CEREBRAL BLOOD-FLOW AND METABOLISM IN DEMENTIA - REGIONAL PATTERNS AND THE BIOLOGY OF ALZHEIMERS-DISEASE

Functional imaging techniques, specifically positron emission tomography and single-photon emission computed tomography, have been used to study dementing illnesses with two general aims: the clinical use of the techniques to diagnose the cause of dementia during life and the use of the techniques to explain the pathophysiology of dementia. In both applications, patterns of perfusion and metabolism provide information of diagnostic and biological use. With regard to diagnosis, the pattern of temporal and parietal hypometabolism and hypoperfusion may be of some utility in determining whether the most common cause of dementia, Alzheimer's disease, is present during life. However, this pattern is not specific, and the sensitivity of the pattern is also still controversial. Limitations in the diagnostic use of the techniques are related to uncertainty about sensitivity and specificity and the lack of a prospective controlled study with pathological validation. With regard to pathophysiology, patterns of abnormal perfusion and metabolism have helped to explain the heterogeneity of the disease by demonstrating relationships between regional functional pathology and behavior. While some lines of evidence suggest that the functional abnormalities may reflect neuropathology, other evidence suggests that the interpretation of metabolic and flow deficits is more complex. Nevertheless, the regional changes in brain function appear to provide important information about where the disease begins in the brain and about how it may progress.