My Husband Was Diagnosed With Periventricular White Matter Disease Back

My husband was diagnosed with Periventricular White Matter disease back in 2012 which resulted in mild memory loss and early dementia. In the last 4 years he has deteriorated greatly. It is not Alzheimers, just severe dementia to the point of not recognizing who I am, (we have been married 48 years) even though he knows he is married and his wife's name. No facial recognition. Does not know children or grandchildren that he sees every day. Can't remember how to feed the dog or make coffee. Would not be able to tell you his address or phone number if his life depended on it. In fact may not realize he is home when sitting in his Lazy-boy in his own living room. There is no rhyme or reason to what he will recall on any given day. Short term, long term, confusion all are part of the package. He has developed the slow unsteady gait and has balance issues. My question is, does this shorten a person's life expectancy? Is it fatal? If so, what is the life expectancy from onset. All I have been able to find refers to strokes and his blood pressure is well managed. I love the old boy and just would like a straight answer on what is coming at us. I can't really discuss this with his Dr. because he is there and I don't want to hurt him or upset him even if he probably wouldn't remember it. Of course the MRIs show spread of the white area from one to the next. I realize this is rambling and I do apologize for that, just would like more information that seems to be on the net!