Alzheimer's is one type of dementia. There are many types of dementia depending on the symptoms and reasons. Alzheimer's is the most common type of dementia and Vascular dementia is the second common one.
You can search google to find out about the types of dementia. It is hard to know the cause and the type. Usually the specialists can conduct some verbal test (MMSE) in office or some physical test such as MRI, Pet scan or ct scan to determine the diagnosis.