ACTH Dependent Cushing’s Syndrome: A 72-Hour Trial of Octreotide will Identify Patients with Pituitary Dependent and Ectopic ACTH Overproduction

Aims: To determine whether the use of an octreotide suppression test will reliably distinguish pituitary from ectopic ACTH overproduction. Somatostatin receptors are expressed in NETs, but are downgraded in the pituitary as the result of hypercortisolaemia. Octreotide should therefore lower ACTH and cortisol levels in patients with NETs but not in patients with Cushing’s disease and pituitary tumors.

Methodology: A cross sectional study was performed in 13 patents with ACTH dependent Cushing’s (8 women, 5 men) with ages ranging between 21 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.

Results: The serum cortisol concentrations 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.

Conclusion: These results indicate that a short trial of octreotide will identify patients with ectopic disease as evidenced by a fall in serum cortisol levels whereas in those with Cushing’s disease and pituitary tumours serum cortisol levels remains unchanged.

Recommendation: We recommend all patients with ACTH dependent Cushing’s syndrome have an octreotide suppression test, even if the MRI shows an adenoma, so as to exclude the possibility of a pituitary incidentaloma in a patient with ectopic disease, or false localization from IPSS to the pituitary gland due to ectopic CRH secretion.