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

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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 . . .