Corticotropin-releasing hormone

The diagnostic accuracy of the CRH test was compared with that of the oral "high-dose" dexamethasone suppression test according to Liddle in the differential-diagnosis of Cushing's syndrome. A false-negative response to CRH was present in 9% (2 of 22) of patients with pituitary-dependent Cushing's disease and to "high-dose" dexamethasone in 11% (2 of 18). All three patients with Cushing's syndrome due to an adrenal adenoma were unresponsive to both CRH and dexamethasone. The only patient with ectopic ACTH secretion in this series had a false-positive response of ACTH to dexamethasone and no response of ACTH to CRH. Simultaneous failure of both tests to indicate the cause of Cushing's syndrome did not occur in this series, except in one patient with Cushing's disease and overt macronodular hyperplasia. We conclude that the diagnostic accuracy of the CRH test in the work-up of the patient with Cushing's syndrome is comparable to that of the Liddle test and that the highest discriminatory score in the differentialdiagnosis of Cushing's syndrome is achieved by performing both a CRH test and a "high-dose" dexamethasone test.