Someetimes the person may have prediabetes or glucose intolerance, and the steroids just push them over the edge. Usually the BG values will go quite high--high 300's - 400's.
It's much worse in the hospital with the large doses of Solu-Medrol, Solu-Cortef, or Decadron IV. But the increased insulin resistance produced by the steroids may continue on lower po doses.
For some people, insulin sensitivity returns to normal after steroids are stopped, but will return when steroids are resumed. In some cases, however, the diabetes remains even after the steroids are stopped.
I have seen pts go home on oral antihyperglycemics in some cases and insulin in others.
If you see a doctor putting someone on steroids on a "mild sliding scale with regular insulin," remind him/her that the severe schedule should be used and Novolog, Humalog, or Apidra are preferred over regular insulin.