How many biomarkers to discriminate neurodegenerative dementia?

A number of cerebrospinal fluid (CSF) biomarkers are currently used for the diagnosis of dementia. Opposite changes in the level of amyloid-beta(1-42) versus total tau and phosphorylated-tau(181) in the CSF reflect the specific pathology of Alzheimer's disease (AD) in the brain. This panel of biomarkers has proven to be effective to differentiate AD from controls and from the major types of neurodegenerative dementia, and to evaluate the progression from mild cognitive impairment to AD. In the absence of specific biomarkers reflecting the pathologies of the other most common forms of dementia, such as Lewy Body disease, Frontotemporal lobar degeneration, Creutzfeldt-Jakob disease, etc., the evaluation of biomarkers of AD pathology is used, attempting to exclude rather than to confirm AD. Other biomarkers included in the common clinical practice do not clearly relate to the underlying pathology: progranulin (PGRN) is a selective marker of frontotemporal dementia with mutations in the PGRN gene; the 14-3-3 protein is a highly sensitive and specific marker for Creutzfeldt-Jakob disease, but has to be used carefully in differentiating rapid progressive dementia; and alpha-synuclein is an emerging candidate biomarker of the different forms of synucleinopathy. This review summarizes several biomarkers of neurodegenerative dementia validated based on the neuropathological processes occurring in brain tissue. Notwithstanding the paucity of pathologically validated biomarkers and their high analytical variability, the combinations of these biomarkers may well represent a key and more precise analytical and diagnostic tool in the complex plethora of degenerative dementia.