Could dementia be the cause of her aggressive and angry behavior?

For what it's worth, I (briefly) dated a man who was in a similar situation. A doctor, he took his widowed mother to live with him when she started having comparatively mild health issues. I believe that she manipulated him from early childhood onwards, but as she aged, her demands grew more unreasonable; as Midkid observes, the woman was as she always had been, but her veneer of normalcy was gone. It got to the point where she would not eat if he wasn't at home, even when his sister or brother were there to help. He said to me wearily at one point, "I guess I'm the only one she trusts to run the microwave." By refusing any assistance other than from him, she effectively dominated him and cut him off from anyone who might have competed with her for his time and attention. It's a wonder he was able to continue working. I do agree with those who suggest looking at a possible UTI, but you need to consider whether this is a departure from the way she's always been, or is merely a rawer, harsher version of herself.

David--
Has she always had a 'mean' side or this new and inexplicable behavior? As seniors age, they often just become more profoundly "who they really are". Kind people get sweeter and sweeter, mean people get meaner, or don't bother to hide their "meanness" with covering behaviors.

I'd check for the UTI, but not expect that to be the main causation.

Mother now has dementia. She is losing her "filter" and says the most atrocious and embarrassing things. I take her places and just want to melt into the floor sometimes. She is just no longer waiting until we are "alone" to comment on people's appearances, etc. Just blurts it all out. I have had to flat out tell some people, after she's said something completely awful "I'm so sorry, Mother has dementia. She doesn't know what she's saying".

Mother has always been all the things you mentioned. But she kept it "under wraps" pretty well. Now, not so. It won't get better, so, hang on for the ride.

Hopefully it IS as simple as a UTI---although Mother gets those every month and they don't alter her behavior at all.

Is she living with you?? For your sake--I hope not.

Davidb1, you mentioned that Mom "had become" aggressive, angry, accusatory, unreasonable, unappreciative, and more.

Have your Mom checked for a Urinary Tract Infection [UTI] as that can cause the very same symptoms you had mentioned. The test is easy, and the cure is antibiotics. Take Mom to her primary doctor or go to a urgent care center where they can run the test and get the results in a few minutes.

Oh yes, definitely some form of dementia! I have dealt with this when Mom had Alzeheimer. (Mom passed this week) We knew she had it, but she seemed normal in a lot of ways. After getting the right medication she was more mellow and more herself. (she was on the wrong medication at the time) Hoping you get a diagnosis.

There could be any number of problems, that could be causing her to act that way, but, I agree that a doctor needs to be informed of what is happening. Is there anyone in the home who can observe other things too. Like, is she bathing, using the bathroom properly, eating enough, etc. I never knew that dementia could start out with the symptoms you describe. I thought it was mainly about memory loss, but, I saw my LO grow very negative and confrontational. She did not understand why she became that way. Eventually, the dementia was apparent and her memory then went as well.  Later, she became nice again though.  They will sometimes go through stages and not stay that way indefinitely.  

I'd work on having her properly diagnosed. Sometimes, medication can help.

Does it matter WHY she's behaving this way?

She needs to be seen by a geriatrics doctor who can start the diagnostic process, refer her to a geriatric psychiatrist for meds for her agitation and aggression, perhaps a geriatric neurologist for diagnosis.

In any event, son needs to decide what he can and cannot do without losing his livelihood and his life.

Just because his mother wants something doesn't mean it has to happen.