POSITRON-EMISSION-TOMOGRAPHY FOR DIAGNOSIS OF ALZHEIMERS-DISEASE AND VASCULAR DEMENTIA

In mild or atypical cases of Alzheimer's disease (AD) the differential diagnosis to other dementing diseases, such as vascular dementia (VD) , may pose a difficult problem. Beside computed tomography (CT) and ma gnetic resonance imaging (MRI), functional neuroimaging by positron em ission tomography (PET) support the clinical diagnosis by visualizing cerebral function. PET of F-18-2-fluoro-2-deoxy-D-glucose (FDG) for me asurement of regional cerebral glucose metabolism (rCMRG1) has shown a typical metabolic pattern in patients with probable AD: hypometabolis m in temporoparietal and frontal association areas, but relative reces sing of primary cortical areas, basal ganglia and cerebellum. In VD a different pattern is seen. It consists of scattered areas with reducti on of rCMRG1 typically extending over cortical and subcortical structu res. Severity of dementia is correlated with rCMRG1 reduction in the t emporoparietal association cortex, irrespective of the cause of dement ia. Also the total volume of hypometabolic regions is related to sever ity of dementia but did not differ between AD and VD, even in patients with small lacunar infarction. This indicates that the total volume o f functional tissue loss is more important, since it also includes the effects of incompletely infarcted tissue and morphologically intact b ut deafferented cortex. The characteristic metabolic pattern has a hig h diagnostic accuracy for the discrimination between probable AD, norm als and VD, even in patients with mild cognitive impairment. Under cli nical and therapeutic aspects the analysis of longitudinal changes of rCMRG1 has shown that neuropsychological and metabolic changes are clo sely related in both, AD and VD.