MULTIPLE SYSTEM ATROPHY AND PROGRESSIVE SUPRANUCLEAR PALSY - DIMINISHED STRIATAL D(2)-DOPAMINE RECEPTOR ACTIVITY DEMONSTRATED BY I-123 IBZM SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY

Objective.-To measure D2 dopamine receptors in the striatum in patients with multiple system atrophy and progressive supranuclear palsy by I 3-iodo-6-methoxybenzamide labeled with iodine I 123 (I-123-IBZM) single photon emission computed tomography and differentiate them from control subjects. Design.-Survey with the following as retrospective criterion standards: (1) parkinsonism, (2) negative apomorphine test, and (3) no or only slight reaction to dopaminergic medication. Setting.-Ambulatory or hospitalized care in an academic referral center. Patients and Control Subjects.-Twenty-one patients with parkinsonism not responding to dopaminergic medication (17 with multiple system atrophy and four with progressive supranuclear palsy) and 21 control subjects without parkinsonism. Intervention.-In vivo imaging by single photon emission computed tomography using the D2 dopamine receptor specific radioligand I-123-IBZM. Main Outcome Measure.-Striatum/occipital cortex ratio of count rate density as semiquantitative measurement for striatal D2 dopamine receptor density. Results.-A highly significant loss of striatal uptake of I-123-IBZM was observed in the patients in comparison to the control subjects with little or no overlap between values. Conclusions.-The hypothesized loss of D2 receptors in multiple system atrophy has been confirmed. Use of I-123-IBZM single photon emission computed tomography may be a cost-effective alternative to positron emission tomography in the differential diagnosis of parkinsonism and in the selection of patients for dopaminergic therapy.