In what ways does vascular dementia differ from alzheimer's disease?

Not many: Clinically, alzheimer's tends to be a smooth decline over time, while vascular dementia declines in steps, as small regions of the brain lose function. Neuropsychological testing may lend evidence for, but not prove, one cause or the other. Brain MRI may show vascular disease. A definitive diagnosis can only be made by brain biopsy (which is rarely done), or at autopsy.

Strokes in VaD: Alzheimer's and vascular dementia (VAD) frequently co-exist. The main evidence for VAD is based on clinical or radiological evidence for stroke.