Olfactory Testing in Frontotemporal Dementia: A Literature Review.

Frontotemporal dementia (FTD) is a heterogeneous disorder featuring language impairment, personality changes, and executive defects, often due to the frontotemporal lobar degeneration (FTLD). Both FTD and FTLD are often associated with olfactory impairment, early biomarker for neurodegeneration, which can be evaluated with different techniques, among which low-cost olfactory tests are widely used. Therefore, we conducted a review of the literature focusing on papers published between January 1, 2007, and June 12, 2017, investigating the usefulness of olfactory testing in FTD/FTLD. A general decrease in the olfactory identification ability was seen in most of the articles and, taken together with a preserved odor discrimination, reveals a higher order impairment, possibly linked to cognitive decrease or language impairments, and not to a specific deficit of the olfactory system. This evidence could represent a useful add-on to the current literature, increasing the diagnostic value of olfactory assessment, particularly in cases where differential diagnosis is difficult.