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Difficulty: MediumEndocrinology and Metabolism

Match the following endocrine laboratory profiles with their most likely underlying pathophysiologic diagnosis.

  • Primary adrenal insufficiencyLow morning cortisol, markedly elevated ACTH, increased plasma renin activity, and low aldosterone.
  • Secondary adrenal insufficiencyLow morning cortisol, decreased or inappropriately normal ACTH, normal plasma renin activity, and normal aldosterone.
  • Cushing diseaseElevated 24-hour urine free cortisol, elevated ACTH, and cortisol suppression following a high-dose dexamethasone test.
  • Ectopic ACTH syndromeMarkedly elevated 24-hour urine free cortisol, significantly elevated ACTH, profound hypokalemia, and lack of cortisol suppression following a high-dose dexamethasone test.

Answer

Primary adrenal insufficiency matches with elevated ACTH, low cortisol, high renin, and low aldosterone. Secondary adrenal insufficiency matches with low ACTH, low cortisol, normal renin, and normal aldosterone. Cushing disease matches with elevated ACTH, high cortisol, and successful high-dose dexamethasone suppression. Ectopic ACTH syndrome matches with very high ACTH, high cortisol, severe hypokalemia, and failure of high-dose dexamethasone suppression.
The correct matches align the pathophysiology of the adrenal axis with the expected laboratory results. Primary failures affect all cortical zones, elevating trophic hormones like ACTH and renin. Secondary failures affect only ACTH-dependent zones. Cushing disease retains some feedback sensitivity, while ectopic sources do not.

Step-by-Step Solution

1
Analyze the cortisol and ACTH levels to determine if the pathology is a state of hypercortisolism or hypocortisolism, and whether it is ACTH-dependent or ACTH-independent.
Cortisol and ACTH profiles separate the profiles into two hypocortisolism states and two hypercortisolism states.
This is the primary branch point in evaluating adrenal cortex disorders.
2
For the hypocortisolism states, evaluate the mineralocorticoid axis (aldosterone and plasma renin activity).
Abnormal aldosterone and renin indicate primary adrenal failure, while normal aldosterone and renin indicate a secondary (pituitary) etiology.
Aldosterone is regulated by the renin-angiotensin-aldosterone system, which remains intact if only the pituitary fails.
3
For the ACTH-dependent hypercortisolism states, evaluate the response to the high-dose dexamethasone suppression test.
Suppression indicates a pituitary adenoma (Cushing disease), while a lack of suppression indicates an ectopic ACTH source.
Pituitary adenomas retain partial negative feedback mechanisms, whereas ectopic tumors are completely autonomous.

Key Concept

Differentiating adrenal cortex disorders based on hypothalamic-pituitary-adrenal axis feedback and mineralocorticoid regulation.
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Topics

Endocrinology and Metabolism

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