The doctors do a diagnosis for themselves, it doesn't really have a lot to do with us. But I think dysthymia is just a fancy word for chronic depression, I don't think it ever has psychosis associated with it:

http://psychcentral.com/disorders/sx14.htm

But like Lenny says, if it helps you to think of yourself that way and work on your problems, that's a good thing. Do you have some article or something you can take with you when you see him as a prop to show him and help him know how important you feel it is?