Cushing's syndrome. How to pinpoint and treat the underlying cause.

In addition to prolonged glucocorticoid therapy (not discussed here), at least five other conditions cause Cushing's syndrome. They are excessive corticotropin secretion by the pituitary gland (which results in Cushing's disease), ectopic production of corticotropin by malignant nonpituitary tumors, benign adrenal adenoma, adrenal carcinoma, and primary adrenocortical nodular dysplasia. Each can be distinguished by a specific pathophysiologic process that triggers the adrenal glands to overproduce glucocorticoids. At present, diagnosis of Cushing's syndrome or disease relies heavily on the dexamethasone (Decadron, Hexadrol) suppression test. After diagnosis, other studies, including computed tomography, magnetic resonance imaging, and corticotropin radioimmunoassay, can be used to localize the site of the lesion. Treatment, of course, depends on the underlying cause.