ABSTRACT
Adrenocorticotropic hormone [ACTH] overproduction is usually due to a pituitary tumour which is often not visible on magnetic resonance imaging [MRI]. However, ACTH overproduction may be due to an ectopic source. This study aimed to develop a simple non-invasive technique to differentiate these sources. This study took place in King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia, and Sultan Qaboos University Hospital, Muscat, Oman, between 1988 and 2012. Serum cortisol levels were measured in nine patients with ACTH-dependent Cushing's syndrome before and during a 72-hour trial of octreotide. All patients underwent computed tomography [CT] scans. MRI scans were performed on six patients. CT scans were abnormal in three patients with ectopic ACTH production. MRI scans showed that three patients had pituitary microadenomas. Serum cortisol levels returned to normal in those with confirmed ectopic ACTH production. No response was found in the other six patients. A 72-hour trial of octreotide is recommended for patients with ACTH-dependent Cushing's syndrome and a normal pituitary MRI. This trial will be a useful alternative to petrosal sinus sampling