Lateralized differences in iodine-123-IBZM uptake in the basal ganglia in asymmetric Parkinson's disease

We used equilibrium analysis of SPECT data from patients with asymmetric Parkinson's disease to determine if lateralized differences in the striatal uptake of [¹²³I]IBZM correlate with asymmetry in clinical findings and, by inference, with lateralized differences in the concentration of extracellular dopamine. Methods: Twelve patients with asymmetric clinical signs of idiopathic Parkinson's disease were injected with a bolus of [¹²³I]IBZM, and multiple SPECT scans recorded the time course of radioligand uptake. The time integral method was used to estimate peak specific binding, so that a ratio of specific-to-nonspecific binding in the left and right striatum of each subject at equilibrium could be determined. Nine patients also had ^99mTc-HMPAO SPECT scans which were examined for evidence of blood flow asymmetries. Results: Paired t-tests comparing [¹²³I]IBZM uptake revealed significantly greater (mean = 7.3%) availability of dopamine-D2 receptors in the basel ganglia contralateral to maximal clinical signs. Differences in receptor availability correlated significantly with differences in every measure of the clinical assessment. No significant differences in regional cerebral blood flow between the two sides were observed with ^99mTc-HMPAO. Conclusion: These results demonstrate the ability of [¹²³I]IBZM SPECT to reveal clinically meaningful variations in striatal dopamine receptor availability in patients with asymmetric Parkinson's disease. The equilibrium analysis technique used to determine these findings is a simple and robust method of measuring relative receptor availability and may be useful in studying other illnesses where dysfunction of dopaminergic neurotransmission is suspected.