18F-FDG in the differential diagnosis of neurodegenerative dementias

The diagnostic workflow of patients with cognitive decline needs an extensive clinical evaluation. The use of FDG-PET can be helpful because the finding of a rather specific pattern of hypometabolism could point to specific neurodegenerative disorders. In patients with memory impairment and visuo-spatial deficits, FDG-PET may reveal a pattern of temporo-parietal hypometabolism that is associated with Alzheimer's disease or a more extended area of hypometabolism that spreads to the occipital cortex, as in posterior cortical atrophy indicating signs of neurodegeneration in the associative visual cortex. In the spectrum of fronto-temporal lobe degeneration, FDG-PET is used to support the diagnosis by excluding AD and to identify areas of hypometabolism that are associated with the behavioural variant of FTD or with progressive primary aphasia. When cognitive impairment develops along with parkinsonism, FDG-PET can be used to differentiate among the different forms of disorders, such as dementia with Lewy bodies, progressive supranuclear palsy and cortico-basal degeneration, occurring with different specific pattern of altered metabolism. In this pictorial essay, we present a series of clinical cases in which the use of FDG-PET contributed to the final diagnosis.