Cerebral metabolic differences in Parkinson's and Alzheimer's diseases matched for dementia severity.

Despite controversial clinicopathological distinctions between Parkinson's disease with dementia (PDD) and Alzheimer's disease (AD), similar patterns of metabolic reduction in the posterior brain were reported previously using PET with [18F]fluorodeoxyglucose. The current study was designed to examine more specific regional differences in cerebral glucose metabolism between PDD and AD using accurate and objective brain mapping techniques. METHODS: This study included nine normal subjects, nine PDD patients and nine AD patients. PDD and AD groups were matched carefully for age, sex and general dementia severity as measured by Mini-Mental State Examination and Clinical Dementia Rating scales. Each subject underwent [18F]fluorodeoxyglucose-PET and neuropsychological testing. After anatomic standardization of PET image sets and stereotactic data extraction, absolute and normalized cerebral metabolic rates were assessed by region of interest and pixel-by-pixel analyses. RESULTS: PDD and AD showed global glucose metabolic reduction with similar regional accentuation involving the lateral parietal, lateral temporal and lateral frontal association cortices and posterior cingulate cortex in comparison to normal controls. When comparing between PDD and AD, however, PDD showed greater metabolic reduction in the visual cortex and relatively preserved metabolism in the medial temporal cortex. CONCLUSION: Although a common feature of metabolic abnormalities in the posterior brain exists in PDD and AD, the presence of regional metabolic differences suggests different degrees and combinations of disease specific underlying pathological and neurochemical processes.