AbstractWe aimed to objectively examine the brain perfusion differences between PD, Parkinson variant of multiple system atrophy, and progressive supranuclear palsy. 99mTc ethylcysteinate dimer single‐photon emission CT (SPECT) was performed in 28 patients with PD, 12 with Parkinson variant of multiple system atrophy, 19 with progressive supranuclear palsy, and 17 age‐ and sex‐matched control subjects. A voxel‐by‐voxel group analysis, using statistical parametric mapping 8, was performed to detect the differences of regional cerebral blood flow among three diseases and control groups. Regional cerebral blood flow was measured using the noninvasive Patlak plot method and calculated using a fully automated region of interest technique. Progressive supranuclear palsy showed decreased regional cerebral blood flow in the cingulate gyrus and thalamus, whereas Parkinson variant of multiple system atrophy showed decreased regional cerebral blood flow in the cerebellum, compared with other patients and controls. Regional cerebral blood flow in the thalamus could be used to discriminate progressive supranuclear palsy from other diseases and control subjects with high sensitivity. These findings suggest that parkinsonian disorders, such as PD, Parkinson variant of multiple system atrophy, and progressive supranuclear palsy show a distinct SPECT pattern in the frontal cortex, thalamus, and cerebellum. Moreover, the measurements of regional cerebral blood flow in the thalamus and cerebellum may be helpful in screening for the differential diagnosis of parkinsonian syndrome. © 2011 Movement Disorder Society