DOPAMINE D-2-RECEPTOR SPECT WITH [I-123] IODOBENZAMIDE IN THE DIAGNOSIS OF PARKINSONS SYNDROME

For effective drug therapy of Parkinson's syndrome (PS), it is necessa ry to distinguish between idiopathic and secondary genesis and PS in n euronal systemic degeneration. [I-123]Iodobenzamide ([I-123] IBZM) is a radiolabelled benzamide and binds specifically to the cerebral dopam ine receptor (D-2) in the basal ganglia. The purpose of this study was to determine the value of the [I-123]IBZM D-2-receptor SPECT in the d ifferential diagnosis of PS. A total of 38 patients (20 females, 18 ma les; age 61 +/- 13.3 years), with typical extrapyramidal symptoms were investigated. Twenty suffered from idiopathic and 11 from secondary P S. Seven patients in whom a neurological disease could be excluded, se rved as controls. SPECT data were acquired 90 min after i.v. injection of 185-200 MBq [I-123]IBZM. After reconstruction with a Butterworth f ilter (cutoff frequency 0.5) and attenuation correction (coefficient 0 .12 cm(-1)) we quantify the IBZM basal ganglia uptake as ratio to the frontal D-2-receptor-free cortex (BG/FC). The patients with idiopathic PS (IPS) and the controls revealed high and specific IBZM uptake in t he basal ganglia compared to the adjacent frontal brain tissue (IFS: B G/ FC = 1.44 +/- 0.10; controls: BG/ FC = 1.48 +/- 0.10). A significan t decreased striatal IBZM uptake is found in cases with secondary PS ( BG/FC = 1.25 +/- 0.10; p < 0.0001, t-test compared to controls and IFS ). The patient group with IFS can be subdivided into patients without L-dopatherapy (BG/ FC = 1.49 +/- 0.07), patients with longstanding L-d opa-therapy demonstrating significantly decreased striatal IBZM uptake (BG/ FC = 1.31 +/- 0.04; p < 0.0001, t-test compared to controls and other IFS), which correlates pathophysiological with a reduction of fr ee D-2 receptors, and patients with de novo PS showing a slight increa sed striatal IBZM uptake (BG/ FC = 1.56 +/- 0.05), which represents D- 2-receptor stimulation. [I-123] IBZM-SPECT is a sensitive and non-inva sive test for striatal D-2-receptor density and activity which permits relatively clear discrimination between idiopathic and secondary PS a nd yields important information for differential therapy.