Has anyone seen someone with dementia suddenly improve...particularly when it might be the end of life?

I know this is sort of like swiss cheese...missing items of importance...but friend raised a question that is curious: relative of his was dx with dementia. He reports she was treated for "another problem" and suddenly seems much improved dementia wise. Cannot help but wonder if she could have received a course of antibiotics and could she have had an underlying UTI or similar for a long while and this cleared it and the dementia symptoms up?