There are many terms here that are related. Dementia (usually with a lower case) is a general term that encompasses many causes of the symptom of decrease cognitive performance. The other terms describe different specific diseases which share some features. Several disease are associated with a buildup of proteins that can form deposits like plaques, but which protein is dominant differs. In Alzheimer’s, the deposits are mainly amyloid-beta, but most patients also have some tau accumulation. In frontotemporal dementia, tau accumulates. In Lewy body disease and Parkinson’s, alpha-synuclein accumulates. Everyone, even healthy, has a little bit of all of these proteins.
Interestingly, researchers recently have found that there appear to be stalls in the brains of mice that overproduce a type of tau protein. We don’t yet know whether these stalls have the same cause as in Alzheimer’s. It will need to be answered in a future study.