Biochemical and radiologic diagnosis of Cushing's syndrome.

In summary, the technological advances in the past decade have greatly improved the biochemical and radiological diagnosis of Cushing's syndrome. Figure 13 illustrates an algorithm for the differential diagnosis of Cushing's syndrome that focuses on the importance of ACTH-IRMA and provides two potential diagnostic approaches for the evaluation of ACTH-dependent hypercortisolism. The first approach directly proceeds to IPSS as the most rapid and possibly most cost effective method to establish an accurate diagnosis. A more traditional approach employs high dose dexamethasone suppression testing followed by MR studies of the pituitary. If the biochemical or radiological studies are the least bit equivocal, IPSS should be performed before definitive therapy is recommended.