Table 2.

Summary of non-invasive strategies and reported diagnostic accuracies for differentiating Cushing’s Disease and ectopic ACTH syndrome (33, 83, 85–87).

Strategy	Positive Result Suggestive of CD	Sensitivity	Specificity
Individual tests
CRH Stimulation Test (83)	• >35% increase in ACTH concentration after CRH administration	90%	90%
High-Dose Dexamethasone Suppression Test (85)	• >50% suppression of cortisol concentrations	81%	66.70%
Pituitary MRI (33)	• Lesion compatible with a pituitary adenoma identified on standard MRI by two experienced radiologists	46-49%	33-50%
Combination tests
CRH Stimulation Test + Desmopressin Stimulation Test (86)	1. >17% increase in cortisol and >37% increase in ACTH following CRH stimulation 2. >18% increase in cortisol and >33% increase in ACTH following desmopressin stimulation	73%	93%
CRH Stimulation Test + Desmopressin Stimulation Test + Pituitary MRI (86)	1. >17% increase in cortisol and >37% increase in ACTH following CRH stimulation 2. >18% increase in cortisol and >33% increase in ACTH following desmopressin stimulation 3. Pituitary lesion compatible with a pituitary adenoma on MRI	49.70%	100%
CRH Stimulation Test + High-Dose Dexamethasone Suppression Test (87)	1. >72% increase in ACTH following CRH administration 2. >52.7% decrease in cortisol following dexamethasone administration	75.60%	100%

CD, Cushing’s Disease; CRH, corticotropin releasing hormone; ACTH, adrenocorticotropic hormone; MRI, magnetic resonance imaging.