Multiple System Atrophy and Progressive Supranuclear Palsy

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 (123I-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 123I-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 123I-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 123I-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.