Renovascular Disease & Hypertensive Nephropathy
A Step 2 CK-focused lesson linking renovascular hypertension (atherosclerotic RAS vs fibromuscular dysplasia) with hypertensive nephrosclerosis (benign vs malignant), built around RAAS pathophysiology, the ACEi/ARB creatinine-rise clue, the imaging ladder, and next-best-step management. It emphasizes board buzzwords (\"string of beads,\" \"flea-bitten kidney,\" \"onion-skin\") and correct hypertensive-emergency BP-lowering targets.
Two ends of one axis
Renovascular disease and hypertensive nephropathy are two sides of one axis: renal artery narrowing that causes hypertension versus chronic hypertension that damages the kidney.
In renovascular hypertension, a stenotic renal artery underperfuses the kidney. The juxtaglomerular apparatus senses low pressure and releases renin, driving angiotensin II (systemic + efferent arteriolar vasoconstriction) and aldosterone (Na/water retention) — renin-dependent HTN with secondary hyperaldosteronism.
Two causes dominate boards:
- Atherosclerotic RAS — older patients, cardiovascular risk factors; ostial/proximal artery.
- Fibromuscular dysplasia (FMD) — young women; mid-to-distal artery, "string of beads."
Key hook: in a stenotic kidney, GFR is propped up by AngII-mediated efferent constriction. Start an ACE inhibitor/ARB and GFR falls — an acute creatinine rise >30% (classically with bilateral RAS or stenosis in a solitary kidney) is a diagnostic clue and a caution, not usually an absolute contraindication.
- Resistant HTN — uncontrolled on ≥3 drugs including a diuretic — or malignant/accelerated HTN.
- Onset before age 30 (think FMD) or new severe HTN after 55 (think atherosclerotic RAS).
- Abdominal/flank bruit — a systolic–diastolic bruit is more specific.
- Acute creatinine rise >30% after starting an ACEi/ARB.
- Recurrent flash pulmonary edema with preserved EF (bilateral RAS — "Pickering syndrome").
- Unexplained asymmetric kidney size (one small kidney) or otherwise unexplained CKD.
- Labs: secondary hyperaldosteronism → hypokalemia + metabolic alkalosis with high plasma renin (though serum K is frequently normal).
Screen for secondary hypertension with ABCDE:
- A — Accuracy (cuff/technique), Apnea (OSA), Aldosteronism (Conn)
- B — Bruits (renovascular / RAS), Bad kidneys (renal parenchymal disease)
- C — Catecholamines (pheochromocytoma), Coarctation, Cushing
- D — Drugs (NSAIDs, OCPs, decongestants, glucocorticoids), Diet (salt, alcohol)
- E — Endocrine (thyroid, hyperparathyroid), Erythropoietin
Renovascular disease lives under B — a bruit + resistant HTN should trigger renal artery imaging.
Fibromuscular dysplasia vs atherosclerotic RAS
| Feature | Fibromuscular dysplasia | Atherosclerotic RAS |
|---|---|---|
| Typical patient | Young woman, <50 | Older >55, diffuse atherosclerosis |
| Artery segment | Mid-to-distal | Ostial/proximal |
| Angiogram | "String of beads" | Focal/eccentric plaque stenosis |
| Natural history | Rarely occludes; low CKD risk | May progress to occlusion / ischemic nephropathy |
| First-line therapy | PTA (angioplasty), usually no stent — often curative | Medical therapy (ACEi/ARB, statin, antiplatelet, risk-factor control) |
| Revascularize when | Standard for hemodynamically significant lesions | Only if refractory HTN, flash edema, or declining function |
Stem: A 68-year-old man with diabetes, tobacco use, and peripheral arterial disease has BP 168/96 on three agents. An ACE inhibitor is added; two weeks later serum creatinine rises 1.3 → 2.1 mg/dL and K is 5.1. Exam reveals an abdominal bruit; prior imaging showed asymmetric kidneys.
Diagnosis: Bilateral atherosclerotic renal artery stenosis — RAAS blockade removed the AngII-dependent efferent tone maintaining GFR.
Next best step:
- Hold the ACE inhibitor; recheck creatinine and potassium.
- Renal artery duplex ultrasound (first-line, no contrast) — or CTA/MRA if body habitus limits duplex.
- Reserve catheter angiography ± stenting for drug-refractory HTN, recurrent flash pulmonary edema, or progressive renal dysfunction — routine stenting did not beat medical therapy (CORAL, ASTRAL).
- First-line imaging: renal artery duplex ultrasound (no contrast, operator-dependent). Use CTA or MRA if inconclusive; avoid gadolinium when eGFR <30 (NSF risk) and iodinated contrast in advanced CKD.
- Confirmatory / gold standard: catheter (digital subtraction) angiography — performed when intervention is planned.
- Medical therapy is first-line for atherosclerotic RAS: ACEi or ARB (monitor Cr/K) plus statin, antiplatelet, BP control, and smoking cessation.
- FMD → percutaneous transluminal angioplasty (PTA), typically without a stent; frequently curative in young patients.
- Revascularize atherosclerotic RAS only for: drug-refractory HTN, recurrent flash pulmonary edema, or rapidly declining renal function — routine stenting showed no benefit over optimal medical therapy (ASTRAL, CORAL).
Hypertensive nephrosclerosis — benign vs malignant
When chronic hypertension is the cause of kidney injury, the lesion is nephrosclerosis.
Benign nephrosclerosis reflects years of moderate HTN: hyaline arteriolosclerosis (plasma-protein deposition thickening the afferent arteriole) plus intimal fibroelastic hyperplasia, producing ischemic glomerular loss. Kidneys become small and symmetric with a finely granular surface; the course is slowly progressive CKD with subnephrotic proteinuria and a bland sediment. It is more common and aggressive in Black patients (linked to APOL1 risk variants) and is a leading cause of ESRD.
Malignant (accelerated) nephrosclerosis accompanies a hypertensive emergency (often diastolic >120–130 mmHg). Arterioles show fibrinoid necrosis and concentric "onion-skin" hyperplastic arteriolosclerosis; petechial surface hemorrhages create the classic "flea-bitten" kidney. It presents as AKI with hematuria and proteinuria, often with microangiopathic hemolytic anemia (schistocytes), papilledema, and encephalopathy.
Benign vs malignant nephrosclerosis
| Feature | Benign nephrosclerosis | Malignant nephrosclerosis |
|---|---|---|
| Setting | Long-standing moderate HTN | Hypertensive emergency (DBP often >120) |
| Vessel histology | Hyaline arteriolosclerosis | Fibrinoid necrosis + hyperplastic "onion-skin" |
| Gross kidney | Small, symmetric, finely granular | "Flea-bitten" (petechiae) |
| Urine / sediment | Bland; subnephrotic proteinuria | Hematuria, proteinuria, RBCs/casts |
| Hematology | Normal | MAHA (schistocytes) ± thrombocytopenia |
| Course | Slow CKD | AKI; papilledema, encephalopathy |
Stem: A 42-year-old man presents with headache and blurred vision; BP is 220/130. Fundoscopy shows papilledema and flame hemorrhages. Labs: creatinine 2.8, urine with RBCs and protein, Hb 9.2 with schistocytes and low haptoglobin, platelets 90k.
Diagnosis: Hypertensive emergency with malignant nephrosclerosis (a thrombotic-microangiopathy pattern driven by severe HTN).
Next best step:
- Admit to ICU; start a titratable IV antihypertensive — nicardipine, labetalol, or clevidipine (use nitroprusside cautiously in renal impairment — thiocyanate/cyanide accumulation).
- Lower BP gradually — MAP by no more than ~25% in the first hour, then toward ~160/100 mmHg over the next 2–6 hours, normalizing over 24–48 h. Too rapid a drop risks watershed cerebral, coronary, or renal ischemia.
- The MAHA here is HTN-driven and improves with BP control — once malignant HTN is confirmed, avoid reflexive plasma exchange for presumed TTP/HUS.
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