What is a multiple stroke syndrome?
Common, well-known strokes make people loose their life or mobility. But there is a different form, which knocks out only parts of the brain at one time. In the beginning, such stroke might temporarily disable clear speaking, or something "harmless" like that. With time, the strokes will get more frequent (every 3rd or 4th month perhaps) and more severe, causing damage to more and more parts of the brain. While there is some helpful medication, like blood thinning, there is no real cure.
The most helpful countermeasure is ... sports. The desease blocks the blood flow within the brain, so strengthening heart and circulation is more helpful than any medication, giving the human body a chance to overcome the resistance by pumping pressure. (Again, this is no cure, but it improves the chances, just like the blood thinning.) In practice, organizing a relevant amount of sports for a 90-year-old might be no trivial task.
This is the theory. If you will ever encounter it practically, it might be like this: You are teased by a charming old lady of good humour in the evening. In the morning, with a chance of 1:100 perhaps, she'll awake as a blabbering something, forcing you to explain, that for walking, one has to move the left foot, then the right one. She might not know where she is, or who you are.
The amazing part is the capability of the brain, to recover from a condition like that, slowly. Old memories will come back first. I don't know why, but perhaps, the replacement by unused brain cells encounters old storage content. Two months later, after investing effort into sports and visiting as many well-known places as possible, you might have a charming old lady again.
The recovery is never 100%, the stroke will eliminate brain cells forever, and the cycle of stroke and recovery gets overlaid by a general tendency. For the results of it, the multiple stroke syndrome is often called multiple stroke dementia. This overlay to the stroke/recovery cycle might add a discouraging element to the recovery attempts.