A patient has Addison's disease (primary adrenal insufficiency). Compared to secondary adrenal insufficiency (pituitary ACTH deficiency), which clinical feature is found in Addison's disease but NOT in secondary AI?

• A Hypoglycemia
• B Hyponatremia
• C Hyperpigmentation and hyperkalemia ✓
• D Fatigue and weakness

Explanation

In primary adrenal insufficiency (Addison's disease), both glucocorticoids and mineralocorticoids are deficient. Absent aldosterone causes Na+ wasting, hyperkalemia, and volume depletion. Loss of cortisol feedback elevates ACTH and MSH (from POMC cleavage), causing hyperpigmentation. In secondary AI, mineralocorticoid secretion (mainly regulated by angiotensin II, not ACTH) is preserved, so hyperkalemia and volume depletion are absent; hyperpigmentation is also absent because ACTH is low. Hyponatremia, hypoglycemia, fatigue, and weakness occur in both types.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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