Alzheimers is one form of
dementia actually.
Dementia is the overall condition,
and there are other caused like
Lewy-Bodies, then there are forms caused by say, other conditions like having clogged carotids that are cutting off blood flow to the brain so the brain is not getting enough O2, and lungs not getting enough O2 so again the brain is not getting enough so the person can recover some on oxygen... also vitamin and hormone issues can be a problem.