Plasma corticosteroids in Cushing's syndrome

Evaluation of steroid laboratory tests and adrenal gland imaging with radiocholesterol in the aetiological diagnosis of Cushing's syndrome

Basal values of the urinary excretion of 17-oxogenic steroids and serum levels of cortisol were not satisfactory in the differentiation of 'suspected' subjects from patients with true Cushing's syndrome. With an RIA method for serum cortisol determination, the overnight dexamethasone suppression test provided the most reliable single test in establishing adrenocortical hyperfunction. Thirty-five normal subjects, fifty-nine obese patients, thirteen 'suspected' patients, and thirteen patients with disease states other than Cushing's syndrome had suppressed values below 4.0 microgram/100 ml. None of the ten patients with Cushing's syndrome had a cortisol concentration less than 16.3 microgram/100 ml. Adrenal gland scintigraphy after radiocholesterol injection is a more valuable tool than the metyrapone test and the high-dose dexamethasone suppression test in the localization and differential diagnosis of adrenocortical lesions causing Cushing's syndrome. It obviates the need for angiographic procedure in the localization of adenomas. It is a reliable technique for identifying functioning adrenal remnants. We therefore propose a schedule for studying patients with suspected adrenocortical hyperfunction.

A rapid screening test for Cushing's syndrome

A combination test consisting of two parts, a single dose of dexamethasone and a (1-24) ACTH injection, has been used for the diagnosis of Cushing's syndrome. The test was performed by administering 1 mg dexamethasone orally at 11 p.m. on the first day and 25 IU synthetic ACTH i.v. at 8 a.m. on the second day. Plasma cortisol was determined at 8 a.m. on the first and second day and 1-1/2 and 2 hours after the ACTH injection. The test was performed in 33 patients with Cushing's syndrome and in 114 controls without adrenal disease. After dexamethasone administration alone, cortisol values frequently overlapped between patients with Cushing's syndrome and controls. The validity of the test was considerably improved by adding ACTH stimulation. The test procedure is recommended as a screening test for Cushing's syndrome in ambulatory practice.