DOPAMINE D(2) RECEPTOR OCCUPANCY MEASURED BY SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY WITH I-123 IODOBENZAMIDE IN CHRONIC-SCHIZOPHRENIA

Single photon emission computed tomography (SPECT) with I-123-iodobenz amide (I-123-IBZM) was used to study 22 chronic schizophrenic patients . The patients, who were receiving maintenance therapy with typical ne uroleptics, had not shown any significant improvement since their admi ssion to the hospital. Basal ganglia/frontal cortex ratios of the upta ke of I-123-IBZM did not show significant differences on the basis of neuroleptic dosage in chlorpromazine equivalents. There were, however, significant differences in I-123-IBZM uptake in the basal ganglia amo ng patients characterized by negative, mixed, and positive symptoms of schizophrenia. Although only a small number of patients had shown a p ositive response to treatment by the time of discharge, D-2 receptor b lockade was significantly higher in responders than in nonresponders. In addition, there was an inverse correlation between reduced activati on as measured by the Brief Psychiatric Rating Scale and the basal gan glia/frontal cortex ratio. These findings suggest a complex pathogenet ic link between the blockade of dopamine D-2 receptors and psychopatho logy in chronic schizophrenic patients. SPECT studies with I-123-IBZM appear to have prognostic value in identifying chronic schizophrenic p atients who respond poorly to neuroleptic treatment.