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Difficulty: HardEndocrinology and Metabolism

Match each set of laboratory findings from the evaluation of the hypothalamic-pituitary-adrenal (HPA) axis to the most likely underlying pathophysiologic diagnosis.

  • Low morning serum cortisol, elevated plasma ACTH, and absent cortisol rise following cosyntropin administrationPrimary adrenal insufficiency (e.g., autoimmune adrenalitis)
  • Low morning serum cortisol, inappropriately low-normal plasma ACTH, and blunted cortisol rise following cosyntropin administrationSecondary adrenal insufficiency (e.g., chronic exogenous glucocorticoids)
  • Elevated 24-hour urine free cortisol, undetectable plasma ACTH, and failure of serum cortisol to suppress with 8 mg dexamethasoneACTH-independent hypercortisolism (e.g., adrenal adenoma)
  • Elevated 24-hour urine free cortisol, normal-to-high plasma ACTH, and >50% suppression of serum cortisol with 8 mg dexamethasonePituitary corticotroph adenoma (Cushing disease)
  • Elevated 24-hour urine free cortisol, markedly elevated plasma ACTH, and failure of serum cortisol to suppress with 8 mg dexamethasoneEctopic ACTH secretion (e.g., small cell lung carcinoma)

Answer

The correct matches align the laboratory patterns with their respective HPA axis defects: primary adrenal insufficiency (L1 to R1), secondary adrenal insufficiency (L2 to R2), ACTH-independent hypercortisolism (L3 to R3), Cushing disease (L4 to R4), and ectopic ACTH secretion (L5 to R5).
Matching these conditions requires tracing physiologic negative feedback loops. In primary adrenal failure, lack of cortisol removes negative feedback, elevating ACTH. In secondary failure, the absence of ACTH causes downstream cortisol deficiency and subsequent adrenal atrophy. In hypercortisolism, the source is isolated by checking ACTH dependence (adrenal tumors suppress ACTH; central/ectopic sources drive it) and checking the response to high-dose dexamethasone (pituitary adenomas retain limited feedback sensitivity; ectopic tumors do not).

Step-by-Step Solution

1
Analyze cortisol and ACTH levels to determine the primary defect in hypocortisolic states.
Low cortisol with elevated ACTH indicates a primary adrenal defect. Low cortisol with inappropriately normal or low ACTH indicates a central (pituitary/hypothalamic) defect.
Intact feedback mechanisms will cause ACTH to rise if the adrenal gland fails, but ACTH will be inappropriately low if the pituitary is the source of the failure.
2
Evaluate the cosyntropin (synthetic ACTH) stimulation test results for the hypocortisolic patterns.
An absent response confirms adrenal destruction (primary). A blunted response in the setting of low ACTH confirms adrenal atrophy secondary to chronic lack of endogenous ACTH stimulation.
Cosyntropin directly stimulates the adrenal cortex. A diseased or chronically atrophied adrenal cortex cannot mount a normal cortisol response.
3
Analyze baseline ACTH levels in the hypercortisolic states.
Suppressed ACTH indicates ACTH-independent hypercortisolism, typically an adrenal source. Normal to high ACTH indicates ACTH-dependent hypercortisolism, either from a pituitary or ectopic source.
Autonomous cortisol production by the adrenal gland exerts negative feedback, fully suppressing normal pituitary ACTH.
4
Use the high-dose dexamethasone suppression test to differentiate ACTH-dependent hypercortisolism causes.
Suppression of cortisol confirms a pituitary source which retains partial feedback sensitivity. Lack of suppression confirms an ectopic source which is completely autonomous.
Pituitary adenomas maintain some functional glucocorticoid receptors and respond to high doses of exogenous steroids, while ectopic neuroendocrine tumors do not.

Key Concept

Diagnostic interpretation of the Hypothalamic-Pituitary-Adrenal (HPA) Axis
Estimated Time:2m 0s
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Topics

Endocrinology and Metabolism

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