What is the difference between Alzheimer's disease and vascular dementia?

It is my understanding that vascular dementia's decline follows a stair-step fashion. Plateau for a while and then a marked decline. That is the way it worked with my mom.

My Mom is healthy as a horse. No heart problems, cancer, diabetes, Parkinson's...nor did she drink or smoke. My Dad has ALZ and Mom's dementia is different. thanx for the input.

It would take a good neurologist to narrow down what type of dementia you are dealing with. For a person with a long history of cardiac issues, the first suspect is vascular dementia. For a person who is actively hallucinating in front of you, Alzheimer's is a guess... because Alzheimer's is only confirmed post mortem. Kidney failure can look like Alzheimer's but the bloodwork would show toxins and low GFR rates. A long history of regular alcohol consumption points to liver failure and again, bloodwork will reveal problems.
And there is always the possibility of more than one kind of dementia being present together.

Yes. Each type of dementia has its own pathology. Symptoms may not always be so distinctive. The pathology can be accurately identified upon autopsy, but some times not before then.

AgingCare has a helpful article about different kinds of dementia, here https://www.agingcare.com/articles/different-forms-of-dementia-138582.htm For a more in-depth explanation try the Alzheimer's Association websit, or other reliable source, like the Mayo Clinic website.

By the way, one way in which the pathologies are different is that ALZ follows a fairly predictable path through the brain. It takes many years but it relentlessly follows its course. Therefore it is possible to describe some distinct "stages" for the disease. Other kinds of dementia follow their own development course, and the ALZ stages absolutely do Not Apply to them!