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Difficulty: MediumEndocrinology and Metabolism

A 4th-year medical student is reviewing the endocrine laboratory profiles of four distinct patients being evaluated for suspected adrenal pathology. Match each patient's serum laboratory and dynamic testing profile to the most likely underlying etiology.

  • Low 8:00 AM serum cortisol, high ACTH, hyponatremia, and hyperkalemiaAutoimmune destruction of the adrenal cortex
  • Low 8:00 AM serum cortisol, low ACTH, normal serum sodium and potassiumAbrupt cessation of long-term prednisone therapy
  • High 8:00 AM serum cortisol, high ACTH, cortisol suppresses >50%>50\% with high-dose dexamethasoneACTH-secreting pituitary microadenoma
  • High 8:00 AM serum cortisol, high ACTH, cortisol does NOT suppress with high-dose dexamethasoneEctopic ACTH secretion from a pulmonary malignancy

Answer

Primary adrenal insufficiency features low cortisol, high ACTH, and electrolyte abnormalities; secondary adrenal insufficiency features low cortisol and ACTH with normal electrolytes; pituitary adenomas feature high cortisol/ACTH that suppress with high-dose dexamethasone; and ectopic ACTH secretion features high cortisol/ACTH that do not suppress.
Each laboratory profile distinctly maps to the underlying pathophysiology of the HPA axis, specifically regarding feedback loops and mineralocorticoid preservation.

Step-by-Step Solution

1
Analyze the patients with low 8:00 AM cortisol to identify the cause of adrenal insufficiency.
Differentiate based on ACTH and electrolyte levels.
High ACTH and abnormal electrolytes indicate primary adrenal failure. Low ACTH and normal electrolytes indicate secondary failure.
2
Analyze the patients with high 8:00 AM cortisol and high ACTH to identify the cause of ACTH-dependent Cushing syndrome.
Differentiate using the high-dose dexamethasone suppression test.
Pituitary sources retain partial feedback sensitivity and suppress; ectopic sources are completely autonomous and do not suppress.

Key Concept

Diagnosis and differentiation of adrenal insufficiency and Cushing syndrome using ACTH levels, electrolyte panels, and dexamethasone suppression testing.
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Topics

Endocrinology and Metabolism

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