A 57 year old women with ...

A 57 year old women with a marked change in personality over the last 5 years. She has become increasingly sexually flirtatious with improper behavior in social situations. Impairment of abstract thinking, memory and planning has become increasingly obvious. However the ability to perform arithmetic task is relatively preserved. Speech output is diminished, there is no motor impairment. Physical examination is unremarkable except for the presence of grasp reflexes. 
What is the most likely diagnosis?