It usually happens in the middle stages, rather than early ones, but I suppose it could happen earlier.
It was when mum started to be convinced that people were coming into her home and stealing things and she thought that the family were all after her money that I suddenly woke up and began to realise that her forgetfulness wasnt just "old age". It was indeed dementia and she had had it for a while, but it was only when it started to affect her behaviour that it dawned on that there was a problem.
Get medication checked by GP.
Strong painkillers can cause problems, especially if not being taken correctly.
Are medications being taken correctly? Don't rely on being told so, what do you see for yourself.
mother of 2, my mum had terrible paranoia, we did not even know that she had alzheimers at the time - daft as that may seem.
She is now on medication for anxiety, depression and anti psychotics - which is another story! but, the paranoia has definitley improved, but not completely gone away. Apparently, mum has middle stage alzheimers, I would only be guessing as to whether the paranoia started in the early stages or not.
Thinking that neighbours were stealing things (mostly things nobody in their right mind would want anyway) was one of the early signs in my FIL, but because we were completely new to it all we didn't realise it was down to dementia.
Once it had clicked, a lot of other behaviour made sense, much of which we had put down to his innate stubbornness - putting tins of soup in the freezer was just one I still remember.