Multicentre 30-year data on the 4-mg intravenous dexamethasone suppression test in the diagnosis of cushing

Caroline Jung; Derbyshire aresa M; Niyati Jauhar; Daniel Bennett; Topliss Duncan J; Reetu Gogna; Nikola Markovic; Burgess John R; Inder Warrick J

doi:10.1530/endoabs.110.P847

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Endocrine Abstracts (2025) 110 P847 | DOI: 10.1530/endoabs.110.P847

ECEESPE2025 Poster Presentations Pituitary, Neuroendocrinology and Puberty (162 abstracts)

Multicentre 30-year data on the 4-mg intravenous dexamethasone suppression test in the diagnosis of cushing’s syndrome

Caroline Jung ^1,2 , Maresa M Derbyshire ¹ , Niyati Jauhar ³ , Daniel Bennett ³ , Duncan J Topliss ^3,4 , Reetu Gogna ⁵ , Nikola Markovic ⁵ , John R Burgess ^5,6 & Warrick J Inder ^7,8

Author affiliations

¹St Vincent’s Hospital, Endocrinology and Diabetes, Melbourne, Australia; ²The University of Melbourne, Melbourne, Australia; ³Alfred Health, Melbourne, Australia; ⁴Monash University, Melbourne, Australia; ⁵Royal Hobart Hospital, Hobart, Australia; ⁶University of Tasmania, Hobart, Australia; ⁷Princess Alexandra Hospital, Brisbane, Australia; ⁸The University of Queensland, Brisbane, Australia

JOINT737

Objective: Differentiating Cushing’s syndrome (CS) from Pseudo-Cushing’s (Low Probability of Cushing’s [LPC]) may be difficult. We evaluated the 4-mg intravenous dexamethasone suppression test (IVDST) to differentiate CS from normal subjects and LPC, and to define responses in CS of various causes.

Design: Data from 140 patients with surgically confirmed Cushing’s Disease (CD) who underwent IVDST(s) before their first pituitary operation, five with ectopic ACTH syndrome (EAS), 28 with adrenal Cushing’s (AC), and 111 with LPC, from four tertiary hospitals between 1995 to 2024 were retrospectively evaluated. Thirty-two control subjects (normal and overweight/obese participants with or without type 2 diabetes) were previously studied. Dexamethasone was infused at 1 mg/h for 4h. Plasma cortisol and ACTH were measured at -60 min (baseline), -5 min, +3h, +4h, +5h and at +23h and +23.5h on Day 2.

Results: The cortisol at baseline, +5h and mean of Day 2 levels are shown in the table. Day 2 cortisol level of >130 nmol/l diagnosed CS with 95% sensitivity and 87% specificity. In the CD group, a partial suppression of cortisol at +5h to less than 70% of the baseline was demonstrated in 97%, with rebound hypercortisolism on Day 2 in 91% of patients. Day 2 cortisol levels were >130 nmol/l in 100% of EAS and 93% of AC. In 19 of 111 patients with LPC, Day 2 cortisol overlapped with CS. Control subjects showed marked suppression of cortisol which was maintained on Day 2.


		Cortisol (nmol/L) mean (range)
	Baseline	+5h	Day 2 mean
CD	600 (226-1442)	182 (33-826)	476 (19-2177)
EAS	2403 (1120-3962)	2403 (841-3082)	2517 (1120-4089)
AC	507 (249-1453)	474 (95-1414)	501 (96-1807)
LPC	431 (94-1364)	97 (19-285)	82 (21-557)
Control	405 (252-651)	56 (23-108)	20 (7-48)

Conclusion: IVDST has high sensitivity for diagnosis of CS. We suggest false negative results may occur when IVDST is performed during mild or subclinical disease or during quiescent phase. The specificity of 87% is lower than previously reported (96%), highlighting the importance of long-term follow-up of LPC. Because only five EAS were studied, the utility of IVDST in differential diagnosis of ACTH-dependent CS is uncertain.