A 45-year-old man with confirmed Addison disease is being counseled about the clinical and biochemical features of his condition. Which of the following statements about Addison disease is NOT correct?

Explanation

## Biochemical and Clinical Features of Addison Disease ### Pathophysiology of Key Features | Feature | Mechanism | Correct/Incorrect | |---------|-----------|-------------------| | Hyperpigmentation | ACTH and POMC-derived peptides (including α-MSH) stimulate melanocytes | ✓ Correct | | Hyponatremia | Aldosterone deficiency → ↓ Na⁺ reabsorption in collecting duct; ADH secretion → water retention | ✓ Correct | | Hypoglycemia | Cortisol deficiency → ↓ gluconeogenesis, ↓ glycogenolysis, relative ↑ insulin effect | ✓ Correct (mechanism is real, even if wording is imprecise) | | Hyperkalemia | **Attributed to cortisol deficiency** in Option D — this is **NOT correct** as the primary mechanism | ✗ **Incorrect** | ### Why Option D is NOT Correct **Key Point:** Hyperkalemia in Addison disease is primarily due to **aldosterone deficiency**, NOT cortisol deficiency. - **Aldosterone** is the principal mineralocorticoid responsible for: - Stimulating Na⁺/K⁺-ATPase in the principal cells of the collecting duct - Promoting **potassium secretion** into the tubular lumen - Promoting **sodium reabsorption** - In Addison disease (primary adrenal insufficiency), **both cortisol and aldosterone** are deficient - The **hyperkalemia** results from **aldosterone deficiency** → impaired K⁺ secretion in the distal tubule and collecting duct - Option D incorrectly attributes hyperkalemia to **cortisol deficiency** — cortisol has only weak mineralocorticoid activity and is NOT the primary regulator of potassium excretion **Clinical Pearl:** Cortisol deficiency alone (as in secondary adrenal insufficiency, where ACTH is low but the renin-angiotensin-aldosterone axis is intact) does **NOT** typically cause significant hyperkalemia, because aldosterone secretion remains functional. This distinguishes primary from secondary adrenal insufficiency. *(Harrison's Principles of Internal Medicine, 21st ed., Chapter on Adrenal Insufficiency)* **High-Yield:** The classic electrolyte triad in Addison disease (primary adrenal insufficiency): 1. **Hyponatremia** — aldosterone deficiency → renal Na⁺ wasting 2. **Hyperkalemia** — **aldosterone deficiency** → impaired K⁺ excretion (NOT cortisol deficiency) 3. **Hypoglycemia** — cortisol deficiency → loss of gluconeogenesis and glycogenolysis **Mnemonic — Addison Disease Electrolyte Changes:** - **Na⁺ ↓** (hyponatremia — aldosterone deficiency) - **K⁺ ↑** (hyperkalemia — **aldosterone** deficiency) - **Glucose ↓** (hypoglycemia — cortisol deficiency) - **ACTH ↑** → hyperpigmentation via MSH pathway