Although you say he had been tested at the time the change started, was he tested for Alzheimer? I'm not a doctor of course, but I know a lady who explains her husband exactly as you do. His personality did a complete 180 and he's totally opposite from the man she married. It is Alzheimer disease. After many years struggling with it he now has all of the other signs as well. But, that was one of the first things to go was his personality.

Like I said I"m not a doctor and I don't know what tests you have done on him. But, that came to me as soon as I started reading.