The ovine corticotropin-releasing hormone stimulation test in the differential diagnosis of adrenocorticotropic hormone-dependent cushing's syndrome.

OBJECTIVE

To determine the efficacy of the ovine corticotropin-releasing hormone (oCRH) stimulation test in distinguishing between adrenocorticotropic hormone (ACTH)-dependent types of Cushing's syndrome.

METHODS

The cortisol and ACTH responses to intravenously administered oCRH were determined in 64 patients with pituitary-dependent Cushing's syndrome and 13 patients with ectopic ACTH production.

RESULTS

Of the 64 patients with pituitary-dependent Cushing's syndrome, 57 (89%) had a positive ACTH response to administration of oCRH (an increase of 50% or more above baseline), and 56 (88%) had a positive cortisol response (an increase of 20% or more above baseline). One patient with an ectopic ACTH-secreting tumor had a false-positive cortisol response to administration of oCRH. Two patients with ectopic ACTH-secreting tumors had false-positive responses to both ACTH and cortisol after oCRH was administered. Because both these patients did not have hypercortisolemia at the time of testing, they were excluded from the statistical analysis. When analyzed on the basis of ACTH response alone, oCRH testing yielded a diagnostic sensitivity and specificity for the diagnosis of pituitary-dependent hypercortisolism of 89% and 100%, respectively. The positive predictive value was 100%, and the negative predictive value was 61%.

CONCLUSION

oCRH testing distinguished between the ectopic ACTH syndrome and pituitary-dependent hyper-cortisolism in most cases. Therefore, this test is a useful procedure in the diagnostic evaluation of ACTH-dependent forms of Cushing's syndrome.