorders. Here we argue that the current use of the term stereotypy falls well short of the precision needed for either clinical or academic use, and fails both to provide a clinically useful diagnostic category and to define a set of conditions that are linked pathophysiologically. The difficulty in defining this concept is not a new one as our review of the history of the term demonstrates. We synthesise this historical background, explore why clinicians have felt it necessary to use the category of stereotypy for certain movements rather than the related category of tics, discuss the multiple uses of the term in current research and clinical practice and on this basis suggest a new definition and classification.