PET imaging in the differential diagnosis of vascular dementia.

Aging leads to a small loss of cortical neurons, but to a significant reduction of synapses, dendrites and myelinated fibers. These age-related changes may cause some cognitive impairment, brain atrophy and frontally accentuated diffuse decrease in metabolism. In pathological disorders leading to dementia, most frequently degenerative Alzheimer's disease, cerebrovascular disease or a combination of both, the changes are more severe, affect predominantly specific regions and result in significant loss of neurons. The differential diagnosis of these disorders is based on symptoms of cognitive and memory impairment and is supported by results of neuropsychological tests and of imaging. Whereas computed tomography and magnetic resonance imaging are able to detect morphologic lesions, these modalities cannot determine functional consequences of the underlying pathologies. Positron emission tomography allows imaging of the localized and/or diffuse metabolic disturbances responsible for cognitive impairment and dementia, and is effective in differentiating vascular from degenerative dementia, as Alzheimer's disease. It can also detect inflammatory changes and their interaction with amyloid depositions for the development of mixed dementias after stroke. Imaging of neurotransmitters and of synaptic function additionally yields insight into disease specific pathophysiology. Despite that the broad clinical application of PET is limited, this technology has a great impact on research in dementia.