No one likes to talk to elder family members about money, it can come across as greedy, but a sign of cognitive impairment that isn't obvious, like drastic memory loss, is 'wealth shock' - a sudden loss of savings.

Wealth shock does not cause dementia or Alzheimer's, sorry IARC epidemiologists, it does not cause cancer either, but it is a symptom of a decline. 

An analysis of 8,082 participants enrolled in the Health and Retirement Study found that  accelerated cognitive decline and elevated risks of dementia among middle-aged and older U.S. adults was associated with negative wealth shock - a loss of 75% or more in total wealth over a 2-year period. The authors made modifications by age and ethnicity.

Of the group, over 20 years 1,441 had developed incident dementia over. Compared with participants who had positive wealth without shock, those with negative wealth shock had accelerated cognitive decline and showed increased risks of dementia. Cognitive performance was quantified with the TICS-m, which contains 3 tests consisting of immediate and delayed recall items, serial subtraction by 7, and counting backward and is considered by some psychologists to be a valid dementia screening tool.

Obviously this is only exploratory and the results will need to be confirmed with further prospective and interventional studies.