Experience with a rapid oral metyrapone test and the plasma ACTH content in determining the cause of Cushing's syndrome

A rapid oral metyrapone test (0.5 Gm. every hour for six doses) and a 4 p.m. plasma ACTH bioassay were performed in 20 consecutive patients with Cushing's syndrome. At surgery, 11 had adrenocortical hyperplasia, six had an adrenocortical adenoma, and three had an adrenocortical carcinoma. None had clinical findings of the ectopic ACTH syndrome and all have been followed at least two years postoperatively. All but one patient with hyperplasia doubled their urinary 17-hydroxycorticosteroids the day of the rapid oral metyrapone test; those with adrenocortical tumors showed no significant rise. Eight patients with hyperplasia had 4 p.m. ACTH measurements and all showed detectable plasma ACTH. Six of those with tumors also had a bioassay and in none was the ACTH detectable. The rapid oral metyrapone test and measurement of the plasma ACTH level are extremely useful in determining the cause of Cushing's syndrome, and considerably reduce the number of hospital days required.