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Difficulty: HardEndocrinology and Metabolism

Match each of the following hypothalamic-pituitary-adrenal axis laboratory profiles with the most likely underlying pathophysiologic diagnosis.

  • Elevated baseline serum cortisol, elevated ACTH, and cortisol suppression >50% following high-dose dexamethasone administration.Pituitary corticotroph adenoma (Cushing disease)
  • Elevated baseline serum cortisol, elevated ACTH, and lack of cortisol suppression following high-dose dexamethasone administration.Ectopic ACTH-secreting tumor
  • Elevated baseline serum cortisol, suppressed ACTH, and lack of cortisol suppression following high-dose dexamethasone administration.Cortisol-secreting adrenal adenoma
  • Low morning serum cortisol, elevated ACTH, hyponatremia, and hyperkalemia.Primary adrenal insufficiency
  • Low morning serum cortisol, decreased ACTH, hyponatremia, and normokalemia.Secondary adrenal insufficiency

Answer

The correct matches rely on identifying ACTH dependence, the presence of negative feedback in high-dose dexamethasone testing, and the integrity of the mineralocorticoid axis via serum potassium levels.
The correct pairings successfully utilize the principles of physiologic negative feedback mechanisms. Cortisol suppresses ACTH; pituitary adenomas retain partial sensitivity to this feedback (high-dose dexamethasone suppression), ectopic tumors do not. Furthermore, the renin-angiotensin-aldosterone axis operates independently of ACTH, distinguishing primary from secondary insufficiency via potassium levels.

Step-by-Step Solution

1
Evaluate hypercortisolism profiles based on ACTH levels to determine the source.
Suppressed ACTH indicates an ACTH-independent primary adrenal source. Elevated ACTH indicates an ACTH-dependent source (pituitary or ectopic).
Cortisol exerts negative feedback on the pituitary gland; high cortisol with concomitantly low ACTH isolates the pathology exclusively to the adrenal gland.
2
Differentiate ACTH-dependent hypercortisolism using the high-dose dexamethasone suppression test.
Suppression of cortisol identifies a pituitary adenoma (Cushing disease). Lack of suppression identifies an ectopic ACTH source.
Pituitary adenomas generally retain high-threshold negative feedback receptors, whereas ectopic tumors are completely autonomous.
3
Evaluate hypocortisolism profiles based on ACTH and electrolyte levels.
High ACTH with hyperkalemia indicates primary adrenal destruction. Low ACTH with normal potassium indicates pituitary failure.
Aldosterone secretion is primarily governed by the renin-angiotensin system and potassium levels, not ACTH. Therefore, secondary adrenal insufficiency spares mineralocorticoid function.

Key Concept

Differentiation of hypothalamic-pituitary-adrenal axis pathologies using ACTH levels, high-dose dexamethasone suppression testing, and mineralocorticoid markers.
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Topics

Endocrinology and Metabolism

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