Neuronuclear imaging in the evaluation of dementia and mild decline in cognition

Recently, the National Institute on Aging and the Alzheimer's Association identified specific structural and functional neuroimaging findings as valuable markers of biological processes occurring in the human brain, especially processes that herald impending dementia caused by Alzheimer's disease (AD) in its prodromal form. In particular, the imaging modalities of magnetic resonance imaging and positron emission tomography (PET) were singled out, along with certain biomarkers in cerebrospinal fluid, to serve this purpose. We review the clinical tests available for neuropsychologic evaluation and in cases when the differential diagnosis for the causes of cognitive impairment is difficult to make, we consider biomarkers, beginning with cerebrospinal fluid, for assessment of cognitive decline. For more direct information on dementia-related pathologic changes in brain tissue, structural features observed in magnetic resonance imaging scans are regarded. We next discuss the use of single-photon emission computed tomography for evaluating functional changes. Then, pertinent to the recent National Institute on Aging and the Alzheimer's Association's consensus statement on the diagnosis of prodromal AD, we focus on assessing the cerebral metabolic changes associated with neurodegenerative diseases that are identified with fluorodeoxyglucose PET, as well as consider the most appropriate roles for amyloid imaging based on recent studies examining the use of PET with tracers having higher retention in brain tissue-harboring plaques composed of insoluble beta-amyloid. We also consider the leading causes for the current underuse of neuronuclear imaging in evaluating patients with cognitive problems, along with strategies for combating them. Finally, we suggest an overall diagnostic algorithm to guide optimal use of all the neuroimaging tools in assessing patients with cognitive decline.