My father passed away in 2008, and since then I have watched over my mother's affairs. She lived on her own in Florida until 2013, when I moved her to an assisted living near me. She has macular degeneration and hearing loss, so she has become more isolated because of that She has also shown more signs of dementia - memory loss, obsession with sorting her clothes, believing someone has stolen clothing she never had. This obsession is fairly recent. She can carry on a conversation with you when she is focused and not tired. She takes care of herself, dresses herself, keeps her room clean, irons her clothes, etc. I believe that her failing eyesight and hearing have exacerbated her dementia. I've never had her diagnosed. We feel it is probably vascular dementia as she has had a heart attack, 5 by-passes, several stints, a stroke, and probably several TIAs. Her carotid arteries are 90% blocked, but the doctor and I agree that operating would be more dangerous than letting her go as long as there are no symptoms causing her pain. My biggest question is whether I should have her see a doctor and get a diagonis as to what kind of dementia she has just in case it is treatable. She will be 93 next week and against having any agressive medical treatments to prolong her life.
The important thing is that all of her carers accept that she has cognitive impairment of some kind -- very possibly vascular. From what I've seen of ALFs and NHs, the good ones treat the residents based on observable symptoms and behaviors. An official diagnosis doesn't make a lot of difference.
If there was family dispute over Mom's care -- one grandchild insisted that she doesn't have dementia and wants to rent her an apartment -- or if the AL was expecting Mom to do things that are beyond her capabilities, then, yes, maybe an "official" notation of dementia would serve a purpose.But if everyone is on the same page for her care, I'm not sure there would be much benefit.
A conclusive diagnosis as to the type of dementia would have to wait upon an autopsy, but a thorough evaluation could probably be reasonably accurate. Then what?
My mom has dementia. We have no idea what kind. Very likely not Alzheimer's and definitely not Lewy Body. She is 95. What could be done differently if we knew she had XYZT type? At this point, not much. Maybe when we reach a point of having better treatment options it would make sense.
Now if you were writing about your sister or brother who is starting to show disturbing signs, I would be pushing hard for a diagnosis. But at 90+, I just don't see the value.