Dyskinetic movement disorder among adults with mental retardation: phenomenology and co-occurrence with stereotypy.

We screened for the occurrence of dyskinetic and stereotypic movement disorders using item-independent screening protocols to determine whether these forms of movement disorder can be distinguished among adults with mental retardation. Stereotypies and dyskinesias were reliably distinguished in terms of topography. Tardive dyskinesia occurred in 18.2% of a cohort of individuals receiving chronic neuroleptic treatment. Stereotypic movement disorder was associated with increased dyskinesia scores and increased prevalence of tardive dyskinesia. Increased dyskinesia scores were also found for subjects exhibiting stereotypy who had been free of neuroleptic treatment for 3 years. Results indicate that dyskinesia and stereotypy are discriminable movement disorders and provide preliminary support for the hypothesis that they may be related by common mechanisms.