Plasma corticosteroids in Cushing's syndrome.

Circadian rhythm of plasma corticosteroids and the plasma corticosteroid response during both the 4-hour ACTH test and the 1 mg dexamethasone suppression test (1 mg-DST) have been studied in seven cases of Cushing's syndrome. The early morning baseline values were normal in five out of seven, but elevated in all cases at 10 p.m. The plasma corticosteroid response during the ACTH test was increased in five cases (Morbus Cushing 3, adrenal adenoma 1, ectopic ACTH syndrome 1), normal in one (Morbus Cushing) and subnormal in one (adrenal carcinoma). In contrast to plasma corticosteroid values of less than 6.2 μg/100 ml during 1 mg-DST in patients without Cushing's syndrome, no values lower than 8.4 μg/100 ml were obtained on 14 occasions in six cases of Cushing's syndrome. Despite sources of error these procedures, particularly the 1 mg-DST, are valuable in the diagnosis of Cushing's syndrome. A striking agreement between urinary excretion of 17-KGS and plasma corticosteroids was obtained during the DST of Liddle. Greatly elevated baseline values of plasma corticosteroids and a subnormal response during the 4-hour ACTH test suggest the presence of extra-pituitary spontaneous Cushing's syndrome.