Tardive dyskinesia and diabetes mellitus.

Two studies examine the prevalence of tardive dyskinesia (TD) in neuroleptic-treated diabetic patients. Study 1 compared 38 diabetic patients with 38 nondiabetic patients treated for psychotic disorders with low to moderate doses of neuroleptics (mean chlorpromazine equivalents = 300 mg/day) for an average of 18 years. Study 2 compared 24 diabetic and 27 nondiabetic patients treated for an average of 2.6 years with a mean 31 mg/day of metoclopramide for gastrointestinal disease. Patients were examined for TD using standardized scales by raters blind to all treatment and illness variables. In both studies, there were no differences between the diabetic and nondiabetic groups in age, sex, type of psychiatric illness, and dose and duration of neuroleptic treatment or severity of parkinsonism. In both studies, the diabetic patients had significantly greater prevalence and severity of TD. No measures of diabetes severity were associated with TD in either study. Possible pathophysiologic mechanisms for the increased prevalence of TD in neuroleptic-treated patients with diabetes will be discussed.