THE PROBLEM of separating adrenocortical hyperplasia, adenoma or carcinoma in the patient with Cushing's syndrome prior to surgery is of considerable importance and has stimulated the development of certain differential laboratory tests. The measurement of urinary hydroxycorticoids is a practical representation of the secretion of cortisol.1 Liddle 2 has shown that in normal individuals the excretion of 17-hydroxycorticoids will be suppressed by small amounts of a potent synthetic steroid, dexamethasone. Cortisol production in the presence of adrenocortical hyperplasia will not be suppressed by the dose of 2 to 3 mg of dexamethasone, but will be reduced to negligible levels by the administration of 8 to 9 mg a day; there will be no suppression in the case of adrenocortical neoplasia. The responsiveness of the adenoma to corticotropin-zinc hydroxide, as measured by cortisol production, is said to distinguish it from a carcinoma,3 but this differentiation has been inconstant.
KATZ J. Failure of Dexamethasone Suppression in Adrenal Hyperplasia. Arch Intern Med. 1966;118(3):265-269. doi:10.1001/archinte.1966.00290150079014