Mom 82 yrs. old talks about someone living under our house. No basement, a closed off crawl space with spiders.

What's Mom's diagnosis?

"She has multiple personalities, bi-polar, dementia, paranoid schizophrenia and sundowners".

Auditory or visual hallucination, changes in personality, mood swings - these can all come under the 'umbrella' of dementia.

Sadly, dementia is not curable. Sometimes medications work to subdue some symptoms but not always.

I have a family member who has auditory hallucinations. She hears things going on all the time that no one else can hear. They are stressful to her and she will call the police to advise them of the woman being beaten or children raped or some other horrible event. Yet she is deemed competent. I think no one would like the voices to go away as much as she would.
Just tell mom you will tell the man to knock it off and change the subject. She tells you about the man because she trusts you. Maybe ask her to keep notes, ask her to put the time and date and what is going on with the man. Then when you have enough evidence you will turn it over to the police. This might distract her a bit. My relative had notebooks of loopy cursive that no one else could read. When she starts in, just say, put it all in your notebook. The police will want to know about that.
All meds have side effects that could be more harmful to her. Maybe talk to the doctor about anti anxiety meds if the voices bother her. If you find it mostly bothers you that you can’t convince her that the man isn’t real, drop that. You will never convince her. Because she truly hears the man.
‘Oh and some meds will make a person sleepy. Keep notes of your own as to number of hours she sleeps, when she hears the voices, etc. it might help the doctor figure out what is going on and how to adjust her meds.
i am sorry for you and mom that you are both dealing with this. There is no perfect answer. Treat her with kindness and yourself as well..

She requires a full neuro-psyc workup. It is the job of such an MD to put together the best diagnosis he is able. It honestly is a bit murky at some point; mental health issues are difficult to diagnose.

With her multitude of mental and cognitive issues, it is very import to work with a single doctor (psychiatrist?) so that she gets continuity of care. This is the only way she will eventually get the right meds in the right doses. Calling 911 or taking her to Urgent Care of the ER won't be helpful in the long term.

You are in a very challenging situation. Please try to remember that no one wants to be mentally ill, no one asks to be. And then at 82, if dementia is also in the mix... not something she asked for or wanted either.

If it becomes overwhelming for you, consider calling in social services for your county to discuss options. They can acquire guardianship of your Mom and then they will take care of her going forward. Just a thought.

I wish you success in finding the right doctor and the best solutions for the both of you!

With all of those other diagnosed disorders, it is hard to determine which one is the most dominant. The psychiatrist could give her medicine to calm her down, but how are her other mental health issues being addressed and is she taking her prescribed medications for those as well.

It sounds like a situation that is very difficult to treat. Just make sure that she gets as much support she can handle at this time.

I know this is a very challenging and frustrating situation to deal with.