Excess and prolonged endogenous glucocorticoid production, whether ACTH-dependent or ACTH-independent, results in the classic clinical and biochemical picture of CS. The diagnosis requires demonstration of an increased cortisol secretion rate, best achieved by determination of 24-h UFC excretion levels. In mild or confusing cases, distinction from the hypercortisolism of pseudo-Cushing states may prove difficult. A dexamethasone/ oCRH test or close monitoring of the patient for a few months may be helpful. Most cases of primary adrenal CS can be ruled out by undetectable basal and/or CRH-stimu-lated plasma ACTH and negative adrenal imaging procedures. ACTH-depen-dent CS can then be differentiated by an oCRH test and imaging procedures. A discrete pituitary lesion on gadolinium-enhanced MRI and a standard oCRH with stimulated ACTH levels consistent with such a lesion are usually sufficient to proceed to transsphenoidal surgery. If no visible pituitary lesion is present, or if the oCRH test is equivocal, bilateral simultaneous inferior petrosal or cavernous sinus sampling with oCRH administration are necessary to distinguish between a pituitary and an ectopic ACTH source. Surgical ablation is the treatment of choice for all types of CS. In the approx 5%-10% of cases with CD in whom transsphenoidal surgery fails and in the 5% of cases in whom the disease recurs, repeat transsphenoidal surgery or radiation therapy in association with mitotane treatment are reasonable alternatives. Bilateral adrenalectomy effectively cures hypercortisolism if resection of the ACTH-secreting tumor is unsuccessful and radiation/medical therapy fail.

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