At what stage of dementia diagnosis would a pet scan be performed to distinguish alzheimer's from frontal lobe dementia?

The onset of frontal lobe dementia (FLD) is often 10 years or more earlier than Alzheimer's disease & significant personality changes & behavior problems are the hallmarks of FLD. However, in early stages of these disorders, the differential diagnosis may be difficult so I' d say FDG PET scan may be helpful in early stages if there's no significant difference in age of onset or manifestations.

There are subcategories of FTD and Alzheimer's which pre-dominantly present with speech difficulties. The clinical appearances may create some confusion, and here diagnostic precision may be enhanced via PET scanning.