Regional differences in cortical benzodiazepine receptors of Alzheimer, vascular, and mixed dementia patients.

OBJECTIVE: We examined regional benzodiazepine receptors (rBZR) using single photon emission CT (SPECT) in patients with Alzheimer disease (AD), vascular dementia (VaD), and mixed AD/VaD dementia (MD) and compared the changes in the availability of rBZR with those of regional cerebral blood flow (rCBF).

METHODS: A total of 7 patients with AD, 6 with MD, and 9 with VaD underwent SPECT studies with N-isopropyl-p-[(123)I] iodoamphetamine and (123)I-iomazenil to measure rCBF and rBZR. The ratios of rCBF and rBZR uptake in brain subregions to the average global activity were compared among these diseases. In addition, we acquired z-score maps using 3-dimensional stereotactic surface projections of SPECT data.

RESULTS: Compared with AD, VaD and MD showed rCBF and rBZR reduction predominantly in the frontal lobe, but rBZR images revealed more extensive and severe defects than rCBF images. In contrast, AD showed rCBF and rBZR reduction predominantly in the parietotemporal lobe compared with VaD and MD, but rCBF images revealed more extensive defects than rBZR images.

CONCLUSION: rCBF imaging can detect parietotemporal abnormalities in AD, while rBZR imaging may enable the demonstration of underlying pathophysiological differences in the frontal lobe between VaD, MD and AD, reflecting neuronal integrity in the cerebral cortex.