LATERALIZED DIFFERENCES IN IODINE-123-IBZM UPTAKE IN THE BASAL GANGLIA IN ASYMMETRIC PARKINSONS-DISEASE

We used equilibirium analysis of SPECT data from patients with asymmet ric Parkinson's disease to determine if lateralized differences in the striatal uptake of [I-123]IBZM correlate with asymmetry in clinical f indings and, by inference, with lateralized differences in the concent ration of extracellular dopamine. Methods: Twelve patients with asymme tric clinical signs of idiopathic Parkinson's disease were injected wi th a bolus of [I-123]IBZM, and multiple SPECT scans recorded the time course of radioligand uptake. The time integral method was used to est imate peak specific binding, so that a ratio of specific-to-nonspecifi c binding in the left and right striatum of each subject at equilibium could be determined. Nine patients also had Tc-99m-HMPAO SPECT scans which were examined for evidence of blood flow asymmetries. Results: P aired t-tests comparing [I-123]IBZM uptake revealed significantly grea ter (mean = 7.3%) availability of dopamine-D2 receptors in the basal g anglia contralateral to maximal clinical signs. Differences in recepto r availability correlated significantly with differences in every meas ure of the clinical assessment. No significant differences in regional cerebral blood flow between the two sides were observed with Tc-99m-H MPAO. Conclusion: These results demonstrate the ability of [I-123]lBZM SPECT to reveal clinically meaningful variations in striatal dopamine receptor availability in patients with asymmetric Parkinson's disease . The equilibirum analysis technique used to determine these findings is a simple and robust method of measuring relative receptor availabil ity and may be useful in studying other illnesses where dysfunction of dopaminergic neurotransmission is suspected.