Cerebral blood flow and dementia in Parkinson's disease.

Regional cerebral blood flow (CBF) was examined in 27 patients with Parkinson's disease using single-photon emission computed tomography and N-isopropyl-p-[123I]iodoamphetamine as a tracer. Their CBF pattern was compared with that of seven patients with Alzheimer's disease and nine age-matched neurologically normal controls. Tracer activity was determined in seven bilateral cerebellar, cortical, and subcortical regions and was expressed as the ratio of activity in each region to the mean tracer activity in the cerebellar region. Nineteen patients with nondemented Parkinson's disease showed significantly decreased tracer activity ratio in the frontal and temporal cortices, basal ganglia, and thalamus compared with that in controls. The eight demented Parkinson's disease patients showed significantly decreased tracer activity ratio in the temporal and parietal cortices compared with the patients without dementia, and demonstrated CBF pattern similar to that of patients with Alzheimer's disease. These findings suggest that in patients with Parkinson's disease, the mechanism of CBF reduction of the frontal cortical region differs from that in the temporoparietal cortical region and support the concept that Parkinson's disease and Alzheimer's disease may overlap in some patients.