I don't know if it's common or not, but it does seem a little peculiar that your bone scans were fine earlier, and that you've developed this late osteoporosis after being off the steroids for years. That makes me wonder, of course, whether there is another cause for the osteoporosis that might be missed, because everyone jumps to the "easy" conclusion that it's due to the past steroid use.
People with one autoimmune disease are at somewhat increased risk for another. Celiac disease (gluten intolerance) has been found to be more prevalent in osteoporotic patients (presumably due to malabsorption of calcium and vitamin D).
Even if you don't have any GI symptoms (many with celiac disease don't) I think you should be screened thoroughly (anti-gliadin IgA and IgG, as well as anti-endomysial or anti-ttg antibody blood tests).
Another much rarer concern would be autoimmune hypoparathyroidism - presumably they already checked your calcium and PTH levels, but do make sure it was done.
