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Difficulty: HardEndocrinology and Metabolism

Match the following clinical and laboratory profiles of patients presenting with suspected hypercortisolism to their most likely underlying etiology.

  • Elevated 24-hour urine free cortisol, elevated plasma ACTH, and >50% suppression of serum cortisol during a high-dose dexamethasone suppression testPituitary ACTH-secreting adenoma (Cushing disease)
  • Elevated 24-hour urine free cortisol, markedly elevated plasma ACTH, and lack of serum cortisol suppression during a high-dose dexamethasone suppression testEctopic ACTH secretion (e.g., neuroendocrine tumor)
  • Elevated 24-hour urine free cortisol, suppressed plasma ACTH, and lack of serum cortisol suppression during a high-dose dexamethasone suppression testPrimary adrenal adenoma or carcinoma
  • Low 24-hour urine free cortisol, suppressed morning serum cortisol, suppressed plasma ACTH, and prominent cushingoid physical featuresExogenous synthetic glucocorticoid use (e.g., dexamethasone)
  • Mildly elevated 24-hour urine free cortisol, lack of suppression with overnight low-dose dexamethasone, but normal midnight salivary cortisolPhysiologic hypercortisolism (Pseudo-Cushing syndrome)

Answer

Profile 1 matches Pituitary ACTH-secreting adenoma; Profile 2 matches Ectopic ACTH secretion; Profile 3 matches Primary adrenal adenoma; Profile 4 matches Exogenous synthetic glucocorticoid use; Profile 5 matches Physiologic hypercortisolism.
The correct matches follow the standard endocrine diagnostic algorithm for hypercortisolism. First, true hypercortisolism must be confirmed (or refuted, as in exogenous dexamethasone use where endogenous levels are low, or pseudo-Cushing where diurnal rhythm is intact). Second, ACTH levels determine if the source is ACTH-dependent (high/normal ACTH) or ACTH-independent (suppressed ACTH, implying an adrenal source). Third, high-dose dexamethasone suppression differentiates the ACTH-dependent causes: pituitary sources (Cushing disease) typically suppress, whereas ectopic sources do not.

Step-by-Step Solution

1
Analyze Profile 4 which presents with paradoxical findings of Cushingoid features but low cortisol levels.
Identifies Exogenous synthetic glucocorticoid use.
Dexamethasone suppresses endogenous ACTH and cortisol but is not detected on standard cortisol assays.
2
Differentiate between ACTH-dependent and ACTH-independent true Cushing syndrome for Profiles 1, 2, and 3.
Profile 3 has suppressed ACTH, indicating an ACTH-independent source (Primary adrenal adenoma).
Autonomous cortisol secretion from the adrenal glands suppresses pituitary ACTH via negative feedback.
3
Differentiate the ACTH-dependent causes (Profiles 1 and 2) using the high-dose dexamethasone suppression test.
Profile 1 suppresses (Pituitary adenoma), while Profile 2 does not suppress (Ectopic ACTH).
Pituitary adenomas retain some negative feedback sensitivity at high dexamethasone doses, whereas ectopic sources typically lack functional glucocorticoid receptors.
4
Analyze Profile 5 for borderline findings in the initial screening tests.
Identifies Physiologic hypercortisolism (Pseudo-Cushing syndrome).
Normal midnight salivary cortisol indicates an intact diurnal rhythm, pointing away from pathological Cushing syndrome.

Key Concept

Diagnostic algorithm for Cushing syndrome and related hypercortisolemic states
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Topics

Endocrinology and Metabolism

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