Latest diagnostic approaches to determine the cause of ACTH-dependent Cushing's syndrome, in the South African setting

Abstract

A case of a 50-year-old woman who was referred for the evaluation of possible ACTH-dependent Cushing's syndrome (CS) is described. The localisation of ACTH-dependent CS remains difficult despite many advances in diagnostic approaches. No single test can accurately determine the location of ACTH excess and therefore a combination of non-invasive imaging, stimulation and suppression tests are advised. The recent advances, current utility and pitfalls of each of these tests are reviewed. If non-invasive tests fail to confidently localise the source of ACTH excess, inferior petrosal sinus sampling (IPSS) should follow. Recent advances improving the diagnostic accuracy of IPSS, such as DDAVP stimulation and simultaneous sampling for prolactin is discussed. Where ectopic ACTH production is suspected, newer nuclear medicine techniques, such as somatostatin receptor imaging that recently became available in South Africa, can be utilised. The role of nuclear medicine imaging in identifying ectopic ACTH production is discussed briefly.