Cushing's syndrome: A prospective study of diagnostic methods

Abstract

In this systematic survey of patients with various features of hypercortisolism, 39 patients were found to have at least one elevated corticosteroid measurement. Only 24 were proved to have Cushing's syndrome; the condition in the remaining 15 patients was termed “Cushingoid obesity.” Plasma cortisol was the least helpful assay parameter. In the patients with Cushing's syndrome, 25 per cent of the 8 AM and 8 PM values were normal, and in the patients with Cushingoid obesity, 47 per cent of the values were spuriously high. The presence or absence of diagonal variation was of little diagnostic significance. After overnight dexamethasone, only one patient with Cushing's syndrome showed normal suppression, however, 53 per cent of the patients with Cushingold obesity falled to show adequate suppression. Routine 17-hydroxycorticosteroid (17-OHCS) and 17-oxogenic steroid (17-KGS) assays also proved to be relatively poor diagnostic parameters. Of the patients with Cushing's syndrome, 17 per cent had normal levels of excretion, and of the patients with “Cushingoid obesity,” the 17-OHCS levels were falsely elevated in 53 per cent and the 17-KGS levels in 62 per cent. During high dosage dexamethasone therapy, none of the patients with Cushing's syndrome showed adequate suppression, however, in all the patients with Cushingoid obesity suppression was normal. Free cortisol excretion provided the most definitive index of adrenocortical hyperfunction. Urinary free cortisol was increased only in the 24 patients with Cushing's syndrome and was not adequately suppressible with dexamethasone. There were no false elevations in any of the 15 patients with Cushingoid obesity, in all of whom suppression was normal with dexamethasone.