en.wikipedia.org/wiki/Scleroderma & Lupus are
auto-immune disorders. Most of the auto-immune disorders have overlapping symptoms, and there are no clear single tests that determine one or the other -- it's more like "choose the group of symptoms that most likely match X", where X is the diagnosis they decide is best fit.
The diagnosis is NOT the most necessary part of the problem -- controlling symptoms IS. And, like I said, the symptoms overlap....or just make sure your dr is symptom-oriented, and everything will work out. If you have a dr that insists on a firm DX *before* treatment -- get another opinion!!!