Functional brain imaging in late-life depression and dementia.

Studies utilizing advanced scanning technologies suggest that brain imaging may have a role in the differential diagnosis of some common neuropsychiatric disorders. In subjects with dementia of the Alzheimer type (DAT), widespread cortical reductions in glucose metabolism and blood flow have been described, with predominant involvement of the temporal and parietal lobes. The primary sensory areas and subcortical regions are relatively spared. When a "patchy" pattern of reductions in cerebral blood flow and metabolism is associated with clinical dementia, a vascular etiology should be suspected. Major depression in the elderly is associated with reductions in whole brain glucose metabolic rates comparable in magnitude with those described in DAT. Relatively distinctive patterns of flow and metabolism also are seen in frontal-temporal dementia and Parkinson's disease with dementia.