Among patients with secondary hypertension, what is the most common identifiable cause?

Explanation

## Secondary Hypertension: Most Common Causes **Key Point:** Among patients with confirmed secondary hypertension, chronic kidney disease (CKD) is the most common identifiable cause, followed by renovascular disease and primary hyperaldosteronism. ### Frequency of Secondary Causes | Cause | Prevalence (% of secondary HTN) | Mechanism | |-------|----------------------------------|----------| | Chronic kidney disease | 25–30% | Sodium retention, RAAS activation, reduced nitric oxide | | Renovascular disease | 10–15% | Renal artery stenosis (atherosclerotic or fibromuscular dysplasia) | | Primary hyperaldosteronism | 5–10% | Aldosterone excess → sodium retention, hypokalemia | | Obstructive sleep apnea | 5–10% | Sympathetic activation, hypoxia-induced vasoconstriction | | Pheochromocytoma | <1% | Catecholamine excess | | Cushing syndrome | <1% | Cortisol excess → sodium retention | ### Why CKD Is Most Common **High-Yield:** Chronic kidney disease causes hypertension through: 1. Sodium and water retention (reduced GFR) 2. Activation of the renin-angiotensin-aldosterone system (RAAS) 3. Sympathetic nervous system overactivity 4. Reduced production of vasodilatory substances (nitric oxide, prostaglandins) 5. Vascular stiffness from uremia **Clinical Pearl:** CKD-related hypertension is bidirectional — hypertension accelerates CKD progression, and CKD causes hypertension. This creates a vicious cycle. ### Distinction: CKD vs. Renovascular Disease **Mnemonic: RAAS-driven HTN — Renovascular vs. CKD** - **Renovascular:** Unilateral renal artery stenosis → focal ischemia → RAAS activation - **CKD:** Bilateral renal parenchymal disease → global sodium/fluid retention + RAAS activation CKD is more prevalent because it encompasses all chronic renal parenchymal diseases (diabetic nephropathy, glomerulonephritis, hypertensive nephrosclerosis, etc.). **Warning:** Do not confuse "most common cause of hypertension overall" (essential HTN, 90–95%) with "most common cause of secondary hypertension" (CKD, ~25–30% of secondary cases). The question asks for the latter. [cite:Harrison 21e Ch 297]