Renal · Hypertension
The facts most likely to be tested
Atherosclerosis is the most common cause of renal artery stenosis in older patients with diffuse vascular disease.
Fibromuscular dysplasia is the most common cause of renal artery stenosis in young women and typically presents with a string-of-beads appearance on angiography.
Renal artery stenosis should be suspected in patients with refractory hypertension or the sudden onset of hypertension after age 55.
The initiation of ACE inhibitors or ARBs in patients with bilateral renal artery stenosis causes a precipitous drop in glomerular filtration rate due to the loss of efferent arteriole vasoconstriction.
Renal artery duplex ultrasonography is the preferred initial screening test for suspected renal artery stenosis.
CT angiography or MR angiography are the diagnostic tests of choice for confirming the diagnosis, though MR angiography must be avoided in patients with severe renal failure due to the risk of nephrogenic systemic fibrosis.
Percutaneous transluminal renal angioplasty with stenting is the treatment of choice for atherosclerotic disease, while angioplasty without stenting is preferred for fibromuscular dysplasia.
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A 32-year-old woman presents to the clinic for evaluation of persistent high blood pressure. She has no significant past medical history and does not smoke. Physical examination reveals a systolic-diastolic abdominal bruit. Laboratory studies show a serum creatinine of 0.9 mg/dL and a potassium level of 3.4 mEq/L. A renal ultrasound shows a small right kidney compared to the left.
What is the most likely underlying pathology in this patient?
Fibromuscular dysplasia
The patient's age, gender, and clinical presentation of secondary hypertension are classic for fibromuscular dysplasia, which is characterized by medial fibroplasia and a 'string-of-beads' appearance.
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High yield triage
Etiology / Epidemiology
Suspect in atherosclerosis (elderly) or fibromuscular dysplasia (young women).
Clinical Manifestations
Look for refractory hypertension and abdominal bruit.
Diagnosis
Renal arteriography is the gold standard; CT angiography is the preferred initial test.
Treatment
ACE inhibitors are first-line, but contraindicated in bilateral stenosis.
Prognosis
Risk of ischemic nephropathy and flash pulmonary edema if untreated.
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Epidemiology & Etiology
Atherosclerotic disease is the most common cause in patients >50 years with systemic vascular risk factors. Fibromuscular dysplasia is the classic etiology in women <50, often presenting with a string of beads appearance on imaging. Both lead to decreased renal perfusion and secondary hypertension.
Pertinent Anatomy
Stenosis typically occurs at the proximal renal artery. The resulting hypoperfusion triggers the juxtaglomerular apparatus in the affected kidney, activating the systemic renin-angiotensin-aldosterone system.
Pathophysiology
Reduced renal blood flow stimulates renin release, causing systemic vasoconstriction and sodium retention. This creates a state of renin-dependent hypertension. Chronic ischemia leads to renal atrophy and potential progression to end-stage renal disease.
Clinical Manifestations
Presentation includes refractory hypertension despite three or more antihypertensives. A systolic-diastolic abdominal bruit is a highly specific physical exam finding. Flash pulmonary edema is a classic red flag for bilateral disease or stenosis of a solitary kidney.
Diagnosis
The gold standard for definitive diagnosis is renal arteriography. CT angiography or MR angiography are commonly used for initial screening. A significant stenosis is typically defined as a >70% reduction in luminal diameter.
Treatment
Medical management with ACE inhibitors or ARBs is first-line for unilateral disease. Contraindicated in bilateral renal artery stenosis as they precipitate acute renal failure by removing efferent arteriolar vasoconstriction. Revascularization via percutaneous transluminal renal angioplasty is indicated for refractory cases.
Prognosis
Untreated patients face high risks of myocardial infarction, stroke, and ischemic nephropathy. Patients on ACE inhibitors require close monitoring of serum creatinine; a rise of >30% after initiation is highly suggestive of significant stenosis.
Differential Diagnosis
Primary Hyperaldosteronism: hypokalemia is common
Pheochromocytoma: episodic palpitations and diaphoresis
Cushing Syndrome: moon facies and striae
Coarctation of the Aorta: blood pressure differential between arms and legs
Essential Hypertension: diagnosis of exclusion in younger patients