Suppression of ACTH by Cortisol in Dexamethasone-Nonsuppressible Cushing's Disease

Abstract

THE high-dose (8 mg per day) dexamethasone suppression test, as described originally by Liddle,¹ has come to be accepted as one of the most reliable means of identifying Gushing's syndrome due to excessive pituitary ACTH secretion (Cushing's disease). However, a few cases of hypercortisolism with bilateral adrenocortical hyperplasia have been described with resistance to dexamethasone suppression.^{2 3 4 5 6 7 8 9} In 1967, Linn et al.¹⁰ found two patients with Cushing's disease who, before adrenalectomy, required large doses (32 mg per day) of dexamethasone to suppress urinary 17-hydroxycorticosteroids to less than 50 per cent of base-line values. These observations were interpreted as indicating that in . . .