Please make an appointment with another doctor to get a second evaluation and opinion. There are many causes for dementia and many types, some of which are treatable. My good friend’s husband was diagnosed with dementia. After more than a year, he was reevaluated and did not have dementia-it was severe depression.
Also, an ultrasound of the carotid arteries is very easy, noninvasive and would show up on that.
I don’t want you to have false hope, but it sounds like you don’t feel like you have all the information you need.