Multiple system atrophy and progressive supranuclear palsy. Diminished striatal D2 dopamine receptor activity demonstrated by 123I-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 (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.