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Difficulty: MediumEndocrinology and Metabolism

Match the following clinical presentations and laboratory profiles with their most likely underlying pathophysiologic diagnosis.

  • A 40-year-old woman with central obesity; elevated ACTH, elevated 24-hour urine free cortisol, and suppression of cortisol with high-dose dexamethasone.Pituitary corticotroph adenoma (Cushing disease)
  • A 60-year-old man with hemoptysis; elevated ACTH, elevated 24-hour urine free cortisol, and lack of cortisol suppression with high-dose dexamethasone.Ectopic ACTH-producing tumor (e.g., small cell lung carcinoma)
  • A 35-year-old woman with hypertension; suppressed ACTH, elevated 24-hour urine free cortisol, and lack of cortisol suppression with high-dose dexamethasone.Adrenal cortical adenoma
  • A 28-year-old woman with fatigue and hyperpigmentation; elevated ACTH, low morning cortisol, and elevated plasma renin activity.Autoimmune adrenalitis (Primary adrenal insufficiency)

Answer

Profile 1 matches Pituitary adenoma; Profile 2 matches Ectopic ACTH; Profile 3 matches Adrenal adenoma; Profile 4 matches Autoimmune adrenalitis.
The diagnosis of adrenal pathology relies heavily on understanding feedback loops. Cortisol exerts negative feedback on pituitary ACTH. If cortisol is high and ACTH is suppressed, the source is primary adrenal overproduction. If both cortisol and ACTH are high, the cause is ACTH-dependent (either central or ectopic). The high-dose dexamethasone test distinguishes between these: it suppresses pituitary sources but not ectopic autonomous sources. Conversely, if cortisol is low and ACTH is high, there is a primary failure of the adrenal gland. Elevated renin confirms the concurrent loss of aldosterone, pointing directly to primary adrenal insufficiency.

Step-by-Step Solution

1
Analyze the first patient presenting with elevated ACTH and cortisol suppression on high-dose dexamethasone.
Identified as Cushing disease (pituitary adenoma).
Pituitary corticotrophs retain partial sensitivity to glucocorticoid negative feedback, distinguishing them from ectopic sources.
2
Analyze the second patient with hemoptysis, elevated ACTH, and no dexamethasone suppression.
Identified as ectopic ACTH syndrome.
Non-pituitary tumors secrete ACTH autonomously and are completely resistant to dexamethasone negative feedback.
3
Analyze the third patient with elevated cortisol but suppressed ACTH.
Identified as primary adrenal adenoma.
An adrenal source of cortisol is ACTH-independent; the high autonomous cortisol levels suppress normal pituitary ACTH release.
4
Analyze the fourth patient with low cortisol, elevated ACTH, and elevated renin.
Identified as primary adrenal insufficiency.
Loss of adrenal tissue impairs both glucocorticoid and mineralocorticoid synthesis, leading to a lack of negative feedback (high ACTH) and volume depletion (high renin).

Key Concept

Hypothalamic-Pituitary-Adrenal Axis Feedback in Endocrine Pathologies
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Topics

Endocrinology and Metabolism

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