Epidemiology and Clinical Diagnosis: Alzheimer Disease.

The initial preclinical phase of Alzheimer disease (AD), which has no symptoms, is followed by a phase whereby cognitive impairment, but no functional impairment is present (mild cognitive impairment), after which comes the third phase of dementia. Diagnosis of AD has primarily been one of exclusion of all other causes of reversible and irreversible dementia. Overlapping clinical presentations of diseases causing neurodegeneration, however, create challenges for accurate diagnosis. Algorithms are provided for the most current guidelines. Use of clinical magnetic resonance and PET imaging modalities increase the specificity of diagnosis, and several new promising experimental approaches are being developed.