Abstract #1371676: A 72-Hour Trial of Octreotide Reliably Distinguishes Between Pituitary and Ectopic ACTH Overproduction in Cushing’s Syndrome

Abstract

To determine whether the use of an octreotide suppression test will reliably distinguish pituitary from ectopic ACTH overproduction. Somatostatin receptors are expressed in neuroendocrine tumors (NETs), but in Cushing’s disease these are downgraded as the result of hypercortsiolaemia. Octreotide should therefore lower ACTH and cortisol levels in patients with non-pituitary NETs but not in patients with Cushing’s disease and an ACTH producing pituitary tumor. At present the gold standard procedure for distinguishing pituitary from ectopic ACTH overproduction is Inferior petrosal sinus sampling (IPSS) with multiple ACTH measurements. However, this procedure is invasive, expensive and not widely available in many countries. On the other hand, a short trial of octreotide is safe, simple and much cheaper. 13 patents with ACTH dependent Cushing’s syndrome (CS) (8 women, 5 men) with ages ranging between 16 to 40 years were studied. Serum cortisol concentrations were measured at 0800 hrs before and during the administration of Octreotide at a dosage of 100 mcg subcutaneously every 8 hours for 72 hours. The serum cortisol concentrations were suppressed and returned to normal in 4 patients who were later documented to have ectopic disease, two with typical bronchial carcinoids and two with pancreatic NETs and metastatic disease. The other 9 patients had no suppression in serum cortisol concentrations and were documented later to have pituitary tumours. We recommend that a 72-hour octreotide suppression test be given to all patients with ACTH-dependent CS even if the MRI shows an adenoma, so as to exclude the possibility of a pituitary incidentaloma in a patient with ectopic disease.