As you search the web you will find tons of stories that sound so similiar . . too bad the researchers aren't doing anything more to help us!
From what I've read over the years, the only difference between UCTD and MCTD is that UCTD they are telling us we don't have any Full blown condition just symptoms of the conditions; but with MCTD you will have at least 3 Full blown conditions. All of the conditions are autoimmune; Lupus, Sjogrens, RA, Scelorderma, etc. But they are all treated the same.
It's so frustrating . . . and when the doctors treat us like we have nothing because the test keep coming back negative, that's even more frustrating. At least there are some docs on our side, just wish the rest of the world would get on board . . just because you can't see what's wrong with my doesn't mean it's not there!