What causes a sudden change in mentation in the elderly with a history of stroke?

Vascular dementia: It is well known that a series of small strokes, called lacunes can eventually add up and cause vascular dementia, similar to alzheimer's. A sudden change may well correlate with a new stroke, perhaps from a larger vessel. Tough to treat, but use a memory enhancing agent plus a drug to prevent strokes. A neurologist who does hospital work would be ideal.