Defining non-functioning adrenal adenomas on the basis of the occurrence of hypocortisolism after adrenalectomy

Background In patients with adrenal incidentalomas (AI), there is uncertainty on how to rule out hypercortisolism. The occurrence of post-surgical (unilateral adrenalectomy) hypocortisolism (PSH) has been proposed as a proof of the presence of a pre-surgical hypercortisolism in AI patients. The aim of this study was to define the thresholds of cortisol level after 1 mg overnight dexamethasone suppression test (F-1mgDST), urinary free cortisol (UFC), midnight serum cortisol (MSC) and adrenocorticotroph hormone (ACTH) able to predict the absence of PSH in AI patients undergoing surgery. Methods In 60 patients who underwent AI excision, cortisol secretion was assessed by low-dose corticotropin stimulation test or insulin tolerance test, when needed. We searched for the lowest pre-surgical value of F-1mgDST, UFC and MSC and the highest value for ACTH in AI patients with PSH as indexes of normal cortisol secretion. Results the lowest values of F-1mgDST, UFC and MSC and the highest value for ACTH in PSH patients were 1.2 µg/dL (33 nmol/L), 10.4 µg/24h (29 nmol/24h), 1.2 µg/dL (33 nmol/L) and 26.9 pg/ml (6 pmol/L), respectively, but only F-1mgDST <1.2 µg/dL (33 nmol/L) was able to predict the absence of PSH. Among AI patients with F-1mgDST <1.2 µg/dL (33 nmol/L) no subjects had diabetes mellitus and/or metabolic syndrome and these subjects tended to have a better metabolic profile than those with F-1mgDST ≥1.2 µg/dL (33nmol/L) Conclusion in AI patients a F-1mgDST <1.2 μg/dL (33 nmol/L) rules out PSH and could be used to exclude hypercortisolism in AI patients.