The usefulness of the combined high-dose dexamethasone suppression test and desmopressin stimulation test in establishing the source of ACTH secretion in ACTH-dependent Cushing's syndrome.

Bilateral inferior petrosal sinus sampling (BIPSS) is the current gold standard test for differentially diagnosing ACTH-dependent Cushing's syndrome (CS). However, BIPSS is an invasive procedure, and its availability is limited. We retrospectively analysed the 24-hour urinary free cortisol (UFC) level during the high-dose dexamethasone suppression test (HDDST) and plasma ACTH/cortisol levels after the desmopressin stimulation test (DDAVP test) in subjects with confirmed Cushing's disease (CD) (n = 92) and ectopic ACTH-dependent CS (EAS) (n = 16), and evaluated the positive predictive value (PPV) of the two combined-tests in the aetiological diagnosis of ACTH-dependent CS. The percent changes in UFC levels after the HDDST and in ACTH/cortisol levels after DDAVP administration relative to the corresponding basal levels and the area under the receiver operating characteristic (ROC) curve (AUC) were analysed. UFC suppression below 62.7% suggested a pituitary origin with a sensitivity (SE) of 80% (95% CI: 70-88) and a specificity (SP) of 80% (95% CI: 52-96). A threshold increase in the ACTH level after DDAVP stimulation of 44.6% identified CD with an SE of 91% (95% CI: 83-97) and an SP of 75% (95% CI: 48-93). The combination of both tests yielded an SE of 95.5% and PPV of 98.4% for CD, and significantly improved the efficiency of the differential diagnosis between CD and EAS. These dual non-invasive endocrine tests may substantially reduce the need for BIPSS in the etiological investigation of ACTH-dependent CS.

A Case of Bilateral Macronodular Adrenal Hyperplasia with Cushing's Syndrome Treated by Unilateral Adrenalectomy / 대한내분비학회지

In order to differentiate the causes of Cushing's syndrome; whether it is pituitary or adrenal-dependent, a high dose dexamethasone suppression test is usually performed but this does not always correlated with the imaging diagnosis. We report a case of bilateral macronodular adrenal hyperplasia, which was thought to be independent to adrenocorticotrophin (ACTH) stimulation. At first we thought it was pituitary-dependent Cushing's syndrome, due to its suppression by high dose dexamethasone. However, we found no abnormal findings on the brain sella magnetic resonance image (MRI). A significant finding, however, we found bilateral adrenal masses on the abdominal computed tomography (CT). We performed percutaneous selective adrenal venous sampling (PSAVS), and confirmed hypercortisolism of the left adrenal mass only. Therefore, we decided to remove the left adrenal gland to preserve the residual function of the right adrenal gland. After the left adrenalectomy, the patient became normotensive, and their buffalo hump disappeared, and her 24 hour urinary free cortisol level returned to normal.