Recognition of dementia relies on a good clinical history, supported by formal cognitive testing, but identifying the subtype of dementia may be wrong in 20 or more of cases. Accuracy may be improved by use of imaging and cerebrospinal fluid (CSF) biomarkers. Structural neuroimaging is recommended for most patients, not just to identify potentially reversible surgical pathology, but also to detect vascular changes and patterns of cerebral atrophy. Functional imaging can help to confirm neurodegeneration and to distinguish dementia subtypes when structural imaging has been inconclusive. Amyloid-positron emission tomography scans reflect neuritic plaque burden and identify the earliest pathological changes in Alzheimer's disease, but their value outside research settings is still uncertain. A combination of low CSF amyloid beta(1-42) and high CSF total-tau or phosphotau also has high predictive power for AD pathology, but diagnostic usefulness decreases with age because of the increased prevalence of AD-type pathology in non-demented people. The need to use biomarkers more routinely will become necessary as disease-modifying treatments become available and accurate subtype diagnosis will be required at an early (ideally pre-dementia) stage. Clinicians should be considering the resources and expertise that will soon be needed for optimal dementia diagnosis.
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