Duration of Treatment Relationships for Involuntary Movements (Tardive Dyskinesia): Concordance Between Cross-sectional, Clinical, and Longitudinal Animal Studies?

To the Editor.—  The extensive literature on tardive dyskinesia fails to reveal any general relationship between length of exposure to neuroleptics and the likelihood of involuntary movements emerging. This has prompted the proposal that any period of maximum risk for the development of tardive dyskinesia might occur over much briefer exposure than has been generally assumed.¹ The recent interesting report from Toenniessen and colleagues² indicates the first systematic data that might support this proposal. However, the problems created by the cross-sectional nature of such studies, in diagnostically heterogeneous populations, are well known and are recognized by the authors. Prospective studies are to be preferred to answer such important questions, but such studies present profound logistic difficulties.We have been working with an animal model of late-onset orofacial dyskinesia seen in rats receiving prolonged neuroleptic administration.³ These studies have the advantage of being prospective in nature and using