Background: The Endocrine Society clinical practice guidelines suggest use of the 1 mg overnight dexamethasone suppression test (ONDST) to screen for cortisol excess in patients with adrenal incidentalomas, followed by the 48-h, 2 mg/day, low-dose dexamethasone-suppression test (LDDST), to confirm a positive result. Visceral fat accumulates in cortisol-excess and accounts for increased cardiovascular risk. In this study, we investigate whether the LDDST offers additional information to the ONDST, and whether there is an association between cortisol excess and the visceral:subcutaneous fat (V:S) ratios in patients with adrenal incidentaloma.
Method: A retrospective, observational study was performed to collect demographic and clinical data on 137 patients diagnosed with incidentalomas. A full clinical and endocrine work up was performed, including either an ONDST or LDDST, or in some patients both tests. The V:S ratio was calculated by two observers in duplicate on a CT workstation by subtraction of the subcutaneous from visceral fat area. Inter-observer reproducibility was 98%.
Results: Of 76/137 (55%) patients had either a positive ONDST and /or LDDST (cortisol>50 nmol/l). Of 60/103 (58%) had a positive ONDST whilst 45/63 (71%) patients had a positive LDDST. Twenty-nine patients had both tests done of which 20/21 patients with a cortisol level >70 nmol/l after the ONDST had a positive LDDST, whilst the other eight patients, all of which had a cortisol level <70 nmol/l post-ONDST, had a negative LDDST. Correlation analysis revealed a significant positive correlation between cortisol levels for both tests (r=0.78; P<0.001). There was a significant increase in mean V:S ratio between subjects who suppressed (<50 nmol/l) and those who did not, 0.8 vs 1.4 (95% CI 0.150.98; P=0.008).
Conclusion: In patients with adrenal incidentaloma and a cortisol level of >70 nmol/l after an ONDST, the LDDST is usually positive and does not offer more information. Furthermore, we show, for the first time, that patients with a positive ONDST have a significantly increased V:S ratio that very likely contributes to the worsened cardiometabolic profile that is well-described in these patients.