Positron-emission tomography in tardive dyskinesia.

Cerebral glucose metabolic rates were determined in normal control subjects (n = 26) and schizophrenic patients with tardive dyskinesia (n = 14). Globus pallidus and primary motor cortex (precentral gyrus) metabolic values divided by those of the cerebral hemispheres were significantly increased in the patient group. A similar metabolic pattern has not been reported for schizophrenic patients without tardive dyskinesia, and the abnormalities were demonstrated despite the normal appearance of the basal ganglia on X-ray CT. The findings differed markedly from the reduced metabolic rates of the basal ganglia previously identified in other choreiform disorders, including Huntington's and Wilson's diseases. The findings suggest that tardive dyskinesia is characterized by increased pallidal synaptic activity resulting from either altered striatopallidal input or increased pallidal interneuron firing.