The objective of this paper is to compare and contrast the clinical, neuropsychological, and neuroimaging findings in patients with mild cognitive impairment (MCI) associated with underlying Alzheimer's disease (AD) versus Lewy body disease (LBD) pathology. MCI refers to a clinical syndrome with impairment in one or more cognitive domains, with essentially normal performance of activities of daily living. Patients with the amnesic subtype of MCI often develop the dementia syndrome and neuroimaging findings characteristic of AD [e.g., hippocampal atrophy on magnetic resonance imaging (MRI), temporoparietal and posterior cingulate hypometabolism on fluorodeoxyglucose positron emission tomography (FDG-PET), positive uptake on amyloid PET, normal striatonigral uptake on dopamine transporter scanning (DAT), etc.]. In contrast, the MCI syndrome associated with LBD pathology regardless of the coexisting presence or absence of parkinsonism is usually characterized by impairment in the executive and/or visuospatial domains, and the cognitive features are often preceded by REM sleep behavior disorder by many years. There is minimal hippocampal atrophy on MRI, minimal if any cortical uptake on amyloid-PET, and one would predict that hypometabolism would be maximal in the occipital cortex on FDG-PET and uptake would be decreased on DAT. The early data suggests that differentiating underlying AD vs LBD in the MCI phase will be feasible.
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